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 com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailNode;
  import com.puppycrawl.tools.checkstyle.api.JavadocTokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  import com.puppycrawl.tools.checkstyle.utils.JavadocUtil;
  
  /**
   * <p>
   * Checks that the block tag is followed by description.
   * </p>
   * <ul>
   * <li>
   * Property {@code violateExecutionOnNonTightHtml} - Control when to print violations
   * if the Javadoc being examined by this check violates the tight html rules defined at
   * <a href="https://checkstyle.org/writingjavadocchecks.html#Tight-HTML_rules">Tight-HTML Rules</a>.
   * Type is {@code boolean}.
   * Default value is {@code false}.
   * </li>
   * <li>
   * Property {@code javadocTokens} - javadoc tokens to check
   * Type is {@code java.lang.String[]}.
   * Validation type is {@code tokenSet}.
   * Default value is
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/JavadocTokenTypes.html#PARAM_LITERAL">
   * PARAM_LITERAL</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/JavadocTokenTypes.html#RETURN_LITERAL">
   * RETURN_LITERAL</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/JavadocTokenTypes.html#THROWS_LITERAL">
   * THROWS_LITERAL</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/JavadocTokenTypes.html#EXCEPTION_LITERAL">
   * EXCEPTION_LITERAL</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/JavadocTokenTypes.html#DEPRECATED_LITERAL">
   * DEPRECATED_LITERAL</a>.
   * </li>
   * </ul>
   * <p>
   * To configure the default check that will check {@code @param}, {@code @deprecated},
   * {@code @throws}, {@code @return}:
   * </p>
   * <pre>
   * &lt;module name="NonEmptyAtclauseDescription"/&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * class Test
   * {
   *  // Violation for param "b" and at tags "deprecated", "throws" and "return".
   *  &#47;**
   *  * Some summary.
   *  * &#64;param a Some description
   *  * &#64;param b
   *  * &#64;deprecated
   *  * &#64;throws Exception
   *  * &#64;return
   *  *&#47;
   * public int method(String a, int b) throws Exception {
   *   return 1;
   *  }
   * }
   * </pre>
   * <p>
   * To configure the check to validate {@code @param}, {@code @throws} tags:
   * </p>
   * <pre>
   * &lt;module name="NonEmptyAtclauseDescription"&gt;
   *   &lt;property name="javadocTokens" value="PARAM_LITERAL,THROWS_LITERAL"/&gt;
   *  &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * class Test
   * {
   *  // Violation for param "b" and at tag "throws".
   *  &#47;**
   *  * Some summary.
   *  * &#64;param a Some description
   *  * &#64;param b
   *  * &#64;deprecated
   *  * &#64;throws Exception
   *  * &#64;return
   *  *&#47;
   * public int method(String a, int b) throws Exception {
   *   return 1;
   *  }
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code javadoc.missed.html.close}
   * </li>
   * <li>
   * {@code javadoc.parse.rule.error}
   * </li>
   * <li>
   * {@code javadoc.wrong.singleton.html.tag}
   * </li>
   * <li>
   * {@code non.empty.atclause}
   * </li>
   * </ul>
   *
   * @since 6.0
   */
  @StatelessCheck
  public class NonEmptyAtclauseDescriptionCheck extends AbstractJavadocCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "non.empty.atclause";
  
      @Override
      public int[] getDefaultJavadocTokens() {
          return new int[] {
              JavadocTokenTypes.PARAM_LITERAL,
              JavadocTokenTypes.RETURN_LITERAL,
              JavadocTokenTypes.THROWS_LITERAL,
              JavadocTokenTypes.EXCEPTION_LITERAL,
              JavadocTokenTypes.DEPRECATED_LITERAL,
          };
      }
  
      @Override
      public void visitJavadocToken(DetailNode ast) {
          if (isEmptyTag(ast.getParent())) {
              log(ast.getLineNumber(), MSG_KEY, ast.getText());
          }
      }
  
      /**
       * Tests if block tag is empty.
       *
       * @param tagNode block tag.
       * @return true, if block tag is empty.
       */
      private static boolean isEmptyTag(DetailNode tagNode) {
          final DetailNode tagDescription =
                  JavadocUtil.findFirstToken(tagNode, JavadocTokenTypes.DESCRIPTION);
          return tagDescription == null
              || hasOnlyEmptyText(tagDescription);
      }
  
      /**
       * Tests if description node is empty (has only new lines and blank strings).
       *
       * @param description description node.
       * @return true, if description node has only new lines and blank strings.
       */
      private static boolean hasOnlyEmptyText(DetailNode description) {
          boolean result = true;
          for (DetailNode child : description.getChildren()) {
              if (child.getType() != JavadocTokenTypes.LEADING_ASTERISK
                      && !CommonUtil.isBlank(child.getText())) {
                  result = false;
                  break;
              }
          }
          return result;
      }
  
  }
  