Fix crash related to contract checking

When "collapsing" heads of list elements from a list's tail into the list's
head the new head can be different.

3 files changed, 20 insertions, 6 deletions

diff --git a/lib/dialyzer/test/small_SUITE_data/src/collapse_lists/a.erl b/lib/dialyzer/test/small_SUITE_data/src/collapse_lists/a.erl
new file mode 100644
index 0000000000..7efe870b0d
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/src/collapse_lists/a.erl
@@ -0,0 +1,9 @@
+-module(a).
+-export([g/1]).
+
+-export_type([a/0, t/0]).
+-type a() :: integer().
+-type t() :: a() | maybe_improper_list(t(), t()).
+
+-spec g(t()) -> t().
+g(X) -> X.
diff --git a/lib/dialyzer/test/small_SUITE_data/src/collapse_lists/b.erl b/lib/dialyzer/test/small_SUITE_data/src/collapse_lists/b.erl
new file mode 100644
index 0000000000..b08bc5e66c
--- /dev/null
+++ b/lib/dialyzer/test/small_SUITE_data/src/collapse_lists/b.erl
@@ -0,0 +1,5 @@
+-module(b).
+-export([f/1]).
+
+-spec f(a:t()) -> a:t().
+f(X) -> a:g(X).
diff --git a/lib/hipe/cerl/erl_types.erl b/lib/hipe/cerl/erl_types.erl
index ceec31742e..1789fc79fa 100644
--- a/lib/hipe/cerl/erl_types.erl
+++ b/lib/hipe/cerl/erl_types.erl
@@ -2555,8 +2555,8 @@ t_subst_dict(?list(Contents, Termination, Size), Dict) ->
 	?nil -> ?list(NewContents, ?nil, Size);
 	?any -> ?list(NewContents, ?any, Size);
 	Other ->
-	  ?list(NewContents, NewTermination, _) = t_cons(NewContents, Other),
-	  ?list(NewContents, NewTermination, Size)
+	  ?list(NewContents2, NewTermination, _) = t_cons(NewContents, Other),
+	  ?list(NewContents2, NewTermination, Size)
       end
   end;
 t_subst_dict(?function(Domain, Range), Dict) ->
@@ -2597,8 +2597,8 @@ t_subst_aux(?list(Contents, Termination, Size), VarMap) ->
 	?nil -> ?list(NewContents, ?nil, Size);
 	?any -> ?list(NewContents, ?any, Size);
 	Other ->
-	  ?list(NewContents, NewTermination, _) = t_cons(NewContents, Other),
-	  ?list(NewContents, NewTermination, Size)
+	  ?list(NewContents2, NewTermination, _) = t_cons(NewContents, Other),
+	  ?list(NewContents2, NewTermination, Size)
       end
   end;
 t_subst_aux(?function(Domain, Range), VarMap) ->
@@ -3186,8 +3186,8 @@ t_abstract_records(?list(Contents, Termination, Size), RecDict) ->
 	?nil -> ?list(NewContents, ?nil, Size);
 	?any -> ?list(NewContents, ?any, Size);
 	Other ->
-	  ?list(NewContents, NewTermination, _) = t_cons(NewContents, Other),
-	  ?list(NewContents, NewTermination, Size)
+	  ?list(NewContents2, NewTermination, _) = t_cons(NewContents, Other),
+	  ?list(NewContents2, NewTermination, Size)
       end
   end;
 t_abstract_records(?function(Domain, Range), RecDict) ->