dialyzer: Improve a warning message

Messages like "Invalid type specification for function
para3:exp_adt/0. The success typing is () -> 3" now look like
"The specification for para3:exp_adt/0 has an opaque subtype
para3_adt:exp1(para3_adt:exp2()) which is violated by the success
typing () -> 3".

The old message did not give any clue as to what invalidated the
contract, namely the opaque subtype.

2 files changed, 33 insertions, 6 deletions

diff --git a/lib/dialyzer/src/dialyzer.erl b/lib/dialyzer/src/dialyzer.erl
index 7f86520c06..aaa2f358d6 100644
--- a/lib/dialyzer/src/dialyzer.erl
+++ b/lib/dialyzer/src/dialyzer.erl
@@ -407,6 +407,10 @@ message_to_string({contract_range, [Contract, M, 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]);
+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]);
 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",
diff --git a/lib/dialyzer/src/dialyzer_contracts.erl b/lib/dialyzer/src/dialyzer_contracts.erl
index a72368f9f8..73b04b305b 100644
--- a/lib/dialyzer/src/dialyzer_contracts.erl
+++ b/lib/dialyzer/src/dialyzer_contracts.erl
@@ -232,7 +232,7 @@ check_contract(#contract{contracts = Contracts}, SuccType, Opaques) ->
       error ->
 	{error, {overlapping_contract, []}};
       ok ->
-	InfList = [erl_types:t_inf(Contract, SuccType, Opaques)
+	InfList = [{Contract, erl_types:t_inf(Contract, SuccType, Opaques)}
 		   || Contract <- Contracts2],
 	case check_contract_inf_list(InfList, SuccType, Opaques) of
 	  {error, _} = Invalid -> Invalid;
@@ -256,10 +256,21 @@ check_domains([Dom|Doms]) ->
 %% Allow a contract if one of the overloaded contracts is possible.
 %% We used to be more strict, e.g., all overloaded contracts had to be
 %% possible.
-check_contract_inf_list([FunType|Left], SuccType, Opaques) ->
+check_contract_inf_list(List, SuccType, Opaques) ->
+  case check_contract_inf_list(List, SuccType, Opaques, []) of
+    ok -> ok;
+    {error, []} -> {error, invalid_contract};
+    {error, [{SigRange, ContrRange}|_]} ->
+      case erl_types:t_find_opaque_mismatch(SigRange, ContrRange, Opaques) of
+        error -> {error, invalid_contract};
+        {ok, _T1, T2} -> {error, {opaque_mismatch, T2}}
+      end
+  end.
+
+check_contract_inf_list([{Contract, FunType}|Left], SuccType, Opaques, OM) ->
   FunArgs = erl_types:t_fun_args(FunType),
   case lists:any(fun erl_types:t_is_none_or_unit/1, FunArgs) of
-    true -> check_contract_inf_list(Left, SuccType, Opaques);
+    true -> check_contract_inf_list(Left, SuccType, Opaques, OM);
     false ->
       STRange = erl_types:t_fun_range(SuccType),
       case erl_types:t_is_none_or_unit(STRange) of
@@ -267,13 +278,16 @@ check_contract_inf_list([FunType|Left], SuccType, Opaques) ->
 	false ->
 	  Range = erl_types:t_fun_range(FunType),
 	  case erl_types:t_is_none(erl_types:t_inf(STRange, Range)) of
-	    true -> check_contract_inf_list(Left, SuccType, Opaques);
+	    true ->
+              CR = erl_types:t_fun_range(Contract),
+              NewOM = [{STRange, CR}|OM],
+              check_contract_inf_list(Left, SuccType, Opaques, NewOM);
 	    false -> ok
 	  end
       end
   end;
-check_contract_inf_list([], _SuccType, _Opaques) ->
-  {error, invalid_contract}.
+check_contract_inf_list([], _SuccType, _Opaques, OM) ->
+  {error, OM}.
 
 check_extraneous([], _SuccType) -> ok;
 check_extraneous([C|Cs], SuccType) ->
@@ -687,6 +701,9 @@ get_invalid_contract_warnings_funs([{MFA, {FileLine, Contract, _Xtra}}|Left],
 	case check_contract(Contract, Sig, Opaques) of
 	  {error, invalid_contract} ->
 	    [invalid_contract_warning(MFA, WarningInfo, Sig, RecDict)|Acc];
+          {error, {opaque_mismatch, T2}} ->
+            W = contract_opaque_warning(MFA, WarningInfo, T2, Sig, RecDict),
+            [W|Acc];
 	  {error, {overlapping_contract, []}} ->
 	    [overlapping_contract_warning(MFA, WarningInfo)|Acc];
 	  {error, {extra_range, ExtraRanges, STRange}} ->
@@ -740,6 +757,12 @@ invalid_contract_warning({M, F, A}, WarningInfo, SuccType, RecDict) ->
   SuccTypeStr = dialyzer_utils:format_sig(SuccType, RecDict),
   {?WARN_CONTRACT_TYPES, WarningInfo, {invalid_contract, [M, F, A, SuccTypeStr]}}.
 
+contract_opaque_warning({M, F, A}, WarningInfo, OpType, SuccType, RecDict) ->
+  OpaqueStr = erl_types:t_to_string(OpType),
+  SuccTypeStr = dialyzer_utils:format_sig(SuccType, RecDict),
+  {?WARN_CONTRACT_TYPES, WarningInfo,
+   {contract_with_opaque, [M, F, A, OpaqueStr, SuccTypeStr]}}.
+
 overlapping_contract_warning({M, F, A}, WarningInfo) ->
   {?WARN_CONTRACT_TYPES, WarningInfo, {overlapping_contract, [M, F, A]}}.