Add a feature flag for the procedural hooks bc layer

Once core is converted, it will be possible for a site to run without any procedural hook implementations at all.

This requires that none of the installed contributed modules implement procedural hooks. Right?

@chi yes that's right, possible not likely ;) I don't think any sites would be able to actually disable procedural hooks until 11.3 at the earliest or even later, but the end of the 11.x cycle maybe. Also if we want to leave the bc layer in until Drupal 13, we could keep it in 12.x this way, but with a status report mention that it's possible to disable (maybe even with some detection of whether it's being relied upon).

++ to option to skip procedural hooks parsing

This sounds great. One request for clarification: the change record → notes that several hooks will "remain procedural", including theme hooks like hook_preprocess() and install hooks like hook_schema() and hook_update(). So does "disable procedural hook discovery" mean "disable all procedural hooks which can be implemented with the OO pattern" or does it mean "disable all procedural hooks period"?

At a minimum I would imagine hooks like hook_update() need to still be supported or sites will break when a contrib module has an update hook.

That's a good question. It needs to be "disable all procedural hooks which can be implemented with the OO pattern" but we will need to make sure that's actually the case when we implement this.

Install hooks are invoked by module installer and don't use module handler at all - so they'd just stay the same, they don't use the bc layer, it's an entirely different system.

Theme hooks I think are in a similar situation but would need to actually double check. However generally if something's relying on the bc layer, it ought to be possible to implement the OOP version. 📌 [PP-1] Explore converting Install hooks to OOP Active is looking at OOP hook support, at which point any added OOP hook support would also fall under this.

There are a couple of specific additional exceptions - hook_hook_info() and hook_module_implements_alter(). hook_hook_info() is incompatible with OOP hooks so it won't matter if it's not fired when the feature flag is off, even if a module implements it, but it will complicate detecting when it's OK to switch off. hook_module_implements_alter()... don't know will need to check.

I think theme hooks should resurrect 📌 Convert theme hooks (defined by hook_theme()) to be objects Needs work to unblock ✨ Add a "context" array variable to all theme hooks and "#context" array property to all elements to provide optional contextual data Needs work

✨ Explore ways to mark hook conversion status per module or file Active is related and ready for review.