Fix crash in ajava-based WPI related to captures

checker/tests/ainfer-index/non-annotated/Dataset6Crash.java

@@ -0,0 +1,57 @@
+// Test case for a WPI crash caused by mismatches between captured type variables
+// and the declared type of a field: in particular, the issue is that base.next()
+// the next field actually have slightly different types: base.next()'s type is
+// a capture that extends T.
+
+import java.util.Iterator;
+
+public class Dataset6Crash {
+
+  public static <T> Iterator<T> limit(final Iterator<? extends T> base, final CountingPredicate<?
+      super T> filter) {
+    return new Iterator<T>() {
+
+      private T next;
+
+      private boolean end;
+
+      private int index = 0;
+
+      public boolean hasNext() {
+        return true;
+      }
+
+      public T next() {
+        fetch();
+        T r = next;
+        next = null;
+        return r;
+      }
+
+      private void fetch() {
+        if (next == null && !end) {
+          if (base.hasNext()) {
+            next = base.next();
+            if (!filter.apply(index++, next)) {
+              next = null;
+              end = true;
+            }
+          } else {
+            end = true;
+          }
+        }
+      }
+
+      public void remove() {
+        throw new UnsupportedOperationException();
+      }
+    };
+  }
+
+
+  private static class CountingPredicate<T> {
+    public boolean apply(int i, T next) {
+      return false;
+    }
+  }
+}

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

@@ -804,7 +804,17 @@ protected void updateAnnotationSet(
 
     AnnotatedTypeMirror atmFromStorage =
         storage.atmFromStorageLocation(rhsATM.getUnderlyingType(), annotationsToUpdate);
-    updateAtmWithLub(rhsATM, atmFromStorage);
+    // It is possible that rhsATM is a type variable but atmFromStorage is not, which
+    // would cause a ClassCastException in updateAtmWithLub(). This can
+    // happen for example when a local variable of type ? extends T is assigned to a
+    // field of type T, such as in the test ainfer-index/non-annotated/Dataset6Crash.java.
+    try {
+      updateAtmWithLub(rhsATM, atmFromStorage);
+    } catch (ClassCastException c) {
+      AnnotatedTypeMirror compatibleRHSAtm =
+          AnnotatedTypes.asSuper(this.atypeFactory, rhsATM, atmFromStorage);
+      updateAtmWithLub(compatibleRHSAtm, atmFromStorage);
+    }
     if (lhsATM instanceof AnnotatedTypeVariable) {
       Set<AnnotationMirror> upperAnnos =
           ((AnnotatedTypeVariable) lhsATM).getUpperBound().getEffectiveAnnotations();