Should cargo package check for new directories?

[ExpHP]

In trying to work around a problem involving excludes I noticed that cargo package does not complain about a build script that creates directories:

build.rs

fn main() {
    // 'cargo package' is designed to fail if you do this:
    // let _ = std::fs::File::create("lol.txt");

    // but it's okay with this:
    let _ = std::fs::create_dir("lol");
}

Is this a feature or a bug?

Notes

cargo 1.36.0-nightly (759b616 2019-05-06)

[lukaslueg]

Empty directories are not tracked by git, therefore creating an empty directory does mark the workspace as being dirty.

[ExpHP]

Sorry for the confusion, I am referring to this error message:

$ cargo package
   Packaging buildme v0.1.0 (/home/lampam/cpp/throwaway/buildme)
   Verifying buildme v0.1.0 (/home/lampam/cpp/throwaway/buildme)
   Compiling buildme v0.1.0 (/home/lampam/cpp/throwaway/buildme/target/package/buildme-0.1.0)
    Finished dev [unoptimized + debuginfo] target(s) in 0.44s
error: failed to verify package tarball

Caused by:
  Source directory was modified by build.rs during cargo publish. Build scripts should not modify anything outside of OUT_DIR.
Added: /home/lampam/cpp/throwaway/buildme/target/package/buildme-0.1.0/lol.txt

where cargo publish detects modifications to target/package/$PACKAGE-$VERSION. If such a crate were published to crates.io, I think it would end up modifying $CARGO_HOME/registry/src/github.com-1ecc6299db9ec823/$PACKAGE-$VERSION.

[ehuss]

Build scripts probably shouldn't be creating empty directories. The "does not modify" check during packaging isn't really intended to be bullet-proof. However, it recently changed and it would be trivial to add a check for directories by checking for a directory here if someone wants to.

[ExpHP]

Looks quite trivial indeed! I'll have a go at it.