fix(mock-api): provide an explainatory error message when the mocks API hoisting doesn't work

[gdorsi]

closes #1084

[netlify]

✅ Deploy Preview for vitest-dev ready!

Name	Link
🔨 Latest commit	b3f8dae
🔍 Latest deploy log	https://app.netlify.com/sites/vitest-dev/deploys/624b734902eb560008ea30a7
😎 Deploy Preview	https://deploy-preview-1098--vitest-dev.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[sheremet-va]

I think it's better to move this to factory evaluation, and check for "ReferenceError". The code is in mocker.ts

[sheremet-va]

I think it's better to move this to factory evaluation, and check for "ReferenceError", to show error for any variable that it tries to reach and cant. The code is in mocker.ts

[gdorsi]

Thanks for the review!

Uhm, I'm not sure I fully understand what you mean, this error happens because after the hoising vi.mock is called before the vi variable declaration.

We never reach the factory evaluation (which happens somewhere around here, right?), because the error is raised at the very start of the module execution.

[sheremet-va]

this error happens because after the hoising vi.mock is called before the vi variable declaration.

Yes, that is why I left a review. I don't like raising the error here, I think better to format an error that actually happens, since parsing is unsafe. vi covers only a fracture of possible hoisting errors, so I'd prefer a more general solution.

We never reach the factory evaluation (which happens somewhere around here, right?), because the error is raised at the very start of the module execution.

Evaluation happens here:

vitest/packages/vitest/src/runtime/mocker.ts

Line 97 in b24fb25

private async callFunctionMock(dep: string, mock: () => any) {

[gdorsi]

In this case callFunctionMock is never reached.

I've tried to throw an error at the start of the function:

  private async callFunctionMock(dep: string, mock: () => any) {
    throw new Error('callFunctionMock')

I still get:

ReferenceError: Cannot access '__vite_ssr_import_0__' before initialization

I think better to format an error that actually happen

WDYT if we wrap the hoisted statements in a try/catch?

I'm thinking about something like this:

packages/vitest/src/node/plugins/mock.ts#L29

-    m.prepend(`${m.slice(startIndex, endIndex)}\n`)
+    m.prepend(`try { ${m.slice(startIndex, endIndex)} } catch(err) { isReferenceError(err) ? throw MOCK_ERROR : throw err } \n`)

Anyway, if this becomes too complex we could simply close the PR.

[sheremet-va]

If it will never be reached, then it shouldn't throw, that's the point.

[gdorsi]

I'm still missing the point, sorry 😞

I think that it throws because the vi.mock(module) is executed before the initialization of the vi variable.

I wanted to make the error look better than Cannot access '__vite_ssr_import_0__' before initialization because it doesn't even mention real the source of the error.

I'm very new to this codebase, so I'm sure I'm missing something big.

[sheremet-va]

I'm still missing the point, sorry 😞

I think that it throws because the vi.mock(module) is executed before the initialization of the vi variable.

I wanted to make the error look better than Cannot access '__vite_ssr_import_0__' before initialization because it doesn't even mention real the source of the error.

I'm very new to this codebase, so I'm sure I'm missing something big.

Oh, wait, you are write. I was thinking about usage inside factory, but it will throw on initializing vi.mock. Sorry, I got confused!