001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2022 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 * <p>
032 * Checks that there is only one statement per line.
033 * </p>
034 * <p>
035 * Rationale: It's very difficult to read multiple statements on one line.
036 * </p>
037 * <p>
038 * In the Java programming language, statements are the fundamental unit of
039 * execution. All statements except blocks are terminated by a semicolon.
040 * Blocks are denoted by open and close curly braces.
041 * </p>
042 * <p>
043 * OneStatementPerLineCheck checks the following types of statements:
044 * variable declaration statements, empty statements, import statements,
045 * assignment statements, expression statements, increment statements,
046 * object creation statements, 'for loop' statements, 'break' statements,
047 * 'continue' statements, 'return' statements, resources statements (optional).
048 * </p>
049 * <ul>
050 * <li>
051 * Property {@code treatTryResourcesAsStatement} - Enable resources processing.
052 * Type is {@code boolean}.
053 * Default value is {@code false}.
054 * </li>
055 * </ul>
056 * <p>
057 * To configure the check:
058 * </p>
059 * <pre>
060 * &lt;module name=&quot;OneStatementPerLine&quot;/&gt;
061 * </pre>
062 * <p>
063 * The following examples will be flagged as a violation:
064 * </p>
065 * <pre>
066 * //Each line causes violation:
067 * int var1; int var2;
068 * var1 = 1; var2 = 2;
069 * int var1 = 1; int var2 = 2;
070 * var1++; var2++;
071 * Object obj1 = new Object(); Object obj2 = new Object();
072 * import java.io.EOFException; import java.io.BufferedReader;
073 * ;; //two empty statements on the same line.
074 *
075 * //Multi-line statements:
076 * int var1 = 1
077 * ; var2 = 2; //violation here
078 * int o = 1, p = 2,
079 * r = 5; int t; //violation here
080 * </pre>
081 * <p>
082 * An example of how to configure the check to treat resources
083 * in a try statement as statements to require them on their own line:
084 * </p>
085 * <pre>
086 * &lt;module name=&quot;OneStatementPerLine&quot;&gt;
087 *   &lt;property name=&quot;treatTryResourcesAsStatement&quot; value=&quot;true&quot;/&gt;
088 * &lt;/module&gt;
089 * </pre>
090 * <p>
091 * Note: resource declarations can contain variable definitions
092 * and variable references (from java9).
093 * When property "treatTryResourcesAsStatement" is enabled,
094 * this check is only applied to variable definitions.
095 * If there are one or more variable references
096 * and one variable definition on the same line in resources declaration,
097 * there is no violation.
098 * The following examples will illustrate difference:
099 * </p>
100 * <pre>
101 * OutputStream s1 = new PipedOutputStream();
102 * OutputStream s2 = new PipedOutputStream();
103 * // only one statement(variable definition) with two variable references
104 * try (s1; s2; OutputStream s3 = new PipedOutputStream();) // OK
105 * {}
106 * // two statements with variable definitions
107 * try (Reader r = new PipedReader(); s2; Reader s3 = new PipedReader() // violation
108 * ) {}
109 * </pre>
110 * <p>
111 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
112 * </p>
113 * <p>
114 * Violation Message Keys:
115 * </p>
116 * <ul>
117 * <li>
118 * {@code multiple.statements.line}
119 * </li>
120 * </ul>
121 *
122 * @since 5.3
123 */
124@FileStatefulCheck
125public final class OneStatementPerLineCheck extends AbstractCheck {
126
127    /**
128     * A key is pointing to the warning message text in "messages.properties"
129     * file.
130     */
131    public static final String MSG_KEY = "multiple.statements.line";
132
133    /**
134     * Counts number of semicolons in nested lambdas.
135     */
136    private final Deque<Integer> countOfSemiInLambda = new ArrayDeque<>();
137
138    /**
139     * Hold the line-number where the last statement ended.
140     */
141    private int lastStatementEnd = -1;
142
143    /**
144     * Hold the line-number where the last 'for-loop' statement ended.
145     */
146    private int forStatementEnd = -1;
147
148    /**
149     * The for-header usually has 3 statements on one line, but THIS IS OK.
150     */
151    private boolean inForHeader;
152
153    /**
154     * Holds if current token is inside lambda.
155     */
156    private boolean isInLambda;
157
158    /**
159     * Hold the line-number where the last lambda statement ended.
160     */
161    private int lambdaStatementEnd = -1;
162
163    /**
164     * Hold the line-number where the last resource variable statement ended.
165     */
166    private int lastVariableResourceStatementEnd = -1;
167
168    /**
169     * Enable resources processing.
170     */
171    private boolean treatTryResourcesAsStatement;
172
173    /**
174     * Setter to enable resources processing.
175     *
176     * @param treatTryResourcesAsStatement user's value of treatTryResourcesAsStatement.
