fxIsFunction gives wrong result for revoked proxy

[devsnek]

const p = Proxy.revocable(function(){}, {});
p.revoke();
print(typeof p.proxy);

should be function, but xs gives object. This happens because xsIsFunction redirects the lookup to proxy.target, but proxy.target is nulled out when the proxy is revoked:

moddable/xs/sources/xsFunction.c

Lines 114 to 129 in 15c5724

	txBoolean fxIsFunction(txMachine* the, txSlot* instance)
	{
	again:
	if (instance) {
	txSlot* exotic = instance->next;
	if (exotic && (exotic->flag & XS_INTERNAL_FLAG)) {
	if (((exotic->kind == XS_CALLBACK_KIND) || (exotic->kind == XS_CALLBACK_X_KIND) || (exotic->kind == XS_CODE_KIND) || (exotic->kind == XS_CODE_X_KIND)))
	return 1;
	if (exotic->kind == XS_PROXY_KIND) {
	instance = exotic->value.proxy.target;
	goto again;
	}
	}
	}
	return 0;
	}

I'm not sure how to run js files with the output of the build, but i did come up with this patch:

diff --git a/xs/sources/xsAll.h b/xs/sources/xsAll.h
index 31deeee4..83b2785d 100644
--- a/xs/sources/xsAll.h
+++ b/xs/sources/xsAll.h
@@ -1718,6 +1718,7 @@ enum {
        XS_LEVEL_FLAG = 32,
        XS_DONT_MARSHALL_FLAG = 64,
        /* XS_MARK_FLAG = 128, */
+       XS_PROXY_IS_CALLABLE_FLAG = 256,
 
        /* property flags */
        XS_INTERNAL_FLAG = 1,
diff --git a/xs/sources/xsFunction.c b/xs/sources/xsFunction.c
index b5df3fc5..89f2c4e9 100644
--- a/xs/sources/xsFunction.c
+++ b/xs/sources/xsFunction.c
@@ -113,15 +113,13 @@ txBoolean fxIsCallable(txMachine* the, txSlot* slot)
 
 txBoolean fxIsFunction(txMachine* the, txSlot* instance)
 {
-again:
        if (instance) {
                txSlot* exotic = instance->next;
                if (exotic && (exotic->flag & XS_INTERNAL_FLAG)) {
                        if (((exotic->kind == XS_CALLBACK_KIND) || (exotic->kind == XS_CALLBACK_X_KIND) || (exotic->kind == XS_CODE_KIND) || (exotic->kind == XS_CODE_X_KIND)))
                                return 1;
                        if (exotic->kind == XS_PROXY_KIND) {
-                               instance = exotic->value.proxy.target;
-                               goto again;
+                               return exotic->flag & XS_PROXY_IS_CALLABLE_FLAG;
                        }
                }
        }
diff --git a/xs/sources/xsProxy.c b/xs/sources/xsProxy.c
index 42017094..4227457d 100644
--- a/xs/sources/xsProxy.c
+++ b/xs/sources/xsProxy.c
@@ -825,6 +825,9 @@ void fx_Proxy(txMachine* the)
        if ((handler->next) && (handler->next->kind == XS_PROXY_KIND) && !handler->next->value.proxy.handler)
                mxTypeError("handler is a revoked proxy");
        instance->flag |= target->flag & XS_CAN_CONSTRUCT_FLAG;
+       if (fxIsCallable(the, target)) {
+               instance->flag |= XS_PROXY_IS_CALLABLE_FLAG;
+       }
        proxy->value.proxy.target = target;
        proxy->value.proxy.handler = handler;
 }
@@ -854,6 +857,10 @@ void fx_Proxy_revocable(txMachine* the)
        mxPushUndefined();
        instance = fxNewProxyInstance(the);
        slot = instance->next;
+       instance->flag |= target->flag & XS_CAN_CONSTRUCT_FLAG;
+       if (fxIsCallable(the, target)) {
+               instance->flag |= XS_PROXY_IS_CALLABLE_FLAG;
+       }
        slot->value.proxy.target = target;
        slot->value.proxy.handler = handler;
        property = fxNextSlotProperty(the, property, the->stack, mxID(_proxy), XS_GET_ONLY);

[devsnek]

bump

[phoddie]

The patch won't work because instance->flag is a byte so the flag value of 256 will be lost. To minimize memory use, critical on microcontrollers targets, it is impractical to increase the size of that field.

I just ran your example with the latest Moddable SDK and the output is function. Are you still able to reproduce the problem?

[devsnek]

This does appear to have been fixed at some point.