refactor(fmt): reuse relative path resolver

packages/rstack/src/fmt/discoverPaths.ts

@@ -4,6 +4,7 @@ import ignore from 'ignore';
 import isBinaryPath from 'is-binary-path';
 import micromatch from 'micromatch';
 import readdir, { type Dirent, type DirentLike } from 'tiny-readdir';
+import { createRelativePathResolver, type RelativePathResolver } from './relativePath.ts';
 
 const defaultIgnoredDirNames = new Set(['.git', '.sl', '.svn', '.hg', '.jj', 'node_modules']);
 
@@ -38,19 +39,6 @@ const isRelativePathInside = (relativePath: string): boolean =>
 const isPathInside = (rootPath: string, filePath: string): boolean =>
   isRelativePathInside(path.relative(rootPath, filePath));
 
-type RelativePathResolver = (filePath: string) => string;
-
-const createRelativePathResolver = (rootPath: string): RelativePathResolver => {
-  const rootPrefix = rootPath.endsWith(path.sep) ? rootPath : `${rootPath}${path.sep}`;
-
-  return (filePath) =>
-    filePath === rootPath
-      ? ''
-      : filePath.startsWith(rootPrefix)
-        ? filePath.slice(rootPrefix.length)
-        : path.relative(rootPath, filePath);
-};
-
 const toPosixPath = (filePath: string): string =>
   path.sep === '\\' ? filePath.replaceAll('\\', '/') : filePath;
 
@@ -86,14 +74,14 @@ const findGitRoot = async (cwd: string): Promise<string> => {
 
 class GitIgnoreMatcher {
   readonly #rootPath: string;
-  readonly #rootPrefix: string;
+  readonly #resolveRelativePath: RelativePathResolver;
   readonly #matchers = new Map<string, ReturnType<typeof ignore>>();
   readonly #loads = new Map<string, Promise<void>>();
   readonly #ignoredDirectories = new Map<string, boolean>();
 
   private constructor(rootPath: string) {
     this.#rootPath = rootPath;
-    this.#rootPrefix = rootPath.endsWith(path.sep) ? rootPath : `${rootPath}${path.sep}`;
+    this.#resolveRelativePath = createRelativePathResolver(rootPath);
   }
 
   static async create(cwd: string): Promise<GitIgnoreMatcher> {
@@ -103,11 +91,11 @@ class GitIgnoreMatcher {
   }
 
   async loadThrough(directoryPath: string): Promise<void> {
-    if (!isPathInside(this.#rootPath, directoryPath)) {
+    const relativePath = this.#resolveRelativePath(directoryPath);
+    if (!isRelativePathInside(relativePath)) {
       return;
     }
 
-    const relativePath = path.relative(this.#rootPath, directoryPath);
     const segments = relativePath ? relativePath.split(path.sep) : [];
     const loads = [this.#load(this.#rootPath)];
     let currentPath = this.#rootPath;
@@ -121,7 +109,7 @@ class GitIgnoreMatcher {
   }
 
   async load(directoryPath: string): Promise<void> {
-    if (isPathInside(this.#rootPath, directoryPath)) {
+    if (isRelativePathInside(this.#resolveRelativePath(directoryPath))) {
       await this.#load(directoryPath);
     }
   }
@@ -131,12 +119,7 @@ class GitIgnoreMatcher {
       return false;
     }
 
-    const relativePath =
-      filePath === this.#rootPath
-        ? ''
-        : filePath.startsWith(this.#rootPrefix)
-          ? filePath.slice(this.#rootPrefix.length)
-          : path.relative(this.#rootPath, filePath);
+    const relativePath = this.#resolveRelativePath(filePath);
     if (relativePath === '' || !isRelativePathInside(relativePath)) {
       return false;
     }
@@ -175,7 +158,7 @@ class GitIgnoreMatcher {
       return cached;
     }
 
-    relativePath ??= path.relative(this.#rootPath, directoryPath);
+    relativePath ??= this.#resolveRelativePath(directoryPath);
 
     // Git cannot re-include a path below an ignored directory.
     const parentPath = path.dirname(directoryPath);

packages/rstack/src/fmt/ignore.ts

@@ -1,6 +1,7 @@
 import { readFile } from 'node:fs/promises';
 import path from 'node:path';
 import createIgnore from 'ignore';
+import { createRelativePathResolver } from './relativePath.ts';
 import type { ResolvedFmtConfig } from './types.ts';
 
 /**
@@ -28,12 +29,10 @@ const createDefaultIgnoreMatcher = (): IgnoreMatcher => {
 
 const createPatternMatcher = (rootPath: string, patterns: string): IgnoreMatcher => {
   const matcher = createIgnore({ allowRelativePaths: true }).add(patterns);
-  const rootPrefix = rootPath.endsWith(path.sep) ? rootPath : `${rootPath}${path.sep}`;
+  const resolveRelativePath = createRelativePathResolver(rootPath);
 
   return (filePath, isDirectory = false) => {
-    const relativePath = filePath.startsWith(rootPrefix)
-      ? filePath.slice(rootPrefix.length)
-      : path.relative(rootPath, filePath);
+    const relativePath = resolveRelativePath(filePath);
     if (relativePath === '') {
       return false;
     }

packages/rstack/src/fmt/relativePath.ts

@@ -0,0 +1,17 @@
+import path from 'node:path';
+
+type RelativePathResolver = (filePath: string) => string;
+
+const createRelativePathResolver = (rootPath: string): RelativePathResolver => {
+  const rootPrefix = rootPath.endsWith(path.sep) ? rootPath : `${rootPath}${path.sep}`;
+
+  return (filePath) =>
+    filePath === rootPath
+      ? ''
+      : filePath.startsWith(rootPrefix)
+        ? filePath.slice(rootPrefix.length)
+        : path.relative(rootPath, filePath);
+};
+
+export { createRelativePathResolver };
+export type { RelativePathResolver };

packages/rstack/tests/fmt/relativePath.test.ts

@@ -0,0 +1,21 @@
+import path from 'node:path';
+import { expect, test } from 'rstack/test';
+import { createRelativePathResolver } from '../../src/fmt/relativePath.ts';
+
+const rootPath = path.join(import.meta.dirname, 'project');
+
+test('resolves paths relative to a fixed root', () => {
+  const resolveRelativePath = createRelativePathResolver(rootPath);
+
+  expect(resolveRelativePath(rootPath)).toBe('');
+  expect(resolveRelativePath(path.join(rootPath, 'src/index.ts'))).toBe(
+    path.join('src', 'index.ts'),
+  );
+});
+
+test('falls back for paths outside the fixed root', () => {
+  const resolveRelativePath = createRelativePathResolver(rootPath);
+  const siblingPath = path.join(`${rootPath}-other`, 'index.ts');
+
+  expect(resolveRelativePath(siblingPath)).toBe(path.relative(rootPath, siblingPath));
+});