Bug 932517 - Treat let as a contextual keyword in sloppy mode and make it versionless. (r=jorendorff)

addon-sdk/source/test/test-sandbox.js

@@ -84,13 +84,6 @@ exports['test exceptions'] = function(assert) {
   }
 };
 
-exports['test opt version'] = function(assert) {
-  let fixture = sandbox();
-  assert.throws(function() {
-    evaluate(fixture, 'let a = 2;', 'test.js', 1, '1.5');
-  }, 'No let in js 1.5');
-};
-
 exports['test load'] = function(assert) {
   let fixture = sandbox();
   load(fixture, fixturesURI + 'sandbox-normal.js');

dom/xbl/test/test_bug389322.xhtml

@@ -116,10 +116,10 @@ function report(testName, success) {
 <script type="text/javascript"><![CDATA[
   try {
     eval("let x = 1;");
-    var success = false;
+    var success = true;
   }
-  catch (e) { success = true; }
-  is(success, true, "JS 1.7 should not work in versionless HTML script tags");
+  catch (e) { success = false; }
+  is(success, true, "let should work in versionless HTML script tags");
 ]]></script>
 </pre>
 </body>

js/src/frontend/Parser.cpp

@@ -5195,6 +5195,10 @@ Parser<FullParseHandler>::forStatement(YieldHandling yieldHandling)
      */
     bool isForDecl = false;
 
+    // True if a 'let' token at the head is parsed as an identifier instead of
+    // as starting a declaration.
+    bool letIsIdentifier = false;
+
     /* Non-null when isForDecl is true for a 'for (let ...)' statement. */
     RootedStaticBlockObject blockObj(context);
 
@@ -5222,19 +5226,38 @@ Parser<FullParseHandler>::forStatement(YieldHandling yieldHandling)
                 isForDecl = true;
                 tokenStream.consumeKnownToken(tt, TokenStream::Operand);
                 pn1 = variables(yieldHandling, PNK_VAR, InForInit);
-            } else if (tt == TOK_LET || tt == TOK_CONST) {
+            } else if (tt == TOK_LET || tt == TOK_CONST ||
+                       (tt == TOK_NAME && tokenStream.nextName() == context->names().let)) {
                 handler.disableSyntaxParser();
-                bool constDecl = tt == TOK_CONST;
-                tokenStream.consumeKnownToken(tt, TokenStream::Operand);
-                isForDecl = true;
-                blockObj = StaticBlockObject::create(context);
-                if (!blockObj)
-                    return null();
-                // Initialize the enclosing scope manually for the call to
-                // |variables| below.
-                blockObj->initEnclosingScopeFromParser(pc->innermostStaticScope());
-                pn1 = variables(yieldHandling, constDecl ? PNK_CONST : PNK_LET, InForInit,
-                                nullptr, blockObj, DontHoistVars);
+
+                // Check for the backwards-compatibility corner case in sloppy
+                // mode like |for (let in e)| where the 'let' token should be
+                // parsed as an identifier.
+                bool parseDecl;
+                if (tt == TOK_NAME) {
+                    if (!peekShouldParseLetDeclaration(&parseDecl, TokenStream::Operand))
+                        return null();
+                    letIsIdentifier = !parseDecl;
+                } else {
+                    parseDecl = true;
+                    tokenStream.consumeKnownToken(tt, TokenStream::Operand);
+                }
+
+                if (parseDecl) {
+                    bool constDecl = tt == TOK_CONST;
+                    isForDecl = true;
+                    blockObj = StaticBlockObject::create(context);
+                    if (!blockObj)
+                        return null();
+
+                    // Initialize the enclosing scope manually for the call to
+                    // |variables| below.
+                    blockObj->initEnclosingScopeFromParser(pc->innermostStaticScope());
+                    pn1 = variables(yieldHandling, constDecl ? PNK_CONST : PNK_LET, InForInit,
+                                    nullptr, blockObj, DontHoistVars);
+                } else {
+                    pn1 = expr(InProhibited, yieldHandling, TripledotProhibited);
+                }
             } else {
                 // Pass |InProhibited| when parsing an expression so that |in|
                 // isn't parsed in a RelationalExpression as a binary operator.
@@ -5309,9 +5332,17 @@ Parser<FullParseHandler>::forStatement(YieldHandling yieldHandling)
         bool isForIn, isForOf;
         if (!matchInOrOf(&isForIn, &isForOf))
             return null();
+
+        // In for-in loops, a 'let' token may be used as an identifier for
+        // backwards-compatibility reasons, e.g., |for (let in e)|. In for-of
+        // loops, a 'let' token is never parsed as an identifier. Forbid
+        // trying to parse a for-of loop if we have parsed a 'let' token as an
+        // identifier above.
+        //
+        // See ES6 13.7.5.1.
         if (isForIn)
             headKind = PNK_FORIN;
-        else if (isForOf)
+        else if (isForOf && !letIsIdentifier)
             headKind = PNK_FOROF;
     }
 
