Pull GitHub repository using Bazel - github

Question

I need to download an entire GitHub repository using Bazel. Since I'm quite new to this tool I'm not really sure how to achieve that.
My main idea is this:
write a custom repository rule in downloadgithubrepo.bzl (which is located in the project root just like the WORKSPACE file) such as:
def _impl(repository_ctx):
repository_ctx.download("url_to_zipped_github_repo", output='relative_path_to_output_file')
github = repository_rule(
implementation = _impl
and in the WORKSPACE file to write something like this:
load("//:downloadgithubrepo.bzl", "github")
and to invoke a build a BUILD file is needed (also located at the project root)
its contents are the following:
cc_library(
name = "testrun",
srcs = "main.c",
)
I had to add the main.c file otherwise the build is failing - that is one issue and the real issue is that this does not work, as in the build is passing but the GitHub repository is not downloaded.
Am I on the right path at all?? Has anyone done something like this before?

Answer 1

What you're looking might already be implemented in the new_git_repository repository rule, or the git_repository rule if the GitHub project already has Bazel BUILD files wired in.
If the GitHub project does not have BUILD files, a BUILD file is required when using new_git_repository. For example, if you want to depend on a file target (e.g. /foo/bar.txt) or rule target (e.g. a cc_library) in https://github.com/example/repository, and the repository does not have BUILD files, write these lines in your project's WORKSPACE file:
new_git_repository(
name = "example_repository",
remote = "https://github.com/example/repository.git",
build_file_content = """
exports_files(["foo/bar.txt"])
# you can also create targets
cc_library(
name = "remote_cc_library",
srcs = ["..."],
hdrs = ["..."],
)
""",
)
In your BUILD file, reference the external repository's targets using the # prefix:
cc_library(
name = "testrun",
srcs = ["main.c"],
data = ["#example_repository//:foo/bar.txt"],
deps = ["#example_repository//:remote_cc_library"],
)
When you run bazel build //:testrun, Bazel will..
Analyze the dependencies of //:testrun, which include the file main.c and targets from the external repository #example_repository.
Look up the WORKSPACE file for an external repository named example_repository, and finds the new_git_repository declaration.
Perform a git clone on the remote attribute specified in the example_repository declaration.
Write a BUILD file containing the build_file_content string at the project root of the cloned repository.
Analyze the targets #example_repository//:foo/bar.txt and #example_repository//:remote_cc_library
Build the dependencies, and hands them to your //:testrun cc_library.
Build //:testrun.
If the GitHub project does have BUILD files, you do not need to provide an BUILD file. You can refer to the targets directly after specifying the WORKSPACE dependency with git_repository:
git_repository(
name = "example_repository",
remote = "https://github.com/example/repository.git",
)
For more information, check out Bazel's documentation on External Repositories.