SD-2321 - fix: negative word-spacing not preserving whitespaces

packages/layout-engine/layout-bridge/src/text-measurement.ts

@@ -41,6 +41,22 @@ const isWordChar = (char: string): boolean => {
   return (code >= 48 && code <= 57) || (code >= 65 && code <= 90) || (code >= 97 && code <= 122) || char === "'";
 };
 
+const lineContainsManualTabWithoutSegments = (block: FlowBlock, line: Line): boolean => {
+  if (block.kind !== 'paragraph') return false;
+  if (line.segments?.some((seg) => seg.x !== undefined)) {
+    return false;
+  }
+  const fromRun = line.fromRun ?? 0;
+  const toRun = line.toRun ?? fromRun;
+  for (let runIndex = fromRun; runIndex <= toRun; runIndex += 1) {
+    const run = block.runs[runIndex];
+    if (run && isTabRun(run)) {
+      return true;
+    }
+  }
+  return false;
+};
+
 const capitalizeText = (text: string): string => {
   if (!text) return text;
   let result = '';
@@ -390,8 +406,17 @@ export function measureCharacterX(
     line.maxWidth ??
     // Fallback: if no maxWidth, approximate available width as line width (no slack)
     line.width;
+  const manualTabWithoutSegments = lineContainsManualTabWithoutSegments(block, line);
   // Pass availableWidth to justify calculation to match painter's word-spacing
-  const justify = getJustifyAdjustment(block, line, availableWidth, alignmentOverride);
+  const justify = getJustifyAdjustment(
+    block,
+    line,
+    availableWidth,
+    alignmentOverride,
+    undefined,
+    undefined,
+    manualTabWithoutSegments,
+  );
   const alignment = alignmentOverride ?? (block.kind === 'paragraph' ? block.attrs?.alignment : undefined);
   // For justify alignment, the line is stretched to fill available width (slack distributed across spaces)
   // For center/right alignment, the line keeps its natural width and is positioned within the available space
@@ -722,7 +747,16 @@ export function findCharacterAtX(
     // Fallback: approximate with line width when no maxWidth is present
     line.width;
   // Pass availableWidth to justify calculation to match painter's word-spacing
-  const justify = getJustifyAdjustment(block, line, availableWidth, alignmentOverride);
+  const manualTabWithoutSegments = lineContainsManualTabWithoutSegments(block, line);
+  const justify = getJustifyAdjustment(
+    block,
+    line,
+    availableWidth,
+    alignmentOverride,
+    undefined,
+    undefined,
+    manualTabWithoutSegments,
+  );
   const alignment = alignmentOverride ?? (block.kind === 'paragraph' ? block.attrs?.alignment : undefined);
   // For justify alignment, the line is stretched to fill available width (slack distributed across spaces)
   // For center/right alignment, the line keeps its natural width and is positioned within the available space

packages/layout-engine/layout-bridge/test/text-measurement.test.ts

@@ -570,6 +570,54 @@ describe('text measurement utility', () => {
       // Last line should NOT be justified (same width)
       expect(lastX).toBe(lastXNormal);
     });
+
+    it('skips justify spacing for manual tabs without explicit segments', () => {
+      const trailingText = 'Item body';
+      const tabWidth = 48;
+      const block = createBlock([
+        { text: '1 ', fontFamily: 'Arial', fontSize: 16 },
+        { kind: 'tab', text: '\t', width: tabWidth },
+        { text: trailingText, fontFamily: 'Arial', fontSize: 16 },
+      ]);
+      (block as any).attrs = { alignment: 'justify' };
+      const line = baseLine({
+        fromRun: 0,
+        toRun: 2,
+        toChar: trailingText.length,
+        width: (2 + trailingText.length) * CHAR_WIDTH + tabWidth,
+        maxWidth: 300,
+      });
+
+      const targetCharOffset = 7;
+      const baseX = measureCharacterX(block, line, targetCharOffset, line.width);
+      const wideX = measureCharacterX(block, line, targetCharOffset, 300);
+      expect(wideX).toBe(baseX);
+
+      const hitResult = findCharacterAtX(block, line, baseX, 0, 300);
+      expect(hitResult.charOffset).toBe(targetCharOffset);
+    });
+
+    it('still applies justify to lines without any tab runs', () => {
+      // Two runs so the first line is not derived as the last line of the paragraph
+      const block = createBlock([
+        { text: 'hello world foo', fontFamily: 'Arial', fontSize: 16 },
+        { text: 'bar baz qux', fontFamily: 'Arial', fontSize: 16 },
+      ]);
+      (block as any).attrs = { alignment: 'justify' };
+      const line = baseLine({
+        fromRun: 0,
+        toRun: 0,
+        toChar: 15,
+        width: 15 * CHAR_WIDTH,
+        maxWidth: 300,
+      });
+
+      const targetCharOffset = 7;
+      const baseX = measureCharacterX(block, line, targetCharOffset, line.width);
+      const wideX = measureCharacterX(block, line, targetCharOffset, 300);
+      // No tabs — justify should apply, so wider available width produces different position
+      expect(wideX).not.toBe(baseX);
+    });
   });
 
