fix: render line-level diff highlights

Author: Astro-Han

internal/ui/diffview.go

@@ -40,7 +40,7 @@ func newDisplayLineCache() *displayLineCache {
 
 // get returns cached rendered lines when the file signature, width, and
 // highlight state match.
-func (c *displayLineCache) get(file *internal.FileDiff, width int, highlightSet map[int]bool, build func() []string) []string {
+func (c *displayLineCache) get(file *internal.FileDiff, width int, highlightSet map[lineKey]bool, build func() []string) []string {
 	if c == nil {
 		return build()
 	}
@@ -67,7 +67,7 @@ func (c *displayLineCache) get(file *internal.FileDiff, width int, highlightSet
 }
 
 // newDisplayLineCacheKey fingerprints the rendered inputs that affect visual lines.
-func newDisplayLineCacheKey(file *internal.FileDiff, width int, highlightSet map[int]bool) displayLineCacheKey {
+func newDisplayLineCacheKey(file *internal.FileDiff, width int, highlightSet map[lineKey]bool) displayLineCacheKey {
 	key := displayLineCacheKey{width: width}
 	if file == nil {
 		return key
@@ -90,7 +90,7 @@ func newDisplayLineCacheKey(file *internal.FileDiff, width int, highlightSet map
 }
 
 // RenderDiffView renders the current file diff within the viewport.
-func RenderDiffView(file *internal.FileDiff, scrollOffset, width, height int, highlightSet map[int]bool) string {
+func RenderDiffView(file *internal.FileDiff, scrollOffset, width, height int, highlightSet map[lineKey]bool) string {
 	lines := diffDisplayLines(file, width, highlightSet)
 	return renderDisplayLines(lines, scrollOffset, height)
 }
@@ -179,7 +179,7 @@ func renderSeparator(width int) string {
 }
 
 // diffDisplayLines expands one file diff into the exact visual lines shown in the viewport.
-func diffDisplayLines(file *internal.FileDiff, width int, highlightSet map[int]bool) []string {
+func diffDisplayLines(file *internal.FileDiff, width int, highlightSet map[lineKey]bool) []string {
 	if file == nil {
 		return nil
 	}
@@ -202,17 +202,17 @@ func diffDisplayLines(file *internal.FileDiff, width int, highlightSet map[int]b
 
 	var lines []string
 	for hunkIdx, hunk := range file.Hunks {
-		highlightedHunk := highlightSet[hunkIdx]
 		lines = append(lines, renderSeparator(width))
-		for _, diffLine := range hunk.Lines {
+		for lineIdx, diffLine := range hunk.Lines {
+			highlightedLine := highlightSet[lineKey{HunkIdx: hunkIdx, LineIdx: lineIdx}]
 			lineNo := displayedLineNo(diffLine)
 			for i, segment := range wrapLineParts(diffLine.Content, contentWidth) {
 				if compactGutter {
 					prefix := "↳"
 					if i == 0 {
 						prefix = diffPrefix(diffLine.Type)
 					}
-					lines = append(lines, renderDiffSegment("", prefix, segment, diffLine.Type, width, file.Path, highlightedHunk))
+					lines = append(lines, renderDiffSegment("", prefix, segment, diffLine.Type, width, file.Path, highlightedLine))
 					continue
 				}
 
@@ -222,7 +222,7 @@ func diffDisplayLines(file *internal.FileDiff, width int, highlightSet map[int]b
 					lineNoText = formatDisplayedLineNo(lineNo, lineNumberWidth)
 					prefix = diffPrefix(diffLine.Type)
 				}
-				lines = append(lines, renderDiffSegment(lineNoText, prefix, segment, diffLine.Type, width, file.Path, highlightedHunk))
+				lines = append(lines, renderDiffSegment(lineNoText, prefix, segment, diffLine.Type, width, file.Path, highlightedLine))
 			}
 		}
 	}
@@ -427,20 +427,25 @@ func renderDiffSegment(lineNoText, prefix, code string, lineType internal.LineTy
 	}
 }
 
-func highlightSignature(highlightSet map[int]bool) uint64 {
+func highlightSignature(highlightSet map[lineKey]bool) uint64 {
 	if len(highlightSet) == 0 {
 		return 0
 	}
 
