How to get WORKSPACE directory in bazel rule

Question

I order to use clang tools like clang-format, clang-tidy or generate a compilation database like this, I need to know the WORKSPACE directory withi

Answer 1

You can probably get around this by using realpath. Something like:

def _impl(ctx):

  ctx.actions.run_shell(
    inputs = ctx.files.srcs,
    outputs = [ctx.outputs.executable],
    command = "\n".join(["echo echo $(realpath \"%s\") >> %s" % (f.path,
              ctx.outputs.executable.path) for f in ctx.files.srcs]),
    execution_requirements = {
        "no-sandbox": "1",
        "no-cache": "1",
        "no-remote": "1",
        "local": "1",
    },
  )

echo_full_path = rule(
    implementation=_impl,
    executable=True,
    attrs={
      "srcs": attr.label_list(allow_files=True),
    }
)

Note the execution_requirements to get around the potential issues in my comment above.

Answer 2

I modified @ahumesky's rule to implicitly use the BUILD file as the source and to write only the workspace directory once:

workspace.bzl

def _write_workspace_dir_impl(ctx):
    src = ctx.files._src[0]
    out = ctx.actions.declare_file(ctx.label.name)
    ctx.actions.run_shell(
        inputs = ctx.files._src,
        outputs = [out],
        command = """
          full_path="$(readlink -f -- "{src_full}")"
          # Trim the src.short_path suffix from full_path. Double braces to
          # output literal brace for shell.
          echo "${{full_path%/{src_short}}}" >> {out_full}
        """.format(src_full = src.path, src_short = src.short_path, out_full = out.path),
        execution_requirements = {
            "no-sandbox": "1",
            "no-remote": "1",
            "local": "1",
        },
    )
    return [DefaultInfo(files = depset([out]))]

write_workspace_dir = rule(
    implementation = _write_workspace_dir_impl,
    attrs = {
        "_src": attr.label(allow_files = True, default = "BUILD"),
    },
    doc = "Writes the full path of the current workspace dir to a file.",
)

BUILD

load(":workspace.bzl", "write_workspace_dir")

write_workspace_dir(
    name = "workspace_dir",
)

Sample output

bazel build //build/bazel:workspace_dir
INFO: Analyzed target //build/bazel:workspace_dir 
INFO: Build completed successfully, 1 total action

cat bazel-bin/build/bazel/workspace_dir
/p/$MY_PROJECT

Answer 3

If you're like me and writing a repository_rule instead of a regular one, resolving the following label can help you: "@//:WORKSPACE"

Then use ctx.path to extract the required data: https://docs.bazel.build/versions/master/skylark/lib/repository_ctx.html#path