Build tasks: Move review app tasks into app/tasks

[colinrotherham]

This PR splits out all "Review app" tasks into app/tasks as part of:

• Split project into separate app, config, lib and tasks packages #2886

This reduces the risk of affecting govuk-frontend output by keeping each build separate:

1. Project-level ./tasks via gulpfile.mjs
2. Review app ./app/tasks via app/gulpfile.mjs

├── app
│   ├── dist
│   ├── src
│   └── tasks
└── tasks

Creating tasks

Whilst Gulp is still used as a task runner, I've switched to the export your tasks pattern vs using gulp.task()

Reminder: This API isn't the recommended pattern anymore - export your tasks.

All our new tasks are now plain async functions:

await files.copy('**/*', {
  srcPath: join(paths.src, 'govuk/assets'),
  destPath: join(paths.app, 'dist/assets')
})

But they can be composed into tasks for Gulp's gulp.series() and gulp.parallel() etc

task.name('copy:assets', () => files.copy('**/*', {
  srcPath: join(paths.src, 'govuk/assets'),
  destPath: join(paths.app, 'dist/assets')
}))

[romaricpascal]

I think it's almost there, just had a couple of questions and little things in the comments 😄 Cheers for the move to plain functions with task.name and the genral tidy up.

[romaricpascal]

I think the naming works, run makes it clear that something will happen while script sounds more like something you'll reference in a variable for later 🙌🏻

[romaricpascal]

question: Wouldn't running the prestart build script guarantee that our tests run against the last build of the server? Is it run some other way?

[colinrotherham]

This is a learning from the GOV.UK Design System
https://github.com/alphagov/govuk-design-system/blob/main/jest-puppeteer.config.js#L6

Every time you run npm test or npx jest ./path/to/spec.test.js it does a full rebuild each time

So here we cheat and give Jest permission to run what's already built

For anyone else running npm start I'd like it to stay nice and simple and build first 😊

Well spotted though

[romaricpascal]

nitpick As we're looking at reducing the complexity of our build, I think I'd be keen to avoid that prestart step that magically links the build to all our start calls. It also allows to keep the build and the start of the app separate without having to know that you need to reach for --ignore-scripts (which is a bit arcane).

I think it'll only be used on heroku so could we maybe make things explicit in the Procfile with something like (cd app && run build && npm start) (or with two --workspace app on each command).

[colinrotherham]

Would you mind if we kept npm start?

Keeps things simple

Although perhaps in future should align start/dev?

Server start

npm start
npm start --workspace app
npm start --workspace docs/examples/webpack

Development

npm run dev
npm run dev --workspace app
npm run dev --workspace docs/examples/webpack

But for now we have a necessary mismatch with npm start at project-level running this:

npm run dev --workspace app

[colinrotherham]

Need to make sure we skip the prestart build here (as it's cached in GitHub Actions)

Suggested change

	run: npm start --workspace app &
	# Start Express.js without "prestart" build script
	run: npm start --ignore-scripts --workspace app &