Sort hook implementations during discovery, not at runtime

Btw, to sort by priority, I generally prefer building nested arrays and using ksort().

[..]
          $implementations_grouped[$instance->hook][$instance->priority][] = [
            $serviceId,
            $instance->moduleName ?? $moduleName,
            $methodName,
          ];
[..]
    if ($implementations_grouped) {
      $result[Hook::class] = array_map(
        static function (array $implementations_by_priority): array {
          ksort($implementations_by_priority);
          return array_merge(...$implementations_by_priority);
        },
        $implementations_grouped,
      );
    }

(This will be part of my PR once I get there)

This also makes me wonder if we should have a priority for alter.
I don't think we need it for replace.

Makes sense to order during discovery.

I'd rather not have anything meaningful in the keys, so we aren't introducing some kind of unintended API. You can currently everything is in the array value itself.

Since it will be as discovery process it doesnt need to be ultra-optimised. Im happy with usort, and with the natural PHP array order that gets serialised.

A general note for future: If this is going to core, I think it would be ideal to introduce a Before/After attribute if the hook in question knows it depends on another. Hux could work out a dependency graph, which would effectively nullify priorities.

Alter could use a new issue for priorities, but it can be deferred (even as a post-core-merge feature).

Pre-review note: the getters on discovery should be documented to mention they are baked with order already.

I'd rather not have anything meaningful in the keys, so we aren't introducing some kind of unintended API. You can currently everything is in the array value itself.

The array key is never exposed outside of the class, thanks to the array_merge(..).

And another benefit is that this sort is stable.
Last time I checked, php sort functions were not stable. But I could be wrong.
In my little experiment it looks stable, so maybe they changed it:
https://3v4l.org/oDK6H

Wow nice!
https://wiki.php.net/rfc/stable_sorting