MDEV-40147 MSAN: use-of-uninitialized-value in my_time_compare

[grooverdan]

Field::get_date and Item::get_date can return true and not have their ltime pointer structure initialized.

This was the case with Field_vers_trx_id::get_date.

Type_handler_time_common::stored_field_cmp_to_item rather than doing a my_time_compare on uninitialized values can return a non-equality (!=0) value for when the fetching of Field or Item fails and avoid the call to my_time_compare.

Added checks for other invalid results before being passed to my_time_compare.

Add nonnull as an attribute on my_time_compare and the unpack_time function it used. Also pack_time since related and it obviously requires a non-null argument.

[gemini-code-assist]

Code Review

This pull request addresses an MSAN uninitialized value issue in my_time_compare (MDEV-40147) by adding __attribute__((nonnull)) to temporal functions, checking return values of get_date before comparisons, and adding a regression test. The review feedback points out an inconsistency in Type_handler_temporal_with_date::stored_field_cmp_to_item where returning 1 when field->get_date fails is incorrect and asymmetric, suggesting it should return -1 instead to match similar comparison handlers.

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[gemini-code-assist]

In Type_handler_temporal_with_date::stored_field_cmp_to_item, if field->get_date fails, returning 1 (which indicates field > item) is inconsistent and incorrect when item is valid. To be consistent with Type_handler_time_common::stored_field_cmp_to_item (lines 9124-9127), we should return -1 when field->get_date fails, and 1 when item->get_date (or its conversion) fails. This ensures symmetric and correct comparison behavior when one of the operands is invalid.

  if (field->get_date(&field_time, Datetime::Options(TIME_INVALID_DATES, thd)))
    return -1;
  if (item->get_date(thd, &item_time, Datetime::Options(TIME_INVALID_DATES, thd)) ||
      (item_time.time_type == MYSQL_TIMESTAMP_TIME &&
       time_to_datetime(thd, &item_time, item_time_cmp= &item_time2)))
    return 1;