Incompatible types error with `@Nullable Void`

[sdeleuze]

Following JSpecify recommandation, I have tried to update a Spring callback from Void to @Nullable Void, but I get the following error with sdeleuze/spring-framework@retry-task-nullability when running ./gradlew build.

> Task :spring-core:compileJava FAILED
/Users/sdeleuze/workspace/spring-framework/spring-core/src/main/java/org/springframework/core/retry/support/RetryTask.java:200: error: [NullAway] incompatible types: TaskCallback<@Nullable Void, RuntimeException> cannot be converted to TaskCallback<V, E>
                RetryTask<@Nullable Void, RuntimeException> rt = new RetryTask<>(TaskCallback.from(task), retryTemplate) {

I am not 100% sure yet that's a NullAway bug, but could be so I would welcome a feedback.

[msridhar]

This looks like a NullAway bug to me; I can reproduce. Will take a look.

[kingg22]

Hiii @msridhar I have a similar case with Void; I don't know if you can take a look at it or if the solution also applies to this case.

In https://github.com/hibernate/hibernate-reactive use a lot of utility generics callbacks with Completion Stage API and functional interfaces, so look this:

	private <S extends Stage.Closeable, T> CompletionStage<T> withSession(
			CompletionStage<S> sessionStage,
			Function<S, CompletionStage<T>> work,
			Context.Key<S> contextKey) {
		return sessionStage.thenCompose( session -> {
			context.put( contextKey, session );
			return voidFuture()
					.thenCompose( v -> work.apply( session ) )
					.handle( this::handler )
					.thenCompose( (Function<@Nullable Void, T> handler) -> { // HERE, if remove the type, nullaway fails
						context.remove( contextKey );
						return session.close()
								.handle( (unused, throwable) -> handler.apply( null ) ); // HERE usage with null -> Void
					} );
		} );
	}

	private <T> Function<@Nullable Void, T> handler(T result, @Nullable Throwable exception) {
		return exception == null ? v -> result : v -> rethrow(exception);
	}

Permalink without null annotations
Fork with some annotations and nullaway enabled

[msridhar]

@kingg22 I think your issue is unrelated to this one. It's almost certainly related to #1360 and possibly also the test in #1462. So, you may want to track one of those issues for the fix.