Currently, gazelle allows absolute imports to be resolved to sibling modules: an import foo statement will resolve to a foo.py file in the same folder if such file exists. This seems to be a Python 2 behavior (ie. pre-from __future__ import absolute_import), and doesn't work on the current rules_python setup.

This behavior is explicitly tested in the siblings_import test case. However, recreating the exact same repository layout from this test case and running bazel test //pkg:unit_test, the test fails with the import failing.

This PR adds a new directive, gazelle:python_resolve_sibling_imports, to allow disabling such behavior.

The actual changes are in 2 places:

• In gazelle/python/target.go, the directive is added to if t.siblingSrcs.Contains(fileName) && fileName != filepath.Base(dep.Filepath), which is where the import is converted to a full absolute import if it matches a sibling file;
• In gazelle/python/generate.go, the handling of conftest.py was dependent on this behavior (ie. it added a dependency on the module conftest, assuming that it would be resolved to the relative module). That was modified to compute the full absolute module path instead.

I also explicitly added gazelle:python_resolve_sibling_imports true to any test that breaks if the default value of this directive is changed to false.