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package org.checkerframework.checker.nullness.qual;

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;
import org.checkerframework.framework.qual.InheritedAnnotation;
import org.checkerframework.framework.qual.PostconditionAnnotation;

// TODO: In a fix for https://tinyurl.com/cfissue/1917, add the text:
// Every prefix expression is also non-null; for example, {@code
// @EnsuresNonNull(expression="a.b.c")} implies that both {@code a.b} and {@code a.b.c} are
// non-null.
/**
 * Indicates that the value expressions are non-null, if the method terminates successfully.
 *
 * This postcondition annotation is useful for methods that initialize a field:
 *
 * 

 * {@literal @}EnsuresNonNull("theMap")
 *  public static void initialize() {
 *    theMap = new HashMap<>();
 *  }
 * 
 *
 * It can also be used for a method that fails if a given expression is null:
 *
 * 
 *  /** Throws an exception if the argument is null. */
 * {@literal @}EnsuresNonNull("#1")
 *  void assertNonNull(Object arg) { ... }
 * 
 *
 * @see NonNull
 * @see org.checkerframework.checker.nullness.NullnessChecker
 * @checker_framework.manual #nullness-checker Nullness Checker
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
@PostconditionAnnotation(qualifier = NonNull.class)
@InheritedAnnotation
@Repeatable(EnsuresNonNull.List.class)
public @interface EnsuresNonNull {
    /**
     * Returns Java expressions that are {@link NonNull} after successful method termination.
     *
     * @return Java expressions that are {@link NonNull} after successful method termination
     * @checker_framework.manual #java-expressions-as-arguments Syntax of Java expressions
     */
    String[] value();

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