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fix: render manual line breaks correctly #2807

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fix: render manual line breaks correctly #2807

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23 changes: 20 additions & 3 deletions packages/layout-engine/layout-bridge/src/remeasure.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1156,11 +1156,22 @@ export function remeasureParagraph(
let endChar = currentChar;
let tabStopCursor = 0;
let didBreakInThisLine = false;
let explicitLineBreakRun = -1;
let resumeRun = -1;
let resumeChar = 0;

for (let r = currentRun; r < runs.length; r += 1) {
const run = runs[r];
if (isLineBreakRun(run)) {
explicitLineBreakRun = r;
if (startRun === r && startChar === 0 && width === 0) {
// Preserve leading/manual explicit break as an empty line.
endRun = r;
endChar = 0;
}
didBreakInThisLine = true;
break;
}
if (run.kind === 'tab') {
const absCurrentX = width + effectiveIndent;
const { target, nextIndex, stop } = getNextTabStopPx(absCurrentX, tabStops, tabStopCursor);
Expand Down Expand Up @@ -1302,7 +1313,7 @@ export function remeasureParagraph(
}

// If we didn't consume any chars (e.g., very long single char), force one char
if (startRun === endRun && startChar === endChar) {
if (explicitLineBreakRun < 0 && startRun === endRun && startChar === endChar) {
endRun = startRun;
endChar = startChar + 1;
}
Expand All @@ -1321,8 +1332,14 @@ export function remeasureParagraph(
lines.push(line);

// Advance to next line start
currentRun = endRun;
currentChar = endChar;
if (explicitLineBreakRun >= 0) {
// Explicit break consumed as a line boundary, continue from run after break.
currentRun = explicitLineBreakRun + 1;
currentChar = 0;
Comment on lines +1335 to +1338
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@chatgpt-codex-connector chatgpt-codex-connector bot Apr 14, 2026

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P1 Badge Preserve trailing explicit lineBreak as final blank line

Advancing currentRun to explicitLineBreakRun + 1 immediately consumes the break run, so when a paragraph ends with lineBreak (or with multiple trailing lineBreak runs), the loop exits without emitting the final empty line(s). This regresses trailing manual-break rendering in remeasure paths (e.g., signature blocks or intentional blank lines at paragraph end) because each trailing break should contribute a visible blank line boundary.

Useful? React with 👍 / 👎.

} else {
currentRun = endRun;
currentChar = endChar;
}
if (currentRun >= runs.length) {
break;
}
Expand Down
25 changes: 24 additions & 1 deletion packages/layout-engine/layout-bridge/test/remeasure.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -872,7 +872,30 @@ describe('remeasureParagraph', () => {
const block = createBlock([textRun('Hello'), { kind: 'lineBreak' } as Run, textRun('World')]);
const measure = remeasureParagraph(block, 200);

expect(measure.lines.length).toBeGreaterThanOrEqual(1);
expect(measure.lines).toHaveLength(2);
expect(measure.lines[0].fromRun).toBe(0);
expect(measure.lines[0].toRun).toBe(0);
expect(measure.lines[1].fromRun).toBe(2);
expect(measure.lines[1].toRun).toBe(2);
});

it('preserves multiple explicit lineBreak boundaries', () => {
const block = createBlock([
textRun('One'),
{ kind: 'lineBreak' } as Run,
textRun('Two'),
{ kind: 'lineBreak' } as Run,
textRun('Three'),
]);
const measure = remeasureParagraph(block, 200);

expect(measure.lines).toHaveLength(3);
expect(measure.lines[0].fromRun).toBe(0);
expect(measure.lines[0].toRun).toBe(0);
expect(measure.lines[1].fromRun).toBe(2);
expect(measure.lines[1].toRun).toBe(2);
expect(measure.lines[2].fromRun).toBe(4);
expect(measure.lines[2].toRun).toBe(4);
});

it('handles tabs followed immediately by line break', () => {
Expand Down
2 changes: 2 additions & 0 deletions packages/layout-engine/measuring/dom/src/index.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -542,6 +542,8 @@ describe('measureBlock', () => {
expect(measure.lines).toHaveLength(2);
expect(measure.lines[0].width).toBeGreaterThan(0);
expect(measure.lines[1].width).toBeGreaterThan(0);
expect(measure.lines[1].fromRun).toBe(2);
expect(measure.lines[1].toRun).toBe(2);
});

it('creates an empty line for leading lineBreak at start of paragraph', async () => {
Expand Down
15 changes: 15 additions & 0 deletions packages/layout-engine/measuring/dom/src/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1397,6 +1397,21 @@ async function measureParagraphBlock(block: ParagraphBlock, maxWidth: number): P
continue;
}

// When a text/tab/atomic run follows an explicit lineBreak, currentLine is a
// placeholder line seeded with the break run index. Re-anchor it so line ranges
// start at the first visible run on the new line.
if (
currentLine &&
currentLine.width === 0 &&
currentLine.fromRun === currentLine.toRun &&
currentLine.fromChar === 0 &&
currentLine.toChar === 0 &&
isLineBreakRun(runsToProcess[currentLine.fromRun] as Run)
) {
currentLine.fromRun = runIndex;
currentLine.toRun = runIndex;
}

// Handle tab runs specially
if (isTabRun(run)) {
// Clear any previous tab group when we encounter a new tab
Expand Down
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