[Policy] SDC backwards compatibility policy

andy-blum → credited lauriii → .

LOL at this excerpt from the IS:

Given the popularity of SDC, it not making it past experimental may also require escape hatches for the human(s) that 👎 it...

The reasoning here makes sense for me. The other alternative I see (which I don't like) is to carve out exceptions for the BC assurances on SDCs inside the stable themes.

I am not sure I follow why we need this part:

To determine if this policy is feasible, it would be worth SDC-ifiying some core components that would benefit from better default styles. Media Library comes to mind.

How does this relate to the policy feasibility?

To determine if this policy is feasible, it would be worth SDC-ifiying some core components that would benefit from better default styles. Media Library comes to mind. How does this relate to the policy feasibility?

Perhaps not the best wording. On paper the "no-BC-for-SDC" sounds good, but an MR that converts some core components to SDC might reveal additional considerations that we're not currently thinking about, and these conversions could included as part of the switch to non-experimental.

I did think of a BC consideration that should probably be in the policy. As detailed in the IS I think it's reasonable to allow SDCs to change as needed without too much BC fuss. However, for Stable 9 extending themes should have some kind of BC protection for components that have been converted to SDC - at minimum preserving the markup but ideally able to leverage the same preprocessor too.

Given the popularity of SDC, it not making it past experimental may also require escape hatches for the human(s) that 👎 it...

Experimental modules are not in a popularity game. Those Experimental modules exist to either try them out and make sure the whole stack work as expected or to use them, provided the site maintainers agrees to some risks and that they are willing to deal with those risks, if any arise. SDC is an exception, as, once stable, it will not be a module.

I am interested to know about the impacts of converting some Twig themes to SDC in Stable. Would that break existing themes using Stable 9 as a base theme? Or will SDC be transparent to any themes expanding upon Stable?

@bnjmnm how do we move this forward? Should we write a document about BC expectations in SDCs inside of Drupal core? Where should that live? I propose a documentation page, child of the official SDC documentation https://www.drupal.org/docs/develop/theming-drupal/using-single-director... → . Any other ideas?

We should probably include a note in https://www.drupal.org/docs/develop/theming-drupal/sub-theming-using-sta... → as well.