Mismatched type parameter nullability

[ben-manes]

Upgrading from 0.12.1 to 0.12.2 and I am confused by these new warnings.

> Task :caffeine:compileJava
/Users/ben/projects/caffeine/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java:3180: warning: [NullAway] Cannot pass parameter of type Function<@org.jspecify.annotations.Nullable V, @org.jspecify.annotations.Nullable V>, as formal parameter has type Function<V, V>, which has mismatched type parameter nullability
            .map(node -> nodeToCacheEntry(node, transformer))
                                                ^
    (see http://t.uber.com/nullaway )
  Did you mean '@SuppressWarnings("NullAway") <T> T snapshot(Iterable<Node<K, V>> iterable, Function<@Nullable V, @Nullable V> transformer,'?

/Users/ben/projects/caffeine/caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java:4014: warning: [NullAway] Cannot pass parameter of type Function<@org.jspecify.annotations.Nullable V, @org.jspecify.annotations.Nullable V>, as formal parameter has type Function<V, V>, which has mismatched type parameter nullability
      return (node == null) ? null : cache.nodeToCacheEntry(node, transformer);
                                                                  ^
    (see http://t.uber.com/nullaway )
  Did you mean '@SuppressWarnings("NullAway") @Override public @Nullable CacheEntry<K, V> getEntryIfPresentQuietly(K key) {'?

The snapshot method and nodeToCacheEntry method both use the same types for the transformer parameter.

  <T> T snapshot(Iterable<Node<K, V>> iterable, Function<@Nullable V, @Nullable V> transformer,
      Function<Stream<CacheEntry<K, V>>, T> mappingFunction)

  @Nullable CacheEntry<K, V> nodeToCacheEntry(
      Node<K, V> node, Function<@Nullable V, @Nullable V> transformer)

The other warning is similar. It appears to be a regression.

Note that you might have to use --rerun, --rerun-tasks or --no-build-cache to force recompilations.

[msridhar]

Thanks for the report; I can reproduce. I know what is wrong, but I'd like to be careful with the fix, which will take a bit of work. Will try to investigate more deeply soon.

[ben-manes]

Here's a wildcard case,

/Users/ben/projects/caffeine/caffeine/src/test/java/com/github/benmanes/caffeine/cache/AsyncCacheTest.java:141: 
warning: [NullAway] Cannot pass parameter of type Function<Int, @Nullable Int>, as formal parameter has type Function<? super Int, ? extends @Nullable Int>, which has mismatched type parameter nullability
    var valueFuture = cache.get(key, k -> null);
                                     ^
    (see http://t.uber.com/nullaway )
  Did you mean '@SuppressWarnings("NullAway") var valueFuture = cache.get(key, k -> null);'?

when I tried to annotate as a nullable return value because it disliked that the Map computation had no result.

@CacheSpec
@Test(dataProvider = "caches")
public void getFunc_absent_null(AsyncCache<Int, @Nullable Int> cache, CacheContext context) {
  Int key = context.absentKey();
  var valueFuture = cache.get(key, k -> null);
  assertThat(context).stats().hits(0).misses(1).success(0).failures(1);

  assertThat(valueFuture).isDone();
  assertThat(cache).doesNotContainKey(key);
}

[msridhar]

This should not have been closed

[msridhar]

@ben-manes FYI I confirmed that with #1143 the warnings that you reported above go away.

[ben-manes]

Thanks! I hope someday ErrorProne adds support for warning of unused suppressions so I don't have to remember when upgrading.

[msridhar]

Thanks! I hope someday ErrorProne adds support for warning of unused suppressions so I don't have to remember when upgrading.

FYI inspired by your comment I put up a draft PR for this: google/error-prone#4828 It's a feature I've wanted for a long time as well. We'll see if we can make it work :-)