dev.mccue.guava.base.ParametricNullness Maven / Gradle / Ivy
/*
* Copyright (C) 2021 The Guava 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.
*/
package dev.mccue.guava.base;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
/**
* Annotates a "top-level" type-variable usage that takes its nullness from the type argument
* supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns
* {@code @ParametricNullness E}, which means:
*
*
* - {@code getElement} on a {@code Multiset.Entry<@NonNull String>} returns {@code @NonNull
* String}.
*
- {@code getElement} on a {@code Multiset.Entry<@Nullable String>} returns {@code @Nullable
* String}.
*
*
* This is the same behavior as type-variable usages have to Kotlin and to the Checker Framework.
* Contrast the method above to:
*
*
* - methods whose return type is a type variable but which can never return {@code null},
* typically because the type forbids nullable type arguments: For example, {@code
* ImmutableList.get} returns {@code E}, but that value is never {@code null}. (Accordingly,
* {@code ImmutableList} is declared to forbid {@code ImmutableList<@Nullable String>}.)
*
- methods whose return type is a type variable but which can return {@code null} regardless
* of the type argument supplied by the user of the class: For example, {@code
* ImmutableMap.get} returns {@code @Nullable E} because the method can return {@code null}
* even on an {@code ImmutableMap
}.
*
*
* Consumers of this annotation include:
*
*
* - Kotlin, for which it makes the type-variable usage (a) a Kotlin platform type when the type
* argument is non-nullable and (b) nullable when the type argument is nullable. We use this
* to "undo" {@link ElementTypesAreNonnullByDefault}. It is the best we can do for Kotlin
* under our current constraints.
*
- NullAway, which will treat it
* identically to {@code Nullable} as of version 0.9.9. To treat it that way before then,
* you can set {@code
* -XepOpt:NullAway:CustomNullableAnnotations=dev.mccue.guava.base.ParametricNullness,...,com.google.common.util.concurrent.ParametricNullness},
* where the {@code ...} contains the names of all the other {@code ParametricNullness}
* annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
* list.
*
- J2ObjC
*
- {@code NullPointerTester}, at least in the Android backport (where the type-use annotations
* {@code NullPointerTester} would need are not available) and in case of JDK-8202469
*
*
* This annotation is a temporary hack. We will remove it after we're able to adopt the JSpecify nullness annotations and tools no longer need
* it.
*/
@Retention(RUNTIME)
@Target({FIELD, METHOD, PARAMETER})
@dev.mccue.jsr305.meta.TypeQualifierNickname
@dev.mccue.jsr305.Nonnull(when = dev.mccue.jsr305.meta.When.UNKNOWN)
@interface ParametricNullness {}