code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 the original author or authors.
  //
  // This library is free software; you can redistribute it and/or
  // modify it under the terms of the GNU Lesser General Public
  // License as published by the Free Software Foundation; either
  // version 2.1 of the License, or (at your option) any later version.
  //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.checks.javadoc;
  
  import java.util.Optional;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.CheckUtil;
  import com.puppycrawl.tools.checkstyle.utils.JavadocUtil;
  
  /**
   * <p>
   * Checks for missing package definition Javadoc comments in package-info.java files.
   * </p>
   * <p>
   * Rationale: description and other related documentation for a package can be written up
   * in the package-info.java file and it gets used in the production of the Javadocs.
   * See <a
   * href="https://docs.oracle.com/javase/8/docs/technotes/tools/windows/javadoc.html#packagecomment"
   * >link</a> for more info.
   * </p>
   * <p>
   * This check specifically only validates package definitions. It will not validate any methods or
   * interfaces declared in the package-info.java file.
   * </p>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name="MissingJavadocPackage"/&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * /**
   * * Provides API classes
   * *&#47;
   * package com.checkstyle.api; // no violation
   * /*
   * * Block comment is not a javadoc
   * *&#47;
   * package com.checkstyle.api; // violation
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code package.javadoc.missing}
   * </li>
   * </ul>
   *
   * @since 8.22
   */
  @StatelessCheck
  public class MissingJavadocPackageCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_PKG_JAVADOC_MISSING = "package.javadoc.missing";
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {TokenTypes.PACKAGE_DEF};
      }
  
      @Override
      public boolean isCommentNodesRequired() {
          return true;
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          if (CheckUtil.isPackageInfo(getFilePath()) && !hasJavadoc(ast)) {
              log(ast, MSG_PKG_JAVADOC_MISSING);
          }
      }
  
      /**
       * Checks that there is javadoc before ast.
       * Because of <a href="https://github.com/checkstyle/checkstyle/issues/4392">parser bug</a>
       * parser can place javadoc comment either as previous sibling of package definition
       * or (if there is annotation between package def and javadoc) inside package definition tree.
       * So we should look for javadoc in both places.
       *
       * @param ast {@link TokenTypes#PACKAGE_DEF} token to check
       * @return true if there is javadoc, false otherwise
       */
      private static boolean hasJavadoc(DetailAST ast) {
          final boolean hasJavadocBefore = ast.getPreviousSibling() != null
              && isJavadoc(ast.getPreviousSibling());
          return hasJavadocBefore || hasJavadocAboveAnnotation(ast);
      }
  
      /**
       * Checks javadoc existence in annotations list.
       *
       * @param ast package def
       * @return true if there is a javadoc, false otherwise
       */
      private static boolean hasJavadocAboveAnnotation(DetailAST ast) {
          final Optional<DetailAST> firstAnnotationChild = Optional.of(ast.getFirstChild())
              .map(DetailAST::getFirstChild)
              .map(DetailAST::getFirstChild);
          boolean result = false;
          if (firstAnnotationChild.isPresent()) {
              for (DetailAST child = firstAnnotationChild.get(); child != null;
                   child = child.getNextSibling()) {
                  if (isJavadoc(child)) {
                      result = true;
                      break;
                  }
              }
          }
          return result;
      }
  
      /**
       * Checks that ast is a javadoc comment.
       *
       * @param ast token to check
       * @return true if ast is a javadoc comment, false otherwise
       */
      private static boolean isJavadoc(DetailAST ast) {
          return ast.getType() == TokenTypes.BLOCK_COMMENT_BEGIN && JavadocUtil.isJavadocComment(ast);
      }
  }
  