Support src-less invocation of py_binary

[aignas]

With the recent addition of the #2671, I find that in most cases I can replace the py_console_script_binary with just a py_binary, e.g:

py_console_script_binary(
    name = "foo",
    deps = [...],
    pkg = "foo",
    script = "bar",
)

versus

py_binary(
    name = "foo",
    deps = [...], # assuming "foo" is in the deps
    main_module = "bar"
)

However I cannot do this, because the srcs cannot be empty here.

An alternative to this could be to use the python_interpreter introduced in #2507

interpreter_binary(
    name = "foo",
    deps = [...],
    args = ["-m", "foo"],
)

[rickeylev]

This sounds like a bug. I changed srcs to no longer be mandatory as part of adding the main module attribute so that such a case could work

[aignas]

Let me double check.

[aignas]

OK, it works if I pass srcs = []. So the attribute specification is mandatory, but the list can be empty. That is a little bit of a rough corner.

[brandonchinn178]

Is this fixed? I'm on 1.5.0, and seeing an error when using main_module without srcs

Error in fail: mandatory 'srcs' files have not been provided

The changelog says

• (rules) {attr}py_binary.srcs and {attr}py_test.srcs is no longer mandatory when
  main_module is specified (for --bootstrap_impl=script)

So it seems like it's only fixed for --bootstrap_impl=script? But the docs don't mention that constraint; is main_module without srcs expected to work without --bootstrap_impl=script?

[aignas]

I think that it is not working without bootstrap_impl=script, a PR to update the docs would be welcome.

[brandonchinn178]

Is it expected to work without bootstrap_impl? If so, should I file a separate bug report? If not, why not?

[aignas]

The way it is implemented right now, I don't think it is expected to work without bootstrap_impl=script, we expect the script to become a default at some point. Feel free to file a separate bug report, but I am not sure how much time the core maintainers will be able to dedicate for this, but at least it will be a known issue for main_module.

[brandonchinn178]

To be clear, it's expected that main_module is only supported with bootstrap_impl=script? Yeah, I think that should be documented, it's very confusing currently, as the docs make it seem like you can just swap main for main_module, but I can't get main_module to work without setting bootstrap_impl

[rickeylev]

Send a PR? Here is where the doc for main_module lives: https://github.com/bazel-contrib/rules_python/blob/main/python/private/py_executable.bzl#L129

Making it work with system_python would also be accepted.

[brandonchinn178]

@rickeylev PR sent!