Addon-docs: Fix MDX IDs from CSF imports

[shilman]

Issue: #12143

This is technically a breaking change but I'd like to treat it as a bugfix since the feature is brand new.

What I did

This is a cheap/hacky way to make sure that the variable is unique.

Consider the following MDX:

import { foo } from './button.stories';

<Story story={foo} />

The compiler was generating the following code (simplified):

import { foo } from './button.stories';

// lots of MDX stuff omitted

export const fooStory = foo;

If I made the export named foo, it would collide with the import name and the generated code would be invalid. However, this modified the Story ID.

This PR modifies the generated code to be:

export const _foo_ = foo;

Which preserves the same ID.

How to test

See attached snapshot & CSF imported MDX example in official-storybook.

[tmeasday]

OK, I guess. Obviously would be better to just transform the import to

import { foo as fooImport } ...

But I guess that's way more complicated.

Was this a new feature in 6.0? Didn't we have this in 5.3?

[shilman]

Yeah, more complicated ☹️

<Story story={ xxx } /> is new in 6.0