001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2024 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.StatelessCheck;
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.TokenUtil;
027
028/**
029 * <p>
030 * Checks that switch statement has a {@code default} clause.
031 * </p>
032 * <p>
033 * Rationale: It's usually a good idea to introduce a
034 * default case in every switch statement. Even if
035 * the developer is sure that all currently possible
036 * cases are covered, this should be expressed in the
037 * default branch, e.g. by using an assertion. This way
038 * the code is protected against later changes, e.g.
039 * introduction of new types in an enumeration type.
040 * </p>
041 * <p>
042 * This check does not validate any switch expressions. Rationale:
043 * The compiler requires switch expressions to be exhaustive. This means
044 * that all possible inputs must be covered.
045 * </p>
046 * <p>
047 * This check does not validate switch statements that use pattern or null
048 * labels. Rationale: Switch statements that use pattern or null labels are
049 * checked by the compiler for exhaustiveness. This means that all possible
050 * inputs must be covered.
051 * </p>
052 * <p>
053 * See the <a href="https://docs.oracle.com/javase/specs/jls/se17/html/jls-15.html#jls-15.28">
054 *     Java Language Specification</a> for more information about switch statements
055 *     and expressions.
056 * </p>
057 * <p>
058 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
059 * </p>
060 * <p>
061 * Violation Message Keys:
062 * </p>
063 * <ul>
064 * <li>
065 * {@code missing.switch.default}
066 * </li>
067 * </ul>
068 *
069 * @since 3.1
070 */
071@StatelessCheck
072public class MissingSwitchDefaultCheck extends AbstractCheck {
073
074    /**
075     * A key is pointing to the warning message text in "messages.properties"
076     * file.
077     */
078    public static final String MSG_KEY = "missing.switch.default";
079
080    @Override
081    public int[] getDefaultTokens() {
082        return getRequiredTokens();
083    }
084
085    @Override
086    public int[] getAcceptableTokens() {
087        return getRequiredTokens();
088    }
089
090    @Override
091    public int[] getRequiredTokens() {
092        return new int[] {TokenTypes.LITERAL_SWITCH};
093    }
094
095    @Override
096    public void visitToken(DetailAST ast) {
097        if (!containsDefaultLabel(ast)
098                && !containsPatternCaseLabelElement(ast)
099                && !containsDefaultCaseLabelElement(ast)
100                && !containsNullCaseLabelElement(ast)
101                && !isSwitchExpression(ast)) {
102            log(ast, MSG_KEY);
103        }
104    }
105
106    /**
107     * Checks if the case group or its sibling contain the 'default' switch.
108     *
109     * @param detailAst first case group to check.
110     * @return true if 'default' switch found.
111     */
112    private static boolean containsDefaultLabel(DetailAST detailAst) {
113        return TokenUtil.findFirstTokenByPredicate(detailAst,
114                ast -> ast.findFirstToken(TokenTypes.LITERAL_DEFAULT) != null
115        ).isPresent();
116    }
117
118    /**
119     * Checks if a switch block contains a case label with a pattern variable definition.
120     * In this situation, the compiler enforces the given switch block to cover
121     * all possible inputs, and we do not need a default label.
122     *
123     * @param detailAst first case group to check.
124     * @return true if switch block contains a pattern case label element
125     */
126    private static boolean containsPatternCaseLabelElement(DetailAST detailAst) {
127        return TokenUtil.findFirstTokenByPredicate(detailAst, ast -> {
128            return ast.getFirstChild() != null
129                    && ast.getFirstChild().findFirstToken(TokenTypes.PATTERN_VARIABLE_DEF) != null;
130        }).isPresent();
131    }
132
133    /**
134     * Checks if a switch block contains a default case label.
135     *
136     * @param detailAst first case group to check.
137     * @return true if switch block contains default case label
138     */
139    private static boolean containsDefaultCaseLabelElement(DetailAST detailAst) {
140        return TokenUtil.findFirstTokenByPredicate(detailAst, ast -> {
141            return ast.getFirstChild() != null
142                    && ast.getFirstChild().findFirstToken(TokenTypes.LITERAL_DEFAULT) != null;
143        }).isPresent();
144    }
145
146    /**
147     * Checks if a switch block contains a null case label.
148     *
149     * @param detailAst first case group to check.
150     * @return true if switch block contains null case label
151     */
152    private static boolean containsNullCaseLabelElement(DetailAST detailAst) {
153        return TokenUtil.findFirstTokenByPredicate(detailAst, ast -> {
154            return ast.getFirstChild() != null
155                     && hasNullCaseLabel(ast.getFirstChild());
156        }).isPresent();
157    }
158
159    /**
160     * Checks if this LITERAL_SWITCH token is part of a switch expression.
161     *
162     * @param ast the switch statement we are checking
163     * @return true if part of a switch expression
164     */
165    private static boolean isSwitchExpression(DetailAST ast) {
166        return ast.getParent().getType() == TokenTypes.EXPR
167                || ast.getParent().getParent().getType() == TokenTypes.EXPR;
168    }
169
170    /**
171     * Checks if the case contains null label.
172     *
173     * @param ast the switch statement we are checking
174     * @return returnValue the ast of null label
175     */
176    private static boolean hasNullCaseLabel(DetailAST ast) {
177        final DetailAST firstChild = ast.getFirstChild();
178        return firstChild != null
179                && TokenUtil.isOfType(firstChild.getFirstChild(), TokenTypes.LITERAL_NULL);
180
181    }
182}