Add macOS support

[kaycebasques]

Hello! Thanks for the helpful library. We're migrating pigweed.dev to a Bazel-based build and are looking into offloading our Doxygen stuff to your rules. Do you have any cycles to add macOS support? Our team is pretty evenly split between Linux and macOS so support for both is very necessary for us. Thanks again.

[TendTo]

Hi, unfortunately I don't have easy access to a Mac OS machine, so I can't really test anything. That's the main reason I postponed support for the platform. I'm also not sure how well Bazel supports the .dmg file.

This said, the process for adding it should be pretty straightforward:

# In the "extensions.bzl" file
# ...
        if ctx.os.name.startswith("windows"):
            doxygen_sha256 = "478fc9897d00ca181835d248a4d3e5c83c26a32d1c7571f4321ddb0f2e97459f"
        elif ctx.os.name == "macos":  # TODO: Update this to the correct version
            doxygen_sha256 = "0" * 64
        elif ctx.os.name == "linux":
            doxygen_sha256 = "db68ca22b43c3d7efd15351329db5af9146ab1ac7eaccd61a894fe36612da8fb"
        else:
            fail("Unsuppported OS: %s" % ctx.os.name)

        for attr in mod.tags.version:
            doxygen_version = attr.version if attr.version != "" else fail("Version must be specified")
            doxygen_sha256 = attr.sha256 if attr.sha256 != "" else "0" * 64

        doxygen_version_dash = doxygen_version.replace(".", "_")

        url = "https://github.com/doxygen/doxygen/releases/download/Release_%s/doxygen-%s.%s"
        if ctx.os.name.startswith("windows"):
            url = url % (doxygen_version_dash, doxygen_version, "windows.x64.bin.zip")
            # elif ctx.os.name == "macos": # TODO: support macos
            # url = url % (doxygen_version_dash, doxygen_version, "dmg")

        elif ctx.os.name == "linux":
            url = url % (doxygen_version_dash, doxygen_version, "linux.bin.tar.gz")
            strip_prefix = "doxygen-%s" % doxygen_version
        else:
            fail("Unsuppported OS: %s" % ctx.os.name)
# ...

and then

# In the "doxygen.BUILD.bazel" file
# ...
filegroup(
    name = "executable",
    srcs = select({
        "@platforms//os:linux": ["bin/doxygen"],
        "@platforms//os:macos": ["doxygen"], # TODO: path to the executable in the extracted dmg folder
        "@platforms//os:windows": ["doxygen.exe"],
    }, "Unsupported platform"),
    visibility = ["//visibility:public"],
)

[TendTo]

By the way, this issue got me thinking that a possible workaround would be to support system-wide installation of doxygen. This is now supported in version 1.2.0 of the rules_doxygen (as soon as it gets pushed in the central repository). I'm not sure if it works for you: you would need to make sure the mac has the right version of doxygen installed. In other words, it is not hermetic anymore.

If you are only concerned about CI/CD pipelines, such as github actions, you may get some inspiration from how I did it in my ci file:

rules_doxygen/.github/workflows/ci.yml

Line 28 in 6feebfe

tests-system-installation:

[kaycebasques]

Thanks for responding and for the pointers. I requested a macOS loaner laptop from my work (which should be arriving today) so hopefully I can submit a PR this week.