AI review done up to commit: 28cf9a1

AI Review Summary:

The pull request introduces significant enhancements to the datetime functions, aiming for better parity with SQLite's datetime modifiers. It also refactors the handling of SELECT statements without a FROM clause and adds a comprehensive SQLite parity testing framework.

Key Changes:

• Datetime Functionality (julian_day.rs, mod.rs, modifiers.rs):

  • The JulianDay struct was simplified by removing the is_subsecond field, centralizing subsecond handling.
  • A new to_calendar_components method was introduced for robust date and time decomposition, including millisecond rounding for precision.
  • The DateTimeModifier enum was redesigned to explicitly represent various SQLite modifiers (e.g., AddYears, ShiftDate, StartOfMonth), moving away from a generic JDNOffset.
  • The parse_modifier function was rewritten to correctly parse a wider range of SQLite-compatible datetime modifier strings, including unit modifiers, date/time shifts (+YYYY-MM-DD HH:MM:SS), and special keywords.
  • Helper functions add_months and add_years were implemented to handle calendar arithmetic, including month/year rollovers and leap year considerations, ensuring accurate date calculations.
  • The weekday modifier logic was carefully implemented to match SQLite's behavior, advancing to the next occurrence of a target weekday.

• SELECT Statement Parsing (select/mod.rs, select_statement.rs):

  • The SQL parser was updated to support SELECT statements that do not include a FROM clause (e.g., SELECT 1; or SELECT date('now');), by creating a temporary, empty table if no source table is specified.

• SQLite Parity Testing (common/parity.rs, main_tests.rs, sqlite_parity.rs):

  • A new ParityManager was introduced to run SQL queries against both Mollycache and an in-memory SQLite database, comparing their results.
  • A values_equal_approx function was implemented to handle floating-point comparisons with an epsilon tolerance, crucial for comparing real numbers across different implementations.
  • New test suites were added to verify parity for basic math, datetime operations, and fundamental CRUD (Create, Read, Update, Delete) operations.

Overall Quality Assessment:

The changes represent a significant improvement in the functional correctness and robustness of the datetime features, bringing them much closer to SQLite's established behavior. The refactoring of the datetime modifier logic is a major step forward, making the system more modular and maintainable. The introduction of the SQLite parity testing framework is an excellent addition, providing a strong safety net for future development and ensuring high fidelity with a well-known SQL database. The code is well-structured, and the logical handling of complex date arithmetic and parsing has been carefully implemented.

Recurring Issues/Patterns:

No recurring issues or significant bugs were observed during the review. The changes consistently demonstrate a focus on correctness and alignment with SQLite's behavior. The datetime functionality is now much more comprehensive and reliable.