Check for proper type

Author: smillst

framework/src/main/java/org/checkerframework/framework/util/typeinference8/constraint/Expression.java

@@ -280,7 +280,11 @@ private ReductionResultPair reduceLambda(Java8InferenceContext context) {
         AbstractType gi = gs.get(i);
         constraintSet.add(new Typing(fi, gi, TypeConstraint.Kind.TYPE_EQUALITY));
       }
-      constraintSet.add(new Typing(tPrime, T, TypeConstraint.Kind.SUBTYPE));
+      @SuppressWarnings("interning:not.interned") // checking for exact object.
+      boolean tPrimeNotSameAsT = tPrime != T;
+      if (tPrimeNotSameAsT) {
+        constraintSet.add(new Typing(tPrime, T, TypeConstraint.Kind.SUBTYPE));
+      }
     } else {
       context.addLambdaParms(lambda.getParameters());
     }

framework/src/main/java/org/checkerframework/framework/util/typeinference8/types/VariableBounds.java

@@ -558,7 +558,7 @@ public boolean hasWildcardParameterizedLowerOrEqualBound() {
   public boolean hasLowerBoundDifferentParam() {
     List<AbstractType> parameteredTypes = new ArrayList<>();
     for (AbstractType type : bounds.get(BoundKind.LOWER)) {
-      if (!type.isUseOfVariable() && type.isParameterizedType()) {
+      if (type.isProper() && type.isParameterizedType()) {
         parameteredTypes.add(type);
       }
     }

framework/tests/all-systems/Issue6753.java

@@ -0,0 +1,23 @@
+package typearginfer;
+
+import java.util.Set;
+import java.util.concurrent.Callable;
+
+public abstract class Issue6753 {
+
+  abstract <E> E call(Callable<E> task);
+
+  abstract <T> Set<T> list();
+
+  void method(int length) {
+    Set<String> resources =
+        call(
+            () -> {
+              if (length > 1) {
+                return list();
+              } else {
+                return list();
+              }
+            });
+  }
+}