1 ////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code for adherence to a set of rules.
3 // Copyright (C) 2001-2019 the original author or authors.
4 //
5 // This library is free software; you can redistribute it and/or
6 // modify it under the terms of the GNU Lesser General Public
7 // License as published by the Free Software Foundation; either
8 // version 2.1 of the License, or (at your option) any later version.
9 //
10 // This library is distributed in the hope that it will be useful,
11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 // Lesser General Public License for more details.
14 //
15 // You should have received a copy of the GNU Lesser General Public
16 // License along with this library; if not, write to the Free Software
17 // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18 ////////////////////////////////////////////////////////////////////////////////
19
20 package com.puppycrawl.tools.checkstyle.checks.coding;
21
22 import java.util.Arrays;
23
24 import com.puppycrawl.tools.checkstyle.StatelessCheck;
25 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
26 import com.puppycrawl.tools.checkstyle.api.DetailAST;
27 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
28
29 /**
30 * <p>
31 * Checks for assignments in subexpressions, such as in
32 * {@code String s = Integer.toString(i = 2);}.
33 * </p>
34 * <p>
35 * Rationale: With the exception of {@code for} iterators and assignment in {@code while} idiom,
36 * all assignments should occur in their own top-level statement to increase readability.
37 * With inner assignments like the one given above, it is difficult to see all places
38 * where a variable is set.
39 * </p>
40 * <p>
41 * Note: Check allows usage of the popular assignment in {@code while} idiom:
42 * </p>
43 * <pre>
44 * String line;
45 * while ((line = bufferedReader.readLine()) != null) {
46 * // process the line
47 * }
48 * </pre>
49 * <p>
50 * Assignment inside a condition is not a problem here, as the assignment is surrounded
51 * by an extra pair of parentheses. The comparison is {@code != null} and there is no chance that
52 * intention was to write {@code line == reader.readLine()}.
53 * </p>
54 * <p>
55 * To configure the check:
56 * </p>
57 * <pre>
58 * <module name="InnerAssignment"/>
59 * </pre>
60 *
61 * @since 3.0
62 */
63 @StatelessCheck
64 public class InnerAssignmentCheck
65 extends AbstractCheck {
66
67 /**
68 * A key is pointing to the warning message text in "messages.properties"
69 * file.
70 */
71 public static final String MSG_KEY = "assignment.inner.avoid";
72
73 /**
74 * List of allowed AST types from an assignment AST node
75 * towards the root.
76 */
77 private static final int[][] ALLOWED_ASSIGNMENT_CONTEXT = {
78 {TokenTypes.EXPR, TokenTypes.SLIST},
79 {TokenTypes.VARIABLE_DEF},
80 {TokenTypes.EXPR, TokenTypes.ELIST, TokenTypes.FOR_INIT},
81 {TokenTypes.EXPR, TokenTypes.ELIST, TokenTypes.FOR_ITERATOR},
82 {TokenTypes.ANNOTATION_MEMBER_VALUE_PAIR}, {
83 TokenTypes.RESOURCE,
84 TokenTypes.RESOURCES,
85 TokenTypes.RESOURCE_SPECIFICATION,
86 },
87 {TokenTypes.EXPR, TokenTypes.LAMBDA},
88 };
89
90 /**
91 * List of allowed AST types from an assignment AST node
92 * towards the root.
93 */
94 private static final int[][] CONTROL_CONTEXT = {
95 {TokenTypes.EXPR, TokenTypes.LITERAL_DO},
96 {TokenTypes.EXPR, TokenTypes.LITERAL_FOR},
97 {TokenTypes.EXPR, TokenTypes.LITERAL_WHILE},
98 {TokenTypes.EXPR, TokenTypes.LITERAL_IF},
99 {TokenTypes.EXPR, TokenTypes.LITERAL_ELSE},
100 };
101
102 /**
103 * List of allowed AST types from a comparison node (above an assignment)
104 * towards the root.
105 */
106 private static final int[][] ALLOWED_ASSIGNMENT_IN_COMPARISON_CONTEXT = {
107 {TokenTypes.EXPR, TokenTypes.LITERAL_WHILE, },
108 };
109
110 /**
111 * The token types that identify comparison operators.
