bun.sh/test/js/node/module/require-extensions.test.ts

import assert from "assert";
import { test, mock, expect } from "bun:test";
import { tempDirWithFiles } from "harness";
import path from "path";

test("require.extensions shape makes sense", () => {
  const extensions = require.extensions;
  expect(extensions).toBeDefined();
  expect(typeof extensions).toBe("object");
  expect(extensions[".js"]).toBeFunction();
  expect(extensions[".json"]).toBeFunction();
  expect(extensions[".node"]).toBeFunction();
  // When --experimental-strip-types is passed, TypeScript files can be loaded.
  expect(extensions[".cts"]).toBeFunction();
  expect(extensions[".ts"]).toBeFunction();
  expect(extensions[".mjs"]).toBeFunction();
  expect(extensions[".mts"]).toBeFunction();
  expect(require('module')._extensions === require.extensions).toBe(true);
});
test("custom require extension 1", () => {
  const custom = require.extensions['.custom'] = mock(function (module, filename) {
    expect(filename).toBe(path.join(import.meta.dir, 'extensions-fixture', 'c.custom'));
    (module as any)._compile(`module.exports = 'custom';`, filename);
  });
  const mod = require('./extensions-fixture/c');
  expect(mod).toBe('custom');
  expect(custom.mock.calls.length).toBe(1);
  delete require.extensions['.custom'];
  expect(() => require('./extensions-fixture/c')).toThrow(/Cannot find module/);
  expect(require('./extensions-fixture/c.custom')).toBe('custom'); // already loaded
  delete require.cache[require.resolve('./extensions-fixture/c.custom')];
  expect(custom.mock.calls.length).toBe(1);
  expect(require('./extensions-fixture/c.custom')).toBe('c dot custom'); // use js loader
});
test("custom require extension overwrite default loader", () => {
  const original = require.extensions['.js'];
  try {
    const custom = require.extensions['.js'] = mock(function (module, filename) {
      expect(filename).toBe(path.join(import.meta.dir, 'extensions-fixture', 'd.js'));
      (module as any)._compile(`module.exports = 'custom';`, filename);
    });
    const mod = require('./extensions-fixture/d');
    expect(mod).toBe('custom');
    expect(custom.mock.calls.length).toBe(1);
    require.extensions['.js'] = original;
    expect(require('./extensions-fixture/d')).toBe('custom'); // already loaded
    delete require.cache[require.resolve('./extensions-fixture/d')];
    expect(custom.mock.calls.length).toBe(1);
    expect(require('./extensions-fixture/d')).toBe('d.js'); // use js loader
  } finally {
    require.extensions['.js'] = original;
  }
});
test("custom require extension overwrite default loader with other default loader", () => {
  const original = require.extensions['.js'];
  try {
    require.extensions['.js'] = require.extensions['.ts']!;
    const mod = require('./extensions-fixture/e.js'); // should not enter JS
    expect(mod).toBe('hello world');
  } finally {
    require.extensions['.js'] = original;
  }
});
test("test that assigning properties weirdly wont do anything bad", () => {
  const original = require.extensions['.js'];
  try {
    function f1() {}
    function f2() {}
    require.extensions['.js'] = f1;
    require.extensions['.abc'] = f2;
    require.extensions['.js'] = f2;
    require.extensions['.js'] = undefined!;
    require.extensions['.abc'] = undefined!;
    require.extensions['.abc'] = f1;
    require.extensions['.js'] = f2;
  } finally {
    require.extensions['.js'] = original;
  }
});
test("wrapping an existing extension with no logic", () => {
  const original = require.extensions['.js'];
  try {
    delete require.cache[require.resolve('./extensions-fixture/d')];
    const mocked = require.extensions['.js'] = mock(function (module, filename) {
      expect(module).toBeDefined();
      expect(filename).toBe(path.join(import.meta.dir, 'extensions-fixture', 'd.js'));
      original(module, filename);
    });
    const mod = require('./extensions-fixture/d');
    expect(mod).toBe('d.js');
    expect(mocked).toBeCalled();
  } finally {
    require.extensions['.js'] = original;
  }
});
test("wrapping an existing extension with mutated compile function", () => {
  const original = require.extensions['.js'];
  try {
    delete require.cache[require.resolve('./extensions-fixture/d')];
    const mocked = require.extensions['.js'] = mock(function (module, filename) {
      expect(module).toBeDefined();
      expect(filename).toBe(path.join(import.meta.dir, 'extensions-fixture', 'd.js'));
      const originalCompile = module._compile;
      module._compile = function (code, filename) {
        expect(code).toBe('\n  module.exports = \"d.js\";\n');
        expect(filename).toBe(path.join(import.meta.dir, 'extensions-fixture', 'd.js'));
        originalCompile.call(module, 'module.exports = "new";', filename);
      };
      original(module, filename);
    });
    const mod = require('./extensions-fixture/d');
    expect(mod).toBe('new');
    expect(mocked).toBeCalled();
  } finally {
    require.extensions['.js'] = original;
  }
});
test("wrapping an existing extension with mutated compile function ts", () => {
  const original = require.extensions['.ts'];
  assert(original);
  try {
    delete require.cache[require.resolve('./extensions-fixture/e.js')];
    const mocked = require.extensions['.js'] = mock(function (module, filename) {
      expect(module).toBeDefined();
      expect(filename).toBe(path.join(import.meta.dir, 'extensions-fixture', 'e.js'));
      const originalCompile = module._compile;
      module._compile = function (code, filename) {
        expect(code).toBe('\n  var J;\n  ((J) => J.x = \"hello\")(J ||= {});\n  const hello = \" world\";\n  module.exports = \"hello world\";\n');
        expect(filename).toBe(path.join(import.meta.dir, 'extensions-fixture', 'e.js'));
        originalCompile.call(module, 'module.exports = "new";', filename);
      };
      original(module, filename);
    });
    const mod = require('./extensions-fixture/e');
    expect(mod).toBe('new');
    expect(mocked).toBeCalled();
  } finally {
    require.extensions['.js'] = original;
  }
});
test("wrapping an existing extension but it's secretly sync esm", () => {
  const original = require.extensions['.ts'];
  assert(original);
  try {
    delete require.cache[require.resolve('./extensions-fixture/secretly_esm.cjs')];
    let called = false;
    const mocked = require.extensions['.cjs'] = mock(function (module, filename) {
      expect(module).toBeDefined();
      expect(filename).toBe(path.join(import.meta.dir, 'extensions-fixture', 'secretly_esm.cjs'));
      module._compile = function (code, filename) {
        called = true;
        throw new Error('should not be called');
      };
      original(module, filename);
    });
    const mod = require('./extensions-fixture/secretly_esm');
    expect(mod).toEqual({ default: 1 });
    expect(mocked).toBeCalled();
  } finally {
    require.extensions['.cjs'] = original;
  }
});
test("mutating extensions is banned by some files", () => {
  // vercel is not allowed to mutate require.extensions
  const files = [
    'node_modules/next/dist/build/next-config-ts/index.js',
    'node_modules/@meteorjs/babel/index.js',
  ];
  const fixture = tempDirWithFiles('extensions-fixture', 
    Object.fromEntries(files.map(file => [file, `
      const assert = require('assert');
      const mock = function (module, filename) {
        throw new Error('should not be called');
      };
      require.extensions['.js'] = mock;
      assert(require.extensions['.js'] !== mock);
      globalThis.pass += 1;
    `])));
  globalThis.pass = 0;

  let n = 0;
  for (const file of files) {
    require(path.join(fixture, file));
    n++;
    expect(globalThis.pass).toBe(n);
  }
});