Source code

001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2018 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 com.puppycrawl.tools.checkstyle.FileStatefulCheck;
023import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
024import com.puppycrawl.tools.checkstyle.api.DetailAST;
025import com.puppycrawl.tools.checkstyle.api.TokenTypes;
026import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
027
028/**
029 * <p>
030 * Checks if unnecessary parentheses are used in a statement or expression.
031 * The check will flag the following with warnings:
032 * </p>
033 * <pre>
034 *     return (x);          // parens around identifier
035 *     return (x + 1);      // parens around return value
036 *     int x = (y / 2 + 1); // parens around assignment rhs
037 *     for (int i = (0); i &lt; 10; i++) {  // parens around literal
038 *     t -= (z + 1);        // parens around assignment rhs</pre>
039 * <p>
040 * The check is not "type aware", that is to say, it can't tell if parentheses
041 * are unnecessary based on the types in an expression.  It also doesn't know
042 * about operator precedence and associativity; therefore it won't catch
043 * something like
044 * </p>
045 * <pre>
046 *     int x = (a + b) + c;</pre>
047 * <p>
048 * In the above case, given that <em>a</em>, <em>b</em>, and <em>c</em> are
049 * all {@code int} variables, the parentheses around {@code a + b}
050 * are not needed.
051 * </p>
052 *
053 */
054@FileStatefulCheck
055public class UnnecessaryParenthesesCheck extends AbstractCheck {
056
057    /**
058     * A key is pointing to the warning message text in "messages.properties"
059     * file.
060     */
061    public static final String MSG_IDENT = "unnecessary.paren.ident";
062
063    /**
064     * A key is pointing to the warning message text in "messages.properties"
065     * file.
066     */
067    public static final String MSG_ASSIGN = "unnecessary.paren.assign";
068
069    /**
070     * A key is pointing to the warning message text in "messages.properties"
071     * file.
072     */
073    public static final String MSG_EXPR = "unnecessary.paren.expr";
074
075    /**
076     * A key is pointing to the warning message text in "messages.properties"
077     * file.
078     */
079    public static final String MSG_LITERAL = "unnecessary.paren.literal";
080
081    /**
082     * A key is pointing to the warning message text in "messages.properties"
083     * file.
084     */
085    public static final String MSG_STRING = "unnecessary.paren.string";
086
087    /**
088     * A key is pointing to the warning message text in "messages.properties"
089     * file.
090     */
091    public static final String MSG_RETURN = "unnecessary.paren.return";
092
093    /**
094     * A key is pointing to the warning message text in "messages.properties"
095     * file.
096     */
097    public static final String MSG_LAMBDA = "unnecessary.paren.lambda";
098
099    /** The maximum string length before we chop the string. */
100    private static final int MAX_QUOTED_LENGTH = 25;
101
102    /** Token types for literals. */
103    private static final int[] LITERALS = {
104        TokenTypes.NUM_DOUBLE,
105        TokenTypes.NUM_FLOAT,
106        TokenTypes.NUM_INT,
107        TokenTypes.NUM_LONG,
108        TokenTypes.STRING_LITERAL,
109        TokenTypes.LITERAL_NULL,
110        TokenTypes.LITERAL_FALSE,
111        TokenTypes.LITERAL_TRUE,
112    };
113
114    /** Token types for assignment operations. */
115    private static final int[] ASSIGNMENTS = {
116        TokenTypes.ASSIGN,
117        TokenTypes.BAND_ASSIGN,
118        TokenTypes.BOR_ASSIGN,
119        TokenTypes.BSR_ASSIGN,
120        TokenTypes.BXOR_ASSIGN,
121        TokenTypes.DIV_ASSIGN,
122        TokenTypes.MINUS_ASSIGN,
123        TokenTypes.MOD_ASSIGN,
124        TokenTypes.PLUS_ASSIGN,
125        TokenTypes.SL_ASSIGN,
126        TokenTypes.SR_ASSIGN,
127        TokenTypes.STAR_ASSIGN,
128    };
129
130    /**
131     * Used to test if logging a warning in a parent node may be skipped
132     * because a warning was already logged on an immediate child node.
