bzlmod external repo name and copts

[fitzner]

Description of the bug:

Bzlmod stores modules as external repos in external/<module>.<version>. By using labels in rules the correct locations are resolved.

However in some cases it is necessary to use copts from cc_binary and cc_library to include further headers and in that case there is no option to define the external workspace via a variable in the rules copts.

Depending on how bzlmod includes external repos the name is different.

Use of the registry
bazel_dep(name = "foo", version = "0.1.0")
=> external/foo.0.1.0

Use of local_path_override
local_path_override(
module_name = "foo",
path = "../projects/foo/"
)
=> external/foo

This behaviour is problematic when referencing an external workspace in the copts.

For an example please see the attachment example.tar.gz.

What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

See example

Which operating system are you running Bazel on?

MacOS Monterey 12.3.1

What is the output of bazel info release?

release 5.1.1

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

No response

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

No response

[fmeum]

Not saying this is a good answer, but you can create a .bzl file containing:

def canonical_repo_name():
    return native.repository_name()[1:] # Skip over the leading '@'

Then, call that function from a BUILD file in foo to get the correct name. Caveat: This will not work if foo is your (main) workspace as native.repository_name returns just @ in that case - if you replace the return value with foo if it is empty, this should work in all situations.

[fitzner]

I just stumbled over the following; this could be used as a workaround.

def _var_workspace_root_impl(ctx):
    return [
      platform_common.TemplateVariableInfo({
          "WORKSPACE_ROOT": ctx.label.workspace_root,
      }),
    ]

var_workspace_root = rule(
    implementation = _var_workspace_root_impl,
    attrs = {}
)

var_workspace_root(
    name = "set_workspace_root_var",
)

cc_library(
    name = "test",
    srcs = [
        "src/foo.cc",
        "include/foo_private.h",
    ],
    hdrs = [
        "include/foo.h"
    ],
    copts = ["-I$(WORKSPACE_ROOT)/include"],
    strip_include_prefix = "include",
    linkstatic = True,
    toolchains = [":set_workspace_root_var"],
)

[cameron-martin]

This feature would make this unnecessary in one case, which in my experience is the most common case.

[Wyverald]

This is partially addressed by the REPO.bazel proposal (#18077), except that default_copts is no longer a thing in Bazel. So I'm keeping this open to figure out next steps.

[meteorcloudy]

Bazel also has to work around a similar issue by

bazel/src/tools/bzlmod/utils.bzl

Lines 17 to 21 in b264850

	def get_canonical_repo_name(apparent_repo_name):
	"""Returns the canonical repo name for the given apparent repo name seen by the module this bzl file belongs to."""
	if not apparent_repo_name.startswith("@"):
	apparent_repo_name = "@" + apparent_repo_name
	return Label(apparent_repo_name).workspace_name

I'll close this one since there is workaround and not much else we can do from Bzlmod side.