001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2025 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 return or yield statements.
031 * For example the following code
032 * </div>
033 * <div class="wrapper"><pre class="prettyprint"><code class="language-java">
034 * if (valid())
035 *   return false;
036 * else
037 *   return true;
038 * </code></pre></div>
039 *
040 * <p>
041 * could be written as
042 * </p>
043 * <div class="wrapper"><pre class="prettyprint"><code class="language-java">
044 * return !valid();
045 * </code></pre></div>
046 *
047 * <p>
048 * The idea for this Check has been shamelessly stolen from the equivalent
049 * <a href="https://pmd.github.io/pmd/pmd_rules_java_design.html#simplifybooleanreturns">
050 *     PMD</a> rule.
051 * </p>
052 *
053 * @since 3.0
054 */
055@StatelessCheck
056public class SimplifyBooleanReturnCheck
057    extends AbstractCheck {
058
059    /**
060     * A key is pointing to the warning message text in "messages.properties"
061     * file.
062     */
063    public static final String MSG_KEY = "simplify.boolReturn";
064
065    @Override
066    public int[] getAcceptableTokens() {
067        return getRequiredTokens();
068    }
069
070    @Override
071    public int[] getDefaultTokens() {
072        return getRequiredTokens();
073    }
074
075    @Override
076    public int[] getRequiredTokens() {
077        return new int[] {TokenTypes.LITERAL_IF};
078    }
079
080    @Override
081    public void visitToken(DetailAST ast) {
082        // LITERAL_IF has the following four or five children:
083        // '('
084        // condition
085        // ')'
086        // thenStatement
087        // [ LITERAL_ELSE (with the elseStatement as a child) ]
088
089        // don't bother if this is not if then else
090        final DetailAST elseLiteral =
091            ast.findFirstToken(TokenTypes.LITERAL_ELSE);
092        if (elseLiteral != null) {
093            final DetailAST elseStatement = elseLiteral.getFirstChild();
094
095            // skip '(' and ')'
096            final DetailAST condition = ast.getFirstChild().getNextSibling();
097            final DetailAST thenStatement = condition.getNextSibling().getNextSibling();
098
099            if (canReturnOrYieldOnlyBooleanLiteral(thenStatement)
100                && canReturnOrYieldOnlyBooleanLiteral(elseStatement)) {
101                log(ast, MSG_KEY);
102            }
103        }
104    }
105
106    /**
107     * Returns if an AST is a return or a yield statement with a boolean literal
108     * or a compound statement that contains only such a return or a yield statement.
109     *
110     * <p>Returns {@code true} iff ast represents
111     * <pre>
112     * return/yield true/false;
113     * </pre>
114     * or
115     * <pre>
116     * {
117     *   return/yield true/false;
118     * }
119     * </pre>
120     *
121     * @param ast the syntax tree to check
122     * @return if ast is a return or a yield statement with a boolean literal.
123     */
124    private static boolean canReturnOrYieldOnlyBooleanLiteral(DetailAST ast) {
125        boolean result = true;
126        if (!isBooleanLiteralReturnOrYieldStatement(ast)) {
127            final DetailAST firstStatement = ast.getFirstChild();
128            result = isBooleanLiteralReturnOrYieldStatement(firstStatement);
129        }
130        return result;
131    }
132
133    /**
134     * Returns if an AST is a return or a yield statement with a boolean literal.
135     *
136     * <p>Returns {@code true} iff ast represents
137     * <pre>
138     * return/yield true/false;
139     * </pre>
140     *
141     * @param ast the syntax tree to check
142     * @return if ast is a return or a yield statement with a boolean literal.
143     */
144    private static boolean isBooleanLiteralReturnOrYieldStatement(DetailAST ast) {
145        boolean booleanReturnStatement = false;
146
147        if (ast != null && (ast.getType() == TokenTypes.LITERAL_RETURN
148                                || ast.getType() == TokenTypes.LITERAL_YIELD)) {
149            final DetailAST expr = ast.getFirstChild();
150
151            if (expr.getType() != TokenTypes.SEMI) {
152                final DetailAST value = expr.getFirstChild();
153                booleanReturnStatement = TokenUtil.isBooleanLiteralType(value.getType());
154            }
155        }
156        return booleanReturnStatement;
157    }
158}