Merge branch 'master' of git-server:otp

14 files changed, 255 insertions, 52 deletions

diff --git a/erts/doc/src/erl_driver.xml b/erts/doc/src/erl_driver.xml
index 8da1836da7..ad37813ac0 100644
--- a/erts/doc/src/erl_driver.xml
+++ b/erts/doc/src/erl_driver.xml
@@ -315,10 +315,13 @@
           <c>ERL_DRV_EXTENDED_MINOR_VERSION</c> will be incremented when
           new features are added. The runtime system uses the minor version
           of the driver to determine what features to use.
-          The runtime system will refuse to load a driver if the major
+          The runtime system will normally refuse to load a driver if the major
           versions differ, or if the major versions are equal and the
           minor version used by the driver is greater than the one used
-          by the runtime system.</p>
+          by the runtime system. Old drivers with lower major versions
+	  will however be allowed after a bump of the major version during
+	  a transition period of two major releases. Such old drivers might
+	  however fail if deprecated features are used.</p>
 	<p>The emulator will refuse to load a driver that does not use
 	  the extended driver interface,
 	  to allow for 64-bit capable drivers,
diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml
index 8b19725c02..6b1f4cccf8 100644
--- a/erts/doc/src/erl_nif.xml
+++ b/erts/doc/src/erl_nif.xml
@@ -316,6 +316,32 @@ ok
       <p>The library initialization callbacks <c>load</c>, <c>reload</c> and
       <c>upgrade</c> are all thread-safe even for shared state data.</p>
       </item>
+
+      <tag><marker id="version_management"/>Version Management</tag>
+      <item><p>
+      When a NIF library is built, information about NIF API version
+      is compiled into the library. When a NIF library is loaded the
+      runtime system verifies that the library is of a compatible version.
+      <c>erl_nif.h</c> defines <c>ERL_NIF_MAJOR_VERSION</c>, and
+      <c>ERL_NIF_MINOR_VERSION</c>. <c>ERL_NIF_MAJOR_VERSION</c> will be
+      incremented when NIF library incompatible changes are made to the
+      Erlang runtime system. Normally it will suffice to recompile the NIF
+      library when the <c>ERL_NIF_MAJOR_VERSION</c> has changed, but it
+      could, under rare circumstances, mean that NIF libraries have to
+      be slightly modified. If so, this will of course be documented.
+      <c>ERL_NIF_MINOR_VERSION</c> will be incremented when
+      new features are added. The runtime system uses the minor version
+      to determine what features to use.
+      </p><p>
+      The runtime system will normally refuse to load a NIF library if
+      the major versions differ, or if the major versions are equal and
+      the minor version used by the NIF library is greater than the one
+      used by the runtime system. Old NIF libraries with lower major
+      versions will however be allowed after a bump of the major version
+      during a transition period of two major releases. Such old NIF
+      libraries might however fail if deprecated features are used.
+      </p></item>
+
       <tag>Dirty NIFs</tag>
       <item><p><marker id="dirty_nifs"/><em>Note that the dirty NIF functionality
       is experimental</em> and that you have to enable support for dirty
diff --git a/erts/emulator/beam/erl_bif_ddll.c b/erts/emulator/beam/erl_bif_ddll.c
index 1728b200f7..56cd2ba04f 100644
--- a/erts/emulator/beam/erl_bif_ddll.c
+++ b/erts/emulator/beam/erl_bif_ddll.c
@@ -1548,8 +1548,10 @@ static int do_load_driver_entry(DE_Handle *dh, char *path, char *name)
 
     switch (dp->extended_marker) {
     case ERL_DRV_EXTENDED_MARKER:
-	if (ERL_DRV_EXTENDED_MAJOR_VERSION != dp->major_version
-	    || ERL_DRV_EXTENDED_MINOR_VERSION < dp->minor_version) {
+	if (dp->major_version < ERL_DRV_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD
+	    || (ERL_DRV_EXTENDED_MAJOR_VERSION < dp->major_version
+		|| (ERL_DRV_EXTENDED_MAJOR_VERSION == dp->major_version
+		    && ERL_DRV_EXTENDED_MINOR_VERSION < dp->minor_version))) {
 	    /* Incompatible driver version */
 	    res = ERL_DE_LOAD_ERROR_INCORRECT_VERSION;
 	    goto error;
diff --git a/erts/emulator/beam/erl_driver.h b/erts/emulator/beam/erl_driver.h
index 5517c26ba4..3ecb379326 100644
--- a/erts/emulator/beam/erl_driver.h
+++ b/erts/emulator/beam/erl_driver.h
@@ -136,6 +136,22 @@ typedef struct {
 #define ERL_DRV_EXTENDED_MINOR_VERSION	0
 
