Fix: Playground build; Remove @babel/polyfill import from the playground

[jorgefilipecosta]

Description

Removes the @babel/polyfill import from the playground. The screen seems to work as expected without it, and with it, the build fails.

How has this been tested?

I executed npm run playground:start
I verified the build was successful without errors, on master it failed.

Fixes #16082.

[aduth]

The screen seems to work as expected without it, and with it, the build fails.

Do we know any more about what caused this?

[aduth]

The screen seems to work as expected without it, and with it, the build fails.

Do we know any more about what caused this?

My guess: The introduction of the playground in #14497 did not define an explicit dependency on @babel/polyfill despite importing it directly. It should have. It probably worked by virtue of some transitive dependency, which since was lost (possibly a result of recent Babel upgrade in #15139.

The polyfill would be important if we wanted to support older browsers. If we want to, we could just as easily install the @babel/polyfill package as an explicit dependency, which I expect would also fix the issue.

[aduth]

If we want to, we could just as easily install the @babel/polyfill package as an explicit dependency, which I expect would also fix the issue.

Hmm, I tried this in my local copy of the branch and I'm still seeing the error.

🚨  /Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/playground/src/index.js: Cannot resolve dependency 'core-js/modules/es6.array.fill'
    at Resolver.resolve (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/parcel-bundler/src/Resolver.js:71:17)

This despite clearly having installed core-js immediately prior in npm install

> [email protected] postinstall /Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/@babel/polyfill/node_modules/core-js
> node scripts/postinstall || echo "ignore"

Thank you for using core-js ( https://github.com/zloirock/core-js ) for polyfilling JavaScript standard library!
...

[gziolo]

I think I know what the issue is. See in https://unpkg.com/[email protected]/package.json:

"@babel/core": "^7.0.0 <7.4.0",

We use Babel 7.4.x but Parcel is still on lower version …

[youknowriad]

I think I'm fine with this fix until parcel updates to the latest babel version or we move away from parcel.

[jorgefilipecosta]

Thank you for the explorations around this problem, I did not had much information about this problem, but I used this "fix" locally to be able to run the playground. I merged the "fix" for now if someone has a better alternative I think we can discuss it in a follow-up PR.