expand/unexpand: fix display width of 3- and 4-byte UTF-8 characters #13352
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expand/unexpand: fix display width of 3- and 4-byte UTF-8 characters #13352sylvestre wants to merge 3 commits into
sylvestre wants to merge 3 commits into
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…lper The UTF-8 sequence length was derived from char::from(b).len_utf8(), which uses the leading byte's value as a codepoint rather than decoding the length from its bit pattern. That is only correct for 2-byte characters; 3- and 4-byte ones were split into single bytes and each counted as one column, so a following tab expanded to the wrong column. Derive the length from the leading byte and measure the display width with unicode-width. expand and unexpand needed identical logic, so it lives in a new uucore::char_width helper (char_width_at) instead of being duplicated. Should make test tests/expand/mb.sh pass
The fast path that batches leading spaces/tabs was gated on --no-utf8, so the default (UTF-8) mode fell back to the per-byte loop, which the display-width fix made measurably slower on ASCII input. Leading whitespace is ASCII and independent of UTF-8 mode, so run the fast path there too, and add the missing lastcol == 0 guard so it does not apply when multiple tab stops cap conversion.
GNU treats a wide blank such as U+3000 (any character for which iswblank is true) as a convertible blank: a run of them that reaches a tab stop is absorbed into a tab, but a run that does not is left as-is. Recognize the Unicode blank set in next_char_info, advance the column by the blank's display width, and remember buffered wide blanks so write_tabs can emit them verbatim when their run is not converted (and never let a tab straddle one). Expose the decoded char from uucore::char_width via char_info_at so unexpand reuses the shared UTF-8 decoding instead of duplicating it. Should make test tests/unexpand/mb.sh pass.
Merging this PR will improve performance by 65.27%
|
| Mode | Benchmark | BASE |
HEAD |
Efficiency | |
|---|---|---|---|---|---|
| ❌ | Simulation | du_all_wide_tree[(5000, 500)] |
16.3 ms | 17.1 ms | -4.14% |
| ⚡ | Simulation | unexpand_large_file[10] |
282.3 ms | 130 ms | ×2.2 |
| ⚡ | Simulation | unexpand_many_lines[100000] |
134.7 ms | 62.1 ms | ×2.2 |
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Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.
Comparing sylvestre:expand-unexpand-mb-width (b21d0d6) with main (3ceaab5)
Footnotes
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46 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩
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