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.metrics;
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.CheckUtil;
030
031/**
032 * <p>
033 * Restricts the number of boolean operators ({@code &amp;&amp;}, {@code ||},
034 * {@code &amp;}, {@code |} and {@code ^}) in an expression.
035 * </p>
036 * <p>
037 * Rationale: Too many conditions leads to code that is difficult to read
038 * and hence debug and maintain.
039 * </p>
040 * <p>
041 * Note that the operators {@code &amp;} and {@code |} are not only integer bitwise
042 * operators, they are also the
043 * <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-15.html#jls-15.22.2">
044 * non-shortcut versions</a> of the boolean operators {@code &amp;&amp;} and {@code ||}.
045 * </p>
046 * <p>
047 * Note that {@code &amp;}, {@code |} and {@code ^} are not checked if they are part
048 * of constructor or method call because they can be applied to non boolean
049 * variables and Checkstyle does not know types of methods from different classes.
050 * </p>
051 * <ul>
052 * <li>
053 * Property {@code max} - Specify the maximum number of boolean operations
054 * allowed in one expression.
055 * Default value is {@code 3}.
056 * </li>
057 * <li>
058 * Property {@code tokens} - tokens to check Default value is:
059 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#LAND">
060 * LAND</a>,
061 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BAND">
062 * BAND</a>,
063 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#LOR">
064 * LOR</a>,
065 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BOR">
066 * BOR</a>,
067 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BXOR">
068 * BXOR</a>.
069 * </li>
070 * </ul>
071 * <p>
072 * To configure the check:
073 * </p>
074 * <pre>
075 * &lt;module name="BooleanExpressionComplexity"/&gt;
076 * </pre>
077 * <p>Code Example:</p>
078 * <pre>
079 * public class Test
080 * {
081 * public static void main(String ... args)
082 * {
083 * boolean a = true;
084 * boolean b = false;
085 *
086 * boolean c = (a &amp; b) | (b ^ a);       // OK, 1(&amp;) + 1(|) + 1(^) = 3 (max allowed 3)
087 *
088 * boolean d = (a &amp; b) ^ (a || b) | a;  // violation, 1(&amp;) + 1(^) + 1(||) + 1(|) = 4
089 * }
090 * }
091 * </pre>
092 * <p>
093 * To configure the check with 5 allowed operation in boolean expression:
094 * </p>
095 * <pre>
096 * &lt;module name="BooleanExpressionComplexity"&gt;
097 *   &lt;property name="max" value="5"/&gt;
098 * &lt;/module&gt;
099 * </pre>
100 * <p>Code Example:</p>
101 * <pre>
102 * public class Test
103 * {
104 *  public static void main(String ... args)
105 *  {
106 *   boolean a = true;
107 *   boolean b = false;
108 *
109 *   boolean c = (a &amp; b) | (b ^ a) | (a ^ b);   // OK, 1(&amp;) + 1(|) + 1(^) + 1(|) + 1(^) = 5
110 *
111 *   boolean d = (a | b) ^ (a | b) ^ (a || b) &amp; b; // violation,
112 *                                               // 1(|) + 1(^) + 1(|) + 1(^) + 1(||) + 1(&amp;) = 6
113 *  }
114 * }
115 * </pre>
116 * <p>
117 * To configure the check to ignore {@code &amp;} and {@code |}:
118 * </p>
119 * <pre>
120 * &lt;module name="BooleanExpressionComplexity"&gt;
121 *   &lt;property name="tokens" value="BXOR,LAND,LOR"/&gt;
122 * &lt;/module&gt;
123 * </pre>
124 * <p>Code Example:</p>
125 * <pre>
126 * public class Test
127 * {
128 *  public static void main(String ... args)
129 *   {
130 *     boolean a = true;
131 *     boolean b = false;
132 *
133 *     boolean c = (!a &amp;&amp; b) | (a || !b) ^ a;    // OK, 1(&amp;&amp;) + 1(||) + 1(^) = 3
134 *                                                // | is ignored here
135 *
136 *     boolean d = a ^ (a || b) ^ (b || a) &amp; a; // violation, 1(^) + 1(||) + 1(^) + 1(||) = 4
137 *                                               // &amp; is ignored here
138 *    }
139 *  }
140 * </pre>
141 *
142 *
143 * @since 3.4
144 */
145@FileStatefulCheck
146public final class BooleanExpressionComplexityCheck extends AbstractCheck {
147
148    /**
149     * A key is pointing to the warning message text in "messages.properties"
150     * file.
