Propose removing imports from components

proposals/007-remove-imports-from-components.md

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+# Remove the imports of settings, tools and helpers layers from components
+
+**Closing date:** 27 March 2020
+
+**Status:** Proposed
+
+## Summary
+
+We plan to remove the imports of the settings, helpers and tools layers from all components in GOV.UK Frontend version 4.0.
+
+We’re doing this to reduce the time it takes to compile GOV.UK Frontend’s Sass to CSS, especially if you’re using the Ruby Sass compiler.
+
+## Problem
+
+If you're using the Ruby Sass compiler to compile Sass to CSS, it can take a long time because GOV.UK Frontend has a lot of imports.
+
+Although Ruby Sass is deprecated, teams (including GOV.UK) are stuck using it for the foreseeable future.
+
+If we make these changes, we'll also improve the compile time in other Sass compilers. Approximately, we expect to see these improvements:
+
+| Compiler  | Compile time now | Compile time after proposed changes | Improvement |
+|-----------|------------------|-------------------------------------|-------------|
+| Ruby Sass | 30s              | 7.8s                                | 74%         |
+| LibSass   | 0.2s             | 0.18s                               | 10%         |
+| Dart Sass | 0.5s             | 0.25s                               | 50%         |
+
+For more context, see [#1671 Slow compilation of SCSS files in Rails apps](https://github.com/alphagov/govuk-frontend/issues/1671).
+
+## Proposal
+
+We propose removing the following imports of the settings, helpers and tools layers from each component:
+
+```scss
+@import "../../settings/all";
+@import "../../tools/all";
+@import "../../helpers/all";
+```
+
+This will have no effect if you currently import `govuk/all`, as all of the layers are already imported in order.
+
+If you selectively import one or more components, you would need to make sure you import the settings, tools and helpers layers first:
+
+```scss
+@import "govuk/settings/all";
+@import "govuk/tools/all";
+@import "govuk/helpers/all";
+
+@import "govuk/components/accordion/accordion";
+@import "govuk/components/button/button";
+```
+
+As this changes the way that some users would import GOV.UK Frontend, this would be a breaking change, which we'd introduce in GOV.UK Frontend version 4.0.