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.coding;
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;
026import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
027
028/**
029 * <div>
030 * Checks for over-complicated boolean expressions. Currently, it finds code like
031 * {@code if (b == true)}, {@code b || true}, {@code !false},
032 * {@code boolean a = q > 12 ? true : false},
033 * etc.
034 * </div>
035 *
036 * <p>
037 * Rationale: Complex boolean logic makes code hard to understand and maintain.
038 * </p>
039 *
040 * @since 3.0
041 */
042@StatelessCheck
043public class SimplifyBooleanExpressionCheck
044        extends AbstractCheck {
045
046    /**
047     * A key is pointing to the warning message text in "messages.properties"
048     * file.
049     */
050    public static final String MSG_KEY = "simplify.expression";
051
052    /**
053     * Creates a new {@code SimplifyBooleanExpressionCheck} instance.
054     */
055    public SimplifyBooleanExpressionCheck() {
056        // no code by default
057    }
058
059    @Override
060    public int[] getDefaultTokens() {
061        return getRequiredTokens();
062    }
063
064    @Override
065    public int[] getAcceptableTokens() {
066        return getRequiredTokens();
067    }
068
069    @Override
070    public int[] getRequiredTokens() {
071        return new int[] {TokenTypes.LITERAL_TRUE, TokenTypes.LITERAL_FALSE};
072    }
073
074    @Override
075    public void visitToken(DetailAST ast) {
076        final DetailAST parent = ast.getParent();
077        switch (parent.getType()) {
078            case TokenTypes.NOT_EQUAL,
079                 TokenTypes.EQUAL,
080                 TokenTypes.LNOT,
081                 TokenTypes.LOR,
082                 TokenTypes.LAND -> log(parent, MSG_KEY);
083
084            case TokenTypes.QUESTION -> {
085                final DetailAST firstChild = skipParentheses(parent.getFirstChild());
086                final DetailAST nextSibling = skipParentheses(ast.getNextSibling());
087                if (TokenUtil.isBooleanLiteralType(firstChild.getType())
088                        || nextSibling != null
089                        && TokenUtil.isBooleanLiteralType(
090                                skipParentheses(nextSibling.getNextSibling()).getType())) {
091                    log(parent, MSG_KEY);
092                }
093            }
094
095            default -> {
096                // do nothing
097            }
098        }
099    }
100
101    /**
102     * Iterates sibling nodes, skipping parentheses.
103     *
104     * @param node The starting node.
105     * @return The first sibling not of type {@code TokenTypes.LPAREN} or
106     *     {@code TokenTypes.RPAREN}, or {@code null} if no such node exists.
107     */
108    private static DetailAST skipParentheses(DetailAST node) {
109        DetailAST result = node;
110        while (TokenUtil.isOfType(result, TokenTypes.LPAREN, TokenTypes.RPAREN)) {
111            result = result.getNextSibling();
112        }
113        return result;
114    }
115
116}