Router Switch is order dependant

[theduke]

Problem

With the below router definition, the router will always match the Home route and ignore the other definitions.

Maybe "/" has some special match-all semantics?

Making Home the last variant will make things work properly.

This is highly confusing behaviour, I spent quite a bit of time tracking this down.

#[derive(yew_router::Switch, Debug, Clone)]
pub enum AppRoute {
   #[to = "/"]
    Home,
    #[to = "/feed/{category}"]
    Feed(String),
    #[to = "/post/{id}"]
    Post(u64),
}

Environment:

• Yew version: 0.17.4
• yew-router: 0.14.0

[hamza1311]

This behavior is documented but I do think it should be made order independent if possible.

[theduke]

It's not documented though that "/" is essentially a "/*" wildcard.

Would also be good to add the warning from your link to the crate docs. (I never checked the web docs, just docs.rs).

[siku2]

This is working as intended, even if is confusing and not appropriately documented.
This is something that should be addressed in router v2.

Off the top of my head I believe there are cases where we need to rely on the order to resolve parsing ambiguities so I don't think we can get rid of it entirely without losing flexibility or redesigning the system. That being said, cases where a route is definitely inaccessible should result in a compilation error. This should hopefully catch most cases where this happens by accident.

[siku2]

It's not documented though that "/" is essentially a "/*" wildcard.

Would also be good to add the warning from your link to the crate docs. (I never checked the web docs, just docs.rs).

This is something that bothers me as well. It isn't directly related to the ordering but I think it should be addressed as well, because the implicit wildcard is quite confusing.

[lukechu10]

We could potentially inspire from Rocket (routing and dynamic paths). The grammar for Rocket routes is here.

Even though I am not familiar with Rocket, it seems like routing is order independent. For ambiguous routes, there is a well defined "ranking" or manually set with a "rank" attribute on the route attribute.

The lexer generator, logos might also be a source of inspiration with "priorities". In the case of logos, when two routes are ambiguous and have the same priority, a compiler error is emitted. This sounds a bit complicated to implement (there is probably some elegant algorithm out there that I am not aware of) but it's probably necessary to make routing order independent. This issue might have some hints about how to do it: maciejhirsz/logos#129

Lastly, it would be really cool if we could also match regex in routes. Again, logos could be a source of inspiration for this.

Edit: Heck, we could just generate a Logos lexer with the proc_macro and leave all the complexity to Logos. Don't know if this is a good idea or not.

Edit 2: On second thought, all those / would be a nightmare to escape in the regexes so maybe this isn't such a good idea.

Edit 3: Logos does not provide a way for extracting values from sub patterns so it will probably not be practical anyways.

[lukechu10]

I think I know how to do this: we create a DFA (deterministic finite state automata) for each route. Then we combine the DFAs together into one finite state automata for all the routes. If an end node can match two different routes and these two different routes have the same priority, throw an error and abort.

Edit: It seems like the current implementation ships nom in the WASM bundle. Would it be possible to just use UrlSearchParams and some simple regex to extract all the information we need about the path? For the matching, we could have the derive macro emit directly a state machine which could match the url segments.

[lukechu10]

Interestingly enough, it seems like [React router] is order dependent. The main difference I can see with the current yew router is that it's not end recursive by default, meaning / will only match the root page.

I think this is a easy way out and is not the best solution. I am trying to implement a URL matcher based on finite state automata where the DFAs of different routes are merged together to remove any ordering restriction. It's in a separate repo for now but I'll make it public once I get a working demo.

Edit: As a bonus with this method, we can compute the finite state automata completely at compile time in the proc macro and have minimal code shipped to the browser.