@@ -5567,12 +5598,12 @@ Parser<SyntaxParseHandler>::forStatement(YieldHandling yieldHandling)
                 isForDecl = true;
                 tokenStream.consumeKnownToken(tt, TokenStream::Operand);
                 lhsNode = variables(yieldHandling, PNK_VAR, InForInit, &simpleForDecl);
-            }
-            else if (tt == TOK_CONST || tt == TOK_LET) {
+            } else if (tt == TOK_CONST || tt == TOK_LET ||
+                       (tt == TOK_NAME && tokenStream.nextName() == context->names().let))
+            {
                 JS_ALWAYS_FALSE(abortIfSyntaxParser());
                 return null();
-            }
-            else {
+            } else {
                 lhsNode = expr(InProhibited, yieldHandling, TripledotProhibited);
             }
             if (!lhsNode)
@@ -6627,6 +6658,71 @@ Parser<SyntaxParseHandler>::classDefinition(YieldHandling yieldHandling,
     return SyntaxParseHandler::NodeFailure;
 }
 
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::shouldParseLetDeclaration(bool* parseDeclOut)
+{
+    // 'let' is a reserved keyword in strict mode and we shouldn't get here.
+    MOZ_ASSERT(!pc->sc->strict());
+
+    TokenKind tt;
+    *parseDeclOut = false;
+
+    if (!tokenStream.peekToken(&tt))
+        return false;
+
+    switch (tt) {
+      case TOK_NAME:
+        // |let let| is disallowed per ES6 13.3.1.1.
+        *parseDeclOut = tokenStream.nextName() != context->names().let;
+        break;
+
+      case TOK_LC:
+      case TOK_LB:
+        // A following name is always a declaration.
+        //
+        // |let {| and |let [| are destructuring declarations.
+        *parseDeclOut = true;
+        break;
+
+      case TOK_LP:
+        // Only parse let blocks for 1.7 and 1.8. Do not expose deprecated let
+        // blocks to content.
+        *parseDeclOut = versionNumber() == JSVERSION_1_7 || versionNumber() == JSVERSION_1_8;
+        break;
+
+      default:
+        break;
+    }
+
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::peekShouldParseLetDeclaration(bool* parseDeclOut,
+                                                    TokenStream::Modifier modifier)
+{
+    *parseDeclOut = false;
+
+#ifdef DEBUG
+    TokenKind tt;
+    if (!tokenStream.peekToken(&tt, modifier))
+        return false;
+    MOZ_ASSERT(tt == TOK_NAME && tokenStream.nextName() == context->names().let);
+#endif
+
+    tokenStream.consumeKnownToken(TOK_NAME, modifier);
+    if (!shouldParseLetDeclaration(parseDeclOut))
+        return false;
+
+    // Unget the TOK_NAME of 'let' if not parsing a declaration.
+    if (!*parseDeclOut)
+        tokenStream.ungetToken();
+
+    return true;
+}
+
 template <typename ParseHandler>
 typename ParseHandler::Node
 Parser<ParseHandler>::statement(YieldHandling yieldHandling, bool canHaveDirectives)
@@ -6696,6 +6792,16 @@ Parser<ParseHandler>::statement(YieldHandling yieldHandling, bool canHaveDirecti
       }
 
