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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 conditional postcondition annotation to indicate that a method ensures that certain expressions
 * have a certain qualifier once the method has terminated, and if the result is as indicated by
 * {@code result}. 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 @}EnsuresQualifierIf(result = true, expression = "#1", qualifier = Odd.class)
 *    boolean isOdd(int p1, int p2) {
 *        return p1 % 2 == 1;
 *    }
 * 
 *
 * This annotation is only applicable to methods with a boolean return type.
 *
 * 
Some type systems have specialized versions of this annotation, such as {@code
 * org.checkerframework.checker.nullness.qual.EnsuresNonNullIf} and {@code
 * org.checkerframework.checker.lock.qual.EnsuresLockHeldIf}.
 *
 * @see EnsuresQualifier
 * @checker_framework.manual #java-expressions-as-arguments Syntax of Java expressions
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
@InheritedAnnotation
@Repeatable(EnsuresQualifierIf.List.class)
public @interface EnsuresQualifierIf {
    /**
     * Returns the return value of the method that needs to hold for the postcondition to hold.
     *
     * @return the return value of the method that needs to hold for the postcondition to hold
     */
    boolean result();

    /**
     * Returns the Java expressions for which the qualifier holds if the method terminates with
     * return value {@link #result()}.
     *
     * @return the Java expressions for which the qualifier holds if the method terminates with
     *     return value {@link #result()}
     * @checker_framework.manual #java-expressions-as-arguments Syntax of Java expressions
     */
    String[] expression();

    /**
     * Returns the qualifier that is guaranteed to hold if the method terminates with return value
     * {@link #result()}.
     *
     * @return the qualifier that is guaranteed to hold if the method terminates with return value
     *     {@link #result()}
     */
    Class qualifier();

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