   describe('center and right alignment', () => {

packages/layout-engine/painters/dom/src/index.test.ts

@@ -441,6 +441,76 @@ describe('DomPainter', () => {
     expect(lines[1].style.wordSpacing).toBe('');
   });
 
+  it('skips justify for lines with manual tab runs but no explicit segment positions', () => {
+    const tabBlock: FlowBlock = {
+      kind: 'paragraph',
+      id: 'tab-justify-block',
+      runs: [
+        { text: '1.', fontFamily: 'Arial', fontSize: 16 },
+        { kind: 'tab', text: '\t', width: 48 },
+        { text: 'a b c d', fontFamily: 'Arial', fontSize: 16 },
+      ],
+      attrs: { alignment: 'justify' },
+    };
+
+    const tabMeasure: Measure = {
+      kind: 'paragraph',
+      lines: [
+        {
+          fromRun: 0,
+          fromChar: 0,
+          toRun: 2,
+          toChar: 7,
+          width: 60,
+          maxWidth: 100,
+          ascent: 12,
+          descent: 4,
+          lineHeight: 20,
+          // No segments with x — this is the "manual tab without segments" case
+        },
+        {
+          fromRun: 2,
+          fromChar: 7,
+          toRun: 2,
+          toChar: 7,
+          width: 0,
+          ascent: 12,
+          descent: 4,
+          lineHeight: 20,
+        },
+      ],
+      totalHeight: 40,
+    };
+
+    const tabLayout: Layout = {
+      pageSize: { w: 200, h: 200 },
+      pages: [
+        {
+          number: 1,
+          fragments: [
+            {
+              kind: 'para',
+              blockId: 'tab-justify-block',
+              fromLine: 0,
+              toLine: 2,
+              x: 0,
+              y: 0,
+              width: 100,
+            },
+          ],
+        },
+      ],
+    };
+
+    const painter = createTestPainter({ blocks: [tabBlock], measures: [tabMeasure] });
+    painter.paint(tabLayout, mount);
+
+    const lines = Array.from(mount.querySelectorAll('.superdoc-line')) as HTMLElement[];
+    expect(lines.length).toBeGreaterThanOrEqual(1);
+    // Manual tab without explicit segment positions should skip justify
+    expect(lines[0].style.wordSpacing).toBe('');
+  });
+
   it('justifies last visible line when paragraph ends with lineBreak', () => {
     // When a paragraph ends with <w:br/> (lineBreak), the visible text before the break
     // should still be justified because the "last line" is the empty line after the break.

packages/layout-engine/painters/dom/src/renderer.ts

@@ -5663,6 +5663,8 @@ export class DomPainter {
 
     // Check if any segments have explicit X positioning (from tab stops)
     const hasExplicitPositioning = line.segments?.some((seg) => seg.x !== undefined);
+    const lineContainsTabRun = runsForLine.some((run) => run.kind === 'tab');
+    const manualTabWithoutSegments = lineContainsTabRun && !hasExplicitPositioning;
     const availableWidth = availableWidthOverride ?? line.maxWidth ?? line.width;
 
     const justifyShouldApply = shouldApplyJustify({
@@ -5671,7 +5673,7 @@ export class DomPainter {
       // Caller already folds last-line + trailing lineBreak behavior into skipJustify.
       isLastLineOfParagraph: false,
       paragraphEndsWithLineBreak: false,
-      skipJustifyOverride: skipJustify,
+      skipJustifyOverride: skipJustify || manualTabWithoutSegments,
     });
 
     const countSpaces = (text: string): number => {