001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2017 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.regex.Matcher;
023import java.util.regex.Pattern;
024
025import com.puppycrawl.tools.checkstyle.StatelessCheck;
026import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
027import com.puppycrawl.tools.checkstyle.api.DetailAST;
028import com.puppycrawl.tools.checkstyle.api.TokenTypes;
029import com.puppycrawl.tools.checkstyle.utils.CommonUtils;
030
031/**
032 * Checks for fall through in switch statements
033 * Finds locations where a case <b>contains</b> Java code -
034 * but lacks a break, return, throw or continue statement.
035 *
036 * <p>
037 * The check honors special comments to suppress warnings about
038 * the fall through. By default the comments "fallthru",
039 * "fall through", "falls through" and "fallthrough" are recognized.
040 * </p>
041 * <p>
042 * The following fragment of code will NOT trigger the check,
043 * because of the comment "fallthru" and absence of any Java code
044 * in case 5.
045 * </p>
046 * <pre>
047 * case 3:
048 *     x = 2;
049 *     // fallthru
050 * case 4:
051 * case 5:
052 * case 6:
053 *     break;
054 * </pre>
055 * <p>
056 * The recognized relief comment can be configured with the property
057 * {@code reliefPattern}. Default value of this regular expression
058 * is "fallthru|fall through|fallthrough|falls through".
059 * </p>
060 * <p>
061 * An example of how to configure the check is:
062 * </p>
063 * <pre>
064 * &lt;module name="FallThrough"&gt;
065 *     &lt;property name=&quot;reliefPattern&quot;
066 *                  value=&quot;Fall Through&quot;/&gt;
067 * &lt;/module&gt;
068 * </pre>
069 *
070 * @author o_sukhodolsky
071 */
072@StatelessCheck
073public class FallThroughCheck extends AbstractCheck {
074
075    /**
076     * A key is pointing to the warning message text in "messages.properties"
077     * file.
078     */
079    public static final String MSG_FALL_THROUGH = "fall.through";
080
081    /**
082     * A key is pointing to the warning message text in "messages.properties"
083     * file.
084     */
085    public static final String MSG_FALL_THROUGH_LAST = "fall.through.last";
086
087    /** Do we need to check last case group. */
088    private boolean checkLastCaseGroup;
089
090    /** Relief regexp to allow fall through to the next case branch. */
091    private Pattern reliefPattern = Pattern.compile("fallthru|falls? ?through");
092
093    @Override
094    public int[] getDefaultTokens() {
095        return getRequiredTokens();
096    }
097
098    @Override
099    public int[] getRequiredTokens() {
100        return new int[] {TokenTypes.CASE_GROUP};
101    }
102
103    @Override
104    public int[] getAcceptableTokens() {
105        return getRequiredTokens();
106    }
107
108    /**
109     * Set the relief pattern.
110     *
111     * @param pattern
112     *            The regular expression pattern.
113     */
114    public void setReliefPattern(Pattern pattern) {
115        reliefPattern = pattern;
116    }
117
118    /**
119     * Configures whether we need to check last case group or not.
120     * @param value new value of the property.
121     */
122    public void setCheckLastCaseGroup(boolean value) {
123        checkLastCaseGroup = value;
124    }
125
126    @Override
127    public void visitToken(DetailAST ast) {
128        final DetailAST nextGroup = ast.getNextSibling();
129        final boolean isLastGroup = nextGroup.getType() != TokenTypes.CASE_GROUP;
130        if (!isLastGroup || checkLastCaseGroup) {
131            final DetailAST slist = ast.findFirstToken(TokenTypes.SLIST);
132
133            if (slist != null && !isTerminated(slist, true, true)
134                && !hasFallThroughComment(ast, nextGroup)) {
135                if (isLastGroup) {
136                    log(ast, MSG_FALL_THROUGH_LAST);
137                }
138                else {
139                    log(nextGroup, MSG_FALL_THROUGH);
140                }
141            }
142        }
143    }
144
145    /**
146     * Checks if a given subtree terminated by return, throw or,
147     * if allowed break, continue.
148     * @param ast root of given subtree
149     * @param useBreak should we consider break as terminator.
150     * @param useContinue should we consider continue as terminator.
151     * @return true if the subtree is terminated.
