From 5a0dcfb2e5be82a88f5223fad5d84a9f06e169af Mon Sep 17 00:00:00 2001
From: neverland <chenjiahan.jait@bytedance.com>
Date: Sat, 8 Aug 2026 10:33:27 +0800
Subject: [PATCH] perf(fmt): avoid absolute path joins in gitignore matching

---
 packages/rstack/src/fmt/discoverPaths.ts       | 18 ++++++++++--------
 .../rstack/tests/fmt/discoverPaths.test.ts     | 17 +++++++++++++++++
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/packages/rstack/src/fmt/discoverPaths.ts b/packages/rstack/src/fmt/discoverPaths.ts
index 6b36951c..fba8da05 100644
--- a/packages/rstack/src/fmt/discoverPaths.ts
+++ b/packages/rstack/src/fmt/discoverPaths.ts
@@ -153,7 +153,8 @@ class GitIgnoreMatcher {
     // Ignore files may disappear or become unreadable during traversal.
     const loading = readFile(path.join(directoryPath, '.gitignore'), 'utf8')
       .then((content) => {
-        this.#matchers.set(directoryPath, ignore().add(content));
+        const relativePath = toPosixPath(this.#resolveRelativePath(directoryPath));
+        this.#matchers.set(relativePath, ignore().add(content));
       })
       .catch(() => undefined);
 
@@ -179,18 +180,19 @@ class GitIgnoreMatcher {
   }
 
   #matches(relativePath: string, isDirectory: boolean): boolean {
+    const pathFromRoot = toPosixPath(relativePath);
+
     // Most repositories only use a root `.gitignore`. Avoid checking every path
     // segment when no nested matcher can override its result.
-    const rootMatcher = this.#matchers.size === 1 ? this.#matchers.get(this.#rootPath) : undefined;
+    const rootMatcher = this.#matchers.size === 1 ? this.#matchers.get('') : undefined;
     if (rootMatcher) {
       // `ignore` expects POSIX separators and uses a trailing slash to distinguish directories.
-      const pathFromMatcher = toPosixPath(relativePath);
-      return rootMatcher.test(isDirectory ? `${pathFromMatcher}/` : pathFromMatcher).ignored;
+      return rootMatcher.test(isDirectory ? `${pathFromRoot}/` : pathFromRoot).ignored;
     }
 
-    const segments = relativePath.split(path.sep);
-    let directoryPath = this.#rootPath;
-    let pathFromMatcher = segments.join('/');
+    const segments = pathFromRoot.split('/');
+    let directoryPath = '';
+    let pathFromMatcher = pathFromRoot;
     let ignored = false;
 
     for (const segment of segments) {
@@ -205,7 +207,7 @@ class GitIgnoreMatcher {
         }
       }
 
-      directoryPath = path.join(directoryPath, segment);
+      directoryPath = directoryPath ? `${directoryPath}/${segment}` : segment;
       pathFromMatcher = pathFromMatcher.slice(segment.length + 1);
     }
 
diff --git a/packages/rstack/tests/fmt/discoverPaths.test.ts b/packages/rstack/tests/fmt/discoverPaths.test.ts
index 6210ba78..22f88b99 100644
--- a/packages/rstack/tests/fmt/discoverPaths.test.ts
+++ b/packages/rstack/tests/fmt/discoverPaths.test.ts
@@ -122,6 +122,23 @@ test('applies nested gitignore rules with child negation', async () => {
   });
 });
 
+test('applies a nested gitignore without a root matcher', async () => {
+  await withTempProject(async (rootPath) => {
+    writeProjectFile(rootPath, 'src/.gitignore', '*.js\n');
+    writeProjectFile(rootPath, 'src/drop.js');
+    writeProjectFile(rootPath, 'src/keep.ts');
+    writeProjectFile(rootPath, 'root.js');
+
+    const files = await discoverFmtPaths({ cwd: rootPath });
+
+    expect(relativePaths(rootPath, files)).toEqual([
+      'root.js',
+      path.join('src', '.gitignore'),
+      path.join('src', 'keep.ts'),
+    ]);
+  });
+});
+
 test('lets explicit files bypass gitignore', async () => {
   await withTempProject(async (rootPath) => {
     writeProjectFile(rootPath, '.gitignore', '/generated/\n');