1 files changed, 35 insertions, 1 deletions

diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index bcd6c30c02..5cb47f2425 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -2472,6 +2472,11 @@ GeneralParser<ParseHandler, Unit>::functionBody(InHandling inHandling,
     }
   }
 
+  if (pc_->numberOfArgumentsNames > 0 || kind == FunctionSyntaxKind::Arrow) {
+    MOZ_ASSERT(pc_->isFunctionBox());
+    pc_->sc()->setIneligibleForArgumentsLength();
+  }
+
   // Declare the 'arguments', 'this', and 'new.target' bindings if necessary
   // before finishing up the scope so these special bindings get marked as
   // closed over if necessary. Arrow functions don't have these bindings.
@@ -6570,6 +6575,8 @@ bool GeneralParser<ParseHandler, Unit>::forHeadStart(
         return false;
       }
     }
+  } else if (handler_.isArgumentsLength(*forInitialPart)) {
+    pc_->sc()->setIneligibleForArgumentsLength();
   } else if (handler_.isPropertyOrPrivateMemberAccess(*forInitialPart)) {
     // Permitted: no additional testing/fixup needed.
   } else if (handler_.isFunctionCall(*forInitialPart)) {
@@ -7917,7 +7924,12 @@ bool GeneralParser<ParseHandler, Unit>::finishClassConstructor(
   bool hasPrivateBrand = classInitializedMembers.hasPrivateBrand();
   if (hasPrivateBrand || numMemberInitializers > 0) {
     // Now that we have full set of initializers, update the constructor.
-    MemberInitializers initializers(hasPrivateBrand, numMemberInitializers);
+    MemberInitializers initializers(
+        hasPrivateBrand,
+#ifdef ENABLE_DECORATORS
+        classInitializedMembers.hasInstanceDecorators,
+#endif
+        numMemberInitializers);
     ctorbox->setMemberInitializers(initializers);
 
     // Field initialization need access to `this`.
@@ -10220,6 +10232,8 @@ typename ParseHandler::NodeResult GeneralParser<ParseHandler, Unit>::assignExpr(
         return errorResult();
       }
     }
+  } else if (handler_.isArgumentsLength(lhs)) {
+    pc_->sc()->setIneligibleForArgumentsLength();
   } else if (handler_.isPropertyOrPrivateMemberAccess(lhs)) {
     // Permitted: no additional testing/fixup needed.
   } else if (handler_.isFunctionCall(lhs)) {
@@ -10280,6 +10294,8 @@ bool GeneralParser<ParseHandler, Unit>::checkIncDecOperand(
         return false;
       }
     }
+  } else if (handler_.isArgumentsLength(operand)) {
+    pc_->sc()->setIneligibleForArgumentsLength();
   } else if (handler_.isPropertyOrPrivateMemberAccess(operand)) {
     // Permitted: no additional testing/fixup needed.
   } else if (handler_.isFunctionCall(operand)) {
@@ -10898,6 +10914,9 @@ template <class ParseHandler>
 inline typename ParseHandler::NameNodeResult
 PerHandlerParser<ParseHandler>::newName(TaggedParserAtomIndex name,
                                         TokenPos pos) {
+  if (name == TaggedParserAtomIndex::WellKnown::arguments()) {
+    this->pc_->numberOfArgumentsNames++;
+  }
   return handler_.newName(name, pos);
 }
 
@@ -10926,6 +10945,13 @@ GeneralParser<ParseHandler, Unit>::memberPropertyAccess(
     MOZ_ASSERT(!handler_.isSuperBase(lhs));
     return handler_.newOptionalPropertyAccess(lhs, name);
   }
+
+  if (handler_.isArgumentsName(lhs) && handler_.isLengthName(name)) {
+    MOZ_ASSERT(pc_->numberOfArgumentsNames > 0);
+    pc_->numberOfArgumentsNames--;
+    return handler_.newArgumentsLength(lhs, name);
+  }
+
   return handler_.newPropertyAccess(lhs, name);
 }
 
@@ -11484,6 +11510,10 @@ void GeneralParser<ParseHandler, Unit>::checkDestructuringAssignmentName(
     return;
   }
 
+  if (handler_.isArgumentsLength(name)) {
+    pc_->sc()->setIneligibleForArgumentsLength();
+  }
+
   if (pc_->sc()->strict()) {
     if (handler_.isArgumentsName(name)) {
       if (pc_->sc()->strict()) {
@@ -12143,6 +12173,10 @@ GeneralParser<ParseHandler, Unit>::objectLiteral(YieldHandling yieldHandling,
           }
         }
 
+        if (handler_.isArgumentsLength(lhs)) {
+          pc_->sc()->setIneligibleForArgumentsLength();
+        }
+
         Node rhs;
         MOZ_TRY_VAR(rhs,
                     assignExpr(InAllowed, yieldHandling, TripledotProhibited));