 /*
+ * The emulator will refuse to load a driver with a major version
+ * lower than ERL_DRV_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD. The load
+ * may however fail if user have not removed use of deprecated
+ * symbols.
+ *
+ * The ERL_DRV_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD have to allow
+ * loading of drivers built at least two major OTP releases
+ * ago.
+ *
+ * Bump of major version to 3 happened in OTP 17. That is, in
+ * OTP 19 we can increase ERL_DRV_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD
+ * to 3.
+ */
+#define ERL_DRV_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD 2
+
+/*
  * The emulator will refuse to load a driver with different major
  * version than the one used by the emulator.
  */
diff --git a/erts/emulator/beam/erl_nif.c b/erts/emulator/beam/erl_nif.c
index 40860e141c..063dba056e 100644
--- a/erts/emulator/beam/erl_nif.c
+++ b/erts/emulator/beam/erl_nif.c
@@ -2049,8 +2049,10 @@ BIF_RETTYPE load_nif_2(BIF_ALIST_2)
 	      (entry = erts_sys_ddll_call_nif_init(init_func)) == NULL)) {
 	ret = load_nif_error(BIF_P, bad_lib, "Library init-call unsuccessful");
     }
-    else if (entry->major != ERL_NIF_MAJOR_VERSION
-	     || entry->minor > ERL_NIF_MINOR_VERSION
+    else if (entry->major < ERL_NIF_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD
+	     || (ERL_NIF_MAJOR_VERSION < entry->major
+		 || (ERL_NIF_MAJOR_VERSION == entry->major
+		     && ERL_NIF_MINOR_VERSION < entry->minor))
 	     || (entry->major==2 && entry->minor == 5)) { /* experimental maps */
 	
 	ret = load_nif_error(BIF_P, bad_lib, "Library version (%d.%d) not compatible (with %d.%d).",
diff --git a/erts/emulator/beam/erl_nif.h b/erts/emulator/beam/erl_nif.h
index c12ba4d554..5b93c2398e 100644
--- a/erts/emulator/beam/erl_nif.h
+++ b/erts/emulator/beam/erl_nif.h
@@ -46,6 +46,18 @@
 #define ERL_NIF_MAJOR_VERSION 2
 #define ERL_NIF_MINOR_VERSION 6
 
+/*
+ * The emulator will refuse to load a nif-lib with a major version
+ * lower than ERL_NIF_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD. The load
+ * may however fail if user have not removed use of deprecated
+ * symbols.
+ *
+ * The ERL_NIF_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD have to allow
+ * loading of nif-libs built at least two major OTP releases
+ * ago.
+ */
+#define ERL_NIF_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD 2
+
 #include <stdlib.h>
 
 #ifdef SIZEOF_CHAR
diff --git a/erts/emulator/test/driver_SUITE_data/smaller_major_vsn_drv.c b/erts/emulator/test/driver_SUITE_data/smaller_major_vsn_drv.c
index a1299fe807..6b9d4745ba 100644
--- a/erts/emulator/test/driver_SUITE_data/smaller_major_vsn_drv.c
+++ b/erts/emulator/test/driver_SUITE_data/smaller_major_vsn_drv.c
@@ -20,12 +20,12 @@
  * Author: Rickard Green
  *
  * Description: Implementation of a driver with a smaller major
- *              driver version than the current system.
+ *              driver version than allowed on load.
  */
 
