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.coding;
  
  import java.util.List;
  import java.util.stream.Collectors;
  
  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.utils.CommonUtil;
  import com.puppycrawl.tools.checkstyle.xpath.AbstractNode;
  import com.puppycrawl.tools.checkstyle.xpath.RootNode;
  import net.sf.saxon.Configuration;
  import net.sf.saxon.om.Item;
  import net.sf.saxon.sxpath.XPathDynamicContext;
  import net.sf.saxon.sxpath.XPathEvaluator;
  import net.sf.saxon.sxpath.XPathExpression;
  import net.sf.saxon.trans.XPathException;
  
  /**
   * <p>
   * Evaluates Xpath query and report violation on all matching AST nodes. This check allows
   * user to implement custom checks using Xpath. If Xpath query is not specified explicitly,
   * then the check does nothing.
   * </p>
   * <p>
   * It is recommended to define custom message for violation to explain what is not allowed and what
   * to use instead, default message might be too abstract. To customize a message you need to
   * add {@code message} element with <b>matchxpath.match</b> as {@code key} attribute and
   * desired message as {@code value} attribute.
   * </p>
   * <p>
   * Please read more about Xpath syntax at
   * <a href="https://www.saxonica.com/html/documentation10/expressions/">Xpath Syntax</a>.
   * Information regarding Xpath functions can be found at
   * <a href="https://www.saxonica.com/html/documentation10/functions/fn/">XSLT/XPath Reference</a>.
   * Note, that <b>@text</b> attribute can be used only with token types that are listed in
   * <a href="https://github.com/checkstyle/checkstyle/search?q=%22TOKEN_TYPES_WITH_TEXT_ATTRIBUTE+%3D+Arrays.asList%22">
   *     XpathUtil</a>.
   * </p>
   * <ul>
   * <li>
   * Property {@code query} - Specify Xpath query.
   * Type is {@code java.lang.String}.
   * Default value is {@code ""}.
   * </li>
   * </ul>
   * <p>
   * Checkstyle provides <a href="https://checkstyle.org/cmdline.html">command line tool</a>
   * and <a href="https://checkstyle.org/writingchecks.html#The_Checkstyle_SDK_Gui">GUI
   * application</a> with options to show AST and to ease usage of Xpath queries.
   * </p>
   * <p><b>-T</b> option prints AST tree of the checked file.</p>
   * <pre>
   * $ java -jar checkstyle-X.XX-all.jar -T Main.java
   * CLASS_DEF -&gt; CLASS_DEF [1:0]
   * |--MODIFIERS -&gt; MODIFIERS [1:0]
   * |   `--LITERAL_PUBLIC -&gt; public [1:0]
   * |--LITERAL_CLASS -&gt; class [1:7]
   * |--IDENT -&gt; Main [1:13]
   * `--OBJBLOCK -&gt; OBJBLOCK [1:18]
   * |--LCURLY -&gt; { [1:18]
   * |--METHOD_DEF -&gt; METHOD_DEF [2:4]
   * |   |--MODIFIERS -&gt; MODIFIERS [2:4]
   * |   |   `--LITERAL_PUBLIC -&gt; public [2:4]
   * |   |--TYPE -&gt; TYPE [2:11]
   * |   |   `--IDENT -&gt; String [2:11]
   * |   |--IDENT -&gt; sayHello [2:18]
   * |   |--LPAREN -&gt; ( [2:26]
   * |   |--PARAMETERS -&gt; PARAMETERS [2:27]
   * |   |   `--PARAMETER_DEF -&gt; PARAMETER_DEF [2:27]
   * |   |       |--MODIFIERS -&gt; MODIFIERS [2:27]
   * |   |       |--TYPE -&gt; TYPE [2:27]
   * |   |       |   `--IDENT -&gt; String [2:27]
   * |   |       `--IDENT -&gt; name [2:34]
   * |   |--RPAREN -&gt; ) [2:38]
   * |   `--SLIST -&gt; { [2:40]
   * |       |--LITERAL_RETURN -&gt; return [3:8]
   * |       |   |--EXPR -&gt; EXPR [3:25]
   * |       |   |   `--PLUS -&gt; + [3:25]
   * |       |   |       |--STRING_LITERAL -&gt; "Hello, " [3:15]
   * |       |   |       `--IDENT -&gt; name [3:27]
   * |       |   `--SEMI -&gt; ; [3:31]
   * |       `--RCURLY -&gt; } [4:4]
   * `--RCURLY -&gt; } [5:0]
   * </pre>
   * <p><b>-b</b> option shows AST nodes that match given Xpath query. This command can be used to
   * validate accuracy of Xpath query against given file.</p>
   * <pre>
   * $ java -jar checkstyle-X.XX-all.jar Main.java -b "//METHOD_DEF[./IDENT[@text='sayHello']]"
   * CLASS_DEF -&gt; CLASS_DEF [1:0]
   * `--OBJBLOCK -&gt; OBJBLOCK [1:18]
   * |--METHOD_DEF -&gt; METHOD_DEF [2:4]
   * </pre>
   * <p>
   * The following example demonstrates validation of methods order, so that public methods should
   * come before the private ones:
   * </p>
   * <pre>
   * &lt;module name="MatchXpath"&gt;
   *  &lt;property name="query" value="//METHOD_DEF[.//LITERAL_PRIVATE and
   *  following-sibling::METHOD_DEF[.//LITERAL_PUBLIC]]"/&gt;
   *  &lt;message key=&quot;matchxpath.match&quot;
   *  value=&quot;Private methods must appear after public methods&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * public class Test {
   *  public void method1() { }
   *  private void method2() { } // violation
   *  public void method3() { }
   *  private void method4() { } // violation
   *  public void method5() { }
   *  private void method6() { } // ok
   * }
   * </pre>
   * <p>
   * To violate if there are any parametrized constructors
   * </p>
   * <pre>
   * &lt;module name="MatchXpath"&gt;
   *  &lt;property name="query" value="//CTOR_DEF[count(./PARAMETERS/*) &gt; 0]"/&gt;
   *  &lt;message key=&quot;matchxpath.match&quot;
   *  value=&quot;Parameterized constructors are not allowed, there should be only default
   *  ctor&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * public class Test {
   *  public Test(Object c) { } // violation
   *  public Test(int a, HashMap&lt;String, Integer&gt; b) { } // violation
   *  public Test() { } // ok
   * }
   * </pre>
   * <p>
   * To violate if method name is 'test' or 'foo'
   * </p>
   * <pre>
   * &lt;module name="MatchXpath"&gt;
   *  &lt;property name="query" value="//METHOD_DEF[./IDENT[@text='test' or @text='foo']]"/&gt;
   *  &lt;message key=&quot;matchxpath.match&quot;
   *  value=&quot;Method name should not be 'test' or 'foo'&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * public class Test {
   *  public void test() {} // violation
   *  public void getName() {} // ok
   *  public void foo() {} // violation
   *  public void sayHello() {} // ok
   * }
   * </pre>
   * <p>
   * To violate if new instance creation was done without <b>var</b> type
   * </p>
   * <pre>
   * &lt;module name=&quot;MatchXpath&quot;&gt;
   *  &lt;property name=&quot;query&quot; value=&quot;//VARIABLE_DEF[./ASSIGN/EXPR/LITERAL_NEW
   *  and not(./TYPE/IDENT[@text='var'])]&quot;/&gt;
   *  &lt;message key=&quot;matchxpath.match&quot;
   *  value=&quot;New instances should be created via 'var' keyword to avoid duplication of type
   *  reference in statement&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * public class Test {
   *   public void foo() {
   *     SomeObject a = new SomeObject(); // violation
   *     var b = new SomeObject(); // OK
   *   }
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code matchxpath.match}
   * </li>
   * </ul>
   *
   * @since 8.39
   */
  @StatelessCheck
  public class MatchXpathCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text provided by user.
       */
      public static final String MSG_KEY = "matchxpath.match";
  
