feat: add boss bar viewer

[RealBauHD]

No description provided.

[WouterGritter]

Why does Set<BossBar> bossBars need to be monotonically non-null? Seems like no real performance gain for less readability.

[WouterGritter]

Suggested change

	public @UnmodifiableView @org.jspecify.annotations.NonNull Iterable<? extends BossBar> activeBossBars() {
	public @UnmodifiableView @NonNull Iterable<? extends BossBar> activeBossBars() {

org.checkerframework.checker.nullness.qual.NonNull is imported

[Timongcraft]

Why does Set<BossBar> bossBars need to be monotonically non-null? Seems like no real performance gain for less readability.

What are you talking about?
For me at least it is Nullable:
https://github.com/PaperMC/Velocity/pull/1756/changes#diff-1cd097c1de92fff8c43bc33eb4f52405eb5396f9e8cc922a4502e4cad12e1f88R189

[WouterGritter]

Why does Set<BossBar> bossBars need to be monotonically non-null? Seems like no real performance gain for less readability.

What are you talking about? For me at least it is Nullable: https://github.com/PaperMC/Velocity/pull/1756/changes#diff-1cd097c1de92fff8c43bc33eb4f52405eb5396f9e8cc922a4502e4cad12e1f88R189

yes but you're treating it as a monotonically non-null value. we can just leave it as a

private final Set<BossBar> bossBars = new HashSet<>();

and omit any null checks down the line. keeping this value null until it's used doesn't seem like it'll affect performance at all, and it makes the code that's using this field less readable (null -> either instantiate this set when modifying it, or assuming an empty set when querying it)

[Timongcraft]

They don't though (https://github.com/PaperMC/Velocity/pull/1756/changes#diff-1cd097c1de92fff8c43bc33eb4f52405eb5396f9e8cc922a4502e4cad12e1f88R613), or am I missing something?

[WouterGritter]

They don't though (https://github.com/PaperMC/Velocity/pull/1756/changes#diff-1cd097c1de92fff8c43bc33eb4f52405eb5396f9e8cc922a4502e4cad12e1f88R613), or am I missing something?

oh yes my bad, its not monotonically non-null, but my point still holds. this can be a HashSet that's initiated once (at construct time of the object) and only updated/queried without null-checks. that'd get rid of null-checks in every method that's using this field