001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2025 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.coding;
021
022import java.util.ArrayDeque;
023import java.util.Deque;
024
025import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
026import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
027import com.puppycrawl.tools.checkstyle.api.DetailAST;
028import com.puppycrawl.tools.checkstyle.api.TokenTypes;
029
030/**
031 * <div>
032 * Checks that there is only one statement per line.
033 * </div>
034 *
035 * <p>
036 * Rationale: It's very difficult to read multiple statements on one line.
037 * </p>
038 *
039 * <p>
040 * In the Java programming language, statements are the fundamental unit of
041 * execution. All statements except blocks are terminated by a semicolon.
042 * Blocks are denoted by open and close curly braces.
043 * </p>
044 *
045 * <p>
046 * OneStatementPerLineCheck checks the following types of statements:
047 * variable declaration statements, empty statements, import statements,
048 * assignment statements, expression statements, increment statements,
049 * object creation statements, 'for loop' statements, 'break' statements,
050 * 'continue' statements, 'return' statements, resources statements (optional).
051 * </p>
052 * <ul>
053 * <li>
054 * Property {@code treatTryResourcesAsStatement} - Enable resources processing.
055 * Type is {@code boolean}.
056 * Default value is {@code false}.
057 * </li>
058 * </ul>
059 *
060 * <p>
061 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
062 * </p>
063 *
064 * <p>
065 * Violation Message Keys:
066 * </p>
067 * <ul>
068 * <li>
069 * {@code multiple.statements.line}
070 * </li>
071 * </ul>
072 *
073 * @since 5.3
074 */
075@FileStatefulCheck
076public final class OneStatementPerLineCheck extends AbstractCheck {
077
078    /**
079     * A key is pointing to the warning message text in "messages.properties"
080     * file.
081     */
082    public static final String MSG_KEY = "multiple.statements.line";
083
084    /**
085     * Counts number of semicolons in nested lambdas.
086     */
087    private final Deque<Integer> countOfSemiInLambda = new ArrayDeque<>();
088
089    /**
090     * Hold the line-number where the last statement ended.
091     */
092    private int lastStatementEnd;
093
094    /**
095     * Hold the line-number where the last 'for-loop' statement ended.
096     */
097    private int forStatementEnd;
098
099    /**
100     * The for-header usually has 3 statements on one line, but THIS IS OK.
101     */
102    private boolean inForHeader;
103
104    /**
105     * Holds if current token is inside lambda.
106     */
107    private boolean isInLambda;
108
109    /**
110     * Hold the line-number where the last lambda statement ended.
111     */
112    private int lambdaStatementEnd;
113
114    /**
115     * Hold the line-number where the last resource variable statement ended.
116     */
117    private int lastVariableResourceStatementEnd;
118
119    /**
120     * Enable resources processing.
121     */
122    private boolean treatTryResourcesAsStatement;
123
124    /**
125     * Setter to enable resources processing.
126     *
127     * @param treatTryResourcesAsStatement user's value of treatTryResourcesAsStatement.
128     * @since 8.23
129     */
130    public void setTreatTryResourcesAsStatement(boolean treatTryResourcesAsStatement) {
131        this.treatTryResourcesAsStatement = treatTryResourcesAsStatement;
132    }
133
134    @Override
135    public int[] getDefaultTokens() {
136        return getRequiredTokens();
137    }
138
139    @Override
140    public int[] getAcceptableTokens() {
141        return getRequiredTokens();
142    }
143
144    @Override
145    public int[] getRequiredTokens() {
146        return new int[] {
147            TokenTypes.SEMI,
148            TokenTypes.FOR_INIT,
149            TokenTypes.FOR_ITERATOR,
150            TokenTypes.LAMBDA,
151        };
152    }
153
154    @Override
155    public void beginTree(DetailAST rootAST) {
156        lastStatementEnd = 0;
157        lastVariableResourceStatementEnd = 0;
158    }
159
160    @Override
161    public void visitToken(DetailAST ast) {
162        switch (ast.getType()) {
163            case TokenTypes.SEMI -> checkIfSemicolonIsInDifferentLineThanPrevious(ast);
164            case TokenTypes.FOR_ITERATOR -> forStatementEnd = ast.getLineNo();
165            case TokenTypes.LAMBDA -> {
166                isInLambda = true;
167                countOfSemiInLambda.push(0);
168            }
169            default -> inForHeader = true;
170        }
171    }
172
173    @Override
174    public void leaveToken(DetailAST ast) {
175        switch (ast.getType()) {
176            case TokenTypes.SEMI -> {
177                lastStatementEnd = ast.getLineNo();
178                forStatementEnd = 0;
179                lambdaStatementEnd = 0;
180            }
181            case TokenTypes.FOR_ITERATOR -> inForHeader = false;
182            case TokenTypes.LAMBDA -> {
183                countOfSemiInLambda.pop();
184                if (countOfSemiInLambda.isEmpty()) {
185                    isInLambda = false;
186                }
187                lambdaStatementEnd = ast.getLineNo();
188            }
189            default -> {
190                // do nothing
191            }
192        }
193    }
194
195    /**
196     * Checks if given semicolon is in different line than previous.
