Passing props into stories through decorators no longer working in Storybook 6.3

Describe the bug Prior to version 6.3 of Storybook, when I create a decorator, I’m able to pass props into it like so

export const withFoobar = (Story, context) => (
  <Story foobar="foo" {...context} />
);

And then I expect to be able to access the props from any story:

const Template = (args, { foobar }) => {
  return (
    <div>
      <Button {...args} />
      <p>
        This value should say 'foo': <code>{foobar}</code>
      </p>
    </div>
  );
};

However, as of 6.3, the props I pass in via the decorator are now undefined.

To Reproduce

https://github.com/JoshTumath/storybook-decorator-props-bug-repro

https://joshtumath.github.io/storybook-decorator-props-bug-repro/?path=/story/example-button--primary&globals=measureEnabled:false

System

Environment Info:

  System:
    OS: macOS 11.4
    CPU: (12) x64 Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
  Binaries:
    Node: 14.15.5 - ~/.nvm/versions/node/v14.15.5/bin/node
    Yarn: 2.4.2 - /usr/local/bin/yarn
    npm: 6.14.11 - ~/.nvm/versions/node/v14.15.5/bin/npm
  Browsers:
    Chrome: 91.0.4472.114
    Safari: 14.1.1
  npmPackages:
    @storybook/addon-actions: ^6.4.0-alpha.4 => 6.4.0-alpha.4 
    @storybook/addon-docs: ^6.4.0-alpha.4 => 6.4.0-alpha.4 
    @storybook/addon-essentials: ^6.4.0-alpha.4 => 6.4.0-alpha.4 
    @storybook/addon-links: ^6.4.0-alpha.4 => 6.4.0-alpha.4 
    @storybook/react: ^6.4.0-alpha.4 => 6.4.0-alpha.4

Additional context None

[shilman]

@JoshTumath Yes, will release in 6.3.x later this week or first thing next

[shilman]

Thanks @JoshTumath. I can confirm this is a regression from 6.2.9 which was introduced in 6.3.0-alpha.15, presumably in this PR: https://github.com/storybookjs/storybook/pull/14692