1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2024 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 com.puppycrawl.tools.checkstyle.StatelessCheck;
23 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
24 import com.puppycrawl.tools.checkstyle.api.DetailAST;
25 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
26 import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
27
28 /**
29 * <p>
30 * Checks that switch statement has a {@code default} clause.
31 * </p>
32 * <p>
33 * Rationale: It's usually a good idea to introduce a
34 * default case in every switch statement. Even if
35 * the developer is sure that all currently possible
36 * cases are covered, this should be expressed in the
37 * default branch, e.g. by using an assertion. This way
38 * the code is protected against later changes, e.g.
39 * introduction of new types in an enumeration type.
40 * </p>
41 * <p>
42 * This check does not validate any switch expressions. Rationale:
43 * The compiler requires switch expressions to be exhaustive. This means
44 * that all possible inputs must be covered.
45 * </p>
46 * <p>
47 * This check does not validate switch statements that use pattern or null
48 * labels. Rationale: Switch statements that use pattern or null labels are
49 * checked by the compiler for exhaustiveness. This means that all possible
50 * inputs must be covered.
51 * </p>
52 * <p>
53 * See the <a href="https://docs.oracle.com/javase/specs/jls/se22/html/jls-15.html#jls-15.28">
54 * Java Language Specification</a> for more information about switch statements
55 * and expressions.
56 * </p>
57 * <p>
58 * See the <a href="https://docs.oracle.com/javase/specs/jls/se22/html/jls-14.html#jls-14.30">
59 * Java Language Specification</a> for more information about patterns.
60 * </p>
61 * <p>
62 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
63 * </p>
64 * <p>
65 * Violation Message Keys:
66 * </p>
67 * <ul>
68 * <li>
69 * {@code missing.switch.default}
70 * </li>
71 * </ul>
72 *
73 * @since 3.1
74 */
75 @StatelessCheck
76 public class MissingSwitchDefaultCheck extends AbstractCheck {
77
78 /**
79 * A key is pointing to the warning message text in "messages.properties"
80 * file.
81 */
82 public static final String MSG_KEY = "missing.switch.default";
83
84 @Override
85 public int[] getDefaultTokens() {
86 return getRequiredTokens();
87 }
88
89 @Override
90 public int[] getAcceptableTokens() {
91 return getRequiredTokens();
92 }
93
94 @Override
95 public int[] getRequiredTokens() {
96 return new int[] {TokenTypes.LITERAL_SWITCH};
97 }
98
99 @Override
100 public void visitToken(DetailAST ast) {
101 if (!containsDefaultLabel(ast)
102 && !containsPatternCaseLabelElement(ast)
103 && !containsDefaultCaseLabelElement(ast)
104 && !containsNullCaseLabelElement(ast)
105 && !isSwitchExpression(ast)) {
106 log(ast, MSG_KEY);
107 }
108 }
109
110 /**
111 * Checks if the case group or its sibling contain the 'default' switch.
112 *
113 * @param detailAst first case group to check.
114 * @return true if 'default' switch found.
115 */
116 private static boolean containsDefaultLabel(DetailAST detailAst) {
117 return TokenUtil.findFirstTokenByPredicate(detailAst,
118 ast -> ast.findFirstToken(TokenTypes.LITERAL_DEFAULT) != null
119 ).isPresent();
120 }
121
122 /**
123 * Checks if a switch block contains a case label with a pattern variable definition
124 * or record pattern definition.
125 * In this situation, the compiler enforces the given switch block to cover
126 * all possible inputs, and we do not need a default label.
127 *
128 * @param detailAst first case group to check.
129 * @return true if switch block contains a pattern case label element
130 */
131 private static boolean containsPatternCaseLabelElement(DetailAST detailAst) {
132 return TokenUtil.findFirstTokenByPredicate(detailAst, ast -> {
133 return ast.getFirstChild() != null
134 && (ast.getFirstChild().findFirstToken(TokenTypes.PATTERN_VARIABLE_DEF) != null
135 || ast.getFirstChild().findFirstToken(TokenTypes.RECORD_PATTERN_DEF) != null);
136 }).isPresent();
137 }
138
139 /**
140 * Checks if a switch block contains a default case label.
141 *
142 * @param detailAst first case group to check.
143 * @return true if switch block contains default case label
144 */
145 private static boolean containsDefaultCaseLabelElement(DetailAST detailAst) {
146 return TokenUtil.findFirstTokenByPredicate(detailAst, ast -> {
147 return ast.getFirstChild() != null
148 && ast.getFirstChild().findFirstToken(TokenTypes.LITERAL_DEFAULT) != null;
149 }).isPresent();
150 }
151
152 /**
153 * Checks if a switch block contains a null case label.
154 *
155 * @param detailAst first case group to check.
156 * @return true if switch block contains null case label
157 */
158 private static boolean containsNullCaseLabelElement(DetailAST detailAst) {
159 return TokenUtil.findFirstTokenByPredicate(detailAst, ast -> {
160 return ast.getFirstChild() != null
161 && hasNullCaseLabel(ast.getFirstChild());
162 }).isPresent();
163 }
164
165 /**
166 * Checks if this LITERAL_SWITCH token is part of a switch expression.
167 *
168 * @param ast the switch statement we are checking
169 * @return true if part of a switch expression
170 */
171 private static boolean isSwitchExpression(DetailAST ast) {
172 final int[] switchStatementParents = {
173 TokenTypes.SLIST,
174 TokenTypes.LITERAL_IF,
175 TokenTypes.LITERAL_ELSE,
176 TokenTypes.LITERAL_DO,
177 TokenTypes.LITERAL_WHILE,
178 TokenTypes.LITERAL_FOR,
179 TokenTypes.LABELED_STAT,
180 };
181
182 return !TokenUtil.isOfType(ast.getParent(), switchStatementParents);
183 }
184
185 /**
186 * Checks if the case contains null label.
187 *
188 * @param detailAST the switch statement we are checking
189 * @return returnValue the ast of null label
190 */
191 private static boolean hasNullCaseLabel(DetailAST detailAST) {
192 return TokenUtil.findFirstTokenByPredicate(detailAST.getParent(), ast -> {
193 final DetailAST expr = ast.findFirstToken(TokenTypes.EXPR);
194 return expr != null && expr.findFirstToken(TokenTypes.LITERAL_NULL) != null;
195 }).isPresent();
196 }
197 }