The "src" source root doesn't apply to tests that exist in a different directory when there is a single BUILD file for each project.

[AlirezaRoshanzamir]

Bug Description:

Using the following famous Python project structure [1,2,3,4], the "src" directory is not appended to the "tests" Python path automatically. Actually, the reason for selecting this structure is forcing the developers to test the installed library (editable in development time, non-editable before pushing to the repository) which prevents some packaging (such as invalid patterns in MANIFEST.in) problems.

.
├── BUILD
├── pants
├── pants.toml
├── src
│   └── foolib
│       ├── __init__.py
│       └── main.py
└── tests
    └── test_main.py

[GLOBAL]
pants_version = '2.10.0'
backend_packages = [
    'pants.backend.python'
]

python_sources(name='src', sources=['src/**/*.py'])
python_tests(name='tests', sources=['tests/**/test_*.py'])

Running ./pants test :tests results:

ModuleNotFoundError: No module named 'foolib'

and the sys.path value for the running tests is:

['/tmp/process-executionPDL4n8/tests', '/home/roshanzamir/.cache/pants/named_caches/pex_root/venvs/c083917077e03ea6059ab65ba9ca23881c240ba2/e8a7fc14ab36c4adbef2284ef08fb2296f9b8bdb', '/usr/lib/python36.zip', '/usr/lib/python3.6', '/usr/lib/python3.6/lib-dynload', '/home/roshanzamir/.cache/pants/named_caches/pex_root/venvs/s/b7bdc59a/venv/lib/python3.6/site-packages', '.']

which doesn't include the src directory. However, the src is determined as a source root by running ./pants roots:

.
src

On the other hand, if you use ./pants tailor which puts different BUILD files for the tests and src/foolib (not the src directory itself) directories, it works well (the src directory is included in sys.path, and the tests run without import problem) while the source roots are the same.

Pants version: 2.10.0
OS: Linux Ubuntu 18.04.4 LTS

[AlirezaRoshanzamir]

It seems that the issue is related to #11646 and #11118 issues. I think the phrase "At some point, source root stripping applied to the targets that owned the sources, rather than to the sources themselves" from #11118 is partly the answer, but I do not fully understand what it means. Both the targets declared in the BUILD file in the repo root directory (/) and src/foolib contain the python_sources target that owned the sources, so, what does the phrase exactly mean?

@stuhood

[benjyw]

Ah, hm, interesting. I think the BUILD file needs to be inside the source root. So you might need to have two BUILD files instead of one (one in src/ and one in test/) but you still don't need one in every subdir (which is what tailor generates) if you don't want that.

[benjyw]

We should at least properly document this though.

[AlirezaRoshanzamir]

That's correct. Finally, I decided to put different BUILD files for the src/ and tests/ directories.