feat: tab completions for file paths (#279)

Made a PR as was requested in the #113

codex-cli/tests/file-system-suggestions.test.ts

@@ -0,0 +1,73 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import fs from "fs";
+import os from "os";
+import path from "path";
+import { getFileSystemSuggestions } from "../src/utils/file-system-suggestions";
+
+vi.mock("fs");
+vi.mock("os");
+
+describe("getFileSystemSuggestions", () => {
+  const mockFs = fs as unknown as {
+    readdirSync: ReturnType<typeof vi.fn>;
+    statSync: ReturnType<typeof vi.fn>;
+  };
+
+  const mockOs = os as unknown as {
+    homedir: ReturnType<typeof vi.fn>;
+  };
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("returns empty array for empty prefix", () => {
+    expect(getFileSystemSuggestions("")).toEqual([]);
+  });
+
+  it("expands ~ to home directory", () => {
+    mockOs.homedir = vi.fn(() => "/home/testuser");
+    mockFs.readdirSync = vi.fn(() => ["file1.txt", "docs"]);
+    mockFs.statSync = vi.fn((p) => ({
+      isDirectory: () => path.basename(p) === "docs",
+    }));
+
+    const result = getFileSystemSuggestions("~/");
+
+    expect(mockFs.readdirSync).toHaveBeenCalledWith("/home/testuser");
+    expect(result).toEqual([
+      path.join("/home/testuser", "file1.txt"),
+      path.join("/home/testuser", "docs" + path.sep),
+    ]);
+  });
+
+  it("filters by prefix if not a directory", () => {
+    mockFs.readdirSync = vi.fn(() => ["abc.txt", "abd.txt", "xyz.txt"]);
+    mockFs.statSync = vi.fn((p) => ({
+      isDirectory: () => p.includes("abd"),
+    }));
+
+    const result = getFileSystemSuggestions("a");
+    expect(result).toEqual(["abc.txt", "abd.txt/"]);
+  });
+
+  it("handles errors gracefully", () => {
+    mockFs.readdirSync = vi.fn(() => {
+      throw new Error("failed");
+    });
+
+    const result = getFileSystemSuggestions("some/path");
+    expect(result).toEqual([]);
+  });
+
+  it("normalizes relative path", () => {
+    mockFs.readdirSync = vi.fn(() => ["foo", "bar"]);
+    mockFs.statSync = vi.fn((_p) => ({
+      isDirectory: () => true,
+    }));
+
+    const result = getFileSystemSuggestions("./");
+    expect(result).toContain("foo/");
+    expect(result).toContain("bar/");
+  });
+});