Bug 1666024 - Clear FunctionFlags::Flags::MUTABLE_FLAGS bits in FunctionBox. r=tcampbell

Differential Revision: https://phabricator.services.mozilla.com/D90755

js/src/frontend/SharedContext.cpp

@@ -235,7 +235,7 @@ FunctionBox::FunctionBox(JSContext* cx, SourceExtent extent,
     : SharedContext(cx, Kind::FunctionBox, compilationInfo, directives, extent),
       atom_(atom),
       funcDataIndex_(index),
-      flags_(flags),
+      flags_(FunctionFlags::clearMutableflags(flags)),
       isTopLevel_(isTopLevel),
       emitBytecode(false),
       isStandalone_(false),

js/src/vm/FunctionFlags.h

@@ -330,6 +330,10 @@ class FunctionFlags {
     }
     return flags;
   }
+
+  static FunctionFlags clearMutableflags(FunctionFlags flags) {
+    return FunctionFlags(flags.toRaw() & ~FunctionFlags::MUTABLE_FLAGS);
+  }
 };
 
 } /* namespace js */

js/src/vm/JSFunction.cpp

@@ -597,7 +597,7 @@ XDRResult js::XDRInterpretedFunction(XDRState<mode>* xdr,
     }
 
     nargs = fun->nargs();
-    flags = (fun->flags().toRaw() & ~FunctionFlags::MUTABLE_FLAGS);
+    flags = FunctionFlags::clearMutableflags(fun->flags()).toRaw();
 
     atom = fun->displayAtom();