🦺 enhance the translation of SQLite timestamp expressions that use current_timestamp within date/time functions

[techouse]

This pull request improves the handling of default values when converting SQLite schemas to MySQL, specifically by enhancing the translation of SQLite timestamp expressions that use current_timestamp within date/time functions. The changes ensure that expressions like datetime(current_timestamp, ...) are correctly mapped to the appropriate MySQL equivalents, addressing cases that were previously missed.

Key changes include:

Enhancements to Timestamp Expression Handling:

• Added a new regex pattern SQLITE_CURRENT_TS_FUNC to match SQLite expressions such as datetime(current_timestamp, ...), allowing for more accurate detection and translation of these defaults.
• Updated the logic in _translate_default_for_mysql to detect when the default value uses datetime, date, or time functions with current_timestamp, and map them to the correct MySQL expressions (CURRENT_TIMESTAMP, UTC_TIMESTAMP, etc.) for TIMESTAMP, DATETIME, DATE, and TIME columns. [1] [2] [3] [4] [5]

Testing Improvements:

• Added new unit tests to verify that SQLite defaults like datetime(current_timestamp, 'localtime') and datetime(current_timestamp, 'utc') are properly converted to CURRENT_TIMESTAMP and UTC_TIMESTAMP (with precision, if specified) in MySQL.

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Partially fixes #154

[coderabbitai]

Walkthrough

The pull request extends SQLite-to-MySQL default value translation by introducing a regex pattern to detect current_timestamp() function variants and enhancements to the translation logic to handle localtime/utc modifiers and preserve fractional seconds in TIMESTAMP, DATETIME, DATE, and TIME default values.

Changes

Cohort / File(s)	Change Summary
Production — Default translation enhancements src/sqlite3_to_mysql/transporter.py	Added class-level regex pattern SQLITE_CURRENT_TS_FUNC to detect current_timestamp() variants. Extended _translate_default_for_mysql() to detect current_timestamp expressions and route them through appropriate MySQL equivalents (CURRENT_TIMESTAMP, UTC_TIMESTAMP) while preserving fractional seconds and respecting localtime/utc modifiers.
Test coverage — New datetime test cases tests/unit/sqlite3_to_mysql_test.py	Added two new parameterised test cases: DATETIME without precision using current_timestamp (localtime path) mapping to CURRENT_TIMESTAMP, and DATETIME(3) with current_timestamp and 'utc' modifier mapping to UTC_TIMESTAMP(3).

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20–30 minutes

• Regex pattern correctness: Verify the SQLITE_CURRENT_TS_FUNC pattern accurately captures all current_timestamp() variants with optional modifiers.
• Conditional branch logic: Review the extended conditional paths for TIMESTAMP/DATETIME/DATE/TIME to ensure all modifier and fractional-second combinations are handled correctly.
• Edge cases: Confirm handling of nested or malformed current_timestamp() expressions and boundary conditions with precision values.

Possibly related PRs

• 🦺 improve SQLite-to-MySQL type and default value translation logic #149 — Also modifies _translate_default_for_mysql() to handle SQLite datetime expressions with modifiers.
• ✨ translate SQLite defaults to MySQL #142 — Introduced the foundational default translation machinery that this PR extends for current_timestamp() support.

Poem

A rabbit hops through timestamp fields,
With current_timestamp calls,
Detecting modifiers—utc and local yields,
Translating defaults through MySQL's halls. 🐰⏰
Fractional seconds preserved with care,
New paths for datetime everywhere!

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarises the main change—enhancing translation of SQLite timestamp expressions using current_timestamp—directly matching the pull request's core objective.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description check	✅ Passed	The pull request description comprehensively covers all required sections: it summarises the changes, explains the motivation (improving timestamp handling), lists key enhancements and testing improvements, and provides context on the specific issue being addressed.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/datetime-defaults

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.05%. Comparing base (c69c712) to head (e703708).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #157   +/-   ##
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  Coverage   98.05%   98.05%           
=======================================
  Files           8        8           
  Lines        1129     1132    +3     
=======================================
+ Hits         1107     1110    +3     
  Misses         22       22           

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