Source code

001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2026 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 java.util.Arrays;
023import java.util.Locale;
024import java.util.Optional;
025
026import com.puppycrawl.tools.checkstyle.StatelessCheck;
027import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
028import com.puppycrawl.tools.checkstyle.api.DetailAST;
029import com.puppycrawl.tools.checkstyle.api.TokenTypes;
030import com.puppycrawl.tools.checkstyle.utils.CodePointUtil;
031import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
032
033/**
034 * <div>
035 * Checks for empty blocks.
036 * </div>
037 *
038 * <p>
039 * This check does not validate sequential blocks. This check does not violate fallthrough.
040 * </p>
041 *
042 * <p>
043 * NOTE: This check processes LITERAL_CASE and LITERAL_DEFAULT separately.
044 * Verification empty block is done for single nearest {@code case} or {@code default}.
045 * </p>
046 *
047 * @since 3.0
048 */
049@StatelessCheck
050public class EmptyBlockCheck extends AbstractCheck {
051
052    /**
053     * A key is pointing to the warning message text in "messages.properties" file.
054     */
055    public static final String MSG_KEY_BLOCK_NO_STATEMENT = "block.noStatement";
056
057    /**
058     * A key is pointing to the warning message text in "messages.properties" file.
059     */
060    public static final String MSG_KEY_BLOCK_EMPTY = "block.empty";
061
062    /** Specify the policy on block contents. */
063    private BlockOption option = BlockOption.STATEMENT;
064
065    /**
066     * Creates a new {@code EmptyBlockCheck} instance.
067     */
068    public EmptyBlockCheck() {
069        // no code by default
070    }
071
072    /**
073     * Setter to specify the policy on block contents.
074     *
075     * @param optionStr string to decode option from
076     * @throws IllegalArgumentException if unable to decode
077     * @since 3.0
078     */
079    public void setOption(String optionStr) {
080        option = BlockOption.valueOf(optionStr.trim().toUpperCase(Locale.ENGLISH));
081    }
082
083    @Override
084    public int[] getDefaultTokens() {
085        return new int[] {
086            TokenTypes.LITERAL_WHILE,
087            TokenTypes.LITERAL_TRY,
088            TokenTypes.LITERAL_FINALLY,
089            TokenTypes.LITERAL_DO,
090            TokenTypes.LITERAL_IF,
091            TokenTypes.LITERAL_ELSE,
092            TokenTypes.LITERAL_FOR,
093            TokenTypes.INSTANCE_INIT,
094            TokenTypes.STATIC_INIT,
095            TokenTypes.LITERAL_SWITCH,
096            TokenTypes.LITERAL_SYNCHRONIZED,
097        };
098    }
099
100    @Override
101    public int[] getAcceptableTokens() {
102        return new int[] {
103            TokenTypes.LITERAL_WHILE,
104            TokenTypes.LITERAL_TRY,
105            TokenTypes.LITERAL_CATCH,
106            TokenTypes.LITERAL_FINALLY,
107            TokenTypes.LITERAL_DO,
108            TokenTypes.LITERAL_IF,
109            TokenTypes.LITERAL_ELSE,
110            TokenTypes.LITERAL_FOR,
111            TokenTypes.INSTANCE_INIT,
112            TokenTypes.STATIC_INIT,
113            TokenTypes.LITERAL_SWITCH,
114            TokenTypes.LITERAL_SYNCHRONIZED,
115            TokenTypes.LITERAL_CASE,
116            TokenTypes.LITERAL_DEFAULT,
117            TokenTypes.ARRAY_INIT,
118        };
119    }
120
121    @Override
122    public int[] getRequiredTokens() {
123        return CommonUtil.EMPTY_INT_ARRAY;
124    }
125
126    @Override
127    public void visitToken(DetailAST ast) {
128        final Optional<DetailAST> leftCurly = getLeftCurly(ast);
129        if (leftCurly.isPresent()) {
130            final DetailAST leftCurlyAST = leftCurly.orElseThrow();
131            if (option == BlockOption.STATEMENT) {
132                final boolean emptyBlock;
133                if (leftCurlyAST.getType() == TokenTypes.LCURLY) {
134                    final DetailAST nextSibling = leftCurlyAST.getNextSibling();
135                    emptyBlock = nextSibling.getType() != TokenTypes.CASE_GROUP
136                            && nextSibling.getType() != TokenTypes.SWITCH_RULE;
137                }
138                else {
139                    emptyBlock = leftCurlyAST.getChildCount() <= 1;
140                }
141                if (emptyBlock) {
142                    log(leftCurlyAST,
143                        MSG_KEY_BLOCK_NO_STATEMENT);
144                }
145            }
146            else if (!hasText(leftCurlyAST)) {
147                log(leftCurlyAST,
148                    MSG_KEY_BLOCK_EMPTY,
149                    ast.getText());
150            }
151        }
152    }
153
154    /**
155     * Checks if SLIST token contains any text.