       case TOK_NAME: {
+        // 'let' is a contextual keyword in sloppy node. In strict mode, it is
+        // always lexed as TOK_LET.
+        if (tokenStream.currentName() == context->names().let) {
+            bool parseDecl;
+            if (!shouldParseLetDeclaration(&parseDecl))
+                return null();
+            if (parseDecl)
+                return lexicalDeclaration(yieldHandling, /* isConst = */ false);
+        }
+
         TokenKind next;
         if (!tokenStream.peekToken(&next))
             return null();

js/src/frontend/Parser.h

@@ -800,6 +800,15 @@ class Parser : private JS::AutoGCRooter, public StrictModeGetter
                                 ParseNodeKind headKind);
     bool checkForHeadConstInitializers(Node pn1);
 
+    // Use when the current token is TOK_NAME and is known to be 'let'.
+    bool shouldParseLetDeclaration(bool* parseDeclOut);
+
+    // Use when the lookahead token is TOK_NAME and is known to be 'let'. If a
+    // let declaration should be parsed, the TOK_NAME token of 'let' is
+    // consumed. Otherwise, the current token remains the TOK_NAME token of
+    // 'let'.
+    bool peekShouldParseLetDeclaration(bool* parseDeclOut, TokenStream::Modifier modifier);
+
   public:
     enum FunctionCallBehavior {
         PermitAssignmentToFunctionCalls,

js/src/frontend/TokenStream.cpp

@@ -999,6 +999,11 @@ TokenStream::checkForKeyword(const KeywordInfo* kw, TokenKind* ttp)
 
     if (kw->tokentype != TOK_STRICT_RESERVED) {
         if (kw->version <= versionNumber()) {
+            // Treat 'let' as an identifier and contextually a keyword in
+            // sloppy mode. It is always a keyword in strict mode.
+            if (kw->tokentype == TOK_LET && !strictMode())
+                return true;
+
             // Working keyword.
             if (ttp) {
                 *ttp = kw->tokentype;
@@ -1006,12 +1011,6 @@ TokenStream::checkForKeyword(const KeywordInfo* kw, TokenKind* ttp)
             }
             return reportError(JSMSG_RESERVED_ID, kw->chars);
         }
-
-        // The keyword is not in this version. Treat it as an identifier, unless
-        // it is let which we treat as TOK_STRICT_RESERVED by falling through to
-        // the code below (ES5 forbids it in strict mode).
-        if (kw->tokentype != TOK_LET)
-            return true;
     }
 
     // Strict reserved word.

js/src/frontend/TokenStream.h

@@ -365,6 +365,13 @@ class MOZ_STACK_CLASS TokenStream
         return currentToken().name();
     }
 
+    PropertyName* nextName() const {
+        if (nextToken().type == TOK_YIELD)
+            return cx->names().yield;
+        MOZ_ASSERT(nextToken().type == TOK_NAME);
+        return nextToken().name();
+    }
+
     bool isCurrentTokenAssignment() const {
         return TokenKindIsAssignment(currentToken().type);
     }
@@ -999,12 +1006,12 @@ class MOZ_STACK_CLASS TokenStream
     void updateLineInfoForEOL();
     void updateFlagsForEOL();
 
-    const Token& nextToken() {
+    const Token& nextToken() const {
         MOZ_ASSERT(hasLookahead());
         return tokens[(cursor + 1) & ntokensMask];
     }
 
-    bool hasLookahead() { return lookahead > 0; }
+    bool hasLookahead() const { return lookahead > 0; }
 
