Sloppy mode webcompat: allow conflicting function declarations in blocks

The web appears to depend on being able to redeclare functions-in-blocks
in sloppy mode (examples seen so far tend to redeclare identical functions,
most likely accidentally).

This patch opens a minimal hole: two same-named function declarations
in the same scope are allowed, only in sloppy mode.

BUG=v8:4693, chromium:579395
LOG=y

Review URL: https://codereview.chromium.org/1622723003

Cr-Commit-Position: refs/heads/master@{#33478}

src/parsing/parser.cc

@@ -1926,6 +1926,7 @@ Variable* Parser::Declare(Declaration* declaration,
   DCHECK(proxy->raw_name() != NULL);
   const AstRawString* name = proxy->raw_name();
   VariableMode mode = declaration->mode();
+  bool is_function_declaration = declaration->IsFunctionDeclaration();
   if (scope == nullptr) scope = scope_;
   Scope* declaration_scope =
       IsLexicalVariableMode(mode) ? scope : scope->DeclarationScope();
@@ -1952,7 +1953,7 @@ Variable* Parser::Declare(Declaration* declaration,
       // Declare the name.
       Variable::Kind kind = Variable::NORMAL;
       int declaration_group_start = -1;
-      if (declaration->IsFunctionDeclaration()) {
+      if (is_function_declaration) {
         kind = Variable::FUNCTION;
       } else if (declaration->IsVariableDeclaration() &&
                  declaration->AsVariableDeclaration()->is_class_declaration()) {
@@ -1963,8 +1964,11 @@ Variable* Parser::Declare(Declaration* declaration,
       var = declaration_scope->DeclareLocal(
           name, mode, declaration->initialization(), kind, kNotAssigned,
           declaration_group_start);
-    } else if (IsLexicalVariableMode(mode) ||
-               IsLexicalVariableMode(var->mode()) ||
+    } else if (((IsLexicalVariableMode(mode) ||
+                 IsLexicalVariableMode(var->mode())) &&
+                // Allow duplicate function decls for web compat, see bug 4693.
+                (is_strict(language_mode()) || !is_function_declaration ||
+                 !var->is_function())) ||
                ((mode == CONST_LEGACY || var->mode() == CONST_LEGACY) &&
                 !declaration_scope->is_script_scope())) {
       // The name was declared in this scope before; check for conflicting

test/mjsunit/regress/regress-4693.js

+// Copyright 2016 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.
+//
+// Flags: --harmony-sloppy-function
+
+// In sloppy mode we allow function redeclarations within blocks for webcompat.
+(function() {
+  assertEquals(undefined, f);  // Annex B
+  if (true) {
+    assertEquals(2, f());
+    function f() { return 1 }
+    assertEquals(2, f());
+    function f() { return 2 }
+    assertEquals(2, f());
+  }
+  assertEquals(2, f());  // Annex B
+})();
+
+// Should still fail in strict mode
+assertThrows(`
+  (function() {
+    "use strict";
+    if (true) {
+      function f() { return 1 }
+      function f() { return 2 }
+    }
+  })();
+`, SyntaxError);

test/test262/test262.status

@@ -448,6 +448,9 @@
   'language/types/number/S8.5_A2.1': [PASS, FAIL_OK],
   'language/types/number/S8.5_A2.2': [PASS, FAIL_OK],
 
+  # https://code.google.com/p/v8/issues/detail?id=4693
+  'language/block-scope/syntax/redeclaration-in-block/attempt-to-redeclare-function-declaration-with-function-declaration': [PASS, FAIL_SLOPPY],
+
   ############################ INVALID TESTS #############################
 
   # The reference value calculated by Test262 is incorrect if you run these