feat(utils): implement and test helper function to find nearest file

Author: matejchalk

packages/utils/src/index.ts

@@ -15,6 +15,7 @@ export {
   fileExists,
   filePathToCliArg,
   findLineNumberInText,
+  findNearestFile,
   importModule,
   logMultipleFileResults,
   pluginWorkDir,

packages/utils/src/lib/file-system.ts

@@ -1,7 +1,7 @@
 import { bold, gray } from 'ansis';
 import { type Options, bundleRequire } from 'bundle-require';
 import { mkdir, readFile, readdir, rm, stat } from 'node:fs/promises';
-import { join } from 'node:path';
+import { dirname, join } from 'node:path';
 import { formatBytes } from './formatting';
 import { logMultipleResults } from './log-results';
 import { ui } from './logging';
@@ -120,6 +120,27 @@ export async function crawlFileSystem<T = string>(
   return resultsNestedArray.flat() as T[];
 }
 
+export async function findNearestFile(
+  fileNames: string[],
+  cwd = process.cwd(),
+): Promise<string | undefined> {
+  // eslint-disable-next-line functional/no-loop-statements
+  for (
+    // eslint-disable-next-line functional/no-let
+    let directory = cwd;
+    directory !== dirname(directory);
+    directory = dirname(directory)
+  ) {
+    // eslint-disable-next-line functional/no-loop-statements
+    for (const file of fileNames) {
+      if (await fileExists(join(directory, file))) {
+        return join(directory, file);
+      }
+    }
+  }
+  return undefined;
+}
+
 export function findLineNumberInText(
   content: string,
   pattern: string,

packages/utils/src/lib/file-system.unit.test.ts

@@ -9,6 +9,7 @@ import {
   ensureDirectoryExists,
   filePathToCliArg,
   findLineNumberInText,
+  findNearestFile,
   logMultipleFileResults,
   projectToFilename,
 } from './file-system';
@@ -57,9 +58,9 @@ describe('crawlFileSystem', () => {
   beforeEach(() => {
     vol.fromJSON(
       {
-        ['README.md']: '# Markdown',
-        ['src/README.md']: '# Markdown',
-        ['src/index.ts']: 'const var = "markdown";',
+        'README.md': '# Markdown',
+        'src/README.md': '# Markdown',
+        'src/index.ts': 'const var = "markdown";',
       },
       MEMFS_VOLUME,
     );
@@ -110,6 +111,108 @@ describe('crawlFileSystem', () => {
   });
 });
 
+describe('findNearestFile', () => {
+  it('should find file in current working directory', async () => {
+    vol.fromJSON(
+      {
+        'eslint.config.js': '',
+      },
+      MEMFS_VOLUME,
+    );
+    await expect(findNearestFile(['eslint.config.js'])).resolves.toBe(
+      join(MEMFS_VOLUME, 'eslint.config.js'),
+    );
+  });
+
+  it('should find first matching file in array', async () => {
+    vol.fromJSON(
+      {
+        'eslint.config.cjs': '',
+        'eslint.config.mjs': '',
+      },
+      MEMFS_VOLUME,
+    );
+    await expect(
+      findNearestFile([
+        'eslint.config.js',
+        'eslint.config.cjs',
+        'eslint.config.mjs',
+      ]),
+    ).resolves.toBe(join(MEMFS_VOLUME, 'eslint.config.cjs'));
+  });
+
+  it('should resolve to undefined if file not found', async () => {
+    vol.fromJSON({ '.eslintrc.json': '' }, MEMFS_VOLUME);
+    await expect(
+      findNearestFile([
+        'eslint.config.js',
+        'eslint.config.cjs',
+        'eslint.config.mjs',
+      ]),
+    ).resolves.toBeUndefined();
+  });
+
+  it('should find file in parent directory', async () => {
+    vol.fromJSON(
+      {
+        'eslint.config.js': '',
+        'e2e/main.spec.js': '',
+      },
+      MEMFS_VOLUME,
+    );
+    await expect(
+      findNearestFile(
+        ['eslint.config.js', 'eslint.config.cjs', 'eslint.config.mjs'],
+        join(MEMFS_VOLUME, 'e2e'),
+      ),
+    ).resolves.toBe(join(MEMFS_VOLUME, 'eslint.config.js'));
+  });
+
+  it('should find file in directory multiple levels up', async () => {
+    vol.fromJSON(
+      {
+        'eslint.config.cjs': '',
+        'packages/core/package.json': '',
+      },
+      MEMFS_VOLUME,
+    );
+    await expect(
+      findNearestFile(
+        ['eslint.config.js', 'eslint.config.cjs', 'eslint.config.mjs'],
+        join(MEMFS_VOLUME, 'packages/core'),
+      ),
+    ).resolves.toBe(join(MEMFS_VOLUME, 'eslint.config.cjs'));
+  });
+
+  it("should find file that's nearest to current folder", async () => {
+    vol.fromJSON(
+      {
+        'eslint.config.js': '',
+        'packages/core/eslint.config.js': '',
+        'packages/core/package.json': '',
+      },
+      MEMFS_VOLUME,
+    );
+    await expect(
+      findNearestFile(
+        ['eslint.config.js', 'eslint.config.cjs', 'eslint.config.mjs'],
+        join(MEMFS_VOLUME, 'packages/core'),
+      ),
+    ).resolves.toBe(join(MEMFS_VOLUME, 'packages/core/eslint.config.js'));
+  });
+
+  it('should not find file in sub-folders of current folder', async () => {
+    vol.fromJSON({ 'packages/core/eslint.config.js': '' }, MEMFS_VOLUME);
+    await expect(
+      findNearestFile([
+        'eslint.config.js',
+        'eslint.config.cjs',
+        'eslint.config.mjs',
+      ]),
+    ).resolves.toBeUndefined();
+  });
+});
+
 describe('findLineNumberInText', () => {
   it('should return correct line number', () => {
     expect(