feat: give helpful message, when using vi.mock (#2047)

examples/mocks/test/error-mock.spec.ts

@@ -0,0 +1,8 @@
+vi.mock('../src/default', () => {
+  throw new Error('some error')
+})
+
+test('when using top level variable, gives helpful message', async () => {
+  await expect(() => import('../src/default').then(m => m.default)).rejects
+    .toThrowErrorMatchingInlineSnapshot('"[vitest] There was an error, when mocking a module. If you are using vi.mock, make sure you are not using top level variables inside, since this call is hoisted. Read more: https://vitest.dev/api/#vi-mock"')
+})

examples/mocks/test/factory.test.ts

@@ -48,11 +48,11 @@ vi.mock('../src/default.ts', () => null)
 
 describe('mocking with factory', () => {
   test('missing exports on mock', () => {
-    expect(() => example.default).toThrowError('[vitest] No "default" export is defined on the "mock:/src/example.ts"')
-    expect(() => example.boolean).toThrowError('[vitest] No "boolean" export is defined on the "mock:/src/example.ts"')
-    expect(() => example.object).toThrowError('[vitest] No "object" export is defined on the "mock:/src/example.ts"')
-    expect(() => example.array).toThrowError('[vitest] No "array" export is defined on the "mock:/src/example.ts"')
-    expect(() => example.someClasses).toThrowError('[vitest] No "someClasses" export is defined on the "mock:/src/example.ts"')
+    expect(() => example.default).toThrowError('[vitest] No "default" export is defined on the "/src/example.ts"')
+    expect(() => example.boolean).toThrowError('[vitest] No "boolean" export is defined on the "/src/example.ts"')
+    expect(() => example.object).toThrowError('[vitest] No "object" export is defined on the "/src/example.ts"')
+    expect(() => example.array).toThrowError('[vitest] No "array" export is defined on the "/src/example.ts"')
+    expect(() => example.someClasses).toThrowError('[vitest] No "someClasses" export is defined on the "/src/example.ts"')
   })
 
   it('non-object return on factory gives error', async () => {

packages/vitest/src/runtime/mocker.ts

@@ -106,13 +106,26 @@ export class VitestMocker {
     const cached = this.moduleCache.get(dep)?.exports
     if (cached)
       return cached
-    const exports = await mock()
+    let exports: any
+    try {
+      exports = await mock()
+    }
+    catch (err) {
+      const vitestError = new Error(
+        '[vitest] There was an error, when mocking a module. '
+      + 'If you are using vi.mock, make sure you are not using top level variables inside, since this call is hoisted. '
+      + 'Read more: https://vitest.dev/api/#vi-mock')
+      vitestError.cause = err
+      throw vitestError
+    }
 
     if (exports === null || typeof exports !== 'object')
       throw new Error('[vitest] vi.mock(path: string, factory?: () => unknown) is not returning an object. Did you mean to return an object with a "default" key?')
 
     this.moduleCache.set(dep, { exports })
 
+    const filepath = dep.slice('mock:'.length)
+
     const exportHandler = {
       get(target: Record<string, any>, prop: any) {
         const val = target[prop]
@@ -123,7 +136,7 @@ export class VitestMocker {
             return target.then.bind(target)
         }
         else if (!(prop in target)) {
-          throw new Error(`[vitest] No "${prop}" export is defined on the "${dep}"`)
+          throw new Error(`[vitest] No "${prop}" export is defined on the "${filepath}"`)
         }
 
         return val