[parsing] When failing due to variable redeclaration, point at the variable.

src/parsing/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/parsing/parser.h"
 
 #include <memory>
 
 #include "src/api.h"
 #include "src/ast/ast-expression-rewriter.h"
@@ skipping 1457 matching lines @@
 }
 
 Declaration* Parser::DeclareVariable(const AstRawString* name,
                                      VariableMode mode, InitializationFlag init,
                                      int pos, bool* ok) {
   DCHECK_NOT_NULL(name);
   VariableProxy* proxy = factory()->NewVariableProxy(
       name, NORMAL_VARIABLE, scanner()->location().beg_pos);
   Declaration* declaration =
       factory()->NewVariableDeclaration(proxy, this->scope(), pos);
-  Declare(declaration, DeclarationDescriptor::NORMAL, mode, init, CHECK_OK);
+  Declare(declaration, DeclarationDescriptor::NORMAL, mode, init, ok, nullptr,
+          scanner()->location().end_pos);
+  if (!*ok) return nullptr;
   return declaration;
 }
 
 Declaration* Parser::DeclareModuleImport(const AstRawString* name, int pos,
                                          bool* ok) {
   DCHECK_EQ(MODULE_SCOPE, scope()->scope_type());
   Declaration* decl =
       DeclareVariable(name, CONST, kNeedsInitialization, pos, CHECK_OK);
   // Allocate imports eagerly as hole check elimination logic in scope
   // analisys depends on identifying imports.
   // TODO(adamk): It's weird to allocate imports long before everything
   // else. We should find a different way of filtering out imports
   // during hole check elimination.
   decl->proxy()->var()->AllocateTo(VariableLocation::MODULE,
                                    Variable::kModuleImportIndex);
   return decl;
 }
 
 Variable* Parser::Declare(Declaration* declaration,
                           DeclarationDescriptor::Kind declaration_kind,
                           VariableMode mode, InitializationFlag init, bool* ok,
-                          Scope* scope) {
+                          Scope* scope, int var_end_pos) {
   if (scope == nullptr) {
     scope = this->scope();
   }
   bool sloppy_mode_block_scope_function_redefinition = false;
   Variable* variable = scope->DeclareVariable(
       declaration, mode, init, allow_harmony_restrictive_generators(),
       &sloppy_mode_block_scope_function_redefinition, ok);
   if (!*ok) {
+    // If we only have the start position of a proxy, we can't highlight the
+    // whole variable name.  Pretend its length is 1 so that we highlight at
+    // least the first character.
+    Scanner::Location loc(
+        declaration->proxy()->position(),
+        var_end_pos >= 0 ? var_end_pos : declaration->proxy()->position() + 1);

[adamk, 2016/10/27 10:32:49]

var_end_pos != kNoSourcePosition

     if (declaration_kind == DeclarationDescriptor::NORMAL) {
-      ReportMessage(MessageTemplate::kVarRedeclaration,
-                    declaration->proxy()->raw_name());
+      ReportMessageAt(loc, MessageTemplate::kVarRedeclaration,
+                      declaration->proxy()->raw_name());
     } else {
-      ReportMessage(MessageTemplate::kParamDupe);
+      ReportMessageAt(loc, MessageTemplate::kParamDupe);
     }
     return nullptr;
   }
   if (sloppy_mode_block_scope_function_redefinition) {
     ++use_counts_[v8::Isolate::kSloppyModeBlockScopedFunctionRedefinition];
   }
   return variable;
 }
 
 Block* Parser::BuildInitializationBlock(
@@ skipping 3886 matching lines @@
 
   return final_loop;
 }
 
 #undef CHECK_OK
 #undef CHECK_OK_VOID
 #undef CHECK_FAILED
 
 }  // namespace internal
 }  // namespace v8