Introduce an alias which represents a callable that may not be defined in the current scope - #6

One thing to note about this. PhpStorm doesn't understand what Maybe_Callable is:

I seem to remember this being why I didn't go that route before.

Presumably other IDEs wouldn't either.

OK, there is a 2-year-old Jetbrains issue requesting support for PHPStan type aliases: https://youtrack.jetbrains.com/projects/WI/issues/WI-79519/PHPStorm-doesnt-recognise-PHPStan-global-type-aliases

So presumably this will land eventually.

However, VS Code + Intelephense doesn't yet support this either: bmewburn/vscode-intelephense#3525

But VS Code + DEVSENSE PHP Tools does support this.

Something else to consider is whether the developer docs parser would need to be updated to support this.

In looking at the docs for \WP_Post::to_array(), I see that it doesn't do any parsing of:

@phpstan-return Data_Array

I also see the same in the docs for \WP_Connector_Registry::register(), that the @return is parsed but the @phpstan-return which includes tyhe type Connector is not mentioned.

So I think it's OK, if we only ever use these PHPStan type aliases in @phpstan- prefixed tags. However, I remember you mentioned the desire to be able to move away from having to do this. If so, then updating the developer docs parser would need to be added to the prerequisites.

I'm still not sure what to do about @phpstan- prefixed tags. I'll draft a make/core post soon.

See also WordPress#13233 which could lessen the need to add @phpstan- prefixed tags.