Warn if Sass is compiled using libsass

[36degrees]

Make use of a difference in behaviour between compilers originally identified in #5918 to ‘detect’ if the Sass is being compiled using libsass. Output a deprecation warning if it is.

[github-actions]

📋 Stats

File sizes

File	Size
dist/govuk-frontend-development.min.css	128.45 KiB
dist/govuk-frontend-development.min.js	48.07 KiB
packages/govuk-frontend/dist/govuk/all.bundle.js	102.17 KiB
packages/govuk-frontend/dist/govuk/all.bundle.mjs	95.95 KiB
packages/govuk-frontend/dist/govuk/all.mjs	1.28 KiB
packages/govuk-frontend/dist/govuk/component.mjs	1.67 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend.min.css	128.44 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend.min.js	48.05 KiB
packages/govuk-frontend/dist/govuk/i18n.mjs	5.55 KiB
packages/govuk-frontend/dist/govuk/init.mjs	6.89 KiB

Modules

File	Size (bundled)	Size (minified)
all.mjs	90.17 KiB	45.66 KiB
accordion.mjs	26.58 KiB	13.41 KiB
button.mjs	9.09 KiB	3.79 KiB
character-count.mjs	25.48 KiB	11 KiB
checkboxes.mjs	7.76 KiB	3.42 KiB
error-summary.mjs	10.99 KiB	4.55 KiB
exit-this-page.mjs	20.2 KiB	10.34 KiB
file-upload.mjs	20.83 KiB	11.11 KiB
header.mjs	6.47 KiB	3.27 KiB
notification-banner.mjs	9.35 KiB	3.71 KiB
password-input.mjs	18.16 KiB	8.34 KiB
radios.mjs	6.76 KiB	2.98 KiB
service-navigation.mjs	6.38 KiB	3.25 KiB
skip-link.mjs	6.34 KiB	2.76 KiB
tabs.mjs	11.98 KiB	6.66 KiB

View stats and visualisations on the review app

---

Action run for d0067a4

[github-actions]

Other changes to npm package

diff --git a/packages/govuk-frontend/dist/govuk/settings/_index.scss b/packages/govuk-frontend/dist/govuk/settings/_index.scss
index e46fb4637..9cbf2779d 100644
--- a/packages/govuk-frontend/dist/govuk/settings/_index.scss
+++ b/packages/govuk-frontend/dist/govuk/settings/_index.scss
@@ -20,4 +20,17 @@
 
 @import "https://github.com/links";
 
+// LibSass evaluates this as a single unquoted string, equivalent to
+// "true == false", whereas Dart Sass evaluates it as "true" == "false".
+// Because a string in Sass is truthy, LibSass will output the warning; Dart
+// Sass will not.
+@if #{true} == #{false} {
+  @include _warning(
+    "libsass",
+    "It looks like you may be using LibSass to compile your Sass. LibSass is " +
+      "deprecated and will not be supported by the next major version of " +
+      "GOV.UK Frontend. See https://sass-lang.com/libsass/ for more information."
+  );
+}
+
 /*# sourceMappingURL=_index.scss.map */

---

Action run for d0067a4

[36degrees]

It feels a bit weird to list this as a new feature, but I didn't want to list it as a deprecation because the deprecation happened ages ago.

[domoscargin]

Could we think of it as a fix, perhaps? Like, "we probably should've been warning you about this ages ago"? It does feel weird as a feature.

[36degrees]

Possibly, but we tend not to include any detail for fixes. I'm not sure it matters that much as long as we're telling people so they know when they start seeing this in their logs.

@seaemsi do you have any thoughts on the best way to communicate this?

[seaemsi]

@36degrees Perhaps something like "you'll now see a deprecation warning" to highlight that there wasn't one before?

[36degrees]

@seaemsi sounds good, thanks. Are you happy with it being listed as a 'new feature'?

[domoscargin]

Looks good to me once the conflict is sorted.