-	indices := make([]int, 0, len(highlightSet))
-	for idx := range highlightSet {
-		indices = append(indices, idx)
+	keys := make([]lineKey, 0, len(highlightSet))
+	for key := range highlightSet {
+		keys = append(keys, key)
 	}
-	sort.Ints(indices)
+	sort.Slice(keys, func(i, j int) bool {
+		if keys[i].HunkIdx != keys[j].HunkIdx {
+			return keys[i].HunkIdx < keys[j].HunkIdx
+		}
+		return keys[i].LineIdx < keys[j].LineIdx
+	})
 
 	hasher := fnv.New64a()
-	for _, idx := range indices {
-		_, _ = hasher.Write([]byte(fmt.Sprintf("%d\x00", idx)))
+	for _, key := range keys {
+		_, _ = hasher.Write([]byte(fmt.Sprintf("%d\x00%d\x00", key.HunkIdx, key.LineIdx)))
 	}
 
 	return hasher.Sum64()

internal/ui/diffview_test.go

@@ -425,7 +425,7 @@ func TestDisplayLineCacheMissesWhenHighlightStateChanges(t *testing.T) {
 	}
 
 	builds := 0
-	cache.get(file, 80, map[int]bool{0: true}, func() []string {
+	cache.get(file, 80, map[lineKey]bool{{HunkIdx: 0, LineIdx: 0}: true}, func() []string {
 		builds++
 		return []string{"first"}
 	})
@@ -675,7 +675,7 @@ func TestDiffDisplayLinesTrueColorPadsBackgroundAcrossViewport(t *testing.T) {
 		}},
 	}
 
-	line := diffDisplayLines(file, 30, map[int]bool{0: true})[1]
+	line := diffDisplayLines(file, 30, map[lineKey]bool{{HunkIdx: 0, LineIdx: 0}: true})[1]
 	if !strings.Contains(line, "\033[48;2;") {
 		t.Fatalf("true-color add line should contain background ANSI, got %q", line)
 	}
@@ -684,6 +684,42 @@ func TestDiffDisplayLinesTrueColorPadsBackgroundAcrossViewport(t *testing.T) {
 	}
 }
 
+// TestDiffDisplayLinesHighlightsOnlyMarkedLine verifies line-level highlight
+// state does not spill across other lines in the same hunk.
+func TestDiffDisplayLinesHighlightsOnlyMarkedLine(t *testing.T) {
+	prevProfile := colorProfileFn
+	colorProfileFn = func() termenv.Profile { return termenv.TrueColor }
+	defer func() { colorProfileFn = prevProfile }()
+	defer setThemeForTest(ThemeDark)()
+
+	file := &internal.FileDiff{
+		Path: "main.go",
+		Hunks: []internal.DiffHunk{{
+			Header: "@@ -0,0 +1,2 @@",
+			Lines: []internal.DiffLine{
+				{
+					Type:      internal.LineAdd,
+					Content:   "first",
+					NewLineNo: 1,
+				},
+				{
+					Type:      internal.LineAdd,
+					Content:   "second",
+					NewLineNo: 2,
+				},
+			},
+		}},
+	}
+
+	lines := diffDisplayLines(file, 30, map[lineKey]bool{{HunkIdx: 0, LineIdx: 1}: true})
+	if strings.Contains(lines[1], "\033[48;2;") {
+		t.Fatalf("first line should not contain background ANSI, got %q", lines[1])
+	}
+	if !strings.Contains(lines[2], "\033[48;2;") {
+		t.Fatalf("second line should contain background ANSI, got %q", lines[2])
+	}
+}
+
 // TestRenderDiffSegmentTrueColorNonHighlightedForcesPrefixColor verifies
 // true-color terminals still color add/delete prefixes when backgrounds are off.
 func TestRenderDiffSegmentTrueColorNonHighlightedForcesPrefixColor(t *testing.T) {

internal/ui/model.go

@@ -505,20 +505,6 @@ func latestHighlightedLine(highlighted map[lineKey]bool) (int, int, bool) {
 	return bestHunkIdx, bestLineIdx, true
 }
 
-// highlightedHunksFromLines temporarily adapts line-level state to the old
-// hunk-level renderer until diffview switches to line-aware highlighting.
-func highlightedHunksFromLines(highlighted map[lineKey]bool) map[int]bool {
-	if len(highlighted) == 0 {
-		return nil
-	}
-
-	hunks := make(map[int]bool, len(highlighted))
-	for key := range highlighted {
-		hunks[key.HunkIdx] = true
-	}
-	return hunks
-}
-
 // clampScrollOffset keeps scroll state within the current diff viewport bounds.
 func (m *Model) clampScrollOffset() {
 	if m.ScrollOffset < 0 {
@@ -561,7 +547,7 @@ func (m Model) View() string {
 	if m.OverlayOpen {
 		content = RenderOverlay(m.OverlaySnapshot, m.OverlayCursor, diffHeight, m.Width)
 	} else if len(m.Files) > 0 && m.CurrentIdx < len(m.Files) {
-		highlightSet := highlightedHunksFromLines(m.highlightedLines[m.Files[m.CurrentIdx].Path])
+		highlightSet := m.highlightedLines[m.Files[m.CurrentIdx].Path]
 		lines := m.displayCache.get(&m.Files[m.CurrentIdx], m.Width, highlightSet, func() []string {
 			return diffDisplayLines(&m.Files[m.CurrentIdx], m.Width, highlightSet)
 		})