From e9eebb939e3825e503903d9939c69d504f74ee91 Mon Sep 17 00:00:00 2001
From: Dwayne Reeves <dreeves@fb.com>
Date: Sat, 11 Jul 2015 12:02:13 -0700
Subject: [PATCH] Fix infinite recursion in Typing_utils.simplified_uerror

Summary: Had a bug where we would continually try to simplify an unification error
produced by an unconstraint expression dependent type. When checking if we
should simplify I need to make sure its not only a expression dependent type
but also wraps some base type.

Reviewed By: @int3

Differential Revision: D2235706
---
 hphp/hack/src/typing/typing_utils.ml                   |  4 ++--
 hphp/hack/test/typecheck/tconst/simplify_error.php     | 14 ++++++++++++++
 hphp/hack/test/typecheck/tconst/simplify_error.php.exp | 14 ++++++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)
 create mode 100644 hphp/hack/test/typecheck/tconst/simplify_error.php
 create mode 100644 hphp/hack/test/typecheck/tconst/simplify_error.php.exp

diff --git a/hphp/hack/src/typing/typing_utils.ml b/hphp/hack/src/typing/typing_utils.ml
index 87ac4579361..57e463c209e 100644
--- a/hphp/hack/src/typing/typing_utils.ml
+++ b/hphp/hack/src/typing/typing_utils.ml
@@ -88,8 +88,8 @@ let simplified_uerror env ty1 ty2 =
   let simplify = match snd ty1, snd ty2 with
     | Tabstract (AKdependent (`static, []), _), Tclass _
     | Tclass _, Tabstract (AKdependent (`static, []), _) -> false
-    | Tabstract (AKdependent _, _), _
-    | _, Tabstract (AKdependent _, _) -> true
+    | Tabstract (AKdependent _, Some _), _
+    | _, Tabstract (AKdependent _, Some _) -> true
     | _, _ -> false in
   (* We unify the base types to see if that produces an error, if not then
    * we use the standard unification error
diff --git a/hphp/hack/test/typecheck/tconst/simplify_error.php b/hphp/hack/test/typecheck/tconst/simplify_error.php
new file mode 100644
index 00000000000..0dc1ae5c57a
--- /dev/null
+++ b/hphp/hack/test/typecheck/tconst/simplify_error.php
@@ -0,0 +1,14 @@
+<?hh // strict
+
+abstract class P<T> {
+  abstract protected function foo(): T;
+}
+
+abstract class C extends P<this::T> {
+  abstract const type T;
+  // Silence the Naming phase errors so we see the
+  // unification error
+  /* HH_IGNORE_ERROR[2002] */
+  /* HH_IGNORE_ERROR[2049] */
+  abstract protected function foo(): T;
+}
diff --git a/hphp/hack/test/typecheck/tconst/simplify_error.php.exp b/hphp/hack/test/typecheck/tconst/simplify_error.php.exp
new file mode 100644
index 00000000000..c403ffa30a7
--- /dev/null
+++ b/hphp/hack/test/typecheck/tconst/simplify_error.php.exp
@@ -0,0 +1,14 @@
+File "simplify_error.php", line 7, characters 16-16:
+This object is of type C (Typing[4110])
+File "simplify_error.php", line 7, characters 26-26:
+It is incompatible with this object of type P
+because some declarations are incompatible.
+Read the following to see why:
+File "simplify_error.php", line 7, characters 28-34:
+This is the abstract type constant C::T
+File "simplify_error.php", line 4, characters 38-38:
+  via this generic T
+File "simplify_error.php", line 8, characters 23-23:
+  resulting from expanding the type constant C::T
+File "simplify_error.php", line 13, characters 38-38:
+It is incompatible with an object of type T
-- 
2.11.4.GIT