Simplify glitch-soc's theming system

[ClearlyClaire]

glitch-soc's over-engineered theming system has been a recurring pain when merging upstream changes, and this is getting significantly worse with upstream making changes to its theming system.

Therefore, this PR aims to simplify it a great deal and bring it closer to upstream.

As upstream's theming system is undergoing changes, glitch-soc's theming system may change as well in the near future, even after this PR gets merged.

Breaking changes

(The following is still subject to change)

For end users

Hopefully, none.

For skin (purely SCSS changes) authors

Although nobody used that to my knowledge, skins allowed multiple entry-points. This has now changed, a skin has a single entry point, with one of the following being used:

• app/javascript/skins/:flavour/:skin.scss
• app/javascript/skins/:flavour/:skin.css
• app/javascript/skins/:flavour/:skin/common.css
• app/javascript/skins/:flavour/:skin/common.scss
• app/javascript/skins/:flavour/:skin/index.css
• app/javascript/skins/:flavour/:skin/index.scss
• app/javascript/skins/:flavour/:skin/application.css
• app/javascript/skins/:flavour/:skin/application.scss

For most, if not all skins, this should require no change whatsoever.

For flavours (javascript pack changes) authors

The following changes have been made to theme.yml:

• pack_directory is no longer optional
• fallback is no longer supported
• pack is no longer supported, entrypoints are directly identified by their filename
• the root attribute signed_in_preload has been added to fulfill the purpose of the preload attribute that was previously pack-specific

In addition, the following changes have been made:

• some packs have been reorganized to match upstream's usage:
  • home is now called application
  • auth does not exist anymore, its contents are in public and two_factor_authentication
  • settings does not exist anymore, its contents are in public
• the common pack is unconditionally loaded in addition to other packs

Additional internal changes

• to match upstream, pack selection is now done in views and no longer in controllers
• the implicit core flavor has been removed
• use_pack, @core and @theme have been removed, replaced with new helpers: preload_locale_pack, flavoured_javascript_pack_tag and preload_signed_in_js_packs

[ClearlyClaire]

@listerine420 I intend to merge this PR shortly, as it will make merging upstream changes a lot easier, but I see you've reacted with a thumbs down emoji. Is there a specific issue with this PR that I should be aware of and possibly address before merging?

[jippi]

Thanks for this simplification! It's so much better - I never quite figured out how the old system worked, so copied it most of the stuff from the glitch theme (without knowing what it did) - the new setup is way clearer!

+++ b/docker/mastodon/flavours/bird-ui/theme.yml
@@ -1,28 +1,22 @@
-pack:
-  admin:
-    - admin.tsx
-    - public.tsx
-  auth: public.tsx
-  common:
-    filename: common.js
-    stylesheet: true
-  embed: public.tsx
-  error: error.js
-  home:
-    filename: application.js
-    preload:
-      - features/compose
-      - features/home_timeline
-      - features/notifications
-  mailer:
-  modal:
-  public: public.tsx
-  settings: public.tsx
-  sign_up: sign_up.js
-  share: share.jsx
+# (REQUIRED) The directory which contains the entry point files.
+pack_directory: app/javascript/entrypoints
 
-pack_directory: app/javascript/packs
 
-fallback:
+# (OPTIONAL) A file to use as the preview screenshot for the flavour,
+# or an array thereof. These are the full path from `app/javascript/`.
+screenshot: images/bird-ui-preview.jpg
-screenshot: images/bird-ui-preview.jpg

[ClearlyClaire]

@jippi I am a bit confused by your use of the theming system. How does bird-ui differ from the vanilla flavor?

[jippi]

This bird-ui doesn't really differ beyond just styling (no functionality)

I (probably misused?) the flavor system to give it a more prominent place in the profile UI than a regular "style" since folks had a hard time finding it in the "vanilla" section, and I wanted to give it a screenshot :)

If there is a better way to achieve this, I'm all ears :D