Addon-docs: Fix source block error on dynamically-generated stories

[jakubriedl]

Issue:
Docs page throw an error Cannot read property 'startBody' of undefined when using generated stories because it cannot get its source code from locationsMap.

TypeError
Cannot read property 'startBody' of undefined
Call Stack
 extractSource  vendors~main.3cb0f4d0aaa9b1174e6e.bundle.js:87896:24
 extract  vendors~main.3cb0f4d0aaa9b1174e6e.bundle.js:64109:43
 enhanceSource  vendors~main.3cb0f4d0aaa9b1174e6e.bundle.js:64126:15
 getSnippet  vendors~main.3cb0f4d0aaa9b1174e6e.bundle.js:63520:51
 undefined  vendors~main.3cb0f4d0aaa9b1174e6e.bundle.js:63537:14
 getSourceProps  vendors~main.3cb0f4d0aaa9b1174e6e.bundle.js:63534:24
 getPreviewProps  vendors~main.3cb0f4d0aaa9b1174e6e.bundle.js:62648:48
 Canvas  vendors~main.3cb0f4d0aaa9b1174e6e.bundle.js:62661:22
 renderWithHooks  vendors~main.3cb0f4d0aaa9b1174e6e.bundle.js:250003:18

What I did

The fix is using the same simple fallback to the whole story file code same as when locationsMap is not passed from caller few lines above.

How to test

To simulate the situation it requires quite specific situation where we generate stories based on api response. (Note everything works well for us this way except the docs throw mentioned error).

story:

export default {
   title: "Some Title"
}

export const Default = () => <Component />

generateStories("Some Title", Default)

async function generateStories(title, BaseStory) {
   const data = await (await fetch("...")).json()
   storyStore?.startConfiguring()
   const stories = storiesOf(title, module)
   for(const item of data) {
       stories.add(title, BaseStory, {
           providedData: item 
       })
   }
   storyStore?.finishConfiguring()
}

• Is this testable with Jest or Chromatic screenshots? (nope)
• Does this need a new example in the kitchen sink apps? (nope)
• Does this need an update to the documentation? (nope)

If your answer is yes to any of these, please make sure to include it in your PR.

[shilman]

LGTM. that said, i would highly discourage this pattern. we're planning to deprecate the storiesOf API in favor of statically analyzable CSF.

[jakubriedl]

Thanks for approving and merging this.

If you plan to deprecate "storiesOf" will be there some other way how to do stories generation? We use all possible variations of API responses to generate and validate how our UI will react to it. It is for us super valuable way of testing.