moonbitlang / core / 1288

Pull #2755

github

Fix partition functions returning absolute position for empty ranges

The partition and partition_by functions were inconsistently returning
absolute positions (actual_start) for empty/invalid ranges while returning
relative positions (i - actual_start) in normal cases. This caused incorrect
pivot position calculations in quick_sort functions.

Changes:
- Fixed partition() to return (0, true) instead of (actual_start, true) for empty ranges
- Fixed partition_by() to return (0, true) instead of (actual_start, true) for empty ranges
- Added comprehensive test cases to verify the fix handles edge cases correctly
- Tests specifically cover non-zero starting positions which would fail with the old bug

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