 #define VSN_MISMATCH_DRV_NAME_STR		"smaller_major_vsn_drv"
 #define VSN_MISMATCH_DRV_NAME			smaller_major_vsn_drv
-#define VSN_MISMATCH_DRV_MAJOR_VSN_DIFF		(-1)
+#define VSN_MISMATCH_DRV_MAJOR_VSN_DIFF		(ERL_DRV_MIN_REQUIRED_MAJOR_VERSION_ON_LOAD - ERL_DRV_EXTENDED_MAJOR_VERSION - 1)
 #define VSN_MISMATCH_DRV_MINOR_VSN_DIFF		0
  
 #include "vsn_mismatch_drv_impl.c"
diff --git a/lib/dialyzer/src/dialyzer_contracts.erl b/lib/dialyzer/src/dialyzer_contracts.erl
index 46eaeaa303..283031eb9a 100644
--- a/lib/dialyzer/src/dialyzer_contracts.erl
+++ b/lib/dialyzer/src/dialyzer_contracts.erl
@@ -20,6 +20,8 @@
 
 -module(dialyzer_contracts).
 
+-compile(export_all).
+
 -export([check_contract/2,
 	 check_contracts/4,
 	 contracts_without_fun/3,
@@ -439,7 +441,8 @@ contract_from_form([], _RecDict, _FileLine, TypeAcc, FormAcc) ->
   {lists:reverse(TypeAcc), lists:reverse(FormAcc)}.
 
 process_constraints(Constrs, RecDict, ExpTypes, AllRecords) ->
-  Init = initialize_constraints(Constrs, RecDict, ExpTypes, AllRecords),
+  Init0 = initialize_constraints(Constrs, RecDict, ExpTypes, AllRecords),
+  Init = remove_cycles(Init0),
   constraints_fixpoint(Init, RecDict, ExpTypes, AllRecords).
 
 initialize_constraints(Constrs, RecDict, ExpTypes, AllRecords) ->
@@ -479,12 +482,9 @@ constraints_fixpoint(OldVarDict, Constrs, RecDict, ExpTypes, AllRecords) ->
       constraints_fixpoint(NewVarDict, Constrs, RecDict, ExpTypes, AllRecords)
   end.
 
--define(TYPE_LIMIT, 4).
-
 final_form(Form, RecDict, ExpTypes, AllRecords, VarDict) ->
   T1 = erl_types:t_from_form(Form, RecDict, VarDict),
-  T2 = erl_types:t_solve_remote(T1, ExpTypes, AllRecords),
-  erl_types:t_limit(T2, ?TYPE_LIMIT).
+  erl_types:t_solve_remote(T1, ExpTypes, AllRecords).
 
 constraints_to_dict(Constrs, RecDict, ExpTypes, AllRecords, VarDict) ->
   Subtypes =
@@ -499,6 +499,74 @@ constraints_to_subs([C|Rest], RecDict, ExpTypes, AllRecords, VarDict, Acc) ->
   NewAcc = [{subtype, T1, T2}|Acc],
   constraints_to_subs(Rest, RecDict, ExpTypes, AllRecords, VarDict, NewAcc).
 
