Add release notes for 2.21.x

[huonw]

This writes out release notes for the 2.21.x branch, up to and including 54a36ea

#20846

[huonw]

Please suggest more highlights!

[cburroughs]

I'm personally very excited for the buildx/cacheing work and the defaults fix, but I'm not sure they quiet qualify as global highlights.

[huonw]

I think the __defaults__ handling of target generators probably does, good call-out!

[cburroughs]

I'm personally very excited for the buildx/cacheing work and the defaults fix, but I'm not sure they quiet qualify as global highlights.

[grihabor]

I've just tried 2.21.0a0 and it slightly broke our expectations. We had

__defaults__(
    extend=True,
    all=dict(
        # This will set PYTHON_IMAGE build arg in all docker images by default.
        extra_build_args=["PYTHON_IMAGE=python:3.11"],
        # This will tell pants that all python sources need to use python 3.11 by default.
        interpreter_constraints=["==3.11.*"],
    ),
)

and the error message was kinda weird:

stderr:
<string> line 1:
PYTHON_IMAGE=python:3.11
Problem parsing 'PYTHON_IMAGE=python:3.11' as a requirement: Expected end or semicolon (after name and no valid version specifier)
    PYTHON_IMAGE=python:3.11
                ^

now we have to do

__defaults__(
    {
        (docker_image,): dict(
            # This will set PYTHON_IMAGE build arg in all docker images by default.
            extra_build_args=["PYTHON_IMAGE=python:3.11"],
        )
    },
    all=dict(
        # This will tell pants that all python sources need to use python 3.11 by default.
        interpreter_constraints=["==3.11.*"],
    ),
    extend=True,
)

This happened because pex_binary.extra_build_args was added, and it has the same name as docker_image.extra_build_args. Maybe it's good to add a note about it

[huonw]

I've just tried 2.21.0a0 and it slightly broke our expectations

Thanks for trying! Did you find some other issues or was it otherwise okay?

This happened because pex_binary.extra_build_args was added, and it has the same name as docker_image.extra_build_args. Maybe it's good to add a note about it

I think that'll be an issue with the addition of extra_build_args to pex_binary that you've identified, rather than with this __defaults__ change. I guess it's unlucky they have the same name but different meanings... but this is somewhat fundamental to __defaults__(all=...). I've filed #20925.

I'll add a note to the release notes too.

[kaos]

Thanks for finding this @grihabor!

[grihabor]

Did you find some other issues or was it otherwise okay?

No, it's the only thing

I'll add a note to the release notes too.

👍

[huonw]

I'm going to merge this, further feedback still accepted! E.g. a comment here or even a PR directly against the notes.

Thanks all for the reviews!

[WorkerPants]

I tried to automatically cherry-pick this change back to each relevant milestone, so that it is available in those older releases of Pants.

❌ 2.21.x

I was unable to cherry-pick this PR to 2.21.x, likely due to merge-conflicts.

Steps to Cherry-Pick locally

To resolve:

1. (Ensure your git working directory is clean)
2. Run the following script to reproduce the merge-conflicts:

   git fetch https://github.com/pantsbuild/pants main \
     && git fetch https://github.com/pantsbuild/pants 2.21.x \
     && git checkout -b cherry-pick-20894-to-2.21.x FETCH_HEAD \
     && git cherry-pick fa60552d2620457e249e93a64b73f1e42834da2f

3. Fix the merge conflicts and commit the changes
4. Run build-support/cherry_pick/make_pr.sh "20894" "2.21.x"

Please note that I cannot re-run CI if a job fails. Please work with your PR approver(s) to re-run CI if necessary.

---

When you're done manually cherry-picking, please remove the needs-cherrypick label on this PR.

Thanks again for your contributions!

🤖 Beep Boop here's my run link