      /** Specify Xpath query. */
      private String query = "";
  
      /** Xpath expression. */
      private XPathExpression xpathExpression;
  
      /**
       * Setter to specify Xpath query.
       *
       * @param query Xpath query.
       * @throws IllegalStateException if creation of xpath expression fails
       */
      public void setQuery(String query) {
          this.query = query;
          if (!query.isEmpty()) {
              try {
                  final XPathEvaluator xpathEvaluator =
                          new XPathEvaluator(Configuration.newConfiguration());
                  xpathExpression = xpathEvaluator.createExpression(query);
              }
              catch (XPathException ex) {
                  throw new IllegalStateException("Creating Xpath expression failed: " + query, ex);
              }
          }
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return CommonUtil.EMPTY_INT_ARRAY;
      }
  
      @Override
      public boolean isCommentNodesRequired() {
          return true;
      }
  
      @Override
      public void beginTree(DetailAST rootAST) {
          if (xpathExpression != null) {
              final List<DetailAST> matchingNodes = findMatchingNodesByXpathQuery(rootAST);
              matchingNodes.forEach(node -> log(node, MSG_KEY));
          }
      }
  
      /**
       * Find nodes that match query.
       *
       * @param rootAST root node
       * @return list of matching nodes
       * @throws IllegalStateException if evaluation of xpath query fails
       */
      private List<DetailAST> findMatchingNodesByXpathQuery(DetailAST rootAST) {
          try {
              final RootNode rootNode = new RootNode(rootAST);
              final XPathDynamicContext xpathDynamicContext =
                      xpathExpression.createDynamicContext(rootNode);
              final List<Item> matchingItems = xpathExpression.evaluate(xpathDynamicContext);
              return matchingItems.stream()
                      .map(item -> (DetailAST) ((AbstractNode) item).getUnderlyingNode())
                      .collect(Collectors.toList());
          }
          catch (XPathException ex) {
              throw new IllegalStateException("Evaluation of Xpath query failed: " + query, ex);
          }
      }
  }
  