package org.checkerframework.checker.interning.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;
import javax.lang.model.type.TypeKind;
import org.checkerframework.framework.qual.DefaultFor;
import org.checkerframework.framework.qual.ImplicitFor;
import org.checkerframework.framework.qual.LiteralKind;
import org.checkerframework.framework.qual.SubtypeOf;
import org.checkerframework.framework.qual.TypeUseLocation;

/**
 * Indicates that a variable has been interned, i.e., that the variable refers to the canonical
 * representation of an object.
 *
 * <p>To specify that all objects of a given type are interned, annotate the class declaration:
 *
 * <pre>
 *   public @Interned class MyInternedClass { ... }
 * </pre>
 *
 * This is equivalent to annotating every use of MyInternedClass, in a declaration or elsewhere. For
 * example, enum classes are implicitly so annotated.
 *
 * <p>This annotation is associated with the {@link
 * org.checkerframework.checker.interning.InterningChecker}.
 *
 * @see org.checkerframework.checker.interning.InterningChecker
 * @checker_framework.manual #interning-checker Interning Checker
 */
@SubtypeOf(UnknownInterned.class)
@ImplicitFor(
    literals = {LiteralKind.ALL},
    types = {
        TypeKind.BOOLEAN,
        TypeKind.BYTE,
        TypeKind.CHAR,
        TypeKind.DOUBLE,
        TypeKind.FLOAT,
        TypeKind.INT,
        TypeKind.LONG,
        TypeKind.SHORT
    },
    typeNames = {Void.class}
)
@DefaultFor(value = {TypeUseLocation.LOWER_BOUND})
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER})
public @interface Interned {}