checker-qual/src/main/java/org/checkerframework/framework/qual/RequiresQualifier.java

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 precondition annotation to indicate that a method requires certain expressions to have a
 * certain qualifier at the time of the call to the method. The expressions for which the annotation
 * must hold after the method's execution are indicated by {@code expression} and are specified
 * using a string. The qualifier is specified by {@code qualifier}.
 *
 * @checker_framework.manual #java-expressions-as-arguments Syntax of Java expressions
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
@Repeatable(RequiresQualifier.List.class)
public @interface RequiresQualifier {
  /**
   * Returns the Java expressions for which the annotation need to be present.
   *
   * @return the Java expressions for which the annotation need to be present
   * @checker_framework.manual #java-expressions-as-arguments Syntax of Java expressions
   */
  String[] expression();

  /**
   * Returns the qualifier that is required.
   *
   * @return the qualifier that is required
   */
  Class<? extends Annotation> qualifier();

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