151     */
152    public static final String MSG_KEY = "booleanExpressionComplexity";
153
154    /** Default allowed complexity. */
155    private static final int DEFAULT_MAX = 3;
156
157    /** Stack of contexts. */
158    private final Deque<Context> contextStack = new ArrayDeque<>();
159    /** Specify the maximum number of boolean operations allowed in one expression. */
160    private int max;
161    /** Current context. */
162    private Context context = new Context(false);
163
164    /** Creates new instance of the check. */
165    public BooleanExpressionComplexityCheck() {
166        max = DEFAULT_MAX;
167    }
168
169    @Override
170    public int[] getDefaultTokens() {
171        return new int[] {
172            TokenTypes.CTOR_DEF,
173            TokenTypes.METHOD_DEF,
174            TokenTypes.EXPR,
175            TokenTypes.LAND,
176            TokenTypes.BAND,
177            TokenTypes.LOR,
178            TokenTypes.BOR,
179            TokenTypes.BXOR,
180        };
181    }
182
183    @Override
184    public int[] getRequiredTokens() {
185        return new int[] {
186            TokenTypes.CTOR_DEF,
187            TokenTypes.METHOD_DEF,
188            TokenTypes.EXPR,
189        };
190    }
191
192    @Override
193    public int[] getAcceptableTokens() {
194        return new int[] {
195            TokenTypes.CTOR_DEF,
196            TokenTypes.METHOD_DEF,
197            TokenTypes.EXPR,
198            TokenTypes.LAND,
199            TokenTypes.BAND,
200            TokenTypes.LOR,
201            TokenTypes.BOR,
202            TokenTypes.BXOR,
203        };
204    }
205
206    /**
207     * Setter to specify the maximum number of boolean operations allowed in one expression.
208     *
209     * @param max new maximum allowed complexity.
210     */
211    public void setMax(int max) {
212        this.max = max;
213    }
214
215    @Override
216    public void visitToken(DetailAST ast) {
217        switch (ast.getType()) {
218            case TokenTypes.CTOR_DEF:
219            case TokenTypes.METHOD_DEF:
220                visitMethodDef(ast);
221                break;
222            case TokenTypes.EXPR:
223                visitExpr();
224                break;
225            case TokenTypes.BOR:
226                if (!isPipeOperator(ast) && !isPassedInParameter(ast)) {
227                    context.visitBooleanOperator();
228                }
229                break;
230            case TokenTypes.BAND:
231            case TokenTypes.BXOR:
232                if (!isPassedInParameter(ast)) {
233                    context.visitBooleanOperator();
234                }
235                break;
236            case TokenTypes.LAND:
237            case TokenTypes.LOR:
238                context.visitBooleanOperator();
239                break;
240            default:
241                throw new IllegalArgumentException("Unknown type: " + ast);
242        }
243    }
244
245    /**
246     * Checks if logical operator is part of constructor or method call.
247     *
248     * @param logicalOperator logical operator
249     * @return true if logical operator is part of constructor or method call
250     */
251    private static boolean isPassedInParameter(DetailAST logicalOperator) {
252        return logicalOperator.getParent().getParent().getType() == TokenTypes.ELIST;
253    }
254
255    /**
256     * Checks if {@link TokenTypes#BOR binary OR} is applied to exceptions
257     * in
258     * <a href="https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20">
259     * multi-catch</a> (pipe-syntax).
260     *
261     * @param binaryOr {@link TokenTypes#BOR binary or}
262     * @return true if binary or is applied to exceptions in multi-catch.
263     */
264    private static boolean isPipeOperator(DetailAST binaryOr) {
265        return binaryOr.getParent().getType() == TokenTypes.TYPE;
266    }
267
268    @Override
269    public void leaveToken(DetailAST ast) {
270        switch (ast.getType()) {
271            case TokenTypes.CTOR_DEF:
272            case TokenTypes.METHOD_DEF:
273                leaveMethodDef();
274                break;
275            case TokenTypes.EXPR:
276                leaveExpr(ast);
277                break;
278            default:
279                // Do nothing
280        }
281    }
282
283    /**
284     * Creates new context for a given method.
285     *
286     * @param ast a method we start to check.
287     */
288    private void visitMethodDef(DetailAST ast) {
289        contextStack.push(context);
290        final boolean check = !CheckUtil.isEqualsMethod(ast);
291        context = new Context(check);
292    }
293
294    /** Removes old context. */
295    private void leaveMethodDef() {
296        context = contextStack.pop();
297    }
298
299    /** Creates and pushes new context. */
300    private void visitExpr() {
301        contextStack.push(context);
302        context = new Context(context.isChecking());
303    }
304
305    /**
306     * Restores previous context.
307     *
308     * @param ast expression we leave.
309     */
310    private void leaveExpr(DetailAST ast) {
311        context.checkCount(ast);
312        context = contextStack.pop();
313    }
314
315    /**
316     * Represents context (method/expression) in which we check complexity.
317     *
318     */
319    private class Context {
320
321        /**
322         * Should we perform check in current context or not.
323         * Usually false if we are inside equals() method.
324         */
325        private final boolean checking;
326        /** Count of boolean operators. */
327        private int count;
328
329        /**
330         * Creates new instance.
331         *
332         * @param checking should we check in current context or not.
333         */
334        /* package */ Context(boolean checking) {
335            this.checking = checking;
336            count = 0;
337        }
338
339        /**
340         * Getter for checking property.
341         *
342         * @return should we check in current context or not.
343         */
344        public boolean isChecking() {
345            return checking;
346        }
347
348        /** Increases operator counter. */
349        public void visitBooleanOperator() {
350            ++count;
351        }
352
353        /**
354         * Checks if we violates maximum allowed complexity.
355         *
356         * @param ast a node we check now.
357         */
358        public void checkCount(DetailAST ast) {
359            if (checking && count > max) {
360                final DetailAST parentAST = ast.getParent();
361
362                log(parentAST, MSG_KEY, count, max);
363            }
364        }
365
366    }
367
368}