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 * <div>
029 * Finds nested blocks (blocks that are used freely in the code).
030 * </div>
031 *
032 * <p>
033 * Rationale: Nested blocks are often leftovers from the
034 * debugging process, they confuse the reader.
035 * </p>
036 *
037 * <p>
038 * For example, this check finds the obsolete braces in
039 * </p>
040 * <pre>
041 * public void guessTheOutput()
042 * {
043 *   int whichIsWhich = 0;
044 *   {
045 *     whichIsWhich = 2;
046 *   }
047 *   System.out.println("value = " + whichIsWhich);
048 * }
049 * </pre>
050 *
051 * <p>
052 * and debugging / refactoring leftovers such as
053 * </p>
054 * <pre>
055 * // if (conditionThatIsNotUsedAnyLonger)
056 * {
057 *   System.out.println("unconditional");
058 * }
059 * </pre>
060 *
061 * <p>
062 * A case in a switch statement does not implicitly form a block.
063 * Thus, to be able to introduce local variables that have case scope
064 * it is necessary to open a nested block. This is supported, set
065 * the allowInSwitchCase property to true and include all statements
066 * of the case in the block.
067 * </p>
068 * <ul>
069 * <li>
070 * Property {@code allowInSwitchCase} - Allow nested blocks if they are the
071 * only child of a switch case.
072 * Type is {@code boolean}.
073 * Default value is {@code false}.
074 * </li>
075 * </ul>
076 *
077 * <p>
078 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
079 * </p>
080 *
081 * <p>
082 * Violation Message Keys:
083 * </p>
084 * <ul>
085 * <li>
086 * {@code block.nested}
087 * </li>
088 * </ul>
089 *
090 * @since 3.1
091 */
092@StatelessCheck
093public class AvoidNestedBlocksCheck extends AbstractCheck {
094
095    /**
096     * A key is pointing to the warning message text in "messages.properties"
097     * file.
098     */
099    public static final String MSG_KEY_BLOCK_NESTED = "block.nested";
100
101    /**
102     * Allow nested blocks if they are the only child of a switch case.
103     */
104    private boolean allowInSwitchCase;
105
106    @Override
107    public int[] getDefaultTokens() {
108        return getRequiredTokens();
109    }
110
111    @Override
112    public int[] getAcceptableTokens() {
113        return getRequiredTokens();
114    }
115
116    @Override
117    public int[] getRequiredTokens() {
118        return new int[] {TokenTypes.SLIST};
119    }
120
121    @Override
122    public void visitToken(DetailAST ast) {
123        final DetailAST parent = ast.getParent();
124        if (parent.getType() == TokenTypes.SLIST
125                && (!allowInSwitchCase || hasSiblings(ast))) {
126            log(ast, MSG_KEY_BLOCK_NESTED);
127        }
128    }
129
130    /**
131     * Checks whether the AST node has any siblings or not.
132     *
133     * @param ast node to examine
134     * @return {@code true} if the node has one or more siblings
135     */
136    private static boolean hasSiblings(DetailAST ast) {
137        return ast.getPreviousSibling() != null || ast.getNextSibling() != null;
138    }
139
140    /**
141     * Setter to allow nested blocks if they are the only child of a switch case.
142     *
143     * @param allowInSwitchCase whether nested blocks are allowed
144     *                 if they are the only child of a switch case.
145     * @since 3.2
146     */
147    public void setAllowInSwitchCase(boolean allowInSwitchCase) {
148        this.allowInSwitchCase = allowInSwitchCase;
149    }
150
151}