MDXv2: non-Story Canvas content shows "no code available"

[vgpena]

Describe the bug
With MDXv2 turned on, if I create a docs page in MDX and add a <Canvas> to that page that doesn't contain <Story> content, the "Show code" button on that <Canvas> says "No code available".

Related to #17514

To Reproduce
Code: https://github.com/vgpena/sb-mdx (see stories/Test.stories.mdx)
Hosted copy: https://vgpena.github.io/sb-mdx/?path=/story/test--page

System
Environment Info:

System:
OS: macOS 12.1
CPU: (10) arm64 Apple M1 Pro
Binaries:
Node: 16.14.0 - ~/.nvm/versions/node/v16.14.0/bin/node
Yarn: 1.22.18 - ~/.yarn/bin/yarn
npm: 8.3.1 - ~/.nvm/versions/node/v16.14.0/bin/npm
Browsers:
Chrome: 102.0.5005.61
Safari: 15.2

Additional context
<Canvas> blocks that include <Story> content continue to have the "Show code" button as expected.

[zhyd1997]

Submitted a PR here: storybookjs/mdx2-csf#16

[shilman]

Jeepers creepers!! I just released https://github.com/storybookjs/storybook/releases/tag/v7.0.0-alpha.48 containing PR #19766 that references this issue. Upgrade today to the @next NPM tag to try it out!

npx sb upgrade --prerelease

Closing this issue. Please re-open if you think there's still more to do.

[wdavidw]

I have tried versions ^7.0.0-beta.19 and the issue is still present. For example, the code

<Canvas>
  <button
    className={clsx(
      "block bg-cyan-500",
      "focus:ring-2 focus:ring-indigo-500 focus:ring-offset-2",
      "rounded-full w-5 h-5",
    )}
  />
</Canvas>

Yields to

By the way, also notice the fixed height in Firefox mentionned in #13814