Add support for .mjs extension from dependencies (such as graphql)

[christemple]

Here is the fix for supporting .mjs files from dependencies referenced here: #4637

I've verified the changes both before and after, here's the after screenshot:

I tried writing some tests for the .mjs support but failed to get the e2e docker tests running on my local machine after following this guide (was failing with user permissions?)

I'm hoping that CI will pick it up and run smoothly, if not I'd really appreciate some help in getting the tests to run locally 👍

[christemple]

Also I just noticed there's been some auto-formatting committed, if you're unhappy with it I'll be happy to remove it

[Timer]

Why does this fix work? Why not include everything and only node_modules?

[Timer]

Per your comment here (#4637 (comment)) it seems this isn't a bug that needs fixed.

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[bugzpodder]

i messed up the autoformatting a while ago, it's ok to include it.

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[christemple]

@Timer I'm a bit confused about your not needing fixed comment, my comment on #4637 (comment) is implying that this is still an issue that needs addressed, I tried the suggested steps and due to semver issues with the sha in the package version it installed a previous version of react-scripts that wasn't using Webpack 4. That's why it appeared as if there was no error.

I've provided an explanation as to why the issue is being caused in the issue

The solution that I am proposing in this PR is to change the default behaviour in Webpack 4 of how it treats .mjs files.

While I suspect the graphql package is the culprit here and isn't producing a valid .mjs compatible package, I am also weary that it may be the first of many.

The change that I've made in the webpack config instructs webpack to treat .mjs files from dependencies exactly like it was in Webpack 3.

I believe doing so will result in a smoother 2.0 milestone release for create-react-app as we'll still get most of the benefits of Webpack 4 without having external dependencies hinder our user experience.

At least until .mjs becomes more widespread and issues get ironed out.

[christemple]

Also, I struggled to get the tests to run on my machine but hoped CI would be more reliable, but it looks like PRs being raised for a simple documentation change is breaking CI.

Are the tests currently stable in next?

Thanks

[Timer]

This looks more like a webpack bug, can we report it there?
Also, tests currently are not stable.

[christemple]

@Timer I'm in the process of narrowing down the issue with either webpack or graphql, and plan on raising issues where appropriate.

However I believe it still makes sense to include the config to mitigate the issue (and possible future ones) in the mean time to prevent blocking the 2.0 milestone release?

[Timer]

Looking at the source makes graphql look fine: https://unpkg.com/[email protected]/jsutils/instanceOf.mjs

And not necessarily, if this is a webpack bug it will be fixed before the 2.0 release and the 2.0 is probably 2-3 months away still.
If users need the old functionality they can use the previous alpha, it is alpha software after all. 😄

[Timer]

We dropped all .mjs support for now. Thanks for your time, though!