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.blocks;
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 * Finds nested blocks (blocks that are used freely in the code).
030 * </p>
031 * <p>
032 * Rationale: Nested blocks are often leftovers from the
033 * debugging process, they confuse the reader.
034 * </p>
035 * <p>
036 * For example, this check finds the obsolete braces in
037 * </p>
038 * <pre>
039 * public void guessTheOutput()
040 * {
041 *   int whichIsWhich = 0;
042 *   {
043 *     whichIsWhich = 2;
044 *   }
045 *   System.out.println("value = " + whichIsWhich);
046 * }
047 * </pre>
048 * <p>
049 * and debugging / refactoring leftovers such as
050 * </p>
051 * <pre>
052 * // if (conditionThatIsNotUsedAnyLonger)
053 * {
054 *   System.out.println("unconditional");
055 * }
056 * </pre>
057 * <p>
058 * A case in a switch statement does not implicitly form a block.
059 * Thus, to be able to introduce local variables that have case scope
060 * it is necessary to open a nested block. This is supported, set
061 * the allowInSwitchCase property to true and include all statements
062 * of the case in the block.
063 * </p>
064 * <ul>
065 * <li>
066 * Property {@code allowInSwitchCase} - Allow nested blocks if they are the
067 * only child of a switch case.
068 * Type is {@code boolean}.
069 * Default value is {@code false}.
070 * </li>
071 * </ul>
072 * <p>
073 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
074 * </p>
075 * <p>
076 * Violation Message Keys:
077 * </p>
078 * <ul>
079 * <li>
080 * {@code block.nested}
081 * </li>
082 * </ul>
083 *
084 * @since 3.1
085 */
086@StatelessCheck
087public class AvoidNestedBlocksCheck extends AbstractCheck {
088
089    /**
090     * A key is pointing to the warning message text in "messages.properties"
091     * file.
092     */
093    public static final String MSG_KEY_BLOCK_NESTED = "block.nested";
094
095    /**
096     * Allow nested blocks if they are the only child of a switch case.
097     */
098    private boolean allowInSwitchCase;
099
100    @Override
101    public int[] getDefaultTokens() {
102        return getRequiredTokens();
103    }
104
105    @Override
106    public int[] getAcceptableTokens() {
107        return getRequiredTokens();
108    }
109
110    @Override
111    public int[] getRequiredTokens() {
112        return new int[] {TokenTypes.SLIST};
113    }
114
115    @Override
116    public void visitToken(DetailAST ast) {
117        final DetailAST parent = ast.getParent();
118        if (parent.getType() == TokenTypes.SLIST
119                && (!allowInSwitchCase || hasSiblings(ast))) {
120            log(ast, MSG_KEY_BLOCK_NESTED);
121        }
122    }
123
124    /**
125     * Checks whether the AST node has any siblings or not.
126     *
127     * @param ast node to examine
128     * @return {@code true} if the node has one or more siblings
129     */
130    private static boolean hasSiblings(DetailAST ast) {
131        return ast.getPreviousSibling() != null || ast.getNextSibling() != null;
132    }
133
134    /**
135     * Setter to allow nested blocks if they are the only child of a switch case.
136     *
137     * @param allowInSwitchCase whether nested blocks are allowed
138     *                 if they are the only child of a switch case.
139     * @since 3.2
140     */
141    public void setAllowInSwitchCase(boolean allowInSwitchCase) {
142        this.allowInSwitchCase = allowInSwitchCase;
143    }
144
145}