Fix Segment._split_cells() to use grapheme-aware splitting for VS16-widened characters#1
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Fix Segment._split_cells() to use grapheme-aware splitting for VS16-widened characters#1
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…idened characters The previous implementation of `_split_cells()` used `cell_len(text[:pos])` to measure prefix width when searching for the correct split point. This ignored VS16 (Variation Selector 16, U+FE0F) context: a character like ♻ (U+267B) measures as 1 cell in isolation, but as part of the grapheme ♻️ (♻ + VS16) it occupies 2 cells. Splitting at cell position 1 through such a grapheme produced a "clean" grapheme-boundary split instead of the correct "replace both halves with spaces" behaviour, silently losing 1 cell of width. Fix: replace the manual while-loop with a delegation to `_split_text()` from `cells.py`, which already uses `split_graphemes()` and handles VS16-widened grapheme clusters correctly. All standard CJK (single-codepoint, 2-cell) characters continue to work as before; the fix closes the correctness gap for multi-codepoint graphemes widened by VS16. Adds regression tests in `test_split_cells_emoji` (parametrized cases) and a new `test_split_cells_vs16` function that exhaustively checks every split position for a repeated VS16-widened grapheme. https://claude.ai/code/session_01JX9WKJ8RbqvGhmd298HxiD
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The previous implementation of
_split_cells()usedcell_len(text[:pos])tomeasure prefix width when searching for the correct split point. This ignored
VS16 (Variation Selector 16, U+FE0F) context: a character like ♻ (U+267B)
measures as 1 cell in isolation, but as part of the grapheme ♻️ (♻ + VS16)
it occupies 2 cells. Splitting at cell position 1 through such a grapheme
produced a "clean" grapheme-boundary split instead of the correct "replace both
halves with spaces" behaviour, silently losing 1 cell of width.
Fix: replace the manual while-loop with a delegation to
_split_text()fromcells.py, which already usessplit_graphemes()and handles VS16-widenedgrapheme clusters correctly. All standard CJK (single-codepoint, 2-cell)
characters continue to work as before; the fix closes the correctness gap for
multi-codepoint graphemes widened by VS16.
Adds regression tests in
test_split_cells_emoji(parametrized cases) and anew
test_split_cells_vs16function that exhaustively checks every splitposition for a repeated VS16-widened grapheme.
https://claude.ai/code/session_01JX9WKJ8RbqvGhmd298HxiD