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Fix: Cursor Positioning After Line Wrap #1943

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Fix: Cursor Positioning After Line Wrap #1943

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b71524b
fix cursor miss positioning after line wrap
MazenSamehR Dec 17, 2025
8961220
remove wrap-ansi from package.json
MazenSamehR Dec 17, 2025
354b8f0
fix checks
MazenSamehR Dec 17, 2025
4004fa4
add a comment explaining the regex pattern for ANSI escape sequences
MazenSamehR Dec 18, 2025
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59 changes: 49 additions & 10 deletions packages/core/src/lib/utils.ts
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Original file line number Diff line number Diff line change
@@ -1,7 +1,5 @@
import cliWidth from 'cli-width';
import wrapAnsi from 'wrap-ansi';
import { readline } from './hook-engine.ts';

/**
* Force line returns at specific width. This function is ANSI code friendly and it'll
* ignore invisible codes during width calculation.
Expand All @@ -10,14 +8,55 @@ import { readline } from './hook-engine.ts';
* @return {string}
*/
export function breakLines(content: string, width: number): string {
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@SBoudrias SBoudrias Dec 18, 2025

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One thing here that isn't clear anymore about this approach;

We were talking of how the bug reported seemed to be an issue with how different terminal auto-wrap content and how that conflicted with the cursor position and the way wrap-ansi would do the wrapping.

Given that, it's unclear why a different wrapping algorithm fix this issue. This would fix it for terminals doing simple wraps, but won't it now break for those who're maybe implementing word wrapping instead?

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@MazenSamehR MazenSamehR Dec 18, 2025

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By implementing character-based wrapping directly in the code rather than relying on wrap-ansi we Make wrapping deterministic, so the exact same wrapping happens on all terminals. So since we control the wrapping, we can accurately calculate cursor positions.

Now a terminal's auto-wrap behavior becomes irrelevant because we've already wrapped the content at exactly width characters, and the terminal receives pre-wrapped lines that fit within its display width. So even if a terminal has word-wrapping enabled, it only applies to content that exceeds the width, which ours won't

Example

Terminal A (word-wrap): "This is a long message"
Terminal B (char-wrap): "This is a long message"

using wrap-ansi:
- Terminal A might wrap: "This is a long" / "message"
- Terminal B might wrap: "This is a lo" / "ng message"
- Cursor calculation broken because we don't know which one we're on!

character-based:
- All terminals receive: "This is a lo" / "ng message"
- Both terminals see it's already wrapped
- Cursor calculation is accurate because we control the wrapping!

return content
.split('\n')
.flatMap((line) =>
wrapAnsi(line, width, { trim: false, hard: true })
.split('\n')
.map((str) => str.trimEnd()),
)
.join('\n');
const lines = content.split('\n');
const result: string[] = [];

for (const line of lines) {
let currentLine = '';
let visibleLength = 0;
let escapeSequence = '';
let inEscape = false;

for (const char of line) {
// Detect start of ANSI escape code
if (char === '\x1b') {
inEscape = true;
escapeSequence += char;
continue;
}

// If inside an escape sequence, accumulate it but don't count width
if (inEscape) {
escapeSequence += char;

// ANSI escape sequences always end with a letter (eg., 'm' in '\x1b[31m')
// This marks the end of the sequence so we can append it without counting its width
if (/[a-zA-Z]/.test(char)) {
inEscape = false;
currentLine += escapeSequence;
escapeSequence = '';
}
continue;
}

// Normal character: Add to line and increment visual width
currentLine += char;
visibleLength++;

// Hard Wrap: If we reached the width limit
if (visibleLength === width) {
result.push(currentLine);
currentLine = '';
visibleLength = 0;
}
}

if (currentLine.length > 0 || result.length === 0) {
result.push(currentLine.trimEnd());
}
}

return result.join('\n');
}

/**
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