Using `Rc<dyn AnyValue>` as an attribute value causes unreachable code to be hit and panics

[mcmah309]

Problem

04:09:20 [web] panicked at /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/dioxus-web-0.7.3/src/mutations.rs:211:18:
internal error: entered unreachable code

Stack:

Error
    at http://127.0.0.1:33870/wasm/languna.js:968:25
    at logError (http://127.0.0.1:33870/wasm/languna.js:1834:18)
    at __wbg_new_00868141024267bc (http://127.0.0.1:33870/wasm/languna.js:967:57)
    at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[25102]:0x3f2a79
    at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[14529]:0x383d25
    at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[3959]:0x244f92
    at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[19054]:0x3bed22
    at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[4762]:0x2701f4
    at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[8443]:0x2ff5bd
    at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[25573]:0x3f419a

Line:

dioxus/packages/web/src/mutations.rs

Line 211 in d01a820

_ => unreachable!(),

Reproducible fragment

let val = Rc::new(String::new()) as Rc<dyn dioxus_core::AnyValue>;
rsx! {
    iframe { srcdoc: val }
}

Originally I wanted to use Rc<str> instead of Rc<String> but it does not implement IntoAttributeValue since str is not Sized. So that is what lead me to this situation.

It seems the temporary solution is to use a String with cloning. For my use case, it is a fairly large String but it won't be hit often so it is not too big of a deal.

Expected behavior

Works with no panic or compiler error.

Environment:

• Dioxus version: v0.7.3
• Rust version: 1.93
• OS info: linux
• App platform: web

[nicoburns]

Using AnyValue for a built-in element (as opposed to a custom Dioxus component) doesn't really make sense because attributes of HTML elements are inherently stringly typed. So it needs to be something that can be converted to a string (event listeners are special cased), and while Rc<String> and Rc<str> could be converted to string, Rc<dyn AnyValue> can't (at least not in a generic way that the framework can know about).

Sounds like you basically have a feature request for reference counted string attributes?

[nicoburns]

(but this probably shouldn't panic - logging a warning then ignoring the attribute would probably be better?)

[mcmah309]

(but this probably shouldn't panic - logging a warning then ignoring the attribute would probably be better?)

If it is one or the other, panic is probably better than a warning. I could imagine someone banging their head against a wall trying to figure out why it does not work, it could be easily missed and they may not have logging disabled.

If left, the panic should not be "unreachable" since obviously it is reachable.

Using AnyValue for a built-in element (as opposed to a custom Dioxus component) doesn't really make sense because attributes of HTML elements are inherently stringly typed.

It should probably take any type that impl AsRef<str> or impl ToString instead then.

Sounds like you basically have a feature request for reference counted string attributes?

Not necessarily, though I think allowing something like Rc<str> however possible is useful, I do see it as a micro optimization for most cases. Therefore if we just want to say we won't support it for now that is fine. But if so, we should be more specific with our types so the compiler should disallow it, rather than panicking at runtime. This is definitely not an urgent bug and can sit for awhile on the backlog if need be.