load_folder() panics when given an absolute path but load() does not

[iliags]

Bevy version

0.11

The issue is currently present in the main branch as well:
https://github.com/bevyengine/bevy/blob/b6a9d8eba7807b63be525e423911c0217706f13a/crates/bevy_asset/src/io/file_asset_io.rs#L112C4-L123C6

What you did

server.load_folder("C:\\Absolute\\Path\\To\\Folder\\")

What went wrong

thread 'Compute Task Pool (3)' panicked at 'called `Result::unwrap()` on an `Err` value: StripPrefixError(())', C:\<user>\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bevy_asset-0.11.0\src\io\file_asset_io.rs:120:47

• What were you expecting?
  • The folder contents are loaded into untyped handles or throw an error for invalid types
• What actually happened?
  • Bevy panics when given an absolute path to a folder

Additional information

I'm using toml files as project files (like Unreal/Unity/Godot) and want to load and watch the files in the project folder for changes; this folder can be anywhere on the filesystem. The 'read_directory' function assumes that the provided path is relative to self and appends the provided path to the self root path which turns into "C:\Path\To\Executable\C:\Absolute\Path\To\Folder\" and panics.

 fn read_directory(
        &self,
        path: &Path,
    ) -> Result<Box<dyn Iterator<Item = PathBuf>>, AssetIoError> {
        let root_path = self.root_path.to_owned();

        // This panics if path is absolute
        Ok(Box::new(fs::read_dir(root_path.join(path))?.map(
            move |entry| {
                let path = entry.unwrap().path();
                path.strip_prefix(&root_path).unwrap().to_owned()
            },
        )))
    }

The load function works as expected but the load_folder variation panics which is inconsistent behavior. I think the best fix would be to auto-detect absolute paths and add the root path if it's not. If that's not in the cards then an optional boolean parameter for is_absolute could work.

[alice-i-cecile]

What OS are you on? File system bugs are sometimes OS specific, so it's good to record it.

[iliags]

I'm on windows but it will have the same behavior on linux. The issue is that load_folder adds the root path regardless of if the provided path is absolute or not while load does not.

The workaround that I found is to set the root directory to the project path; if that's the intended use then maybe it would be better to add a line or two in the docs rather than a code fix.

Edit:
Allowing multiple asset roots (key value pair) could be a better solution because it would allow unrelated asset sources to be used in one project.

[bushrat011899]

he 'read_directory' function assumes that the provided path is relative to self and appends the provided path to the self root path which turns into "C:\Path\To\Executable\C:\Absolute\Path\To\Folder" and panics.

I don't believe this is true. According to the Path::join docs, a.join(b) will yield b if b is already an absolute path. The real error is that Path::strip_prefix will return an error if you attempt to strip a prefix that does not match the current path. You can't strip a from b if b does not already start with a.

To follow-up on your example:

let a: Path; // "C:\Path\To\Executable\"
let b: Path; // "C:\Absolute\Path\To\Folder\"

let c = a.join(b); // "C:\Absolute\Path\To\Folder\"
let d = c.strip_prefix(&a); // Error: `c` does not start with `a`

The minimal change that would resolve this bug would be to construct a relative path from a to b. It looks like the most appropriate solution for that problem is using pathdiff::diff_paths.

fn read_directory(
    &self,
    path: &Path,
) -> Result<Box<dyn Iterator<Item = PathBuf>>, AssetIoError> {
    let root_path = self.root_path.to_owned();
    Ok(Box::new(fs::read_dir(root_path.join(path))?.map(
        move |entry| {
            let path = entry.unwrap().path();
            pathdiff::diff_paths(path, root_path).unwrap()
        },
    )))
}

[iliags]

I'm new to rust so I'm not used to a sane(er) standard library; this is nice to learn.