From b579e0567c887743d24c2745065b71bb06fea4f8 Mon Sep 17 00:00:00 2001
From: wolfbeast <mcwerewolf@wolfbeast.com>
Date: Sat, 6 Apr 2019 10:46:15 +0200
Subject: Simplify checking of the left-hand side of assignment and compound
 assignment expressions.

---
 js/src/frontend/Parser.cpp | 74 ++++++++++++++++++----------------------------
 js/src/frontend/Parser.h   |  4 ---
 2 files changed, 28 insertions(+), 50 deletions(-)

(limited to 'js/src')

diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index c979e38c3..3a5b5d6d7 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -7470,45 +7470,6 @@ Parser<ParseHandler>::condExpr1(InHandling inHandling, YieldHandling yieldHandli
     return handler.newConditional(condition, thenExpr, elseExpr);
 }
 
-template <typename ParseHandler>
-bool
-Parser<ParseHandler>::checkAndMarkAsAssignmentLhs(Node target, AssignmentFlavor flavor,
-                                                  PossibleError* possibleError)
-{
-    MOZ_ASSERT(flavor != KeyedDestructuringAssignment,
-               "destructuring must use special checking/marking code, not "
-               "this method");
-
-    if (handler.isUnparenthesizedDestructuringPattern(target)) {
-        if (flavor == CompoundAssignment) {
-            error(JSMSG_BAD_DESTRUCT_ASS);
-            return false;
-        }
-
-        return checkDestructuringPattern(target, Nothing(), possibleError);
-    }
-
-    // All other permitted targets are simple.
-    if (!reportIfNotValidSimpleAssignmentTarget(target, flavor))
-        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;
-    }
-
-    MOZ_ASSERT(handler.isFunctionCall(target));
-    return checkAssignmentToCall(target, JSMSG_BAD_LEFTSIDE_OF_ASS);
-}
-
 class AutoClearInDestructuringDecl
 {
     ParseContext* pc_;
@@ -7553,6 +7514,8 @@ Parser<ParseHandler>::assignExpr(InHandling inHandling, YieldHandling yieldHandl
     if (!tokenStream.getToken(&tt, TokenStream::Operand))
         return null();
 
+    uint32_t exprOffset = pos().begin;
+
     bool endsExpr;
 
     if (tt == TOK_NAME) {
@@ -7752,9 +7715,33 @@ Parser<ParseHandler>::assignExpr(InHandling inHandling, YieldHandling yieldHandl
         return lhs;
     }
 
-    AssignmentFlavor flavor = kind == PNK_ASSIGN ? PlainAssignment : CompoundAssignment;
-    if (!checkAndMarkAsAssignmentLhs(lhs, flavor, &possibleErrorInner))
+    // Verify the left-hand side expression doesn't have a forbidden form.
+    if (handler.isUnparenthesizedDestructuringPattern(lhs)) {
+        if (kind != PNK_ASSIGN) {
+            error(JSMSG_BAD_DESTRUCT_ASS);
+            return null();
+        }
+
+        if (!checkDestructuringPattern(lhs, Nothing(), &possibleErrorInner))
+            return null();
+    } else if (handler.isNameAnyParentheses(lhs)) {
+        if (const char* chars = handler.nameIsArgumentsEvalAnyParentheses(lhs, context)) {
+            // |chars| is "arguments" or "eval" here.
+            if (!strictModeErrorAt(exprOffset, JSMSG_BAD_STRICT_ASSIGN, chars))
+                return null();
+        }
+
+        handler.adjustGetToSet(lhs);
+    } else if (handler.isPropertyAccess(lhs)) {
+        // Permitted: no additional testing/fixup needed.
+    } else if (handler.isFunctionCall(lhs)) {
+        if (!strictModeErrorAt(exprOffset, JSMSG_BAD_LEFTSIDE_OF_ASS))
+            return null();
+    } else {
+        errorAt(exprOffset, JSMSG_BAD_LEFTSIDE_OF_ASS);
         return null();
+    }
+
     if (!possibleErrorInner.checkForExpressionError())
         return null();
 
@@ -7852,11 +7839,6 @@ Parser<ParseHandler>::reportIfNotValidSimpleAssignmentTarget(Node target, Assign
       case KeyedDestructuringAssignment:
         errnum = JSMSG_BAD_DESTRUCT_TARGET;
         break;
-
-      case PlainAssignment:
-      case CompoundAssignment:
-        errnum = JSMSG_BAD_LEFTSIDE_OF_ASS;
-        break;
     }
 
     reportWithNode(ParseError, pc->sc()->strict(), target, errnum, extra);
diff --git a/js/src/frontend/Parser.h b/js/src/frontend/Parser.h
index e3827d953..70d382501 100644
--- a/js/src/frontend/Parser.h
+++ b/js/src/frontend/Parser.h
@@ -1332,15 +1332,11 @@ class Parser final : private JS::AutoGCRooter, public StrictModeGetter
     }
 
     enum AssignmentFlavor {
-        PlainAssignment,
-        CompoundAssignment,
         KeyedDestructuringAssignment,
         IncrementAssignment,
         DecrementAssignment,
     };
 
-    bool checkAndMarkAsAssignmentLhs(Node pn, AssignmentFlavor flavor,
-                                     PossibleError* possibleError=nullptr);
     bool matchInOrOf(bool* isForInp, bool* isForOfp);
 
     bool hasUsedFunctionSpecialName(HandlePropertyName name);
-- 
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