Merge branch 'hasse/unicode_atoms/OTP-14285'

* hasse/unicode_atoms/OTP-14285:
  compiler: Handle (bad) Unicode parse transform module names
  kernel: Improve handling of Unicode filenames
  stdlib: Handle Unicode atoms in ms_transform
  stdlib: Improve Unicode handling of the Erlang parser
  stdlib: Handle unknown compiler options with Unicode
  stdlib: Handle Unicode macro names
  stdlib: Correct Unicode handling in escript
  dialyzer: Improve handling of Unicode
  parsetools: Improve handling of Unicode atoms
  stdlib: Handle Unicode atoms when formatting stacktraces
  stdlib: Add more checks of module names to the linter
  stdlib: Handle Unicode atoms better in io_lib_format
  stdlib: Handle Unicode atoms in c.erl

44 files changed, 702 insertions, 501 deletions

diff --git a/lib/compiler/src/compile.erl b/lib/compiler/src/compile.erl
index d05b8a9530..aa2d224bb4 100644
--- a/lib/compiler/src/compile.erl
+++ b/lib/compiler/src/compile.erl
@@ -264,9 +264,9 @@ format_error({delete_temp,File,Error}) ->
     io_lib:format("failed to delete temporary file ~ts: ~ts",
 		  [File,file:format_error(Error)]);
 format_error({parse_transform,M,R}) ->
-    io_lib:format("error in parse transform '~s': ~tp", [M, R]);
+    io_lib:format("error in parse transform '~ts': ~tp", [M, R]);
 format_error({undef_parse_transform,M}) ->
-    io_lib:format("undefined parse transform '~s'", [M]);
+    io_lib:format("undefined parse transform '~ts'", [M]);
 format_error({core_transform,M,R}) ->
     io_lib:format("error in core transform '~s': ~tp", [M, R]);
 format_error({crash,Pass,Reason}) ->
diff --git a/lib/dialyzer/src/dialyzer.erl b/lib/dialyzer/src/dialyzer.erl
index ab137bd170..c319acb2fb 100644
--- a/lib/dialyzer/src/dialyzer.erl
+++ b/lib/dialyzer/src/dialyzer.erl
@@ -111,13 +111,13 @@ get_plt_info([PLT|PLTs]) ->
   String =
     case dialyzer_plt:included_files(PLT) of
       {ok, Files} ->
-	io_lib:format("The PLT ~s includes the following files:\n~p\n\n",
+	io_lib:format("The PLT ~ts includes the following files:\n~tp\n\n",
 		      [PLT, Files]);
       {error, read_error} ->
-	Msg = io_lib:format("Could not read the PLT file ~p\n\n", [PLT]),
+	Msg = io_lib:format("Could not read the PLT file ~tp\n\n", [PLT]),
 	throw({dialyzer_error, Msg});
       {error, no_such_file} ->
-	Msg = io_lib:format("The PLT file ~p does not exist\n\n", [PLT]),
+	Msg = io_lib:format("The PLT file ~tp does not exist\n\n", [PLT]),
 	throw({dialyzer_error, Msg})
     end,
   String ++ get_plt_info(PLTs);
@@ -126,16 +126,16 @@ get_plt_info([]) -> "".
 do_print_plt_info(PLTInfo, OutputFile) ->
   case OutputFile =:= none of
     true ->
-      io:format("~s", [PLTInfo]),
+      io:format("~ts", [PLTInfo]),
       ?RET_NOTHING_SUSPICIOUS;
     false ->
       case file:open(OutputFile, [write]) of
 	{ok, FileDesc} ->
-	  io:format(FileDesc, "~s", [PLTInfo]),
+	  io:format(FileDesc, "~ts", [PLTInfo]),
 	  ok = file:close(FileDesc),
 	  ?RET_NOTHING_SUSPICIOUS;
 	{error, Reason} ->
-	  Msg1 = io_lib:format("Could not open output file ~p, Reason: ~p\n",
+	  Msg1 = io_lib:format("Could not open output file ~tp, Reason: ~p\n",
 			       [OutputFile, Reason]),
 	  throw({dialyzer_error, Msg1})
       end
@@ -264,7 +264,7 @@ cl_halt({ok, R = ?RET_DISCREPANCIES}, #options{output_file = Output}) ->
   halt(R);
 cl_halt({error, Msg1}, #options{output_file = Output}) ->
   %% Msg2 = "dialyzer: Internal problems were encountered in the analysis",
-  io:format("\ndialyzer: ~s\n", [Msg1]),
+  io:format("\ndialyzer: ~ts\n", [Msg1]),
   cl_check_log(Output),
   halt(?RET_INTERNAL_ERROR).
 
@@ -273,7 +273,7 @@ cl_halt({error, Msg1}, #options{output_file = Output}) ->
 cl_check_log(none) ->
   ok;
 cl_check_log(Output) ->
-  io:format("  Check output file `~s' for details\n", [Output]).
+  io:format("  Check output file `~ts' for details\n", [Output]).
 
 -spec format_warning(raw_warning() | dial_warning()) -> string().
 
@@ -291,7 +291,7 @@ format_warning({_Tag, {File, Line}, Msg}, FOpt) when is_list(File),
 	basename -> filename:basename(File)
       end,
   String = lists:flatten(message_to_string(Msg)),
-  lists:flatten(io_lib:format("~s:~w: ~s", [F, Line, String])).
+  lists:flatten(io_lib:format("~ts:~w: ~ts", [F, Line, String])).
 
 
 %%-----------------------------------------------------------------------------
@@ -302,54 +302,55 @@ format_warning({_Tag, {File, Line}, Msg}, FOpt) when is_list(File),
 %%----- Warnings for general discrepancies ----------------
 message_to_string({apply, [Args, ArgNs, FailReason,
 			   SigArgs, SigRet, Contract]}) ->
-  io_lib:format("Fun application with arguments ~s ", [Args]) ++
+  io_lib:format("Fun application with arguments ~ts ", [Args]) ++
     call_or_apply_to_string(ArgNs, FailReason, SigArgs, SigRet, Contract);
 message_to_string({app_call, [M, F, Args, Culprit, ExpectedType, FoundType]}) ->
-  io_lib:format("The call ~s:~s~s requires that ~s is of type ~s not ~s\n",
+  io_lib:format("The call ~s:~ts~ts requires that ~ts is of type ~ts not ~ts\n",
 		[M, F, Args, Culprit, ExpectedType, FoundType]);
 message_to_string({bin_construction, [Culprit, Size, Seg, Type]}) ->
   io_lib:format("Binary construction will fail since the ~s field ~s in"
 		" segment ~s has type ~s\n", [Culprit, Size, Seg, Type]);
 message_to_string({call, [M, F, Args, ArgNs, FailReason,
 			  SigArgs, SigRet, Contract]}) ->
-  io_lib:format("The call ~w:~w~s ", [M, F, Args]) ++
+  io_lib:format("The call ~w:~tw~ts ", [M, F, Args]) ++
     call_or_apply_to_string(ArgNs, FailReason, SigArgs, SigRet, Contract);
 message_to_string({call_to_missing, [M, F, A]}) ->
-  io_lib:format("Call to missing or unexported function ~w:~w/~w\n", [M, F, A]);
+  io_lib:format("Call to missing or unexported function ~w:~tw/~w\n",
+                [M, F, A]);
 message_to_string({exact_eq, [Type1, Op, Type2]}) ->
-  io_lib:format("The test ~s ~s ~s can never evaluate to 'true'\n",
+  io_lib:format("The test ~ts ~s ~ts can never evaluate to 'true'\n",
 		[Type1, Op, Type2]);
 message_to_string({fun_app_args, [Args, Type]}) ->
-  io_lib:format("Fun application with arguments ~s will fail"
-		" since the function has type ~s\n", [Args, Type]);
+  io_lib:format("Fun application with arguments ~ts will fail"
+		" since the function has type ~ts\n", [Args, Type]);
 message_to_string({fun_app_no_fun, [Op, Type, Arity]}) ->
-  io_lib:format("Fun application will fail since ~s :: ~s"
+  io_lib:format("Fun application will fail since ~ts :: ~ts"
 		" is not a function of arity ~w\n", [Op, Type, Arity]);
 message_to_string({guard_fail, []}) ->
   "Clause guard cannot succeed.\n";
 message_to_string({guard_fail, [Arg1, Infix, Arg2]}) ->
-  io_lib:format("Guard test ~s ~s ~s can never succeed\n", [Arg1, Infix, Arg2]);
+  io_lib:format("Guard test ~ts ~s ~ts can never succeed\n", [Arg1, Infix, Arg2]);
 message_to_string({map_update, [Type, Key]}) ->
-  io_lib:format("A key of type ~s cannot exist "
-		"in a map of type ~s\n", [Key, Type]);
+  io_lib:format("A key of type ~ts cannot exist "
+		"in a map of type ~ts\n", [Key, Type]);
 message_to_string({neg_guard_fail, [Arg1, Infix, Arg2]}) ->
-  io_lib:format("Guard test not(~s ~s ~s) can never succeed\n",
+  io_lib:format("Guard test not(~ts ~s ~ts) can never succeed\n",
 		[Arg1, Infix, Arg2]);
 message_to_string({guard_fail, [Guard, Args]}) ->
-  io_lib:format("Guard test ~w~s can never succeed\n", [Guard, Args]);
+  io_lib:format("Guard test ~w~ts can never succeed\n", [Guard, Args]);
 message_to_string({neg_guard_fail, [Guard, Args]}) ->
-  io_lib:format("Guard test not(~w~s) can never succeed\n", [Guard, Args]);
+  io_lib:format("Guard test not(~w~ts) can never succeed\n", [Guard, Args]);
 message_to_string({guard_fail_pat, [Pat, Type]}) ->
-  io_lib:format("Clause guard cannot succeed. The ~s was matched"
-		" against the type ~s\n", [Pat, Type]);
+  io_lib:format("Clause guard cannot succeed. The ~ts was matched"
+		" against the type ~ts\n", [Pat, Type]);
 message_to_string({improper_list_constr, [TlType]}) ->
   io_lib:format("Cons will produce an improper list"
-		" since its 2nd argument is ~s\n", [TlType]);
+		" since its 2nd argument is ~ts\n", [TlType]);
 message_to_string({no_return, [Type|Name]}) ->
   NameString =
     case Name of
       [] -> "The created fun ";
-      [F, A] -> io_lib:format("Function ~w/~w ", [F, A])
+      [F, A] -> io_lib:format("Function ~tw/~w ", [F, A])
     end,
   case Type of
     no_match -> NameString ++ "has no clauses that will ever match\n";
@@ -358,129 +359,129 @@ message_to_string({no_return, [Type|Name]}) ->
     both -> NameString ++ "has no local return\n"
   end;
 message_to_string({record_constr, [RecConstr, FieldDiffs]}) ->
-  io_lib:format("Record construction ~s violates the"
-		" declared type of field ~s\n", [RecConstr, FieldDiffs]);
+  io_lib:format("Record construction ~ts violates the"
+		" declared type of field ~ts\n", [RecConstr, FieldDiffs]);
 message_to_string({record_constr, [Name, Field, Type]}) ->
-  io_lib:format("Record construction violates the declared type for #~w{}"
-		" since ~s cannot be of type ~s\n", [Name, Field, Type]);
+  io_lib:format("Record construction violates the declared type for #~tw{}"
+		" since ~ts cannot be of type ~ts\n", [Name, Field, Type]);
 message_to_string({record_matching, [String, Name]}) ->
-  io_lib:format("The ~s violates the"
-		" declared type for #~w{}\n", [String, Name]);
+  io_lib:format("The ~ts violates the"
+		" declared type for #~tw{}\n", [String, Name]);
 message_to_string({record_match, [Pat, Type]}) ->
-  io_lib:format("Matching of ~s tagged with a record name violates the declared"
-		" type of ~s\n", [Pat, Type]);
+  io_lib:format("Matching of ~ts tagged with a record name violates"
+                " the declared type of ~ts\n", [Pat, Type]);
 message_to_string({pattern_match, [Pat, Type]}) ->
-  io_lib:format("The ~s can never match the type ~s\n", [Pat, Type]);
+  io_lib:format("The ~ts can never match the type ~ts\n", [Pat, Type]);
 message_to_string({pattern_match_cov, [Pat, Type]}) ->
-  io_lib:format("The ~s can never match since previous"
-		" clauses completely covered the type ~s\n",
+  io_lib:format("The ~ts can never match since previous"
+		" clauses completely covered the type ~ts\n",
 		[Pat, Type]);
 message_to_string({unmatched_return, [Type]}) ->
-  io_lib:format("Expression produces a value of type ~s,"
+  io_lib:format("Expression produces a value of type ~ts,"
 		" but this value is unmatched\n", [Type]);
 message_to_string({unused_fun, [F, A]}) ->
-  io_lib:format("Function ~w/~w will never be called\n", [F, A]);
+  io_lib:format("Function ~tw/~w will never be called\n", [F, A]);
 %%----- Warnings for specs and contracts -------------------
 message_to_string({contract_diff, [M, F, _A, Contract, Sig]}) ->
-  io_lib:format("Type specification ~w:~w~s"
-		" is not equal to the success typing: ~w:~w~s\n",
+  io_lib:format("Type specification ~w:~tw~ts"
+		" is not equal to the success typing: ~w:~tw~ts\n",
 		[M, F, Contract, M, F, Sig]);
 message_to_string({contract_subtype, [M, F, _A, Contract, Sig]}) ->
-  io_lib:format("Type specification ~w:~w~s"
-		" is a subtype of the success typing: ~w:~w~s\n",
+  io_lib:format("Type specification ~w:~tw~ts"
+		" is a subtype of the success typing: ~w:~tw~ts\n",
 		[M, F, Contract, M, F, Sig]);
 message_to_string({contract_supertype, [M, F, _A, Contract, Sig]}) ->
-  io_lib:format("Type specification ~w:~w~s"
-		" is a supertype of the success typing: ~w:~w~s\n",
+  io_lib:format("Type specification ~w:~tw~ts"
+		" is a supertype of the success typing: ~w:~tw~ts\n",
 		[M, F, Contract, M, F, Sig]);
 message_to_string({contract_range, [Contract, M, F, ArgStrings, Line, CRet]}) ->
-  io_lib:format("The contract ~w:~w~s cannot be right because the inferred"
-		" return for ~w~s on line ~w is ~s\n",
+  io_lib:format("The contract ~w:~tw~ts cannot be right because the inferred"
+		" return for ~tw~ts on line ~w is ~ts\n",
 		[M, F, Contract, F, ArgStrings, Line, CRet]);
 message_to_string({invalid_contract, [M, F, A, Sig]}) ->
-  io_lib:format("Invalid type specification for function ~w:~w/~w."
-		" The success typing is ~s\n", [M, F, A, Sig]);
+  io_lib:format("Invalid type specification for function ~w:~tw/~w."
+		" The success typing is ~ts\n", [M, F, A, Sig]);
 message_to_string({contract_with_opaque, [M, F, A, OpaqueType, SigType]}) ->
-  io_lib:format("The specification for ~w:~w/~w"
-                " has an opaque subtype ~s which is violated by the"
-                " success typing ~s\n", [M, F, A, OpaqueType, SigType]);
+  io_lib:format("The specification for ~w:~tw/~w"
+                " has an opaque subtype ~ts which is violated by the"
+                " success typing ~ts\n", [M, F, A, OpaqueType, SigType]);
 message_to_string({extra_range, [M, F, A, ExtraRanges, SigRange]}) ->
-  io_lib:format("The specification for ~w:~w/~w states that the function"
-		" might also return ~s but the inferred return is ~s\n",
+  io_lib:format("The specification for ~w:~tw/~w states that the function"
+		" might also return ~ts but the inferred return is ~ts\n",
 		[M, F, A, ExtraRanges, SigRange]);
 message_to_string({overlapping_contract, [M, F, A]}) ->
-  io_lib:format("Overloaded contract for ~w:~w/~w has overlapping domains;"
+  io_lib:format("Overloaded contract for ~w:~tw/~w has overlapping domains;"
 		" such contracts are currently unsupported and are simply ignored\n",
 		[M, F, A]);
 message_to_string({spec_missing_fun, [M, F, A]}) ->
-  io_lib:format("Contract for function that does not exist: ~w:~w/~w\n",
+  io_lib:format("Contract for function that does not exist: ~w:~tw/~w\n",
 		[M, F, A]);
 %%----- Warnings for opaque type violations -------------------
 message_to_string({call_with_opaque, [M, F, Args, ArgNs, ExpArgs]}) ->
-  io_lib:format("The call ~w:~w~s contains ~s when ~s\n",
+  io_lib:format("The call ~w:~tw~ts contains ~ts when ~ts\n",
 		[M, F, Args, form_positions(ArgNs), form_expected(ExpArgs)]);
 message_to_string({call_without_opaque, [M, F, Args, ExpectedTriples]}) ->
-  io_lib:format("The call ~w:~w~s does not have ~s\n",
+  io_lib:format("The call ~w:~tw~ts does not have ~ts\n",
 		[M, F, Args, form_expected_without_opaque(ExpectedTriples)]);
 message_to_string({opaque_eq, [Type, _Op, OpaqueType]}) ->
-  io_lib:format("Attempt to test for equality between a term of type ~s"
-		" and a term of opaque type ~s\n", [Type, OpaqueType]);
+  io_lib:format("Attempt to test for equality between a term of type ~ts"
+		" and a term of opaque type ~ts\n", [Type, OpaqueType]);
 message_to_string({opaque_guard, [Arg1, Infix, Arg2, ArgNs]}) ->
-  io_lib:format("Guard test ~s ~s ~s contains ~s\n",
+  io_lib:format("Guard test ~ts ~s ~ts contains ~s\n",
 		[Arg1, Infix, Arg2, form_positions(ArgNs)]);
 message_to_string({opaque_guard, [Guard, Args]}) ->
-  io_lib:format("Guard test ~w~s breaks the opacity of its argument\n",
+  io_lib:format("Guard test ~w~ts breaks the opacity of its argument\n",
 		[Guard, Args]);
 message_to_string({opaque_match, [Pat, OpaqueType, OpaqueTerm]}) ->
   Term = if OpaqueType =:= OpaqueTerm -> "the term";
 	    true -> OpaqueTerm
 	 end,
-  io_lib:format("The attempt to match a term of type ~s against the ~s"
-		" breaks the opacity of ~s\n", [OpaqueType, Pat, Term]);
+  io_lib:format("The attempt to match a term of type ~s against the ~ts"
+		" breaks the opacity of ~ts\n", [OpaqueType, Pat, Term]);
 message_to_string({opaque_neq, [Type, _Op, OpaqueType]}) ->
-  io_lib:format("Attempt to test for inequality between a term of type ~s"
-		" and a term of opaque type ~s\n", [Type, OpaqueType]);
+  io_lib:format("Attempt to test for inequality between a term of type ~ts"
+		" and a term of opaque type ~ts\n", [Type, OpaqueType]);
 message_to_string({opaque_type_test, [Fun, Args, Arg, ArgType]}) ->
-  io_lib:format("The type test ~s~s breaks the opacity of the term ~s~s\n",
+  io_lib:format("The type test ~ts~ts breaks the opacity of the term ~ts~ts\n",
                 [Fun, Args, Arg, ArgType]);
 message_to_string({opaque_size, [SizeType, Size]}) ->
-  io_lib:format("The size ~s breaks the opacity of ~s\n",
+  io_lib:format("The size ~ts breaks the opacity of ~ts\n",
                 [SizeType, Size]);
 message_to_string({opaque_call, [M, F, Args, Culprit, OpaqueType]}) ->
-  io_lib:format("The call ~s:~s~s breaks the opacity of the term ~s :: ~s\n",
+  io_lib:format("The call ~s:~ts~ts breaks the opacity of the term ~ts :: ~ts\n",
                 [M, F, Args, Culprit, OpaqueType]);
 %%----- Warnings for concurrency errors --------------------
 message_to_string({race_condition, [M, F, Args, Reason]}) ->
-  io_lib:format("The call ~w:~w~s ~s\n", [M, F, Args, Reason]);
+  io_lib:format("The call ~w:~tw~ts ~ts\n", [M, F, Args, Reason]);
 %%----- Warnings for behaviour errors --------------------
 message_to_string({callback_type_mismatch, [B, F, A, ST, CT]}) ->
-  io_lib:format("The inferred return type of ~w/~w (~s) has nothing in common"
-		" with ~s, which is the expected return type for the callback of"
-		" ~w behaviour\n", [F, A, ST, CT, B]);
+  io_lib:format("The inferred return type of ~tw/~w (~ts) has nothing in"
+                " common with ~ts, which is the expected return type for"
+                " the callback of the ~w behaviour\n", [F, A, ST, CT, B]);
 message_to_string({callback_arg_type_mismatch, [B, F, A, N, ST, CT]}) ->
-  io_lib:format("The inferred type for the ~s argument of ~w/~w (~s) is"
-		" not a supertype of ~s, which is expected type for this"
+  io_lib:format("The inferred type for the ~s argument of ~tw/~w (~ts) is"
+		" not a supertype of ~ts, which is expected type for this"
 		" argument in the callback of the ~w behaviour\n",
 		[ordinal(N), F, A, ST, CT, B]);
 message_to_string({callback_spec_type_mismatch, [B, F, A, ST, CT]}) ->
-  io_lib:format("The return type ~s in the specification of ~w/~w is not a"
-		" subtype of ~s, which is the expected return type for the"
-		" callback of ~w behaviour\n", [ST, F, A, CT, B]);
+  io_lib:format("The return type ~ts in the specification of ~tw/~w is not a"
+		" subtype of ~ts, which is the expected return type for the"
+		" callback of the ~w behaviour\n", [ST, F, A, CT, B]);
 message_to_string({callback_spec_arg_type_mismatch, [B, F, A, N, ST, CT]}) ->
-  io_lib:format("The specified type for the ~s argument of ~w/~w (~s) is"
-		" not a supertype of ~s, which is expected type for this"
+  io_lib:format("The specified type for the ~ts argument of ~tw/~w (~ts) is"
+		" not a supertype of ~ts, which is expected type for this"
 		" argument in the callback of the ~w behaviour\n",
 		[ordinal(N), F, A, ST, CT, B]);
 message_to_string({callback_missing, [B, F, A]}) ->
-  io_lib:format("Undefined callback function ~w/~w (behaviour '~w')\n",
+  io_lib:format("Undefined callback function ~tw/~w (behaviour ~w)\n",
 		[F, A, B]);
 message_to_string({callback_info_missing, [B]}) ->
   io_lib:format("Callback info about the ~w behaviour is not available\n", [B]);
 %%----- Warnings for unknown functions, types, and behaviours -------------
 message_to_string({unknown_type, {M, F, A}}) ->
-  io_lib:format("Unknown type ~w:~w/~w", [M, F, A]);
+  io_lib:format("Unknown type ~w:~tw/~w", [M, F, A]);
 message_to_string({unknown_function, {M, F, A}}) ->
-  io_lib:format("Unknown function ~w:~w/~w", [M, F, A]);
+  io_lib:format("Unknown function ~w:~tw/~w", [M, F, A]);
 message_to_string({unknown_behaviour, B}) ->
   io_lib:format("Unknown behaviour ~w", [B]).
 
diff --git a/lib/dialyzer/src/dialyzer_analysis_callgraph.erl b/lib/dialyzer/src/dialyzer_analysis_callgraph.erl
index 29aa25b98e..2a2dcd55f0 100644
--- a/lib/dialyzer/src/dialyzer_analysis_callgraph.erl
+++ b/lib/dialyzer/src/dialyzer_analysis_callgraph.erl
@@ -287,7 +287,7 @@ compile_and_store(Files, #analysis_state{codeserver = CServer,
                     dict:new(), Files),
       check_for_duplicate_modules(ModDict);
     false ->
-      Msg = io_lib:format("Could not scan the following file(s):~n~s",
+      Msg = io_lib:format("Could not scan the following file(s):~n~ts",
       			  [[Reason || {_Filename, Reason} <- Failed]]),
       exit({error, Msg})
   end,
@@ -683,12 +683,13 @@ dump_callgraph(CallGraph, _State, #analysis{callgraph_file = File}, ".ps") ->
   Args = "-Gratio=compress -Gsize=\"100,100\"",
   dialyzer_callgraph:to_ps(CallGraph, File, Args);
 dump_callgraph(CallGraph, State, #analysis{callgraph_file = File}, _Ext) ->
+  %% TODO: write the graph, not the ETS table identifiers.
   case file:open(File, [write]) of
     {ok, Fd} ->
       io:format(Fd, "~p", [CallGraph]),
       ok = file:close(Fd);
     {error, Reason} ->
-      Msg = io_lib:format("Could not open output file ~p, Reason: ~p\n",
+      Msg = io_lib:format("Could not open output file ~tp, Reason: ~p\n",
 			  [File, Reason]),
       send_log(State#analysis_state.parent, Msg)
   end.
diff --git a/lib/dialyzer/src/dialyzer_callgraph.erl b/lib/dialyzer/src/dialyzer_callgraph.erl
index 6387f3d1e4..a83a0bda59 100644
--- a/lib/dialyzer/src/dialyzer_callgraph.erl
+++ b/lib/dialyzer/src/dialyzer_callgraph.erl
@@ -755,6 +755,7 @@ put_behaviour_api_calls(Calls,
 -spec to_dot(callgraph(), file:filename()) -> 'ok'.
 
