Fix PR#6768: Typechecker overflow the stack on cyclic type

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15810 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

Changes

@@ -136,6 +136,7 @@ Bug fixes:
 - PR#6727: Printf.sprintf "%F" misbehavior
   (Benoît Vaugon, report by Vassili Karpov)
 - PR#6763: #show with -short-paths doesn't select shortest type paths
+- PR#6768: Typechecker overflow the stack on cyclic type
 - ocamlbuild on cygwin cannot find ocamlfind
   (user 'algoriddle')
 - allow android build with pthreads support (since SDK r10c)

testsuite/tests/typing-misc/wellfounded.ml

@@ -0,0 +1,11 @@
+(* PR#6768 *)
+
+type _ prod = Prod : ('a * 'y) prod;;
+
+let f : type t. t prod -> _ = function Prod ->
+  let module M =
+    struct
+      type d = d * d
+    end
+  in ()
+;;

testsuite/tests/typing-misc/wellfounded.ml.principal.reference

@@ -0,0 +1,7 @@
+
+#     type _ prod = Prod : ('a * 'y) prod
+#               Characters 87-96:
+        type d = d * d
+             ^^^^^^^^^
+Error: The type abbreviation d is cyclic
+# 

testsuite/tests/typing-misc/wellfounded.ml.reference

@@ -0,0 +1,7 @@
+
+#     type _ prod = Prod : ('a * 'y) prod
+#               Characters 87-96:
+        type d = d * d
+             ^^^^^^^^^
+Error: The type abbreviation d is cyclic
+# 

typing/typedecl.ml

@@ -523,7 +523,7 @@ let check_well_founded env loc path to_check ty =
         (* Will be detected by check_recursion *)
         Btype.backtrack snap
   in
-  check ty TypeSet.empty ty
+  Ctype.wrap_trace_gadt_instances env (check ty TypeSet.empty) ty
 
 let check_well_founded_manifest env loc path decl =
   if decl.type_manifest = None then () else