Hello, I’m trying to write a plugin to provide custom setup_py() Kwargs based on this doc. The custom rule should run a git

Process

to read tags and populate the

version

kwarg. However, I’m not sure what

input_digest

and/or

working_dir

should be provided to the Git process 🧵

Hello!

the process fails since cannot locate the .git  dir

Oh, hm...that will indeed be a problem because Pants ignores

.git

, which is almost always the right thing to do, but not here.

PathGlobs

won't be able to see that directory as a result 🤔 -- So, someone has done Git before by sidestepping the Rules API abstractions. Which you can do if you mark things as uncacheable. Use

@_uncacheable_rule

instead of

@rule

, and then in that function you can do normally unsafe things like

subprocess.run(["git", ...)

It must be marked uncacheable because this is not safe to ever cache, e.g. Pants will not monitor the filesystem to know when to invalidate the cache Does that make sense?

You can avoid going behind the Pants rule systems back with

@_uncacheable_rule

/ subprocess by leveraging GIT_DIR / GIT_WORK_TREE (c.f.: https://git-scm.com/book/en/v2/Git-Internals-Environment-Variables) Here's a fully working demo where you can continually run

./pants git --work-tree=/some/other/repo -- describe

and get back new results every time you go over to that repo and

git reset

it to some new head: https://github.com/pantsbuild/pants/pull/12071/files#diff-31fcb2cbc80628cb417c19f397c0aac0d5578741d7e3954253ff68065d007726R61

Neat! Thanks John! To check my understanding, setting

GIT_DIR

and

GIT_WORK_TREE

allows the process to escape the chroot and read from the build root's .git folder, right?

Correct. Our own tests use this git feature: https://github.com/pantsbuild/pants/blob/065fd1186498336587044edac4ad562cc9aea22d/src/python/pants/vcs/git_test.py#L33

thanks John and Eric. This is helpful. I’ll try with the Git env vars

This is neat! is this worth documenting, in the context of setup_py or elsewhere?

I think likely! I really want to rewrite our example-plugin repo and have it use a dedicated folder of self-contained examples per plugin hook, rather than trying to ram everything into a coherent cohesive Bash plugin So here, I want multiple distinct examples of the setup-py plugin hook, and one should include Git

I'm not sure. At the end of the day this is just a git feature. The thing to document is probably escaping the sandbox for read-only operations which involves a combo of absolute paths and cache_scope=NEVER