133     */
134    private DetailAST parentToSkip;
135    /** Depth of nested assignments.  Normally this will be 0 or 1. */
136    private int assignDepth;
137
138    @Override
139    public int[] getDefaultTokens() {
140        return new int[] {
141            TokenTypes.EXPR,
142            TokenTypes.IDENT,
143            TokenTypes.NUM_DOUBLE,
144            TokenTypes.NUM_FLOAT,
145            TokenTypes.NUM_INT,
146            TokenTypes.NUM_LONG,
147            TokenTypes.STRING_LITERAL,
148            TokenTypes.LITERAL_NULL,
149            TokenTypes.LITERAL_FALSE,
150            TokenTypes.LITERAL_TRUE,
151            TokenTypes.ASSIGN,
152            TokenTypes.BAND_ASSIGN,
153            TokenTypes.BOR_ASSIGN,
154            TokenTypes.BSR_ASSIGN,
155            TokenTypes.BXOR_ASSIGN,
156            TokenTypes.DIV_ASSIGN,
157            TokenTypes.MINUS_ASSIGN,
158            TokenTypes.MOD_ASSIGN,
159            TokenTypes.PLUS_ASSIGN,
160            TokenTypes.SL_ASSIGN,
161            TokenTypes.SR_ASSIGN,
162            TokenTypes.STAR_ASSIGN,
163            TokenTypes.LAMBDA,
164        };
165    }
166
167    @Override
168    public int[] getAcceptableTokens() {
169        return new int[] {
170            TokenTypes.EXPR,
171            TokenTypes.IDENT,
172            TokenTypes.NUM_DOUBLE,
173            TokenTypes.NUM_FLOAT,
174            TokenTypes.NUM_INT,
175            TokenTypes.NUM_LONG,
176            TokenTypes.STRING_LITERAL,
177            TokenTypes.LITERAL_NULL,
178            TokenTypes.LITERAL_FALSE,
179            TokenTypes.LITERAL_TRUE,
180            TokenTypes.ASSIGN,
181            TokenTypes.BAND_ASSIGN,
182            TokenTypes.BOR_ASSIGN,
183            TokenTypes.BSR_ASSIGN,
184            TokenTypes.BXOR_ASSIGN,
185            TokenTypes.DIV_ASSIGN,
186            TokenTypes.MINUS_ASSIGN,
187            TokenTypes.MOD_ASSIGN,
188            TokenTypes.PLUS_ASSIGN,
189            TokenTypes.SL_ASSIGN,
190            TokenTypes.SR_ASSIGN,
191            TokenTypes.STAR_ASSIGN,
192            TokenTypes.LAMBDA,
193        };
194    }
195
196    @Override
197    public int[] getRequiredTokens() {
198        // Check can work with any of acceptable tokens
199        return CommonUtil.EMPTY_INT_ARRAY;
200    }
201
202    // -@cs[CyclomaticComplexity] All logs should be in visit token.
203    @Override
204    public void visitToken(DetailAST ast) {
205        final int type = ast.getType();
206        final DetailAST parent = ast.getParent();
207
208        if (type == TokenTypes.LAMBDA && isLambdaSingleParameterSurrounded(ast)) {
209            log(ast, MSG_LAMBDA, ast.getText());
210        }
211        else if (type != TokenTypes.ASSIGN
212            || parent.getType() != TokenTypes.ANNOTATION_MEMBER_VALUE_PAIR) {
213            final boolean surrounded = isSurrounded(ast);
214            // An identifier surrounded by parentheses.
215            if (surrounded && type == TokenTypes.IDENT) {
216                parentToSkip = ast.getParent();
217                log(ast, MSG_IDENT, ast.getText());
218            }
219            // A literal (numeric or string) surrounded by parentheses.
220            else if (surrounded && isInTokenList(type, LITERALS)) {
221                parentToSkip = ast.getParent();
222                if (type == TokenTypes.STRING_LITERAL) {
223                    log(ast, MSG_STRING,
224                        chopString(ast.getText()));
225                }
226                else {
227                    log(ast, MSG_LITERAL, ast.getText());
228                }
229            }
230            // The rhs of an assignment surrounded by parentheses.
231            else if (isInTokenList(type, ASSIGNMENTS)) {
232                assignDepth++;
233                final DetailAST last = ast.getLastChild();
234                if (last.getType() == TokenTypes.RPAREN) {
235                    log(ast, MSG_ASSIGN);
236                }
237            }
238        }
239    }
240
241    @Override
242    public void leaveToken(DetailAST ast) {
243        final int type = ast.getType();
244        final DetailAST parent = ast.getParent();
245
246        // shouldn't process assign in annotation pairs
247        if (type != TokenTypes.ASSIGN
248            || parent.getType() != TokenTypes.ANNOTATION_MEMBER_VALUE_PAIR) {
249            // An expression is surrounded by parentheses.
