Support GOV.UK Frontend v5 plugin

[nataliecarey]

What

GOV.UK Frontend v5 changes must be handled by the Prototype Kit to prevent broken prototypes and support issues

A test version (or pre-release) will be ready for teams to test at the end of October 2023. This gives us an opportunity to receive feedback and make necessary changes before a full release. We expect that the full release will be ready between November and December 2023.

To reduce impact on the team, management and error pages should stay on GOV.UK Frontend v4 for now

We also have various package files using $legacy parameters now deprecated in GOV.UK Frontend v5. We should suppress these deprecation warnings until the following files can be updated:

• govuk-prototype-kit/lib/assets/sass/patterns/_pagination.scss
• govuk-prototype-kit-step-by-step/sass/_step-by-step-navigation.scss
• govuk-prototype-kit-step-by-step/sass/_step-by-step-navigation-header.scss

Why

GOV.UK Frontend v5 is a breaking change due to:

1. Compiled assets, fonts, views, scripts, stylesheets moving into child directory
2. JavaScript includes switching from <script> to <script type="module">
3. Legacy colour palette is now deprecated

The legacy palette was replaced in GOV.UK Frontend v3.0.0:
https://designnotes.blog.gov.uk/2019/07/29/weve-updated-the-gov-uk-colours-and-font/

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• Update management and error pages to use only "internal" GOV.UK Frontend
• Support added for <script type="module"> plugin scripts
• Suppress Sass warnings for $legacy deprecated colour palette
• Defer prototype application.js to load after plugin scripts

[colinrotherham]

I've update the description to include all known remaining tasks

[colinrotherham]

Just an update to track progress a little better

The following changes were made by the Prototype Kit team:

• Plugin authors can now use scripts with type module #2088
• Make the manage prototype pages independent of the govuk-frontend plugin #2118
• Using internal Govuk Frontend more widely #2317
• Add metadata to Prototype Kit plugin config govuk-frontend#4101

With support fixes contributed by GOV.UK Frontend:

• Locate GOV.UK Frontend using require.resolve() #2306
• Fix errors.json logging ENOENT: no such file or directory #2332
• Fix error server /manage-prototype/dependencies #2333
• Fix GOV.UK Frontend initAll() on management pages #2349
• Prevent management pages using "plugin" GOV.UK Frontend views #2355

But with extra backwards compatibility considerations from GOV.UK Frontend too:

• Bump govuk-frontend from 4.5.0 to 4.7.0 #2334
• Suppress Sass warnings for $legacy deprecated colour palette #2358
• Defer prototype application.js to load after plugin scripts #2359

[colinrotherham]

I think this one is done now? Management pages will be updated in:

• Use GOV.UK Frontend v5 on management pages and tests #2327