pip_parse and pip_install can now parse entry points from wheels

[UebelAndre]

PR Checklist

Please check if your PR fulfills the following requirements:

• Does not include precompiled binaries, eg. .par files. See CONTRIBUTING.md for info
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature (please, look at the "Scope of the project" section in the README.md file)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Currently, there is no way to access binaries (or entry points) associated with a wheel in python. This has been a rather annoying problem since it expects users to manually generate it themselves. A process for which there's currently there's no guidance on. This PR aims to solve that by generating these targets automatically.

Issue Number: #341

What is the new behavior?

Both pip_install and pip_parse now generate py_binary targets for each entry point in a wheel. These are accessible via the entry_point macro which has been added to the requirements.bzl files generated by these repository rules.

To use this new functionality, you simply load the entry_point macro:

load("@pip_deps//:requirements.bzl", "entry_point")

alias(
    name = "flake8",
    actual = entry_point("flake8"),
)

Then. the target can be run just like any other py_binary.

bazel run //:flake8 -- --version

3.9.2 (mccabe: 0.6.1, pycodestyle: 2.7.0, pyflakes: 2.3.1) CPython 3.9.6 on Darwin

Does this PR introduce a breaking change?

• Yes
• No

Other information

[alexeagle]

This is awesome! thanks, I'll merge and go patch into a client codebase and see if we can remove some of our wrappers.

I bet the working directory issue will still be a problem, but that's a missing feature in py_binary to essentially cd right before invoking the python interpreter

[alexeagle]

🌮