+%% Replaces variables with '_' when necessary to break up cycles among
+%% the constraints.
+
+remove_cycles(Constrs0) ->
+  Uses = find_uses(Constrs0),
+  G = digraph:new(),
+  Vs0 = [V || {V, _} <- Uses] ++ [V || {_, V} <- Uses],
+  Vs = lists:usort(Vs0),
+  lists:foreach(fun(V) -> _ = digraph:add_vertex(G, V) end, Vs),
+  lists:foreach(fun({From, To}) ->
+                    _ = digraph:add_edge(G, {From, To}, From, To, [])
+                end, Uses),
+  ok = remove_cycles(G, Vs),
+  ToRemove = ordsets:subtract(ordsets:from_list(Uses),
+                              ordsets:from_list(digraph:edges(G))),
+  Constrs = remove_uses(ToRemove, Constrs0),
+  digraph:delete(G),
+  Constrs.
+
+find_uses([{Var, Form}|Constrs]) ->
+  UsedVars = form_vars(Form, []),
+  VarName = erl_types:t_var_name(Var),
+  [{VarName, UsedVar} || UsedVar <- UsedVars] ++ find_uses(Constrs);
+find_uses([]) ->
+  [].
+
+form_vars({var, _, '_'}, Vs) -> Vs;
+form_vars({var, _, V}, Vs) -> [V|Vs];
+form_vars(T, Vs) when is_tuple(T) ->
+  form_vars(tuple_to_list(T), Vs);
+form_vars([E|Es], Vs) ->
+  form_vars(Es, form_vars(E, Vs));
+form_vars(_, Vs) -> Vs.
+
+remove_cycles(G, Vs) ->
+  NumberOfEdges = digraph:no_edges(G),
+  lists:foreach(fun(V) ->
+                        case digraph:get_cycle(G, V) of
+                          false -> true;
+                          [V] -> digraph:del_edge(G, {V, V});
+                          [V, V1|_] -> digraph:del_edge(G, {V, V1})
+                        end
+                    end, Vs),
+  case digraph:no_edges(G) =:= NumberOfEdges of
+    true -> ok;
+    false -> remove_cycles(G, Vs)
+  end.
+
+remove_uses([], Constrs) -> Constrs;
+remove_uses([{Var, Use}|ToRemove], Constrs0) ->
+  Constrs = remove_uses(Var, Use, Constrs0),
+  remove_uses(ToRemove, Constrs).
+
+remove_uses(_Var, _Use, []) -> [];
+remove_uses(Var, Use, [Constr|Constrs]) ->
+  {V, Form} = Constr,
+  case erl_types:t_var_name(V) =:= Var of
+    true -> [{V, remove_use(Form, Use)}|Constrs];
+    false -> [Constr|remove_uses(Var, Use, Constrs)]
+  end.
+
+remove_use({var, L, V}, V) -> {var, L, '_'};
+remove_use(T, V) when is_tuple(T) ->
+  list_to_tuple(remove_use(tuple_to_list(T), V));
+remove_use([E|Es], V) ->
+  [remove_use(E, V)|remove_use(Es, V)];
+remove_use(T, _V) -> T.
+
 %% Gets the most general domain of a list of domains of all
 %% the overloaded contracts
 
diff --git a/lib/dialyzer/test/small_SUITE_data/results/contracts_with_subtypes b/lib/dialyzer/test/small_SUITE_data/results/contracts_with_subtypes
index bfa33cd296..fbdd182358 100644
--- a/lib/dialyzer/test/small_SUITE_data/results/contracts_with_subtypes
+++ b/lib/dialyzer/test/small_SUITE_data/results/contracts_with_subtypes
@@ -1,27 +1,28 @@
 
