Support cudf-polars epoch

[brandon-b-miller]

Part of #16481

[vyasr]

@brandon-b-miller what's the status on this PR?

[copy-pr-bot]

This pull request requires additional validation before any workflows can run on NVIDIA's runners.

Pull request vetters can view their responsibilities here.

Contributors can view more details about this message here.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 33283c51-79a4-4b12-b044-91f3bea9fc57

📥 Commits

Reviewing files that changed from the base of the PR and between 259cc88 and 12de897.

📒 Files selected for processing (1)

• python/cudf_polars/cudf_polars/dsl/expressions/datetime.py

💤 Files with no reviewable changes (1)

• python/cudf_polars/cudf_polars/dsl/expressions/datetime.py

---

📝 Walkthrough

Summary by CodeRabbit

• New Features

  • Enhanced datetime/timestamp epoch conversion to support additional time_unit resolutions: milliseconds, microseconds, nanoseconds, seconds, and days (including Date and Datetime inputs).

• Tests

  • Added GPU-validated, parametrized test coverage for epoch operations across multiple datetime-like dtypes and time_unit values (ms, us, ns, s, d).

Walkthrough

Adds TimeStamp support to the TemporalFunction DSL in the cudf-polars GPU expression evaluator. The implementation registers the op in _valid_ops, adds imports for polars and DataType, and inserts an evaluation branch that rescales the input column via an intermediate pl.Datetime(time_unit) cast before casting to the final output dtype. A new parametrized test_epoch test validates the feature across multiple datetime dtypes and time units.

Changes

TemporalFunction TimeStamp Support

Layer / File(s)	Summary
TimeStamp implementation in TemporalFunction python/cudf_polars/cudf_polars/dsl/expressions/datetime.py	Adds polars and DataType imports, registers Name.TimeStamp in _valid_ops, and inserts a do_evaluate branch that evaluates the child column, rescales it to pl.Datetime(time_unit) via intermediate cast, and then casts to the expression's output dtype.
test_epoch parametrized test python/cudf_polars/tests/expressions/test_datetime_basic.py	Adds test_epoch covering pl.Date and pl.Datetime("ms"/"us"/"ns") dtypes with time_unit values "s", "d", "ms", "us", "ns", asserting GPU results via assert_gpu_result_equal.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title 'Support cudf-polars epoch' accurately describes the main change: adding epoch functionality support to the cudf-polars module.
Description check	✅ Passed	The PR description references issue #16481 and indicates this is part of a larger effort to support epoch functionality in cudf-polars, which is directly related to the changeset.
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.}

[brandon-b-miller]

/merge