Let bound iteration variables in for-loops

TEST=mjsunit/harmony/block-for.js

Review URL: http://codereview.chromium.org/7837028

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9658 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/parser.cc

@@ -1631,6 +1631,7 @@ Block* Parser::ParseVariableStatement(VariableDeclarationContext var_context,
 
   Handle<String> ignore;
   Block* result = ParseVariableDeclarations(var_context,
+                                            NULL,
                                             &ignore,
                                             CHECK_OK);
   ExpectSemicolon(CHECK_OK);
@@ -1649,9 +1650,11 @@ bool Parser::IsEvalOrArguments(Handle<String> string) {
 // *var is untouched; in particular, it is the caller's responsibility
 // to initialize it properly. This mechanism is used for the parsing
 // of 'for-in' loops.
-Block* Parser::ParseVariableDeclarations(VariableDeclarationContext var_context,
-                                         Handle<String>* out,
-                                         bool* ok) {
+Block* Parser::ParseVariableDeclarations(
+    VariableDeclarationContext var_context,
+    VariableDeclarationProperties* decl_props,
+    Handle<String>* out,
+    bool* ok) {
   // VariableDeclarations ::
   //   ('var' | 'const') (Identifier ('=' AssignmentExpression)?)+[',']
 
@@ -1789,6 +1792,7 @@ Block* Parser::ParseVariableDeclarations(VariableDeclarationContext var_context,
       } else {
         fni_->RemoveLastFunction();
       }
+      if (decl_props != NULL) *decl_props = kHasInitializers;
     }
 
     // Make sure that 'const x' and 'let x' initialize 'x' to undefined.
@@ -2369,13 +2373,21 @@ Statement* Parser::ParseForStatement(ZoneStringList* labels, bool* ok) {
 
   Statement* init = NULL;
 
+  // Create an in-between scope for let-bound iteration variables.
+  Scope* saved_scope = top_scope_;
+  Scope* for_scope = NewScope(top_scope_, Scope::BLOCK_SCOPE);
+  if (top_scope_->is_strict_mode()) {
+    for_scope->EnableStrictMode();
+  }
+  top_scope_ = for_scope;
+
   Expect(Token::FOR, CHECK_OK);
   Expect(Token::LPAREN, CHECK_OK);
   if (peek() != Token::SEMICOLON) {
     if (peek() == Token::VAR || peek() == Token::CONST) {
       Handle<String> name;
       Block* variable_statement =
-          ParseVariableDeclarations(kForStatement, &name, CHECK_OK);
+          ParseVariableDeclarations(kForStatement, NULL, &name, CHECK_OK);
 
       if (peek() == Token::IN && !name.is_null()) {
         VariableProxy* each = top_scope_->NewUnresolved(name);
@@ -2391,12 +2403,71 @@ Statement* Parser::ParseForStatement(ZoneStringList* labels, bool* ok) {
         Block* result = new(zone()) Block(isolate(), NULL, 2, false);
         result->AddStatement(variable_statement);
         result->AddStatement(loop);
+        top_scope_ = saved_scope;
+        for_scope = for_scope->FinalizeBlockScope();
+        ASSERT(for_scope == NULL);
         // Parsed for-in loop w/ variable/const declaration.
         return result;
       } else {
         init = variable_statement;
       }
+    } else if (peek() == Token::LET) {
+      Handle<String> name;
+      VariableDeclarationProperties decl_props = kHasNoInitializers;
+      Block* variable_statement =
+          ParseVariableDeclarations(kForStatement,
+                                    &decl_props,
+                                    &name,
+                                    CHECK_OK);
+      bool accept_IN = !name.is_null() && decl_props != kHasInitializers;
+      if (peek() == Token::IN && accept_IN) {
+        // Rewrite a for-in statement of the form
+        //
+        //   for (let x in e) b
+        //
+        // into
+        //
+        //   <let x' be a temporary variable>
+        //   for (x' in e) {
+        //     let x;
+        //     x = x';
+        //     b;
+        //   }
+
+        // TODO(keuchel): Move the temporary variable to the block scope, after
+        // implementing stack allocated block scoped variables.
+        Variable* temp = top_scope_->DeclarationScope()->NewTemporary(name);
+        VariableProxy* temp_proxy = new(zone()) VariableProxy(isolate(), temp);
+        VariableProxy* each = top_scope_->NewUnresolved(name, inside_with());
+        ForInStatement* loop = new(zone()) ForInStatement(isolate(), labels);
+        Target target(&this->target_stack_, loop);
+
+        Expect(Token::IN, CHECK_OK);
+        Expression* enumerable = ParseExpression(true, CHECK_OK);
+        Expect(Token::RPAREN, CHECK_OK);
+
+        Statement* body = ParseStatement(NULL, CHECK_OK);
+        Block* body_block = new(zone()) Block(isolate(), NULL, 3, false);
+        Assignment* assignment = new(zone()) Assignment(isolate(),
+                                                        Token::ASSIGN,
+                                                        each,
+                                                        temp_proxy,
+                                                        RelocInfo::kNoPosition);
+        Statement* assignment_statement =
+            new(zone()) ExpressionStatement(assignment);
+        body_block->AddStatement(variable_statement);
+        body_block->AddStatement(assignment_statement);
+        body_block->AddStatement(body);
+        loop->Initialize(temp_proxy, enumerable, body_block);
+        top_scope_ = saved_scope;
+        for_scope = for_scope->FinalizeBlockScope();
+        body_block->set_block_scope(for_scope);
+        // Parsed for-in loop w/ let declaration.
+        return loop;
 