152     */
153    private boolean isTerminated(final DetailAST ast, boolean useBreak,
154                                 boolean useContinue) {
155        final boolean terminated;
156
157        switch (ast.getType()) {
158            case TokenTypes.LITERAL_RETURN:
159            case TokenTypes.LITERAL_THROW:
160                terminated = true;
161                break;
162            case TokenTypes.LITERAL_BREAK:
163                terminated = useBreak;
164                break;
165            case TokenTypes.LITERAL_CONTINUE:
166                terminated = useContinue;
167                break;
168            case TokenTypes.SLIST:
169                terminated = checkSlist(ast, useBreak, useContinue);
170                break;
171            case TokenTypes.LITERAL_IF:
172                terminated = checkIf(ast, useBreak, useContinue);
173                break;
174            case TokenTypes.LITERAL_FOR:
175            case TokenTypes.LITERAL_WHILE:
176            case TokenTypes.LITERAL_DO:
177                terminated = checkLoop(ast);
178                break;
179            case TokenTypes.LITERAL_TRY:
180                terminated = checkTry(ast, useBreak, useContinue);
181                break;
182            case TokenTypes.LITERAL_SWITCH:
183                terminated = checkSwitch(ast, useContinue);
184                break;
185            case TokenTypes.LITERAL_SYNCHRONIZED:
186                terminated = checkSynchronized(ast, useBreak, useContinue);
187                break;
188            default:
189                terminated = false;
190        }
191        return terminated;
192    }
193
194    /**
195     * Checks if a given SLIST terminated by return, throw or,
196     * if allowed break, continue.
197     * @param slistAst SLIST to check
198     * @param useBreak should we consider break as terminator.
199     * @param useContinue should we consider continue as terminator.
200     * @return true if SLIST is terminated.
201     */
202    private boolean checkSlist(final DetailAST slistAst, boolean useBreak,
203                               boolean useContinue) {
204        DetailAST lastStmt = slistAst.getLastChild();
205
206        if (lastStmt.getType() == TokenTypes.RCURLY) {
207            lastStmt = lastStmt.getPreviousSibling();
208        }
209
210        return lastStmt != null
211            && isTerminated(lastStmt, useBreak, useContinue);
212    }
213
214    /**
215     * Checks if a given IF terminated by return, throw or,
216     * if allowed break, continue.
217     * @param ast IF to check
218     * @param useBreak should we consider break as terminator.
219     * @param useContinue should we consider continue as terminator.
220     * @return true if IF is terminated.
221     */
222    private boolean checkIf(final DetailAST ast, boolean useBreak,
223                            boolean useContinue) {
224        final DetailAST thenStmt = ast.findFirstToken(TokenTypes.RPAREN)
225                .getNextSibling();
226        final DetailAST elseStmt = thenStmt.getNextSibling();
227        boolean isTerminated = isTerminated(thenStmt, useBreak, useContinue);
228
229        if (isTerminated && elseStmt != null) {
230            isTerminated = isTerminated(elseStmt.getFirstChild(),
231                useBreak, useContinue);
232        }
233        else if (elseStmt == null) {
234            isTerminated = false;
235        }
236        return isTerminated;
237    }
238
239    /**
240     * Checks if a given loop terminated by return, throw or,
241     * if allowed break, continue.
242     * @param ast loop to check
243     * @return true if loop is terminated.
244     */
245    private boolean checkLoop(final DetailAST ast) {
246        final DetailAST loopBody;
247        if (ast.getType() == TokenTypes.LITERAL_DO) {
248            final DetailAST lparen = ast.findFirstToken(TokenTypes.DO_WHILE);
249            loopBody = lparen.getPreviousSibling();
250        }
251        else {
252            final DetailAST rparen = ast.findFirstToken(TokenTypes.RPAREN);
253            loopBody = rparen.getNextSibling();
254        }
255        return isTerminated(loopBody, false, false);
256    }
257
258    /**
259     * Checks if a given try/catch/finally block terminated by return, throw or,
260     * if allowed break, continue.
261     * @param ast loop to check
262     * @param useBreak should we consider break as terminator.
263     * @param useContinue should we consider continue as terminator.
264     * @return true if try/catch/finally block is terminated.
265     */
266    private boolean checkTry(final DetailAST ast, boolean useBreak,
267                             boolean useContinue) {
268        final DetailAST finalStmt = ast.getLastChild();
269        boolean isTerminated = false;
270        if (finalStmt.getType() == TokenTypes.LITERAL_FINALLY) {
271            isTerminated = isTerminated(finalStmt.findFirstToken(TokenTypes.SLIST),
272                                useBreak, useContinue);
273        }
274
275        if (!isTerminated) {
276            DetailAST firstChild = ast.getFirstChild();
277
278            if (firstChild.getType() == TokenTypes.RESOURCE_SPECIFICATION) {
279                firstChild = firstChild.getNextSibling();
280            }
281
282            isTerminated = isTerminated(firstChild,
283                    useBreak, useContinue);
284
285            DetailAST catchStmt = ast.findFirstToken(TokenTypes.LITERAL_CATCH);
286            while (catchStmt != null
287                    && isTerminated
288                    && catchStmt.getType() == TokenTypes.LITERAL_CATCH) {
289                final DetailAST catchBody =
290                        catchStmt.findFirstToken(TokenTypes.SLIST);
291                isTerminated = isTerminated(catchBody, useBreak, useContinue);
292                catchStmt = catchStmt.getNextSibling();
293            }
294        }
295        return isTerminated;
296    }
297
298    /**
299     * Checks if a given switch terminated by return, throw or,
300     * if allowed break, continue.
