[jakezwang]

Negative millisecond and microsecond timestamps apply the fractional digits with a positive sign. For example, -1570308760263111 parses as 1920-03-29 03:07:20.263111 in UTC instead of 1920-03-29 03:07:19.736889.

Normalize negative timestamps into whole seconds and a nonnegative microsecond remainder before converting the timezone. The calculation uses integers to preserve microsecond precision. Add seven parser regressions covering milliseconds, microseconds, zero fractions, and the microsecond boundaries.

Validation after syncing with current master:

• TZ=UTC tox -e all on Python 3.14.7, with calendar and language detection extras: 24,627 passed, 4 skipped, 1 expected failure.
• tox -e mypy: no issues in 285 source files (Python 3.10).
• tox -e pre-commit: Ruff lint/format and zizmor passed.
• git diff --check passed.

The initial local run in America/New_York hit two unchanged upstream clean-API tests that assume the default timezone differs from EST. The full suite passes with TZ=UTC, matching the CI configuration.

[codspeed]

Merging this PR will not alter performance

✅ 7 untouched benchmarks

---

_{Comparing jakezwang:fix/negative-subsecond-timestamps (861d522) with master (5e77cac)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.21%. Comparing base (5e77cac) to head (861d522).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1387   +/-   ##
=======================================
  Coverage   97.20%   97.21%           
=======================================
  Files         236      236           
  Lines        3081     3083    +2     
=======================================
+ Hits         2995     2997    +2     
  Misses         86       86           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jakezwang]

Merged current master in 2db57e7 and resolved the test conflict by preserving both the timestamp regressions and upstream type annotations.

Validation: TZ=UTC tox -e all passed 24,627 tests (4 skipped, 1 expected failure) on Python 3.14.7. The full mypy and pre-commit environments also pass. The initial run under America/New_York hit two unrelated upstream timezone assumptions; the successful full run uses the same UTC setting as CI.

The new workflows are waiting for approval; could a maintainer approve the CI runs?

[serhii73]

Reviewed the diff. Negative sub-second timestamps are now floored correctly via divmod, so -1015673450000001 gives 12:29:09.999999 instead of 12:29:10.000001. The updated expectation is right, and the new tests cover the boundaries. Full suite passes on this branch merged with current master (24793 passed).