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checker-qual contains annotations (type qualifiers) that a programmer writes to specify Java code for type-checking by the Checker Framework.

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package org.checkerframework.framework.qual;

import java.lang.annotation.Annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * A postcondition annotation to indicate that a method ensures that certain expressions have a
 * certain type qualifier once the method has successfully terminated. The expressions for which the
 * qualifier holds after the method's execution are indicated by {@code expression} and are
 * specified using a string. The qualifier is specified by the {@code qualifier} annotation element.
 *
 * Here is an example use:
 *
 * 

 *  {@literal @}EnsuresQualifier(expression = "p.f1", qualifier = Odd.class)
 *   void oddF1_1() {
 *       p.f1 = null;
 *   }
 * 
 *
 * Some type systems have specialized versions of this annotation, such as {@code
 * org.checkerframework.checker.nullness.qual.EnsuresNonNull} and {@code
 * org.checkerframework.checker.lock.qual.EnsuresLockHeld}.
 *
 * @see EnsuresQualifierIf
 * @checker_framework.manual #java-expressions-as-arguments Syntax of Java expressions
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
@InheritedAnnotation
@Repeatable(EnsuresQualifier.List.class)
public @interface EnsuresQualifier {
    /**
     * Returns the Java expressions for which the qualifier holds after successful method
     * termination.
     *
     * @return the Java expressions for which the qualifier holds after successful method
     *     termination
     * @checker_framework.manual #java-expressions-as-arguments Syntax of Java expressions
     */
    String[] expression();

    /**
     * Returns the qualifier that is guaranteed to hold on successful termination of the method.
     *
     * @return the qualifier that is guaranteed to hold on successful termination of the method
     */
    Class qualifier();

    /**
     * A wrapper annotation that makes the {@link EnsuresQualifier} annotation repeatable.
     *
     * Programmers generally do not need to write this. It is created by Java when a programmer
     * writes more than one {@link EnsuresQualifier} annotation at the same location.
     */
    @Documented
    @Retention(RetentionPolicy.RUNTIME)
    @Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
    @InheritedAnnotation
    public static @interface List {
        /**
         * Return the repeatable annotations.
         *
         * @return the repeatable annotations
         */
        EnsuresQualifier[] value();
    }
}