177     */
178    public void setTreatTryResourcesAsStatement(boolean treatTryResourcesAsStatement) {
179        this.treatTryResourcesAsStatement = treatTryResourcesAsStatement;
180    }
181
182    @Override
183    public int[] getDefaultTokens() {
184        return getRequiredTokens();
185    }
186
187    @Override
188    public int[] getAcceptableTokens() {
189        return getRequiredTokens();
190    }
191
192    @Override
193    public int[] getRequiredTokens() {
194        return new int[] {
195            TokenTypes.SEMI,
196            TokenTypes.FOR_INIT,
197            TokenTypes.FOR_ITERATOR,
198            TokenTypes.LAMBDA,
199        };
200    }
201
202    @Override
203    public void beginTree(DetailAST rootAST) {
204        inForHeader = false;
205        lastStatementEnd = -1;
206        forStatementEnd = -1;
207        isInLambda = false;
208        lastVariableResourceStatementEnd = -1;
209    }
210
211    @Override
212    public void visitToken(DetailAST ast) {
213        switch (ast.getType()) {
214            case TokenTypes.SEMI:
215                checkIfSemicolonIsInDifferentLineThanPrevious(ast);
216                break;
217            case TokenTypes.FOR_ITERATOR:
218                forStatementEnd = ast.getLineNo();
219                break;
220            case TokenTypes.LAMBDA:
221                isInLambda = true;
222                countOfSemiInLambda.push(0);
223                break;
224            default:
225                inForHeader = true;
226                break;
227        }
228    }
229
230    @Override
231    public void leaveToken(DetailAST ast) {
232        switch (ast.getType()) {
233            case TokenTypes.SEMI:
234                lastStatementEnd = ast.getLineNo();
235                forStatementEnd = -1;
236                lambdaStatementEnd = -1;
237                break;
238            case TokenTypes.FOR_ITERATOR:
239                inForHeader = false;
240                break;
241            case TokenTypes.LAMBDA:
242                countOfSemiInLambda.pop();
243                if (countOfSemiInLambda.isEmpty()) {
244                    isInLambda = false;
245                }
246                lambdaStatementEnd = ast.getLineNo();
247                break;
248            default:
249                break;
250        }
251    }
252
253    /**
254     * Checks if given semicolon is in different line than previous.
255     *
256     * @param ast semicolon to check
257     */
258    private void checkIfSemicolonIsInDifferentLineThanPrevious(DetailAST ast) {
259        DetailAST currentStatement = ast;
260        final DetailAST previousSibling = ast.getPreviousSibling();
261        final boolean isUnnecessarySemicolon = previousSibling == null
262            || previousSibling.getType() == TokenTypes.RESOURCES
263            || ast.getParent().getType() == TokenTypes.COMPILATION_UNIT;
264        if (!isUnnecessarySemicolon) {
265            currentStatement = ast.getPreviousSibling();
266        }
267        if (isInLambda) {
268            checkLambda(ast, currentStatement);
269        }
270        else if (isResource(ast.getParent())) {
271            checkResourceVariable(ast);
272        }
273        else if (!inForHeader && isOnTheSameLine(currentStatement, lastStatementEnd,
274                forStatementEnd, lambdaStatementEnd)) {
275            log(ast, MSG_KEY);
276        }
277    }
278
279    /**
280     * Checks semicolon placement in lambda.
281     *
282     * @param ast semicolon to check
283     * @param currentStatement current statement
284     */
285    private void checkLambda(DetailAST ast, DetailAST currentStatement) {
286        int countOfSemiInCurrentLambda = countOfSemiInLambda.pop();
287        countOfSemiInCurrentLambda++;
288        countOfSemiInLambda.push(countOfSemiInCurrentLambda);
289        if (!inForHeader && countOfSemiInCurrentLambda > 1
290                && isOnTheSameLine(currentStatement,
291                lastStatementEnd, forStatementEnd,
292                lambdaStatementEnd)) {
293            log(ast, MSG_KEY);
294        }
295    }
296
297    /**
298     * Checks that given node is a resource.
299     *
300     * @param ast semicolon to check
301     * @return true if node is a resource
302     */
303    private static boolean isResource(DetailAST ast) {
304        return ast.getType() == TokenTypes.RESOURCES
305                 || ast.getType() == TokenTypes.RESOURCE_SPECIFICATION;
306    }
307
308    /**
309     * Checks resource variable.
310     *
311     * @param currentStatement current statement
312     */
313    private void checkResourceVariable(DetailAST currentStatement) {
314        if (treatTryResourcesAsStatement) {
315            final DetailAST nextNode = currentStatement.getNextSibling();
316            if (currentStatement.getPreviousSibling().findFirstToken(TokenTypes.ASSIGN) != null) {
317                lastVariableResourceStatementEnd = currentStatement.getLineNo();
318            }
319            if (nextNode.findFirstToken(TokenTypes.ASSIGN) != null
320                && nextNode.getLineNo() == lastVariableResourceStatementEnd) {
321                log(currentStatement, MSG_KEY);
322            }
323        }
324    }
325
326    /**
327     * Checks whether two statements are on the same line.
328     *
329     * @param ast token for the current statement.
330     * @param lastStatementEnd the line-number where the last statement ended.
331     * @param forStatementEnd the line-number where the last 'for-loop'
332     *                        statement ended.
333     * @param lambdaStatementEnd the line-number where the last lambda
334     *                        statement ended.
335     * @return true if two statements are on the same line.
336     */
337    private static boolean isOnTheSameLine(DetailAST ast, int lastStatementEnd,
338                                           int forStatementEnd, int lambdaStatementEnd) {
339        return lastStatementEnd == ast.getLineNo() && forStatementEnd != ast.getLineNo()
340                && lambdaStatementEnd != ast.getLineNo();
341    }
342
343}