 to_dot(#callgraph{digraph = DG, esc = Esc} = CG, File) ->
+  %% TODO: handle Unicode names.
   Fun = fun(L) ->
 	    case lookup_name(L, CG) of
 	      error -> L;
@@ -769,9 +770,10 @@ to_dot(#callgraph{digraph = DG, esc = Esc} = CG, File) ->
 -spec to_ps(callgraph(), file:filename(), string()) -> 'ok'.
 
 to_ps(#callgraph{} = CG, File, Args) ->
+  %% TODO: handle Unicode names.
   Dot_File = filename:rootname(File) ++ ".dot",
   to_dot(CG, Dot_File),
-  Command = io_lib:format("dot -Tps ~s -o ~s ~s", [Args, File, Dot_File]),
+  Command = io_lib:format("dot -Tps ~ts -o ~ts ~ts", [Args, File, Dot_File]),
   _ = os:cmd(Command),
   ok.
 
diff --git a/lib/dialyzer/src/dialyzer_cl.erl b/lib/dialyzer/src/dialyzer_cl.erl
index 8500c59ebe..d72ae1dc86 100644
--- a/lib/dialyzer/src/dialyzer_cl.erl
+++ b/lib/dialyzer/src/dialyzer_cl.erl
@@ -77,7 +77,7 @@ init_opts_for_build(Opts) ->
 	[] -> Opts#options{output_plt = get_default_output_plt()};
 	[Plt] -> Opts#options{init_plts = [], output_plt = Plt};
         Plts ->
-          Msg = io_lib:format("Could not build multiple PLT files: ~s\n",
+          Msg = io_lib:format("Could not build multiple PLT files: ~ts\n",
                               [format_plts(Plts)]),
           cl_error(Msg)
       end;
@@ -99,7 +99,7 @@ init_opts_for_add(Opts) ->
                            init_plts = get_default_init_plt()};
 	[Plt] -> Opts#options{output_plt = Plt};
         Plts ->
-          Msg = io_lib:format("Could not add to multiple PLT files: ~s\n",
+          Msg = io_lib:format("Could not add to multiple PLT files: ~ts\n",
                               [format_plts(Plts)]),
           cl_error(Msg)
       end;
@@ -165,7 +165,7 @@ init_opts_for_remove(Opts) ->
                            init_plts = get_default_init_plt()};
 	[Plt] -> Opts#options{output_plt = Plt};
         Plts ->
-          Msg = io_lib:format("Could not remove from multiple PLT files: ~s\n",
+          Msg = io_lib:format("Could not remove from multiple PLT files: ~ts\n",
                               [format_plts(Plts)]),
           cl_error(Msg)
       end;
@@ -212,19 +212,19 @@ plt_common(#options{init_plts = [InitPlt]} = Opts, RemoveFiles, AddFiles) ->
 	  do_analysis(AnalFiles, Opts, Plt, {Md5, ModDeps1})
       end;
     {error, no_such_file} ->
-      Msg = io_lib:format("Could not find the PLT: ~s\n~s",
+      Msg = io_lib:format("Could not find the PLT: ~ts\n~s",
 			  [InitPlt, default_plt_error_msg()]),
       cl_error(Msg);
     {error, not_valid} ->
-      Msg = io_lib:format("The file: ~s is not a valid PLT file\n~s",
+      Msg = io_lib:format("The file: ~ts is not a valid PLT file\n~s",
 			  [InitPlt, default_plt_error_msg()]),
       cl_error(Msg);
     {error, read_error} ->
-      Msg = io_lib:format("Could not read the PLT: ~s\n~s",
+      Msg = io_lib:format("Could not read the PLT: ~ts\n~s",
 			  [InitPlt, default_plt_error_msg()]),
       cl_error(Msg);
     {error, {no_file_to_remove, F}} ->
-      Msg = io_lib:format("Could not remove the file ~s from the PLT: ~s\n",
+      Msg = io_lib:format("Could not remove the file ~ts from the PLT: ~ts\n",
 			  [F, InitPlt]),
       cl_error(Msg)
   end.
@@ -264,7 +264,7 @@ report_check(#options{report_mode = ReportMode, init_plts = [InitPlt]}) ->
   case ReportMode of
     quiet -> ok;
     _ ->
-      io:format("  Checking whether the PLT ~s is up-to-date...", [InitPlt])
+      io:format("  Checking whether the PLT ~ts is up-to-date...", [InitPlt])
   end.
 
 report_old_version(#options{report_mode = ReportMode, init_plts = [InitPlt]}) ->
@@ -272,7 +272,7 @@ report_old_version(#options{report_mode = ReportMode, init_plts = [InitPlt]}) ->
     quiet -> ok;
     _ ->
       io:put_chars(" no\n"),
-      io:format("    (the PLT ~s was built with an old version of Dialyzer)\n",
+      io:format("    (the PLT ~ts was built with an old version of Dialyzer)\n",
 		[InitPlt])
   end.
 
@@ -300,19 +300,19 @@ report_analysis_start(#options{analysis_type = Type,
 	plt_add ->
           [InitPlt] = InitPlts,
 	  case InitPlt =:= OutputPlt of
-	    true -> io:format("Adding information to ~s...", [OutputPlt]);
-	    false -> io:format("Adding information from ~s to ~s...", 
+	    true -> io:format("Adding information to ~ts...", [OutputPlt]);
+	    false -> io:format("Adding information from ~ts to ~ts...",
 			       [InitPlt, OutputPlt])
 	  end;
 	plt_build ->
-	  io:format("Creating PLT ~s ...", [OutputPlt]);
+	  io:format("Creating PLT ~ts ...", [OutputPlt]);
 	plt_check ->
-	  io:format("Rebuilding the information in ~s...", [OutputPlt]);
+	  io:format("Rebuilding the information in ~ts...", [OutputPlt]);
 	plt_remove ->
           [InitPlt] = InitPlts,
 	  case InitPlt =:= OutputPlt of
-	    true -> io:format("Removing information from ~s...", [OutputPlt]);
-	    false -> io:format("Removing information from ~s to ~s...", 
+	    true -> io:format("Removing information from ~ts...", [OutputPlt]);
+	    false -> io:format("Removing information from ~ts to ~ts...",
 			       [InitPlt, OutputPlt])
 	  end;
 	succ_typings -> io:format("Proceeding with analysis...")
@@ -420,7 +420,7 @@ assert_writable(PltFile) ->
   case check_if_writable(PltFile) of
     true -> ok;
     false ->
-      Msg = io_lib:format("    The PLT file ~s is not writable", [PltFile]),
+      Msg = io_lib:format("    The PLT file ~ts is not writable", [PltFile]),
       cl_error(Msg)
   end.
 
@@ -596,9 +596,11 @@ init_output(State0, #options{output_file = OutFile,
     false ->
       case file:open(OutFile, [write]) of
 	{ok, File} ->
+          %% Warnings and errors can include Unicode characters.
+          ok = io:setopts(File, [{encoding, unicode}]),
 	  State#cl_state{output = File};
 	{error, Reason} ->
-	  Msg = io_lib:format("Could not open output file ~p, Reason: ~p\n",
+	  Msg = io_lib:format("Could not open output file ~tp, Reason: ~p\n",
 			      [OutFile, Reason]),
 	  cl_error(State, lists:flatten(Msg))
       end
@@ -687,7 +689,7 @@ cl_error(Msg) ->
 cl_error(State, Msg) ->
   case State#cl_state.output of
     standard_io -> ok;
-    Outfile -> io:format(Outfile, "\n~s\n", [Msg])
+    Outfile -> io:format(Outfile, "\n~ts\n", [Msg])
   end,
   maybe_close_output_file(State),
   throw({dialyzer_error, lists:flatten(Msg)}).
@@ -792,7 +794,7 @@ print_ext_calls(#cl_state{output = Output,
   end.
 
 do_print_ext_calls(Output, [{M,F,A}|T], Before) ->
-  io:format(Output, "~s~p:~p/~p\n", [Before,M,F,A]),
+  io:format(Output, "~s~tp:~tp/~p\n", [Before,M,F,A]),
   do_print_ext_calls(Output, T, Before);
 do_print_ext_calls(_, [], _) ->
   ok.
@@ -825,7 +827,7 @@ print_ext_types(#cl_state{output = Output,
   end.
 
 do_print_ext_types(Output, [{M,F,A}|T], Before) ->
-  io:format(Output, "~s~p:~p/~p\n", [Before,M,F,A]),
+  io:format(Output, "~s~tp:~tp/~p\n", [Before,M,F,A]),
   do_print_ext_types(Output, T, Before);
 do_print_ext_types(_, [], _) ->
   ok.
@@ -844,10 +846,10 @@ print_warnings(#cl_state{output = Output,
 	    formatted ->
 	      [dialyzer:format_warning(W, FOpt) || W <- PrWarnings];
 	    raw ->
-	      [io_lib:format("~p. \n",
+	      [io_lib:format("~tp. \n",
                              [W]) || W <- set_warning_id(PrWarnings)]
 	  end,
-      io:format(Output, "\n~s", [S])
+      io:format(Output, "\n~ts", [S])
   end.
 
 -spec process_warnings([raw_warning()]) -> [raw_warning()].
diff --git a/lib/dialyzer/src/dialyzer_cl_parse.erl b/lib/dialyzer/src/dialyzer_cl_parse.erl
index baeffe99d8..a456d38e64 100644
--- a/lib/dialyzer/src/dialyzer_cl_parse.erl
+++ b/lib/dialyzer/src/dialyzer_cl_parse.erl
@@ -37,11 +37,12 @@ start() ->
   init(),
   Args = init:get_plain_arguments(),
   try
-    cl(Args)
+    Ret = cl(Args),
+    Ret
   catch
     throw:{dialyzer_cl_parse_error, Msg} -> {error, Msg};
     _:R ->
-      Msg = io_lib:format("~p\n~p\n", [R, erlang:get_stacktrace()]),
+      Msg = io_lib:format("~tp\n~tp\n", [R, erlang:get_stacktrace()]),
       {error, lists:flatten(Msg)}
   end.
 
diff --git a/lib/dialyzer/src/dialyzer_contracts.erl b/lib/dialyzer/src/dialyzer_contracts.erl
index 5f24b5a668..300af7956d 100644
--- a/lib/dialyzer/src/dialyzer_contracts.erl
+++ b/lib/dialyzer/src/dialyzer_contracts.erl
@@ -293,7 +293,7 @@ check_extraneous_1(Contract, SuccType) ->
   CRng = erl_types:t_fun_range(Contract),
   CRngs = erl_types:t_elements(CRng),
   STRng = erl_types:t_fun_range(SuccType),
-  ?debug("CR = ~p\nSR = ~p\n", [CRngs, STRng]),
+  ?debug("CR = ~tp\nSR = ~tp\n", [CRngs, STRng]),
   case [CR || CR <- CRngs,
               erl_types:t_is_none(erl_types:t_inf(CR, STRng))] of
     [] ->
@@ -360,7 +360,7 @@ process_contract({Contract, Constraints}, CallTypes0) ->
   CallTypesFun = erl_types:t_fun(CallTypes0, erl_types:t_any()),
   ContArgsFun = erl_types:t_fun(erl_types:t_fun_args(Contract),
 				erl_types:t_any()),
-  ?debug("Instance: Contract:  ~s\n          Arguments: ~s\n",
+  ?debug("Instance: Contract:  ~ts\n          Arguments: ~ts\n",
 	 [erl_types:t_to_string(ContArgsFun),
 	  erl_types:t_to_string(CallTypesFun)]),
   case solve_constraints(ContArgsFun, CallTypesFun, Constraints) of
@@ -427,7 +427,7 @@ insert_constraints([{subtype, Type1, Type2}|Left], Map) ->
     false ->
       %% A lot of things should change to add supertypes
       throw({error, io_lib:format("First argument of is_subtype constraint "
-				  "must be a type variable: ~p\n", [Type1])})
+				  "must be a type variable: ~tp\n", [Type1])})
   end;
 insert_constraints([], Map) -> Map.
 
@@ -439,9 +439,9 @@ insert_constraints([], Map) -> Map.
         contracts().
 
 store_tmp_contract(MFA, FileLine, {TypeSpec, Xtra}, SpecMap, RecordsDict) ->
-  %% io:format("contract from form: ~p\n", [TypeSpec]),
+  %% io:format("contract from form: ~tp\n", [TypeSpec]),
   TmpContract = contract_from_form(TypeSpec, MFA, RecordsDict, FileLine),
-  %% io:format("contract: ~p\n", [TmpContract]),
+  %% io:format("contract: ~tp\n", [TmpContract]),
   maps:put(MFA, {FileLine, TmpContract, Xtra}, SpecMap).
 
 contract_from_form(Forms, MFA, RecDict, FileLine) ->
@@ -458,8 +458,8 @@ contract_from_form([{type, _, 'fun', [_, _]} = Form | Left], MFA, RecDict,
 	  catch
 	    throw:{error, Msg} ->
 	      {File, Line} = FileLine,
-	      NewMsg = io_lib:format("~s:~p: ~s", [filename:basename(File),
-                                                   Line, Msg]),
+	      NewMsg = io_lib:format("~ts:~p: ~ts", [filename:basename(File),
+                                                     Line, Msg]),
 	      throw({error, NewMsg})
 	  end,
         NewTypeNoVars = erl_types:subst_all_vars_to_any(NewType),
@@ -514,7 +514,7 @@ initialize_constraints([Constr|Rest], MFA, RecDict, ExpTypes, RecordTable,
     {type, _, constraint, [{atom,_,Name}, List]} ->
       N = length(List),
       throw({error,
-	     io_lib:format("Unsupported type guard ~w/~w\n", [Name, N])})
+	     io_lib:format("Unsupported type guard ~tw/~w\n", [Name, N])})
   end.
 
 constraints_fixpoint(Constrs, MFA, RecDict, ExpTypes, RecordTable, Cache) ->
@@ -686,7 +686,7 @@ get_invalid_contract_warnings_funs([{MFA, {FileLine, Contract, _Xtra}}|Left],
     {value, {Ret, Args}} ->
       Sig = erl_types:t_fun(Args, Ret),
       {M, _F, _A} = MFA,
-      %% io:format("MFA ~p~n", [MFA]),
+      %% io:format("MFA ~tp~n", [MFA]),
       Opaques = FindOpaques(M),
       {File, Line} = FileLine,
       WarningInfo = {File, Line, MFA},
diff --git a/lib/dialyzer/src/dialyzer_dataflow.erl b/lib/dialyzer/src/dialyzer_dataflow.erl
index 4c29b4f1eb..46a8f01360 100644
--- a/lib/dialyzer/src/dialyzer_dataflow.erl
+++ b/lib/dialyzer/src/dialyzer_dataflow.erl
@@ -191,19 +191,19 @@ analyze_loop(State) ->
       {ArgTypes, IsCalled} = state__get_args_and_status(Fun, NewState1),
       case not IsCalled of
 	true ->
-	  ?debug("Not handling (not called) ~w: ~s\n",
+	  ?debug("Not handling (not called) ~w: ~ts\n",
 		 [NewState1#state.curr_fun,
 		  t_to_string(t_product(ArgTypes))]),
 	  analyze_loop(NewState1);
 	false ->
 	  case state__fun_env(Fun, NewState1) of
 	    none ->
-	      ?debug("Not handling (no env) ~w: ~s\n",
+	      ?debug("Not handling (no env) ~w: ~ts\n",
 		     [NewState1#state.curr_fun,
 		      t_to_string(t_product(ArgTypes))]),
 	      analyze_loop(NewState1);
 	    Map ->
-	      ?debug("Handling fun ~p: ~s\n",
+	      ?debug("Handling fun ~p: ~ts\n",
 		     [NewState1#state.curr_fun,
 		      t_to_string(state__fun_type(Fun, NewState1))]),
 	      Vars = cerl:fun_vars(Fun),
@@ -222,7 +222,7 @@ analyze_loop(State) ->
                 end,
 	      {NewState4, _Map2, BodyType} =
 		traverse(Body, Map1, NewState3),
-	      ?debug("Done analyzing: ~w:~s\n",
+	      ?debug("Done analyzing: ~w:~ts\n",
 		     [NewState1#state.curr_fun,
 		      t_to_string(t_fun(ArgTypes, BodyType))]),
               NewState5 =
@@ -232,7 +232,7 @@ analyze_loop(State) ->
                 end,
               NewState6 =
                 state__update_fun_entry(Fun, ArgTypes, BodyType, NewState5),
-              ?debug("done adding stuff for ~w\n",
+              ?debug("done adding stuff for ~tw\n",
                      [state__lookup_name(get_label(Fun), State)]),
               analyze_loop(NewState6)
 	  end
@@ -487,23 +487,23 @@ handle_apply_or_call([{TypeOfApply, {Fun, Sig, Contr, LocalRet}}|Left],
     end,
 
   ?debug("--------------------------------------------------------\n", []),
-  ?debug("Fun: ~p\n", [state__lookup_name(Fun, State)]),
+  ?debug("Fun: ~tp\n", [state__lookup_name(Fun, State)]),
   ?debug("Module ~p\n", [State#state.module]),
-  ?debug("CArgs ~s\n", [erl_types:t_to_string(t_product(CArgs))]),
-  ?debug("ArgTypes ~s\n", [erl_types:t_to_string(t_product(ArgTypes))]),
-  ?debug("BifArgs ~p\n", [erl_types:t_to_string(t_product(BifArgs))]),
+  ?debug("CArgs ~ts\n", [erl_types:t_to_string(t_product(CArgs))]),
+  ?debug("ArgTypes ~ts\n", [erl_types:t_to_string(t_product(ArgTypes))]),
+  ?debug("BifArgs ~tp\n", [erl_types:t_to_string(t_product(BifArgs))]),
 
   NewArgsSig = t_inf_lists(SigArgs, ArgTypes, Opaques),
-  ?debug("SigArgs ~s\n", [erl_types:t_to_string(t_product(SigArgs))]),
-  ?debug("NewArgsSig: ~s\n", [erl_types:t_to_string(t_product(NewArgsSig))]),
+  ?debug("SigArgs ~ts\n", [erl_types:t_to_string(t_product(SigArgs))]),
+  ?debug("NewArgsSig: ~ts\n", [erl_types:t_to_string(t_product(NewArgsSig))]),
   NewArgsContract = t_inf_lists(CArgs, ArgTypes, Opaques),
-  ?debug("NewArgsContract: ~s\n",
+  ?debug("NewArgsContract: ~ts\n",
 	 [erl_types:t_to_string(t_product(NewArgsContract))]),
   NewArgsBif = t_inf_lists(BifArgs, ArgTypes, Opaques),
-  ?debug("NewArgsBif: ~s\n", [erl_types:t_to_string(t_product(NewArgsBif))]),
+  ?debug("NewArgsBif: ~ts\n", [erl_types:t_to_string(t_product(NewArgsBif))]),
   NewArgTypes0 = t_inf_lists(NewArgsSig, NewArgsContract),
   NewArgTypes = t_inf_lists(NewArgTypes0, NewArgsBif, Opaques),
-  ?debug("NewArgTypes ~s\n", [erl_types:t_to_string(t_product(NewArgTypes))]),
+  ?debug("NewArgTypes ~ts\n", [erl_types:t_to_string(t_product(NewArgTypes))]),
   ?debug("\n", []),
 
   BifRet = BifRange(NewArgTypes),
@@ -511,12 +511,12 @@ handle_apply_or_call([{TypeOfApply, {Fun, Sig, Contr, LocalRet}}|Left],
   RetWithoutContr = t_inf(SigRange, BifRet),
   RetWithoutLocal = t_inf(ContrRet, RetWithoutContr),
 
-  ?debug("RetWithoutContr: ~s\n",[erl_types:t_to_string(RetWithoutContr)]),
-  ?debug("RetWithoutLocal: ~s\n", [erl_types:t_to_string(RetWithoutLocal)]),
-  ?debug("BifRet: ~s\n", [erl_types:t_to_string(BifRange(NewArgTypes))]),
-  ?debug("SigRange: ~s\n", [erl_types:t_to_string(SigRange)]),
-  ?debug("ContrRet: ~s\n", [erl_types:t_to_string(ContrRet)]),
-  ?debug("LocalRet: ~s\n", [erl_types:t_to_string(LocalRet)]),
+  ?debug("RetWithoutContr: ~ts\n",[erl_types:t_to_string(RetWithoutContr)]),
+  ?debug("RetWithoutLocal: ~ts\n", [erl_types:t_to_string(RetWithoutLocal)]),
+  ?debug("BifRet: ~ts\n", [erl_types:t_to_string(BifRange(NewArgTypes))]),
+  ?debug("SigRange: ~ts\n", [erl_types:t_to_string(SigRange)]),
+  ?debug("ContrRet: ~ts\n", [erl_types:t_to_string(ContrRet)]),
+  ?debug("LocalRet: ~ts\n", [erl_types:t_to_string(LocalRet)]),
 
   State1 =
     case is_race_analysis_enabled(State) of
@@ -596,7 +596,7 @@ handle_apply_or_call([{TypeOfApply, {Fun, Sig, Contr, LocalRet}}|Left],
       false -> t_inf(RetWithoutLocal, LocalRet)
     end,
   NewAccRet = t_sup(AccRet, TotalRet),
-  ?debug("NewAccRet: ~s\n", [t_to_string(NewAccRet)]),
+  ?debug("NewAccRet: ~ts\n", [t_to_string(NewAccRet)]),
   {NewWarnings, State4} = state__remove_added_warnings(State, State3),
   {HowMany, OldWarnings} = Warns,
   NewWarns =
@@ -1335,7 +1335,7 @@ do_clause(C, Arg, ArgType0, OrigArgType, Map, State, Warns) ->
     end,
   case BindRes of
     {error, ErrorType, NewPats, Type, OpaqueTerm} ->
-      ?debug("Failed binding pattern: ~s\nto ~s\n",
+      ?debug("Failed binding pattern: ~ts\nto ~ts\n",
 	     [cerl_prettypr:format(C), format_type(ArgType0, State1)]),
       case state__warning_mode(State1) of
         false ->
@@ -1451,7 +1451,7 @@ do_clause(C, Arg, ArgType0, OrigArgType, Map, State, Warns) ->
 	end,
       case bind_guard(Guard, Map3, State1) of
 	{error, Reason} ->
-	  ?debug("Failed guard: ~s\n",
+	  ?debug("Failed guard: ~ts\n",
 		 [cerl_prettypr:format(C, [{hook, cerl_typean:pp_hook()}])]),
 	  PatString = format_patterns(Pats),
 	  DefaultMsg =
@@ -1532,7 +1532,7 @@ bind_pat_vars_reverse(Pats, Types, Acc, Map, State) ->
   end.
 
 bind_pat_vars([Pat|PatLeft], [Type|TypeLeft], Acc, Map, State, Rev) ->
-  ?debug("Binding pat: ~w to ~s\n", [cerl:type(Pat), format_type(Type, State)]
+  ?debug("Binding pat: ~tw to ~ts\n", [cerl:type(Pat), format_type(Type, State)]
 ),
   Opaques = State#state.opaques,
   {NewMap, TypeOut} =
@@ -1830,7 +1830,7 @@ bind_guard(Guard, Map, State) ->
   end.
 