+      } else {
+        init = variable_statement;
+      }
     } else {
       Expression* expression = ParseExpression(false, CHECK_OK);
       if (peek() == Token::IN) {
@@ -2418,6 +2489,9 @@ Statement* Parser::ParseForStatement(ZoneStringList* labels, bool* ok) {
 
         Statement* body = ParseStatement(NULL, CHECK_OK);
         if (loop) loop->Initialize(expression, enumerable, body);
+        top_scope_ = saved_scope;
+        for_scope = for_scope->FinalizeBlockScope();
+        ASSERT(for_scope == NULL);
         // Parsed for-in loop.
         return loop;
 
@@ -2448,8 +2522,30 @@ Statement* Parser::ParseForStatement(ZoneStringList* labels, bool* ok) {
   Expect(Token::RPAREN, CHECK_OK);
 
   Statement* body = ParseStatement(NULL, CHECK_OK);
-  if (loop) loop->Initialize(init, cond, next, body);
-  return loop;
+  top_scope_ = saved_scope;
+  for_scope = for_scope->FinalizeBlockScope();
+  if (for_scope != NULL) {
+    // Rewrite a for statement of the form
+    //
+    //   for (let x = i; c; n) b
+    //
+    // into
+    //
+    //   {
+    //     let x = i;
+    //     for (; c; n) b
+    //   }
+    ASSERT(init != NULL);
+    Block* result = new(zone()) Block(isolate(), NULL, 2, false);
+    result->AddStatement(init);
+    result->AddStatement(loop);
+    result->set_block_scope(for_scope);
+    if (loop) loop->Initialize(NULL, cond, next, body);
+    return result;
+  } else {
+    if (loop) loop->Initialize(init, cond, next, body);
+    return loop;
+  }
 }
 
 

src/parser.h

@@ -460,6 +460,12 @@ class Parser {
     kForStatement
   };
 
+  // If a list of variable declarations includes any initializers.
+  enum VariableDeclarationProperties {
+    kHasInitializers,
+    kHasNoInitializers
+  };
+
   Isolate* isolate() { return isolate_; }
   Zone* zone() { return isolate_->zone(); }
 
@@ -497,6 +503,7 @@ class Parser {
   Block* ParseVariableStatement(VariableDeclarationContext var_context,
                                 bool* ok);
   Block* ParseVariableDeclarations(VariableDeclarationContext var_context,
+                                   VariableDeclarationProperties* decl_props,
                                    Handle<String>* out,
                                    bool* ok);
   Statement* ParseExpressionOrLabelledStatement(ZoneStringList* labels,

src/preparser.cc

@@ -311,6 +311,7 @@ PreParser::Statement PreParser::ParseVariableStatement(
   //   VariableDeclarations ';'
 
   Statement result = ParseVariableDeclarations(var_context,
+                                               NULL,
                                                NULL,
                                                CHECK_OK);
   ExpectSemicolon(CHECK_OK);
@@ -325,6 +326,7 @@ PreParser::Statement PreParser::ParseVariableStatement(
 // of 'for-in' loops.
 PreParser::Statement PreParser::ParseVariableDeclarations(
     VariableDeclarationContext var_context,
+    VariableDeclarationProperties* decl_props,
     int* num_decl,
     bool* ok) {
   // VariableDeclarations ::
@@ -375,6 +377,7 @@ PreParser::Statement PreParser::ParseVariableDeclarations(
     if (peek() == i::Token::ASSIGN) {
       Expect(i::Token::ASSIGN, CHECK_OK);
       ParseAssignmentExpression(var_context != kForStatement, CHECK_OK);
+      if (decl_props != NULL) *decl_props = kHasInitializers;
     }
   } while (peek() == i::Token::COMMA);
 
