Support @CheckForNull annotation

[ben-manes]

error: [NullAway] method returns @Nullable, but superclass method com.github.benmanes.caffeine.cache.AsyncLoadingCache.getIfPresent(java.lang.Object) returns @NonNull
  public @Nullable CompletableFuture<V> getIfPresent(@Nonnull Object key) {

However, this method is annotated with @CheckForNull which should implicitly mean @Nullable.

[msridhar]

Which library provides the @CheckForNull annotation?

[ben-manes]

javax.annotation (jsr305 / findbugs)

[msridhar]

Cool, this should be easy to support

[chengniansun]

Just for your information, Guava is migrating off from jsr305.

google/guava#2960

[uhafner]

Are you ok with a pull request that adds support for a @CheckForNull annotation? From the code it looks like that I just need to update

NullAway/nullaway/src/main/java/com/uber/nullaway/Nullness.java

Line 149 in cc7869b

public static boolean isNullableAnnotation(String annotName, Config config) {

and provide a test.

Or is there something conceptional wrong with this issue? Supporting CheckForNull would help projects a lot that use NullAway and SpotBugs

[msridhar]

I would be open to a PR that just adds @CheckForNull support. @lazaroclapp please comment if you see an issue with that.

[lazaroclapp]

I am fine with it. The idea is just to make CheckForNull another supported nullable annotation, right? As an exact alias for @Nullable, correct? Reading the previous discussion, we were a bit concerned about overhead of equality checking so many annotations if we just supported a custom list. But given that there seems to be interest for this particular annotation, I'd say go ahead.

We can open a separate task to optimize isNullableAnnotation and profile later.

[uhafner]

I am fine with it. The idea is just to make @CheckForNull another supported nullable annotation, right? As an exact alias for @Nullable, correct?

Yes, just an alias for @Nullable. (The reason is that SpotBugs treats @Nullable differently: such references might be null but should not be flagged by a tool. In Spotbugs the semantics of @CheckForNull is the same as your @Nullable annotation). Then teams can use SpotBugs and NullAway to check the code...