 bind_guard(Guard, Map, Env, Eval, State) ->
-  ?debug("Handling ~w guard: ~s\n",
+  ?debug("Handling ~tw guard: ~ts\n",
 	 [Eval, cerl_prettypr:format(Guard, [{noann, true}])]),
   case cerl:type(Guard) of
     binary ->
@@ -2009,7 +2009,7 @@ handle_guard_type_test(Guard, F, Map, Env, Eval, State) ->
       ?debug("Type test: ~w failed\n", [F]),
       signal_guard_fail(Eval, Guard, [ArgType], State);
     {ok, NewArgType, Ret} ->
-      ?debug("Type test: ~w succeeded, NewType: ~s, Ret: ~s\n",
+      ?debug("Type test: ~w succeeded, NewType: ~ts, Ret: ~ts\n",
 	     [F, t_to_string(NewArgType), t_to_string(Ret)]),
       {enter_type(Arg, NewArgType, Map1), Ret}
   end.
@@ -2295,8 +2295,8 @@ handle_guard_eqeq(Guard, Map, Env, Eval, State) ->
 bind_eqeq_guard(Guard, Arg1, Arg2, Map, Env, Eval, State) ->
   {Map1, Type1} = bind_guard(Arg1, Map, Env, dont_know, State),
   {Map2, Type2} = bind_guard(Arg2, Map1, Env, dont_know, State),
-  ?debug("Types are:~s =:= ~s\n", [t_to_string(Type1),
-				   t_to_string(Type2)]),
+  ?debug("Types are:~ts =:= ~ts\n", [t_to_string(Type1),
+                                     t_to_string(Type2)]),
   Opaques = State#state.opaques,
   Inf = t_inf(Type1, Type2, Opaques),
   case t_is_none(Inf) of
@@ -2840,7 +2840,7 @@ enter_type(Key, Val, MS) ->
 	      ?debug("Binding ~p to ~p\n", [KeyLabel, NewKey]),
 	      enter_type(NewKey, Val, MS);
 	    error ->
-	      ?debug("Entering ~p :: ~s\n", [KeyLabel, t_to_string(Val)]),
+	      ?debug("Entering ~p :: ~ts\n", [KeyLabel, t_to_string(Val)]),
 	      case maps:find(KeyLabel, Map) of
 		{ok, Value} ->
                   case erl_types:t_is_equal(Val, Value) of
@@ -2940,7 +2940,7 @@ debug_pp_map(#map{map = Map}=MapRec) ->
   Keys = maps:keys(Map),
   io:format("Map:\n", []),
   lists:foreach(fun (Key) ->
-		    io:format("\t~w :: ~s\n",
+		    io:format("\t~w :: ~ts\n",
 			      [Key, t_to_string(lookup_type(Key, MapRec))])
 		end, Keys),
   ok.
@@ -3095,7 +3095,7 @@ state__add_warning(#state{warnings = Warnings, warning_mode = true} = State,
                      abs(get_line(Ann)),
                      State#state.curr_fun},
       Warn = {Tag, WarningInfo, Msg},
-      ?debug("MSG ~s\n", [dialyzer:format_warning(Warn)]),
+      ?debug("MSG ~ts\n", [dialyzer:format_warning(Warn)]),
       State#state{warnings = [Warn|Warnings]};
     false ->
       case is_compiler_generated(Ann) of
@@ -3107,7 +3107,7 @@ state__add_warning(#state{warnings = Warnings, warning_mode = true} = State,
           Warn = {Tag, WarningInfo, Msg},
           case Tag of
             ?WARN_CONTRACT_RANGE -> ok;
-            _ -> ?debug("MSG ~s\n", [dialyzer:format_warning(Warn)])
+            _ -> ?debug("MSG ~ts\n", [dialyzer:format_warning(Warn)])
           end,
           State#state{warnings = [Warn|Warnings]}
       end
@@ -3351,14 +3351,14 @@ state__update_fun_entry(Tree, ArgTypes, Out0,
   SameOut = t_is_equal(OldOut, Out),
   if
     SameArgs, SameOut ->
-      ?debug("Fixpoint for ~w: ~s\n",
+      ?debug("Fixpoint for ~tw: ~ts\n",
 	     [state__lookup_name(Fun, State),
 	      t_to_string(t_fun(ArgTypes, Out))]),
       State;
     true ->
       %% Can only happen in self-recursive functions.
       NewEntry = {OldArgTypes, Out},
-      ?debug("New Entry for ~w: ~s\n",
+      ?debug("New Entry for ~tw: ~ts\n",
 	     [state__lookup_name(Fun, State),
 	      t_to_string(t_fun(OldArgTypes, Out))]),
       NewFunTab = dict:store(Fun, NewEntry, FunTab),
@@ -3380,7 +3380,7 @@ state__add_work_from_fun(Tree, #state{callgraph = Callgraph,
 		       || MFA <- MFAList],
 	  %% Must filter the result for results in this module.
 	  FilteredList = [L || {ok, L} <- LabelList, dict:is_key(L, TreeMap)],
-	  ?debug("~w: Will try to add:~w\n",
+	  ?debug("~tw: Will try to add:~tw\n",
 		 [state__lookup_name(Label, State), MFAList]),
 	  lists:foldl(fun(L, AccState) ->
 			  state__add_work(L, AccState)
@@ -3427,7 +3427,7 @@ state__fun_info(Fun, #state{callgraph = CG, fun_tab = FunTab, plt = PLT}) ->
       {not_handled, {_Args, Ret}} -> Ret;
       {_Args, Ret} -> Ret
     end,
-  ?debug("LocalRet: ~s\n", [t_to_string(LocalRet)]),
+  ?debug("LocalRet: ~ts\n", [t_to_string(LocalRet)]),
   {Fun, Sig, Contract, LocalRet}.
 
 forward_args(Fun, ArgTypes, #state{work = Work, fun_tab = FunTab} = State) ->
@@ -3445,7 +3445,7 @@ forward_args(Fun, ArgTypes, #state{work = Work, fun_tab = FunTab} = State) ->
       NewArgTypes = [t_sup(X, Y) ||
                       {X, Y} <- lists:zip(ArgTypes, OldArgTypes)],
       NewWork = add_work(Fun, Work),
-      ?debug("~w: forwarding args ~s\n",
+      ?debug("~tw: forwarding args ~ts\n",
 	     [state__lookup_name(Fun, State),
 	      t_to_string(t_product(NewArgTypes))]),
       NewFunTab = dict:store(Fun, {NewArgTypes, OldOut}, FunTab),
diff --git a/lib/dialyzer/src/dialyzer_gui_wx.erl b/lib/dialyzer/src/dialyzer_gui_wx.erl
index d1b955044b..bcaeca4cdc 100644
--- a/lib/dialyzer/src/dialyzer_gui_wx.erl
+++ b/lib/dialyzer/src/dialyzer_gui_wx.erl
@@ -469,18 +469,18 @@ gui_loop(#gui_state{backend_pid = BackendPid, doc_plt = DocPlt,
       Msg = io_lib:format("The following functions are called "
 			  "but type information about them is not available.\n"
 			  "The analysis might get more precise by including "
-			  "the modules containing these functions:\n\n\t~p\n", 
+			  "the modules containing these functions:\n\n\t~tp\n",
 			  [ExtCalls]),
       free_editor(State,"Analysis Done",  Msg),
       gui_loop(State);
     {BackendPid, ext_types, ExtTypes} ->
-      Map = fun({M,F,A}) -> io_lib:format("~p:~p/~p",[M,F,A]) end,
+      Map = fun({M,F,A}) -> io_lib:format("~tp:~tp/~p",[M,F,A]) end,
       ExtTypeString = string:join(lists:map(Map, ExtTypes), "\n"),
       Msg = io_lib:format("The following remote types are being used "
 			  "but information about them is not available.\n"
 			  "The analysis might get more precise by including "
 			  "the modules containing these types and making sure "
-			  "that they are exported:\n~s\n", [ExtTypeString]),
+			  "that they are exported:\n~ts\n", [ExtTypeString]),
       free_editor(State, "Analysis done", Msg),
       gui_loop(State);
     {BackendPid, log, LogMsg} ->
@@ -508,7 +508,7 @@ gui_loop(#gui_state{backend_pid = BackendPid, doc_plt = DocPlt,
       config_gui_stop(State),
       gui_loop(State);
     {'EXIT', BackendPid, Reason} when Reason =/= 'normal' ->
-      free_editor(State, ?DIALYZER_ERROR_TITLE, io_lib:format("~p", [Reason])),
+      free_editor(State, ?DIALYZER_ERROR_TITLE, io_lib:format("~tp", [Reason])),
       config_gui_stop(State),
       gui_loop(State)
   end.
@@ -926,7 +926,7 @@ include_dialog(#gui_state{gui = Wx, frame = Frame, options = Options}) ->
   wxButton:connect(DeleteAllButton, command_button_clicked),
   wxButton:connect(Ok, command_button_clicked),
   wxButton:connect(Cancel, command_button_clicked),
-  Dirs = [io_lib:format("~s", [X]) || X <- Options#options.include_dirs],
+  Dirs = [io_lib:format("~ts", [X]) || X <- Options#options.include_dirs],
   wxListBox:set(Box, Dirs),
   Layout = wxBoxSizer:new(?wxVERTICAL),
   Buttons = wxBoxSizer:new(?wxHORIZONTAL),
@@ -1118,13 +1118,13 @@ handle_help(State, Title, Txt) ->
   case file:open(FileName, [read]) of
     {error, Reason} ->
       error_sms(State, 
-		io_lib:format("Could not find doc/~s file!\n\n ~p", 
+		io_lib:format("Could not find doc/~ts file!\n\n ~tp",
 			      [Txt, Reason]));
     {ok, _Handle} ->
       case file:read_file(FileName) of
 	{error, Reason} ->
 	  error_sms(State, 
-		    io_lib:format("Could not read doc/~s file!\n\n ~p", 
+		    io_lib:format("Could not read doc/~ts file!\n\n ~tp",
 				  [Txt, Reason]));
 	{ok, Binary} ->
 	  Contents = binary_to_list(Binary),
@@ -1223,7 +1223,7 @@ update_explanation(#gui_state{explanation_box = Box}, Explanation) ->
   wxTextCtrl:appendText(Box, ExplString).
 
 format_explanation({function_return, {M, F, A}, NewList}) ->
-  io_lib:format("The function ~p: ~p/~p returns ~p\n",
+  io_lib:format("The function ~w:~tw/~w returns ~ts\n",
 		[M, F, A, erl_types:t_to_string(NewList)]);
 format_explanation(Explanation) ->
   io_lib:format("~p\n", [Explanation]).
diff --git a/lib/dialyzer/src/dialyzer_options.erl b/lib/dialyzer/src/dialyzer_options.erl
index ec3f41311d..03040f8e38 100644
--- a/lib/dialyzer/src/dialyzer_options.erl
+++ b/lib/dialyzer/src/dialyzer_options.erl
@@ -112,7 +112,7 @@ adapt_get_warnings(Opts = #options{analysis_type = Mode,
 -spec bad_option(string(), term()) -> no_return().
 
 bad_option(String, Term) ->
-  Msg = io_lib:format("~s: ~P", [String, Term, 25]),
+  Msg = io_lib:format("~ts: ~tP", [String, Term, 25]),
   throw({dialyzer_options_error, lists:flatten(Msg)}).
 
 build_options([{OptName, undefined}|Rest], Options) when is_atom(OptName) ->
diff --git a/lib/dialyzer/src/dialyzer_plt.erl b/lib/dialyzer/src/dialyzer_plt.erl
index 847faab2f4..f36a008739 100644
--- a/lib/dialyzer/src/dialyzer_plt.erl
+++ b/lib/dialyzer/src/dialyzer_plt.erl
@@ -253,7 +253,7 @@ from_file(FileName, ReturnInfo) ->
     {ok, Rec} ->
       case check_version(Rec) of
 	error ->
-	  Msg = io_lib:format("Old PLT file ~s\n", [FileName]),
+	  Msg = io_lib:format("Old PLT file ~ts\n", [FileName]),
 	  plt_error(Msg);
 	ok ->
           Types = [{Mod, maps:from_list(dict:to_list(Types))} ||
@@ -272,7 +272,7 @@ from_file(FileName, ReturnInfo) ->
 	  end
       end;
     {error, Reason} ->
-      Msg = io_lib:format("Could not read PLT file ~s: ~p\n",
+      Msg = io_lib:format("Could not read PLT file ~ts: ~p\n",
 			  [FileName, Reason]),
       plt_error(Msg)
   end.
@@ -356,7 +356,7 @@ merge_plts_or_report_conflicts(PltFiles, Plts) ->
       ConfFiles = find_duplicates(IncFiles),
       Msg = io_lib:format("Could not merge PLTs since they are not disjoint\n"
                           "The following files are included in more than one "
-                          "PLTs:\n~p\n", [ConfFiles]),
+                          "PLTs:\n~tp\n", [ConfFiles]),
       plt_error(Msg)
   end.
 
@@ -391,7 +391,7 @@ to_file(FileName,
   case file:write_file(FileName, Bin) of
     ok -> ok;
     {error, Reason} ->
-      Msg = io_lib:format("Could not write PLT file ~s: ~w\n",
+      Msg = io_lib:format("Could not write PLT file ~ts: ~w\n",
 			  [FileName, Reason]),
       throw({dialyzer_error, Msg})
   end.
@@ -467,7 +467,7 @@ compute_md5_from_files(Files) ->
 compute_md5_from_file(File) ->
   case filelib:is_regular(File) of
     false ->
-      Msg = io_lib:format("Not a regular file: ~s\n", [File]),
+      Msg = io_lib:format("Not a regular file: ~ts\n", [File]),
       throw({dialyzer_error, Msg});
     true ->
       case dialyzer_utils:get_core_from_beam(File) of
@@ -635,7 +635,7 @@ get_specs(#plt{info = Info}, M, F, A) when is_atom(M), is_atom(F) ->
   end.
 
 create_specs([{{M, F, _A}, {Ret, Args}}|Left], M) ->
-  [io_lib:format("-spec ~w(~s) -> ~s\n",
+  [io_lib:format("-spec ~tw(~ts) -> ~ts\n",
 		 [F, expand_args(Args), erl_types:t_to_string(Ret)])
    | create_specs(Left, M)];
 create_specs(List = [{{M, _F, _A}, {_Ret, _Args}}| _], _M) ->
@@ -802,7 +802,7 @@ pp_non_returning() ->
   io:format("=                Loops                  =\n"),
   io:format("=========================================\n\n"),
   lists:foreach(fun({{M, F, _}, Type}) ->
-		    io:format("~w:~w~s.\n",
+		    io:format("~w:~tw~ts.\n",
 			      [M, F, dialyzer_utils:format_sig(Type)])
 		end, lists:sort(Unit)),
   io:format("\n"),
@@ -824,7 +824,7 @@ pp_mod(Mod) when is_atom(Mod) ->
       lists:foreach(fun({{_, F, _}, Ret, Args}) ->
 			T = erl_types:t_fun(Args, Ret),
 			S = dialyzer_utils:format_sig(T),
-			io:format("-spec ~w~s.\n", [F, S])
+			io:format("-spec ~tw~ts.\n", [F, S])
 		    end, lists:sort(List));
     none ->
       io:format("dialyzer: Found no module named '~s' in the PLT\n", [Mod])
diff --git a/lib/dialyzer/src/dialyzer_succ_typings.erl b/lib/dialyzer/src/dialyzer_succ_typings.erl
index be685baf22..66c6c5e9ed 100644
--- a/lib/dialyzer/src/dialyzer_succ_typings.erl
+++ b/lib/dialyzer/src/dialyzer_succ_typings.erl
@@ -260,8 +260,8 @@ refine_one_module(M, {CodeServer, Callgraph, Plt, _Solvers}) ->
   FindOpaques = find_opaques_fun(Records),
   DecoratedFunTypes =
     decorate_succ_typings(Contracts, Callgraph, NewFunTypes, FindOpaques),
-  %% ?debug("NewFunTypes       ~p\n   ~n", [dict:to_list(NewFunTypes)]),
-  %% ?debug("refine DecoratedFunTypes ~p\n   ~n", [dict:to_list(DecoratedFunTypes)]),
+  %% ?debug("NewFunTypes       ~tp\n   ~n", [dict:to_list(NewFunTypes)]),
+  %% ?debug("refine DecoratedFunTypes ~tp\n   ~n", [dict:to_list(DecoratedFunTypes)]),
   debug_pp_functions("Refine", NewFunTypes, DecoratedFunTypes, Callgraph),
 
   case reached_fixpoint(FunTypes, DecoratedFunTypes) of
@@ -314,7 +314,7 @@ compare_types_1([{X, Type1}|Left1], [{X, Type2}|Left2], Strict, NotFixpoint) ->
   case Res of
     true -> compare_types_1(Left1, Left2, Strict, NotFixpoint);
     false -> 
-      ?debug("Failed fixpoint for ~w: ~s =/= ~s\n",
+      ?debug("Failed fixpoint for ~w: ~ts =/= ~ts\n",
 	     [X, erl_types:t_to_string(Type1), erl_types:t_to_string(Type2)]),
       compare_types_1(Left1, Left2, Strict, [{X, Type2}|NotFixpoint])
   end;
@@ -371,8 +371,8 @@ find_succ_types_for_scc(SCC0, {Codeserver, Callgraph, Plt, Solvers}) ->
   PltContracts =
     dialyzer_contracts:check_contracts(Contracts3, Callgraph,
                                        DecoratedFunTypes, FindOpaques),
-  %% ?debug("FilteredFunTypes ~p\n   ~n", [dict:to_list(FilteredFunTypes)]),
-  %% ?debug("SCC DecoratedFunTypes ~p\n   ~n", [dict:to_list(DecoratedFunTypes)]),
+  %% ?debug("FilteredFunTypes ~tp\n   ~n", [dict:to_list(FilteredFunTypes)]),
+  %% ?debug("SCC DecoratedFunTypes ~tp\n   ~n", [dict:to_list(DecoratedFunTypes)]),
   debug_pp_functions("SCC", FilteredFunTypes, DecoratedFunTypes, Callgraph),
   ContractFixpoint =
     lists:all(fun({MFA, _C}) ->
@@ -388,7 +388,7 @@ find_succ_types_for_scc(SCC0, {Codeserver, Callgraph, Plt, Solvers}) ->
 	reached_fixpoint_strict(PropTypes, DecoratedFunTypes)) of
     true -> [];
     false ->
-      ?debug("Not fixpoint for: ~w\n", [AllFuns]),
+      ?debug("Not fixpoint for: ~tw\n", [AllFuns]),
       [Fun || {Fun, _Arity} <- AllFuns]
   end.
 
@@ -476,11 +476,11 @@ format_succ_types([], _Callgraph, Acc) ->
 -ifdef(DEBUG).
 debug_pp_succ_typings(SuccTypes) ->
   ?debug("Succ typings:\n", []),
-  [?debug("  ~w :: ~s\n", 
+  [?debug("  ~tw :: ~ts\n",
 	  [MFA, erl_types:t_to_string(erl_types:t_fun(ArgT, RetT))])
    || {MFA, {RetT, ArgT}} <- SuccTypes],
   ?debug("Contracts:\n", []),
-  [?debug("  ~w :: ~s\n", 
+  [?debug("  ~tw :: ~ts\n",
 	  [MFA, erl_types:t_to_string(erl_types:t_fun(ArgT, RetFun(ArgT)))])
    || {MFA, {contract, RetFun, ArgT}} <- SuccTypes],
   ?debug("\n", []),
@@ -492,12 +492,12 @@ debug_pp_functions(Header, FunTypes, DecoratedFunTypes, Callgraph) ->
   DTypes = lists:keysort(1, dict:to_list(DecoratedFunTypes)),
   Fun = fun({{Label, Type},{Label, DecoratedType}}) ->
             Name = lookup_name(Label, Callgraph),
-            ?debug("~w (~w): ~s\n",
+            ?debug("~tw (~w): ~ts\n",
                    [Name, Label, erl_types:t_to_string(Type)]),
             case erl_types:t_is_equal(Type, DecoratedType) of
               true -> ok;
               false ->
-                ?debug("  With opaque types: ~s\n",
+                ?debug("  With opaque types: ~ts\n",
                        [erl_types:t_to_string(DecoratedType)])
             end
         end,
diff --git a/lib/dialyzer/src/dialyzer_typesig.erl b/lib/dialyzer/src/dialyzer_typesig.erl
index c3ba44fde7..a0a69cb2ea 100644
--- a/lib/dialyzer/src/dialyzer_typesig.erl
+++ b/lib/dialyzer/src/dialyzer_typesig.erl
@@ -771,7 +771,7 @@ handle_call(Call, DefinedVars, State) ->
 	{ok, Var} ->
 	  %% This is part of the SCC currently analyzed.
 	  %% Intercept and change this to an apply instead.
-	  ?debug("Found the call to ~w\n", [MFA]),
+	  ?debug("Found the call to ~tw\n", [MFA]),
 	  Label = cerl_trees:get_label(Call),
 	  Apply = cerl:ann_c_apply([{label, Label}], Var, Args),
 	  traverse(Apply, DefinedVars, State)
@@ -1789,11 +1789,11 @@ get_bif_test_constr(Dst, Arg, Type, _State) ->
 %%=============================================================================
 
 solve([Fun], State) ->
-  ?debug("============ Analyzing Fun: ~w ===========\n",
+  ?debug("============ Analyzing Fun: ~tw ===========\n",
 	 [debug_lookup_name(Fun)]),
   solve_fun(Fun, map_new(), State);
 solve([_|_] = SCC, State) ->
-  ?debug("============ Analyzing SCC: ~w ===========\n",
+  ?debug("============ Analyzing SCC: ~tw ===========\n",
 	 [[debug_lookup_name(F) || F <- SCC]]),
   Users = comp_users(SCC, State),
   solve_scc(SCC, map_new(), State, Users, _ToSolve=SCC, false).
@@ -1829,13 +1829,13 @@ solve_scc(SCC, Map, State, Users, ToSolve, TryingUnit) ->
 			     erase_type(t_var_name(Fun), AccFunMap)
 			 end, Map, ToSolve),
   Map1 = enter_type_lists(Vars, RecTypes, CleanMap),
-  ?debug("Checking SCC: ~w\n", [[debug_lookup_name(F) || F <- SCC]]),
+  ?debug("Checking SCC: ~tw\n", [[debug_lookup_name(F) || F <- SCC]]),
   SolveFun = fun(X, Y) -> scc_fold_fun(X, Y, State) end,
   Map2 = lists:foldl(SolveFun, Map1, ToSolve),
   Updated = updated_vars_only(Vars, Map, Map2),
   case Updated =:= [] of
     true ->
-      ?debug("SCC ~w reached fixpoint\n", [SCC]),
+      ?debug("SCC ~tw reached fixpoint\n", [SCC]),
       NewTypes = unsafe_lookup_type_list(Funs, Map2),
       case erl_types:any_none([t_fun_range(T) || T <- NewTypes])
 	andalso TryingUnit =:= false of
@@ -1851,7 +1851,7 @@ solve_scc(SCC, Map, State, Users, ToSolve, TryingUnit) ->
 	  Map2
       end;
     false ->
-      ?debug("SCC ~w did not reach fixpoint\n", [SCC]),
+      ?debug("SCC ~tw did not reach fixpoint\n", [SCC]),
       ToSolve1 = affected(Updated, Users),
       solve_scc(SCC, Map2, State, Users, ToSolve1, TryingUnit)
   end.
@@ -1875,8 +1875,8 @@ scc_fold_fun(F, FunMap, State) ->
 		error ->
 		  enter_type(F, NewType, FunMap)
 	      end,
-  ?debug("Done solving for function ~w :: ~s\n", [debug_lookup_name(F),
-						  format_type(NewType)]),
+  ?debug("Done solving for function ~tw :: ~ts\n", [debug_lookup_name(F),
+                                                    format_type(NewType)]),
   NewFunMap.
 
 solve(Fun, Cs, FunMap, State) ->
@@ -1895,7 +1895,7 @@ solver(Solver, SolveFun) ->
              [Solver, _R, 60]),
       throw(error)
   catch E:R ->
-      io:format("Solver ~w failed: ~w:~p\n ~p\n",
+      io:format("Solver ~w failed: ~w:~p\n ~tp\n",
                 [Solver, E, R, erlang:get_stacktrace()]),
       throw(error)
   end.
@@ -1932,9 +1932,9 @@ sane_maps(Map1, Map2, Keys, _S1, _S2) ->
                   true -> true;
                   false ->
                     ?debug("Constraint solvers do not agree on ~w\n", [Key]),
-                    ?debug("~w: ~s\n",
+                    ?debug("~w: ~ts\n",
                            [_S1, format_type(unsafe_lookup_type(Key, Map1))]),
-                    ?debug("~w: ~s\n",
+                    ?debug("~w: ~ts\n",
                            [_S2, format_type(unsafe_lookup_type(Key, Map2))]),
                     false
                 end
@@ -1966,7 +1966,7 @@ v2_solve(#constraint_ref{id = Id}, Map, V2State) ->
   v2_solve_reference(Id, Map, V2State).
 
