001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2021 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 java.util.Objects;
023
024import com.puppycrawl.tools.checkstyle.StatelessCheck;
025import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
026import com.puppycrawl.tools.checkstyle.api.DetailAST;
027import com.puppycrawl.tools.checkstyle.api.TokenTypes;
028
029/**
030 * <p>
031 * Check that the {@code default} is after all the cases in a {@code switch} statement.
032 * </p>
033 * <p>
034 * Rationale: Java allows {@code default} anywhere within the
035 * {@code switch} statement. But it is more readable if it comes after the last {@code case}.
036 * </p>
037 * <ul>
038 * <li>
039 * Property {@code skipIfLastAndSharedWithCase} - Control whether to allow {@code default}
040 * along with {@code case} if they are not last.
041 * Type is {@code boolean}.
042 * Default value is {@code false}.
043 * </li>
044 * </ul>
045 * <p>
046 * To configure the check:
047 * </p>
048 * <pre>
049 * &lt;module name=&quot;DefaultComesLast&quot;/&gt;
050 * </pre>
051 * <p>Example:</p>
052 * <pre>
053 * switch (i) {
054 *   case 1:
055 *     break;
056 *   case 2:
057 *     break;
058 *   default: // OK
059 *     break;
060 * }
061 *
062 * switch (i) {
063 *   case 1:
064 *     break;
065 *   case 2:
066 *     break; // OK, no default
067 * }
068 *
069 * switch (i) {
070 *   case 1:
071 *     break;
072 *   default: // violation, 'default' before 'case'
073 *     break;
074 *   case 2:
075 *     break;
076 * }
077 *
078 * switch (i) {
079 *   case 1:
080 *   default: // violation, 'default' before 'case'
081 *     break;
082 *   case 2:
083 *     break;
084 * }
085 * </pre>
086 * <p>To configure the check to allow default label to be not last if it is shared with case:
087 * </p>
088 * <pre>
089 * &lt;module name=&quot;DefaultComesLast&quot;&gt;
090 *   &lt;property name=&quot;skipIfLastAndSharedWithCase&quot; value=&quot;true&quot;/&gt;
091 * &lt;/module&gt;
092 * </pre>
093 * <p>Example:</p>
094 * <pre>
095 * switch (i) {
096 *   case 1:
097 *     break;
098 *   case 2:
099 *   default: // OK
100 *     break;
101 *   case 3:
102 *     break;
103 * }
104 *
105 * switch (i) {
106 *   case 1:
107 *     break;
108 *   default: // violation
109 *   case 2:
110 *     break;
111 * }
112 *
113 * // Switch rules are not subject to fall through, so this is still a violation:
114 * switch (i) {
115 *   case 1 -&gt; x = 9;
116 *   default -&gt; x = 10; // violation
117 *   case 2 -&gt; x = 32;
118 * }
119 * </pre>
120 * <p>
121 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
122 * </p>
123 * <p>
124 * Violation Message Keys:
125 * </p>
126 * <ul>
127 * <li>
128 * {@code default.comes.last}
129 * </li>
130 * <li>
131 * {@code default.comes.last.in.casegroup}
132 * </li>
133 * </ul>
134 *
135 * @since 3.4
136 */
137@StatelessCheck
138public class DefaultComesLastCheck extends AbstractCheck {
139
140    /**
141     * A key is pointing to the warning message text in "messages.properties"
142     * file.
143     */
144    public static final String MSG_KEY = "default.comes.last";
145
146    /**
147     * A key is pointing to the warning message text in "messages.properties"
148     * file.
149     */
150    public static final String MSG_KEY_SKIP_IF_LAST_AND_SHARED_WITH_CASE =
151            "default.comes.last.in.casegroup";
152
153    /** Control whether to allow {@code default} along with {@code case} if they are not last. */
154    private boolean skipIfLastAndSharedWithCase;
155
156    @Override
157    public int[] getAcceptableTokens() {
158        return getRequiredTokens();
159    }
160
161    @Override
162    public int[] getDefaultTokens() {
163        return getRequiredTokens();
164    }
165
166    @Override
167    public int[] getRequiredTokens() {
168        return new int[] {
169            TokenTypes.LITERAL_DEFAULT,
170        };
171    }
172
173    /**
174     * Setter to control whether to allow {@code default} along with
175     * {@code case} if they are not last.
176     *
177     * @param newValue whether to ignore checking.
178     */
179    public void setSkipIfLastAndSharedWithCase(boolean newValue) {
180        skipIfLastAndSharedWithCase = newValue;
181    }
182
183    @Override
184    public void visitToken(DetailAST ast) {
185        final DetailAST defaultGroupAST = ast.getParent();
186
187        // Switch rules are not subject to fall through.
188        final boolean isSwitchRule = defaultGroupAST.getType() == TokenTypes.SWITCH_RULE;
189
190        if (skipIfLastAndSharedWithCase && !isSwitchRule) {
191            if (Objects.nonNull(findNextSibling(ast, TokenTypes.LITERAL_CASE))) {
192                log(ast, MSG_KEY_SKIP_IF_LAST_AND_SHARED_WITH_CASE);
193            }
194            else if (ast.getPreviousSibling() == null
195                && Objects.nonNull(findNextSibling(defaultGroupAST,
196                                                   TokenTypes.CASE_GROUP))) {
197                log(ast, MSG_KEY);
198            }
199        }
200        else if (Objects.nonNull(findNextSibling(defaultGroupAST,
201                                            TokenTypes.CASE_GROUP))
202                    || Objects.nonNull(findNextSibling(defaultGroupAST,
203                                            TokenTypes.SWITCH_RULE))) {
204            log(ast, MSG_KEY);
205        }
206    }
207
208    /**
209     * Return token type only if passed tokenType in argument is found or returns -1.
210     *
211     * @param ast root node.
212     * @param tokenType tokentype to be processed.
213     * @return token if desired token is found or else null.
214     */
215    private static DetailAST findNextSibling(DetailAST ast, int tokenType) {
216        DetailAST token = null;
217        DetailAST node = ast.getNextSibling();
218        while (node != null) {
219            if (node.getType() == tokenType) {
220                token = node;
221                break;
222            }
223            node = node.getNextSibling();
224        }
225        return token;
226    }
227
228}