feat(core, cli): Introduce high-performance FileSearch engine (#5136)

Co-authored-by: Jacob Richman <jacob314@gmail.com>

packages/test-utils/src/file-system-test-helpers.ts

@@ -0,0 +1,98 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as fs from 'fs/promises';
+import * as path from 'path';
+import * as os from 'os';
+
+/**
+ * Defines the structure of a virtual file system to be created for testing.
+ * Keys are file or directory names, and values can be:
+ * - A string: The content of a file.
+ * - A `FileSystemStructure` object: Represents a subdirectory with its own structure.
+ * - An array of strings or `FileSystemStructure` objects: Represents a directory
+ *   where strings are empty files and objects are subdirectories.
+ *
+ * @example
+ * // Example 1: Simple files and directories
+ * const structure1 = {
+ *   'file1.txt': 'Hello, world!',
+ *   'empty-dir': [],
+ *   'src': {
+ *     'main.js': '// Main application file',
+ *     'utils.ts': '// Utility functions',
+ *   },
+ * };
+ *
+ * @example
+ * // Example 2: Nested directories and empty files within an array
+ * const structure2 = {
+ *   'config.json': '{ "port": 3000 }',
+ *   'data': [
+ *     'users.csv',
+ *     'products.json',
+ *     {
+ *       'logs': [
+ *         'error.log',
+ *         'access.log',
+ *       ],
+ *     },
+ *   ],
+ * };
+ */
+export type FileSystemStructure = {
+  [name: string]:
+    | string
+    | FileSystemStructure
+    | Array<string | FileSystemStructure>;
+};
+
+/**
+ * Recursively creates files and directories based on the provided `FileSystemStructure`.
+ * @param dir The base directory where the structure will be created.
+ * @param structure The `FileSystemStructure` defining the files and directories.
+ */
+async function create(dir: string, structure: FileSystemStructure) {
+  for (const [name, content] of Object.entries(structure)) {
+    const newPath = path.join(dir, name);
+    if (typeof content === 'string') {
+      await fs.writeFile(newPath, content);
+    } else if (Array.isArray(content)) {
+      await fs.mkdir(newPath, { recursive: true });
+      for (const item of content) {
+        if (typeof item === 'string') {
+          await fs.writeFile(path.join(newPath, item), '');
+        } else {
+          await create(newPath, item as FileSystemStructure);
+        }
+      }
+    } else if (typeof content === 'object' && content !== null) {
+      await fs.mkdir(newPath, { recursive: true });
+      await create(newPath, content as FileSystemStructure);
+    }
+  }
+}
+
+/**
+ * Creates a temporary directory and populates it with a given file system structure.
+ * @param structure The `FileSystemStructure` to create within the temporary directory.
+ * @returns A promise that resolves to the absolute path of the created temporary directory.
+ */
+export async function createTmpDir(
+  structure: FileSystemStructure,
+): Promise<string> {
+  const tmpDir = await fs.mkdtemp(path.join(os.tmpdir(), 'gemini-cli-test-'));
+  await create(tmpDir, structure);
+  return tmpDir;
+}
+
+/**
+ * Cleans up (deletes) a temporary directory and its contents.
+ * @param dir The absolute path to the temporary directory to clean up.
+ */
+export async function cleanupTmpDir(dir: string) {
+  await fs.rm(dir, { recursive: true, force: true });
+}