 v2_solve_reference(Id, Map, V2State0) ->
-  ?debug("Checking ref to fun: ~w\n", [debug_lookup_name(Id)]),
+  ?debug("Checking ref to fun: ~tw\n", [debug_lookup_name(Id)]),
   pp_map("Map", Map),
   pp_constr_data("solve_ref", V2State0),
   Map1 = restore_local_map(V2State0, Id, Map),
@@ -1980,7 +1980,7 @@ v2_solve_reference(Id, Map, V2State0) ->
   {FunType, V2State} =
     case Res of
       {error, V2State1} ->
-        ?debug("Error solving for function ~p\n", [debug_lookup_name(Id)]),
+        ?debug("Error solving for function ~tp\n", [debug_lookup_name(Id)]),
         Arity = state__fun_arity(Id, State),
         FunType0 =
           case state__prop_domain(t_var_name(Id), State) of
@@ -1989,12 +1989,12 @@ v2_solve_reference(Id, Map, V2State0) ->
           end,
         {FunType0, V2State1};
       {ok, NewMap, V2State1, U} ->
-        ?debug("Done solving fun: ~p\n", [debug_lookup_name(Id)]),
+        ?debug("Done solving fun: ~tp\n", [debug_lookup_name(Id)]),
         FunType0 = lookup_type(Id, NewMap),
         V2State2 = save_local_map(V2State1, Id, U, NewMap),
         {FunType0, V2State2}
     end,
-  ?debug("ref Id=~w Assigned ~s\n", [Id, format_type(FunType)]),
+  ?debug("ref Id=~w Assigned ~ts\n", [Id, format_type(FunType)]),
   {NewMap1, U1} = enter_var_type(Id, FunType, Map),
   {NewMap2, U2} =
     case state__get_rec_var(Id, State) of
@@ -2004,10 +2004,10 @@ v2_solve_reference(Id, Map, V2State0) ->
   {ok, NewMap2, V2State, lists:umerge(U1, U2)}.
 
 v2_solve_self_recursive(Cs, Map, Id, RecType0, V2State0) ->
-  ?debug("Solving self recursive ~w\n", [debug_lookup_name(Id)]),
+  ?debug("Solving self recursive ~tw\n", [debug_lookup_name(Id)]),
   State = V2State0#v2_state.state,
   {ok, RecVar} = state__get_rec_var(Id, State),
-  ?debug("OldRecType ~s\n", [format_type(RecType0)]),
+  ?debug("OldRecType ~ts\n", [format_type(RecType0)]),
   RecType = t_limit(RecType0, ?TYPE_LIMIT),
   {Map1, U0} = enter_var_type(RecVar, RecType, Map),
   V2State1 = save_updated_vars1(V2State0, Cs, U0), % Probably not necessary
@@ -2319,7 +2319,7 @@ solve_ref_or_list(#constraint_ref{id = Id, deps = Deps},
       error -> {map_new(), false};
       {ok, M} -> {M, true}
     end,
-  ?debug("Checking ref to fun: ~w\n", [debug_lookup_name(Id)]),
+  ?debug("Checking ref to fun: ~tw\n", [debug_lookup_name(Id)]),
   %% Note: mk_constraint_ref() has already removed Id from Deps. The
   %% reason for doing it there is that it makes it easy for
   %% calculate_masks() to make the corresponding adjustment for
@@ -2341,7 +2341,7 @@ solve_ref_or_list(#constraint_ref{id = Id, deps = Deps},
       {NewMapDict, FunType} =
 	case Res of
 	  {error, NewMapDict0} ->
-	    ?debug("Error solving for function ~p\n", [debug_lookup_name(Id)]),
+	    ?debug("Error solving for function ~tp\n", [debug_lookup_name(Id)]),
 	    Arity = state__fun_arity(Id, State),
 	    FunType0 =
 	      case state__prop_domain(t_var_name(Id), State) of
@@ -2350,11 +2350,11 @@ solve_ref_or_list(#constraint_ref{id = Id, deps = Deps},
 	      end,
 	    {NewMapDict0, FunType0};
 	  {ok, NewMapDict0, NewMap} ->
-	    ?debug("Done solving fun: ~p\n", [debug_lookup_name(Id)]),
+	    ?debug("Done solving fun: ~tp\n", [debug_lookup_name(Id)]),
 	    FunType0 = lookup_type(Id, NewMap),
 	    {NewMapDict0, FunType0}
 	end,
-      ?debug("  Id=~w Assigned ~s\n", [Id, format_type(FunType)]),
+      ?debug("  Id=~w Assigned ~ts\n", [Id, format_type(FunType)]),
       NewMap1 = enter_type(Id, FunType, Map),
       NewMap2 =
 	case state__get_rec_var(Id, State) of
@@ -2376,18 +2376,18 @@ solve_ref_or_list(#constraint_list{type=Type, list = Cs, deps = Deps, id = Id},
     true ->
       case Check andalso maps_are_equal(OldLocalMap, Map, Deps) of
         true ->
-          ?debug("~w equal ~w\n", [Type, Id]),
+          ?debug("~tw equal ~w\n", [Type, Id]),
           {ok, MapDict, Map};
         false ->
-          ?debug("~w not equal: ~w. Solving\n", [Type, Id]),
+          ?debug("~tw not equal: ~w. Solving\n", [Type, Id]),
           solve_clist(Cs, Type, Id, Deps, MapDict, Map, State)
       end
   end.
 
 solve_self_recursive(Cs, Map, MapDict, Id, RecType0, State) ->
-  ?debug("Solving self recursive ~w\n", [debug_lookup_name(Id)]),
+  ?debug("Solving self recursive ~tw\n", [debug_lookup_name(Id)]),
   {ok, RecVar} = state__get_rec_var(Id, State),
-  ?debug("OldRecType ~s\n", [format_type(RecType0)]),
+  ?debug("OldRecType ~ts\n", [format_type(RecType0)]),
   RecType = t_limit(RecType0, ?TYPE_LIMIT),
   Map1 = enter_type(RecVar, RecType, erase_type(t_var_name(Id), Map)),
   pp_map("Map1", Map1),
@@ -2469,7 +2469,7 @@ solve_one_c(#constraint{lhs = Lhs, rhs = Rhs, op = Op}, Map) ->
   LhsType = lookup_type(Lhs, Map),
   RhsType = lookup_type(Rhs, Map),
   Inf = t_inf(LhsType, RhsType),
-  ?debug("Solving: ~s :: ~s ~w ~s :: ~s\n\tInf: ~s\n",
+  ?debug("Solving: ~ts :: ~ts ~w ~ts :: ~ts\n\tInf: ~ts\n",
 	 [format_type(Lhs), format_type(LhsType), Op,
 	  format_type(Rhs), format_type(RhsType), format_type(Inf)]),
   case t_is_none(Inf) of
@@ -2501,14 +2501,14 @@ solve_subtype(Type, Inf, Map) ->
 	{_, List} -> {ok, enter_type_list(List, Map)}
       catch
 	throw:{mismatch, _T1, _T2} ->
-	  ?debug("Mismatch between ~s and ~s\n",
+	  ?debug("Mismatch between ~ts and ~ts\n",
 		 [format_type(_T1), format_type(_T2)]),
 	  error
       end.
   %% end.
 
 report_failed_constraint(_C, _Map) ->
-  ?debug("+++++++++++\nFailed: ~s :: ~s ~w ~s :: ~s\n+++++++++++\n",
+  ?debug("+++++++++++\nFailed: ~ts :: ~ts ~w ~ts :: ~ts\n+++++++++++\n",
          [format_type(_C#constraint.lhs),
           format_type(lookup_type(_C#constraint.lhs, _Map)),
           _C#constraint.op,
@@ -2566,7 +2566,7 @@ maps_are_equal_1(Map1, Map2, [H|Tail]) ->
   case is_equal(T1, T2) of
     true -> maps_are_equal_1(Map1, Map2, Tail);
     false ->
-      ?debug("~w: ~s =/= ~s\n", [H, format_type(T1), format_type(T2)]),
+      ?debug("~w: ~ts =/= ~ts\n", [H, format_type(T1), format_type(T2)]),
       false
   end;
 maps_are_equal_1(_Map1, _Map2, []) ->
@@ -2594,7 +2594,7 @@ prune_keys(Map1, Map2, Deps) ->
   end.
 
 enter_type(Key, Val, Map) when is_integer(Key) ->
-  ?debug("Entering ~s :: ~s\n", [format_type(t_var(Key)), format_type(Val)]),
+  ?debug("Entering ~ts :: ~ts\n", [format_type(t_var(Key)), format_type(Val)]),
   %% Keep any() in the map if it is opaque:
   case is_equal(Val, t_any()) of
     true ->
@@ -2603,7 +2603,7 @@ enter_type(Key, Val, Map) when is_integer(Key) ->
       LimitedVal = t_limit(Val, ?INTERNAL_TYPE_LIMIT),
       case is_equal(LimitedVal, Val) of
 	true -> ok;
-	false -> ?debug("LimitedVal ~s\n", [format_type(LimitedVal)])
+	false -> ?debug("LimitedVal ~ts\n", [format_type(LimitedVal)])
       end,
       case maps:find(Key, Map) of
         {ok, Value} ->
@@ -2638,7 +2638,7 @@ enter_type2(Key, Val, Map) ->
   {Map1, [Key || not is_same(Key, Map, Map1)]}.
 
 map_store(Key, Val, Map) ->
-  ?debug("Storing ~w :: ~s\n", [Key, format_type(Val)]),
+  ?debug("Storing ~tw :: ~ts\n", [Key, format_type(Val)]),
   maps:put(Key, Val, Map).
 
 erase_type(Key, Map) ->
@@ -2703,7 +2703,7 @@ is_equal(Type1, Type2) ->
   t_is_equal(Type1, Type2).
 
 pp_map(_S, _Map) ->
-  ?debug("\t~s: ~p\n",
+  ?debug("\t~s: ~tp\n",
             [_S, [{X, lists:flatten(format_type(Y))} ||
                   {X, Y} <- lists:keysort(1, maps:to_list(_Map))]]).
 
@@ -2846,7 +2846,7 @@ state__add_prop_constrs(Tree, #state{prop_types = PropTypes} = State) ->
 	  case erl_types:any_none(ArgTypes) of
 	    true -> not_called;
 	    false ->
-	      ?debug("Adding propagated constr: ~s for function ~w\n",
+	      ?debug("Adding propagated constr: ~ts for function ~tw\n",
 		     [format_type(FunType), debug_lookup_name(mk_var(Tree))]),
 	      FunVar = mk_var(Tree),
 	      state__store_conj(FunVar, sub, FunType, State)
@@ -3381,10 +3381,10 @@ family(L) ->
 -ifdef(DEBUG).
 format_type(#fun_var{deps = Deps, origin = Origin}) ->
   L = [format_type(t_var(X)) || X <- Deps],
-  io_lib:format("Fun@L~p(~s)", [Origin, join_chars(L, ",")]);
+  io_lib:format("Fun@L~p(~ts)", [Origin, join_chars(L, ",")]);
 format_type(Type) ->
   case cerl:is_literal(Type) of
-    true -> io_lib:format("~w", [cerl:concrete(Type)]);
+    true -> io_lib:format("~tw", [cerl:concrete(Type)]);
     false -> erl_types:t_to_string(Type)
   end.
 
@@ -3426,7 +3426,7 @@ pp_constrs_scc(SCC, State) ->
   [pp_constrs(Fun, state__get_cs(Fun, State), State) || Fun <- SCC].
 
 pp_constrs(Fun, Cs, State) ->
-  io:format("Constraints for fun: ~w", [debug_lookup_name(Fun)]),
+  io:format("Constraints for fun: ~tw", [debug_lookup_name(Fun)]),
   MaxDepth = pp_constraints(Cs, State),
   io:format("Depth: ~w\n", [MaxDepth]).
 
@@ -3464,7 +3464,7 @@ pp_constraints([#constraint_list{type = Type, list = List, id = Id}|Tail],
 
 pp_op(#constraint{lhs = Lhs, op = Op, rhs = Rhs}, Level) ->
   pp_indent(Level),
-  io:format("~s ~w ~s", [format_type(Lhs), Op, format_type(Rhs)]).
+  io:format("~ts ~w ~ts", [format_type(Lhs), Op, format_type(Rhs)]).
 
 pp_indent(Level) ->
   io:format("\n~*s", [Level*2, ""]).
@@ -3476,19 +3476,25 @@ pp_constrs_scc(_SCC, _State) ->
 -ifdef(TO_DOT).
 
 constraints_to_dot_scc(SCC, State) ->
-  io:format("SCC: ~p\n", [SCC]),
-  Name = lists:flatten([io_lib:format("'~w'", [debug_lookup_name(Fun)])
-			|| Fun <- SCC]),
+  %% TODO: handle Unicode names.
+  io:format("SCC: ~tp\n", [SCC]),
+  Name = lists:flatten([format_lookup_name(debug_lookup_name(Fun))
+                        || Fun <- SCC]),
   Cs = [state__get_cs(Fun, State) || Fun <- SCC],
   constraints_to_dot(Cs, Name, State).
 
+format_lookup_name({FunName, Arity}) ->
+  TupleS = io_lib:format("{~ts,~w}", [atom_to_list(FunName), Arity]),
+  io_lib:format("~tw", [list_to_atom(lists:flatten(TupleS))]).
+
 constraints_to_dot(Cs0, Name, State) ->
   NofCs = length(Cs0),
   Cs = lists:zip(lists:seq(1, NofCs), Cs0),
   {Graph, Opts, _N} = constraints_to_nodes(Cs, NofCs + 1, 1, [], [], State),
   hipe_dot:translate_list(Graph, "/tmp/cs.dot", "foo", Opts),
+  %% "-T ps" works for Latin-1. hipe_dot cannot handle UTF-8 either.
   Res = os:cmd("dot -o /tmp/"++ Name ++ ".ps -T ps /tmp/cs.dot"),
-  io:format("Res: ~p~n", [Res]),
+  io:format("Res: ~ts~n", [Res]),
   ok.
 
 constraints_to_nodes([{Name, #constraint_list{type = Type, list = List, id=Id}}
@@ -3507,7 +3513,7 @@ constraints_to_nodes([{Name, #constraint_list{type = Type, list = List, id=Id}}
   constraints_to_nodes(Left, N2, Level, NewGraph, NewOpts, State);
 constraints_to_nodes([{Name, #constraint{lhs = Lhs, op = Op, rhs = Rhs}}|Left],
 		     N, Level, Graph, Opts, State) ->
-  Label = lists:flatten(io_lib:format("~s ~w ~s",
+  Label = lists:flatten(io_lib:format("~ts ~w ~ts",
 				      [format_type(Lhs), Op,
 				       format_type(Rhs)])),
   ThisNode = [{Name, Opt} || Opt <- [{label, Label}, {level, Level}]],
diff --git a/lib/dialyzer/src/dialyzer_utils.erl b/lib/dialyzer/src/dialyzer_utils.erl
index 75d6e3bc65..e5941d0ab8 100644
--- a/lib/dialyzer/src/dialyzer_utils.erl
+++ b/lib/dialyzer/src/dialyzer_utils.erl
@@ -56,15 +56,15 @@ print_types1([], _) ->
   ok;
 print_types1([{type, _Name, _NArgs} = Key|T], RecDict) ->
   {ok, {{_Mod, _FileLine, _Form, _Args}, Type}} = dict:find(Key, RecDict),
-  io:format("\n~w: ~w\n", [Key, Type]),
+  io:format("\n~tw: ~tw\n", [Key, Type]),
   print_types1(T, RecDict);
 print_types1([{opaque, _Name, _NArgs} = Key|T], RecDict) ->
   {ok, {{_Mod, _FileLine, _Form, _Args}, Type}} = dict:find(Key, RecDict),
-  io:format("\n~w: ~w\n", [Key, Type]),
+  io:format("\n~tw: ~tw\n", [Key, Type]),
   print_types1(T, RecDict);
 print_types1([{record, _Name} = Key|T], RecDict) ->
   {ok, {_FileLine, [{_Arity, _Fields} = AF]}} = dict:find(Key, RecDict),
-  io:format("~w: ~w\n\n", [Key, AF]),
+  io:format("~tw: ~tw\n\n", [Key, AF]),
   print_types1(T, RecDict).
 -define(debug(D_), print_types(D_)).
 -else.
@@ -268,7 +268,7 @@ add_new_type(TypeOrOpaque, Name, TypeForm, ArgForms, Module, FN,
   Arity = length(ArgForms),
   case erl_types:type_is_defined(TypeOrOpaque, Name, Arity, RecDict) of
     true ->
-      Msg = flat_format("Type ~s/~w already defined\n", [Name, Arity]),
+      Msg = flat_format("Type ~ts/~w already defined\n", [Name, Arity]),
       throw({error, Msg});
     false ->
       try erl_types:t_var_names(ArgForms) of
@@ -278,7 +278,7 @@ add_new_type(TypeOrOpaque, Name, TypeForm, ArgForms, Module, FN,
                     erl_types:t_any()}, RecDict)
       catch
         _:_ ->
-	  throw({error, flat_format("Type declaration for ~w does not "
+	  throw({error, flat_format("Type declaration for ~tw does not "
 				    "have variables as parameters", [Name])})
       end
   end.
@@ -433,7 +433,7 @@ msg_with_position(Fun, FileLine) ->
     throw:{error, Msg} ->
       {File, Line} = FileLine,
       BaseName = filename:basename(File),
-      NewMsg = io_lib:format("~s:~p: ~s", [BaseName, Line, Msg]),
+      NewMsg = io_lib:format("~ts:~p: ~ts", [BaseName, Line, Msg]),
       throw({error, NewMsg})
   end.
 
@@ -526,13 +526,13 @@ get_spec_info([{Contract, Ln, [{Id, TypeSpec}]}|Left],
 		    RecordsMap, ModName, OptCb, File);
     {ok, {{OtherFile, L}, _D}} ->
       {Mod, Fun, Arity} = MFA,
-      Msg = flat_format("  Contract/callback for function ~w:~w/~w "
-			"already defined in ~s:~w\n",
+      Msg = flat_format("  Contract/callback for function ~w:~tw/~w "
+			"already defined in ~ts:~w\n",
 			[Mod, Fun, Arity, OtherFile, L]),
       throw({error, Msg})
   catch
     throw:{error, Error} ->
-      {error, flat_format("  Error while parsing contract in line ~w: ~s\n",
+      {error, flat_format("  Error while parsing contract in line ~w: ~ts\n",
 			  [Ln, Error])}
   end;
 get_spec_info([{file, _, [{IncludeFile, _}]}|Left],
@@ -635,7 +635,7 @@ get_options1([{Args, L, File}|Left], Warnings) ->
       get_options1(Left, NewWarnings)
   catch
     throw:{dialyzer_options_error, Msg} ->
-      Msg1 = flat_format("  ~s:~w: ~s", [File, L, Msg]),
+      Msg1 = flat_format("  ~ts:~w: ~ts", [File, L, Msg]),
       throw({error, Msg1})
   end;
 get_options1([], Warnings) ->
@@ -714,7 +714,7 @@ src_compiler_opts() ->
 
 format_errors([{Mod, Errors}|Left]) ->
   FormatedError =
-    [io_lib:format("~s:~w: ~s\n", [Mod, Line, M:format_error(Desc)])
+    [io_lib:format("~ts:~w: ~ts\n", [Mod, Line, M:format_error(Desc)])
      || {Line, M, Desc} <- Errors],
   [lists:flatten(FormatedError) | format_errors(Left)];
 format_errors([]) ->
@@ -759,14 +759,14 @@ check_fa_list1([{Args, L, File}|Left], Tag, Funcs) ->
   case lists:dropwhile(fun({_, T}) -> is_fa(T) end, TermsL) of
     [] -> ok;
     [{_, Bad}|_] ->
-      Msg1 = flat_format("  Bad function ~w in line ~s:~w",
+      Msg1 = flat_format("  Bad function ~tw in line ~ts:~w",
                          [Bad, File, L]),
       throw({error, Msg1})
   end,
   case lists:dropwhile(fun({_, FA}) -> is_known(FA, Funcs) end, TermsL) of
     [] -> ok;
     [{_, {F, A}}|_] ->
-      Msg2 = flat_format("  Unknown function ~w/~w in line ~s:~w",
+      Msg2 = flat_format("  Unknown function ~tw/~w in line ~ts:~w",
                          [F, A, File, L]),
       throw({error, Msg2})
   end,
diff --git a/lib/dialyzer/src/typer.erl b/lib/dialyzer/src/typer.erl
index 86c7c62f98..43e03be740 100644
--- a/lib/dialyzer/src/typer.erl
+++ b/lib/dialyzer/src/typer.erl
@@ -74,6 +74,7 @@
 -spec start() -> no_return().
 
 start() ->
+_ = io:setopts(standard_error, [{encoding,unicode}]),
   {Args, Analysis} = process_cl_args(),
   %% io:format("Args: ~p\n", [Args]),
   %% io:format("Analysis: ~p\n", [Analysis]),
@@ -81,7 +82,7 @@ start() ->
   TrustedFiles = filter_fd(Args#args.trusted, [], fun is_erl_file/1),
   Analysis2 = extract(Analysis, TrustedFiles),
   All_Files = get_all_files(Args),
-  %% io:format("All_Files: ~p\n", [All_Files]),
+  %% io:format("All_Files: ~tp\n", [All_Files]),
   Analysis3 = Analysis2#analysis{files = All_Files},
   Analysis4 = collect_info(Analysis3),
   %% io:format("Final: ~p\n", [Analysis4#analysis.fms]),
@@ -164,10 +165,10 @@ get_type_info(#analysis{callgraph = CallGraph,
     Analysis#analysis{callgraph = StrippedCallGraph, trust_plt = NewPlt}
   catch
     error:What ->
-      fatal_error(io_lib:format("Analysis failed with message: ~p", 
+      fatal_error(io_lib:format("Analysis failed with message: ~tp",
 				[{What, erlang:get_stacktrace()}]));
     throw:{dialyzer_succ_typing_error, Msg} ->
-      fatal_error(io_lib:format("Analysis failed with message: ~s", [Msg]))
+      fatal_error(io_lib:format("Analysis failed with message: ~ts", [Msg]))
   end.
 
