From 34fb87c9fed12369111f5c3f5b25e4721b758b71 Mon Sep 17 00:00:00 2001
From: James Wu <jjwu@fb.com>
Date: Fri, 17 Aug 2018 10:51:13 -0700
Subject: [PATCH] Do not allow interfaces to use traits

Summary: title; runtime already bans it but we might as well ban it in the typechecker as well.

Reviewed By: kmeht

Differential Revision: D9324929

fbshipit-source-id: 5a3000d3b5e72791a9143106c77f1f3c4f66fa03
---
 hphp/hack/src/errors/error_codes.ml                  | 1 +
 hphp/hack/src/errors/errors.ml                       | 4 ++++
 hphp/hack/src/errors/errors_sig.ml                   | 1 +
 hphp/hack/src/typing/nastCheck.ml                    | 3 +++
 hphp/hack/test/errors/error_map.ml                   | 1 +
 hphp/hack/test/typecheck/interface_use_trait.php     | 5 +++++
 hphp/hack/test/typecheck/interface_use_trait.php.exp | 2 ++
 7 files changed, 17 insertions(+)
 create mode 100644 hphp/hack/test/typecheck/interface_use_trait.php
 create mode 100644 hphp/hack/test/typecheck/interface_use_trait.php.exp

diff --git a/hphp/hack/src/errors/error_codes.ml b/hphp/hack/src/errors/error_codes.ml
index f31b585f7d4..a872fe2d6f3 100644
--- a/hphp/hack/src/errors/error_codes.ml
+++ b/hphp/hack/src/errors/error_codes.ml
@@ -219,6 +219,7 @@ module NastCheck                            = struct
   | ConflictingMutableAndMaybeMutableAttributes
   | MaybeMutableMethodsMustBeReactive
   | RequiresFinalClass
+  | InterfaceUsesTrait
   (* EXTEND HERE WITH NEW VALUES IF NEEDED *)
   [@@ deriving enum, show { with_path = false } ]
   let err_code = to_enum
diff --git a/hphp/hack/src/errors/errors.ml b/hphp/hack/src/errors/errors.ml
index 891b889e097..b482dd5149f 100644
--- a/hphp/hack/src/errors/errors.ml
+++ b/hphp/hack/src/errors/errors.ml
@@ -1286,6 +1286,10 @@ let await_in_sync_function p =
   add (NastCheck.err_code NastCheck.AwaitInSyncFunction) p
     "await can only be used inside async functions"
 
+let interface_use_trait p =
+  add (NastCheck.err_code NastCheck.InterfaceUsesTrait) p
+    "Interfaces cannot use traits"
+
 let await_not_allowed p =
   add (NastCheck.err_code NastCheck.AwaitNotAllowed) p
     "await is only permitted as a statement, expression in a return statement \
diff --git a/hphp/hack/src/errors/errors_sig.ml b/hphp/hack/src/errors/errors_sig.ml
index 718723ed13b..5024e6c3f4a 100644
--- a/hphp/hack/src/errors/errors_sig.ml
+++ b/hphp/hack/src/errors/errors_sig.ml
@@ -588,4 +588,5 @@ module type S = sig
   val misplaced_rx_of_scope: Pos.t -> unit
   val rx_of_scope_and_explicit_rx: Pos.t -> unit
   val lateinit_with_default: Pos.t -> unit
+  val interface_use_trait: Pos.t -> unit
 end
diff --git a/hphp/hack/src/typing/nastCheck.ml b/hphp/hack/src/typing/nastCheck.ml
index 8492f9472b1..506219b0c81 100644
--- a/hphp/hack/src/typing/nastCheck.ml
+++ b/hphp/hack/src/typing/nastCheck.ml
@@ -841,6 +841,9 @@ and interface c =
   (* make sure constructor has no body *)
   Option.iter c.c_constructor enforce_no_body;
   Option.iter c.c_constructor enforce_not_async;
+  List.iter (c.c_uses) (fun (p, _) ->
+    Errors.interface_use_trait p
+  );
   (* make sure that interfaces don't have any member variables *)
   match c.c_vars with
   | hd::_ ->
diff --git a/hphp/hack/test/errors/error_map.ml b/hphp/hack/test/errors/error_map.ml
index a440fc23425..69fd347d8fe 100644
--- a/hphp/hack/test/errors/error_map.ml
+++ b/hphp/hack/test/errors/error_map.ml
@@ -218,6 +218,7 @@ MaybeMutableAttributeOnFunction = 3069
 ConflictingMutableAndMaybeMutableAttributes = 3070
 MaybeMutableMethodsMustBeReactive = 3071
 RequiresFinalClass = 3072
+InterfaceUsesTrait = 3073
 
 Typing Errors:
 AbstractClassFinalDEPRECATED = 4001
diff --git a/hphp/hack/test/typecheck/interface_use_trait.php b/hphp/hack/test/typecheck/interface_use_trait.php
new file mode 100644
index 00000000000..6be070f08f0
--- /dev/null
+++ b/hphp/hack/test/typecheck/interface_use_trait.php
@@ -0,0 +1,5 @@
+<?hh
+trait Hello {}
+interface I {
+  use Hello;
+}
diff --git a/hphp/hack/test/typecheck/interface_use_trait.php.exp b/hphp/hack/test/typecheck/interface_use_trait.php.exp
new file mode 100644
index 00000000000..81529fec58d
--- /dev/null
+++ b/hphp/hack/test/typecheck/interface_use_trait.php.exp
@@ -0,0 +1,2 @@
+File "interface_use_trait.php", line 4, characters 7-11:
+Interfaces cannot use traits (NastCheck[3073])
-- 
2.11.4.GIT