`embedded_asset!` is broken on Windows Wasm builds

[janhohenheim]

Bevy version

0.14.0

Relevant system information

• rustc --version: rustc 1.81.0-nightly (6292b2af6 2024-07-02)
• Running Windows 11

`AdapterInfo { name: "NVIDIA GeForce GTX 1080 Ti", vendor: 4318, device: 6918, device_type: DiscreteGpu, driver: "NVIDIA", driver_info: "555.99", backend: Vulkan }`

What you did

There's a minimal reproduction here: https://github.com/janhohenheim/asset-crash

The relevant code is just this main.rs:

use bevy::{asset::embedded_asset, prelude::*};

fn main() {
    let mut app = App::new();
    app.add_plugins(DefaultPlugins);
    embedded_asset!(app, "splash.png");
    app.run();
}

The setup is:

• crate
  • src/
    • main.rs
    • splash.png

What went wrong

Running this with cargo run works.
Running it on Wasm on Windows instead gives me:

Failed to find src_prefix "src" in "src\\screen\\splash\\mod.rs"

This is the part of the Bevy code that panics: https://github.com/bevyengine/bevy/blob/main/crates/bevy_asset/src/io/embedded/mod.rs#L141
And this is the PR that introduced it: #10383

Note that this is not reproducible on Linux

Additional information

The minimal example has a workaround. Move crate/src/splash.png into crate/assets/splash.png and embed it with embedded_asset!(app, "../assets/splash.png");.
For reasons unknown to me, doing the same workaround on https://github.com/TheBevyFlock/bevy-template does not work.

I also tried running the embedded assets example with cargo build --example ... and that one works.

Using load_internal_binary_asset like this works as well:

    load_internal_binary_asset!(
        app,
        SPLASH_IMAGE_HANDLE,
        "splash.png",
        |bytes, _path: String| {
            Image::from_buffer(
                bytes,
                ImageType::Extension("png"),
                default(),
                true,
                ImageSampler::linear(),
                RenderAssetUsages::RENDER_WORLD | RenderAssetUsages::MAIN_WORLD,
            )
            .unwrap()
        }
    );

[benfrankel]

load_internal_binary_asset! doesn't have this issue, but it's awkward to use.

Bevy doesn't seem to use embedded_asset! anywhere internally -- it only uses load_internal_binary_asset! -- so bugs like this take longer to surface.

[kristoff3r]

This seems like a rustc bug. The argument to embedded_asset! that behaves weirdly comes straight from the built-in file! macro, and it seems like it has an edge case. Here is a code snippet I ran inside the bevy template:

let path: &Path = file!().as_ref();
let components = path.components().into_iter().collect::<Vec<_>>();
panic!("path: {} components: {:?}", path.display(), components);

This results in:

Windows native:

path: src\screen\splash.rs components: [Normal("src"), Normal("screen"), Normal("splash.rs")]

Windows wasm:

path: src\screen\splash.rs components: [Normal("src\\screen\\splash.rs")]

And, just to top it off, windows native in a separate project I made to test this:

path: src/main.rs components: [Normal("src"), Normal("main.rs")]

I don't know why file! has both behaviors on Windows yet, but it makes sense that the Windows paths aren't parsed properly on wasm.

[janhohenheim]

@kristoff3r that last point sounds like an explanation for why the workaround I reported works in one project but not the other

[kristoff3r]

I found the difference between the 2 projects, it happens when a project has both a lib.rs and a main.rs.

So as far as I can tell the file macro gives unix paths in crates without a lib.rs, and windows path with lib.rs.

[janhohenheim]

@kristoff3r did you submit a bug report to rustc? If so, could you link it? If not, do you want me to file one for you?
Marking this as blocked in the meantime