@@ -569,9 +572,14 @@ PreParser::Statement PreParser::ParseForStatement(bool* ok) {
   if (peek() != i::Token::SEMICOLON) {
     if (peek() == i::Token::VAR || peek() == i::Token::CONST ||
         peek() == i::Token::LET) {
+      bool is_let = peek() == i::Token::LET;
       int decl_count;
-      ParseVariableDeclarations(kForStatement, &decl_count, CHECK_OK);
-      if (peek() == i::Token::IN && decl_count == 1) {
+      VariableDeclarationProperties decl_props = kHasNoInitializers;
+      ParseVariableDeclarations(
+          kForStatement, &decl_props, &decl_count, CHECK_OK);
+      bool accept_IN = decl_count == 1 &&
+          !(is_let && decl_props == kHasInitializers);
+      if (peek() == i::Token::IN && accept_IN) {
         Expect(i::Token::IN, CHECK_OK);
         ParseExpression(true, CHECK_OK);
         Expect(i::Token::RPAREN, CHECK_OK);

src/preparser.h

@@ -179,6 +179,12 @@ class PreParser {
     kForStatement
   };
 
+  // If a list of variable declarations includes any initializers.
+  enum VariableDeclarationProperties {
+    kHasInitializers,
+    kHasNoInitializers
+  };
+
   class Expression;
 
   class Identifier {
@@ -493,6 +499,7 @@ class PreParser {
   Statement ParseVariableStatement(VariableDeclarationContext var_context,
                                    bool* ok);
   Statement ParseVariableDeclarations(VariableDeclarationContext var_context,
+                                      VariableDeclarationProperties* decl_props,
                                       int* num_decl,
                                       bool* ok);
   Statement ParseExpressionOrLabelledStatement(bool* ok);

test/mjsunit/harmony/block-for.js

+// Copyright 2011 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --harmony-scoping
+
+function props(x) {
+  var array = [];
+  for (let p in x) array.push(p);
+  return array.sort();
+}
+
+assertEquals(0, props({}).length);
+assertEquals(1, props({x:1}).length);
+assertEquals(2, props({x:1, y:2}).length);
+
+assertArrayEquals(["x"], props({x:1}));
+assertArrayEquals(["x", "y"], props({x:1, y:2}));
+assertArrayEquals(["x", "y", "zoom"], props({x:1, y:2, zoom:3}));
+
+assertEquals(0, props([]).length);
+assertEquals(1, props([1]).length);
+assertEquals(2, props([1,2]).length);
+
+assertArrayEquals(["0"], props([1]));
+assertArrayEquals(["0", "1"], props([1,2]));
+assertArrayEquals(["0", "1", "2"], props([1,2,3]));
+
+var o = {};
+var a = [];
+let i = "outer_i";
+let s = "outer_s";
+for (let i = 0x0020; i < 0x01ff; i+=2) {
+  let s = 'char:' + String.fromCharCode(i);
+  a.push(s);
+  o[s] = i;
+}
+assertArrayEquals(a, props(o));
+assertEquals(i, "outer_i");
+assertEquals(s, "outer_s");
+
+var a = [];
+assertEquals(0, props(a).length);
+a[Math.pow(2,30)-1] = 0;
+assertEquals(1, props(a).length);
+a[Math.pow(2,31)-1] = 0;
+assertEquals(2, props(a).length);
+a[1] = 0;
+assertEquals(3, props(a).length);
+
+var result = '';
+for (let p in {a : [0], b : 1}) { result += p; }
+assertEquals('ab', result);
+
+var result = '';
+for (let p in {a : {v:1}, b : 1}) { result += p; }
+assertEquals('ab', result);
+
+var result = '';
+for (let p in { get a() {}, b : 1}) { result += p; }
+assertEquals('ab', result);
+
+var result = '';
+for (let p in { get a() {}, set a(x) {}, b : 1}) { result += p; }
+assertEquals('ab', result);
+
+
+// Check that there is exactly one variable without initializer
+// in a for-in statement with let variables.
+assertThrows("function foo() { for (let in {}) { } }", SyntaxError);
+assertThrows("function foo() { for (let x = 3 in {}) { } }", SyntaxError);
+assertThrows("function foo() { for (let x, y in {}) { } }", SyntaxError);
+assertThrows("function foo() { for (let x = 3, y in {}) { } }", SyntaxError);
+assertThrows("function foo() { for (let x, y = 4 in {}) { } }", SyntaxError);
+assertThrows("function foo() { for (let x = 3, y = 4 in {}) { } }", SyntaxError);
+
+
+// In a normal for statement the iteration variable is not
+// freshly allocated for each iteration.
+function closures1() {
+  let a = [];
+  for (let i = 0; i < 5; ++i) {
+    a.push(function () { return i; });
+  }
+  for (let j = 0; j < 5; ++j) {
+    assertEquals(5, a[j]());
+  }
+}
+closures1();
+
+
+function closures2() {
+  let a = [], b = [];
+  for (let i = 0, j = 10; i < 5; ++i, ++j) {
+    a.push(function () { return i; });
+    b.push(function () { return j; });
+  }
+  for (let k = 0; k < 5; ++k) {
+    assertEquals(5, a[k]());
+    assertEquals(15, b[k]());
+  }
+}
+closures2();
+
+
+// In a for-in statement the iteration variable is fresh
+// for earch iteration.
+function closures3(x) {
+  let a = [];
+  for (let p in x) {
+    a.push(function () { return p; });
+  }
+  let k = 0;
+  for (let q in x) {
+    assertEquals(q, a[k]());
+    ++k;
+  }
+}
+closures3({a : [0], b : 1, c : {v : 1}, get d() {}, set e(x) {}});

