Support jSpecify @NullMarked and @NullUnmarked

[gaeljw]

In addition to the already supported (or ongoing development) for @NonNull and @Nullable:

• add jspecify NonNull annotation to NotNullAnnots list #24487
• Consider nullable annotations in explicit nulls #21629 and Consider nullable annotations in explicit nulls #21953

It would be nice to have support for @NullMarked and @NullUnmarked. These 2 annotations can be set on a module/package/class and respectively mean that all items in the scope can be considered @NonNull/@Nullable unless explicitly flagged as the opposite.

• jSpecify spec
• Discussion in Contributors forums

[TheDrawingCoder-Gamer]

think it would be useful to document cases where this would be very helpful, to bolster why people should PLEASE HELP ME on my PR #26456

Minecraft since 26.1 is now deobfuscated and that means it now preserves annotations, and mojang uses @NullMarked in basically every single package.

Let's take for example in 26.1.2 Item#use.
Copy of its java signature for completeness:

public InteractionResult use(final Level level, final Player player, final InteractionHand hand)

It lives in a NullMarked package so languages like Kotlin, when your IDE autocompletes, will correctly override this as a completely non nullable method.

HOWEVER, in VSCode (or any editor using Metals), a scala project will instead give you this override signature:

override def use(level: (Level)?, player: (Player)?, hand: (InteractionHand)?): (InteractionResult)? = ???

this isn't kotlin, so ? doesn't mean "nullable" it means "platform type" which is non denotable so this is just an error you have to fix. Ignoring the weird jank in platform type overrides, it shouldn't even be a platform type. These should be non nullable!
The signature the compile should infer is this:

override def use(level: Level, player: Player, hand: InteractionHand): InteractionResult = ???

Of course scala doesn't actually support @NullMarked so it sees only unannotated types.

If anyone else has use cases (that aren't in relative niches like modding minecraft with scala, of all languages) please share!