Source code

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.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;
029import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
030
031/**
032 * <p>
033 * Checks that there is only one statement per line.
034 * </p>
035 * <p>
036 * Rationale: It's very difficult to read multiple statements on one line.
037 * </p>
038 * <p>
039 * In the Java programming language, statements are the fundamental unit of
040 * execution. All statements except blocks are terminated by a semicolon.
041 * Blocks are denoted by open and close curly braces.
042 * </p>
043 * <p>
044 * OneStatementPerLineCheck checks the following types of statements:
045 * variable declaration statements, empty statements, import statements,
046 * assignment statements, expression statements, increment statements,
047 * object creation statements, 'for loop' statements, 'break' statements,
048 * 'continue' statements, 'return' statements, resources statements (optional).
049 * </p>
050 * <ul>
051 * <li>
052 * Property {@code treatTryResourcesAsStatement} - Enable resources processing.
053 * Default value is {@code false}.
054 * </li>
055 * </ul>
056 * <p>
057 * An example of how to configure this 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 *
111 * @since 5.3
112 */
113@FileStatefulCheck
114public final class OneStatementPerLineCheck extends AbstractCheck {
115
116    /**
117     * A key is pointing to the warning message text in "messages.properties"
118     * file.
119     */
120    public static final String MSG_KEY = "multiple.statements.line";
121
122    /**
123     * Counts number of semicolons in nested lambdas.
124     */
125    private final Deque<Integer> countOfSemiInLambda = new ArrayDeque<>();
126
127    /**
128     * Hold the line-number where the last statement ended.
129     */
130    private int lastStatementEnd = -1;
131
132    /**
133     * Hold the line-number where the last 'for-loop' statement ended.
134     */
135    private int forStatementEnd = -1;
136
137    /**
138     * The for-header usually has 3 statements on one line, but THIS IS OK.
139     */
140    private boolean inForHeader;
141
142    /**
143     * Holds if current token is inside lambda.
144     */
145    private boolean isInLambda;
146
147    /**
148     * Hold the line-number where the last lambda statement ended.
149     */
150    private int lambdaStatementEnd = -1;
151
152    /**
153     * Hold the line-number where the last resource variable statement ended.
154     */
155    private int lastVariableResourceStatementEnd = -1;
156
157    /**
158     * Enable resources processing.
159     */
160    private boolean treatTryResourcesAsStatement;
161
162    /**
163     * Setter to enable resources processing.
164     *
165     * @param treatTryResourcesAsStatement user's value of treatTryResourcesAsStatement.
166     */
167    public void setTreatTryResourcesAsStatement(boolean treatTryResourcesAsStatement) {
168        this.treatTryResourcesAsStatement = treatTryResourcesAsStatement;
169    }
170
171    @Override
172    public int[] getDefaultTokens() {
173        return getRequiredTokens();
174    }
175
176    @Override
177    public int[] getAcceptableTokens() {
178        return getRequiredTokens();
179    }
180
181    @Override
182    public int[] getRequiredTokens() {
183        return new int[] {
184            TokenTypes.SEMI,
185            TokenTypes.FOR_INIT,
186            TokenTypes.FOR_ITERATOR,
187            TokenTypes.LAMBDA,
188        };
189    }
190
191    @Override
192    public void beginTree(DetailAST rootAST) {
193        inForHeader = false;
194        lastStatementEnd = -1;
195        forStatementEnd = -1;
196        isInLambda = false;
197        lastVariableResourceStatementEnd = -1;
198    }
199
200    @Override
201    public void visitToken(DetailAST ast) {
202        switch (ast.getType()) {
203            case TokenTypes.SEMI:
204                checkIfSemicolonIsInDifferentLineThanPrevious(ast);
205                break;
206            case TokenTypes.FOR_ITERATOR:
207                forStatementEnd = ast.getLineNo();
208                break;
209            case TokenTypes.LAMBDA:
210                isInLambda = true;
211                countOfSemiInLambda.push(0);
212                break;
213            default:
214                inForHeader = true;
215                break;
216        }
217    }
218
219    @Override
220    public void leaveToken(DetailAST ast) {
221        switch (ast.getType()) {
222            case TokenTypes.SEMI:
223                lastStatementEnd = ast.getLineNo();
224                forStatementEnd = -1;
225                lambdaStatementEnd = -1;
226                break;
227            case TokenTypes.FOR_ITERATOR:
228                inForHeader = false;
229                break;
230            case TokenTypes.LAMBDA:
231                countOfSemiInLambda.pop();
232                if (countOfSemiInLambda.isEmpty()) {
233                    isInLambda = false;
234                }
235                lambdaStatementEnd = ast.getLineNo();
236                break;
237            default:
238                break;
239        }
240    }
241
242    /**
243     * Checks if given semicolon is in different line than previous.
