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I'm writing some validation code for a bazel build rule and I need to do some path validation. I need to check that a certain file exists in the same directory as the BUILD file. I notice that there's a context attribute build_file_path which points to the BUILD file. I'd like to extract the parent directory from this.

It looks like I can't create a new path object - I don't see a constructor/initializer. It also seems like Starlark doesn't support os.path like python because imports aren't supported.

What's the canonical way to get the parent directory of a string object representing a path in Starlark?

Paymahn Moghadasian
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  • Any chance you ever solved this? I'm trying to do a very similar thing. I need to create a symlink, but [unresolved symlinks are only in expermintal](https://docs.bazel.build/versions/master/skylark/lib/actions.html#symlink). I cannot find anywhere in the api that makes a path object available to you when executing a rule. – Sam Feb 28 '21 at 03:33
  • Unfortunately I didn't and I don't remember if I ended up dropping the task that required this validation work (it's been so long...) – Paymahn Moghadasian Feb 28 '21 at 15:16

2 Answers2

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I can't answer your final question, but hopefully the following will help with the initial problem:

You could use the Label of the target for which this instance of the rule is being built and find its package. This will give you a string representing the parent directory of the BUILD file.

i.e. ctx.label.package

MHStag
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load("@bazel_skylib//lib:paths.bzl", "paths")

paths.dirname(path_str)

See https://github.com/bazelbuild/bazel-skylib/blob/main/docs/paths_doc.md

Eric
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jsaoa
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  • Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Mar 27 '22 at 16:08