This proposed policy comes from a discussion in #3050374: Create Drupal 9 stable theme
In Drupal 8 the stable theme includes copies of all image assets from modules and core/misc. In the process of creating the Stable 9 theme, @lauriii and @bnjmnm wondered if this copying of images is necessary or helpful as multiple copies of the same image is confusing for developers and adds to Drupal's download size. Plus, in the case of Drupal 9, this would result in three copies of the same image assets, the originals, copies for the deprecated Stable (8), and copies for Stable 9. Sincere attempts were made to track down the rationale for copying all images, but nothing more detailed than #2575737: Copy templates, CSS, and related assets to Stable and override core libraries' CSS could be found, which approached the image copying as a given.
The proposed solution is:
- Do not add copies of image assets to Stable 9 or future versions of stable
- When a Stable theme is moved to contrib, the images should be copied to the theme
- In the event that an image in misc or modules is changed, the original version of that image should be added to Stable to ensure backwards compatibility. Based on a git history review this occurs infrequently at most, but needs to remain an option.
With this solution we hope to reduce the overhead of multiple copies of identical files, while still preserving backwards compatibility. This will inform how the Stable 9 theme is created.