[es6] Scoping & initialization for var shadowing non-simple parameters

Var-bindings may shadow parameters from a non-simple parameter list. When that happens: they create separate bindings, but are initialised with the respective parameter value. Thus:

(function(x, f = () => x) { var x; var y = x; x = 2; return [x, y, f()] })(1) -->  [2, 1, 1]

This CL implements that by inserting a suitable assignment for every shadwowing var-variable (e.g., x = outer_x above) at the beginning of the function's body block.

R=adamk@chromium.org
BUG=v8:4440,v8:811
LOG=N

Review URL: https://codereview.chromium.org/1371333004

Cr-Commit-Position: refs/heads/master@{#31042}

src/parser.cc

@@ -4682,6 +4682,7 @@ ZoneList<Statement*>* Parser::ParseEagerFunctionBody(
     inner_scope = inner_scope->FinalizeBlockScope();
     if (inner_scope != nullptr) {
       CheckConflictingVarDeclarations(inner_scope, CHECK_OK);
+      InsertShadowingVarBindingInitializers(inner_block);
     }
 
     result->Add(init_block, zone());
@@ -4941,8 +4942,7 @@ Literal* Parser::GetLiteralUndefined(int position) {
 void Parser::CheckConflictingVarDeclarations(Scope* scope, bool* ok) {
   Declaration* decl = scope->CheckConflictingVarDeclarations();
   if (decl != NULL) {
-    // In harmony mode we treat conflicting variable bindinds as early
-    // errors. See ES5 16 for a definition of early errors.
+    // In ES6, conflicting variable bindings are early errors.
     const AstRawString* name = decl->proxy()->raw_name();
     int position = decl->proxy()->position();
     Scanner::Location location = position == RelocInfo::kNoPosition
@@ -4955,6 +4955,31 @@ void Parser::CheckConflictingVarDeclarations(Scope* scope, bool* ok) {
 }
 
 
+void Parser::InsertShadowingVarBindingInitializers(Block* inner_block) {
+  // For each var-binding that shadows a parameter, insert an assignment
+  // initializing the variable with the parameter.
+  Scope* inner_scope = inner_block->scope();
+  DCHECK(inner_scope->is_declaration_scope());
+  Scope* function_scope = inner_scope->outer_scope();
+  DCHECK(function_scope->is_function_scope());
+  ZoneList<Declaration*>* decls = inner_scope->declarations();
+  for (int i = 0; i < decls->length(); ++i) {
+    Declaration* decl = decls->at(i);
+    if (decl->mode() != VAR || !decl->IsVariableDeclaration()) continue;
+    const AstRawString* name = decl->proxy()->raw_name();
+    Variable* parameter = function_scope->LookupLocal(name);
+    if (parameter == nullptr) continue;
+    VariableProxy* to = inner_scope->NewUnresolved(factory(), name);
+    VariableProxy* from = factory()->NewVariableProxy(parameter);
+    Expression* assignment = factory()->NewAssignment(
+        Token::ASSIGN, to, from, RelocInfo::kNoPosition);
+    Statement* statement = factory()->NewExpressionStatement(
+        assignment, RelocInfo::kNoPosition);
+    inner_block->statements()->InsertAt(0, statement, zone());
+  }
+}
+
+
 void Parser::InsertSloppyBlockFunctionVarBindings(Scope* scope, bool* ok) {
   // For each variable which is used as a function declaration in a sloppy
   // block,

src/parser.h

@@ -1123,8 +1123,8 @@ class Parser : public ParserBase<ParserTraits> {
   // Get odd-ball literals.
   Literal* GetLiteralUndefined(int position);
 
-  // For harmony block scoping mode: Check if the scope has conflicting var/let
-  // declarations from different scopes. It covers for example
+  // Check if the scope has conflicting var/let declarations from different
+  // scopes. This covers for example
   //
   // function f() { { { var x; } let x; } }
   // function g() { { var x; let x; } }
@@ -1134,6 +1134,10 @@ class Parser : public ParserBase<ParserTraits> {
   // hoisted over such a scope.
   void CheckConflictingVarDeclarations(Scope* scope, bool* ok);
 
+  // Insert initializer statements for var-bindings shadowing parameter bindings
+  // from a non-simple parameter list.
+  void InsertShadowingVarBindingInitializers(Block* block);
+
   // Implement sloppy block-scoped functions, ES2015 Annex B 3.3
   void InsertSloppyBlockFunctionVarBindings(Scope* scope, bool* ok);
 

src/scopes.cc

@@ -601,10 +601,6 @@ Declaration* Scope::CheckConflictingVarDeclarations() {
     const AstRawString* name = decl->proxy()->raw_name();
 
