fix(web): match .gitattributes patterns in subdirectories

resolveLanguageFromGitAttributes passed each .gitattributes pattern straight to micromatch against the full repo path. A pattern with no slash, such as `*.h linguist-language=C`, only matched files at the repo root, so the override never applied to `src/foo.h`. Root-anchored patterns like `/config.in` never matched at all. Follow the gitattributes rules: a pattern with no slash matches the file name at any depth; any other pattern is matched from the repository root with a leading slash removed. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
breken-ai · Sep 25, 2026 · Sep 26, 2026 · Sep 27, 2026 · Sep 27, 2026 · Sep 27, 2026
commit 5cb2d5dec973aa4df7d2401b25768b7ab9e5a736
diff --git a/packages/web/src/lib/gitattributes.test.ts b/packages/web/src/lib/gitattributes.test.ts
@@ -0,0 +1,32 @@
+import { describe, expect, test } from 'vitest';
+import { parseGitAttributes, resolveLanguageFromGitAttributes } from './gitattributes';
+
+describe('resolveLanguageFromGitAttributes', () => {
+    test('a pattern without a slash matches files in any directory', () => {
+        const attrs = parseGitAttributes('*.h linguist-language=C\n');
+
+        expect(resolveLanguageFromGitAttributes('foo.h', attrs)).toBe('C');
+        expect(resolveLanguageFromGitAttributes('src/include/foo.h', attrs)).toBe('C');
+    });
+
+    test('a pattern with a leading slash is anchored to the repository root', () => {
+        const attrs = parseGitAttributes('/config.in linguist-language=Makefile\n');
+
+        expect(resolveLanguageFromGitAttributes('config.in', attrs)).toBe('Makefile');
+        expect(resolveLanguageFromGitAttributes('sub/config.in', attrs)).toBeUndefined();
+    });
+
+    test('a pattern with an inner slash is matched relative to the repository root', () => {
+        const attrs = parseGitAttributes('docs/*.txt linguist-language=Markdown\n');
+
+        expect(resolveLanguageFromGitAttributes('docs/intro.txt', attrs)).toBe('Markdown');
+        expect(resolveLanguageFromGitAttributes('other/docs/intro.txt', attrs)).toBeUndefined();
+    });
+
+    test('the last matching rule wins', () => {
+        const attrs = parseGitAttributes('*.inc linguist-language=PHP\nlegacy/*.inc linguist-language=Pascal\n');
+
+        expect(resolveLanguageFromGitAttributes('src/a.inc', attrs)).toBe('PHP');
+        expect(resolveLanguageFromGitAttributes('legacy/a.inc', attrs)).toBe('Pascal');
+    });
+});
diff --git a/packages/web/src/lib/gitattributes.ts b/packages/web/src/lib/gitattributes.ts
@@ -58,13 +58,25 @@ export function parseGitAttributes(content: string): GitAttributes {
     return { rules };
 }
 
+// matchesGitAttributesPattern applies gitattributes pattern rules: a pattern
+// without a slash matches the file name at any depth, and any other pattern
+// is matched against the full path from the repository root.
+// @see https://git-scm.com/docs/gitattributes#_description
+function matchesGitAttributesPattern(filePath: string, pattern: string): boolean {
+    if (!pattern.includes('/')) {
+        const fileName = filePath.slice(filePath.lastIndexOf('/') + 1);
+        return micromatch.isMatch(fileName, pattern, { dot: true });
+    }
+    return micromatch.isMatch(filePath, pattern.replace(/^\//, ''), { dot: true });
+}
+
 // resolveLanguageFromGitAttributes returns the linguist-language override for
 // the given file path based on the parsed .gitattributes rules, or undefined
 // if no rule matches. Last matching rule wins, consistent with gitattributes semantics.
 export function resolveLanguageFromGitAttributes(filePath: string, gitAttributes: GitAttributes): string | undefined {
     let language: string | undefined;
     for (const rule of gitAttributes.rules) {
-        if (micromatch.isMatch(filePath, rule.pattern) && rule.attrs['linguist-language']) {
+        if (matchesGitAttributesPattern(filePath, rule.pattern) && rule.attrs['linguist-language']) {
             language = rule.attrs['linguist-language'];
         }
     }