Turn //python/private into a package.

[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?

See #557

This turns ./python/private into a Bazel package

Issue Number: #557

What is the new behavior?

This change adds the //python/private package

Instead of loading //python:private/reexports.bzl, users will now need to load //python/private:reexports.bzl

Does this PR introduce a breaking change?

This is not marked as a breaking change, because loads under the /private folder were never public API.

• Yes
• No

[UebelAndre]

This PR includes the changes in #556

[alexeagle]

I'm not clear what's the benefit of making another package under the private/ folder vs. what we have now?

[UebelAndre]

I'm not clear what's the benefit of making another package under the private/ folder vs. what we have now?

Please see #554 (comment)

[alexeagle]

https://github.com/bazelbuild/buildtools/blob/master/WARNINGS.md#bzl-visibility doesn't mention packages, but rather directories.

However I have a few minutes to find out for sure:

alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ touch WORKSPACE
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ mkdir dir
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ mkdir pkg
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ mkdir dir/private
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ mkdir pkg/private
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ echo "A = []" > dir/private/a.bzl
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ echo "B = []" > pkg/private/b.bzl
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ echo 'load("//dir:private/a.bzl", "A")' >> BUILD
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ echo 'load("//pkg/private:b.bzl", "B")' >> BUILD
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ touch dir/BUILD
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ touch pkg/private/BUILD
alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ echo 'C = A + B' >> BUILD

alexeagle@system76-pc:/tmp/tmp.TN7MzAjbHR$ buildifier --lint=warn BUILD 
BUILD:2: bzl-visibility: Module "//pkg/private:b.bzl" can only be loaded from files located inside "//pkg", not from "//BUILD". (https://github.com/bazelbuild/buildtools/blob/master/WARNINGS.md#bzl-visibility)
BUILD:3: unused-variable: Variable "C" is unused. Please remove it.
To disable the warning, add '@unused' in a comment. (https://github.com/bazelbuild/buildtools/blob/master/WARNINGS.md#unused-variable)

So I think this means you're right, if private is a directory but not a nested package, users won't get a warning about using private APIs.

Confirmed also that adding this line to one of our examples

load("@rules_python//python:private/reexports.bzl", "internal_PyInfo")

doesn't cause a bzl-visibility lint.

So there's actually an issue being fixed here.

[alexeagle]

Filed #557 which is the explanation I was looking for :)

[alexeagle]

thanks!