feat(module): support src as a function in addModule (#4956)

packages/core/src/module.js

@@ -115,8 +115,8 @@ export default class ModuleContainer {
     let options
     let handler
 
-    // Type 1: String
-    if (typeof moduleOpts === 'string') {
+    // Type 1: String or Function
+    if (typeof moduleOpts === 'string' || typeof moduleOpts === 'function') {
       src = moduleOpts
     } else if (Array.isArray(moduleOpts)) {
       // Type 2: Babel style array
@@ -126,6 +126,11 @@ export default class ModuleContainer {
       ({ src, options, handler } = moduleOpts)
     }
 
+    // Define handler if src is a function
+    if (typeof src === 'function') {
+      handler = src
+    }
+
     // Resolve handler
     if (!handler) {
       handler = this.nuxt.resolver.requireModule(src)

packages/core/test/module.test.js

@@ -309,6 +309,31 @@ describe('core: module', () => {
     expect(result).toEqual({ src: 'moduleTest', options: {} })
   })
 
+  test('should add function module', async () => {
+    const module = new ModuleContainer({
+      resolver: { requireModule },
+      options: {}
+    })
+
+    const functionModule = function (options) {
+      return Promise.resolve(options)
+    }
+
+    functionModule.meta = { name: 'moduleTest' }
+
+    const result = await module.addModule(functionModule)
+
+    expect(requireModule).not.toBeCalled()
+    expect(module.requiredModules).toEqual({
+      moduleTest: {
+        handler: expect.any(Function),
+        options: undefined,
+        src: functionModule
+      }
+    })
+    expect(result).toEqual({ })
+  })
+
   test('should add array module', async () => {
     const module = new ModuleContainer({
       resolver: { requireModule },