112 */
113 private static final int[] COMPARISON_TYPES = {
114 TokenTypes.EQUAL,
115 TokenTypes.GE,
116 TokenTypes.GT,
117 TokenTypes.LE,
118 TokenTypes.LT,
119 TokenTypes.NOT_EQUAL,
120 };
121
122 static {
123 Arrays.sort(COMPARISON_TYPES);
124 }
125
126 @Override
127 public int[] getDefaultTokens() {
128 return getRequiredTokens();
129 }
130
131 @Override
132 public int[] getAcceptableTokens() {
133 return getRequiredTokens();
134 }
135
136 @Override
137 public int[] getRequiredTokens() {
138 return new int[] {
139 TokenTypes.ASSIGN, // '='
140 TokenTypes.DIV_ASSIGN, // "/="
141 TokenTypes.PLUS_ASSIGN, // "+="
142 TokenTypes.MINUS_ASSIGN, //"-="
143 TokenTypes.STAR_ASSIGN, // "*="
144 TokenTypes.MOD_ASSIGN, // "%="
145 TokenTypes.SR_ASSIGN, // ">>="
146 TokenTypes.BSR_ASSIGN, // ">>>="
147 TokenTypes.SL_ASSIGN, // "<<="
148 TokenTypes.BXOR_ASSIGN, // "^="
149 TokenTypes.BOR_ASSIGN, // "|="
150 TokenTypes.BAND_ASSIGN, // "&="
151 };
152 }
153
154 @Override
155 public void visitToken(DetailAST ast) {
156 if (!isInContext(ast, ALLOWED_ASSIGNMENT_CONTEXT)
157 && !isInNoBraceControlStatement(ast)
158 && !isInWhileIdiom(ast)) {
159 log(ast, MSG_KEY);
160 }
161 }
162
163 /**
164 * Determines if ast is in the body of a flow control statement without
165 * braces. An example of such a statement would be
166 * <p>
167 * <pre>
168 * if (y < 0)
169 * x = y;
170 * </pre>
171 * </p>
172 * <p>
173 * This leads to the following AST structure:
174 * </p>
175 * <p>
176 * <pre>
177 * LITERAL_IF
178 * LPAREN
179 * EXPR // test
180 * RPAREN
181 * EXPR // body
182 * SEMI
183 * </pre>
184 * </p>
185 * <p>
186 * We need to ensure that ast is in the body and not in the test.
187 * </p>
188 *
189 * @param ast an assignment operator AST
190 * @return whether ast is in the body of a flow control statement
191 */
192 private static boolean isInNoBraceControlStatement(DetailAST ast) {
193 boolean result = false;
194 if (isInContext(ast, CONTROL_CONTEXT)) {
195 final DetailAST expr = ast.getParent();
196 final DetailAST exprNext = expr.getNextSibling();
197 result = exprNext.getType() == TokenTypes.SEMI;
198 }
199 return result;
200 }
201
202 /**
203 * Tests whether the given AST is used in the "assignment in while" idiom.
204 * <pre>
205 * String line;
206 * while ((line = bufferedReader.readLine()) != null) {
207 * // process the line
208 * }
209 * </pre>
210 * Assignment inside a condition is not a problem here, as the assignment is surrounded by an
211 * extra pair of parentheses. The comparison is {@code != null} and there is no chance that
212 * intention was to write {@code line == reader.readLine()}.
213 *
214 * @param ast assignment AST
215 * @return whether the context of the assignment AST indicates the idiom
216 */
217 private static boolean isInWhileIdiom(DetailAST ast) {
218 boolean result = false;
219 if (isComparison(ast.getParent())) {
220 result = isInContext(
221 ast.getParent(), ALLOWED_ASSIGNMENT_IN_COMPARISON_CONTEXT);
222 }
223 return result;
224 }
225
226 /**
227 * Checks if an AST is a comparison operator.
228 * @param ast the AST to check
229 * @return true iff ast is a comparison operator.
230 */
231 private static boolean isComparison(DetailAST ast) {
232 final int astType = ast.getType();
233 return Arrays.binarySearch(COMPARISON_TYPES, astType) >= 0;
234 }
235
236 /**
237 * Tests whether the provided AST is in
238 * one of the given contexts.
239 *
240 * @param ast the AST from which to start walking towards root
241 * @param contextSet the contexts to test against.
242 *
243 * @return whether the parents nodes of ast match one of the allowed type paths.
244 */
245 private static boolean isInContext(DetailAST ast, int[]... contextSet) {
246 boolean found = false;
247 for (int[] element : contextSet) {
248 DetailAST current = ast;
249 for (int anElement : element) {
250 current = current.getParent();
251 if (current.getType() == anElement) {
252 found = true;
253 }
254 else {
255 found = false;
256 break;
257 }
258 }
259
260 if (found) {
261 break;
262 }
263 }
264 return found;
265 }
266
267 }