Empty __init__.py files are being generated for repo root and runfiles root

[brandjon]

This happens only for targets that are referenced by their full repo name, i.e. @//foo:bar or //foo:bar. This probably includes all external repo targets (though I have not tested that), and main repo targets when the main repo's full name is not used and when --incompatible_remap_main_repo is false.

See here for a more detailed explanation.

The effect of this bug is that some targets have been able to get away with omitting a dependency on the top-level __init__.py file of their repo, provided that the legacy_create_init attribute is true (default). Fixing this bug may break these targets.

It's also questionable whether we should bother fixing this behavior at all, or just go ahead and deprecate automatic init creation.

[brandjon]

Note, however, that targets that have been getting away with not declaring a dependency on the top-level init file will likely break when --incompatible_remap_main_repo is flipped on. In fact, flipping that flag may have the side-effect of effectively fixing this bug, or at least making it inaccessible. (@dkelmer)

[eacousineau]

I think relates #3998 (for remote repos)? (along the lines of legacy_create_init)

[brandjon]

They're both import-related, but that bug's about name clashes between multiple things on the PYTHONPATH, and this is about __init__.py getting created in places where it isn't expected.

[EricCousineau-TRI]

FTR, here's a doc link for current version of Bazel (3.1.0):
https://docs.bazel.build/versions/3.1.0/be/python.html#py_binary.legacy_create_init

In those docs, there's the flag --incompatible_default_to_explicit_init_py, which can be used to override.

As a small related note, without control over how the runfiles tree is generated, it may be impossible to do things like workaround #4594 for Python, where the implicit module allows on to do a hack like import external.{repository}.{package}.
See example solution here:
RobotLocomotion/drake#8240
Code: https://github.com/EricCousineau-TRI/drake/blob/de4f7a74afc78c221c85d76601e834f06e825e97/bindings/pydrake/__init__.py#L17

EDIT: I lied. The above Python workaround can be done using Rlocation stuff.

[sgowroji]

Hi there! We're doing a clean up of old issues and will be closing this one. Please reopen if you’d like to discuss anything further. We’ll respond as soon as we have the bandwidth/resources to do so.