     // Options used for parsing/tokenizing.
     const ReadOnlyCompileOptions& options_;

js/src/jit-test/tests/basic/destructuring-rest-identifiers.js

@@ -57,7 +57,7 @@ var strictIdentifiers = [
   'static'
 ];
 assertThrowsInstanceOf(() => new Function('[...yield] = []'), SyntaxError);
-assertThrowsInstanceOf(() => new Function('[...let] = []'), SyntaxError);
+assertThrowsInstanceOf(() => new Function('"use strict"; [...let] = []'), SyntaxError);
 
 strictIdentifiers.forEach(ident =>
   assertThrowsInstanceOf(() =>

js/src/jit-test/tests/parser/letContextualKeyword.js

@@ -0,0 +1,29 @@
+function expectError(str) {
+  var log = "";
+  try {
+    eval(str);
+  } catch (e) {
+    log += "e";
+    assertEq(e instanceof SyntaxError, true);
+  }
+  assertEq(log, "e");
+}
+
+eval(`let x = 42; assertEq(x, 42);`);
+eval(`var let = 42; assertEq(let, 42);`);
+eval(`let;`);
+eval(`[...let] = [];`);
+eval(`function let() { return 42; } assertEq(let(), 42);`)
+eval(`let {x:x} = {x:42}; assertEq(x, 42);`);
+eval(`let [x] = [42]; assertEq(x, 42);`);
+eval(`for (let x in [1]) { assertEq(x, "0"); }`);
+eval(`for (let x of [1]) { assertEq(x, 1); }`);
+eval(`for (let i = 0; i < 1; i++) { assertEq(i, 0); }`);
+eval(`for (let in [1]) { assertEq(let, "0"); }`);
+eval(`for (let of of [1]) { assertEq(of, 1); }`);
+eval(`for (let/1;;) { break; }`);
+expectError(`for (let of [1]) { }`);
+expectError(`let let = 42;`);
+expectError(`"use strict"; var let = 42;`);
+expectError(`"use strict"; function let() {}`);
+expectError(`"use strict"; for (let of [1]) {}`);

js/src/jit-test/tests/parser/truncation.js

@@ -6,7 +6,6 @@ var cases = [
     "var",
     "var x,",
     "var x =",
-    "let",
     "let x,",
     "let x =",
     "const",

js/src/tests/js1_6/extensions/regress-352392.js

@@ -1,38 +0,0 @@
-/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-//-----------------------------------------------------------------------------
-var BUGNUMBER = 352392;
-var summary = 'Do not hang/crash |for each| over object with getter set to map';
-var actual = 'No Crash';
-var expect = 'No Crash';
-
-
-//-----------------------------------------------------------------------------
-test();
-//-----------------------------------------------------------------------------
-
-function test()
-{
-  enterFunc ('test');
-  printBugNumber(BUGNUMBER);
-  printStatus (summary);
-
-  expect = 'SyntaxError: invalid for each loop';
-  try
-  {
-    var obj = { };
-    Object.defineProperty(obj, "y", { get: Array.prototype.map, enumerable: true, configurable: true });
-    eval('(function() { for each(let z in obj) { } })()');
-  }
-  catch(ex)
-  {
-    actual = ex + '';
-  }
-
-  reportCompare(expect, actual, summary);
-
-  exitFunc ('test');
-}

js/src/tests/js1_7/lexical/regress-351515.js

@@ -40,7 +40,7 @@ reportCompare(expect, actual, summary + ': local: yield = 1');
 
 try
 {
-  expect = "SyntaxError";
+  expect = "No Error";
   eval('let = 1;');
   actual = 'No Error';
 }
@@ -83,7 +83,7 @@ function test()
 
   try
   {
-    expect = "SyntaxError";
+    expect = "No Error";
     eval('var let = 1;');
     actual = 'No Error';
   }

js/src/vm/Keywords.h

@@ -62,10 +62,6 @@
      * when strict.  Punt logic to parser. \
      */ \
     macro(yield, yield, TOK_YIELD, JSVERSION_DEFAULT) \
-    /* \
-     * Let is a future reserved keyword in strict mode, and a keyword in \
-     * JS1.7. \
-     */ \
-    macro(let, let, TOK_LET, JSVERSION_1_7)
+    macro(let, let, TOK_LET, JSVERSION_DEFAULT)
 
 #endif /* vm_Keywords_h */