197     *
198     * @param ast semicolon to check
199     */
200    private void checkIfSemicolonIsInDifferentLineThanPrevious(DetailAST ast) {
201        DetailAST currentStatement = ast;
202        final DetailAST previousSibling = ast.getPreviousSibling();
203        final boolean isUnnecessarySemicolon = previousSibling == null
204            || previousSibling.getType() == TokenTypes.RESOURCES
205            || ast.getParent().getType() == TokenTypes.COMPILATION_UNIT;
206        if (!isUnnecessarySemicolon) {
207            currentStatement = ast.getPreviousSibling();
208        }
209        if (isInLambda) {
210            checkLambda(ast, currentStatement);
211        }
212        else if (isResource(ast.getParent())) {
213            checkResourceVariable(ast);
214        }
215        else if (!inForHeader && isOnTheSameLine(currentStatement, lastStatementEnd,
216                forStatementEnd, lambdaStatementEnd)) {
217            log(ast, MSG_KEY);
218        }
219    }
220
221    /**
222     * Checks semicolon placement in lambda.
223     *
224     * @param ast semicolon to check
225     * @param currentStatement current statement
226     */
227    private void checkLambda(DetailAST ast, DetailAST currentStatement) {
228        int countOfSemiInCurrentLambda = countOfSemiInLambda.pop();
229        countOfSemiInCurrentLambda++;
230        countOfSemiInLambda.push(countOfSemiInCurrentLambda);
231        if (!inForHeader && countOfSemiInCurrentLambda > 1
232                && isOnTheSameLine(currentStatement,
233                lastStatementEnd, forStatementEnd,
234                lambdaStatementEnd)) {
235            log(ast, MSG_KEY);
236        }
237    }
238
239    /**
240     * Checks that given node is a resource.
241     *
242     * @param ast semicolon to check
243     * @return true if node is a resource
244     */
245    private static boolean isResource(DetailAST ast) {
246        return ast.getType() == TokenTypes.RESOURCES
247                 || ast.getType() == TokenTypes.RESOURCE_SPECIFICATION;
248    }
249
250    /**
251     * Checks resource variable.
252     *
253     * @param currentStatement current statement
254     */
255    private void checkResourceVariable(DetailAST currentStatement) {
256        if (treatTryResourcesAsStatement) {
257            final DetailAST nextNode = currentStatement.getNextSibling();
258            if (currentStatement.getPreviousSibling().findFirstToken(TokenTypes.ASSIGN) != null) {
259                lastVariableResourceStatementEnd = currentStatement.getLineNo();
260            }
261            if (nextNode.findFirstToken(TokenTypes.ASSIGN) != null
262                && nextNode.getLineNo() == lastVariableResourceStatementEnd) {
263                log(currentStatement, MSG_KEY);
264            }
265        }
266    }
267
268    /**
269     * Checks whether two statements are on the same line.
270     *
271     * @param ast token for the current statement.
272     * @param lastStatementEnd the line-number where the last statement ended.
273     * @param forStatementEnd the line-number where the last 'for-loop'
274     *                        statement ended.
275     * @param lambdaStatementEnd the line-number where the last lambda
276     *                        statement ended.
277     * @return true if two statements are on the same line.
278     */
279    private static boolean isOnTheSameLine(DetailAST ast, int lastStatementEnd,
280                                           int forStatementEnd, int lambdaStatementEnd) {
281        return lastStatementEnd == ast.getLineNo() && forStatementEnd != ast.getLineNo()
282                && lambdaStatementEnd != ast.getLineNo();
283    }
284
285}