[parser] use-strict directives in function body affect init block

test/mjsunit/strong/destructuring.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Flags: --harmony-destructuring --harmony-computed-property-names
+// Flags: --harmony-arrow-functions --strong-mode --allow-natives-syntax
+
+(function() {
+  function f({ x = function() { return []; } }) { "use strong"; return x(); }
+  var a = f({ x: undefined });

[caitp (gmail), 2015/07/15 20:35:44]

this move kind of makes destructuring initializers not very good, but maybe this
is actually intentional? Not sure.

[rossberg, 2015/07/16 12:53:47]

Not sure I understand. What's not good?

Btw, language mode vs parameter destructuring is a much bigger problem than I
thought yesterday. Will post something later.

[caitp (gmail), 2015/07/16 13:03:57]

It's okay for the VM, but having to fill out each field is sort of inconvenient
and hurts one of the conveniences of using destructuring in the first place.

eg, `function f({ x = true }) { "use strong"; return x; } f({})` would throw
because `x` does not exist in `{}` --- so it makes destructuring initializers
sort of pointless, because you always need to be explicit.
Yeah, this doesn't quite cut it although it does keep existing tests passing at
least.

[rossberg, 2015/07/16 13:21:05]

Ah, I see. Yes, that shouldn't throw in strong mode either, defaults are
supposed to continue to work for absent properties. But that needs some
adaptation of the desugaring, which we haven't done yet.

+  assertTrue(%IsStrong(a));
+
+  function weakf({ x = function() { return []; } }) { return x(); }
+  a = weakf({});
+  assertFalse(%IsStrong(a));
+
+  function outerf() { return []; }
+  function f2({ x = outerf }) { "use strong"; return x(); }
+  a = f2({ x: undefined });
+  assertFalse(%IsStrong(a));
+})();