 -spec remove_external(callgraph(), plt()) -> callgraph().
@@ -177,11 +178,11 @@ remove_external(CallGraph, PLT) ->
   case get_external(Ext, PLT) of
     [] -> ok;
     Externals ->
-      msg(io_lib:format(" Unknown functions: ~p\n", [lists:usort(Externals)])),
+      msg(io_lib:format(" Unknown functions: ~tp\n", [lists:usort(Externals)])),
       ExtTypes = rcv_ext_types(),
       case ExtTypes of
         [] -> ok;
-        _ -> msg(io_lib:format(" Unknown types: ~p\n", [ExtTypes]))
+        _ -> msg(io_lib:format(" Unknown types: ~tp\n", [ExtTypes]))
       end
   end,
   StrippedCG0.
@@ -257,9 +258,9 @@ write_inc_files(Inc) ->
 		     records = maps:new(),
 		     %% Note we need to sort functions here!
 		     functions = lists:keysort(1, Functions)},
-	%% io:format("Types ~p\n", [Info#info.types]),
-	%% io:format("Functions ~p\n", [Info#info.functions]),
-	%% io:format("Records ~p\n", [Info#info.records]),
+	%% io:format("Types ~tp\n", [Info#info.types]),
+	%% io:format("Functions ~tp\n", [Info#info.functions]),
+	%% io:format("Records ~tp\n", [Info#info.records]),
 	write_typed_file(File, Info)
     end,
   lists:foreach(Fun, dict:fetch_keys(Inc#inc.map)).
@@ -349,8 +350,8 @@ check_imported_functions({File, {Line, F, A}}, Inc, Types) ->
   end.
 
 inc_warning({F, A}, File) ->
-  io:format("      ***Warning: Skip function ~p/~p ", [F, A]),
-  io:format("in file ~p because of inconsistent type\n", [File]).
+  io:format("      ***Warning: Skip function ~tp/~p ", [F, A]),
+  io:format("in file ~tp because of inconsistent type\n", [File]).
 
 clean_inc(Inc) ->
   Inc1 = remove_yecc_generated_file(Inc),
@@ -407,13 +408,13 @@ get_type({{M, F, A} = MFA, Range, Arg}, CodeServer, Records) ->
 	{error, invalid_contract} ->
 	  CString = dialyzer_contracts:contract_to_string(Contract),
 	  SigString = dialyzer_utils:format_sig(Sig, Records),
-	  Msg = io_lib:format("Error in contract of function ~w:~w/~w\n" 
+	  Msg = io_lib:format("Error in contract of function ~w:~tw/~w\n"
 			      "\t The contract is: " ++ CString ++ "\n" ++
-			      "\t but the inferred signature is: ~s",
+			      "\t but the inferred signature is: ~ts",
 			      [M, F, A, SigString]),
 	  fatal_error(Msg);
 	{error, ErrorStr} when is_list(ErrorStr) -> % ErrorStr is a string()
-	  Msg = io_lib:format("Error in contract of function ~w:~w/~w: ~s",
+	  Msg = io_lib:format("Error in contract of function ~w:~tw/~w: ~ts",
 			      [M, F, A, ErrorStr]),
 	  fatal_error(Msg)
       end
@@ -448,7 +449,7 @@ remove_module_info(FunInfoList) ->
   lists:filter(F, FunInfoList).
 
 write_typed_file(File, Info) ->
-  io:format("      Processing file: ~p\n", [File]),
+  io:format("      Processing file: ~tp\n", [File]),
   Dir = filename:dirname(File),
   RootName = filename:basename(filename:rootname(File)),
   Ext = filename:extension(File),
@@ -463,18 +464,18 @@ write_typed_file(File, Info) ->
 	    ok -> ok;
 	    {error, enoent} -> ok;
 	    {error, _} ->
-	      Msg = io_lib:format("Error in deleting file ~s\n", [NewFileName]),
+	      Msg = io_lib:format("Error in deleting file ~ts\n", [NewFileName]),
 	      fatal_error(Msg)
 	  end,
 	  write_typed_file(File, Info, NewFileName);
 	enospc ->
-	  Msg = io_lib:format("Not enough space in ~p\n", [Dir]),
+	  Msg = io_lib:format("Not enough space in ~tp\n", [Dir]),
 	  fatal_error(Msg);
 	eacces ->
-	  Msg = io_lib:format("No write permission in ~p\n", [Dir]),
+	  Msg = io_lib:format("No write permission in ~tp\n", [Dir]),
 	  fatal_error(Msg);
 	_ ->
-	  Msg = io_lib:format("Unhandled error ~s when writing ~p\n",
+	  Msg = io_lib:format("Unhandled error ~ts when writing ~tp\n",
 			      [Reason, Dir]),
 	  fatal_error(Msg)
       end;
@@ -486,7 +487,7 @@ write_typed_file(File, Info, NewFileName) ->
   {ok, Binary} = file:read_file(File),
   Chars = binary_to_list(Binary),
   write_typed_file(Chars, NewFileName, Info, 1, []),
-  io:format("             Saved as: ~p\n", [NewFileName]).
+  io:format("             Saved as: ~tp\n", [NewFileName]).
 
 write_typed_file(Chars, File, #info{functions = []}, _LNo, _Acc) ->
   ok = file:write_file(File, list_to_binary(Chars), [append]);
@@ -546,12 +547,12 @@ get_type_string(F, A, Info, Mode) ->
   end.
  
 show_type_info(File, Info) ->
-  io:format("\n%% File: ~p\n%% ", [File]),
+  io:format("\n%% File: ~tp\n%% ", [File]),
   OutputString = lists:concat(["~.", length(File)+8, "c~n"]),
   io:fwrite(OutputString, [$-]),
   Fun = fun ({_LineNo, F, A}) ->
 	    TypeInfo = get_type_string(F, A, Info, show),
-	    io:format("~s\n", [TypeInfo])
+	    io:format("~ts\n", [TypeInfo])
 	end,
   lists:foreach(Fun, Info#info.functions).
 
@@ -561,7 +562,7 @@ get_type_info(Func, Types) ->
       %% Note: Typeinfo of any function should exist in
       %% the result offered by dialyzer, otherwise there 
       %% *must* be something wrong with the analysis
-      Msg = io_lib:format("No type info for function: ~p\n", [Func]),
+      Msg = io_lib:format("No type info for function: ~tp\n", [Func]),
       fatal_error(Msg);
     {contract, _Fun} = C -> C;
     {_RetType, _ArgType} = RA -> RA 
@@ -575,7 +576,7 @@ get_type_info(Func, Types) ->
 
 process_cl_args() ->
   ArgList = init:get_plain_arguments(),
-  %% io:format("Args is ~p\n", [ArgList]),
+  %% io:format("Args is ~tp\n", [ArgList]),
   {Args, Analysis} = analyze_args(ArgList, #args{}, #analysis{}),
   %% if the mode has not been set, set it to the default mode (show)
   {Args, case Analysis#analysis.mode of
@@ -848,7 +849,7 @@ collect_one_file_info(File, Analysis) ->
   Options = dialyzer_utils:src_compiler_opts() ++ Is ++ Ds,
   case dialyzer_utils:get_core_from_src(File, Options) of
     {error, Reason} ->
-      %% io:format("File=~p\n,Options=~p\n,Error=~p\n", [File,Options,Reason]),
+      %% io:format("File=~tp\n,Options=~p\n,Error=~p\n", [File,Options,Reason]),
       compile_error(Reason);
     {ok, Core} ->
       case dialyzer_utils:get_record_and_type_info(Core) of
@@ -922,7 +923,7 @@ analyze_one_function({Var, FunBody} = Function, Acc) ->
   {FuncAcc, IncFuncAcc} =
     case (FileName =:= OriginalName) orelse (BaseName =:= OriginalName) of
       true -> %% Coming from original file
-	%% io:format("Added function ~p\n", [{LineNo, F, A}]),
+	%% io:format("Added function ~tp\n", [{LineNo, F, A}]),
 	{Acc#tmpAcc.funcAcc ++ [FuncInfo], Acc#tmpAcc.incFuncAcc};
       false ->
 	%% Coming from other sourses, including:
@@ -972,7 +973,7 @@ get_exported_types_from_core(Core) ->
 -spec fatal_error(string()) -> no_return().
 
 fatal_error(Slogan) ->
-  msg(io_lib:format("typer: ~s\n", [Slogan])),
+  msg(io_lib:format("typer: ~ts\n", [Slogan])),
   erlang:halt(1).
 
 -spec mode_error(mode(), mode()) -> no_return().
@@ -993,7 +994,7 @@ compile_error(Reason) ->
 -spec msg(string()) -> 'ok'.
 
 msg(Msg) ->
-  io:format(standard_error, "~s", [Msg]).
+  io:format(standard_error, "~ts", [Msg]).
 
 %%--------------------------------------------------------------------
 %% Version and help messages.
diff --git a/lib/dialyzer/test/behaviour_SUITE_data/results/callbacks_and_specs b/lib/dialyzer/test/behaviour_SUITE_data/results/callbacks_and_specs
index 38999e8919..843d26ee59 100644
--- a/lib/dialyzer/test/behaviour_SUITE_data/results/callbacks_and_specs
+++ b/lib/dialyzer/test/behaviour_SUITE_data/results/callbacks_and_specs
@@ -1,5 +1,5 @@
 
-my_callbacks_wrong.erl:26: The return type #state{parent::pid(),status::'closed' | 'init' | 'open',subscribe::[{pid(),integer()}],counter::integer()} in the specification of callback_init/1 is not a subtype of {'ok',_}, which is the expected return type for the callback of my_behaviour behaviour
-my_callbacks_wrong.erl:28: The inferred return type of callback_init/1 (#state{parent::pid(),status::'init',subscribe::[],counter::1}) has nothing in common with {'ok',_}, which is the expected return type for the callback of my_behaviour behaviour
-my_callbacks_wrong.erl:30: The return type {'reply',#state{parent::pid(),status::'closed' | 'init' | 'open',subscribe::[{pid(),integer()}],counter::integer()}} in the specification of callback_cast/3 is not a subtype of {'noreply',_}, which is the expected return type for the callback of my_behaviour behaviour
+my_callbacks_wrong.erl:26: The return type #state{parent::pid(),status::'closed' | 'init' | 'open',subscribe::[{pid(),integer()}],counter::integer()} in the specification of callback_init/1 is not a subtype of {'ok',_}, which is the expected return type for the callback of the my_behaviour behaviour
+my_callbacks_wrong.erl:28: The inferred return type of callback_init/1 (#state{parent::pid(),status::'init',subscribe::[],counter::1}) has nothing in common with {'ok',_}, which is the expected return type for the callback of the my_behaviour behaviour
+my_callbacks_wrong.erl:30: The return type {'reply',#state{parent::pid(),status::'closed' | 'init' | 'open',subscribe::[{pid(),integer()}],counter::integer()}} in the specification of callback_cast/3 is not a subtype of {'noreply',_}, which is the expected return type for the callback of the my_behaviour behaviour
 my_callbacks_wrong.erl:39: The specified type for the 2nd argument of callback_call/3 (atom()) is not a supertype of pid(), which is expected type for this argument in the callback of the my_behaviour behaviour
diff --git a/lib/dialyzer/test/behaviour_SUITE_data/results/gen_event_incorrect_return b/lib/dialyzer/test/behaviour_SUITE_data/results/gen_event_incorrect_return
index e646eea383..c3ebee05da 100644
--- a/lib/dialyzer/test/behaviour_SUITE_data/results/gen_event_incorrect_return
+++ b/lib/dialyzer/test/behaviour_SUITE_data/results/gen_event_incorrect_return
@@ -1,2 +1,2 @@
 
-gen_event_incorrect_return.erl:16: The inferred return type of init/1 ('error') has nothing in common with {'error',_} | {'ok',_} | {'ok',_,'hibernate'}, which is the expected return type for the callback of gen_event behaviour
+gen_event_incorrect_return.erl:16: The inferred return type of init/1 ('error') has nothing in common with {'error',_} | {'ok',_} | {'ok',_,'hibernate'}, which is the expected return type for the callback of the gen_event behaviour
diff --git a/lib/dialyzer/test/behaviour_SUITE_data/results/gen_server_incorrect_args b/lib/dialyzer/test/behaviour_SUITE_data/results/gen_server_incorrect_args
index 2f504d3c72..1eb8cd455b 100644
--- a/lib/dialyzer/test/behaviour_SUITE_data/results/gen_server_incorrect_args
+++ b/lib/dialyzer/test/behaviour_SUITE_data/results/gen_server_incorrect_args
@@ -1,5 +1,5 @@
 
-gen_server_incorrect_args.erl:3: Undefined callback function handle_cast/2 (behaviour 'gen_server')
-gen_server_incorrect_args.erl:3: Undefined callback function init/1 (behaviour 'gen_server')
-gen_server_incorrect_args.erl:7: The inferred return type of handle_call/3 ({'no'} | {'ok'}) has nothing in common with {'noreply',_} | {'noreply',_,'hibernate' | 'infinity' | non_neg_integer()} | {'reply',_,_} | {'stop',_,_} | {'reply',_,_,'hibernate' | 'infinity' | non_neg_integer()} | {'stop',_,_,_}, which is the expected return type for the callback of gen_server behaviour
+gen_server_incorrect_args.erl:3: Undefined callback function handle_cast/2 (behaviour gen_server)
+gen_server_incorrect_args.erl:3: Undefined callback function init/1 (behaviour gen_server)
+gen_server_incorrect_args.erl:7: The inferred return type of handle_call/3 ({'no'} | {'ok'}) has nothing in common with {'noreply',_} | {'noreply',_,'hibernate' | 'infinity' | non_neg_integer()} | {'reply',_,_} | {'stop',_,_} | {'reply',_,_,'hibernate' | 'infinity' | non_neg_integer()} | {'stop',_,_,_}, which is the expected return type for the callback of the gen_server behaviour
 gen_server_incorrect_args.erl:7: The inferred type for the 2nd argument of handle_call/3 ('boo' | 'foo') is not a supertype of {pid(),_}, which is expected type for this argument in the callback of the gen_server behaviour
diff --git a/lib/dialyzer/test/behaviour_SUITE_data/results/gen_server_missing_callbacks b/lib/dialyzer/test/behaviour_SUITE_data/results/gen_server_missing_callbacks
index 0a7642a9b5..188f7822fa 100644
--- a/lib/dialyzer/test/behaviour_SUITE_data/results/gen_server_missing_callbacks
+++ b/lib/dialyzer/test/behaviour_SUITE_data/results/gen_server_missing_callbacks
@@ -1,2 +1,2 @@
 
-gen_server_missing_callbacks.erl:3: Undefined callback function handle_cast/2 (behaviour 'gen_server')
+gen_server_missing_callbacks.erl:3: Undefined callback function handle_cast/2 (behaviour gen_server)
diff --git a/lib/dialyzer/test/behaviour_SUITE_data/results/sample_behaviour b/lib/dialyzer/test/behaviour_SUITE_data/results/sample_behaviour
index 8cecabccaa..68adf4cfa0 100644
--- a/lib/dialyzer/test/behaviour_SUITE_data/results/sample_behaviour
+++ b/lib/dialyzer/test/behaviour_SUITE_data/results/sample_behaviour
@@ -1,9 +1,9 @@
 
-sample_callback_wrong.erl:16: The inferred return type of sample_callback_2/0 (42) has nothing in common with atom(), which is the expected return type for the callback of sample_behaviour behaviour
-sample_callback_wrong.erl:17: The inferred return type of sample_callback_3/0 ('fair') has nothing in common with 'fail' | {'ok',1..255}, which is the expected return type for the callback of sample_behaviour behaviour
-sample_callback_wrong.erl:18: The inferred return type of sample_callback_4/1 ('fail') has nothing in common with 'ok', which is the expected return type for the callback of sample_behaviour behaviour
-sample_callback_wrong.erl:20: The inferred return type of sample_callback_5/1 (string()) has nothing in common with 'fail' | 'ok', which is the expected return type for the callback of sample_behaviour behaviour
+sample_callback_wrong.erl:16: The inferred return type of sample_callback_2/0 (42) has nothing in common with atom(), which is the expected return type for the callback of the sample_behaviour behaviour
+sample_callback_wrong.erl:17: The inferred return type of sample_callback_3/0 ('fair') has nothing in common with 'fail' | {'ok',1..255}, which is the expected return type for the callback of the sample_behaviour behaviour
+sample_callback_wrong.erl:18: The inferred return type of sample_callback_4/1 ('fail') has nothing in common with 'ok', which is the expected return type for the callback of the sample_behaviour behaviour
+sample_callback_wrong.erl:20: The inferred return type of sample_callback_5/1 (string()) has nothing in common with 'fail' | 'ok', which is the expected return type for the callback of the sample_behaviour behaviour
 sample_callback_wrong.erl:20: The inferred type for the 1st argument of sample_callback_5/1 (atom()) is not a supertype of 1..255, which is expected type for this argument in the callback of the sample_behaviour behaviour
-sample_callback_wrong.erl:22: The inferred return type of sample_callback_6/3 ({'okk',number()}) has nothing in common with 'fail' | {'ok',1..255}, which is the expected return type for the callback of sample_behaviour behaviour
+sample_callback_wrong.erl:22: The inferred return type of sample_callback_6/3 ({'okk',number()}) has nothing in common with 'fail' | {'ok',1..255}, which is the expected return type for the callback of the sample_behaviour behaviour
 sample_callback_wrong.erl:22: The inferred type for the 3rd argument of sample_callback_6/3 (atom()) is not a supertype of string(), which is expected type for this argument in the callback of the sample_behaviour behaviour
-sample_callback_wrong.erl:4: Undefined callback function sample_callback_1/0 (behaviour 'sample_behaviour')
+sample_callback_wrong.erl:4: Undefined callback function sample_callback_1/0 (behaviour sample_behaviour)
diff --git a/lib/dialyzer/test/behaviour_SUITE_data/results/sample_behaviour_old b/lib/dialyzer/test/behaviour_SUITE_data/results/sample_behaviour_old
index f0181bb59c..67aa872984 100644
--- a/lib/dialyzer/test/behaviour_SUITE_data/results/sample_behaviour_old
+++ b/lib/dialyzer/test/behaviour_SUITE_data/results/sample_behaviour_old
@@ -1,4 +1,4 @@
 
 incorrect_args_callback.erl:12: The inferred type for the 2nd argument of bar/2 ('yes') is not a supertype of [any()], which is expected type for this argument in the callback of the correct_behaviour behaviour
-incorrect_return_callback.erl:9: The inferred return type of foo/0 ('error') has nothing in common with 'no' | 'yes', which is the expected return type for the callback of correct_behaviour behaviour
-missing_callback.erl:5: Undefined callback function foo/0 (behaviour 'correct_behaviour')
+incorrect_return_callback.erl:9: The inferred return type of foo/0 ('error') has nothing in common with 'no' | 'yes', which is the expected return type for the callback of the correct_behaviour behaviour
+missing_callback.erl:5: Undefined callback function foo/0 (behaviour correct_behaviour)
diff --git a/lib/dialyzer/test/behaviour_SUITE_data/results/supervisor_incorrect_return b/lib/dialyzer/test/behaviour_SUITE_data/results/supervisor_incorrect_return
index 638d031923..5a063a12b8 100644
--- a/lib/dialyzer/test/behaviour_SUITE_data/results/supervisor_incorrect_return
+++ b/lib/dialyzer/test/behaviour_SUITE_data/results/supervisor_incorrect_return
@@ -1,2 +1,2 @@
 
-supervisor_incorrect_return.erl:14: The inferred return type of init/1 ({'ok',{{'one_against_one',0,1},[{_,_,_,_,_,_},...]}}) has nothing in common with 'ignore' | {'ok',{{'one_for_all',non_neg_integer(),pos_integer()} | {'one_for_one',non_neg_integer(),pos_integer()} | {'rest_for_one',non_neg_integer(),pos_integer()} | {'simple_one_for_one',non_neg_integer(),pos_integer()} | #{'intensity'=>non_neg_integer(), 'period'=>pos_integer(), 'strategy'=>'one_for_all' | 'one_for_one' | 'rest_for_one' | 'simple_one_for_one'},[{_,{atom(),atom(),'undefined' | [any()]},'permanent' | 'temporary' | 'transient','brutal_kill' | 'infinity' | non_neg_integer(),'supervisor' | 'worker','dynamic' | [atom()]} | #{'id':=_, 'start':={atom(),atom(),'undefined' | [any()]}, 'modules'=>'dynamic' | [atom()], 'restart'=>'permanent' | 'temporary' | 'transient', 'shutdown'=>'brutal_kill' | 'infinity' | non_neg_integer(), 'type'=>'supervisor' | 'worker'}]}}, which is the expected return type for the callback of supervisor behaviour
+supervisor_incorrect_return.erl:14: The inferred return type of init/1 ({'ok',{{'one_against_one',0,1},[{_,_,_,_,_,_},...]}}) has nothing in common with 'ignore' | {'ok',{{'one_for_all',non_neg_integer(),pos_integer()} | {'one_for_one',non_neg_integer(),pos_integer()} | {'rest_for_one',non_neg_integer(),pos_integer()} | {'simple_one_for_one',non_neg_integer(),pos_integer()} | #{'intensity'=>non_neg_integer(), 'period'=>pos_integer(), 'strategy'=>'one_for_all' | 'one_for_one' | 'rest_for_one' | 'simple_one_for_one'},[{_,{atom(),atom(),'undefined' | [any()]},'permanent' | 'temporary' | 'transient','brutal_kill' | 'infinity' | non_neg_integer(),'supervisor' | 'worker','dynamic' | [atom()]} | #{'id':=_, 'start':={atom(),atom(),'undefined' | [any()]}, 'modules'=>'dynamic' | [atom()], 'restart'=>'permanent' | 'temporary' | 'transient', 'shutdown'=>'brutal_kill' | 'infinity' | non_neg_integer(), 'type'=>'supervisor' | 'worker'}]}}, which is the expected return type for the callback of the supervisor behaviour
diff --git a/lib/dialyzer/test/behaviour_SUITE_data/results/vars_in_beh_spec b/lib/dialyzer/test/behaviour_SUITE_data/results/vars_in_beh_spec
index 512dcdd758..f313c24420 100644
--- a/lib/dialyzer/test/behaviour_SUITE_data/results/vars_in_beh_spec
+++ b/lib/dialyzer/test/behaviour_SUITE_data/results/vars_in_beh_spec
@@ -1,4 +1,4 @@
 
-vars_in_beh_spec.erl:3: Undefined callback function handle_call/3 (behaviour 'gen_server')
-vars_in_beh_spec.erl:3: Undefined callback function handle_cast/2 (behaviour 'gen_server')
-vars_in_beh_spec.erl:3: Undefined callback function init/1 (behaviour 'gen_server')
+vars_in_beh_spec.erl:3: Undefined callback function handle_call/3 (behaviour gen_server)
+vars_in_beh_spec.erl:3: Undefined callback function handle_cast/2 (behaviour gen_server)
+vars_in_beh_spec.erl:3: Undefined callback function init/1 (behaviour gen_server)
diff --git a/lib/hipe/cerl/erl_types.erl b/lib/hipe/cerl/erl_types.erl
index 4cfa80f153..4d7f1be513 100644
--- a/lib/hipe/cerl/erl_types.erl
+++ b/lib/hipe/cerl/erl_types.erl
@@ -4249,8 +4249,8 @@ t_to_string(?opaque(Set), RecDict) ->
                   <- set_to_list(Set)],
 	      " | ");
 t_to_string(?matchstate(Pres, Slots), RecDict) ->
-  flat_format("ms(~s,~s)", [t_to_string(Pres, RecDict),
-                            t_to_string(Slots,RecDict)]);
+  flat_format("ms(~ts,~ts)", [t_to_string(Pres, RecDict),
+                              t_to_string(Slots,RecDict)]);
 t_to_string(?nil, _RecDict) ->
   "[]";
 t_to_string(?nonempty_list(Contents, Termination), RecDict) ->
@@ -4428,10 +4428,10 @@ opaque_type(Mod, Name, Args, _S, RecDict) ->
 
 opaque_name(Mod, Name, Extra) ->
   S = mod_name(Mod, Name),
-  flat_format("~s(~s)", [S, Extra]).
+  flat_format("~ts(~ts)", [S, Extra]).
 
 mod_name(Mod, Name) ->
-  flat_format("~w:~w", [Mod, Name]).
+  flat_format("~w:~tw", [Mod, Name]).
 
 %%=============================================================================
 %% 
@@ -4800,7 +4800,7 @@ type_from_form1(Name, Args, ArgsLen, R, TypeName, TypeNames, S, D, L, C) ->
           {NewType, L3, C4}
       end;
     error ->
-      Msg = io_lib:format("Unable to find type ~w/~w\n",
+      Msg = io_lib:format("Unable to find type ~tw/~w\n",
                           [Name, ArgsLen]),
       throw({error, Msg})
   end.
@@ -4872,7 +4872,7 @@ remote_from_form1(RemMod, Name, Args, ArgsLen, RemDict, RemType, TypeNames,
           {NewType, L3, C4}
       end;
     error ->
-      Msg = io_lib:format("Unable to find remote type ~w:~w()\n",
+      Msg = io_lib:format("Unable to find remote type ~w:~tw()\n",
                           [RemMod, Name]),
       throw({error, Msg})
   end.
@@ -4917,7 +4917,7 @@ record_from_form({atom, _, Name}, ModFields, S, D0, L0, C) ->
                     case GetModRec of
                       {error, FieldName} ->
                         throw({error,
-                               io_lib:format("Illegal declaration of #~w{~w}\n",
+                               io_lib:format("Illegal declaration of #~tw{~tw}\n",
                                              [Name, FieldName])});
                       {ok, NewFields} ->
                         S2 = S1#from_form{vtab = var_table__new()},
@@ -4931,7 +4931,7 @@ record_from_form({atom, _, Name}, ModFields, S, D0, L0, C) ->
                 end,
           recur_limit(Fun, D0, L0, RecordType, TypeNames);
         error ->
-          throw({error, io_lib:format("Unknown record #~w{}\n", [Name])})
+          throw({error, io_lib:format("Unknown record #~tw{}\n", [Name])})
       end;
     false ->
        {t_any(), L0, C}
@@ -5105,8 +5105,8 @@ check_record({atom, _, Name}, ModFields, S, C) ->
   {ok, DeclFields} = lookup_record(Name, R),
   case check_fields(Name, ModFields, DeclFields, S, C1) of
     {error, FieldName} ->
-       throw({error, io_lib:format("Illegal declaration of #~w{~w}\n",
-                                   [Name, FieldName])});
+      throw({error, io_lib:format("Illegal declaration of #~tw{~tw}\n",
+                                  [Name, FieldName])});
     C2 -> C2
   end.
 
