fix: Replicates SPM default behavior for publicHeadersPath: If this is nil, the directory is set to include

[0xLucasMarcal]

Match SPM's default behavior for public headers path

When SPM processes a target without an explicit publicHeadersPath, it follows these rules:

1. If publicHeadersPath is nil and an include/ directory exists, use include/ as the public headers path
2. This makes all headers in the include/ directory visible to dependent targets

This PR replicates this canonical behavior by:

• Checking for the existence of include/ directory when publicHeadersPath is not set
• Using include/ as the public headers path if it exists
• Making all headers in include/*.h visible to clang targets

https://developer.apple.com/documentation/packagedescription/target/publicheaderspath

[brentleyjones]

Does this fix a certain use case? If so, can we add or adjust an example to show it?

[0xLucasMarcal]

Does this fix a certain use case? If so, can we add or adjust an example to show it?

It was causing tree-sitter build to fail, but after fixing the header not found by patching rules_swift_package_manager, the build started failing with a new error, that tree-sitter wasn't exposing all the source files to SPM. So I sent a PR fixing that and explicitly setting include as publicHeadersPath. So now, I have no fully running example 😓

What do you suggest in this case?

[cgrindel]

So, we have support for magical public header directories here. Do you understand why this is not working for the tree-sitter case?

[0xLucasMarcal]

This search runs on the public headers list. Without this patch, the list was empty, so there were no headers to check if it was in a magical directory.

[0xLucasMarcal]

All the other Clang libraries that I used defined modulemaps to expose the headers and define modules.

[cgrindel]

Sorry, I don't understand. If there are no header files in the include directory, why does the build fail?

[0xLucasMarcal]

Here's a small project with instructions to reproduce the failure: https://github.com/0xLucasMarcal/rules_spm_implicit_include_dir_issue

[0xLucasMarcal]

Basically what happens is that when the clang target doesn’t have publicHeadersDir set and also doesn’t have a modulemap, the rspm doesn’t reach the headers inside of include dir

[cgrindel]

Thank you for providing the repro! Let's add your repro package to the pkg_manifest_minimal example. That will be a good test.

[cgrindel]

Thank you for providing the repro! Let's add your repro package to the pkg_manifest_minimal example. That will be a good test.

[cgrindel]

Suggested change

	# If public includes were specified, use them.
	# Else if the Swift package manifest does not specify a public headers path,
	# use the default "include" directory, if it exists.
	# This copies the behavior of the canonical Swift Package Manager implementation.
	# https://developer.apple.com/documentation/packagedescription/target/publicheaderspath
	public_includes = []
	if public_hdrs_path != None:
	public_includes.append(
	paths.normalize(paths.join(abs_target_path, public_hdrs_path)),
	)
	elif repository_files.path_exists(
	repository_ctx,
	paths.join(abs_target_path, "include"),
	):
	public_includes.append(paths.join(abs_target_path, "include"))

[cgrindel]

This suggested code combines the previous if statement with your new logic.