Don't ignore type arguments (Fixes #3443.) (#3456)

checker/tests/nullness/Issue3443.java

@@ -0,0 +1,19 @@
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+class Issue3443 {
+    static <T extends Supplier3443<@Nullable String>> Supplier3443<String> passThrough(T t) {
+        // :: error: (return.type.incompatible)
+        return t;
+    }
+
+    public static void main(String[] args) {
+        Supplier3443<@Nullable String> s1 = () -> null;
+        // TODO: passThrough(s1) should cause an error. #979.
+        Supplier3443<String> s2 = passThrough(s1);
+        s2.get().toString();
+    }
+}
+
+interface Supplier3443<T> {
+    T get();
+}

framework/src/main/java/org/checkerframework/framework/type/DefaultTypeHierarchy.java

@@ -1048,7 +1048,6 @@ && isPrimarySubtype(ub, supertype)) {
                 }
                 return false;
             }
-            return isPrimarySubtype(upperBound, supertype);
         }
         return checkAndSubtype(upperBound, supertype);
     }