@@ -5199,10 +5199,10 @@ t_form_to_string({op, _L, _Op, _Arg1, _Arg2} = Op) ->
 t_form_to_string({ann_type, _L, [Var, Type]}) ->
   t_form_to_string(Var) ++ "::" ++ t_form_to_string(Type);
 t_form_to_string({paren_type, _L, [Type]}) ->
-  flat_format("(~s)", [t_form_to_string(Type)]);
+  flat_format("(~ts)", [t_form_to_string(Type)]);
 t_form_to_string({remote_type, _L, [{atom, _, Mod}, {atom, _, Name}, Args]}) ->
   ArgString = "(" ++ string:join(t_form_to_string_list(Args), ",") ++ ")",
-  flat_format("~w:~w", [Mod, Name]) ++ ArgString;
+  flat_format("~w:~tw", [Mod, Name]) ++ ArgString;
 t_form_to_string({type, _L, arity, []}) -> "arity()";
 t_form_to_string({type, _L, binary, []}) -> "binary()";
 t_form_to_string({type, _L, binary, [Base, Unit]} = Type) ->
@@ -5252,12 +5252,12 @@ t_form_to_string({type, _L, range, [From, To]} = Type) ->
     _ -> flat_format("Badly formed type ~w",[Type])
   end;
 t_form_to_string({type, _L, record, [{atom, _, Name}]}) ->
-  flat_format("#~w{}", [Name]);
+  flat_format("#~tw{}", [Name]);
 t_form_to_string({type, _L, record, [{atom, _, Name}|Fields]}) ->
   FieldString = string:join(t_form_to_string_list(Fields), ","),
-  flat_format("#~w{~s}", [Name, FieldString]);
+  flat_format("#~tw{~ts}", [Name, FieldString]);
 t_form_to_string({type, _L, field_type, [{atom, _, Name}, Type]}) ->
-  flat_format("~w::~s", [Name, t_form_to_string(Type)]);
+  flat_format("~tw::~ts", [Name, t_form_to_string(Type)]);
 t_form_to_string({type, _L, term, []}) -> "term()";
 t_form_to_string({type, _L, timeout, []}) -> "timeout()";
 t_form_to_string({type, _L, tuple, any}) -> "tuple()";
@@ -5281,7 +5281,7 @@ t_form_to_string({type, _L, Name, []} = T) ->
   catch throw:{error, _} -> atom_to_string(Name) ++ "()"
   end;
 t_form_to_string({user_type, _L, Name, List}) ->
-  flat_format("~w(~s)",
+  flat_format("~tw(~ts)",
               [Name, string:join(t_form_to_string_list(List), ",")]);
 t_form_to_string({type, L, Name, List}) ->
   %% Compatibility: modules compiled before Erlang/OTP 18.0.
@@ -5298,7 +5298,7 @@ t_form_to_string_list([], Acc) ->
 -spec atom_to_string(atom()) -> string().
 
 atom_to_string(Atom) ->
-  flat_format("~w", [Atom]).
+  flat_format("~tw", [Atom]).
 
 %%=============================================================================
 %% 
@@ -5551,7 +5551,7 @@ set_size(Set) ->
 set_to_string(Set) ->
   L = [case is_atom(X) of
 	 true -> io_lib:write_string(atom_to_list(X), $'); % stupid emacs '
-	 false -> flat_format("~w", [X])
+	 false -> flat_format("~tw", [X])
        end || X <- set_to_list(Set)],
   string:join(L, " | ").
 
diff --git a/lib/kernel/src/group_history.erl b/lib/kernel/src/group_history.erl
index 5ca5e2d1dd..91f3663cc5 100644
--- a/lib/kernel/src/group_history.erl
+++ b/lib/kernel/src/group_history.erl
@@ -218,7 +218,7 @@ handle_open_error({invalid_header, Term}) ->
          [Term]);
 handle_open_error({file_error, FileName, Reason}) ->
     show('$#erlang-history-file-error',
-         "Error handling File ~s. Reason: ~p~n"
+         "Error handling File ~ts. Reason: ~p~n"
          "History logging will be disabled.~n",
          [FileName, Reason]);
 handle_open_error(Err) ->
@@ -309,7 +309,7 @@ show_rename_warning() ->
 
 show_invalid_file_warning(FileName) ->
     show('$#erlang-history-invalid-file',
-         "Shell history expects to be able to use the file ~s "
+         "Shell history expects to be able to use the file ~ts "
          "which currently exists and is not a file usable for "
          "history logging purposes. History logging will be "
          "disabled.~n", [FileName]).
diff --git a/lib/kernel/src/inet_tcp_dist.erl b/lib/kernel/src/inet_tcp_dist.erl
index 8c8fe86811..e3fdb1bb22 100644
--- a/lib/kernel/src/inet_tcp_dist.erl
+++ b/lib/kernel/src/inet_tcp_dist.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 1997-2016. All Rights Reserved.
+%% Copyright Ericsson AB 1997-2017. All Rights Reserved.
 %% 
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -390,14 +390,14 @@ splitnode(Driver, Node, LongOrShortNames) ->
                             error_msg("** System running to use "
                                       "fully qualified "
                                       "hostnames **~n"
-                                      "** Hostname ~s is illegal **~n",
+                                      "** Hostname ~ts is illegal **~n",
                                       [Host]),
                             ?shutdown(Node)
                     end;
 		L when length(L) > 1, LongOrShortNames =:= shortnames ->
 		    error_msg("** System NOT running to use fully qualified "
 			      "hostnames **~n"
-			      "** Hostname ~s is illegal **~n",
+			      "** Hostname ~ts is illegal **~n",
 			      [Host]),
 		    ?shutdown(Node);
 		_ ->
diff --git a/lib/parsetools/include/yeccpre.hrl b/lib/parsetools/include/yeccpre.hrl
index fe958e9738..91d6cd49a6 100644
--- a/lib/parsetools/include/yeccpre.hrl
+++ b/lib/parsetools/include/yeccpre.hrl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1996-2015. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2017. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -151,21 +151,20 @@ yecctoken_location(Token) ->
     end.
 
 -compile({nowarn_unused_function, yecctoken2string/1}).
-yecctoken2string({atom, _, A}) -> io_lib:write(A);
+yecctoken2string({atom, _, A}) -> io_lib:write_atom(A);
 yecctoken2string({integer,_,N}) -> io_lib:write(N);
 yecctoken2string({float,_,F}) -> io_lib:write(F);
 yecctoken2string({char,_,C}) -> io_lib:write_char(C);
 yecctoken2string({var,_,V}) -> io_lib:format("~s", [V]);
 yecctoken2string({string,_,S}) -> io_lib:write_string(S);
 yecctoken2string({reserved_symbol, _, A}) -> io_lib:write(A);
-yecctoken2string({_Cat, _, Val}) -> io_lib:format("~p",[Val]);
+yecctoken2string({_Cat, _, Val}) -> io_lib:format("~tp", [Val]);
 yecctoken2string({dot, _}) -> "'.'";
-yecctoken2string({'$end', _}) ->
-    [];
+yecctoken2string({'$end', _}) -> [];
 yecctoken2string({Other, _}) when is_atom(Other) ->
-    io_lib:write(Other);
+    io_lib:write_atom(Other);
 yecctoken2string(Other) ->
-    io_lib:write(Other).
+    io_lib:format("~tp", [Other]).
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
diff --git a/lib/parsetools/src/yecc.erl b/lib/parsetools/src/yecc.erl
index 48559ec402..36e33b52a4 100644
--- a/lib/parsetools/src/yecc.erl
+++ b/lib/parsetools/src/yecc.erl
@@ -2597,18 +2597,18 @@ format_symbol(Symbol) ->
     String = concat([Symbol]),
     case erl_scan:string(String) of
         {ok, [{atom, _, _}], _} ->
-            io_lib:fwrite(<<"~w">>, [Symbol]);
+            io_lib:fwrite(<<"~tw">>, [Symbol]);
         {ok, [{Word, _}], _} when Word =/= ':', Word =/= '->' ->
             case erl_scan:reserved_word(Word) of
                 true ->
                     String;
                 false ->
-                    io_lib:fwrite(<<"~w">>, [Symbol])
+                    io_lib:fwrite(<<"~tw">>, [Symbol])
             end;
         {ok, [{var, _, _}], _} ->
             String;
         _ -> 
-            io_lib:fwrite(<<"~w">>, [Symbol])
+            io_lib:fwrite(<<"~tw">>, [Symbol])
     end.
 
 inverse(L) ->
diff --git a/lib/runtime_tools/src/dbg.erl b/lib/runtime_tools/src/dbg.erl
index f17aa528ed..9989cf5c07 100644
--- a/lib/runtime_tools/src/dbg.erl
+++ b/lib/runtime_tools/src/dbg.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1996-2016. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2017. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -50,7 +50,7 @@ fun2ms(ShellFun) when is_function(ShellFun) ->
             case ms_transform:transform_from_shell(
                    ?MODULE,Clauses,ImportList) of
                 {error,[{_,[{_,_,Code}|_]}|_],_} ->
-                    io:format("Error: ~s~n",
+                    io:format("Error: ~ts~n",
                               [ms_transform:format_error(Code)]),
                     {error,transform_error};
                 Else ->
diff --git a/lib/stdlib/src/c.erl b/lib/stdlib/src/c.erl
index bb7b485490..4ab9234b81 100644
--- a/lib/stdlib/src/c.erl
+++ b/lib/stdlib/src/c.erl
@@ -144,7 +144,7 @@ c(SrcFile, NewOpts, Filter, BeamFile, Info) ->
     F = fun (Opt) -> not is_outdir_opt(Opt) andalso Filter(Opt) end,
     Options = (NewOpts ++ [{outdir,filename:dirname(BeamFile)}]
                ++ lists:filter(F, old_options(Info))),
-    format("Recompiling ~s\n", [SrcFile]),
+    format("Recompiling ~ts\n", [SrcFile]),
     safe_recompile(SrcFile, Options, BeamFile).
 
 old_options(Info) ->
@@ -548,7 +548,7 @@ mfa_string(Fun) when is_function(Fun) ->
     {arity,A} = erlang:fun_info(Fun, arity),
     mfa_string({M,F,A});
 mfa_string({M,F,A}) ->
-    io_lib:format("~w:~w/~w", [M,F,A]);
+    io_lib:format("~w:~tw/~w", [M,F,A]);
 mfa_string(X) ->
     w(X).
 
@@ -572,7 +572,7 @@ display_info(Pid) ->
 		    w(Reds), w(LM)),
 	    iformat(case fetch(registered_name, Info) of
 			0 -> "";
-			X -> w(X)
+			X -> io_lib:format("~tw", [X])
 		    end,
 		    mfa_string(Curr),
 		    w(SS),
@@ -594,7 +594,7 @@ initial_call(Info)  ->
     end.
 
 iformat(A1, A2, A3, A4, A5) ->
-    format("~-21s ~-33s ~8s ~8s ~4s~n", [A1,A2,A3,A4,A5]).
+    format("~-21ts ~-33ts ~8s ~8s ~4s~n", [A1,A2,A3,A4,A5]).
 
 all_procs() ->
     case is_alive() of
@@ -767,7 +767,7 @@ print_exports(X) when length(X) > 16 ->
     split_print_exports(X);
 print_exports([]) -> ok;
 print_exports([{F, A} |Tail]) ->
-    format("         ~w/~w~n",[F, A]),
+    format("         ~tw/~w~n",[F, A]),
     print_exports(Tail).
 
 split_print_exports(L) ->
@@ -779,11 +779,11 @@ split_print_exports(L) ->
 
 split_print_exports([], [{F, A}|T]) ->
     Str = " ",
-    format("~-30s~w/~w~n", [Str, F, A]),
+    format("~-30ts~tw/~w~n", [Str, F, A]),
     split_print_exports([], T);
 split_print_exports([{F1, A1}|T1], [{F2, A2} | T2]) ->
-    Str = flatten(io_lib:format("~w/~w", [F1, A1])),
-    format("~-30s~w/~w~n", [Str, F2, A2]),
+    Str = flatten(io_lib:format("~tw/~w", [F1, A1])),
+    format("~-30ts~tw/~w~n", [Str, F2, A2]),
     split_print_exports(T1, T2);
 split_print_exports([], []) -> ok.
 
@@ -883,22 +883,22 @@ procline(Name, Info, Pid) ->
     Call = initial_call(Info),
     Reds  = fetch(reductions, Info),
     LM = length(fetch(messages, Info)),
-    procformat(io_lib:format("~w",[Name]),
+    procformat(io_lib:format("~tw",[Name]),
 	       io_lib:format("~w",[Pid]),
-	       io_lib:format("~s",[mfa_string(Call)]),
+	       io_lib:format("~ts",[mfa_string(Call)]),
 	       integer_to_list(Reds), integer_to_list(LM)).
 
 procformat(Name, Pid, Call, Reds, LM) ->
-    format("~-21s ~-12s ~-25s ~12s ~4s~n", [Name,Pid,Call,Reds,LM]).
+    format("~-21ts ~-12s ~-25ts ~12s ~4s~n", [Name,Pid,Call,Reds,LM]).
 
 portline(Name, Info, Id) ->
     Cmd = fetch(name, Info),
-    portformat(io_lib:format("~w",[Name]), 
+    portformat(io_lib:format("~tw",[Name]),
 	       erlang:port_to_list(Id),
 	       Cmd).
 
 portformat(Name, Id, Cmd) ->
-    format("~-21s ~-15s ~-40s~n", [Name,Id,Cmd]).
+    format("~-21ts ~-15s ~-40ts~n", [Name,Id,Cmd]).
 
 %% pwd()
 %% cd(Directory)
diff --git a/lib/stdlib/src/epp.erl b/lib/stdlib/src/epp.erl
index b35e9575a4..31d0d499e3 100644
--- a/lib/stdlib/src/epp.erl
+++ b/lib/stdlib/src/epp.erl
@@ -194,27 +194,27 @@ format_error(missing_parenthesis) ->
 format_error(premature_end) ->
     "premature end";
 format_error({call,What}) ->
-    io_lib:format("illegal macro call '~s'",[What]);
+    io_lib:format("illegal macro call '~ts'",[What]);
 format_error({undefined,M,none}) ->
-    io_lib:format("undefined macro '~s'", [M]);
+    io_lib:format("undefined macro '~ts'", [M]);
 format_error({undefined,M,A}) ->
-    io_lib:format("undefined macro '~s/~p'", [M,A]);
+    io_lib:format("undefined macro '~ts/~p'", [M,A]);
 format_error({depth,What}) ->
     io_lib:format("~s too deep",[What]);
 format_error({mismatch,M}) ->
-    io_lib:format("argument mismatch for macro '~s'", [M]);
+    io_lib:format("argument mismatch for macro '~ts'", [M]);
 format_error({arg_error,M}) ->
-    io_lib:format("badly formed argument for macro '~s'", [M]);
+    io_lib:format("badly formed argument for macro '~ts'", [M]);
 format_error({redefine,M}) ->
-    io_lib:format("redefining macro '~s'", [M]);
+    io_lib:format("redefining macro '~ts'", [M]);
 format_error({redefine_predef,M}) ->
     io_lib:format("redefining predefined macro '~s'", [M]);
 format_error({circular,M,none}) ->
-    io_lib:format("circular macro '~s'", [M]);
+    io_lib:format("circular macro '~ts'", [M]);
 format_error({circular,M,A}) ->
-    io_lib:format("circular macro '~s/~p'", [M,A]);
+    io_lib:format("circular macro '~ts/~p'", [M,A]);
 format_error({include,W,F}) ->
-    io_lib:format("can't find include ~s \"~s\"", [W,F]);
+    io_lib:format("can't find include ~s \"~ts\"", [W,F]);
 format_error({illegal,How,What}) ->
     io_lib:format("~s '-~s'", [How,What]);
 format_error({illegal_function,Macro}) ->
@@ -224,9 +224,9 @@ format_error({illegal_function_usage,Macro}) ->
 format_error({'NYI',What}) ->
     io_lib:format("not yet implemented '~s'", [What]);
 format_error({error,Term}) ->
-    io_lib:format("-error(~p).", [Term]);
+    io_lib:format("-error(~tp).", [Term]);
 format_error({warning,Term}) ->
-    io_lib:format("-warning(~p).", [Term]);
+    io_lib:format("-warning(~tp).", [Term]);
 format_error(E) -> file:format_error(E).
 
 -spec parse_file(FileName, IncludePath, PredefMacros) ->
@@ -1307,7 +1307,7 @@ expand_macros([{'?',_Lq},Token|_Toks], _St) ->
                 Text;
             undefined ->
                 Symbol = erl_scan:symbol(Token),
-                io_lib:write(Symbol)
+                io_lib:fwrite(<<"~tp">>, [Symbol])
         end,
     throw({error,loc(Token),{call,[$?|T]}});
 expand_macros([T|Ts], St) ->
diff --git a/lib/stdlib/src/erl_compile.erl b/lib/stdlib/src/erl_compile.erl
index 76db2eeacd..18d7548fdc 100644
--- a/lib/stdlib/src/erl_compile.erl
+++ b/lib/stdlib/src/erl_compile.erl
@@ -181,7 +181,7 @@ parse_generic_option("P", T, #options{specific=Spec}=Opts) ->
 parse_generic_option("S", T, #options{specific=Spec}=Opts) ->
     compile1(T, Opts#options{specific=['S'|Spec]});
 parse_generic_option(Option, _T, _Opts) ->
-    io:format(?STDERR, "Unknown option: -~s\n", [Option]),
+    io:format(?STDERR, "Unknown option: -~ts\n", [Option]),
     usage().
 
 parse_dep_option("", T) ->
@@ -202,7 +202,7 @@ parse_dep_option("T"++Opt, T0) ->
     {Target,T} = get_option("MT", Opt, T0),
     {[{makedep_target,Target}],T};
 parse_dep_option(Opt, _T) ->
-    io:format(?STDERR, "Unknown option: -M~s\n", [Opt]),
+    io:format(?STDERR, "Unknown option: -M~ts\n", [Opt]),
     usage().
 
 usage() ->
diff --git a/lib/stdlib/src/erl_lint.erl b/lib/stdlib/src/erl_lint.erl
index d53a31db0d..fcfd0d8493 100644
--- a/lib/stdlib/src/erl_lint.erl
+++ b/lib/stdlib/src/erl_lint.erl
@@ -175,49 +175,50 @@ format_error(invalid_record) ->
     "invalid record expression";
 
 format_error({attribute,A}) ->
-    io_lib:format("attribute '~w' after function definitions", [A]);
+    io_lib:format("attribute ~tw after function definitions", [A]);
 format_error({missing_qlc_hrl,A}) ->
     io_lib:format("qlc:q/~w called, but \"qlc.hrl\" not included", [A]);
 format_error({redefine_import,{{F,A},M}}) ->
-    io_lib:format("function ~w/~w already imported from ~w", [F,A,M]);
+    io_lib:format("function ~tw/~w already imported from ~w", [F,A,M]);
 format_error({bad_inline,{F,A}}) ->
-    io_lib:format("inlined function ~w/~w undefined", [F,A]);
+    io_lib:format("inlined function ~tw/~w undefined", [F,A]);
 format_error({invalid_deprecated,D}) ->
-    io_lib:format("badly formed deprecated attribute ~w", [D]);
+    io_lib:format("badly formed deprecated attribute ~tw", [D]);
 format_error({bad_deprecated,{F,A}}) ->
-    io_lib:format("deprecated function ~w/~w undefined or not exported", [F,A]);
+    io_lib:format("deprecated function ~tw/~w undefined or not exported",
+                  [F,A]);
 format_error({bad_nowarn_unused_function,{F,A}}) ->
-    io_lib:format("function ~w/~w undefined", [F,A]);
+    io_lib:format("function ~tw/~w undefined", [F,A]);
 format_error({bad_nowarn_bif_clash,{F,A}}) ->
-    io_lib:format("function ~w/~w undefined", [F,A]);
+    io_lib:format("function ~tw/~w undefined", [F,A]);
 format_error(disallowed_nowarn_bif_clash) ->
     io_lib:format("compile directive nowarn_bif_clash is no longer allowed,~n"
 		  " - use explicit module names or -compile({no_auto_import, [F/A]})", []);
 format_error({bad_nowarn_deprecated_function,{M,F,A}}) ->
-    io_lib:format("~w:~w/~w is not a deprecated function", [M,F,A]);
+    io_lib:format("~tw:~tw/~w is not a deprecated function", [M,F,A]);
 format_error({bad_on_load,Term}) ->
-    io_lib:format("badly formed on_load attribute: ~w", [Term]);
+    io_lib:format("badly formed on_load attribute: ~tw", [Term]);
 format_error(multiple_on_loads) ->
     "more than one on_load attribute";
 format_error({bad_on_load_arity,{F,A}}) ->
-    io_lib:format("function ~w/~w has wrong arity (must be 0)", [F,A]);
+    io_lib:format("function ~tw/~w has wrong arity (must be 0)", [F,A]);
 format_error({undefined_on_load,{F,A}}) ->
-    io_lib:format("function ~w/~w undefined", [F,A]);
+    io_lib:format("function ~tw/~w undefined", [F,A]);
 
