dfa: overriding @NotNull has precedence over super method @Nullable

java/java-psi-api/src/com/intellij/codeInsight/NullableNotNullManager.java

@@ -169,13 +169,16 @@ public abstract class NullableNotNullManager implements PersistentStateComponent
 
   @Nullable 
   private PsiAnnotation findNullabilityAnnotationWithDefault(@NotNull PsiModifierListOwner owner, boolean checkBases, boolean nullable) {
-    PsiAnnotation annotation = findPlainNullabilityAnnotation(owner, checkBases, nullable);
+    PsiAnnotation annotation = findPlainNullabilityAnnotation(owner, checkBases);
     if (annotation != null) {
+      String qName = annotation.getQualifiedName();
+      if (qName == null) return null;
+
+      List<String> contradictory = nullable ? getNotNulls() : getNullables();
+      if (contradictory.contains(qName)) return null;
+
       return annotation;
     }
-    if (findPlainNullabilityAnnotation(owner, checkBases, !nullable) != null) {
-      return null;
-    }
 
     PsiType type = getOwnerType(owner);
     if (type == null || TypeConversionUtil.isPrimitiveAndNotNull(type)) return null;
@@ -192,8 +195,9 @@ public abstract class NullableNotNullManager implements PersistentStateComponent
     return findNullabilityDefaultInHierarchy(owner, nullable);
   }
 
-  private PsiAnnotation findPlainNullabilityAnnotation(@NotNull PsiModifierListOwner owner, boolean checkBases, boolean nullable) {
-    Set<String> qNames = ContainerUtil.newHashSet(nullable ? getNullables() : getNotNulls());
+  private PsiAnnotation findPlainNullabilityAnnotation(@NotNull PsiModifierListOwner owner, boolean checkBases) {
+    Set<String> qNames = ContainerUtil.newHashSet(getNullables());
+    qNames.addAll(getNotNulls());
     return checkBases && owner instanceof PsiMethod
            ? AnnotationUtil.findAnnotationInHierarchy(owner, qNames)
            : AnnotationUtil.findAnnotation(owner, qNames);

java/java-tests/testData/inspection/dataFlow/fixture/NotNullOverridesNullable.java

@@ -0,0 +1,26 @@
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.Object;
+import java.lang.Override;
+
+class Super {
+  @Nullable Object foo() {
+    return null;
+  }
+}
+
+class Main extends Super {
+  @NotNull
+  @Override
+  Object foo() {
+    return 2;
+  }
+
+  void bar(@NotNull Object o) {}
+
+  void goo() {
+    bar(foo());
+  }
+
+}

java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspectionTest.java

@@ -279,6 +279,8 @@ public class DataFlowInspectionTest extends LightCodeInsightFixtureTestCase {
   public void testSameComparisonTwice() { doTest(); }
   public void testRootThrowableCause() { doTest(); }
 
+  public void testNotNullOverridesNullable() { doTest(); }
+
   public void testOverridingInferredNotNullMethod() { doTest(); }
   public void testUseInferredContracts() { doTest(); }
   public void testContractWithNoArgs() { doTest(); }

java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspectionTestSuite.java

@@ -37,6 +37,8 @@ public class DataFlowInspectionTestSuite {
     suite.addTestSuite(SliceBackwardTest.class);
     suite.addTestSuite(SmartTypeCompletionDfaTest.class);
     suite.addTestSuite(NormalCompletionDfaTest.class);
+    suite.addTestSuite(NullableStuffInspectionTest.class);
+    suite.addTestSuite(NullableStuffInspection14Test.class);
     return suite;
   }
 }