Fix convergence condition for loops

Summary:
We were only looking for stability of the Next continuation to establish that the typing environment reached a fixpoint. This is unsound.

This diff fixes it by looking for stability of all continuations.

Reviewed By: andrewjkennedy

Differential Revision: D36345984

fbshipit-source-id: ade3cdca30f0e28393d6b1e93c5b3a43e701aad9

hphp/hack/src/typing/typing.ml

@@ -2289,17 +2289,21 @@ and stmt_ env pos st =
     let env = { env with in_loop = true } in
     let rec loop env n =
       (* Remember the old environment *)
-      let old_next_entry = Env.next_cont_opt env in
+      let old_conts = env.lenv.per_cont_env in
       let (env, result) = f env in
-      let new_next_entry = Env.next_cont_opt env in
+      let new_conts = env.lenv.per_cont_env in
       (* Finish if we reach the bound, or if the environments match *)
       if
         Int.equal n alias_depth
-        || Typing_per_cont_ops.is_sub_opt_entry
-             Typing_subtype.is_sub_type
-             env
-             new_next_entry
-             old_next_entry
+        || CMap.for_all2
+             ~f:(fun _ old_cont_entry new_cont_entry ->
+               Typing_per_cont_ops.is_sub_opt_entry
+                 Typing_subtype.is_sub_type
+                 env
+                 new_cont_entry
+                 old_cont_entry)
+             old_conts
+             new_conts
       then
         let env = { env with in_loop = in_loop_outer } in
         (env, result)

hphp/hack/test/typecheck/T120247995.php.exp

@@ -0,0 +1,4 @@
+File "T120247995.php", line 10, characters 13-16:
+You are trying to access the method `ohno` but this is an int (Typing[4062])
+  File "interfaces.hhi", line 92, characters 46-47:
+  Definition is here

hphp/hack/test/typecheck/control_flow/lambda.php.exp

@@ -14,6 +14,14 @@ File "lambda.php", line 51, characters 11-21:[2]
   [unresolved]
 File "lambda.php", line 71, characters 9-19:[2]
   ([unresolved] | exact D | exact G | exact J)
+File "lambda.php", line 23, characters 5-15:[3]
+  (exact A | exact B | exact C)
+File "lambda.php", line 24, characters 5-15:[3]
+  (exact A | exact B | exact C)
+File "lambda.php", line 51, characters 11-21:[3]
+  [unresolved]
+File "lambda.php", line 71, characters 9-19:[3]
+  ([unresolved] | exact D | exact G | exact J)
 File "lambda.php", line 86, characters 3-13:
   (exact A | exact B | exact C | exact E)
 File "lambda.php", line 87, characters 3-13: