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package org.checkerframework.common.subtyping.qual;
import java.lang.annotation.ElementType;
import java.lang.annotation.Target;
import org.checkerframework.framework.qual.SubtypeOf;
import org.checkerframework.framework.qual.TargetLocations;
import org.checkerframework.framework.qual.TypeUseLocation;
/**
* A special annotation intended solely for representing the bottom type in the qualifier hierarchy.
* It should not be used! Instead, each type system should define its own dedicated bottom type.
*
* This qualifier is used automatically if the existing qualifiers do not have a bottom type.
* This only works the user never runs two type systems together. Furthermore, because it has no
* {@code @RetentionPolicy} meta-annotation, this qualifier will not be stored in bytecode. So, only
* use this qualifier during prototyping of very simple type systems. For realistic systems,
* introduce a top and bottom qualifier that gets stored in bytecode.
*
*
To use this qualifier, the type system designer needs to use methods like {@link
* org.checkerframework.framework.type.treeannotator.ImplicitsTreeAnnotator#addTreeKind(com.sun.source.tree.Tree.Kind,
* javax.lang.model.element.AnnotationMirror)} to add implicit annotations and needs to manually add
* the bottom qualifier to the qualifier hierarchy.
*
* @see org.checkerframework.framework.type.QualifierHierarchy#getBottomAnnotations()
*/
@SubtypeOf({})
@Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER})
@TargetLocations({TypeUseLocation.EXPLICIT_LOWER_BOUND, TypeUseLocation.EXPLICIT_UPPER_BOUND})
public @interface Bottom {}