Add infrastructure for the -export_type() attribute

erl_lint has been updated so that it takes the new -export_type()
attribute into account.
This means:
 - do not complain about types which are defined but nowhere used in the
   module but exported to other modules
 - check that all types which are exported are indeed defined in the module
 - warn when there are multiple occurrences of exported types.

In doing this change, I've also taken the liberty to introduce many types and
specs for functions of this module and to do small cleanups here and there.

2 files changed, 52 insertions, 21 deletions

diff --git a/bootstrap/lib/stdlib/ebin/erl_lint.beam b/bootstrap/lib/stdlib/ebin/erl_lint.beam
index 481c7a17fb..6862410a3a 100644
--- a/bootstrap/lib/stdlib/ebin/erl_lint.beam
+++ b/bootstrap/lib/stdlib/ebin/erl_lint.beam
diff --git a/lib/stdlib/src/erl_lint.erl b/lib/stdlib/src/erl_lint.erl
index 229d455e06..06e07523f9 100644
--- a/lib/stdlib/src/erl_lint.erl
+++ b/lib/stdlib/src/erl_lint.erl
@@ -40,7 +40,7 @@
 %%              Value.
 %%  The option handling functions.
 
--spec bool_option(atom(), atom(), boolean(), [_]) -> boolean().
+-spec bool_option(atom(), atom(), boolean(), [compile:option()]) -> boolean().
 
 bool_option(On, Off, Default, Opts) ->
     foldl(fun (Opt, _Def) when Opt =:= On -> true;
@@ -72,6 +72,10 @@ value_option(Flag, Default, On, OnVal, Off, OffVal, Opts) ->
 %%-define(DEBUGF(X,Y), io:format(X, Y)).
 -define(DEBUGF(X,Y), void).
 
+-type line() :: erl_scan:line().     % a convenient alias
+-type fa()   :: {atom(), arity()}.   % function+arity
+-type ta()   :: {atom(), arity()}.   % type+arity
+
 %% Usage of records, functions, and imports. The variable table, which
 %% is passed on as an argument, holds the usage of variables.
 -record(usage, {
@@ -97,8 +101,8 @@ value_option(Flag, Default, On, OnVal, Off, OffVal, Opts) ->
                locals=gb_sets:empty()	:: gb_set(),	%All defined functions (prescanned)
 	       no_auto=gb_sets:empty()	:: gb_set(),	%Functions explicitly not autoimported
                defined=gb_sets:empty()	:: gb_set(),	%Defined fuctions
-	       on_load=[] :: [{atom(),integer()}], 	%On-load function
-	       on_load_line=0 :: integer(),		%Line for on_load
+	       on_load=[] :: [fa()],		%On-load function
+	       on_load_line=0 :: line(),	%Line for on_load
 	       clashes=[],			%Exported functions named as BIFs
                not_deprecated=[],               %Not considered deprecated
                func=[],                         %Current function
@@ -112,13 +116,14 @@ value_option(Flag, Default, On, OnVal, Off, OffVal, Opts) ->
 						%outside any fun or lc
                xqlc= false :: boolean(),	%true if qlc.hrl included
                new = false :: boolean(),	%Has user-defined 'new/N'
-               called= [],			%Called functions
+               called= [] :: [{fa(),line()}],		%Called functions
                usage = #usage{}		:: #usage{},
 	       specs = dict:new()	:: dict(),	%Type specifications
-	       types = dict:new()	:: dict()	%Type definitions
+	       types = dict:new()	:: dict(),	%Type definitions
+	       exp_types=gb_sets:empty():: gb_set()	%Exported types
               }).
 
-%% -type lint_state() :: #lint{}.
+-type lint_state() :: #lint{}.
 
 %% format_error(Error)
 %%  Return a string describing the error.
@@ -303,6 +308,8 @@ format_error({ill_defined_behaviour_callbacks,Behaviour}) ->
 %% --- types and specs ---
 format_error({singleton_typevar, Name}) ->
     io_lib:format("type variable ~w is only used once (is unbound)", [Name]);
+format_error({duplicated_export_type, {T, A}}) ->
+    io_lib:format("type ~w/~w already exported", [T, A]);
 format_error({undefined_type, {TypeName, Arity}}) ->
     io_lib:format("type ~w~s undefined", [TypeName, gen_type_paren(Arity)]);
 format_error({unused_type, {TypeName, Arity}}) ->
@@ -684,6 +691,8 @@ attribute_state({attribute,L,extends,_M}, St) ->
     add_error(L, invalid_extends, St);
 attribute_state({attribute,L,export,Es}, St) ->
     export(L, Es, St);
+attribute_state({attribute,L,export_type,Es}, St) ->
+    export_type(L, Es, St);
 attribute_state({attribute,L,import,Is}, St) ->
     import(L, Is, St);
 attribute_state({attribute,L,record,{Name,Fields}}, St) ->
@@ -1093,7 +1102,7 @@ check_unused_records(Forms, St0) ->
 %% For storing the import list we use the orddict module.
 %% We know an empty set is [].
 
