[es6] conditionally ignore TDZ semantics for formals

test/mjsunit/harmony/destructuring.js

Index: test/mjsunit/harmony/destructuring.js
diff --git a/test/mjsunit/harmony/destructuring.js b/test/mjsunit/harmony/destructuring.js
index 703e521912eb2b6bee292c9271142fa08028c477..4fae90c64a1dd87ba1d860fcebc27da4ed67515e 100644
--- a/test/mjsunit/harmony/destructuring.js
+++ b/test/mjsunit/harmony/destructuring.js
@@ -956,8 +956,10 @@
   function ok2(x) { 'use strict'; { let x = 2; return x; } };
   assertEquals(2, ok2(1));
 
-  assertThrows("function f({x}) { var x; }; f({});", SyntaxError);
-  assertThrows("function f({x}) { { var x; } }; f({});", SyntaxError);
+  assertDoesNotThrow("function f({x}) { var x; }; f({});");

[adamk, 2015/09/09 00:07:02]

So this is no longer an error, but yet

function f({x = undefined}) { var x; }

is an error.

Seems like there's a deeper problem here. I need to tech up my spec-reading to
fully grok IteratorBindingInitialization, but it seems like the let-binding-ness
shouldn't have anything to do with the ContainsExpression bit.

[caitp (gmail), 2015/09/09 00:24:48]

That's a known issue. I have two plans to fix it. But, there's a cost: one
requires the implementation of the spec change from July 29th re: directives in
functions with non-simple parameters, and the other requires a change to the ast
node to track the declaration kind of a variable declaration. So i thought I'd
keep that as a TODO for now. What do you think? The AST change is just so the
redeclaration error can be avoided for lexical parameters.

+  assertDoesNotThrow("function f({x}) { { var x; } }; f({});");
+  assertDoesNotThrow("'use strict'; function f({x}) { var x; }; f({});");
+  assertDoesNotThrow("'use strict'; function f({x}) { { var x; } }; f({});");
   assertThrows("'use strict'; function f(x) { let x = 0; }; f({});", SyntaxError);
   assertThrows("'use strict'; function f({x}) { let x = 0; }; f({});", SyntaxError);
 }());