contributing: Replace manual env exports with generate-then-source pattern

[wenzeslaus]

Instead of requiring command substitution on every test invocation,
document a pattern where resolved paths are written to a .grass_build_env
file once and sourced before each pytest call. Add the generated file
to .gitignore.

[echoix]

So finally, you're reinventing the .env convention, but with another file name? There exist some tooling to help preventing .env commuting. There's also some conventions for how to name other production, staging, etc. .env files. Why not try that?

There's even some pytest plugins for that

[wenzeslaus]

I meant to open as draft. What was your suggestion for .env?

[echoix]

For the name, either .env or .env.something, and the contents are plain KEY=Value lines. And it works on windows too. The contents of that file are already well defined and understood, across various programming languages/environments

[wenzeslaus]

I'm not sure if I understand what you think should happen next with .env. How do you think it should work with pytest?

From what I understood so far, PYTHONPATH needs to be set from outside, pytest-dotenv seems to deal with variables, not path, which fits with .env, but does not allow the modification of sys.path we need. LD_LIBRARY_PATH needs to be set up before the process starts for the library loading automation to work. PATH works, but if we can't import from the grass package, it is not that useful.

A conftest.py file in repo root would help, but we can have that. pytest plugins need to be importable, so no help there either. The only thing I can see that pytest's pythonpath and addopts may work together. Did you consider this in the past?

  [tool.pytest.ini_options]                                                                                                                                                                   
  pythonpath = ["python/grass/tests"]
  addopts = "-p grass_test_env" 

# Exists
ls python/grass/tests/grass_test_env.py

[wenzeslaus]

In the pythonpath+addopts scenario, the python/grass/tests/grass_test_env.py (or maybe utils/grass_test_env.py) file needs to at least partially duplicate init code, but in a more hardcore way than grass.py or the grass package because it does not have any of those paths to start with (grass.py is running or the grass package was imported, so they know about themselves at least and can fill in the other part). Alternatively, the file needs to be generated by the user/agent, but than it is not part of the repo, so addopts links to a non-existent file.