 contracts_with_subtypes.erl:106: The call contracts_with_subtypes:rec_arg({'a','b'}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,{'a',A} | {'b',B}), is_subtype(A,'a' | {'b',B}), is_subtype(B,'b' | {'a',A})
 contracts_with_subtypes.erl:107: The call contracts_with_subtypes:rec_arg({'b','a'}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,{'a',A} | {'b',B}), is_subtype(A,'a' | {'b',B}), is_subtype(B,'b' | {'a',A})
-contracts_with_subtypes.erl:108: The call contracts_with_subtypes:rec_arg({'a',{'b','a'}}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,{'a',A} | {'b',B}), is_subtype(A,'a' | {'b',B}), is_subtype(B,'b' | {'a',A})
 contracts_with_subtypes.erl:109: The call contracts_with_subtypes:rec_arg({'b',{'a','b'}}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,{'a',A} | {'b',B}), is_subtype(A,'a' | {'b',B}), is_subtype(B,'b' | {'a',A})
-contracts_with_subtypes.erl:110: The call contracts_with_subtypes:rec_arg({'a',{'b',{'a','b'}}}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,{'a',A} | {'b',B}), is_subtype(A,'a' | {'b',B}), is_subtype(B,'b' | {'a',A})
-contracts_with_subtypes.erl:111: The call contracts_with_subtypes:rec_arg({'b',{'a',{'b','a'}}}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,{'a',A} | {'b',B}), is_subtype(A,'a' | {'b',B}), is_subtype(B,'b' | {'a',A})
-contracts_with_subtypes.erl:142: The pattern 1 can never match the type string()
-contracts_with_subtypes.erl:145: The pattern 'alpha' can never match the type {'ok',_} | {'ok',_,string()}
-contracts_with_subtypes.erl:147: The pattern 42 can never match the type {'ok',_} | {'ok',_,string()}
-contracts_with_subtypes.erl:163: The pattern 'alpha' can never match the type {'ok',_}
-contracts_with_subtypes.erl:165: The pattern 42 can never match the type {'ok',_}
-contracts_with_subtypes.erl:183: The pattern 'alpha' can never match the type {'ok',_}
-contracts_with_subtypes.erl:185: The pattern 42 can never match the type {'ok',_}
-contracts_with_subtypes.erl:202: The pattern 1 can never match the type string()
-contracts_with_subtypes.erl:205: The pattern {'ok', _} can never match the type {'ok',_,string()}
-contracts_with_subtypes.erl:206: The pattern 'alpha' can never match the type {'ok',_,string()}
-contracts_with_subtypes.erl:207: The pattern {'ok', 42} can never match the type {'ok',_,string()}
-contracts_with_subtypes.erl:208: The pattern 42 can never match the type {'ok',_,string()}
-contracts_with_subtypes.erl:234: Function flat_ets_new_t/0 has no local return
-contracts_with_subtypes.erl:235: The call contracts_with_subtypes:flat_ets_new(12,[]) breaks the contract (Name,Options) -> atom() when is_subtype(Name,atom()), is_subtype(Options,[Option]), is_subtype(Option,'set' | 'ordered_set' | 'bag' | 'duplicate_bag' | 'public' | 'protected' | 'private' | 'named_table' | {'keypos',integer()} | {'heir',pid(),term()} | {'heir','none'} | {'write_concurrency',boolean()} | {'read_concurrency',boolean()} | 'compressed')
+contracts_with_subtypes.erl:135: The call contracts_with_subtypes:rec2({'a','b'}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,ab())
+contracts_with_subtypes.erl:136: The call contracts_with_subtypes:rec2({'b','a'}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,ab())
+contracts_with_subtypes.erl:137: The call contracts_with_subtypes:rec2({'a',{'b','a'}}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,ab())
+contracts_with_subtypes.erl:138: The call contracts_with_subtypes:rec2({'b',{'a','b'}}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,ab())
+contracts_with_subtypes.erl:171: The pattern 1 can never match the type string()
+contracts_with_subtypes.erl:174: The pattern 'alpha' can never match the type {'ok',_} | {'ok',_,string()}
+contracts_with_subtypes.erl:176: The pattern 42 can never match the type {'ok',_} | {'ok',_,string()}
+contracts_with_subtypes.erl:192: The pattern 'alpha' can never match the type {'ok',_}
+contracts_with_subtypes.erl:194: The pattern 42 can never match the type {'ok',_}
+contracts_with_subtypes.erl:212: The pattern 'alpha' can never match the type {'ok',_}
