fix(web): support multiline highlight ranges in LightweightCodeHighlighter

CHANGELOG.md

@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Decoded percent-encoded characters in repo names derived from direct generic git URLs. [#1666](https://github.com/sourcebot-dev/sourcebot/pull/1666)
 - Fixed `.gitattributes` `linguist-language` overrides being ignored for files in subdirectories. [#1692](https://github.com/sourcebot-dev/sourcebot/pull/1692)
 - Fixed selected language and repository filters disappearing when filtering the available options. [#1685](https://github.com/sourcebot-dev/sourcebot/pull/1685)
+- Fixed code highlights not covering every line of a multi-line range. [#1699](https://github.com/sourcebot-dev/sourcebot/pull/1699)
 
 ## [5.1.15] - 2026-09-29
 

packages/web/src/app/(app)/components/lightweightCodeHighlighter.test.ts

@@ -0,0 +1,98 @@
+import { describe, expect, it } from 'vitest';
+import { SourceRange } from '@/features/search';
+import { computeLineHighlightRanges } from './lightweightCodeHighlighter';
+
+describe('computeLineHighlightRanges', () => {
+    it('returns empty array when highlightRanges is undefined or empty', () => {
+        expect(computeLineHighlightRanges(undefined, 1, 20)).toEqual([]);
+        expect(computeLineHighlightRanges([], 1, 20)).toEqual([]);
+    });
+
+    it('correctly maps a single-line range on the target line and ignores other lines', () => {
+        const ranges: SourceRange[] = [
+            {
+                start: { lineNumber: 2, column: 5, byteOffset: 4 },
+                end: { lineNumber: 2, column: 12, byteOffset: 11 },
+            },
+        ];
+
+        // Before target line
+        expect(computeLineHighlightRanges(ranges, 1, 30)).toEqual([]);
+
+        // On target line: column 5 (0-indexed 4) to column 12 (0-indexed 11)
+        expect(computeLineHighlightRanges(ranges, 2, 30)).toEqual([
+            { from: 4, to: 11 },
+        ]);
+
+        // After target line
+        expect(computeLineHighlightRanges(ranges, 3, 30)).toEqual([]);
+    });
+
+    it('correctly splits multi-line ranges across start, intermediate, and end lines', () => {
+        const multilineRange: SourceRange = {
+            start: { lineNumber: 1, column: 15, byteOffset: 14 },
+            end: { lineNumber: 3, column: 10, byteOffset: 50 },
+        };
+
+        const line1 = 'const handleOrder = async ('; // length 27
+        const line2 = '    userId: string,';        // length 19
+        const line3 = '    items: CartItem[]';      // length 21
+        const line4 = ');';                         // length 2
+
+        // Line 1: Starts at column 15 (0-indexed 14) and highlights to end of line
+        expect(computeLineHighlightRanges([multilineRange], 1, line1.length)).toEqual([
+            { from: 14, to: line1.length },
+        ]);
+
+        // Line 2 (intermediate line): Highlights entire line (0 to length)
+        expect(computeLineHighlightRanges([multilineRange], 2, line2.length)).toEqual([
+            { from: 0, to: line2.length },
+        ]);
+
+        // Line 3 (end line): Highlights from beginning (0) to end column (0-indexed 9)
+        expect(computeLineHighlightRanges([multilineRange], 3, line3.length)).toEqual([
+            { from: 0, to: 9 },
+        ]);
+
+        // Line 4: Outside range
+        expect(computeLineHighlightRanges([multilineRange], 4, line4.length)).toEqual([]);
+    });
+
+    it('clamps end column to lineLength if end column exceeds line length', () => {
+        const range: SourceRange = {
+            start: { lineNumber: 1, column: 1, byteOffset: 0 },
+            end: { lineNumber: 1, column: 50, byteOffset: 49 },
+        };
+
+        expect(computeLineHighlightRanges([range], 1, 20)).toEqual([
+            { from: 0, to: 20 },
+        ]);
+    });
+
+    it('filters out invalid or empty ranges where to <= from', () => {
+        const emptyRange: SourceRange = {
+            start: { lineNumber: 1, column: 5, byteOffset: 4 },
+            end: { lineNumber: 1, column: 5, byteOffset: 4 },
+        };
+
+        expect(computeLineHighlightRanges([emptyRange], 1, 20)).toEqual([]);
+    });
+
+    it('handles multiple ranges on the same line', () => {
+        const ranges: SourceRange[] = [
+            {
+                start: { lineNumber: 1, column: 1, byteOffset: 0 },
+                end: { lineNumber: 1, column: 5, byteOffset: 4 },
+            },
+            {
+                start: { lineNumber: 1, column: 10, byteOffset: 9 },
+                end: { lineNumber: 1, column: 15, byteOffset: 14 },
+            },
+        ];
+
+        expect(computeLineHighlightRanges(ranges, 1, 30)).toEqual([
+            { from: 0, to: 4 },
+            { from: 9, to: 14 },
+        ]);
+    });
+});

packages/web/src/app/(app)/components/lightweightCodeHighlighter.tsx

@@ -30,6 +30,37 @@ const MAX_NUMBER_OF_CHARACTER_PER_LINE = 1000;
  * 
  * Inspired by: https://github.com/craftzdog/react-codemirror-runmode
  */
+/**
+ * Calculates 0-based character ranges to highlight on a specific line from 1-based SourceRanges,
+ * handling single-line, start, intermediate, and end lines of multi-line ranges.
+ */
+export const computeLineHighlightRanges = (
+    highlightRanges: SourceRange[] | undefined,
+    lineNumber: number,
+    lineLength: number,
+): { from: number; to: number }[] => {
+    if (!highlightRanges || highlightRanges.length === 0) {
+        return [];
+    }
+
+    return highlightRanges
+        .filter(
+            (range) =>
+                lineNumber >= range.start.lineNumber &&
+                lineNumber <= range.end.lineNumber,
+        )
+        .map((range) => {
+            const isStart = range.start.lineNumber === lineNumber;
+            const isEnd = range.end.lineNumber === lineNumber;
+
+            const from = isStart ? Math.max(0, range.start.column - 1) : 0;
+            const to = isEnd ? Math.min(lineLength, range.end.column - 1) : lineLength;
+
+            return { from, to };
+        })
+        .filter((range) => range.to > range.from);
+};
+
 export const LightweightCodeHighlighter = memo<LightweightCodeHighlighter>((props: LightweightCodeHighlighter) => {
     const {
         language,
@@ -64,13 +95,11 @@ export const LightweightCodeHighlighter = memo<LightweightCodeHighlighter>((prop
                 .map(async (line, index) => {
                     const lineNumber = index + lineNumbersOffset;
 
-                    // @todo: we will need to handle the case where a range spans multiple lines.
-                    const ranges = highlightRanges?.filter(range => {
-                        return range.start.lineNumber === lineNumber || range.end.lineNumber === lineNumber;
-                    }).map(range => ({
-                        from: range.start.column - 1,
-                        to: range.end.column - 1,
-                    }));
+                    const ranges = computeLineHighlightRanges(
+                        highlightRanges,
+                        lineNumber,
+                        line.length,
+                    );
 
                     const snippets = await highlightCode(
                         language,