Custom asset source does not work with GLTF

[torsteingrindvik]

Bevy version

Recent main: d2614f2

What you did

Added a custom asset source and tried loading a GLTF with it.
Loading simple assets (e.g. single file images) works fine.

What went wrong

It finds the gltf file, but fails to load the scene.bin mentioned within the GLTF.

Additional information

Logs

2023-12-07T13:22:34.813576Z ERROR bevy_asset::server: Failed to load asset 'gltf://FlightHelmet.gltf' with asset loader 'bevy_gltf::loader::GltfLoader': failed to read bytes from an asset path: path not found: <path>/bevy/assets/FlightHelmet.bin
2023-12-07T13:22:34.813584Z ERROR bevy_asset::server: Failed to load asset 'gltf://FlightHelmet.gltf' with asset loader 'bevy_gltf::loader::GltfLoader': failed to read bytes from an asset path: path not found: <path>/bevy/assets/FlightHelmet.bin

Minimal reproduction

Make a folder foo and copy-paste the flight helmet files into it first.

use bevy::asset::io::*;
use bevy::{gltf::Gltf, prelude::*};

pub struct GltfFailomatic;

impl Plugin for GltfFailomatic {
    fn build(&self, app: &mut App) {
        app.register_asset_source(
            AssetSourceId::from("gltf"),
            AssetSource::build().with_reader(AssetSource::get_default_reader("foo".into())),
        );
    }
}
fn main() {
    App::new()
        .add_plugins((GltfFailomatic, DefaultPlugins))
        .add_systems(Startup, (setup, setup2))
        .run();
}

fn setup(asset_server: Res<AssetServer>) {
    let _: Handle<Gltf> = asset_server.load("gltf://FlightHelmet.gltf");
}

fn setup2(asset_server: Res<AssetServer>) {
    let _: Handle<Scene> = asset_server.load("gltf://FlightHelmet.gltf#Scene0");
}

It seems when loading the scene.bin it tries look in the default asset source instead of the one used for the GLTF "parent asset".

[cart]

This is the problem that would be resolved by Relative Asset Paths. See the end of this PR description for details: #9885.

I don't think we have an issue tracking this yet so we can use this one.

[torsteingrindvik]

Just making a note that I tried this on Bevy 0.13 and the results were the same:

Adding a custom asset source and doing my-assets://FlightHelmet.gltf finds the GLTF file in the correct location, but the related FlightHelmet.bin is not found since the GltfLoader is not aware of the initiating asset source.