package org.checkerframework.framework.qual;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* A meta-annotation that restricts the type-use locations where a type qualifier may be written.
* When written together with {@code @Target({ElementType.TYPE_USE})}, the given type qualifier may
* be written only at locations listed in the {@code @TargetLocations(...)} meta-annotation.
* {@code @Target({ElementType.TYPE_USE})} together with no {@code @TargetLocations(...)} means that
* the qualifier can be written on any type use.
*
* <p>This enables a type system designer to permit a qualifier to be written only in certain
* locations. For example, some type systems' top and bottom qualifier (such as {@link
* org.checkerframework.checker.nullness.qual.KeyForBottom}) should only be written on an explicit
* wildcard upper or lower bound. This meta-annotation is a declarative, coarse-grained approach to
* enable that. A {@link org.checkerframework.common.basetype.TypeValidator} must be implemented if
* finer-grained control is necessary.
*/
// TODO: Verify this meta-annotation (step 3 in https://github.com/typetools/checker-framework/issues/515).
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface TargetLocations {
/** Type uses at which the qualifier is permitted to be written in source code. */
TypeUseLocation[] value();
}