Bazel: Allow workspaces to reference themselves canonically

[jart]

This is a blocking issue for the Closure Rules.

If I say:

workspace(name = "io_bazel_rules_closure")

Then I should be able to say within my workspace:

deps = ["@io_bazel_rules_closure//foo/bar"]

Which makes the codebase more copy/pasteable. But most importantly, I need to be able to say:

"_jschecker": attr.label(default=Label("@io_bazel_rules_closure//closure/compiler/jschecker"), executable=True)

Because otherwise the bzl rule will have no way to reference its own tooling. This is because a bzl rule exists in the namespace to which it's loaded. Without the ability to specify a fully canonical name, the rule will only work from other repositories. But if I run bazel test ... within the Closure rules repository, it will not be able to test itself.

CC: @damienmg

[damienmg]

Hi Justine,

We decided this week to do be able to use the Label() function to refer to the repository containing the skylark extension. @kchodorow will work on that.

@kchodorow also work on a more principle ways to refer to external repository but that will take time.

[jart]

Is there an estimated timeline for this functionality becoming available in Bazel head?

[bsilver8192]

For reference, this sounds like it came out of the (fairly extensive) discussion in #975.

[kchodorow]

Label("//foo") referring to the skylark rule's repo should be available this week, barring unforeseen issues on the code review.

[kchodorow]

This is now committed (https://github.com/bazelbuild/bazel/commit/6f15335deac0c04cfae11623efbe745f11e177ff). The options are:

• Label("//foo") refers to the Skylark file's repository.
• Label("//foo", relative_to_caller_repository = True) refers to the repository the BUILD file is that's using the Skylark rule.
• Label("@//foo") refers to the repository the build is happening from.

[brian-peloton]

This is a different issue that still doesn't seem to be fixed. This bug is about "@io_bazel_rules_closure//:something" working from the closure repository itself. It definitely does not work in a build_file attribute with current Bazel master.

Once this is fixed, bazelbuild/rules_closure#9 will be easy to fix.

[brian-peloton]

On second thought, this doesn't actually block anything any more. Just using default-repository labels should work fine... However, it would be still nice if referring to the main repository by name worked for consistency.