feat: support file returning async functions when loading it (#272)

Use Case:

dynamically load mysql connection configuration from a remote config
center to keep it secure.

```ts
// config.default.ts

export default async function() {
  return {
    mysql: {
      ...(await nacos.get('mysqlConfig'))
    }
  };
}
```

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Enhanced asynchronous file loading capabilities, including support for
both CommonJS and ES modules.
- Introduction of new modules that return promises with configuration
data.

- **Bug Fixes**
	- Improved handling of promises in the file loading process.

- **Tests**
- Added multiple test cases to verify the functionality of loading
various types of modules, including asynchronous functions and
promise-based exports.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

src/loader/egg_loader.ts

@@ -2,8 +2,8 @@ import fs from 'node:fs';
 import path from 'node:path';
 import assert from 'node:assert';
 import { debuglog, inspect } from 'node:util';
-import { isAsyncFunction, isClass, isGeneratorFunction, isObject } from 'is-type-of';
 import { homedir } from 'node-homedir';
+import { isAsyncFunction, isClass, isGeneratorFunction, isObject, isPromise } from 'is-type-of';
 import type { Logger } from 'egg-logger';
 import { getParamNames, readJSONSync, readJSON } from 'utility';
 import { extend } from 'extend2';
@@ -1447,6 +1447,9 @@ export class EggLoader {
     let mod = await this.requireFile(fullpath);
     if (typeof mod === 'function' && !isClass(mod)) {
       mod = mod(...inject);
+      if (isPromise(mod)) {
+        mod = await mod;
+      }
     }
     return mod;
   }

test/fixtures/load_file/async.js

@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = async () => {
+  return { clients: "Test Config" };
+};

test/fixtures/load_file/es-module-default-async.js

@@ -0,0 +1,5 @@
+"use strict";
+exports.__esModule = true;
+exports["default"] = async function () {
+  return { clients: "Test Config" };
+};

test/fixtures/load_file/es-module-default-null.js

@@ -0,0 +1,3 @@
+"use strict";
+exports.__esModule = true;
+exports["default"] = null;

test/fixtures/load_file/es-module-default-promise.js

@@ -0,0 +1,5 @@
+"use strict";
+exports.__esModule = true;
+exports["default"] = function () {
+  return Promise.resolve({ clients: "Test Config" });
+};

test/fixtures/load_file/es-module-default.js

@@ -0,0 +1,5 @@
+"use strict";
+exports.__esModule = true;
+exports["default"] = {
+  fn() {}
+};

test/fixtures/load_file/promise_function.js

@@ -0,0 +1,3 @@
+module.exports = function () {
+  return Promise.resolve({ clients: "Test Config" });
+};

test/fixtures/loadfile-esm/es-module-default-async.js

@@ -0,0 +1,4 @@
+"use strict";
+export default async function () {
+  return { clients: "Test Config" };
+};

test/fixtures/loadfile-esm/es-module-default-promise.js

@@ -0,0 +1,4 @@
+"use strict";
+export default function () {
+  return Promise.resolve({ clients: "Test Config" });
+};

test/fixtures/loadfile/es-module-default-async.js

@@ -0,0 +1,5 @@
+"use strict";
+exports.__esModule = true;
+exports["default"] = async function () {
+  return { clients: "Test Config" };
+};

test/fixtures/loadfile/es-module-default-promise.js

@@ -0,0 +1,5 @@
+"use strict";
+exports.__esModule = true;
+exports["default"] = function () {
+  return Promise.resolve({ clients: "Test Config" });
+};

test/loader/load_file.test.ts

@@ -36,4 +36,40 @@ describe('test/loader/load_file.test.ts', () => {
     }
     assert.equal(result, '---\nmap:\n a: 1\n b: 2');
   });
+
+  it('should load cjs module file which returns function returning a promise', async () => {
+    app = createApp('load_file');
+    const result = (await app.loader.loadFile(getFilepath('load_file/promise_function.js')));
+    assert.deepEqual(result, { clients: 'Test Config' });
+  });
+
+  it('should load cjs module file which returns async function', async () => {
+    app = createApp('load_file');
+    const result = (await app.loader.loadFile(getFilepath('load_file/async.js')));
+    assert.deepEqual(result, { clients: 'Test Config' });
+  });
+
+  it('should load compiled es module file', async () => {
+    app = createApp('load_file');
+    const result = (await app.loader.loadFile(getFilepath('load_file/es-module-default.js')));
+    assert(result.fn);
+  });
+
+  it('should load compiled es module file which default = null', async () => {
+    app = createApp('load_file');
+    const result = (await app.loader.loadFile(getFilepath('load_file/es-module-default-null.js')));
+    assert.equal(result, null);
+  });
+
+  it('should load compiled es module file which default = function returning a promise', async () => {
+    app = createApp('load_file');
+    const result = (await app.loader.loadFile(getFilepath('load_file/es-module-default-promise.js')));
+    assert.deepEqual(result, { clients: 'Test Config' });
+  });
+
+  it('should load compiled es module file which default = async function', async () => {
+    app = createApp('load_file');
+    const result = (await app.loader.loadFile(getFilepath('load_file/es-module-default-async.js')));
+    assert.deepEqual(result, { clients: 'Test Config' });
+  });
 });

test/utils/index.test.ts

@@ -57,6 +57,16 @@ describe('test/utils/index.test.ts', () => {
       assert.equal(result, null);
     });
 
+    it('should load es module with default = async function', async () => {
+      const result = await utils.loadFile(path.join(baseDir, 'es-module-default-async.js'));
+      assert(typeof result().then === 'function');
+    });
+
+    it('should load es module with default = function returning a promise', async () => {
+      const result = await utils.loadFile(path.join(baseDir, 'es-module-default-promise.js'));
+      assert(typeof result().then === 'function');
+    });
+
     it('should load no js file', async () => {
       let result = (await utils.loadFile(path.join(baseDir, 'no-js.yml'))).toString();
       if (process.platform === 'win32') {
@@ -110,6 +120,16 @@ describe('test/utils/index.test.ts', () => {
       assert.equal(result, null);
     });
 
+    it('should load es module with default = async function', async () => {
+      const result = await utils.loadFile(path.join(baseDir, 'es-module-default-async.js'));
+      assert(typeof result().then === 'function');
+    });
+
+    it('should load es module with default = function returning a promise', async () => {
+      const result = await utils.loadFile(path.join(baseDir, 'es-module-default-promise.js'));
+      assert(typeof result().then === 'function');
+    });
+
     it('should load no js file', async () => {
       let result = (await utils.loadFile(path.join(baseDir, 'no-js.yml'))).toString();
       if (process.platform === 'win32') {