Test only oldest and newest supported polars versions in PR CI

[Matt711]

Description

The polars compat test job runs the cudf-polars test suite against every
supported polars version, which helps make it one of the longest running CI jobs.

Since regressions are most likely to appear at the boundaries of the support
matrix, restrict PR CI to only the oldest and newest supported versions.
The middle versions are retained in nightly CI via test.yaml, which continues
to run the full matrix.

The script accepts a POLARS_VERSIONS=endpoints environment variable to
select this mode, so the full matrix can still be run locally or in nightlies
without any script changes — useful when updating polars version pins to
verify the right version guards are in place.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[coderabbitai]

Note

Reviews paused

It looks like this branch is under active development. To avoid overwhelming you with review comments due to an influx of new commits, CodeRabbit has automatically paused this review. You can configure this behavior by changing the reviews.auto_review.auto_pause_after_reviewed_commits setting.

Use the following commands to manage reviews:

• @coderabbitai resume to resume automatic reviews.
• @coderabbitai review to trigger a single review.

Use the checkboxes below for quick actions:

• ▶️ Resume reviews
• 🔍 Trigger review

📝 Walkthrough

Walkthrough

The PR adds POLARS_VERSIONS=endpoints as a job-level environment variable in the PR workflow for the wheel-tests-cudf-polars job, and implements a corresponding conditional block in ci/test_wheel_cudf_polars.sh that, when POLARS_VERSIONS equals endpoints, truncates the VERSIONS array to only its first and last elements. A CI trigger comment is added to python/cudf_polars/cudf_polars/__init__.py to force workflow re-evaluation. SPDX copyright headers are updated in the modified files.

Changes

Polars version endpoint filtering and CI trigger

Layer / File(s)	Summary
Endpoint version filtering in workflow, test script, and CI trigger .github/workflows/pr.yaml, ci/test_wheel_cudf_polars.sh, python/cudf_polars/cudf_polars/__init__.py	The PR workflow sets POLARS_VERSIONS=endpoints for the wheel-tests-cudf-polars job; the test script checks this variable and truncates VERSIONS to its first and last elements before running the per-version test loop. A CI trigger comment is added to force workflow re-evaluation.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• rapidsai/cudf#22189: Both PRs modify ci/test_wheel_cudf_polars.sh's Polars compatibility version selection logic—this PR conditionally narrows the computed versions via POLARS_VERSIONS=endpoints, while the retrieved PR changes the source to come from dependencies.yaml.
• rapidsai/cudf#22467: Both PRs modify the wheel-tests-cudf-polars CI path through ci/test_wheel_cudf_polars.sh, affecting how wheel tests are executed in PR workflows.

Suggested reviewers

• bdice
• jameslamb
• TomAugspurger

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: restricting PR CI testing to only the oldest and newest Polars versions instead of the full matrix.
Description check	✅ Passed	The description is directly related to the changeset, explaining the rationale for testing only endpoint versions and how the environment variable enables the feature.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

_{Comment @coderabbitai help to get the list of available commands.}

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@ci/test_wheel_cudf_polars.sh`:
- Around line 24-28: Add validation in the conditional block where
POLARS_VERSIONS is checked for "endpoints" to ensure the VERSIONS array contains
at least two elements before attempting to access ${VERSIONS[0]} and
${VERSIONS[-1]}. If the array has fewer than two elements, the script should
exit with a meaningful error message that explains the issue (such as "VERSIONS
array must contain at least 2 elements for endpoints comparison"), rather than
silently proceeding with potentially incorrect behavior or unclear failure
messages.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: e4a96843-060d-43ca-a080-377723d24108

📥 Commits

Reviewing files that changed from the base of the PR and between 18e8ccd and d20d472.

📒 Files selected for processing (2)

• .github/workflows/pr.yaml
• ci/test_wheel_cudf_polars.sh

[gforsyth]

Suggested change

	env: "POLARS_VERSIONS=endpoints"
	env: "POLARS_VERSIONS=endpoints"

This needs to be at the same level as with, not inside of it

[Matt711]

/merge