fix: make conftest.py special with gazelle

[f0rmiga]

conftest.py is a special file that should be used only with tests, so we create a py_library for it and add it as a dependency to py_test. By special-casing it, we take advantage of all the dependency resolution Gazelle offers. In contrast, when adding it to a py_test with # keep and excluding it from Gazelle, we also have to manage its dependencies manually.

[hrfuller]

is the __test__.py file a gazelle convention that automatically becomes the test entrypoint, or is it generated? Reason I'm asking is this file name doesn't seem to match the allowed test patterns in generate, but gets included in the py_test sources.

[f0rmiga]

It's special for Gazelle. The following is the main logic (though they are used in some other places).

rules_python/gazelle/generate.go

Lines 27 to 28 in 24a8b74

	pyTestEntrypointFilename = "__test__.py"
	pyTestEntrypointTargetname = "__test__"

rules_python/gazelle/generate.go

Lines 82 to 83 in 24a8b74

	} else if !hasPyTestFile && f == pyTestEntrypointFilename {
	hasPyTestFile = true

rules_python/gazelle/generate.go

Lines 271 to 275 in 24a8b74

	if hasPyTestFile {
	// Only add the pyTestEntrypointFilename to the pyTestFilenames if
	// the file exists on disk.
	pyTestFilenames.Add(pyTestEntrypointFilename)
	}

[f0rmiga]

@hrfuller want to take another look? I changed the approach slightly since @mattem pointed out that it's good to have a separate py_library for it so we could add parent conftest.py files to a given py_test.

[ewhauser]

Trying to upgrade from 0.13.0 to 0.14.0. I'm getting all sorts of resolution errors around existing tests, and this appears to be the culprit since it was the only Gazelle change in the release. Is it expected for this to be able to work with existing tests were conftest isn't in it's own library?

[f0rmiga]

@ewhauser I just got one of these myself. I'm not sure yet what causes it, but if I clear the BUILD file and ask Gazelle to generate it again, it does the right thing. I'll work on a fix.

[kersson]

Hi @f0rmiga. Any progress on a fix? Minimally, I feel like this feature should be documented in the top-level README. Perhaps, also add a flag to disable it if you want to handle conftest yourself.

As a future feature idea, it would be great if the generated py_library(name="conftest") was automatically added as a dependency of all subpackages since that's how it works for pytest.