2 files changed, 26 insertions, 38 deletions

diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index fe30328de..94573fce7 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -5417,37 +5417,6 @@ Parser<ParseHandler>::matchInOrOf(bool* isForInp, bool* isForOfp)
 
 template <class ParseHandler>
 bool
-Parser<ParseHandler>::validateForInOrOfLHSExpression(Node target, PossibleError* possibleError)
-{
-    if (handler.isUnparenthesizedDestructuringPattern(target))
-        return checkDestructuringPattern(target, Nothing(), possibleError);
-
-    // All other permitted targets are simple.
-    if (!reportIfNotValidSimpleAssignmentTarget(target, ForInOrOfTarget))
-        return false;
-
-    if (handler.isPropertyAccess(target))
-        return true;
-
-    if (handler.isNameAnyParentheses(target)) {
-        // The arguments/eval identifiers are simple in non-strict mode code,
-        // but warn to discourage use nonetheless.
-        if (!reportIfArgumentsEvalTarget(target))
-            return false;
-
-        handler.adjustGetToSet(target);
-        return true;
-    }
-
-    if (handler.isFunctionCall(target))
-        return checkAssignmentToCall(target, JSMSG_BAD_FOR_LEFTSIDE);
-
-    reportWithNode(ParseError, false, target, JSMSG_BAD_FOR_LEFTSIDE);
-    return false;
-}
-
-template <class ParseHandler>
-bool
 Parser<ParseHandler>::forHeadStart(YieldHandling yieldHandling,
                                    ParseNodeKind* forHeadKind,
                                    Node* forInitialPart,
@@ -5526,6 +5495,10 @@ Parser<ParseHandler>::forHeadStart(YieldHandling yieldHandling,
         return *forInitialPart != null();
     }
 
+    uint32_t exprOffset;
+    if (!tokenStream.peekOffset(&exprOffset, TokenStream::Operand))
+        return false;
+
     // Finally, handle for-loops that start with expressions.  Pass
     // |InProhibited| so that |in| isn't parsed in a RelationalExpression as a
     // binary operator.  |in| makes it a for-in loop, *not* an |in| expression.
@@ -5569,8 +5542,29 @@ Parser<ParseHandler>::forHeadStart(YieldHandling yieldHandling,
 
     *forHeadKind = isForIn ? PNK_FORIN : PNK_FOROF;
 
-    if (!validateForInOrOfLHSExpression(*forInitialPart, &possibleError))
+    // Verify the left-hand side expression doesn't have a forbidden form.
+    if (handler.isUnparenthesizedDestructuringPattern(*forInitialPart)) {
+        if (!checkDestructuringPattern(*forInitialPart, Nothing(), &possibleError))
+            return false;
+    } else if (handler.isNameAnyParentheses(*forInitialPart)) {
+        const char* chars = handler.nameIsArgumentsEvalAnyParentheses(*forInitialPart, context);
+        if (chars) {
+            // |chars| is "arguments" or "eval" here.
+            if (!strictModeErrorAt(exprOffset, JSMSG_BAD_STRICT_ASSIGN, chars))
+                return false;
+        }
+
+        handler.adjustGetToSet(*forInitialPart);
+    } else if (handler.isPropertyAccess(*forInitialPart)) {
+        // Permitted: no additional testing/fixup needed.
+    } else if (handler.isFunctionCall(*forInitialPart)) {
+        if (!strictModeErrorAt(exprOffset, JSMSG_BAD_FOR_LEFTSIDE))
+            return false;
+    } else {
+        errorAt(exprOffset, JSMSG_BAD_FOR_LEFTSIDE);
         return false;
+    }
+
     if (!possibleError.checkForExpressionError())
         return false;
 
@@ -7869,10 +7863,6 @@ Parser<ParseHandler>::reportIfNotValidSimpleAssignmentTarget(Node target, Assign
       case CompoundAssignment:
         errnum = JSMSG_BAD_LEFTSIDE_OF_ASS;
         break;
-
-      case ForInOrOfTarget:
-        errnum = JSMSG_BAD_FOR_LEFTSIDE;
-        break;
     }
 
     reportWithNode(ParseError, pc->sc()->strict(), target, errnum, extra);
diff --git a/js/src/frontend/Parser.h b/js/src/frontend/Parser.h
index 6bd7e586e..e3827d953 100644
--- a/js/src/frontend/Parser.h
+++ b/js/src/frontend/Parser.h
@@ -1139,7 +1139,6 @@ class Parser final : private JS::AutoGCRooter, public StrictModeGetter
                       Node* forInitialPart,
                       mozilla::Maybe<ParseContext::Scope>& forLetImpliedScope,
                       Node* forInOrOfExpression);
-    bool validateForInOrOfLHSExpression(Node target, PossibleError* possibleError);
     Node expressionAfterForInOrOf(ParseNodeKind forHeadKind, YieldHandling yieldHandling);
 
     Node switchStatement(YieldHandling yieldHandling);
@@ -1338,7 +1337,6 @@ class Parser final : private JS::AutoGCRooter, public StrictModeGetter
         KeyedDestructuringAssignment,
         IncrementAssignment,
         DecrementAssignment,
-        ForInOrOfTarget
     };
 
     bool checkAndMarkAsAssignmentLhs(Node pn, AssignmentFlavor flavor,