+contracts_with_subtypes.erl:214: The pattern 42 can never match the type {'ok',_}
+contracts_with_subtypes.erl:231: The pattern 1 can never match the type string()
+contracts_with_subtypes.erl:234: The pattern {'ok', _} can never match the type {'ok',_,string()}
+contracts_with_subtypes.erl:235: The pattern 'alpha' can never match the type {'ok',_,string()}
+contracts_with_subtypes.erl:236: The pattern {'ok', 42} can never match the type {'ok',_,string()}
+contracts_with_subtypes.erl:237: The pattern 42 can never match the type {'ok',_,string()}
 contracts_with_subtypes.erl:23: Invalid type specification for function contracts_with_subtypes:extract2/0. The success typing is () -> 'something'
-contracts_with_subtypes.erl:261: Function factored_ets_new_t/0 has no local return
-contracts_with_subtypes.erl:262: The call contracts_with_subtypes:factored_ets_new(12,[]) breaks the contract (Name,Options) -> atom() when is_subtype(Name,atom()), is_subtype(Options,[Option]), is_subtype(Option,Type | Access | 'named_table' | {'keypos',Pos} | {'heir',Pid::pid(),HeirData} | {'heir','none'} | Tweaks), is_subtype(Type,type()), is_subtype(Access,access()), is_subtype(Tweaks,{'write_concurrency',boolean()} | {'read_concurrency',boolean()} | 'compressed'), is_subtype(Pos,pos_integer()), is_subtype(HeirData,term())
+contracts_with_subtypes.erl:263: Function flat_ets_new_t/0 has no local return
+contracts_with_subtypes.erl:264: The call contracts_with_subtypes:flat_ets_new(12,[]) breaks the contract (Name,Options) -> atom() when is_subtype(Name,atom()), is_subtype(Options,[Option]), is_subtype(Option,'set' | 'ordered_set' | 'bag' | 'duplicate_bag' | 'public' | 'protected' | 'private' | 'named_table' | {'keypos',integer()} | {'heir',pid(),term()} | {'heir','none'} | {'write_concurrency',boolean()} | {'read_concurrency',boolean()} | 'compressed')
+contracts_with_subtypes.erl:290: Function factored_ets_new_t/0 has no local return
+contracts_with_subtypes.erl:291: The call contracts_with_subtypes:factored_ets_new(12,[]) breaks the contract (Name,Options) -> atom() when is_subtype(Name,atom()), is_subtype(Options,[Option]), is_subtype(Option,Type | Access | 'named_table' | {'keypos',Pos} | {'heir',Pid::pid(),HeirData} | {'heir','none'} | Tweaks), is_subtype(Type,type()), is_subtype(Access,access()), is_subtype(Tweaks,{'write_concurrency',boolean()} | {'read_concurrency',boolean()} | 'compressed'), is_subtype(Pos,pos_integer()), is_subtype(HeirData,term())
 contracts_with_subtypes.erl:77: The call contracts_with_subtypes:foo1(5) breaks the contract (Arg1) -> Res when is_subtype(Arg1,atom()), is_subtype(Res,atom())
 contracts_with_subtypes.erl:78: The call contracts_with_subtypes:foo2(5) breaks the contract (Arg1) -> Res when is_subtype(Arg1,Arg2), is_subtype(Arg2,atom()), is_subtype(Res,atom())
 contracts_with_subtypes.erl:79: The call contracts_with_subtypes:foo3(5) breaks the contract (Arg1) -> Res when is_subtype(Arg2,atom()), is_subtype(Arg1,Arg2), is_subtype(Res,atom())
diff --git a/lib/dialyzer/test/small_SUITE_data/results/contracts_with_subtypes2 b/lib/dialyzer/test/small_SUITE_data/results/contracts_with_subtypes2
new file mode 100644
index 0000000000..9f5433a13d
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/results/contracts_with_subtypes2
@@ -0,0 +1,3 @@
+
+contracts_with_subtypes2.erl:18: Function t/0 has no local return
+contracts_with_subtypes2.erl:19: The call contracts_with_subtypes2:t({'a',{'b',{'c',{'d',{'e',{'g',3}}}}}}) breaks the contract (Arg) -> 'ok' when is_subtype(Arg,{'a',A}), is_subtype(A,{'b',B}), is_subtype(B,{'c',C}), is_subtype(C,{'d',D}), is_subtype(D,{'e',E}), is_subtype(E,{'f',_})
diff --git a/lib/dialyzer/test/small_SUITE_data/src/contracts_with_subtypes.erl b/lib/dialyzer/test/small_SUITE_data/src/contracts_with_subtypes.erl
index d72138d509..d7dfd9752e 100644
--- a/lib/dialyzer/test/small_SUITE_data/src/contracts_with_subtypes.erl
+++ b/lib/dialyzer/test/small_SUITE_data/src/contracts_with_subtypes.erl
@@ -103,15 +103,44 @@ c(babb) -> rec_arg({b, {a, {b, b}}});
 c(ababb) -> rec_arg({a, {b, {a, {b, b}}}});
 c(babaa) -> rec_arg({b, {a, {b, {a, a}}}}).
 
