001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2020 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 * <pre>
065 * switch (a)
066 * {
067 *   case 0:
068 *     // Never OK, break outside block
069 *     {
070 *       x = 1;
071 *     }
072 *     break;
073 *   case 1:
074 *     // Never OK, statement outside block
075 *     System.out.println("Hello");
076 *     {
077 *       x = 2;
078 *       break;
079 *     }
080 *   case 2:
081 *     // OK if allowInSwitchCase is true
082 *     {
083 *       System.out.println("Hello");
084 *       x = 3;
085 *       break;
086 *     }
087 * }
088 * </pre>
089 * <ul>
090 * <li>
091 * Property {@code allowInSwitchCase} - Allow nested blocks if they are the
092 * only child of a switch case.
093 * Type is {@code boolean}.
094 * Default value is {@code false}.
095 * </li>
096 * </ul>
097 * <p>
098 * To configure the check:
099 * </p>
100 * <pre>
101 * &lt;module name="AvoidNestedBlocks"/&gt;
102 * </pre>
103 * <p>
104 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
105 * </p>
106 * <p>
107 * Violation Message Keys:
108 * </p>
109 * <ul>
110 * <li>
111 * {@code block.nested}
112 * </li>
113 * </ul>
114 *
115 * @since 3.1
116 */
117@StatelessCheck
118public class AvoidNestedBlocksCheck extends AbstractCheck {
119
120    /**
121     * A key is pointing to the warning message text in "messages.properties"
122     * file.
123     */
124    public static final String MSG_KEY_BLOCK_NESTED = "block.nested";
125
126    /**
127     * Allow nested blocks if they are the only child of a switch case.
128     */
129    private boolean allowInSwitchCase;
130
131    @Override
132    public int[] getDefaultTokens() {
133        return getRequiredTokens();
134    }
135
136    @Override
137    public int[] getAcceptableTokens() {
138        return getRequiredTokens();
139    }
140
141    @Override
142    public int[] getRequiredTokens() {
143        return new int[] {TokenTypes.SLIST};
144    }
145
146    @Override
147    public void visitToken(DetailAST ast) {
148        final DetailAST parent = ast.getParent();
149        if (parent.getType() == TokenTypes.SLIST
150                && (!allowInSwitchCase || hasSiblings(ast))) {
151            log(ast, MSG_KEY_BLOCK_NESTED);
152        }
153    }
154
155    /**
156     * Checks whether the AST node has any siblings or not.
157     *
158     * @param ast node to examine
159     * @return {@code true} if the node has one or more siblings
160     */
161    private static boolean hasSiblings(DetailAST ast) {
162        return ast.getPreviousSibling() != null || ast.getNextSibling() != null;
163    }
164
165    /**
166     * Setter to allow nested blocks if they are the only child of a switch case.
167     *
168     * @param allowInSwitchCase whether nested blocks are allowed
169     *                 if they are the only child of a switch case.
170     */
171    public void setAllowInSwitchCase(boolean allowInSwitchCase) {
172        this.allowInSwitchCase = allowInSwitchCase;
173    }
174
175}