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.

1 files changed, 4 insertions, 0 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",