When making a Slack announcement I noticed that the changelog could be
clarified.

…ed by Bazel 8 (#2383)

This upgrades some module dependencies to versions that will be needed
in order to
support Bazel 8. More upgrades will be necessary, but these are some
easy ones
that don't cause compatibility issues.


* skylib 1.7.1
* (dev) rules_shell 0.3.0
* (dev) rules_bazel_integration_test 0.26.1


Work towards #2378

Before this PR freethreaded toolchains were not possible to be used,
this adds the minimum plumbing to get the things working. Coverage
support is also added.

Whilst at it:
- Add plumbing to print checksums only for a particular python version.
- Bump the remaining toolchain versions that used to use the 20241008
release
- Pass around the loaded platform list so that we are only defining
toolchains for the platforms that we have loaded the hermetic toolchain
for.

Tested:
```
$ bazel run --//python/config_settings:python_version=3.13.0 --//python/config_settings:py_freethreaded="yes" //python/private:current_interpreter_executable
...
Python 3.13.0 experimental free-threading build (main, Oct 16 2024, 03:26:14) [Clang 18.1.8 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
```

Closes #2129.
Work towards #2386.

With this PR we are changing the defaults in the upcoming `0.39`
version, and
if all goes well, the release after that will be `1.0`.

Work towards #1361

This adds attributes and fields for storing the runtimes ABI flags
value, i.e. `sys.abiflags`.

For freethreaded interpreters, the abi flags contain `t`, which is used
creating e.g.
virtualenvs.

The attribute can be directly specified, or if it's not, will be
computed based on the
`--py_freethreaded` flag.

Various changes to support Bazel 8. An important note is dependencies
have forced
us to change the versions of Bazel we support.

Summary of changes:
* rules_cc 0.0.14: Releases after 0.0.9 have some Bazel 8 fixes, but
also broke
  some things. Things seemed to have settled by 0.0.14.
* protobuf 29.0-rc1: Technically 28.0 works, however:
  1. 29.0-rc1 is coming via a transitive dependency anyways, and
2. In protobuf 28.0, compile warnings are treated as errors, which our
Debian CI
     respects (and thus fails), while other platforms ignore.
* stardoc 0.7.1: Fixes an issue with Bazel 8 and stardoc using empty
globs.
* Bazel 7.4 is now the minimum supported Bazel version. This
requirements comes via
  dependencies.
* Drop Bazel 6 bzlmod support. This requirement comes via dependencies.
* Add a presubmit job for `last_rc` Bazel (currently the 8.x RC).
* Use a local patch so Gazelle works with Bazel 8. This can be removed
once bazel-contrib/bazel-gazelle#1959 is fixed
and released.
* Fix a `$(rpathlocation)` call in bootstrap tests.
* Update bzl_library deps after upgrading deps: the set of targets that
provide
  bzl sources changed in rules_cc and protobuf in these newer versions.

Sorting this all out and finding the right combination of dependency
versions was
fairly involved. The details of that are in
#2378.

Work towards #2378,
#2387

Referring to @rules_cc//cc:defs.bzl, refers to
@protobuf//bazel:cc_proto_library.bzl, which fetches protobuf
repository.
Referring directly to what's needed limits the fetches just to rules_cc.

Fix reference to bzl libs in rules_cc that are needed for docs
generation.

This requires rules_cc 0.0.13 or higher.

Work towards #2387,
#2378

---------

Co-authored-by: Richard Levasseur <rlevasseur@google.com>

Version check needs to work on Bazel@HEAD as well and version later than
Bazel 8.

…patibility (#2395)

In Bazel 8, the singular `$(rootpath)` expansions require that the
target expands to a
single file. The py rules have an unfortunate legacy behavior where
their default outputs
are the executable and the main py file, thus causing an error.

To fix, use the plural `$(rootpaths)`, then post-process the
space-separated string to get
just the executable portion of it.

Along the way...
* Add tests/integration/py_cc_toolchain_registered/bazel-* symlink to
Bazel ignore.
This avoids an infinite symlink expansions error and performance issues
when those
  symlinks exist.

Work towards #2378

---------

Co-authored-by: Ivo List <ilist@google.com>

When the `@bazel_tools//python/tools:python_autodetecting` toolchain is
used, it returns
the Bazel-builtin PyRuntimeInfo provider. Because this provider doesn't
support the
additional fields needed for precompiling (`pyc_tag`, among others), it
would result in
an attribute error.

To fix, detect the absence of the `pyc_tag` attribute and return early,
as is done when
the pyc_tag field is empty.

Fixes #2364

Just tidy up the config. I've put my name in there, but I am happy to
make the
BCR app use someone else's name as well. @oprypin, @rickeylev, what do
you
think?

Update changelog for 0.39.0 release

Along the away, stash a template for the "Unreleased" text in a comment
for easier copy/pasting
in the future.