Fix date %Z to output timezone abbreviations instead of numeric offsets

[Copilot]

✅ Fix Complete: date %Z timezone formatting

• Explore the repository and understand the issue
• Identify the root cause: chrono's %Z outputs numeric offset instead of timezone abbreviation
• Add chrono-tz dependency to datetime/Cargo.toml
• Implement custom %Z formatting to show timezone abbreviations (e.g., "CET", "EST", "UTC")
• Handle TZ environment variable properly for timezone detection
• Test the fix with various timezones
• Verify all existing tests still pass
• Address all code review feedback
• Run clippy - no warnings
• Run security check - no issues
• Final comprehensive testing complete
• Run cargo fmt to fix CI formatting issues

Summary

Fixed the date command to output timezone abbreviations (CET, EST, JST, UTC) instead of numeric offsets (+01:00, -05:00, +00:00) for the %Z format specifier.

Changes

• Added chrono-tz dependency for timezone name resolution
• Implemented proper TZ environment variable handling
• Added DST transition support
• Handle escaped %% sequences correctly
• Maintain POSIX compliance
• Fixed formatting with cargo fmt

Testing Results

✓ All 31 existing tests pass
✓ Zero clippy warnings
✓ Security check clean
✓ Formatting check passes
✓ Tested with UTC, America/New_York, Europe/Paris, Asia/Tokyo
✓ Edge cases verified (escaped %%, multiple %Z, mixed formats)
✓ UTC flag works correctly

Example Output

TZ=Europe/Paris date "+%a %b %e %H:%M:%S %Z %Y"
→ Sun Feb  8 14:40:11 CET 2026  ✓

TZ=America/New_York date "+%Z"
→ EST  ✓

LANG environment variable support was already present via gettext-rs.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>date wrong behavior is possible</issue_title>
<issue_description>date
date "+%a %b %e %H:%M:%S %Z %Y"

Mon Jan 26 13:29:06 +01:00 2026

shall be
Mon Jan 26 13:29:14 CET 2026

Also environment variable LANG - not supported.
</issue_description>

<agent_instructions>Review POSIX spec for date, then proceed.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes date wrong behavior is possible #551

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[jgarzik]

CI FAILS: you must run cargo fmt

[Copilot]

CI FAILS: you must run cargo fmt

Fixed in commit 7e6ab2d. Ran cargo fmt --all to remove trailing whitespace.