301     * @param literalSwitchAst loop to check
302     * @param useContinue should we consider continue as terminator.
303     * @return true if switch is terminated.
304     */
305    private boolean checkSwitch(final DetailAST literalSwitchAst, boolean useContinue) {
306        DetailAST caseGroup = literalSwitchAst.findFirstToken(TokenTypes.CASE_GROUP);
307        boolean isTerminated = caseGroup != null;
308        while (isTerminated && caseGroup.getType() != TokenTypes.RCURLY) {
309            final DetailAST caseBody =
310                caseGroup.findFirstToken(TokenTypes.SLIST);
311            isTerminated = caseBody != null && isTerminated(caseBody, false, useContinue);
312            caseGroup = caseGroup.getNextSibling();
313        }
314        return isTerminated;
315    }
316
317    /**
318     * Checks if a given synchronized block terminated by return, throw or,
319     * if allowed break, continue.
320     * @param synchronizedAst synchronized block to check.
321     * @param useBreak should we consider break as terminator.
322     * @param useContinue should we consider continue as terminator.
323     * @return true if synchronized block is terminated.
324     */
325    private boolean checkSynchronized(final DetailAST synchronizedAst, boolean useBreak,
326                                      boolean useContinue) {
327        return isTerminated(
328            synchronizedAst.findFirstToken(TokenTypes.SLIST), useBreak, useContinue);
329    }
330
331    /**
332     * Determines if the fall through case between {@code currentCase} and
333     * {@code nextCase} is relieved by a appropriate comment.
334     *
335     * @param currentCase AST of the case that falls through to the next case.
336     * @param nextCase AST of the next case.
337     * @return True if a relief comment was found
338     */
339    private boolean hasFallThroughComment(DetailAST currentCase, DetailAST nextCase) {
340        boolean allThroughComment = false;
341        final int endLineNo = nextCase.getLineNo();
342        final int endColNo = nextCase.getColumnNo();
343
344        // Remember: The lines number returned from the AST is 1-based, but
345        // the lines number in this array are 0-based. So you will often
346        // see a "lineNo-1" etc.
347        final String[] lines = getLines();
348
349        // Handle:
350        //    case 1:
351        //    /+ FALLTHRU +/ case 2:
352        //    ....
353        // and
354        //    switch(i) {
355        //    default:
356        //    /+ FALLTHRU +/}
357        //
358        final String linePart = lines[endLineNo - 1].substring(0, endColNo);
359        if (matchesComment(reliefPattern, linePart, endLineNo)) {
360            allThroughComment = true;
361        }
362        else {
363            // Handle:
364            //    case 1:
365            //    .....
366            //    // FALLTHRU
367            //    case 2:
368            //    ....
369            // and
370            //    switch(i) {
371            //    default:
372            //    // FALLTHRU
373            //    }
374            final int startLineNo = currentCase.getLineNo();
375            for (int i = endLineNo - 2; i > startLineNo - 1; i--) {
376                if (!CommonUtils.isBlank(lines[i])) {
377                    allThroughComment = matchesComment(reliefPattern, lines[i], i + 1);
378                    break;
379                }
380            }
381        }
382        return allThroughComment;
383    }
384
385    /**
386     * Does a regular expression match on the given line and checks that a
387     * possible match is within a comment.
388     * @param pattern The regular expression pattern to use.
389     * @param line The line of test to do the match on.
390     * @param lineNo The line number in the file.
391     * @return True if a match was found inside a comment.
392     */
393    private boolean matchesComment(Pattern pattern, String line, int lineNo) {
394        final Matcher matcher = pattern.matcher(line);
395        boolean matches = false;
396
397        if (matcher.find()) {
398            // -1 because it returns the char position beyond the match
399            matches = getFileContents().hasIntersectionWithComment(lineNo, matcher.start(),
400                    lineNo, matcher.end() - 1);
401        }
402        return matches;
403    }
404}