 format_error(export_all) ->
     "export_all flag enabled - all functions will be exported";
 format_error({duplicated_export, {F,A}}) ->
-    io_lib:format("function ~w/~w already exported", [F,A]);
+    io_lib:format("function ~tw/~w already exported", [F,A]);
 format_error({unused_import,{{F,A},M}}) ->
-    io_lib:format("import ~w:~w/~w is unused", [M,F,A]);
+    io_lib:format("import ~w:~tw/~w is unused", [M,F,A]);
 format_error({undefined_function,{F,A}}) ->
-    io_lib:format("function ~w/~w undefined", [F,A]);
+    io_lib:format("function ~tw/~w undefined", [F,A]);
 format_error({redefine_function,{F,A}}) ->
-    io_lib:format("function ~w/~w already defined", [F,A]);
+    io_lib:format("function ~tw/~w already defined", [F,A]);
 format_error({define_import,{F,A}}) ->
-    io_lib:format("defining imported function ~w/~w", [F,A]);
+    io_lib:format("defining imported function ~tw/~w", [F,A]);
 format_error({unused_function,{F,A}}) ->
-    io_lib:format("function ~w/~w is unused", [F,A]);
+    io_lib:format("function ~tw/~w is unused", [F,A]);
 format_error({call_to_redefined_bif,{F,A}}) ->
     io_lib:format("ambiguous call of overridden auto-imported BIF ~w/~w~n"
 		  " - use erlang:~w/~w or \"-compile({no_auto_import,[~w/~w]}).\" "
@@ -273,7 +274,7 @@ format_error(illegal_bin_pattern) ->
     "binary patterns cannot be matched in parallel using '='";
 format_error(illegal_expr) -> "illegal expression";
 format_error({illegal_guard_local_call, {F,A}}) -> 
-    io_lib:format("call to local/imported function ~w/~w is illegal in guard",
+    io_lib:format("call to local/imported function ~tw/~w is illegal in guard",
 		  [F,A]);
 format_error(illegal_guard_expr) -> "illegal guard expression";
 %% --- maps ---
@@ -281,23 +282,23 @@ format_error(illegal_map_construction) ->
     "only association operators '=>' are allowed in map construction";
 %% --- records ---
 format_error({undefined_record,T}) ->
-    io_lib:format("record ~w undefined", [T]);
+    io_lib:format("record ~tw undefined", [T]);
 format_error({redefine_record,T}) ->
-    io_lib:format("record ~w already defined", [T]);
+    io_lib:format("record ~tw already defined", [T]);
 format_error({redefine_field,T,F}) ->
-    io_lib:format("field ~w already defined in record ~w", [F,T]);
+    io_lib:format("field ~tw already defined in record ~tw", [F,T]);
 format_error({undefined_field,T,F}) ->
-    io_lib:format("field ~w undefined in record ~w", [F,T]);
+    io_lib:format("field ~tw undefined in record ~tw", [F,T]);
 format_error(illegal_record_info) ->
     "illegal record info";
 format_error({field_name_is_variable,T,F}) ->
-    io_lib:format("field ~w is not an atom or _ in record ~w", [F,T]);
+    io_lib:format("field ~tw is not an atom or _ in record ~tw", [F,T]);
 format_error({wildcard_in_update,T}) ->
-    io_lib:format("meaningless use of _ in update of record ~w", [T]);
+    io_lib:format("meaningless use of _ in update of record ~tw", [T]);
 format_error({unused_record,T}) ->
-    io_lib:format("record ~w is unused", [T]);
+    io_lib:format("record ~tw is unused", [T]);
 format_error({untyped_record,T}) ->
-    io_lib:format("record ~w has field(s) without type information", [T]);
+    io_lib:format("record ~tw has field(s) without type information", [T]);
 %% --- variables ----
 format_error({unbound_var,V}) ->
     io_lib:format("variable ~w is unbound", [V]);
@@ -315,7 +316,7 @@ format_error({variable_in_record_def,V}) ->
     io_lib:format("variable ~w in record definition", [V]);
 %% --- binaries ---
 format_error({undefined_bittype,Type}) ->
-    io_lib:format("bit type ~w undefined", [Type]);
+    io_lib:format("bit type ~tw undefined", [Type]);
 format_error({bittype_mismatch,Val1,Val2,What}) ->
     io_lib:format("conflict in ~s specification for bit field: '~p' and '~p'",
 		  [What,Val1,Val2]);
@@ -335,13 +336,13 @@ format_error(unsized_binary_in_bin_gen_pattern) ->
     "binary fields without size are not allowed in patterns of bit string generators";
 %% --- behaviours ---
 format_error({conflicting_behaviours,{Name,Arity},B,FirstL,FirstB}) ->
-    io_lib:format("conflicting behaviours - callback ~w/~w required by both '~p' "
+    io_lib:format("conflicting behaviours - callback ~tw/~w required by both '~p' "
 		  "and '~p' ~s", [Name,Arity,B,FirstB,format_where(FirstL)]);
 format_error({undefined_behaviour_func, {Func,Arity}, Behaviour}) ->
-    io_lib:format("undefined callback function ~w/~w (behaviour '~w')",
+    io_lib:format("undefined callback function ~tw/~w (behaviour '~w')",
 		  [Func,Arity,Behaviour]);
 format_error({undefined_behaviour,Behaviour}) ->
-    io_lib:format("behaviour ~w undefined", [Behaviour]);
+    io_lib:format("behaviour ~tw undefined", [Behaviour]);
 format_error({undefined_behaviour_callbacks,Behaviour}) ->
     io_lib:format("behaviour ~w callback functions are undefined",
 		  [Behaviour]);
@@ -352,23 +353,23 @@ format_error({ill_defined_optional_callbacks,Behaviour}) ->
     io_lib:format("behaviour ~w optional callback functions erroneously defined",
 		  [Behaviour]);
 format_error({behaviour_info, {_M,F,A}}) ->
-    io_lib:format("cannot define callback attibute for ~w/~w when "
+    io_lib:format("cannot define callback attibute for ~tw/~w when "
                   "behaviour_info is defined",[F,A]);
 format_error({redefine_optional_callback, {F, A}}) ->
-    io_lib:format("optional callback ~w/~w duplicated", [F, A]);
+    io_lib:format("optional callback ~tw/~w duplicated", [F, A]);
 format_error({undefined_callback, {_M, F, A}}) ->
-    io_lib:format("callback ~w/~w is undefined", [F, A]);
+    io_lib:format("callback ~tw/~w is undefined", [F, A]);
 %% --- types and specs ---
 format_error({singleton_typevar, Name}) ->
     io_lib:format("type variable ~w is only used once (is unbound)", [Name]);
 format_error({bad_export_type, _ETs}) ->
     io_lib:format("bad export_type declaration", []);
 format_error({duplicated_export_type, {T, A}}) ->
-    io_lib:format("type ~w/~w already exported", [T, A]);
+    io_lib:format("type ~tw/~w already exported", [T, A]);
 format_error({undefined_type, {TypeName, Arity}}) ->
-    io_lib:format("type ~w~s undefined", [TypeName, gen_type_paren(Arity)]);
+    io_lib:format("type ~tw~s undefined", [TypeName, gen_type_paren(Arity)]);
 format_error({unused_type, {TypeName, Arity}}) ->
-    io_lib:format("type ~w~s is unused", [TypeName, gen_type_paren(Arity)]);
+    io_lib:format("type ~tw~s is unused", [TypeName, gen_type_paren(Arity)]);
 format_error({new_builtin_type, {TypeName, Arity}}) ->
     io_lib:format("type ~w~s is a new builtin type; "
 		  "its (re)definition is allowed only until the next release",
@@ -380,25 +381,26 @@ format_error({renamed_type, OldName, NewName}) ->
     io_lib:format("type ~w() is now called ~w(); "
 		  "please use the new name instead", [OldName, NewName]);
 format_error({redefine_type, {TypeName, Arity}}) ->
-    io_lib:format("type ~w~s already defined",
+    io_lib:format("type ~tw~s already defined",
 		  [TypeName, gen_type_paren(Arity)]);
 format_error({type_syntax, Constr}) ->
-    io_lib:format("bad ~w type", [Constr]);
+    io_lib:format("bad ~tw type", [Constr]);
 format_error(old_abstract_code) ->
     io_lib:format("abstract code generated before Erlang/OTP 19.0 and "
                   "having typed record fields cannot be compiled", []);
 format_error({redefine_spec, {M, F, A}}) ->
-    io_lib:format("spec for ~w:~w/~w already defined", [M, F, A]);
+    io_lib:format("spec for ~tw:~tw/~w already defined", [M, F, A]);
 format_error({redefine_spec, {F, A}}) ->
-    io_lib:format("spec for ~w/~w already defined", [F, A]);
+    io_lib:format("spec for ~tw/~w already defined", [F, A]);
 format_error({redefine_callback, {F, A}}) ->
-    io_lib:format("callback ~w/~w already defined", [F, A]);
+    io_lib:format("callback ~tw/~w already defined", [F, A]);
 format_error({bad_callback, {M, F, A}}) ->
-    io_lib:format("explicit module not allowed for callback ~w:~w/~w ", [M, F, A]);
+    io_lib:format("explicit module not allowed for callback ~tw:~tw/~w",
+                  [M, F, A]);
 format_error({spec_fun_undefined, {F, A}}) ->
-    io_lib:format("spec for undefined function ~w/~w", [F, A]);
+    io_lib:format("spec for undefined function ~tw/~w", [F, A]);
 format_error({missing_spec, {F,A}}) ->
-    io_lib:format("missing specification for function ~w/~w", [F, A]);
+    io_lib:format("missing specification for function ~tw/~w", [F, A]);
 format_error(spec_wrong_arity) ->
     "spec has wrong arity";
 format_error(callback_wrong_arity) ->
@@ -417,15 +419,15 @@ format_error({deprecated_builtin_type, {Name, Arity},
                   "removed in ~s; use ~s",
                   [Name, Arity, Rel, UseS]);
 format_error({not_exported_opaque, {TypeName, Arity}}) ->
-    io_lib:format("opaque type ~w~s is not exported",
+    io_lib:format("opaque type ~tw~s is not exported",
                   [TypeName, gen_type_paren(Arity)]);
 format_error({underspecified_opaque, {TypeName, Arity}}) ->
-    io_lib:format("opaque type ~w~s is underspecified and therefore meaningless",
+    io_lib:format("opaque type ~tw~s is underspecified and therefore meaningless",
                   [TypeName, gen_type_paren(Arity)]);
 format_error({bad_dialyzer_attribute,Term}) ->
-    io_lib:format("badly formed dialyzer attribute: ~w", [Term]);
+    io_lib:format("badly formed dialyzer attribute: ~tw", [Term]);
 format_error({bad_dialyzer_option,Term}) ->
-    io_lib:format("unknown dialyzer warning option: ~w", [Term]);
+    io_lib:format("unknown dialyzer warning option: ~tw", [Term]);
 %% --- obsolete? unused? ---
 format_error({format_error, {Fmt, Args}}) ->
     io_lib:format(Fmt, Args).
@@ -763,12 +765,7 @@ start_state({attribute,Line,module,{_,_}}=Form, St0) ->
 start_state({attribute,Line,module,M}, St0) ->
     St1 = St0#lint{module=M},
     St2 = St1#lint{state=attribute},
-    case is_non_latin1_name(M) of
-        true ->
-            add_error(Line, non_latin1_module_unsupported, St2);
-        false ->
-            St2
-    end;
+    check_module_name(M, Line, St2);
 start_state(Form, St) ->
     Anno = case Form of
                {eof, L} -> erl_anno:new(L);
@@ -778,9 +775,6 @@ start_state(Form, St) ->
     St1 = add_error(Anno, undefined_module, St),
     attribute_state(Form, St1#lint{state=attribute}).
 
-is_non_latin1_name(Name) ->
-    lists:any(fun(C) -> C > 255 end, atom_to_list(Name)).
-
 %% attribute_state(Form, State) ->
 %%      State'
 
@@ -865,7 +859,11 @@ not_deprecated(Forms, St0) ->
     Bad = [MFAL || {{M,F,A},_L}=MFAL <- MFAsL,
                    otp_internal:obsolete(M, F, A) =:= no],
     St1 = func_line_warning(bad_nowarn_deprecated_function, Bad, St0),
-    St1#lint{not_deprecated = ordsets:from_list(Nowarn)}.
+    ML = [{M,L} || {{M,_F,_A},L} <- MFAsL, is_atom(M)],
+    St3 = foldl(fun ({M,L}, St2) ->
+                        check_module_name(M, L, St2)
+                end, St1, ML),
+    St3#lint{not_deprecated = ordsets:from_list(Nowarn)}.
 
 %% The nowarn_bif_clash directive is not only deprecated, it's actually an error from R14A
 disallowed_compile_flags(Forms, St0) ->
@@ -972,7 +970,8 @@ behaviour_callbacks(Line, B, St0) ->
     catch
         _:_ ->
             St1 = add_warning(Line, {undefined_behaviour, B}, St0),
-            {[], [], St1}
+            St2 = check_module_name(B, Line, St1),
+            {[], [], St2}
     end.
 
 behaviour_missing_callbacks([{{Line,B},Bfs0,OBfs}|T], St0) ->
@@ -1310,7 +1309,8 @@ exports(#lint{compile = Opts, defined = Defs, exports = Es}) ->
 -type import() :: {module(), [fa()]} | module().
 -spec import(line(), import(), lint_state()) -> lint_state().
 
-import(Line, {Mod,Fs}, St) ->
+import(Line, {Mod,Fs}, St00) ->
+    St = check_module_name(Mod, Line, St00),
     Mfs = ordsets:from_list(Fs),
     case check_imports(Line, Mfs, St#lint.imports) of
 	[] ->
@@ -2294,11 +2294,18 @@ expr({call,L,{tuple,Lt,[{atom,Lm,erlang},{atom,Lf,is_record}]},As}, Vt, St) ->
 expr({call,Line,{remote,_Lr,{atom,_Lm,M},{atom,Lf,F}},As}, Vt, St0) ->
     St1 = keyword_warning(Lf, F, St0),
     St2 = check_remote_function(Line, M, F, As, St1),
-    expr_list(As, Vt, St2);
+    St3 = check_module_name(M, Line, St2),
+    expr_list(As, Vt, St3);
 expr({call,Line,{remote,_Lr,M,F},As}, Vt, St0) ->
     St1 = keyword_warning(Line, M, St0),
     St2 = keyword_warning(Line, F, St1),
-    expr_list([M,F|As], Vt, St2);
+    St3 = case M of
+              {atom,Lm,Mod} ->
+                  check_module_name(Mod, Lm, St2);
+              _ ->
+                  St2
+          end,
+    expr_list([M,F|As], Vt, St3);
 expr({call,Line,{atom,La,F},As}, Vt, St0) ->
     St1 = keyword_warning(La, F, St0),
     {Asvt,St2} = expr_list(As, Vt, St1),
@@ -2814,7 +2821,8 @@ check_type(Types, St) ->
 check_type({ann_type, _L, [_Var, Type]}, SeenVars, St) ->
     check_type(Type, SeenVars, St);
 check_type({remote_type, L, [{atom, _, Mod}, {atom, _, Name}, Args]},
-	   SeenVars, St0) ->
+	   SeenVars, St00) ->
+    St0 = check_module_name(Mod, L, St00),
     St = deprecated_type(L, Mod, Name, Args, St0),
     CurrentMod = St#lint.module,
     case Mod =:= CurrentMod of
@@ -2973,11 +2981,12 @@ obsolete_builtin_type({Name, A}) when is_atom(Name), is_integer(A) -> no.
 
 %% spec_decl(Line, Fun, Types, State) -> State.
 
-spec_decl(Line, MFA0, TypeSpecs, St0 = #lint{specs = Specs, module = Mod}) ->
+spec_decl(Line, MFA0, TypeSpecs, St00 = #lint{specs = Specs, module = Mod}) ->
     MFA = case MFA0 of
 	      {F, Arity} -> {Mod, F, Arity};
 	      {_M, _F, Arity} -> MFA0
 	  end,
+    St0 = check_module_name(element(1, MFA), Line, St00),
     St1 = St0#lint{specs = dict:store(MFA, Line, Specs)},
     case dict:is_key(MFA, Specs) of
 	true -> add_error(Line, {redefine_spec, MFA0}, St1);
@@ -2989,7 +2998,9 @@ spec_decl(Line, MFA0, TypeSpecs, St0 = #lint{specs = Specs, module = Mod}) ->
 callback_decl(Line, MFA0, TypeSpecs,
 	      St0 = #lint{callbacks = Callbacks, module = Mod}) ->
     case MFA0 of
-        {_M, _F, _A} -> add_error(Line, {bad_callback, MFA0}, St0);
+        {M, _F, _A} ->
+            St1 = check_module_name(M, Line, St0),
+            add_error(Line, {bad_callback, MFA0}, St1);
         {F, Arity} ->
             MFA = {Mod, F, Arity},
             St1 = St0#lint{callbacks = dict:store(MFA, Line, Callbacks)},
@@ -3033,6 +3044,16 @@ is_fa({FuncName, Arity})
   when is_atom(FuncName), is_integer(Arity), Arity >= 0 -> true;
 is_fa(_) -> false.
 
+check_module_name(M, Line, St) ->
+    case is_latin1_name(M) of
+        true -> St;
+        false ->
+            add_error(Line, non_latin1_module_unsupported, St)
+    end.
+
+is_latin1_name(Name) ->
+    io_lib:latin1_char_list(atom_to_list(Name)).
+
 check_specs([FunType|Left], ETag, Arity, St0) ->
     {FunType1, CTypes} =
 	case FunType of
diff --git a/lib/stdlib/src/erl_parse.yrl b/lib/stdlib/src/erl_parse.yrl
index 733932e711..6e72d64acc 100644
--- a/lib/stdlib/src/erl_parse.yrl
+++ b/lib/stdlib/src/erl_parse.yrl
@@ -1097,12 +1097,12 @@ build_compat_constraint({atom, _, is_subtype}, [{var, _, _}=LHS, Type]) ->
 build_compat_constraint({atom, _, is_subtype}, [LHS, _Type]) ->
     ret_err(?anno(LHS), "bad type variable");
 build_compat_constraint({atom, A, Atom}, _Types) ->
-    ret_err(A, io_lib:format("unsupported constraint ~w", [Atom])).
+    ret_err(A, io_lib:format("unsupported constraint ~tw", [Atom])).
 
 build_constraint({atom, _, is_subtype}, [{var, _, _}=LHS, Type]) ->
     build_constraint(LHS, Type);
 build_constraint({atom, A, Atom}, _Foo) ->
-    ret_err(A, io_lib:format("unsupported constraint ~w", [Atom]));
+    ret_err(A, io_lib:format("unsupported constraint ~tw", [Atom]));
 build_constraint({var, A, '_'}, _Types) ->
     ret_err(A, "bad type variable");
 build_constraint(LHS, Type) ->
@@ -1220,7 +1220,7 @@ attribute_farity_map(Args) ->
 -spec error_bad_decl(erl_anno:anno(), attributes()) -> no_return().
 
 error_bad_decl(Anno, S) ->
-    ret_err(Anno, io_lib:format("bad ~w declaration", [S])).
+    ret_err(Anno, io_lib:format("bad ~tw declaration", [S])).
 
 farity_list({cons,_Ac,{op,_Ao,'/',{atom,_Aa,A},{integer,_Ai,I}},Tail}) ->
     [{A,I}|farity_list(Tail)];
diff --git a/lib/stdlib/src/escript.erl b/lib/stdlib/src/escript.erl
index f2629a47c2..2093916a7c 100644
--- a/lib/stdlib/src/escript.erl
+++ b/lib/stdlib/src/escript.erl
@@ -281,12 +281,12 @@ start(EscriptOptions) ->
         end
     catch
         throw:Str ->
-            io:format("escript: ~s\n", [Str]),
+            io:format("escript: ~ts\n", [Str]),
             my_halt(127);
         _:Reason ->
             Stk = erlang:get_stacktrace(),
-            io:format("escript: Internal error: ~p\n", [Reason]),
-            io:format("~p\n", [Stk]),
+            io:format("escript: Internal error: ~tp\n", [Reason]),
+            io:format("~tp\n", [Stk]),
             my_halt(127)
     end.
 
diff --git a/lib/stdlib/src/io_lib_format.erl b/lib/stdlib/src/io_lib_format.erl
index 14d925bacf..4b2d15c8b3 100644
--- a/lib/stdlib/src/io_lib_format.erl
+++ b/lib/stdlib/src/io_lib_format.erl
@@ -335,7 +335,7 @@ base(B) when is_integer(B) ->
 term(T, none, _Adj, none, _Pad) -> T;
 term(T, none, Adj, P, Pad) -> term(T, P, Adj, P, Pad);
 term(T, F, Adj, P0, Pad) ->
-    L = lists:flatlength(T),
+    L = string:length(T),
     P = erlang:min(L, case P0 of none -> F; _ -> min(P0, F) end),
     if
 	L > P ->
@@ -675,11 +675,11 @@ cdata_to_chars(B) when is_binary(B) ->
 
 string(S, none, _Adj, none, _Pad) -> S;
 string(S, F, Adj, none, Pad) ->
-    string_field(S, F, Adj, lists:flatlength(S), Pad);
+    string_field(S, F, Adj, string:length(S), Pad);
 string(S, none, _Adj, P, Pad) ->
-    string_field(S, P, left, lists:flatlength(S), Pad);
+    string_field(S, P, left, string:length(S), Pad);
 string(S, F, Adj, P, Pad) when F >= P ->
-    N = lists:flatlength(S),
+    N = string:length(S),
     if F > P ->
 	    if N > P ->
 		    adjust(flat_trunc(S, P), chars(Pad, F-P), Adj);
@@ -749,18 +749,7 @@ adjust(Data, Pad, right) -> [Pad|Data].
 %% Flatten and truncate a deep list to at most N elements.
 
 flat_trunc(List, N) when is_integer(N), N >= 0 ->
-    flat_trunc(List, N, [], []).
-
-flat_trunc(L, 0, _, R) when is_list(L) ->
-    lists:reverse(R);
-flat_trunc([H|T], N, S, R) when is_list(H) ->
-    flat_trunc(H, N, [T|S], R);
-flat_trunc([H|T], N, S, R) ->
-    flat_trunc(T, N-1, S, [H|R]);
-flat_trunc([], N, [H|S], R) ->
-    flat_trunc(H, N, S, R);
-flat_trunc([], _, [], R) ->
-    lists:reverse(R).
+    string:slice(List, 0, N).
 
 %% A deep version of string:chars/2,3
 
diff --git a/lib/stdlib/src/io_lib_pretty.erl b/lib/stdlib/src/io_lib_pretty.erl
index ff368d02da..505613b80e 100644
--- a/lib/stdlib/src/io_lib_pretty.erl
+++ b/lib/stdlib/src/io_lib_pretty.erl
@@ -473,7 +473,7 @@ print_length(<<_/bitstring>>=Bin, D, _RF, Enc, Str) ->
 print_length(Term, _D, _RF, _Enc, _Str) ->
     S = io_lib:write(Term),
     %% S can contain unicode, so iolist_size(S) cannot be used here
-    {S, lists:flatlength(S)}.
+    {S, string:length(S)}.
 
 print_length_map(_Map, 1, _RF, _Enc, _Str) ->
     {"#{...}", 6};
diff --git a/lib/stdlib/src/lib.erl b/lib/stdlib/src/lib.erl
index aa6797bce6..c6eb0d7915 100644
--- a/lib/stdlib/src/lib.erl
+++ b/lib/stdlib/src/lib.erl
@@ -27,7 +27,7 @@
 
 -export([format_exception/6, format_exception/7,
          format_stacktrace/4, format_stacktrace/5,
-         format_call/4, format_call/5, format_fun/1]).
+         format_call/4, format_call/5, format_fun/1, format_fun/2]).
 
 -spec flush_receive() -> 'ok'.
 
@@ -400,7 +400,11 @@ format_call(I, ForMForFun, As, FormatFun, Enc)
     format_call("", n_spaces(I-1), ForMForFun, As, FormatFun, Enc).
 
 %% -> iolist() (no \n at end)
-format_fun(Fun) when is_function(Fun) ->
+format_fun(Fun) ->
+    format_fun(Fun, latin1).
+
+%% -> iolist() (no \n at end)
+format_fun(Fun, Enc) when is_function(Fun) ->
     {module, M} = erlang:fun_info(Fun, module),
     {name, F} = erlang:fun_info(Fun, name),
     {arity, A} = erlang:fun_info(Fun, arity),
@@ -410,9 +414,9 @@ format_fun(Fun) when is_function(Fun) ->
         {type, local} when M =:= erl_eval ->
             io_lib:fwrite(<<"interpreted function with arity ~w">>, [A]);
         {type, local} ->
-            mfa_to_string(M, F, A);
+            mfa_to_string(M, F, A, Enc);
         {type, external} ->
-            mfa_to_string(M, F, A)
+            mfa_to_string(M, F, A, Enc)
     end.
 
 analyze_exception(error, Term, Stack) ->
@@ -454,11 +458,11 @@ explain_reason({badarg,V}, error=Cl, [], PF, S, _Enc) -> % orelse, andalso
     format_value(V, <<"bad argument: ">>, Cl, PF, S);
 explain_reason(badarith, error, [], _PF, _S, _Enc) ->
     <<"an error occurred when evaluating an arithmetic expression">>;
-explain_reason({badarity,{Fun,As}}, error, [], _PF, _S, _Enc)
+explain_reason({badarity,{Fun,As}}, error, [], _PF, _S, Enc)
                                       when is_function(Fun) ->
     %% Only the arity is displayed, not the arguments As.
-    io_lib:fwrite(<<"~s called with ~s">>, 
-                  [format_fun(Fun), argss(length(As))]);
+    io_lib:fwrite(<<"~ts called with ~s">>,
+                  [format_fun(Fun, Enc), argss(length(As))]);
 explain_reason({badfun,Term}, error=Cl, [], PF, S, _Enc) ->
     format_value(Term, <<"bad function ">>, Cl, PF, S);
 explain_reason({badmatch,Term}, error=Cl, [], PF, S, _Enc) ->
@@ -489,14 +493,15 @@ explain_reason({try_clause,V}, error=Cl, [], PF, S, _Enc) ->
     %% "there is no try clause with a true guard sequence and a
     %% pattern matching..."
     format_value(V, <<"no try clause matching ">>, Cl, PF, S);
-explain_reason(undef, error, [{M,F,A,_}], _PF, _S, _Enc) ->
+explain_reason(undef, error, [{M,F,A,_}], _PF, _S, Enc) ->
     %% Only the arity is displayed, not the arguments, if there are any.
-    io_lib:fwrite(<<"undefined function ~s">>, 
-                  [mfa_to_string(M, F, n_args(A))]);
-explain_reason({shell_undef,F,A,_}, error, [], _PF, _S, _Enc) ->
+    io_lib:fwrite(<<"undefined function ~ts">>,
+                  [mfa_to_string(M, F, n_args(A), Enc)]);
+explain_reason({shell_undef,F,A,_}, error, [], _PF, _S, Enc) ->
     %% Give nicer reports for undefined shell functions
     %% (but not when the user actively calls shell_default:F(...)).
-    io_lib:fwrite(<<"undefined shell command ~s/~w">>, [F, n_args(A)]);
+    FS = to_string(F, Enc),
+    io_lib:fwrite(<<"undefined shell command ~ts/~w">>, [FS, n_args(A)]);
 %% Exit codes returned by erl_eval only:
 explain_reason({argument_limit,_Fun}, error, [], _PF, _S, _Enc) ->
     io_lib:fwrite(<<"limit of number of arguments to interpreted function"
@@ -546,17 +551,18 @@ format_stacktrace1(S0, Stack0, PF, SF, Enc) ->
     format_stacktrace2(S, Stack, 1, PF, Enc).
 
 format_stacktrace2(S, [{M,F,A,L}|Fs], N, PF, Enc) when is_integer(A) ->
-    [io_lib:fwrite(<<"~s~s ~s ~s">>,
+    [io_lib:fwrite(<<"~s~s ~ts ~s">>,
                    [sep(N, S), origin(N, M, F, A),
-		    mfa_to_string(M, F, A),
+		    mfa_to_string(M, F, A, Enc),
 		    location(L)])
      | format_stacktrace2(S, Fs, N + 1, PF, Enc)];
 format_stacktrace2(S, [{M,F,As,_}|Fs], N, PF, Enc) when is_list(As) ->
     A = length(As),
     CalledAs = [S,<<"   called as ">>],
     C = format_call("", CalledAs, {M,F}, As, PF, Enc),
-    [io_lib:fwrite(<<"~s~s ~s\n~s~ts">>,
-		   [sep(N, S), origin(N, M, F, A), mfa_to_string(M, F, A),
+    [io_lib:fwrite(<<"~s~s ~ts\n~s~ts">>,
+		   [sep(N, S), origin(N, M, F, A),
+                    mfa_to_string(M, F, A, Enc),
                     CalledAs, C])
      | format_stacktrace2(S, Fs, N + 1, PF, Enc)];
 format_stacktrace2(_S, [], _N, _PF, _Enc) ->
@@ -594,10 +600,10 @@ format_call(ErrStr, Pre1, ForMForFun, As, PF, Enc) ->
          {yes,Op} -> 
              format_op(ErrStr, Pre1, Op, As, PF, Enc);
          no ->
-             MFs = mf_to_string(ForMForFun, Arity),
-             I1 = iolist_size([Pre1,ErrStr|MFs]),
+             MFs = mf_to_string(ForMForFun, Arity, Enc),
+             I1 = string:length([Pre1,ErrStr|MFs]),
              S1 = pp_arguments(PF, As, I1, Enc),
-             S2 = pp_arguments(PF, As, iolist_size([Pre1|MFs]), Enc),
+             S2 = pp_arguments(PF, As, string:length([Pre1|MFs]), Enc),
              Long = count_nl(pp_arguments(PF, [a2345,b2345], I1, Enc)) > 0,
              case Long or (count_nl(S2) < count_nl(S1)) of
                  true ->
@@ -656,10 +662,10 @@ printable_list(latin1, As) ->
 printable_list(_, As) ->
     io_lib:printable_list(As).
 
