[es6] Self-assignment in a default parameter initializer should throw

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index 354f1c33187a33196be7b7db2813f089baa507b3..fcc6b5bc0fb3949c0e5fc492264476ad7809daf5 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -4660,7 +4660,7 @@ Block* Parser::BuildParameterInitializationBlock(
     {
       BlockState block_state(&scope_, param_scope);
       DeclarationParsingResult::Declaration decl(
-          parameter.pattern, parameter.pattern->position(), initial_value);
+          parameter.pattern, descriptor.initialization_pos, initial_value);

[Dan Ehrenberg, 2015/11/24 00:37:35]

I think you want the position to be the end of the expression, not the
beginning. This is what let declarations do. What if the self-reference isn't
the first token in the default expression--then Fullcodegen could still
eliminate your hole check.

[adamk, 2015/11/24 01:08:51]

Great catch. I made the test more complex and added a test for arrow functions.
This then required me to store an initializer position for each parameter (for
arrows, we don't easily have that information available, see the TODO). I'm
going to see if I can do something cleaner for arrows.

       PatternRewriter::DeclareAndInitializeVariables(param_block, &descriptor,
                                                      &decl, nullptr, CHECK_OK);
     }