WPI: decision on whether to infer a type for a type variable should be made based on explicit annotations

checker/src/test/java/org/checkerframework/checker/test/junit/ainferrunners/AinferNullnessAjavaTest.java

@@ -28,7 +28,7 @@ public AinferNullnessAjavaTest(List<File> testFiles) {
         NullnessChecker.class,
         "ainfer-nullness/non-annotated",
         "-Ainfer=ajava",
-        // "-Aajava=tests/ainfer-nullness/input-annotation-files/",
+        "-Aajava=tests/ainfer-nullness/input-annotation-files/",
         "-Awarns");
   }
 

checker/tests/ainfer-nullness/input-annotation-files/TypeVarReturnAnnotated-org.checkerframework.checker.nullness.NullnessChecker.ajava

@@ -0,0 +1,10 @@
+// Code like this caused WPI to loop infinitely, because the annotation on the return type
+// was only sometimes inferred. Based on an example from
+// https://github.com/dd482IT/cache2k-wpi/blob/0eaa156bdecd617b2aa4c745d0f8844a32609697/cache2k-api/src/main/java/org/cache2k/config/ToggleFeature.java#L73
+@org.checkerframework.framework.qual.AnnotatedFor("org.checkerframework.checker.nullness.NullnessChecker")
+public class TypeVarReturnAnnotated {
+
+    public static <T extends TypeVarReturnAnnotated> @org.checkerframework.checker.initialization.qual.FBCBottom @org.checkerframework.checker.nullness.qual.Nullable T extract() {
+        return null;
+    }
+}

checker/tests/ainfer-nullness/non-annotated/TypeVarReturnAnnotated.java

@@ -0,0 +1,9 @@
+// Code like this caused WPI to loop infinitely, because the annotation on the return type
+// was only sometimes inferred. Based on an example from
+// https://github.com/dd482IT/cache2k-wpi/blob/0eaa156bdecd617b2aa4c745d0f8844a32609697/cache2k-api/src/main/java/org/cache2k/config/ToggleFeature.java#L73
+
+public class TypeVarReturnAnnotated {
+  public static <T extends TypeVarReturnAnnotated> T extract() {
+    return null;
+  }
+}

framework/src/main/java/org/checkerframework/common/wholeprograminference/WholeProgramInferenceImplementation.java

@@ -860,7 +860,7 @@ protected void updateAnnotationSet(
     // bound.
     if (defLoc != TypeUseLocation.FIELD && lhsATM instanceof AnnotatedTypeVariable) {
       AnnotationMirrorSet upperAnnos =
-          ((AnnotatedTypeVariable) lhsATM).getUpperBound().getEffectiveAnnotations();
+          ((AnnotatedTypeVariable) lhsATM).getUpperBound().getExplicitAnnotations();
       // If the inferred type is a subtype of the upper bounds of the
       // current type in the source code, do nothing.
       if (upperAnnos.size() == rhsATM.getAnnotations().size()