Better error message for redefined local names

runtime/vm/parser.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/parser.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/bigint_operations.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
@@ skipping 5122 matching lines @@
     ErrorMsg(ident_pos,
     "missing initialization of 'final' or 'const' variable");
   } else {
     // Initialize variable with null.
     AstNode* null_expr = new LiteralNode(ident_pos, Instance::ZoneHandle());
     initialization = new StoreLocalNode(ident_pos, variable, null_expr);
   }
   // Add variable to scope after parsing the initalizer expression.
   // The expression must not be able to refer to the variable.
   if (!current_block_->scope->AddVariable(variable)) {
-    ErrorMsg(ident_pos, "identifier '%s' already defined",
-             variable->name().ToCString());
+    LocalVariable* existing_var =
+        current_block_->scope->LookupVariable(variable->name(), true);
+    ASSERT(existing_var != NULL);
+    if (existing_var->owner() == current_block_->scope) {
+      ErrorMsg(ident_pos, "identifier '%s' already defined",
+               variable->name().ToCString());
+    } else {
+      ErrorMsg(ident_pos,
+               "'%s' from outer scope has already been used, cannot redefine",
+               variable->name().ToCString());
+    }
   }
   if (is_final || is_const) {
     variable->set_is_final();
   }
   return initialization;
 }
 
 
 // Parses ('var' | 'final' [type] | 'const' [type] | type).
 // The presence of 'final' or 'const' must be detected and remembered
@@ skipping 138 matching lines @@
 
     // Add the function variable to the scope before parsing the function in
     // order to allow self reference from inside the function.
     function_variable = new LocalVariable(ident_pos,
                                           *variable_name,
                                           function_type);
     function_variable->set_is_final();
     ASSERT(current_block_ != NULL);
     ASSERT(current_block_->scope != NULL);
     if (!current_block_->scope->AddVariable(function_variable)) {
-      ErrorMsg(ident_pos, "identifier '%s' already defined",
-               function_variable->name().ToCString());
+      LocalVariable* existing_var =
+          current_block_->scope->LookupVariable(function_variable->name(),
+                                                true);
+      ASSERT(existing_var != NULL);
+      if (existing_var->owner() == current_block_->scope) {
+        ErrorMsg(ident_pos, "identifier '%s' already defined",
+                 function_variable->name().ToCString());
+      } else {
+        ErrorMsg(ident_pos,
+                 "'%s' from outer scope has already been used, cannot redefine",
+                 function_variable->name().ToCString());
+      }
     }
   }
 
   // Parse the local function.
   Array& default_parameter_values = Array::Handle();
   SequenceNode* statements = Parser::ParseFunc(function,
                                                default_parameter_values);
   ASSERT(is_new_closure || (function.end_token_pos() == (TokenPos() - 1)));
   function.set_end_token_pos(TokenPos() - 1);
 
@@ skipping 4963 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart