E0283 trait ambiguity when using chained conditional &str in rsx! attributes

[huntario]

Problem

Type inference error (E0283) occurs when using if/else if/else conditional expressions for attribute values in the rsx! macro
when reqwest is included as a dependency.

The compiler reports:
error[E0283]: type annotations needed
cannot infer type
= note: cannot satisfy : IntoAttributeValue<>

This happens because both bytes::Bytes and reqwest::Body implement From<&'static str>, creating an ambiguity during the
rsx! macro expansion that the compiler cannot resolve.

Steps To Reproduce

1. Add dependencies to Cargo.toml:

[dependencies]
dioxus = { version = "0.6", features = ["web"] }
reqwest = { version = "0.12", features = ["json"] }

2. Create a component with conditional class attribute using if/else if/else:

 use dioxus::prelude::*;  

 fn App() -> Element {
     let is_recording = use_signal(|| false);
     let is_transcribing = use_signal(|| false);

     rsx! {
         div {
             button {
                 class: if is_recording() {
                     "bg-red-600"
                 } else if is_transcribing() {
                     "bg-gray-600"
                 } else {
                     "bg-gray-700"
                 },
                 "Click me"
             }
         }
     }
 }

3. Build for WASM: dx build --platform web
4. Compilation fails with E0283 error

08:24:32 [cargo] error[E0283]: type annotations needed
  --> src/main.rs:67:5
   |
67  | /     rsx! {
68  | |         div {
69  | |             button {
70  | |                 class: if is_recording() {
...   |
80  | |     }
   | |_____^ cannot infer type
   |
   = note: cannot satisfy `_: IntoAttributeValue<_>`
   = help: the following types implement trait `IntoAttributeValue<T>`:
             &str
             Arguments<'_>
             AttributeValue
             MappedSignal<O, S>
             Memo<T>
             Option<T>
             Rc<(dyn AnyValue + 'static)>
             ReadOnlySignal<T>
           and 18 others

Expected behavior

Conditional if/else if/else expressions should work for attribute values without type inference errors. The macro should be able to infer that string literals should be converted to IntoAttributeValue without ambiguity, even when multiple crates in the
dependency tree implement From<&str> for different types.

Environment:

• Dioxus version: v0.6
• Rust version: 1.83.0 (stable)
• OS info: macOS 14.4 (also occurs on Linux)
• App platform: web (wasm32-unknown-unknown)

Workarounds

Two workarounds exist:

1. Wrap conditional in format!():

class: format!("{}",
    if is_recording() { "bg-red-600" }
    else if is_transcribing() { "bg-gray-600" }
    else { "bg-gray-700" }
)

2. Assign to a variable first:

let class_name = if is_recording() { "bg-red-600" }
    else if is_transcribing() { "bg-gray-600" }
    else { "bg-gray-700" };

rsx! {
    button { class: class_name, "Click me" }
}

Root Cause Analysis

The issue stems from:

• reqwest depends on bytes crate (transitive dependency)
• Both bytes::Bytes and reqwest::Body implement From<&'static str>
• The rsx! macro expansion with conditional expressions creates a context where Rust cannot determine which From impl to use
• Simple if/else may work, but if/else if/else consistently triggers the error

Questionnaire
I'm interested in fixing this myself but don't know where to start.

[ealmloff]

It looks like request isn't required to reproduce the issue and the bug is also present in 0.7.0-rc.0. Nesting the if statements instead of chaining them fixes the issue:

use dioxus::prelude::*;

fn App() -> Element {
    let is_recording = use_signal(|| false);
    let is_transcribing = use_signal(|| false);

    rsx! {
        div {
            button {
                class: if is_recording() {
                    "bg-red-600"
                } else {
                    if is_transcribing() {
                        "bg-gray-600"
                    } else {
                        "bg-gray-700"
                    }
                },
                "Click me"
            }
        }
    }
}