From f07f943f77da018dfd46aa3379be1944a1df47e7 Mon Sep 17 00:00:00 2001
From: Vassil Mladenov <vmladenov@fb.com>
Date: Tue, 19 Dec 2017 15:55:10 -0800
Subject: [PATCH] Fixed list difference algorithm

Summary: Changed $$\exists$$ to $$\forall$$ in filter.

Reviewed By: jamesjwu

Differential Revision: D6604685

fbshipit-source-id: 0e4483d806b81190f2a88ba4ff58f4cc42ceff82
---
 hphp/hack/src/typing/typing_taccess.ml             |  4 +++-
 .../generic_self_type_access_failure.php           | 22 ++++++++++++++++++++++
 .../generic_self_type_access_failure.php.exp       | 22 ++++++++++++++++++++++
 .../generic_self_type_access_failure.php.no_format |  0
 4 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php
 create mode 100644 hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php.exp
 create mode 100644 hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php.no_format

diff --git a/hphp/hack/src/typing/typing_taccess.ml b/hphp/hack/src/typing/typing_taccess.ml
index 6f69470b369..5025abf3c44 100644
--- a/hphp/hack/src/typing/typing_taccess.ml
+++ b/hphp/hack/src/typing/typing_taccess.ml
@@ -99,9 +99,11 @@ and expand_ env (root_reason, root_ty as root) =
         let upper_bounds = Env.get_upper_bounds env.tenv s in
         (* Ignore upper bounds that are equal to ones we've seen, to avoid
           an infinite loop
+
+          let upper_bounds = upper_bounds - env.gen_seen
         *)
         let upper_bounds = List.filter ~f:(fun ty ->
-            List.exists env.gen_seen
+            List.for_all env.gen_seen
             ~f:(fun ty2 -> not (ty_equal ty ty2))) upper_bounds in
         let env, tyl = List.map_env env upper_bounds begin fun prev_env ty ->
           let env, ty = expand_ env ty in
diff --git a/hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php b/hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php
new file mode 100644
index 00000000000..f8e6c553944
--- /dev/null
+++ b/hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php
@@ -0,0 +1,22 @@
+<?hh // strict
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+// This code attempts to access T::T and should fail.
+interface Intf {};
+abstract class Box {
+  abstract const type T as Intf;
+}
+
+// class provides constrained function
+abstract class AbstractGeneric<TX as Box> {
+  abstract public function f<T>(T $t): void
+  where TX::T = T;
+}
+
+class Consumer<TX as Box> {
+  // incorrectly constrains AbstractGeneric class
+  public function crash<T as Intf>(AbstractGeneric<T> $arg, T $t): void
+  where TX::T = T {
+    $arg->f($t);
+  }
+}
diff --git a/hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php.exp b/hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php.exp
new file mode 100644
index 00000000000..faddbda0288
--- /dev/null
+++ b/hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php.exp
@@ -0,0 +1,22 @@
+File "generic_self_type_access_failure.php", line 18, characters 36-50:
+Some type constraint(s) here are violated (Typing[4110])
+  File "generic_self_type_access_failure.php", line 11, characters 32-33:
+  'TX' is a constrained type parameter
+  File "generic_self_type_access_failure.php", line 18, characters 52-52:
+  'T' is a constrained type parameter
+  File "generic_self_type_access_failure.php", line 11, characters 38-40:
+  This is an object of type Box
+  File "generic_self_type_access_failure.php", line 18, characters 30-33:
+  It is incompatible with an object of type Intf
+File "generic_self_type_access_failure.php", line 13, characters 13-13:
+Could not find type constant T in type Intf (Typing[4090])
+  File "generic_self_type_access_failure.php", line 5, characters 11-14:
+  Declaration of Intf is here
+File "generic_self_type_access_failure.php", line 20, characters 11-11:
+A 'where' type constraint is violated here (Typing[4090])
+  File "generic_self_type_access_failure.php", line 12, characters 28-28:
+  This method's where constraints contain a generic type access
+  File "generic_self_type_access_failure.php", line 13, characters 13-13:
+  Could not find type constant T in type Intf
+  File "generic_self_type_access_failure.php", line 5, characters 11-14:
+  Declaration of Intf is here
diff --git a/hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php.no_format b/hphp/hack/test/typecheck/constraints/generic_self_type_access_failure.php.no_format
new file mode 100644
index 00000000000..e69de29bb2d
-- 
2.11.4.GIT