Stream: wit-bindgen

Topic: Adding support for customizing the dependency dir

Celarye (Sep 24 2026 at 12:51):

I am working on adding support for customizing the WIT package dependency directory path like:

wit_bindgen::generate!({ path: "../wit", deps: "../wit-deps" });

At the moment the deps directory is hardcoded in wit-parser's internal Resolve::_push_dir method:

fn _push_dir(&mut self, path: &Path) -> Result<(super::PackageId, PackageSourceMap)> {
    let top_pkg = self
        .parse_dir(path)
        .with_context(|| format!("failed to parse package: {}", path.display()))?;
    let deps = path.join("deps");
    let deps = self
        .parse_deps_dir(&deps)
        .with_context(|| format!("failed to parse dependency directory: {}", deps.display()))?;

    let (pkg_id, inner) = self.sort_unresolved_packages(top_pkg, deps)?;
    Ok((pkg_id, PackageSourceMap::from_inner(inner)))
}

I would solve this by adding deps: impl AsRef<Path> as a parameter to the internal _push_dir method.

My question is if I should update the public push_dir method as well or if I should create a new push_dir_with_deps method instead?

Another question is then how we actually use this. As wit-bindgen relies on Resolve::push_path.

I am of the opinion to have wit-bindgen use Resolve::push_dir_with_deps in case a user provided a custom value for deps and path is a directory.

We could of course update Resolve::push_path as well but that would break a lot of things.

Let me know what you guys think is the best way forward.

Related GitHub issue: https://github.com/bytecodealliance/wit-bindgen/issues/1675

Celarye (Sep 24 2026 at 17:38):

Maybe someone else has a better alternative solution, I am not really sure what’s acceptable :sweat_smile:

Pat Hickey (Sep 24 2026 at 20:32):

This seems reasonable to me, and I've also desired the same basic thing you desire but haven't done any of the actual work, so thanks for noodling on it

Pat Hickey (Sep 24 2026 at 20:32):

re https://github.com/bytecodealliance/wasm-tools/pull/2677

Pat Hickey (Sep 24 2026 at 20:32):

before I hit approve on that just want to flag for @Alex Crichton, do you have any thoughts or concerns on this?

Alex Crichton (Sep 24 2026 at 20:55):

nah that seems reasonable to me too!

Celarye (Sep 25 2026 at 04:03):

Thanks for the quick response and merge! I’ll now keep an eye out for when a new wasm-tools release goes out and then update wasmtime and wit bindgen.

Celarye (Sep 25 2026 at 12:55):

I am gonna look into writing some simple tests for custom dependency directories in wit-parser

Celarye (Sep 26 2026 at 17:26):

I came to the realization that custom dependency directories would actually make sense for single WIT package files (non directories) as well. I am looking into adding support for this use case as well.

Celarye (Sep 26 2026 at 21:40):

Here you go: https://github.com/bytecodealliance/wasm-tools/pull/2681

Could make a case that it could replace the previous API as a breaking change but I don't really feel comfortable updating all dependents and tests for this unique of a use case.

I do still plan to make another follow up PR to cover this with some tests.

Last updated: Oct 11 2026 at 04:10 UTC