250            if (type == TokenTypes.EXPR) {
251                // If 'parentToSkip' == 'ast', then we've already logged a
252                // warning about an immediate child node in visitToken, so we don't
253                // need to log another one here.
254
255                if (parentToSkip != ast && isExprSurrounded(ast)) {
256                    if (assignDepth >= 1) {
257                        log(ast, MSG_ASSIGN);
258                    }
259                    else if (ast.getParent().getType() == TokenTypes.LITERAL_RETURN) {
260                        log(ast, MSG_RETURN);
261                    }
262                    else {
263                        log(ast, MSG_EXPR);
264                    }
265                }
266
267                parentToSkip = null;
268            }
269            else if (isInTokenList(type, ASSIGNMENTS)) {
270                assignDepth--;
271            }
272        }
273    }
274
275    /**
276     * Tests if the given {@code DetailAST} is surrounded by parentheses.
277     * In short, does {@code ast} have a previous sibling whose type is
278     * {@code TokenTypes.LPAREN} and a next sibling whose type is {@code
279     * TokenTypes.RPAREN}.
280     * @param ast the {@code DetailAST} to check if it is surrounded by
281     *        parentheses.
282     * @return {@code true} if {@code ast} is surrounded by
283     *         parentheses.
284     */
285    private static boolean isSurrounded(DetailAST ast) {
286        // if previous sibling is left parenthesis,
287        // next sibling can't be other than right parenthesis
288        final DetailAST prev = ast.getPreviousSibling();
289        return prev != null && prev.getType() == TokenTypes.LPAREN;
290    }
291
292    /**
293     * Tests if the given expression node is surrounded by parentheses.
294     * @param ast a {@code DetailAST} whose type is
295     *        {@code TokenTypes.EXPR}.
296     * @return {@code true} if the expression is surrounded by
297     *         parentheses.
298     */
299    private static boolean isExprSurrounded(DetailAST ast) {
300        return ast.getFirstChild().getType() == TokenTypes.LPAREN;
301    }
302
303    /**
304     * Tests if the given lambda node has a single parameter, no defined type, and is surrounded
305     * by parentheses.
306     * @param ast a {@code DetailAST} whose type is
307     *        {@code TokenTypes.LAMBDA}.
308     * @return {@code true} if the lambda has a single parameter, no defined type, and is
309     *         surrounded by parentheses.
310     */
311    private static boolean isLambdaSingleParameterSurrounded(DetailAST ast) {
312        final DetailAST firstChild = ast.getFirstChild();
313        return firstChild.getType() == TokenTypes.LPAREN
314                && firstChild.getNextSibling().getChildCount(TokenTypes.PARAMETER_DEF) == 1
315                && firstChild.getNextSibling().getFirstChild().findFirstToken(TokenTypes.TYPE)
316                        .getChildCount() == 0;
317    }
318
319    /**
320     * Check if the given token type can be found in an array of token types.
321     * @param type the token type.
322     * @param tokens an array of token types to search.
323     * @return {@code true} if {@code type} was found in {@code
324     *         tokens}.
325     */
326    private static boolean isInTokenList(int type, int... tokens) {
327        // NOTE: Given the small size of the two arrays searched, I'm not sure
328        //       it's worth bothering with doing a binary search or using a
329        //       HashMap to do the searches.
330
331        boolean found = false;
332        for (int i = 0; i < tokens.length && !found; i++) {
333            found = tokens[i] == type;
334        }
335        return found;
336    }
337
338    /**
339     * Returns the specified string chopped to {@code MAX_QUOTED_LENGTH}
340     * plus an ellipsis (...) if the length of the string exceeds {@code
341     * MAX_QUOTED_LENGTH}.
342     * @param value the string to potentially chop.
343     * @return the chopped string if {@code string} is longer than
344     *         {@code MAX_QUOTED_LENGTH}; otherwise {@code string}.
345     */
346    private static String chopString(String value) {
347        String result = value;
348        if (value.length() > MAX_QUOTED_LENGTH) {
349            result = value.substring(0, MAX_QUOTED_LENGTH) + "...\"";
350        }
351        return result;
352    }
353
354}