-%% export(Line, Exports, State) -> State.
+-spec export(line(), [fa()], lint_state()) -> lint_state().
 %%  Mark functions as exported, also as called from the export line.
 
 export(Line, Es, #lint{exports = Es0, called = Called} = St0) ->
@@ -1101,7 +1110,8 @@ export(Line, Es, #lint{exports = Es0, called = Called} = St0) ->
         foldl(fun (NA, {E,C,St2}) ->
                       St = case gb_sets:is_element(NA, E) of
                                true ->
-                                   add_warning(Line, {duplicated_export, NA}, St2);
+                                   Warn = {duplicated_export,NA},
+                                   add_warning(Line, Warn, St2);
                                false ->
                                    St2
                            end,
@@ -1110,8 +1120,26 @@ export(Line, Es, #lint{exports = Es0, called = Called} = St0) ->
               {Es0,Called,St0}, Es),
     St1#lint{exports = Es1, called = C1}.
 
-%% import(Line, Imports, State) -> State.
-%% imported(Name, Arity, State) -> {yes,Module} | no.
+-spec export_type(line(), [ta()], lint_state()) -> lint_state().
+%%  Mark types as exported, also as called from the export line.
+
+export_type(Line, ETs, #lint{exp_types = ETs0} = St0) ->
+    {ETs1,St1} =
+	foldl(fun (TA, {E,St2}) ->
+		      St = case gb_sets:is_element(TA, E) of
+			       true ->
+				   Warn = {duplicated_export_type,TA},
+				   add_warning(Line, Warn, St2);
+			       false ->
+				   St2
+			   end,
+		      {gb_sets:add_element(TA, E), St}
+	      end,
+	      {ETs0,St0}, ETs),
+    St1#lint{exp_types = ETs1}.
+
+-type import() :: {module(), [fa()]} | module().
+-spec import(line(), import(), lint_state()) -> lint_state().
 
 import(Line, {Mod,Fs}, St) ->
     Mod1 = package_to_string(Mod),
@@ -1200,13 +1228,15 @@ check_imports(_Line, Fs, Is) ->
 add_imports(Mod, Fs, Is) ->
     foldl(fun (F, Is0) -> orddict:store(F, Mod, Is0) end, Is, Fs).
 
+-spec imported(atom(), arity(), lint_state()) -> {'yes',module()} | 'no'.
+
 imported(F, A, St) ->
     case orddict:find({F,A}, St#lint.imports) of
         {ok,Mod} -> {yes,Mod};
         error -> no
     end.
 
-%% on_load(Line, Val, State) -> State.
+-spec on_load(line(), fa(), lint_state()) -> lint_state().
 %%  Check an on_load directive and remember it.
 
 on_load(Line, {Name,Arity}=Fa, #lint{on_load=OnLoad0}=St0)
@@ -1238,7 +1268,7 @@ check_on_load(#lint{defined=Defined,on_load=[{_,0}=Fa],
     end;
 check_on_load(St) -> St.
 
-%% call_function(Line, Name, Arity, State) -> State.
+-spec call_function(line(), atom(), arity(), lint_state()) -> lint_state().
 %%  Add to both called and calls.
 
 call_function(Line, F, A, #lint{usage=Usage0,called=Cd,func=Func}=St) ->
@@ -1258,7 +1288,7 @@ function(Line, Name, Arity, Cs, St0) ->
     St1 = define_function(Line, Name, Arity, St0#lint{func={Name,Arity}}),
     clauses(Cs, St1#lint.global_vt, St1).
 
-%% define_function(Line, Name, Arity, State) -> State.
+-spec define_function(line(), atom(), arity(), lint_state()) -> lint_state().
 
 define_function(Line, Name, Arity, St0) ->
     St1 = keyword_warning(Line, Name, St0),
@@ -2744,10 +2774,12 @@ add_missing_spec_warnings(Forms, St0, Type) ->
 		  add_warning(L, {missing_spec,FA}, St)
 	  end, St0, Warns).
 
-check_unused_types(Forms, St = #lint{usage=Usage, types=Types}) ->
+check_unused_types(Forms, #lint{usage=Usage, types=Ts, exp_types=ExpTs}=St) ->
     case [File || {attribute,_L,file,{File,_Line}} <- Forms] of
 	[FirstFile|_] ->
-	    UsedTypes = Usage#usage.used_types,
+	    D = Usage#usage.used_types,
+	    L = gb_sets:to_list(ExpTs) ++ dict:fetch_keys(D),
+	    UsedTypes = gb_sets:from_list(L),
 	    FoldFun =
 		fun(_Type, -1, AccSt) ->
 			%% Default type
@@ -2755,19 +2787,18 @@ check_unused_types(Forms, St = #lint{usage=Usage, types=Types}) ->
 		   (Type, FileLine, AccSt) ->
                         case loc(FileLine) of
 			    {FirstFile, _} ->
-				case dict:is_key(Type, UsedTypes) of
+				case gb_sets:is_member(Type, UsedTypes) of
 				    true -> AccSt;
 				    false ->
-					add_warning(FileLine,
-                                                    {unused_type, Type},
-						    AccSt)
+					Warn = {unused_type,Type},
+					add_warning(FileLine, Warn, AccSt)
 				end;
 			    _ ->
-				%% Don't warn about unused types in include file
+				%% No warns about unused types in include files
 				AccSt
 			end
 		end,
-	    dict:fold(FoldFun, St, Types);
+	    dict:fold(FoldFun, St, Ts);
 	[] ->
 	    St
     end.