001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2026 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 * <div>
029 * Checks that sealed classes and interfaces have a permits list.
030 * </div>
031 *
032 * <p>
033 *     Rationale: When a permits clause is omitted from a sealed class,
034 *     any class within the same compilation unit can extend it. This differs
035 *     from other sealed classes where permitted subclasses are explicitly
036 *     declared, making them readily visible to the reader. Without a permits
037 *     clause, identifying potential subclasses requires searching the entire
038 *     compilation unit, which can be challenging, especially in large files
039 *     with complex class hierarchies.
040 * </p>
041 *
042 * <p>
043 * See the <a href="https://docs.oracle.com/javase/specs/jls/se22/html/jls-13.html#jls-13.4.2">
044 * Java Language Specification</a> for more information about sealed classes.
045 * </p>
046 *
047 * @since 10.18.0
048 */
049
050@StatelessCheck
051public class SealedShouldHavePermitsListCheck extends AbstractCheck {
052
053    /**
054     * A key is pointing to the warning message text in "messages.properties" file.
055     */
056    public static final String MSG_KEY = "sealed.should.have.permits";
057
058    /**
059     * Creates a new {@code SealedShouldHavePermitsListCheck} instance.
060     */
061    public SealedShouldHavePermitsListCheck() {
062        // no code by default
063    }
064
065    @Override
066    public int[] getDefaultTokens() {
067        return getRequiredTokens();
068    }
069
070    @Override
071    public int[] getAcceptableTokens() {
072        return getRequiredTokens();
073    }
074
075    @Override
076    public int[] getRequiredTokens() {
077        return new int[] {
078            TokenTypes.CLASS_DEF,
079            TokenTypes.INTERFACE_DEF,
080        };
081    }
082
083    @Override
084    public void visitToken(DetailAST ast) {
085        final DetailAST modifiers = ast.findFirstToken(TokenTypes.MODIFIERS);
086        final boolean isSealed = modifiers.findFirstToken(TokenTypes.LITERAL_SEALED) != null;
087        final boolean hasPermitsList = ast.findFirstToken(TokenTypes.PERMITS_CLAUSE) != null;
088
089        if (isSealed && !hasPermitsList) {
090            log(ast, MSG_KEY);
091        }
092    }
093
094}