001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2024 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle.checks.design;
021
022import com.puppycrawl.tools.checkstyle.StatelessCheck;
023import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
024import com.puppycrawl.tools.checkstyle.api.DetailAST;
025import com.puppycrawl.tools.checkstyle.api.TokenTypes;
026
027/**
028 * <p>
029 * Checks that sealed classes and interfaces have a permits list.
030 * </p>
031 * <p>
032 *     Rationale: When a permits clause is omitted from a sealed class,
033 *     any class within the same compilation unit can extend it. This differs
034 *     from other sealed classes where permitted subclasses are explicitly
035 *     declared, making them readily visible to the reader. Without a permits
036 *     clause, identifying potential subclasses requires searching the entire
037 *     compilation unit, which can be challenging, especially in large files
038 *     with complex class hierarchies.
039 * </p>
040 * <p>
041 * See the <a href="https://docs.oracle.com/javase/specs/jls/se22/html/jls-13.html#jls-13.4.2">
042 * Java Language Specification</a> for more information about sealed classes.
043 * </p>
044 * <p>
045 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
046 * </p>
047 * <p>
048 * Violation Message Keys:
049 * </p>
050 * <ul>
051 * <li>
052 * {@code sealed.should.have.permits}
053 * </li>
054 * </ul>
055 *
056 * @since 10.18.0
057 */
058
059@StatelessCheck
060public class SealedShouldHavePermitsListCheck extends AbstractCheck {
061
062    /**
063     * A key is pointing to the warning message text in "messages.properties"
064     * file.
065     */
066    public static final String MSG_KEY = "sealed.should.have.permits";
067
068    @Override
069    public int[] getDefaultTokens() {
070        return getRequiredTokens();
071    }
072
073    @Override
074    public int[] getAcceptableTokens() {
075        return getRequiredTokens();
076    }
077
078    @Override
079    public int[] getRequiredTokens() {
080        return new int[] {
081            TokenTypes.CLASS_DEF,
082            TokenTypes.INTERFACE_DEF,
083        };
084    }
085
086    @Override
087    public void visitToken(DetailAST ast) {
088        final DetailAST modifiers = ast.findFirstToken(TokenTypes.MODIFIERS);
089        final boolean isSealed = modifiers.findFirstToken(TokenTypes.LITERAL_SEALED) != null;
090        final boolean hasPermitsList = ast.findFirstToken(TokenTypes.PERMITS_CLAUSE) != null;
091
092        if (isSealed && !hasPermitsList) {
093            log(ast, MSG_KEY);
094        }
095    }
096}