xref: /aosp_15_r20/external/jspecify/samples/AugmentedInferenceAgreesWithBaseInference.java (revision 2167191df2fa07300797f1ac5b707370b5f38c48)
1 /*
2  * Copyright 2020 The JSpecify Authors.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *     http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 import org.jspecify.annotations.NullMarked;
17 import org.jspecify.annotations.Nullable;
18 
19 @NullMarked
20 abstract class AugmentedInferenceAgreesWithBaseInference {
x(Foo<Object> a, Foo<@Nullable Object> b)21   void x(Foo<Object> a, Foo<@Nullable Object> b) {
22     // List of possibly heterogeneous Foo types.
23     List<Foo<?>> l1 = makeList(a, b);
24 
25     /*
26      * List of some unspecified homogeneous Foo type. There is such a type under plain Java (since
27      * the base type for both is Foo<Object>) but not under JSpecify (since one is Foo<Object> and
28      * the other is Foo<@Nullable Object>).
29      *
30      * Notice that `makeList(a, b)` is fine "in a vacuum" even under JSpecify (as shown above). Only
31      * here, where the type of the expression is forced to conform to the target type, is there a
32      * problem.
33      */
34     // jspecify_nullness_mismatch
35     List<? extends Foo<?>> l2 = makeList(a, b);
36   }
37 
makeList(T a, T b)38   abstract <T extends @Nullable Object> List<T> makeList(T a, T b);
39 
40   interface Foo<T extends @Nullable Object> {}
41 
42   interface List<T extends @Nullable Object> {}
43 }
44