Fix lower bound of type variables and unspecified subtypes. (#175)

src/main/java/com/google/jspecify/nullness/NullSpecAnnotatedTypeFactory.java

@@ -14,7 +14,7 @@
 
 package com.google.jspecify.nullness;
 
-import static com.google.jspecify.nullness.NullSpecAnnotatedTypeFactory.IsDeclaredOrArray.IS_DECLARED_OR_ARRAY;
+import static com.google.jspecify.nullness.NullSpecAnnotatedTypeFactory.IsDeclaredOrArrayOrNull.IS_DECLARED_OR_ARRAY_OR_NULL;
 import static com.google.jspecify.nullness.Util.nameMatches;
 import static com.sun.source.tree.Tree.Kind.IDENTIFIER;
 import static com.sun.source.tree.Tree.Kind.MEMBER_SELECT;
@@ -29,6 +29,7 @@
 import static javax.lang.model.element.ElementKind.ENUM_CONSTANT;
 import static javax.lang.model.type.TypeKind.ARRAY;
 import static javax.lang.model.type.TypeKind.DECLARED;
+import static javax.lang.model.type.TypeKind.NULL;
 import static javax.lang.model.type.TypeKind.TYPEVAR;
 import static javax.lang.model.type.TypeKind.WILDCARD;
 import static org.checkerframework.framework.util.AnnotatedTypes.asSuper;
@@ -139,7 +140,6 @@ final class NullSpecAnnotatedTypeFactory
       new TypeUseLocation[] {
         TypeUseLocation.CONSTRUCTOR_RESULT,
         TypeUseLocation.EXCEPTION_PARAMETER,
-        TypeUseLocation.IMPLICIT_LOWER_BOUND,
         TypeUseLocation.RECEIVER,
       };
 
@@ -152,6 +152,10 @@ final class NullSpecAnnotatedTypeFactory
 
   private static final TypeUseLocation[] defaultLocationsUnspecified =
       new TypeUseLocation[] {
+        // Lower bounds could be MinusNull, but all uses in unmarked code would become unspecified
+        // anyways.
+        // Revisit once https://github.com/eisop/checker-framework/issues/741 is fixed.
+        TypeUseLocation.IMPLICIT_LOWER_BOUND,
         TypeUseLocation.IMPLICIT_WILDCARD_UPPER_BOUND_NO_SUPER,
         TypeUseLocation.TYPE_VARIABLE_USE,
         TypeUseLocation.OTHERWISE
@@ -699,7 +703,7 @@ && isNullInclusiveUnderEveryParameterization(
   }
 
   boolean isNullExclusiveUnderEveryParameterization(AnnotatedTypeMirror type) {
-    return nullnessEstablishingPathExists(type, IS_DECLARED_OR_ARRAY);
+    return nullnessEstablishingPathExists(type, IS_DECLARED_OR_ARRAY_OR_NULL);
   }
 
   private boolean nullnessEstablishingPathExists(
@@ -1852,12 +1856,12 @@ private AnnotatedDeclaredType createType(TypeElement element) {
 
   // Avoid lambdas so that our Predicates can have a useful toString() for logging purposes.
 
-  enum IsDeclaredOrArray implements Predicate<TypeMirror> {
-    IS_DECLARED_OR_ARRAY;
+  enum IsDeclaredOrArrayOrNull implements Predicate<TypeMirror> {
+    IS_DECLARED_OR_ARRAY_OR_NULL;
 
     @Override
     public boolean test(TypeMirror t) {
-      return t.getKind() == DECLARED || t.getKind() == ARRAY;
+      return t.getKind() == DECLARED || t.getKind() == ARRAY || t.getKind() == NULL;
     }
   }
 

tests/regression/Issue172.java

@@ -0,0 +1,33 @@
+// Copyright 2024 The JSpecify Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Test case for Issue 172:
+// https://github.com/jspecify/jspecify-reference-checker/issues/172
+
+import org.jspecify.annotations.NullMarked;
+
+class Issue172<E> {
+  E e() {
+    return null;
+  }
+}
+
+class Issue172UnmarkedUse {
+  void foo(Issue172<Object> p) {}
+}
+
+@NullMarked
+class Issue172MarkedUse {
+  void foo(Issue172<Object> p) {}
+}