Triggering state changes as part of an on_visit handler

[murtyjones]

Hi!

I'd like to trigger a change to state (in this case, to hide an element) when a page is visited. To do so I put a .msg() in an on_visit handler, like so:

#[route(
  path = "/mypage",
  on_visit = hide_side_nav
)]
fn my_route(store: Provided<Rc<RefCell<Store>>>) -> VirtualNode {
    MyView::new(Rc::clone(&store)).render()
}

fn hide_side_nav(store: Provided<Rc<RefCell<Store>>>) {
    store.borrow_mut().msg(&Msg::HideSideNav);
}

Expected behavior

Page loads and the element I've specified is hidden as a result of the above message being sent

Actual behavior

This runtime error:

panicked at 'already borrowed: BorrowMutError'

Minimal Reproducible Example

In the isomorphic example, you can reproduce by changing download_contributers_json to send a message like so:

#[route(
  path = "/contributors",
  on_visit = download_contributors_json
)]
fn contributors_route(store: Provided<Rc<RefCell<Store>>>) -> VirtualNode {
    ContributorsView::new(Rc::clone(&store)).render()
}

fn download_contributors_json(store: Provided<Rc<RefCell<Store>>>) {
    store.borrow_mut().msg(&Msg::InitiatedContributorsDownload); // Arbitrary message
}

Notes

From reading a little bit about the error is that it's more of an Rc/RefCell problem than a percy problem. I thought would be useful to post it here anyways because I imagine others will get snagged on it at some point.

[chinedufn]

Yeah you're running into this:

percy/examples/isomorphic/app/src/lib.rs

Lines 83 to 86 in e41857e

	// In order to check if the download has already been initiated, we must
	// wrap the possibility of a download attempt in a closure and pass it to
	// request_animation_frame. This is due to store already being mutably
	// borrowed, since this method will be called from the `Store.msg` function.

Which was recently discovered by @austinsheep

---

I haven't yet thought about what changes in state management approach could fix this problem - so for now you might just use the same requestAnimationFrame strategy.

Open to any ideas you have of course!

I'll leave this issue open as this is definitely a problem that should be resolved!

[chinedufn]

More context

Basically on_visit gets called while Store is mutably borrowed so you can't just borrow it again.

percy/examples/isomorphic/app/src/store.rs

Lines 25 to 34 in e41857e

	pub fn msg(&mut self, msg: &Msg) {
	match msg {
	// TODO: Right now `on_visit` cannot borrow store since it's already borrowed.
	// So we might want to explore wraping our `on_visit` in requestAnimationFrame
	// so that by the time it runs we are no longer borrowing store ... or something ...
	Msg::SetPath(path) => {
	if let Some(router) = &self.router {
	if let Some(route_handler) = router.matching_routerhandler(path.as_str()) {
	route_handler.on_visit(path.as_str());
	}

[murtyjones]

Should've read the comments. Makes sense! Thank you

[chinedufn]

If you don't mind - going to keep this open until we land on a better way to handle this scenario which, like you said, other people will surely run into.

Thanks!