test/mjsunit/harmony/debug-blockscopes.js

@@ -464,3 +464,112 @@ listener_delegate = function(exec_state) {
 };
 closure_1(1)();
 EndTest();
+
+
+// Simple for-in loop over the keys of an object.
+BeginTest("For loop 1");
+
+function for_loop_1() {
+  for (let x in {y:undefined}) {
+    debugger;
+  }
+}
+
+listener_delegate = function(exec_state) {
+  CheckScopeChain([debug.ScopeType.Block,
+                   debug.ScopeType.Local,
+                   debug.ScopeType.Global], exec_state);
+  CheckScopeContent({x:'y'}, 0, exec_state);
+  // The function scope contains a temporary iteration variable.
+  CheckScopeContent({x:'y'}, 1, exec_state);
+};
+for_loop_1();
+EndTest();
+
+
+// For-in loop over the keys of an object with a block scoped let variable
+// shadowing the iteration variable.
+BeginTest("For loop 2");
+
+function for_loop_2() {
+  for (let x in {y:undefined}) {
+    let x = 3;
+    debugger;
+  }
+}
+
+listener_delegate = function(exec_state) {
+  CheckScopeChain([debug.ScopeType.Block,
+                   debug.ScopeType.Block,
+                   debug.ScopeType.Local,
+                   debug.ScopeType.Global], exec_state);
+  CheckScopeContent({x:3}, 0, exec_state);
+  CheckScopeContent({x:'y'}, 1, exec_state);
+  // The function scope contains a temporary iteration variable.
+  CheckScopeContent({x:'y'}, 2, exec_state);
+};
+for_loop_2();
+EndTest();
+
+
+// Simple for loop.
+BeginTest("For loop 3");
+
+function for_loop_3() {
+  for (let x = 3; x < 4; ++x) {
+    debugger;
+  }
+}
+
+listener_delegate = function(exec_state) {
+  CheckScopeChain([debug.ScopeType.Block,
+                   debug.ScopeType.Local,
+                   debug.ScopeType.Global], exec_state);
+  CheckScopeContent({x:3}, 0, exec_state);
+  CheckScopeContent({}, 1, exec_state);
+};
+for_loop_3();
+EndTest();
+
+
+// For loop with a block scoped let variable shadowing the iteration variable.
+BeginTest("For loop 4");
+
+function for_loop_4() {
+  for (let x = 3; x < 4; ++x) {
+    let x = 5;
+    debugger;
+  }
+}
+
+listener_delegate = function(exec_state) {
+  CheckScopeChain([debug.ScopeType.Block,
+                   debug.ScopeType.Block,
+                   debug.ScopeType.Local,
+                   debug.ScopeType.Global], exec_state);
+  CheckScopeContent({x:5}, 0, exec_state);
+  CheckScopeContent({x:3}, 1, exec_state);
+  CheckScopeContent({}, 2, exec_state);
+};
+for_loop_4();
+EndTest();
+
+
+// For loop with two variable declarations.
+BeginTest("For loop 5");
+
+function for_loop_5() {
+  for (let x = 3, y = 5; x < 4; ++x) {
+    debugger;
+  }
+}
+
+listener_delegate = function(exec_state) {
+  CheckScopeChain([debug.ScopeType.Block,
+                   debug.ScopeType.Local,
+                   debug.ScopeType.Global], exec_state);
+  CheckScopeContent({x:3,y:5}, 0, exec_state);
+  CheckScopeContent({}, 1, exec_state);
+};
+for_loop_5();
+EndTest();