dialyzer: Fix another pattern literal bug

dialyzer_typesig:traverse/3 would perform an unsafe optimisation when
given a cons pattern that contained a map and could be folded into a
literal with cerl:fold_literal/1. In this case, when traversing the map
a type variable would be generated, but this variable would be dropped
by the erl_types:t_cons/2 constructor by in turn calling t_sup(),
producing the overapproximation any(). However, in this particular case,
dialyzer_typesig:traverse/3 is not allowed to overapproximate, since its
result is used in an EQ-constraint.

Although erl_types:t_tuple/1 does not overapproximate like t_cons/2,
which makes the bug unlikely to affect tuples too, the fix was
nevertheless applied defensively to the case of tuples as well.

Also, fix a bug where dialyzer_utils:refold_pattern/1 would generate
syntax nodes with two {label, _} attributes.

1 files changed, 9 insertions, 2 deletions

diff --git a/lib/dialyzer/src/dialyzer_utils.erl b/lib/dialyzer/src/dialyzer_utils.erl
index 721c2c000a..d37701f03b 100644
--- a/lib/dialyzer/src/dialyzer_utils.erl
+++ b/lib/dialyzer/src/dialyzer_utils.erl
@@ -873,8 +873,15 @@ refold_pattern(Pat) ->
   case cerl:is_literal(Pat) andalso find_map(cerl:concrete(Pat)) of
     true ->
       Tree = refold_concrete_pat(cerl:concrete(Pat)),
-      [{label, Label}] = cerl:get_ann(Tree),
-      cerl:set_ann(Tree, [{label, Label}|cerl:get_ann(Pat)]);
+      PatAnn = cerl:get_ann(Pat),
+      case proplists:is_defined(label, PatAnn) of
+	%% Literals are not normally annotated with a label, but can be if, for
+	%% example, they were created by cerl:fold_literal/1.
+	true -> cerl:set_ann(Tree, PatAnn);
+	false ->
+	  [{label, Label}] = cerl:get_ann(Tree),
+	  cerl:set_ann(Tree, [{label, Label}|PatAnn])
+      end;
     false -> Pat
   end.