Allow analysis tests to support for_dependency_resolution on the target_under_test

[Bocete]

This attribute is necessary to analysis test dormant targets. It's hard to assert anything useful without materializing what's behind the target_under_test, and that requires setting for_dependency_resolution on the target_under_test.

See https://bazel.build/rules/lib/toplevel/attr#label.for_dependency_resolution for more info on this attribute. It's a new bazel feature.

[Bocete]

I suspect this is blocked on a blaze release? Dormant deps are still experimental, and the CI tests are failing because of syntax that's made available via experimental flags. @lberki to comment

[lberki]

I don't think it's technically blocked on a Blaze release, only its use internally is for reasons complicated and irrelevant to Bazel. So as long as the code is fine, feel free to merge it.

[Bocete]

Hmm the build checks, here on github, are failing because:

(23:17:46) ERROR: Traceback (most recent call last):
	File "/workdir/tests/unittest_tests.bzl", line 284, column 28, in <toplevel>
		"dormant_dep": attr.dormant_label(),
Error: 'attr' value has no field or method 'dormant_label'

That's telling me something needs to be enabled blaze-side, no? Or maybe the CI system here needs to be tweaked to add a flag? Please tell me what to do here, thanks!

[lberki]

I'm not familiar with the unit testing framework so take the reviewers' advice over mine, but how about adding something like this:

if hasattr(attr, "dormant_label"):
  inspect_dormant_target_fake_rule = rule(attrs = {"dormant_dep": attr.dormant_label()})
else:
  inspect_dormant_target_fake_rule = rule(implementation = _always_fail)

that way, Skylib remains compatible with older Bazel versions while still allowing you to add these symbols.