-mfa_to_string(M, F, A) ->
-    io_lib:fwrite(<<"~s/~w">>, [mf_to_string({M, F}, A), A]).
+mfa_to_string(M, F, A, Enc) ->
+    io_lib:fwrite(<<"~ts/~w">>, [mf_to_string({M, F}, A, Enc), A]).
 
-mf_to_string({M, F}, A) ->
+mf_to_string({M, F}, A, Enc) ->
     case erl_internal:bif(M, F, A) of
         true ->
             io_lib:fwrite(<<"~w">>, [F]);
@@ -670,13 +676,15 @@ mf_to_string({M, F}, A) ->
                 {yes, F} ->
                     atom_to_list(F);
                 no ->
-                    io_lib:fwrite(<<"~w:~w">>, [M, F])
+                    FS = to_string(F, Enc),
+                    io_lib:fwrite(<<"~w:~ts">>, [M, FS])
             end
     end;
-mf_to_string(Fun, _A) when is_function(Fun) ->
-    format_fun(Fun);
-mf_to_string(F, _A) ->
-    io_lib:fwrite(<<"~w">>, [F]).
+mf_to_string(Fun, _A, Enc) when is_function(Fun) ->
+    format_fun(Fun, Enc);
+mf_to_string(F, _A, Enc) ->
+    FS = to_string(F, Enc),
+    io_lib:fwrite(<<"~ts">>, [FS]).
 
 format_value(V, ErrStr, Class, PF, S) ->
     Pre1Sz = exited_size(Class),
@@ -725,9 +733,14 @@ exited(exit) ->
 exited(throw) ->
     <<"exception throw: ">>.
 
+to_string(A, latin1) ->
+    io_lib:write_atom_as_latin1(A);
+to_string(A, _) ->
+    io_lib:write_atom(A).
+
 size(latin1, S) ->
     {iolist_size(S),S};
 size(_, S0) ->
     S = unicode:characters_to_list(S0, unicode),
     true = is_list(S),
-    {length(S),S}.
+    {string:length(S),S}.
diff --git a/lib/stdlib/src/ms_transform.erl b/lib/stdlib/src/ms_transform.erl
index 98745b13f3..c1c09f091c 100644
--- a/lib/stdlib/src/ms_transform.erl
+++ b/lib/stdlib/src/ms_transform.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 2002-2016. All Rights Reserved.
+%% Copyright Ericsson AB 2002-2017. All Rights Reserved.
 %% 
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -91,12 +91,12 @@ format_error(?ERR_GUARDMATCH) ->
     "fun with guard matching ('=' in guard) is illegal as match_spec as well";
 format_error({?ERR_GUARDLOCALCALL, Name, Arithy}) ->	    
     lists:flatten(io_lib:format("fun containing the local function call "
-				"'~w/~w' (called in guard) "
+				"'~tw/~w' (called in guard) "
 				"cannot be translated into match_spec",
 				[Name, Arithy]));
 format_error({?ERR_GUARDREMOTECALL, Module, Name, Arithy}) ->	    
     lists:flatten(io_lib:format("fun containing the remote function call "
-				"'~w:~w/~w' (called in guard) "
+				"'~w:~tw/~w' (called in guard) "
 				"cannot be translated into match_spec",
 				[Module,Name,Arithy]));
 format_error({?ERR_GUARDELEMENT, Str}) ->
@@ -117,12 +117,12 @@ format_error(?ERR_BODYMATCH) ->
     "fun with body matching ('=' in body) is illegal as match_spec";
 format_error({?ERR_BODYLOCALCALL, Name, Arithy}) ->	    
     lists:flatten(io_lib:format("fun containing the local function "
-				"call '~w/~w' (called in body) "
+				"call '~tw/~w' (called in body) "
 				"cannot be translated into match_spec",
 				[Name,Arithy]));
 format_error({?ERR_BODYREMOTECALL, Module, Name, Arithy}) ->	    
     lists:flatten(io_lib:format("fun containing the remote function call "
-				"'~w:~w/~w' (called in body) "
+				"'~w:~tw/~w' (called in body) "
 				"cannot be translated into match_spec",
 				[Module,Name,Arithy]));
 format_error({?ERR_BODYELEMENT, Str}) ->
@@ -147,15 +147,15 @@ format_error({?ERR_UNBOUND_VARIABLE, Str}) ->
 		    "into match_spec", [Str]));
 format_error({?ERR_HEADBADREC,Name}) ->	    
     lists:flatten(
-      io_lib:format("fun head contains unknown record type ~w",[Name]));
+      io_lib:format("fun head contains unknown record type ~tw",[Name]));
 format_error({?ERR_HEADBADFIELD,RName,FName}) ->	    
     lists:flatten(
-      io_lib:format("fun head contains reference to unknown field ~w in "
-		    "record type ~w",[FName, RName]));
+      io_lib:format("fun head contains reference to unknown field ~tw in "
+		    "record type ~tw",[FName, RName]));
 format_error({?ERR_HEADMULTIFIELD,RName,FName}) ->	    
     lists:flatten(
-      io_lib:format("fun head contains already defined field ~w in "
-		    "record type ~w",[FName, RName]));
+      io_lib:format("fun head contains already defined field ~tw in "
+		    "record type ~tw",[FName, RName]));
 format_error({?ERR_HEADDOLLARATOM,Atom}) ->	    
     lists:flatten(
       io_lib:format("fun head contains atom ~w, which conflics with reserved "
@@ -166,28 +166,28 @@ format_error({?ERR_HEADBINMATCH,Atom}) ->
 		    "which cannot be translated into match_spec", [Atom]));
 format_error({?ERR_GUARDBADREC,Name}) ->	    
     lists:flatten(
-      io_lib:format("fun guard contains unknown record type ~w",[Name]));
+      io_lib:format("fun guard contains unknown record type ~tw",[Name]));
 format_error({?ERR_GUARDBADFIELD,RName,FName}) ->	    
     lists:flatten(
-      io_lib:format("fun guard contains reference to unknown field ~w in "
-		    "record type ~w",[FName, RName]));
+      io_lib:format("fun guard contains reference to unknown field ~tw in "
+		    "record type ~tw",[FName, RName]));
 format_error({?ERR_GUARDMULTIFIELD,RName,FName}) ->	    
     lists:flatten(
-      io_lib:format("fun guard contains already defined field ~w in "
-		    "record type ~w",[FName, RName]));
+      io_lib:format("fun guard contains already defined field ~tw in "
+		    "record type ~tw",[FName, RName]));
 format_error({?ERR_BODYBADREC,Name}) ->	    
     lists:flatten(
-      io_lib:format("fun body contains unknown record type ~w",[Name]));
+      io_lib:format("fun body contains unknown record type ~tw",[Name]));
 format_error({?ERR_BODYBADFIELD,RName,FName}) ->	    
     lists:flatten(
-      io_lib:format("fun body contains reference to unknown field ~w in "
-		    "record type ~w",[FName, RName]));
+      io_lib:format("fun body contains reference to unknown field ~tw in "
+		    "record type ~tw",[FName, RName]));
 format_error({?ERR_BODYMULTIFIELD,RName,FName}) ->	    
     lists:flatten(
-      io_lib:format("fun body contains already defined field ~w in "
-		    "record type ~w",[FName, RName]));
+      io_lib:format("fun body contains already defined field ~tw in "
+		    "record type ~tw",[FName, RName]));
 format_error(Else) ->
-    lists:flatten(io_lib:format("Unknown error code ~w",[Else])).
+    lists:flatten(io_lib:format("Unknown error code ~tw",[Else])).
 
 %%
 %% Called when translating in shell
@@ -723,7 +723,7 @@ tg(T,B) when is_tuple(T), tuple_size(T) >= 2 ->
     throw({error,Line,{?ERR_GENELEMENT+B#tgd.eb,
 		       translate_language_element(Element)}}); 
 tg(Other,B) ->
-    Element = io_lib:format("unknown element ~w", [Other]),
+    Element = io_lib:format("unknown element ~tw", [Other]),
     throw({error,unknown,{?ERR_GENELEMENT+B#tgd.eb,Element}}).
 
 transform_head([V],OuterBound) ->
diff --git a/lib/stdlib/src/proc_lib.erl b/lib/stdlib/src/proc_lib.erl
index 3fa54cd0d5..9ce8e7d60e 100644
--- a/lib/stdlib/src/proc_lib.erl
+++ b/lib/stdlib/src/proc_lib.erl
@@ -805,16 +805,21 @@ format_exception(Class, Reason, StackTrace, {Enc,_}=Extra) ->
     [EI, lib:format_exception(1+length(EI), Class, Reason, 
                               StackTrace, StackFun, PF, Enc), "\n"].
 
-format_mfa(Indent, {M,F,Args}=StartF, Extra) ->
+format_mfa(Indent, {M,F,Args}=StartF, {Enc,_}=Extra) ->
     try
 	A = length(Args),
-	[Indent,"initial call: ",atom_to_list(M),$:,atom_to_list(F),$/,
+	[Indent,"initial call: ",atom_to_list(M),$:,to_string(F, Enc),$/,
 	 integer_to_list(A),"\n"]
     catch
 	error:_ ->
 	    format_tag(Indent, initial_call, StartF, Extra)
     end.
 
+to_string(A, latin1) ->
+    io_lib:write_atom_as_latin1(A);
+to_string(A, _) ->
+    io_lib:write_atom(A).
+
 pp_fun({Enc,Depth}) ->
     {Letter,Tl} = case Depth of
 		      unlimited -> {"p",[]};
diff --git a/lib/stdlib/test/epp_SUITE.erl b/lib/stdlib/test/epp_SUITE.erl
index 71d6820c47..915f478dfa 100644
--- a/lib/stdlib/test/epp_SUITE.erl
+++ b/lib/stdlib/test/epp_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1998-2016. All Rights Reserved.
+%% Copyright Ericsson AB 1998-2017. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -28,7 +28,7 @@
          otp_8130/1, overload_mac/1, otp_8388/1, otp_8470/1,
          otp_8562/1, otp_8665/1, otp_8911/1, otp_10302/1, otp_10820/1,
          otp_11728/1, encoding/1, extends/1,  function_macro/1,
-	 test_error/1, test_warning/1]).
+	 test_error/1, test_warning/1, otp_14285/1]).
 
 -export([epp_parse_erl_form/2]).
 
@@ -68,7 +68,8 @@ all() ->
      not_circular, skip_header, otp_6277, otp_7702, otp_8130,
      overload_mac, otp_8388, otp_8470, otp_8562,
      otp_8665, otp_8911, otp_10302, otp_10820, otp_11728,
-     encoding, extends, function_macro, test_error, test_warning].
+     encoding, extends, function_macro, test_error, test_warning,
+     otp_14285].
 
 groups() -> 
     [{upcase_mac, [], [upcase_mac_1, upcase_mac_2]},
@@ -677,7 +678,7 @@ otp_8130(Config) when is_list(Config) ->
           {otp_8130_c6,
            <<"-define(M3(), A).\n"
              "t() -> A = 1, ?3.14159}.\n">>,
-           {errors,[{{2,16},epp,{call,"?3.14159"}}],[]}},
+           {errors,[{{2,16},epp,{call,[$?,"3.14159"]}}],[]}},
 
           {otp_8130_c7,
            <<"\nt() -> ?A.\n">>,
@@ -1384,6 +1385,26 @@ do_otp_10820(File, C, PC) ->
     true = test_server:stop_node(Node),
     ok.
 
+%% OTP_14285: Unicode atoms.
+otp_14285(Config) when is_list(Config) ->
+    %% This is just a sample of errors.
+    Cs = [{otp_8562,
+           <<"-export([f/0]).
+              -define('a\x{400}b', 'a\x{400}d').
+              f() ->
+                  ?'a\x{400}b'.
+              g() ->
+                  ?\"a\x{400}b\".
+              h() ->
+                  ?'a\x{400}no'().
+              "/utf8>>,
+           {errors,[{6,epp,{call,[63,[91,["97",44,"1024",44,"98"],93]]}},
+                    {8,epp,{undefined,'a\x{400}no',0}}],
+            []}}
+         ],
+    [] = compile(Config, Cs),
+    ok.
+
 %% OTP-11728. Bugfix circular macro.
 otp_11728(Config) when is_list(Config) ->
     Dir = proplists:get_value(priv_dir, Config),
diff --git a/lib/stdlib/test/erl_lint_SUITE.erl b/lib/stdlib/test/erl_lint_SUITE.erl
index cc3d605840..6a75eaa737 100644
--- a/lib/stdlib/test/erl_lint_SUITE.erl
+++ b/lib/stdlib/test/erl_lint_SUITE.erl
@@ -66,7 +66,7 @@
          otp_11851/1,otp_11879/1,otp_13230/1,
          record_errors/1, otp_11879_cont/1,
          non_latin1_module/1, otp_14323/1,
-         get_stacktrace/1]).
+         get_stacktrace/1, otp_14285/1]).
 
 suite() ->
     [{ct_hooks,[ts_install_cth]},
@@ -87,7 +87,7 @@ all() ->
      maps, maps_type, maps_parallel_match,
      otp_11851, otp_11879, otp_13230,
      record_errors, otp_11879_cont, non_latin1_module, otp_14323,
-     get_stacktrace].
+     get_stacktrace, otp_14285].
 
 groups() -> 
     [{unused_vars_warn, [],
@@ -3922,10 +3922,72 @@ otp_11879_cont(Config) ->
 
 %% OTP-14285: We currently don't support non-latin1 module names.
 
-non_latin1_module(_Config) ->
+non_latin1_module(Config) ->
     do_non_latin1_module('юникод'),
     do_non_latin1_module(list_to_atom([256,$a,$b,$c])),
     do_non_latin1_module(list_to_atom([$a,$b,256,$c])),
+
+    "module names with non-latin1 characters are not supported" =
+        format_error(non_latin1_module_unsupported),
+    BadCallback =
+        {bad_callback,{'кирилли́ческий атом','кирилли́ческий атом',0}},
+    "explicit module not allowed for callback "
+    "'кирилли́ческий атом':'кирилли́ческий атом'/0" =
+        format_error(BadCallback),
+    UndefBehav = {undefined_behaviour,'кирилли́ческий атом'},
+    "behaviour 'кирилли́ческий атом' undefined" =
+        format_error(UndefBehav),
+    BadDepr = {bad_nowarn_deprecated_function,
+               {'кирилли́ческий атом','кирилли́ческий атом',18}},
+    "'кирилли́ческий атом':'кирилли́ческий атом'/18 is not a deprecated "
+    "function" = format_error(BadDepr),
+    Ts = [{non_latin1_module,
+           <<"
+            %% Report uses of module names with non-Latin-1 characters.
+
+            -import('кирилли́ческий атом', []).
+            -behaviour('кирилли́ческий атом').
+            -behavior('кирилли́ческий атом').
+
+            -callback 'кирилли́ческий атом':'кирилли́ческий атом'() -> a.
+
+            -compile([{nowarn_deprecated_function,
+                       [{'кирилли́ческий атом','кирилли́ческий атом',18}]}]).
+
+            %% erl_lint:gexpr/3 is not extended to check module name here:
+            t1() when 'кирилли́ческий атом':'кирилли́ческий атом'(1) ->
+                b.
+
+            t2() ->
+                'кирилли́ческий атом':'кирилли́ческий атом'().
+
+            -spec 'кирилли́ческий атом':'кирилли́ческий атом'() -> atom().
+
+            -spec 'кирилли́ческий атом'(integer()) ->
+              'кирилли́ческий атом':'кирилли́ческий атом'().
+
+            'кирилли́ческий атом'(1) ->
+                'кирилли́ческий атом':f(),
+                F = f,
+                'кирилли́ческий атом':F()."/utf8>>,
+           [],
+           {error,
+            [{4,erl_lint,non_latin1_module_unsupported},
+             {5,erl_lint,non_latin1_module_unsupported},
+             {6,erl_lint,non_latin1_module_unsupported},
+             {8,erl_lint,non_latin1_module_unsupported},
+             {8,erl_lint,BadCallback},
+             {10,erl_lint,non_latin1_module_unsupported},
+             {14,erl_lint,illegal_guard_expr},
+             {18,erl_lint,non_latin1_module_unsupported},
+             {20,erl_lint,non_latin1_module_unsupported},
+             {23,erl_lint,non_latin1_module_unsupported},
+             {26,erl_lint,non_latin1_module_unsupported},
+             {28,erl_lint,non_latin1_module_unsupported}],
+            [{5,erl_lint,UndefBehav},
+             {6,erl_lint,UndefBehav},
+             {10,erl_lint,BadDepr}]}}],
+    run(Config, Ts),
     ok.
 
 do_non_latin1_module(Mod) ->
@@ -4042,6 +4104,53 @@ get_stacktrace(Config) ->
     run(Config, Ts),
     ok.
 
+%% Unicode atoms.
+otp_14285(Config) ->
+    %% A small sample of all the errors and warnings in module erl_lint.
+    E1 = {redefine_function,{'кирилли́ческий атом',0}},
+    E2 = {attribute,'кирилли́ческий атом'},
+    E3 = {undefined_record,'кирилли́ческий атом'},
+    E4 = {undefined_bittype,'кирилли́ческий атом'},
+    "function 'кирилли́ческий атом'/0 already defined" = format_error(E1),
+    "attribute 'кирилли́ческий атом' after function definitions" =
+        format_error(E2),
+    "record 'кирилли́ческий атом' undefined" = format_error(E3),
+    "bit type 'кирилли́ческий атом' undefined" = format_error(E4),
+    Ts = [{otp_14285_1,
+           <<"'кирилли́ческий атом'() -> a.
+              'кирилли́ческий атом'() -> a.
+             "/utf8>>,
+           [],
+           {errors,
+            [{2,erl_lint,E1}],
+            []}},
+         {otp_14285_2,
+           <<"'кирилли́ческий атом'() -> a.
+              -'кирилли́ческий атом'(a).
+             "/utf8>>,
+           [],
+           {errors,
+            [{2,erl_lint,E2}],
+            []}},
+         {otp_14285_3,
+           <<"'кирилли́ческий атом'() -> #'кирилли́ческий атом'{}.
+             "/utf8>>,
+           [],
+           {errors,
+            [{1,erl_lint,E3}],
+            []}},
+         {otp_14285_4,
+           <<"t() -> <<34/'кирилли́ческий атом'>>.
+             "/utf8>>,
+           [],
+           {errors,
+            [{1,erl_lint,E4}],
+            []}}],
+    run(Config, Ts),
+    ok.
+
+format_error(E) ->
+    lists:flatten(erl_lint:format_error(E)).
 
 run(Config, Tests) ->
     F = fun({N,P,Ws,E}, BadL) ->
diff --git a/lib/stdlib/test/proc_lib_SUITE.erl b/lib/stdlib/test/proc_lib_SUITE.erl
index a53e99afc9..029e6286e4 100644
--- a/lib/stdlib/test/proc_lib_SUITE.erl
+++ b/lib/stdlib/test/proc_lib_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 1996-2016. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2017. All Rights Reserved.
 %% 
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -27,7 +27,7 @@
 -export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1, 
 	 init_per_group/2,end_per_group/2, 
 	 crash/1, stacktrace/1, sync_start_nolink/1, sync_start_link/1,
-         spawn_opt/1, sp1/0, sp2/0, sp3/1, sp4/2, sp5/1,
+         spawn_opt/1, sp1/0, sp2/0, sp3/1, sp4/2, sp5/1, '\x{447}'/0,
 	 hibernate/1, stop/1, t_format/1]).
 -export([ otp_6345/1, init_dont_hang/1]).
 
@@ -139,6 +139,14 @@ crash(Config) when is_list(Config) ->
 	    {error_info,{exit,abnormal,{stacktrace}}}],
     analyse_crash(Pid5, Exp5, []),
 
+    %% Unicode atom
+    Pid6 = proc_lib:spawn(?MODULE, '\x{447}', []),
+    Pid6 ! die,
+    Exp6 = [{initial_call,{?MODULE,'\x{447}',[]}},
+	    {ancestors,[self()]},
+	    {error_info,{exit,die,{stacktrace}}}],
+    analyse_crash(Pid6, Exp6, []),
+
     error_logger:delete_report_handler(?MODULE),
     ok.
 
@@ -304,6 +312,12 @@ sp4(Parent, Tester) ->
     end,
     proc_lib:init_ack(Parent, self()).
 
+'\x{447}'() ->
+    receive
+	die -> exit(die);
+	_ -> sp1()
+    end.
+
 hibernate(Config) when is_list(Config) ->
     Ref = make_ref(),
     Self = self(),
diff --git a/lib/stdlib/test/shell_SUITE.erl b/lib/stdlib/test/shell_SUITE.erl
index 5a929157d3..4f0fdc4c6a 100644
--- a/lib/stdlib/test/shell_SUITE.erl
+++ b/lib/stdlib/test/shell_SUITE.erl
@@ -2680,7 +2680,7 @@ prompt_err(B) ->
     S = string:strip(S2, both, $"),
     string:strip(S, right, $.).
 
-%% OTP-10302. Unicode.
+%% OTP-10302. Unicode. Also OTP-14285, Unicode atoms.
 otp_10302(Config) when is_list(Config) ->
     {ok,Node} = start_node(shell_suite_helper_2,
 			   "-pa "++proplists:get_value(priv_dir,Config)++
@@ -2818,6 +2818,22 @@ otp_10302(Config) when is_list(Config) ->
     "                    erl_eval:'-inside-an-interpreted-fun-'(65,\"\x{441}\")"
     " .\n" = t({Node,Test13}),
 
+    %% Unicode atoms.
+    Test14 = <<"'\\x{447}\\x{435}'().">>,
+    "** exception error: undefined shell command '\\x{447}\\x{435}'/0.\n" =
+        t(Test14),
+    Test15 = <<"io:setopts([{encoding,utf8}]).
+                '\\x{447}\\x{435}'().">>,
+    "ok.\n** exception error: undefined shell command '\x{447}\x{435}'/0.\n" =
+        t({Node,Test15}),
+    Test16 = <<"shell_SUITE:'\\x{447}\\x{435}'().">>,
+    "** exception error: undefined function "
+   "shell_SUITE:'\\x{447}\\x{435}'/0.\n" = t(Test16),
+    Test17 = <<"io:setopts([{encoding,utf8}]).
+                shell_SUITE:'\\x{447}\\x{435}'().">>,
+    "ok.\n** exception error: undefined function "
+    "shell_SUITE:'\x{447}\x{435}'/0.\n" =
+        t({Node,Test17}),
     test_server:stop_node(Node),
     ok.