-w(ab) -> rec_arg({a, b});
-w(ba) -> rec_arg({b, a});
-w(aba) -> rec_arg({a, {b, a}});
-w(bab) -> rec_arg({b, {a, b}});
-w(abab) -> rec_arg({a, {b, {a, b}}});
-w(baba) -> rec_arg({b, {a, {b, a}}});
+w(ab) -> rec_arg({a, b}); % breaks the contract
+w(ba) -> rec_arg({b, a}); % breaks the contract
+w(aba) -> rec_arg({a, {b, a}}); % no longer breaks the contract
+w(bab) -> rec_arg({b, {a, b}}); % breaks the contract
+w(abab) -> rec_arg({a, {b, {a, b}}}); % no longer breaks the contract
+w(baba) -> rec_arg({b, {a, {b, a}}}); % no longer breaks the contract
 w(ababa) -> rec_arg({a, {b, {a, {b, a}}}});
 w(babab) -> rec_arg({b, {a, {b, {a, b}}}}).
 
+%% For comparison: the same thing with types
+
+-type ab() :: {a, a()} | {b, b()}.
+-type a() :: a | {b, b()}.
+-type b() :: b | {a, a()}.
+
+-spec rec2(Arg) -> ok when
+      Arg :: ab().
+
+rec2(X) -> get(X).
+
+d(aa) -> rec2({a, a});
+d(bb) -> rec2({b, b});
+d(abb) -> rec2({a, {b, b}});
+d(baa) -> rec2({b, {a, a}});
+d(abaa) -> rec2({a, {b, {a, a}}});
+d(babb) -> rec2({b, {a, {b, b}}});
+d(ababb) -> rec2({a, {b, {a, {b, b}}}});
+d(babaa) -> rec2({b, {a, {b, {a, a}}}}).
+
+q(ab) -> rec2({a, b}); % breaks the contract
+q(ba) -> rec2({b, a}); % breaks the contract
+q(aba) -> rec2({a, {b, a}}); % breaks the contract
+q(bab) -> rec2({b, {a, b}}); % breaks the contract
+q(abab) -> rec2({a, {b, {a, b}}});
+q(baba) -> rec2({b, {a, {b, a}}});
+q(ababa) -> rec2({a, {b, {a, {b, a}}}});
+q(babab) -> rec2({b, {a, {b, {a, b}}}}).
+
 %===============================================================================
 
 -type dublo(X) :: {X, X}.
@@ -143,7 +172,7 @@ st(X) when is_atom(X) ->
 		_Other -> ok
 	    end;
 	alpha -> bad;
-	{ok, 42} -> bad;
+	{ok, 42} -> ok;
 	42 -> bad
     end.
 
@@ -161,7 +190,7 @@ dt(X) when is_atom(X) ->
 	err2 -> ok;
 	{ok, X} -> ok;
 	alpha -> bad;
-	{ok, 42} -> bad;
+	{ok, 42} -> ok;
 	42 -> bad
     end.
 
@@ -181,7 +210,7 @@ dt2(X) when is_atom(X) ->
 	err2 -> ok;
 	{ok, X} -> ok;
 	alpha -> bad;
-	{ok, 42} -> bad;
+	{ok, 42} -> ok;
 	42 -> bad
     end.
 
