fix: annotate to_timestamp array results with the execution timezone

[adriangb]

Which issue does this PR close?

• Closes to_timestamp with string input returns an array whose timezone does not match its declared return type #24632.

Rationale for this change

With datafusion.execution.time_zone set, to_timestamp on a string column declared a
return type of Timestamp(ns, <tz>) but produced an array of Timestamp(ns, None). The
declared type and the produced array disagreed, so any plan that materialized the column
failed at execution:

SET datafusion.execution.time_zone = 'UTC';
SELECT to_timestamp(s) AS v FROM (VALUES ('2026-01-01T00:00:00')) AS t(s);
-- Internal error: Function 'to_timestamp' returned value of type 'Timestamp(ns)' while
-- the following type was promised at planning time and expected: 'Timestamp(ns, "UTC")'

A second symptom: because the planner trusts the declared type it inserts no coercion, so a
comparison against another timezone-aware value reached the Arrow kernel with mismatched
types (Invalid comparison operation: Timestamp(ns) <= Timestamp(ns, "UTC")).

Scalar arguments were unaffected — they are constant-folded through a different code path
that did pick up the timezone — which is why every existing test passed.

What changes are included in this PR?

handle/handle_multiple in datafusion/functions/src/datetime/common.rs built the result
array straight from O::DATA_TYPE, which for timestamps carries no timezone, and ignored
the dt return type they were passed. The scalar branches of the same functions went
through scalar_value(dt, ..) and did carry the timezone — hence the mismatch.

The array branches now re-annotate the result with dt before returning it. to_date, the
other caller, returns Date32 and is unaffected.

Two existing unit tests in to_timestamp.rs asserted Timestamp(_, None) for array results
even though their helpers configure "UTC" as the execution timezone; those expectations
encoded the bug and are updated.

Are these changes tested?

Yes.

• to_timestamp_timezone.slt gains coverage for non-constant-folded (array) input: the
  arrow_typeof and value for to_timestamp under UTC and America/New_York, the
  explicit-format overload, all four precision variants, the comparison from the issue, and
  a to_date case confirming it is unaffected. Every one of these fails on main.
• A new to_timestamp_array_respects_execution_timezone unit test asserts, for each of the
  five to_timestamp* UDFs and both overloads, that the returned array's type equals what
  return_type advertises.

The full sqllogictest suite and the extended workspace test suite pass, as does
./dev/rust_lint.sh.

Are there any user-facing changes?

Yes, a bug fix: to_timestamp* on a string column now returns an array annotated with
datafusion.execution.time_zone, matching its declared return type, instead of failing at
execution. No API changes.

🤖 Generated with Claude Code

[adriangb]

@kosiew @Omega359 would one of you be willing to review?

[Copilot]

Pull request overview

Fixes timezone metadata mismatches for array-based to_timestamp* results.

Changes:

• Re-annotates parsed arrays with the declared return type.
• Updates unit-test expectations and adds coverage across timestamp variants.
• Adds SQL regression coverage for timezone-aware arrays and comparisons.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
datafusion/functions/src/datetime/common.rs	Applies declared timestamp timezone metadata to result arrays.
datafusion/functions/src/datetime/to_timestamp.rs	Updates and expands unit tests.
datafusion/sqllogictest/test_files/to_timestamp_timezone.slt	Adds end-to-end timezone regression tests.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.12346% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.43%. Comparing base (26b40dd) to head (09ca1ce).

Files with missing lines	Patch %	Lines
datafusion/functions/src/datetime/common.rs	83.33%	3 Missing and 2 partials ⚠️
datafusion/functions/src/datetime/to_timestamp.rs	94.11%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24636      +/-   ##
==========================================
- Coverage   81.43%   81.43%   -0.01%     
==========================================
  Files        1118     1118              
  Lines      399414   399469      +55     
  Branches   399414   399469      +55     
==========================================
+ Hits       325278   325313      +35     
- Misses      55145    55157      +12     
- Partials    18991    18999       +8     

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[Omega359]

I'll try and review this tonight @adriangb