Add PR diff comments for npm package changes

[colinrotherham]

This PR adds "Diff changes to package" to the Tests GitHub Actions workflow to close #4258

This new workflow adds git diff comments for packages/govuk-frontend/dist in every PR

Diff comment examples

Have a look at 1x small and 1x big example:

• Fix header product name wrapping onto new line #4498 (comment)
• Export type declarations *.d.mts #4094 (comment)

PR diff comments follow the same approach as #4039

[github-actions]

📋 Stats

File sizes

File	Size
dist/govuk-frontend-development.min.css	113.65 KiB
dist/govuk-frontend-development.min.js	38.28 KiB
packages/govuk-frontend/dist/govuk/all.bundle.js	77.78 KiB
packages/govuk-frontend/dist/govuk/all.bundle.mjs	73.09 KiB
packages/govuk-frontend/dist/govuk/all.mjs	3.86 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend-component.mjs	359 B
packages/govuk-frontend/dist/govuk/govuk-frontend.min.css	113.64 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend.min.js	38.27 KiB
packages/govuk-frontend/dist/govuk/i18n.mjs	5.38 KiB

Modules

File	Size
all.mjs	69.41 KiB
components/accordion/accordion.mjs	21.67 KiB
components/button/button.mjs	4.7 KiB
components/character-count/character-count.mjs	21.24 KiB
components/checkboxes/checkboxes.mjs	5.83 KiB
components/error-summary/error-summary.mjs	6.09 KiB
components/exit-this-page/exit-this-page.mjs	16.08 KiB
components/header/header.mjs	3.9 KiB
components/notification-banner/notification-banner.mjs	4.54 KiB
components/radios/radios.mjs	4.83 KiB
components/skip-link/skip-link.mjs	3.81 KiB
components/tabs/tabs.mjs	9.66 KiB

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Action run for 8881365

[github-actions]

JavaScript changes to npm package

No changes found.

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Action run for 8881365

[github-actions]

Stylesheets changes to npm package

No changes found.

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Action run for 8881365

[github-actions]

Other changes to npm package

No changes found.

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Action run for 8881365

[domoscargin]

I think this is great - imho, more information is always good.

Coupla thoughts:

• Are other devs OK with the increased noise (I say, let's merge and see...)
• Are the comments always going to generate in order? For example, it's weird to see "Other changes" first on 🚀 Pre-release v5.0.0-internal.0 #4373
• I wonder if it's worth rethinking the grouping down the line - feels slightly strange to see CSS and SCSS changes split up on Fix header product name wrapping onto new line #4498 , especially since they directly relate to each other. That could be a whole spiral of work though.
• Another potential future idea: Can we merge in the size stats with these comments? Only highlight a size change if there's some diff in the relevant files? Should we have a comment for each of the files currently in the stats comment, if they have a difference?

[domoscargin]

Are these needed because of the move to a workflow_call?

[colinrotherham]

Ah this is a long story

We know we want to use git diff for js-beautify formatting but the npm package isn't committed

Running git diff on uncommitted files

Since we need to build both the "before" (base) and "after" (head) npm packages:

Idea 1: Build into two directories and run git diff --no-index
Idea 2: Build + commit twice, then run git diff HEAD^ HEAD on the last 2 commits

Sadly we can't use ":(exclude)**/*.min.*" pathspec with git diff --no-index

But to commit each build we need user.name and user.email even though they never go anywhere

[colinrotherham]

Thanks @domoscargin

Appreciate the code review

• Are other devs OK with the increased noise (I say, let's merge and see...)

I'm happy with the noise to avoid accidental npm package changes creeping in such as:

1. Browserslist caniuse-lite CSS changes like -webkit prefix removals
2. Babel adding code transforms (or injecting polyfills)
3. PostCSS or Sass changing the CSS bundle output
4. Rollup changing the JS bundle output

We can remove the "No changes found" default in future perhaps?

• Are the comments always going to generate in order? For example, it's weird to see "Other changes" first on 🚀 Pre-release v5.0.0-internal.0 #4373

☝️ Ah I hadn't noticed this but it'll be a side effect of racing them to the finish in:

govuk-frontend/.github/workflows/scripts/comments.mjs

Lines 15 to 16 in 6c712d7

	// Run the comments in parallel to avoid that an early one failing prevents the others
	// and use `allSettled` to avoid the promise rejecting on the first failure but wait

I won't merge this PR just yet until we get some more feedback

Like all the future ideas though