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 java.util.ArrayList;
23 import java.util.Collections;
24 import java.util.List;
25 import java.util.Optional;
26
27 import com.puppycrawl.tools.checkstyle.StatelessCheck;
28 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
29 import com.puppycrawl.tools.checkstyle.api.DetailAST;
30 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
31 import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
32
33 /**
34 * <p>
35 * Checks that a given switch statement or expression that use a reference type in its selector
36 * expression has a {@code null} case label.
37 * </p>
38 * <p>
39 * Rationale: switch statements and expressions in Java throw a
40 * {@code NullPointerException} if the selector expression evaluates to {@code null}.
41 * As of Java 21, it is now possible to integrate a null check within the switch,
42 * eliminating the risk of {@code NullPointerException} and simplifies the code
43 * as there is no need for an external null check before entering the switch.
44 * </p>
45 * <p>
46 * See the <a href="https://docs.oracle.com/javase/specs/jls/se22/html/jls-15.html#jls-15.28">
47 * Java Language Specification</a> for more information about switch statements and expressions.
48 * </p>
49 * <p>
50 * Specifically, this check validates switch statement or expression
51 * that use patterns or strings in their case labels.
52 * </p>
53 * <p>
54 * Due to Checkstyle not being type-aware, this check cannot validate other reference types,
55 * such as enums; syntactically, these are no different from other constants.
56 * </p>
57 * <p>
58 * <b>Attention</b>: this Check should be activated only on source code
59 * that is compiled by jdk21 or above.
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.nullcase}
70 * </li>
71 * </ul>
72 *
73 * @since 10.18.0
74 */
75
76 @StatelessCheck
77 public class MissingNullCaseInSwitchCheck extends AbstractCheck {
78
79 /**
80 * A key is pointing to the warning message text in "messages.properties"
81 * file.
82 */
83 public static final String MSG_KEY = "missing.switch.nullcase";
84
85 @Override
86 public int[] getDefaultTokens() {
87 return getRequiredTokens();
88 }
89
90 @Override
91 public int[] getAcceptableTokens() {
92 return getRequiredTokens();
93 }
94
95 @Override
96 public int[] getRequiredTokens() {
97 return new int[] {TokenTypes.LITERAL_SWITCH};
98 }
99
100 @Override
101 public void visitToken(DetailAST ast) {
102 final List<DetailAST> caseLabels = getAllCaseLabels(ast);
103 final boolean hasNullCaseLabel = caseLabels.stream()
104 .anyMatch(MissingNullCaseInSwitchCheck::hasLiteralNull);
105 if (!hasNullCaseLabel) {
106 final boolean hasPatternCaseLabel = caseLabels.stream()
107 .anyMatch(MissingNullCaseInSwitchCheck::hasPatternCaseLabel);
108 final boolean hasStringCaseLabel = caseLabels.stream()
109 .anyMatch(MissingNullCaseInSwitchCheck::hasStringCaseLabel);
110 if (hasPatternCaseLabel || hasStringCaseLabel) {
111 log(ast, MSG_KEY);
112 }
113 }
114 }
115
116 /**
117 * Gets all case labels in the given switch AST node.
118 *
119 * @param switchAST the AST node representing {@code LITERAL_SWITCH}
120 * @return a list of all case labels in the switch
121 */
122 private static List<DetailAST> getAllCaseLabels(DetailAST switchAST) {
123 final List<DetailAST> caseLabels = new ArrayList<>();
124 DetailAST ast = switchAST.getFirstChild();
125 while (ast != null) {
126 // case group token may have several LITERAL_CASE tokens
127 TokenUtil.forEachChild(ast, TokenTypes.LITERAL_CASE, caseLabels::add);
128 ast = ast.getNextSibling();
129 }
130 return Collections.unmodifiableList(caseLabels);
131 }
132
133 /**
134 * Checks if the given case AST node has a null label.
135 *
136 * @param caseAST the AST node representing {@code LITERAL_CASE}
137 * @return true if the case has {@code null} label, false otherwise
138 */
139 private static boolean hasLiteralNull(DetailAST caseAST) {
140 return Optional.ofNullable(caseAST.findFirstToken(TokenTypes.EXPR))
141 .map(exp -> exp.findFirstToken(TokenTypes.LITERAL_NULL))
142 .isPresent();
143 }
144
145 /**
146 * Checks if the given case AST node has a pattern variable declaration label
147 * or record pattern definition label.
148 *
149 * @param caseAST the AST node representing {@code LITERAL_CASE}
150 * @return true if case has a pattern in its label
151 */
152 private static boolean hasPatternCaseLabel(DetailAST caseAST) {
153 return caseAST.findFirstToken(TokenTypes.RECORD_PATTERN_DEF) != null
154 || caseAST.findFirstToken(TokenTypes.PATTERN_VARIABLE_DEF) != null
155 || caseAST.findFirstToken(TokenTypes.PATTERN_DEF) != null;
156 }
157
158 /**
159 * Checks if the given case contains a string in its label.
160 * It may contain a single string literal or a string literal
161 * in a concatenated expression.
162 *
163 * @param caseAST the AST node representing {@code LITERAL_CASE}
164 * @return true if switch block contains a string case label
165 */
166 private static boolean hasStringCaseLabel(DetailAST caseAST) {
167 DetailAST curNode = caseAST;
168 boolean hasStringCaseLabel = false;
169 boolean exitCaseLabelExpression = false;
170 while (!exitCaseLabelExpression) {
171 DetailAST toVisit = curNode.getFirstChild();
172 if (curNode.getType() == TokenTypes.STRING_LITERAL) {
173 hasStringCaseLabel = true;
174 break;
175 }
176 while (toVisit == null) {
177 toVisit = curNode.getNextSibling();
178 curNode = curNode.getParent();
179 }
180 curNode = toVisit;
181 exitCaseLabelExpression = TokenUtil.isOfType(curNode, TokenTypes.COLON,
182 TokenTypes.LAMBDA);
183 }
184 return hasStringCaseLabel;
185 }
186 }