chore(gatsby): upgrade webpack

[wardpeet]

Description

Upgrades webpack to the latest again so we can remove the mjs hack. It got fixed by webpack upgrading to acorn@^6.

I've linked an issue below that seems to have issues with webpack 4.29.0 on npm. I've tried reproduce it with their repo's and npm versions but sadly no way for me to reproduce.

To let people test I created a gatsby version on npm. npm install gatsby@webpack-acorn

Related Issues

#11198
fixes #15775

[freiksenet]

Did you try it with developrunner?

[DSchau]

Marking as blocked until we fix this comment

Also @wardpeet you'll want to remove the .mjs tests for webpack.config :)

[wardpeet]

This is currently blocked by @pieh/friendly-errors-webpack-plugin on npm.

There was a problem loading the local build command. Gatsby may not be installed. Perhaps you need to run "npm install"? Cannot find module 'webpack/lib/RequestShortener'



  Error: Cannot find module 'webpack/lib/RequestShortener'

This is fixed in friendly-errors-webpack-plugin@v2.0.0-beta.2 still in beta.

[pieh]

This is currently blocked by @pieh/friendly-errors-webpack-plugin on npm.

I have to check but maybe we don't need to use my fork anymore

[wardpeet]

@pieh we do, unless we are ok with going for a beta package? Your pr got merged but is only published in the beta package

[pieh]

@pieh we do, unless we are ok with going for a beta package? Your pr got merged but is only published in the beta package

Is the actual error:

  Error: Cannot find module 'webpack/lib/RequestShortener'

fixed there as well?

--edit:
https://github.com/geowarin/friendly-errors-webpack-plugin/blob/master/src/core/extractWebpackError.js
It's still there, so maybe is something we can fix for now in my fork and create another PR against friendly-errors-webpack-plugin (tho not sure how much value is there in this - because we will need to drop that plugin altogether for structured logging)

[sidharthachatterjee]

Looks like Renovate upgraded us to ~4.39.2 (latest) so closing this.

We can open another PR to revert that upgrade if the issue that this was blocked by is still around.