Emit a warning if a file is excluded from the archive by matching the target

[e-nomem]

This implements the proposal in #2867

[Copilot]

Pull request overview

This PR implements a deprecation warning for files excluded from archives by matching the target path instead of the source path on the filesystem, as proposed in issue #2867. The implementation helps users identify when their exclude patterns are matching archive paths rather than source paths, preparing them for a future breaking change.

Key Changes:

• Added early exclusion check for source paths before processing (wheel_writer.rs and sdist_writer.rs)
• Emits deprecation warnings when files are excluded by target path matching
• Ensures files excluded by source path return silently without warnings

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
src/module_writer/wheel_writer.rs	Added source path exclusion check and deprecation warning for target path exclusion in wheel archives
src/module_writer/sdist_writer.rs	Added source path exclusion check and deprecation warning for target path exclusion in source distributions

[Copilot]

This warning message is duplicated in sdist_writer.rs (lines 55-61). Consider extracting it to a shared function or constant to maintain consistency and reduce duplication. For example:

// In mod.rs or a util module
fn warn_target_path_exclusion(target: &Path) {
    eprintln!(
        "⚠️ Warning: {} was excluded from the archive by the target path in the archive instead of the source path on the filesystem",
        target.display(),
    );
    eprintln!(
        "           This behavior is deprecated and will be removed in future versions of maturin"
    );
}

Then call it from both WheelWriter::add_bytes and SDistWriter::add_bytes.

[e-nomem]

I'm not a huge fan of the duplicate code but, if you don't mind it for the moment, I do have a plan to extract the file tracking and exclusion logic out of the wheel and sdist writers into a 'virtual' writer layer (the reason for this is unrelated to file exclusions but it happens to be a useful side-effect). That code isn't ready for review yet but if you're curious you can see it here: https://github.com/e-nomem/maturin/tree/virtual-writer