error: [methodref.return] Incompatible return type

[rionda]

Consider the following classes:

MapEntryGetValueWorks:

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentMap;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class MapEntryGetWorks {
    public static void main(String[] args) {
        ConcurrentMap<Integer, List<List<Integer>>> m =
                IntStream.range(0, 100)
                        .mapToObj(i -> List.of(i, i  % 2))
                        .collect(Collectors.groupingByConcurrent(l -> ((List<Integer>) l).get(1)));

        ArrayList<Integer> list = m.entrySet()
                        .stream()
                        .sorted(Map.Entry.comparingByKey())
                        .mapToInt(Map.Entry::getKey)
                        .collect(ArrayList::new, ArrayList::add, ArrayList::addAll);
    }
}

and MapEntryGetFails

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class MapEntryGetFails {

    public static void main(String[] args) {
        ArrayList<Integer> list = IntStream.range(0, 100)
                .mapToObj(i -> List.of(i, i  % 2))
                .collect(Collectors.groupingByConcurrent(l -> ((List<Integer>) l).get(1)))
                .entrySet()
                .stream()
                .sorted(Map.Entry.comparingByKey())
                .mapToInt(Map.Entry::getKey)
                .collect(ArrayList::new, ArrayList::add, ArrayList::addAll);
    }
}

They do the same thing, but the Works one split the code in two statements, which is not really needed.

When running ~/checker-framework-3.35.0/checker/bin/javac -processor Nullness src/main/java/MapEntryGetWorks.java, I get no errors.

When running ~/checker-framework-3.35.0/checker/bin/javac -processor Nullness src/main/java/MapEntryGetFails.java, I get

src/main/java/MapEntryGetFails.java:16: error: [methodref.return] Incompatible return type
                .mapToInt(Map.Entry::getKey)
                          ^
  found   : /*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object
  required: @Initialized @NonNull int
  Consequence: method in @Initialized @NonNull Entry</*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object, /*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object>
    /*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object getKey(@Initialized @NonNull Entry</*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object, /*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object> this)
  is not a valid method reference for method in @Initialized @NonNull ToIntFunction<@Initialized @NonNull Entry</*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object, /*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object>>
    @Initialized @NonNull int applyAsInt(@Initialized @NonNull ToIntFunction<@Initialized @NonNull Entry</*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object, /*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object>> this, @Initialized @NonNull Entry</*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object, /*INFERENCE FAILED for:*/ ? extends @Initialized @Nullable Object> p0)
1 error

One can build similar error cases using Map.Entry::getValue instead of getKey.

I'm not sure if it is a bug.

[smillst]

This test case now passes in master.