Storybook comes up empty with 6.4.0-alpha.20 and later (it's ok up to 6.4.0-alpha.19)

Describe the bug When I update the version of @storybook/react and related @storybook packages to 6.4.0-alpha.20 or above, my storybook comes up empty. With previous versions of storybook, up to and including 6.4.0-alpha.19, it comes up fine with stories in. I wonder if there is a regression in #15399. NB our storybook is produced with a list of explicit files, not a glob.

To Reproduce Here is a cut-down version of our repo: https://github.com/dcwarwick/ibm-cloud-cognitive/tree/storybook-640alpha20

To reproduce:

• clone that branch
• run yarn and yarn:storybook
• Storybook comes up empty (“Oh no! Your Storybook is empty.”)

If the @storybook versions in /packages/core/package.json are pulled back to 6.4.0-alpha.19 or below, yarn:storybook will produce a storybook with stories in as expected.

Here is a running instance of the above branch: https://deploy-preview-1108--ibm-cloud-cognitive.netlify.app/

Here is a running instance of the full repo using @storybook version 6.3.6: https://ibm-cloud-cognitive.netlify.app/?path=/story/cloud-cognitive-released-aboutmodal--about-modal

System Please paste the results of npx sb@next info here.

$ npx sb@next info

Environment Info:

  System:
    OS: macOS 11.4
    CPU: (16) x64 Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
  Binaries:
    Node: 14.16.0 - ~/.nvm/versions/node/v14.16.0/bin/node
    Yarn: 1.22.10 - /usr/local/bin/yarn
    npm: 6.14.11 - ~/.nvm/versions/node/v14.16.0/bin/npm
  Browsers:
    Chrome: 92.0.4515.131
    Firefox: 88.0.1
    Safari: 14.1.1

Additional context The storybook configuration files are all in /packages/core.

I’ve produced a cut-down version of our real-life case rather than attempting to make a minimal reproduction, as I suspect there is something significant in the way we have configured storybook and it might be difficult to recreate that from scratch.

Here is the module.exports from our main.js:

{
  core: { builder: 'webpack5' },
  addons: [
    '@storybook/addon-actions',
    '@storybook/addon-docs',
    '@storybook/addon-controls',
    '@storybook/addon-knobs',
    '@storybook/addon-storysource',
    '@storybook/addon-viewport',
    '@carbon/storybook-addon-theme/register'
  ],
  reactOptions: { strictMode: true },
  stories: [
    '/Users/dave/git/ibm-cloud-cognitive/packages/cloud-cognitive/src/components/AboutModal/AboutModal.stories.js',
    '/Users/dave/git/ibm-cloud-cognitive/packages/core/docs/getting-started.stories.mdx'
  ],
  webpackFinal: [AsyncFunction: webpackFinal]
}

[shilman]

Huzzah!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.4.0-alpha.25 containing PR #15775 that references this issue. Upgrade today to the @next NPM tag to try it out!

npx sb upgrade --prerelease

[lkuechler]

@shilman I have created a PR that should solve this issue. #15775

@dcwarwick thank you for the detailed analysis and the suggestion on how to solve this. Could you check if the test really matches with the issue that you where having?