diff --git a/lib/dialyzer/test/small_SUITE_data/src/contracts_with_subtypes2.erl b/lib/dialyzer/test/small_SUITE_data/src/contracts_with_subtypes2.erl
new file mode 100644
index 0000000000..d2f945b284
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/src/contracts_with_subtypes2.erl
@@ -0,0 +1,40 @@
+-module(contracts_with_subtypes2).
+
+-compile(export_all).
+
+-behaviour(supervisor).
+
+-spec t(Arg) -> ok when
+      Arg :: {a, A},
+      A :: {b, B},
+      B :: {c, C},
+      C :: {d, D},
+      D :: {e, E},
+      E :: {f, _}.
+
+t(X) ->
+    get(X).
+
+t() ->
+    t({a, {b, {c, {d, {e, {g, 3}}}}}}). % breaks the contract
+
+%% This one should possibly result in warnings about unused variables.
+-spec l() -> ok when
+      X :: Y,
+      Y :: X.
+
+l() ->
+    ok.
+
+%% This is the example from seq12547 (ticket OTP-11798).
+%% There used to be a warning.
+
+-spec init(term()) -> Result when
+      Result :: {ok, {{supervisor:strategy(),
+                       non_neg_integer(),
+                       pos_integer()},
+                      [supervisor:child_spec()]}}
+              | ignore.
+
+init(_) ->
+    foo:bar().
diff --git a/lib/kernel/doc/src/app.xml b/lib/kernel/doc/src/app.xml
index b24a2bd7bd..8575d94048 100644
--- a/lib/kernel/doc/src/app.xml
+++ b/lib/kernel/doc/src/app.xml
@@ -213,8 +213,8 @@ RTDeps       [ApplicationVersion] []
       OTP 17.0. The type of its value might be subject to changes during
       the OTP 17 release.</p></warning>
       <warning><p>All runtime dependencies specified in OTP applications
-      during the OTP 17 release might not be completely correct. This
-      is actively worked on. Declared runtime dependencies in OTP
+      during the OTP 17 release may not be completely correct. This
+      is actively being worked on. Declared runtime dependencies in OTP
       applications are expected to be correct in OTP 18.</p></warning>
       </item>
     </taglist>
diff --git a/system/doc/system_principles/versions.xml b/system/doc/system_principles/versions.xml
index 6bfa9d1eed..2bf0d18010 100644
--- a/system/doc/system_principles/versions.xml
+++ b/system/doc/system_principles/versions.xml
@@ -79,18 +79,18 @@
     </section>
 
     <section><title>OTP Versions Table</title>
-    <p>The text file <c>&lt;OTP source root&gt;/otp_versions.table</c>
-    part of the source code contains information about all OTP versions
+    <p>The text file <c>&lt;OTP source root&gt;/otp_versions.table</c> that
+    is part of the source code contains information about all OTP versions
     from OTP 17.0 up to current OTP version. Each line contains information
-    about application versions part of a specific OTP version, and is on
-    the format:</p>
+    about application versions that are part of a specific OTP version, and
+    is on the format:</p>
 <pre>
-&lt;OtpVersion&gt; : &lt;ChangedAppVersions&gt; # &lt;UnchangedAppVersions&gt;
+&lt;OtpVersion&gt; : &lt;ChangedAppVersions&gt; # &lt;UnchangedAppVersions&gt; :
 </pre>
     <p><c>&lt;OtpVersion&gt;</c> is on the format <c>OTP-&lt;VSN&gt;</c>, i.e.,
     the same as the git tag used to identify the source.
     <c>&lt;ChangedAppVersions&gt;</c> and <c>&lt;UnchangedAppVersions&gt;</c>
-    are white space separated lists of application versions on the
+    are space separated lists of application versions on the
     format <c>&lt;application&gt;-&lt;vsn&gt;</c>. 
     <c>&lt;ChangedAppVersions&gt;</c> corresponds to changed applications
     with new version numbers in this OTP version, and
@@ -99,14 +99,15 @@
     not at the same time. If &lt;ChangedAppVersions&gt; is empty, no changes
     has been made that change the build result of any application. This could
     for example be a pure bug fix of the build system. The order of lines
-    is undefined.</p>
+    is undefined. All white space characters in this file are either space
+    (character 32) or line-break (character 10).</p>
     <p>Using ordinary UNIX tools like <c>sed</c> and <c>grep</c> one
     can easily find answers to various questions like:</p>
     <taglist>
       <tag>Which OTP versions are <c>kernel-3.0</c> part of?</tag>
-      <item><p><c> $ grep 'kernel-3\.0' otp_versions.table</c></p></item>
+      <item><p><c> $ grep ' kernel-3\.0 ' otp_versions.table</c></p></item>
       <tag>In which OTP version was <c>kernel-3.0</c> introduced?</tag>
-      <item><p><c> $ sed 's/#.*//;/kernel-3\.0/!d' otp_versions.table</c></p></item>
+      <item><p><c> $ sed 's/#.*//;/ kernel-3\.0 /!d' otp_versions.table</c></p></item>
     </taglist>
     <p>The above commands give a bit more information than the exact answers,
     but adequate information when manually searching for answers to these