[meta] Requirements for tagging Drupal 10.0.0-beta1

Must-haves prior to tagging 10.0.0-beta1

We can eventually file child metas for these, but a list is sufficient for now.

1. Update or decouple/remove PHP (Composer) dependencies.
   • Symfony:
     • Make Drupal 9 fully compatible with Symfony 5 as soon as possible: #3055180: [META] Symfony 5 compatibility and #3197482: Update Drupal 10 to depend on Symfony 5
     • Test with Symfony 6 as soon as a development version is available, and determine feasibility of requiring Symfony 6 for a longer Drupal 10 support lifetime. #3161889: [META] Symfony 6 compatibility and #3197483: Evaluate the potential update of Drupal 10 to Symfony 6 and do it if possible.
   • Twig: Consider requiring Twig 3 #3126632: Require Twig 3
   • Guzzle: Update to Guzzle 7.
     • Blocker: #3187315: Remove mink-goutte-driver as a core dependency
     • #3104353: Upgrade to Guzzle 7
   • Composer 2: Remove any code paths that are Composer 1 specific (needs issue)
   • Shift incorrect production dependencies to dev: #3133749: Deprecate masterminds/html5 as a production dependency for Drupal 10
   • #3210486: Remove typo3/phar-stream-wrapper once core requires PHP 8
   • Re-evaluate other backend dependencies in early to mid-2021.
   • (Other leftover issues from the Drupal 9 cycle to decouple/remove dependencies, etc.?)
2. Update or decouple/remove frontend dependencies.
   • CKEditor: Replace CKEditor 4 with CKEditor 5. See #2966864: Add optional support for CKEditor 5 in D9 so we can remove CKE 4 from Drupal 10
   • jQuery UI: Replace remaining jQuery UI components, deprecate them in Drupal 9, and remove them in Drupal 10.
     • Finish deprecations: #3113400: Deprecate more jQuery UI library definitions
     • Autocomplete: #3076171: Provide a new library to replace jQuery UI autocomplete
     • Dialog: #2158943: Replace jQuery UI dialog with supported library or polyfill
   • jQuery: Upgrade to jQuery 4. https://github.com/jquery/jquery/milestone/7
   • Re-evaluate other frontend dependencies in early to mid-2021.
3. Remove all deprecated code, libraries, and BC layers.
   • #3213858: [META] Remove deprecated modules on the Drupal 10 branch
   • #3213895: [META] Remove deprecated classes, methods, procedural functions and code paths outside of deprecated modules on the Drupal 10 branch
   • #3097889: Remove deprecated theme functions
   • #3179048: [META] Various updates when PHP 8.0 will become required
4. Resolve critical 9.x -> 9.x upgrade path bugs.
5. Remove old upgrade paths based on the outcome of #2942096: [policy, no patch] Remove old update hooks prior to each major version (Drupal 10 and later), and discuss what to do with \Drupal::CORE_MINIMUM_SCHEMA_VERSION.
6. Resolve any 10.0.x-only security or data integrity issues.
7. Define the Drupal 10 theme API. #2659890: [Plan] Drupal 9 and 10 markup and CSS backwards compatibility
   • At a minimum, create the Stable 10 base theme and deprecate Stable 9.

Should-haves prior to tagging 10.0.0-beta1

These become beta targets if they are not completed by the deadline, and may contribute to other adjustments to the schedule (TBD).

• (Possibly a must-have; TBD) Stabilize Starterkit, ensure a Drupal 10 version of the starter theme is generated, and move Classy and Stable 8 to contrib.
• Update backend and frontend development dependencies.
• Other issues TBD.