244     *
245     * @param ast semicolon to check
246     */
247    private void checkIfSemicolonIsInDifferentLineThanPrevious(DetailAST ast) {
248        DetailAST currentStatement = ast;
249        final boolean hasResourcesPrevSibling =
250                currentStatement.getPreviousSibling() != null
251                        && currentStatement.getPreviousSibling().getType() == TokenTypes.RESOURCES;
252        if (!hasResourcesPrevSibling && isMultilineStatement(currentStatement)) {
253            currentStatement = ast.getPreviousSibling();
254        }
255        if (isInLambda) {
256            checkLambda(ast, currentStatement);
257        }
258        else if (isResource(ast.getParent())) {
259            checkResourceVariable(ast);
260        }
261        else if (!inForHeader && isOnTheSameLine(currentStatement, lastStatementEnd,
262                forStatementEnd, lambdaStatementEnd)) {
263            log(ast, MSG_KEY);
264        }
265    }
266
267    private void checkLambda(DetailAST ast, DetailAST currentStatement) {
268        int countOfSemiInCurrentLambda = countOfSemiInLambda.pop();
269        countOfSemiInCurrentLambda++;
270        countOfSemiInLambda.push(countOfSemiInCurrentLambda);
271        if (!inForHeader && countOfSemiInCurrentLambda > 1
272                && isOnTheSameLine(currentStatement,
273                lastStatementEnd, forStatementEnd,
274                lambdaStatementEnd)) {
275            log(ast, MSG_KEY);
276        }
277    }
278
279    private static boolean isResource(DetailAST ast) {
280        return ast != null
281            && (ast.getType() == TokenTypes.RESOURCES
282                 || ast.getType() == TokenTypes.RESOURCE_SPECIFICATION);
283    }
284
285    private void checkResourceVariable(DetailAST currentStatement) {
286        if (treatTryResourcesAsStatement) {
287            final DetailAST nextNode = currentStatement.getNextSibling();
288            if (currentStatement.getPreviousSibling().findFirstToken(TokenTypes.ASSIGN) != null) {
289                lastVariableResourceStatementEnd = currentStatement.getLineNo();
290            }
291            if (nextNode.findFirstToken(TokenTypes.ASSIGN) != null
292                && nextNode.getLineNo() == lastVariableResourceStatementEnd) {
293                log(currentStatement, MSG_KEY);
294            }
295        }
296    }
297
298    /**
299     * Checks whether two statements are on the same line.
300     *
301     * @param ast token for the current statement.
302     * @param lastStatementEnd the line-number where the last statement ended.
303     * @param forStatementEnd the line-number where the last 'for-loop'
304     *                        statement ended.
305     * @param lambdaStatementEnd the line-number where the last lambda
306     *                        statement ended.
307     * @return true if two statements are on the same line.
308     */
309    private static boolean isOnTheSameLine(DetailAST ast, int lastStatementEnd,
310                                           int forStatementEnd, int lambdaStatementEnd) {
311        return lastStatementEnd == ast.getLineNo() && forStatementEnd != ast.getLineNo()
312                && lambdaStatementEnd != ast.getLineNo();
313    }
314
315    /**
316     * Checks whether statement is multiline.
317     *
318     * @param ast token for the current statement.
319     * @return true if one statement is distributed over two or more lines.
320     */
321    private static boolean isMultilineStatement(DetailAST ast) {
322        final boolean multiline;
323        if (ast.getPreviousSibling() == null) {
324            multiline = false;
325        }
326        else {
327            final DetailAST prevSibling = ast.getPreviousSibling();
328            multiline = !TokenUtil.areOnSameLine(prevSibling, ast)
329                    && ast.getParent() != null;
330        }
331        return multiline;
332    }
333
334}