Repository dependencies in workspace rules

[mboes]

Description of the problem / feature request:

In a workspace rule, I can specify attributes of Label type. These labels, however, can only be used in limited ways. In particular, when fed to repository_ctx.path() they must refer to one regular file, and a regular file at that, and one that can't be generated. If I want one external repository A to depend on the entire content of another repository B, I can't express that. I have to list specific files as inputs. If the content of those files I list as inputs doesn't change as frequently as B, then I get an under approximation of how often the rule for A has to be rerun.

Feature requests: what underlying problem are you trying to solve with this feature?

In BUILD files, I can depend on targets rather than files. So I can have a target that stands for say a filegroup of all files under a directory. In WORKSPACE files, I don't have that. Understandably, I can't depend on generated files, but it would be very convenient if target-like special cases would be supported. For example, I would imagine that allowing a label that refers to the entire external repository would be easy to implement.

For the sake of discussion, let me steal some syntax for such a label. Say @foo means "all the files in repository foo". Then I could have:

some_rule(
  name = "bar",
  deps = ["@foo"],
  ...
)

Then Bazel would always rerun the rule for @bar if it reran the rule for @foo.

cc @guibou

[Globegitter]

I have also run into limitations: #8674 - agreed it would be nice if more advanced cases would be possible here.

[mvgijssel]

Just ran into this issue as well, trying to include all the source files from a repository rule into another repository rule.

[github-actions]

Thank you for contributing to the Bazel repository! This issue has been marked as stale since it has not had any activity in the last 1+ years. It will be closed in the next 14 days unless any other activity occurs or one of the following labels is added: "not stale", "awaiting-bazeler". Please reach out to the triage team (@bazelbuild/triage) if you think this issue is still relevant or you are interested in getting the issue resolved.

[fmeum]

See https://docs.google.com/document/d/17RZKMuMjAIgNfFdrsLhqNsMTQDSS-BBA-S-fCSBPV7M/edit# for a proposal aiming to address this issue.

[fmeum]

@bazelbuild/triage not stale