     // Iterate through all scopes until and including the declaration scope.
-    // If the declaration scope is a (declaration) block scope, also continue
-    // (that is to handle the special inner scope of functions with
-    // destructuring parameters, which may not shadow any variables from
-    // the surrounding function scope).
     Scope* previous = NULL;
     Scope* current = decl->scope();
     // Lexical vs lexical conflicts within the same scope have already been
@@ -620,7 +616,7 @@ Declaration* Scope::CheckConflictingVarDeclarations() {
       }
       previous = current;
       current = current->outer_scope_;
-    } while (!previous->is_declaration_scope() || previous->is_block_scope());
+    } while (!previous->is_declaration_scope());
   }
   return NULL;
 }

test/mjsunit/harmony/destructuring.js

@@ -957,11 +957,85 @@
   assertEquals(1, ok1(1));
   function ok2(x) { 'use strict'; { let x = 2; return x; } };
   assertEquals(2, ok2(1));
+}());
+
+
+(function TestShadowingOfParameters() {
+  function f1({x}) { var x = 2; return x }
+  assertEquals(2, f1({x: 1}));
+  function f2({x}) { { var x = 2; } return x; }
+  assertEquals(2, f2({x: 1}));
+  function f3({x}) { var y = x; var x = 2; return y; }
+  assertEquals(1, f3({x: 1}));
+  function f4({x}) { { var y = x; var x = 2; } return y; }
+  assertEquals(1, f4({x: 1}));
+  function f5({x}, g = () => x) { var x = 2; return g(); }
+  assertEquals(1, f5({x: 1}));
+  function f6({x}, g = () => x) { { var x = 2; } return g(); }
+  assertEquals(1, f6({x: 1}));
+  function f7({x}) { var g = () => x; var x = 2; return g(); }
+  assertEquals(2, f7({x: 1}));
+  function f8({x}) { { var g = () => x; var x = 2; } return g(); }
+  assertEquals(2, f8({x: 1}));
+  function f9({x}, g = () => eval("x")) { var x = 2; return g(); }
+  assertEquals(1, f9({x: 1}));
+
+  function f10({x}, y) { var y; return y }
+  assertEquals(2, f10({x: 6}, 2));
+  function f11({x}, y) { var z = y; var y = 2; return z; }
+  assertEquals(1, f11({x: 6}, 1));
+  function f12(y, g = () => y) { var y = 2; return g(); }
+  assertEquals(1, f12(1));
+  function f13({x}, y, [z], v) { var x, y, z; return x*y*z*v }
+  assertEquals(210, f13({x: 2}, 3, [5], 7));
+
+  function f20({x}) { function x() { return 2 }; return x(); }
+  assertEquals(2, f20({x: 1}));
+  function f21({x}) { { function x() { return 2 } } return x(); }
+  assertEquals(2, f21({x: 1}));
+
+  var g1 = ({x}) => { var x = 2; return x };
+  assertEquals(2, g1({x: 1}));
+  var g2 = ({x}) => { { var x = 2; } return x; };
+  assertEquals(2, g2({x: 1}));
+  var g3 = ({x}) => { var y = x; var x = 2; return y; };
+  assertEquals(1, g3({x: 1}));
+  var g4 = ({x}) => { { var y = x; var x = 2; } return y; };
+  assertEquals(1, g4({x: 1}));
+  var g5 = ({x}, g = () => x) => { var x = 2; return g(); };
+  assertEquals(1, g5({x: 1}));
+  var g6 = ({x}, g = () => x) => { { var x = 2; } return g(); };
+  assertEquals(1, g6({x: 1}));
+  var g7 = ({x}) => { var g = () => x; var x = 2; return g(); };
+  assertEquals(2, g7({x: 1}));
+  var g8 = ({x}) => { { var g = () => x; var x = 2; } return g(); };
+  assertEquals(2, g8({x: 1}));
+  var g9 = ({x}, g = () => eval("x")) => { var x = 2; return g(); };
+  assertEquals(1, g9({x: 1}));
+
+  var g10 = ({x}, y) => { var y; return y };
+  assertEquals(2, g10({x: 6}, 2));
+  var g11 = ({x}, y) => { var z = y; var y = 2; return z; };
+  assertEquals(1, g11({x: 6}, 1));
+  var g12 = (y, g = () => y) => { var y = 2; return g(); };
+  assertEquals(1, g12(1));
+  var g13 = ({x}, y, [z], v) => { var x, y, z; return x*y*z*v };
+  assertEquals(210, g13({x: 2}, 3, [5], 7));
+
+  var g20 = ({x}) => { function x() { return 2 }; return x(); }
+  assertEquals(2, g20({x: 1}));
+  var g21 = ({x}) => { { function x() { return 2 } } return x(); }
+  assertEquals(2, g21({x: 1}));
 
-  assertThrows("function f({x}) { var x; }; f({});", SyntaxError);
-  assertThrows("function f({x}) { { var x; } }; f({});", SyntaxError);
   assertThrows("'use strict'; function f(x) { let x = 0; }; f({});", SyntaxError);
   assertThrows("'use strict'; function f({x}) { let x = 0; }; f({});", SyntaxError);
+  assertThrows("'use strict'; function f(x) { const x = 0; }; f({});", SyntaxError);
+  assertThrows("'use strict'; function f({x}) { const x = 0; }; f({});", SyntaxError);
+
+  assertThrows("'use strict'; let g = (x) => { let x = 0; }; f({});", SyntaxError);
+  assertThrows("'use strict'; let g = ({x}) => { let x = 0; }; f({});", SyntaxError);
+  assertThrows("'use strict'; let g = (x) => { const x = 0; }; f({});", SyntaxError);
+  assertThrows("'use strict'; let g = ({x}) => { const x = 0; }; f({});", SyntaxError);
 }());