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

src/parser.cc

 // Copyright 2012 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.
 
 #include "src/parser.h"
 
 #include "src/api.h"
 #include "src/ast.h"
 #include "src/ast-literal-reindexer.h"
 #include "src/bailout-reason.h"
@@ skipping 4642 matching lines @@
       param_scope->set_end_position(RelocInfo::kNoPosition);
       param_scope->RecordEvalCall();
       param_block = factory()->NewBlock(NULL, 8, true, RelocInfo::kNoPosition);
       param_block->set_scope(param_scope);
       descriptor.hoist_scope = scope_;
     }
 
     {
       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);
     }
 
     if (!parameter.is_simple() && scope_->calls_sloppy_eval()) {
       param_scope = param_scope->FinalizeBlockScope();
       if (param_scope != nullptr) {
         CheckConflictingVarDeclarations(param_scope, CHECK_OK);
       }
       init_block->statements()->Add(param_block, zone());
@@ skipping 1782 matching lines @@
 }
 
 
 void Parser::RaiseLanguageMode(LanguageMode mode) {
   SetLanguageMode(scope_,
                   static_cast<LanguageMode>(scope_->language_mode() | mode));
 }
 
 }  // namespace internal
 }  // namespace v8