Bug 1438232 - Handle lazy scripts in CanReuseScriptForClone without forcing a delazify/clone. r=shu

js/src/vm/JSFunction.cpp

@@ -2038,10 +2038,10 @@ js::CanReuseScriptForClone(JSCompartment* compartment, HandleFunction fun,
         return true;
 
     // We need to clone the script if we're not already marked as having a
-    // non-syntactic scope. If we're lazy, go ahead and clone the script; see
-    // the big comment at the end of CopyScriptInternal for the explanation of
-    // what's going on there.
-    return fun->hasScript() && fun->nonLazyScript()->hasNonSyntacticScope();
+    // non-syntactic scope.
+    return fun->hasScript()
+        ? fun->nonLazyScript()->hasNonSyntacticScope()
+        : fun->lazyScript()->enclosingScope()->hasOnChain(ScopeKind::NonSyntactic);
 }
 
 static inline JSFunction*

js/src/vm/JSScript.cpp

@@ -3674,23 +3674,6 @@ js::detail::CopyScript(JSContext* cx, HandleScript src, HandleScript dst,
             Rebase<uint32_t>(dst, src, src->yieldAndAwaitOffsets().vector_);
     }
 
-    /*
-     * Function delazification assumes that their script does not have a
-     * non-syntactic global scope.  We ensure that as follows:
-     *
-     * 1) Initial parsing only creates lazy functions if
-     *    !hasNonSyntacticScope.
-     * 2) Cloning a lazy function into a non-global scope will always require
-     *    that its script be cloned.  See comments in
-     *    CloneFunctionObjectUseSameScript.
-     * 3) Cloning a script never sets a lazyScript on the clone, so the function
-     *    cannot be relazified.
-     *
-     * If you decide that lazy functions should be supported with a
-     * non-syntactic global scope, make sure delazification can deal.
-     */
-    MOZ_ASSERT_IF(dst->hasNonSyntacticScope(), !dst->maybeLazyScript());
-    MOZ_ASSERT_IF(dst->hasNonSyntacticScope(), !dst->isRelazifiable());
     return true;
 }