Including the JavaScript source map in the prototype kit config

[nataliecarey]

A fix for #3254

[colinrotherham]

Thanks @nataliecarey

Would you mind updating the *.mjs file instead of the *.js
./src/govuk-prototype-kit/govuk-prototype-kit.config.mjs#L30

We've generated it since this PR

• Support Prototype Kit v13 #2851

@36degrees Will we want to add tests for "expected source maps" like we do in this one?
./tasks/gulp/tests/after-build-package.test.mjs

For example we also have:

/govuk/common.js.map
/govuk/i18n.js.map

We can either choose to exclude these, or otherwise ensure we include them?

I'm not too familiar with the Prototype Kit but lots of other tooling has "load maps" options where source maps from other files can be included to supplement stack traces etc

Gulp source maps (example)
https://github.com/gulp-sourcemaps/gulp-sourcemaps#load-existing-source-maps

gulp.src('src/**/*.js')
  .pipe(sourcemaps.init({ loadMaps: true }))

[colinrotherham]

Brilliant, thanks @nataliecarey

Before we approve would you mind dropping the ./package/** changes? My fault for not explaining, we'll hold off any dist or package builds for a release commit:

(Here's the one from v4.5.0 5bc602a)

[nataliecarey]

Thanks Colin, re-reading your comment it was clear but I missed it. I've reverted the package changes and force pushed to keep the package history in tact.

[colinrotherham]

Thanks @nataliecarey

I'm thinking those paths need to be /govuk-prototype-kit /govuk and not forgetting all.js.map?

'/govuk/assets',
'/govuk/all.js.map',
'/govuk/common.js.map',
'/govuk/i18n.js.map'

Sorry for causing all this hassle

[colinrotherham]

@nataliecarey Do you want us to pick this up?

We've added #3254 to our next release milestone

[romaricpascal]

@nataliecarey Colin and I picked it up to get it through the line and add a CHANGELOG entry. Hope you don't mind 😄