( str: string, start: number, end?: number, )
| 24 | * sequences because @alcalzone/ansi-tokenize tokenizes them correctly. |
| 25 | */ |
| 26 | export default function sliceAnsi( |
| 27 | str: string, |
| 28 | start: number, |
| 29 | end?: number, |
| 30 | ): string { |
| 31 | // Don't pass `end` to tokenize — it counts code units, not display cells, |
| 32 | // so it drops tokens early for text with zero-width combining marks. |
| 33 | const tokens = tokenize(str) |
| 34 | let activeCodes: AnsiCode[] = [] |
| 35 | let position = 0 |
| 36 | let result = '' |
| 37 | let include = false |
| 38 | |
| 39 | for (const token of tokens) { |
| 40 | // Advance by display width, not code units. Combining marks (Devanagari |
| 41 | // matras, virama, diacritics) are width 0 — counting them via .length |
| 42 | // advanced position past `end` early and truncated the slice. Callers |
| 43 | // pass start/end in display cells (via stringWidth), so position must |
| 44 | // track the same units. |
| 45 | const width = |
| 46 | token.type === 'ansi' ? 0 : token.fullWidth ? 2 : stringWidth(token.value) |
| 47 | |
| 48 | // Break AFTER trailing zero-width marks — a combining mark attaches to |
| 49 | // the preceding base char, so "भा" (भ + ा, 1 display cell) sliced at |
| 50 | // end=1 must include the ा. Breaking on position >= end BEFORE the |
| 51 | // zero-width check would drop it and render भ bare. ANSI codes are |
| 52 | // width 0 but must NOT be included past end (they open new style runs |
| 53 | // that leak into the undo sequence), so gate on char type too. The |
| 54 | // !include guard ensures empty slices (start===end) stay empty even |
| 55 | // when the string starts with a zero-width char (BOM, ZWJ). |
| 56 | if (end !== undefined && position >= end) { |
| 57 | if (token.type === 'ansi' || width > 0 || !include) break |
| 58 | } |
| 59 | |
| 60 | if (token.type === 'ansi') { |
| 61 | activeCodes.push(token) |
| 62 | if (include) { |
| 63 | // Emit all ANSI codes during the slice |
| 64 | result += token.code |
| 65 | } |
| 66 | } else { |
| 67 | if (!include && position >= start) { |
| 68 | // Skip leading zero-width marks at the start boundary — they belong |
| 69 | // to the preceding base char in the left half. Without this, the |
| 70 | // mark appears in BOTH halves: left+right ≠ original. Only applies |
| 71 | // when start > 0 (otherwise there's no preceding char to own it). |
| 72 | if (start > 0 && width === 0) continue |
| 73 | include = true |
| 74 | // Reduce and filter to only active start codes |
| 75 | activeCodes = filterStartCodes(reduceAnsiCodes(activeCodes)) |
| 76 | result = ansiCodesToString(activeCodes) |
| 77 | } |
| 78 | |
| 79 | if (include) { |
| 80 | result += token.value |
| 81 | } |
| 82 | |
| 83 | position += width |
no test coverage detected