Copying config headers for new_http_archive

[par...@gmail.com]

Hi,
Ares (https://github.com/c-ares/c-ares) generates few files using cmake (ares_build.h.cmake or ares_config.h.cmake). Its hard to generate these using bazel, so one of the tricks used is to pregenerate them (For example in grpc: https://github.com/grpc/grpc/tree/master/third_party/cares these files are checkedin).

I am using cares with following in WORKSPACE:

new_http_archive(
name = "com_github_cares_cares",
url = "https://github.com/c-ares/c-ares/archive/cares-1_13_0.tar.gz",
strip_prefix = "c-ares-cares-1_13_0",
build_file = "build/com_github_cares_cares.BUILD",
)

but am having hard time building since I can't figure out a way to generate these (ares_build.h and ares_config.h). I tied to copy these from one of the folders in my workspace using genrule, but unable to do it because of sandboxing.

Is there a better way to generate these without hardcoding these file into genrule in my BUILD files?

Thanks,
Param

[Marcel Hlopko]

I'm sorry I didn't get everything. So you want to use cares. Cares uses cmake, and you need to run cmake to get ares_build.h.cmake, which is required to build cares. And you don't want to run cmake in genrule? Can you use pregenerated header declared in cc_library in build/com_github_cares_cares.BUILD together with precompiled .a or .so library?

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Marcel Hlopko | Software Engineer | hlo...@google.com | 

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[Paul Johnston]

I would consider writing a repository rule that downloads the cares repo and symlinks (or copies) your custom ares_build.h, _config.h files into place.  Something like (not tested):

def _cares_repository_impl(repository_ctx):

    repository_ctx.download_and_extract(cares_url)

    repository_ctx.symlink(repository_ctx.path(ctx.attr.build_h_file), "ares_build.h")

    ...

    repository_ctx.file("BUILD.bazel", """

cc_library(

   name = "cares"

   srcs = [...]

   ...

)

"""

cares_repository = repository_rule(

    implementation = _cares_repository_impl,

    attrs = {

        "build_h_file": attr.label(allow_files = True), 

        "config_h_file": attr.label(allow_files = True),