src/main/java/com/puppycrawl/tools/checkstyle/checks/blocks/AvoidNestedBlocksCheck.java

////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code for adherence to a set of rules.
// Copyright (C) 2001-2017 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
////////////////////////////////////////////////////////////////////////////////

package com.puppycrawl.tools.checkstyle.checks.blocks;

import com.puppycrawl.tools.checkstyle.StatelessCheck;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;

/**
 * Finds nested blocks.
 *
 * <p>
 * For example this Check flags confusing code like
 * </p>
 * <pre>
 * public void guessTheOutput()
 * {
 *     int whichIsWhich = 0;
 *     {
 *         int whichIsWhich = 2;
 *     }
 *     System.out.println("value = " + whichIsWhich);
 * }
 * </pre>
 * and debugging / refactoring leftovers such as
 *
 * <pre>
 * // if (someOldCondition)
 * {
 *     System.out.println("unconditional");
 * }
 * </pre>
 *
 * <p>
 * A case in a switch statement does not implicitly form a block.
 * Thus to be able to introduce local variables that have case scope
 * it is necessary to open a nested block. This is supported, set
 * the allowInSwitchCase property to true and include all statements
 * of the case in the block.
 * </p>
 *
 * <pre>
 * switch (a)
 * {
 *     case 0:
 *         // Never OK, break outside block
 *         {
 *             x = 1;
 *         }
 *         break;
 *     case 1:
 *         // Never OK, statement outside block
 *         System.out.println("Hello");
 *         {
 *             x = 2;
 *             break;
 *         }
 *     case 1:
 *         // OK if allowInSwitchCase is true
 *         {
 *             System.out.println("Hello");
 *             x = 2;
 *             break;
 *         }
 * }
 * </pre>
 *
 * @author lkuehne
 */
@StatelessCheck
public class AvoidNestedBlocksCheck extends AbstractCheck {
    /**
     * A key is pointing to the warning message text in "messages.properties"
     * file.
     */
    public static final String MSG_KEY_BLOCK_NESTED = "block.nested";

    /**
     * Whether nested blocks are allowed if they are the
     * only child of a switch case.
     */
    private boolean allowInSwitchCase;

    @Override
    public int[] getDefaultTokens() {
        return getAcceptableTokens();
    }

    @Override
    public int[] getAcceptableTokens() {
        return new int[] {TokenTypes.SLIST};
    }

    @Override
    public int[] getRequiredTokens() {
        return getAcceptableTokens();
    }

    @Override
    public void visitToken(DetailAST ast) {
        final DetailAST parent = ast.getParent();
        if (parent.getType() == TokenTypes.SLIST
                && (!allowInSwitchCase
                    || parent.getParent().getType() != TokenTypes.CASE_GROUP
                    || parent.getNumberOfChildren() != 1)) {
            log(ast.getLineNo(), ast.getColumnNo(), MSG_KEY_BLOCK_NESTED);
        }
    }

    /**
     * Setter for allowInSwitchCase property.
     * @param allowInSwitchCase whether nested blocks are allowed
     *                 if they are the only child of a switch case.
     */
    public void setAllowInSwitchCase(boolean allowInSwitchCase) {
        this.allowInSwitchCase = allowInSwitchCase;
    }
}