Build script that compiles a crate: Re-run if its local "path dependencies" have changed

[timotree3]

Describe the problem you are trying to solve

I'm writing a library that contains several smaller crates, compiles them to Wasm, and exports those Wasm blobs as constants.

In order to be able to export them as constants, I'm using a build.rs to compile them using cargo. It looks something like this:

fn main() {
    let out_dir = std::env::var_os("OUT_DIR").unwrap();

    let cargo_toml = std::path::Path::new("foo/Cargo.toml");

    let cargo_command = std::env::var_os("CARGO");
    let cargo_command = cargo_command
        .as_ref()
        .map(|s| &**s)
        .unwrap_or_else(|| "cargo".as_ref());

    let status = std::process::Command::new(cargo_command)
        .arg("build")
        .arg("--manifest-path")
        .arg(cargo_toml)
        .arg("--release")
        .arg("--target")
        .arg("wasm32-unknown-unknown")
        .env("CARGO_TARGET_DIR", out_dir)
        .status()
        .unwrap();

    assert!(status.success());
}

Unfortunately, this breaks down when foo has local "path dependencies" that it needs to keep up-to-date with: Since the build.rs is only re-run if files in its parent directory change, I can arrive at confusing situations where I've changed foo's dependency and I've changed my test to account for the new behavior, but foo doesn't actually update because nothing in the relevant directory has changed.

Describe the solution you'd like

I would like to be able to express to Cargo that my build script compiles a crate, and should be re-run whenever that crate's source changes or whenever one of it's dependencies would no longer be valid to use (i.e. a yanked crate or a change path dependency)

Notes

In the meantime, my solution is to emit cargo:rerun-if-changed=A file name that I know won't exist. This has the behavior of re-running my build script upon every single build of my library, which probably isn't ideal.

[epage]

#8084 would work for this though it would cause extra re-runs of the build script.