156     *
157     * @param slistAST a {@code DetailAST} value
158     * @return whether the SLIST token contains any text.
159     */
160    private boolean hasText(final DetailAST slistAST) {
161        final DetailAST rightCurly = slistAST.findFirstToken(TokenTypes.RCURLY);
162        final DetailAST rcurlyAST;
163
164        if (rightCurly == null) {
165            rcurlyAST = slistAST.getParent().findFirstToken(TokenTypes.RCURLY);
166        }
167        else {
168            rcurlyAST = rightCurly;
169        }
170        final int slistLineNo = slistAST.getLineNo();
171        final int slistColNo = slistAST.getColumnNo();
172        final int rcurlyLineNo = rcurlyAST.getLineNo();
173        final int rcurlyColNo = rcurlyAST.getColumnNo();
174        boolean returnValue = false;
175        if (slistLineNo == rcurlyLineNo) {
176            // Handle braces on the same line
177            final int[] txt = Arrays.copyOfRange(getLineCodePoints(slistLineNo - 1),
178                    slistColNo + 1, rcurlyColNo);
179
180            if (!CodePointUtil.isBlank(txt)) {
181                returnValue = true;
182            }
183        }
184        else {
185            final int[] codePointsFirstLine = getLineCodePoints(slistLineNo - 1);
186            final int[] firstLine = Arrays.copyOfRange(codePointsFirstLine,
187                    slistColNo + 1, codePointsFirstLine.length);
188            final int[] codePointsLastLine = getLineCodePoints(rcurlyLineNo - 1);
189            final int[] lastLine = Arrays.copyOfRange(codePointsLastLine, 0, rcurlyColNo);
190            // check if all lines are also only whitespace
191            returnValue = !(CodePointUtil.isBlank(firstLine) && CodePointUtil.isBlank(lastLine))
192                    || !checkIsAllLinesAreWhitespace(slistLineNo, rcurlyLineNo);
193        }
194        return returnValue;
195    }
196
197    /**
198     * Checks is all lines from 'lineFrom' to 'lineTo' (exclusive) contain whitespaces only.
199     *
200     * @param lineFrom
201     *            check from this line number
202     * @param lineTo
203     *            check to this line numbers
204     * @return true if lines contain only whitespaces
205     */
206    private boolean checkIsAllLinesAreWhitespace(int lineFrom, int lineTo) {
207        boolean result = true;
208        for (int index = lineFrom; index < lineTo - 1; index++) {
209            if (!CodePointUtil.isBlank(getLineCodePoints(index))) {
210                result = false;
211                break;
212            }
213        }
214        return result;
215    }
216
217    /**
218     * Calculates the left curly corresponding to the block to be checked.
219     *
220     * @param ast a {@code DetailAST} value
221     * @return the left curly corresponding to the block to be checked
222     */
223    private static Optional<DetailAST> getLeftCurly(DetailAST ast) {
224        final DetailAST parent = ast.getParent();
225        final int parentType = parent.getType();
226        final Optional<DetailAST> leftCurly;
227
228        if (parentType == TokenTypes.SWITCH_RULE) {
229            // get left curly of a case or default that is in switch rule
230            leftCurly = Optional.ofNullable(parent.findFirstToken(TokenTypes.SLIST));
231        }
232        else if (parentType == TokenTypes.CASE_GROUP) {
233            // get left curly of a case or default that is in switch statement
234            leftCurly = Optional.ofNullable(ast.getNextSibling())
235                         .map(DetailAST::getFirstChild)
236                         .filter(node -> node.getType() == TokenTypes.SLIST);
237        }
238        else if (ast.findFirstToken(TokenTypes.SLIST) != null) {
239            // we have a left curly that is part of a statement list, but not in a case or default
240            leftCurly = Optional.of(ast.findFirstToken(TokenTypes.SLIST));
241        }
242        else {
243            // get the first left curly that we can find, if it is present
244            leftCurly = Optional.ofNullable(ast.findFirstToken(TokenTypes.LCURLY));
245        }
246        return leftCurly;
247    }
248
249}