Source code

001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2020 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.ArrayDeque;
023import java.util.Arrays;
024import java.util.Deque;
025import java.util.HashSet;
026import java.util.LinkedList;
027import java.util.List;
028import java.util.Set;
029import java.util.stream.Collectors;
030
031import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
032import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
033import com.puppycrawl.tools.checkstyle.api.DetailAST;
034import com.puppycrawl.tools.checkstyle.api.TokenTypes;
035
036/**
037 * <p>
038 * Checks that for loop control variables are not modified
039 * inside the for block. An example is:
040 * </p>
041 * <pre>
042 * for (int i = 0; i &lt; 1; i++) {
043 *   i++; //violation
044 * }
045 * </pre>
046 * <p>
047 * Rationale: If the control variable is modified inside the loop
048 * body, the program flow becomes more difficult to follow.
049 * See <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-14.html#jls-14.14">
050 * FOR statement</a> specification for more details.
051 * </p>
052 * <p>
053 * Such loop would be suppressed:
054 * </p>
055 * <pre>
056 * for (int i = 0; i &lt; 10;) {
057 *   i++;
058 * }
059 * </pre>
060 * <ul>
061 * <li>
062 * Property {@code skipEnhancedForLoopVariable} - Control whether to check
063 * <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-14.html#jls-14.14.2">
064 * enhanced for-loop</a> variable.
065 * Default value is {@code false}.
066 * </li>
067 * </ul>
068 * <p>
069 * To configure the check:
070 * </p>
071 * <pre>
072 * &lt;module name="ModifiedControlVariable"/&gt;
073 * </pre>
074 * <p>
075 * By default, This Check validates
076 *  <a href = "https://docs.oracle.com/javase/specs/jls/se11/html/jls-14.html#jls-14.14.2">
077 * Enhanced For-Loop</a>.
078 * </p>
079 * <p>
080 * Option 'skipEnhancedForLoopVariable' could be used to skip check of variable
081 *  from Enhanced For Loop.
082 * </p>
083 * <p>
084 * An example of how to configure the check so that it skips enhanced For Loop Variable is:
085 * </p>
086 * <pre>
087 * &lt;module name="ModifiedControlVariable"&gt;
088 *   &lt;property name="skipEnhancedForLoopVariable" value="true"/&gt;
089 * &lt;/module&gt;
090 * </pre>
091 * <p>Example:</p>
092 *
093 * <pre>
094 * for (String line: lines) {
095 *   line = line.trim();   // it will skip this violation
096 * }
097 * </pre>
098 *
099 * @since 3.5
100 */
101@FileStatefulCheck
102public final class ModifiedControlVariableCheck extends AbstractCheck {
103
104    /**
105     * A key is pointing to the warning message text in "messages.properties"
106     * file.
107     */
108    public static final String MSG_KEY = "modified.control.variable";
109
110    /**
111     * Message thrown with IllegalStateException.
112     */
113    private static final String ILLEGAL_TYPE_OF_TOKEN = "Illegal type of token: ";
114
115    /** Operations which can change control variable in update part of the loop. */
116    private static final Set<Integer> MUTATION_OPERATIONS =
117        Arrays.stream(new Integer[] {
118            TokenTypes.POST_INC,
119            TokenTypes.POST_DEC,
120            TokenTypes.DEC,
121            TokenTypes.INC,
122            TokenTypes.ASSIGN,
123        }).collect(Collectors.toSet());
124
125    /** Stack of block parameters. */
126    private final Deque<Deque<String>> variableStack = new ArrayDeque<>();
127
128    /**
129     * Control whether to check
130     * <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-14.html#jls-14.14.2">
131     * enhanced for-loop</a> variable.
132     */
133    private boolean skipEnhancedForLoopVariable;
134
135    /**
136     * Setter to control whether to check
137     * <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-14.html#jls-14.14.2">
138     * enhanced for-loop</a> variable.
139     * @param skipEnhancedForLoopVariable whether to skip enhanced for-loop variable
140     */
141    public void setSkipEnhancedForLoopVariable(boolean skipEnhancedForLoopVariable) {
142        this.skipEnhancedForLoopVariable = skipEnhancedForLoopVariable;
143    }
144
145    @Override
146    public int[] getDefaultTokens() {
147        return getRequiredTokens();
148    }
149
150    @Override
151    public int[] getRequiredTokens() {
152        return new int[] {
153            TokenTypes.OBJBLOCK,
154            TokenTypes.LITERAL_FOR,
155            TokenTypes.FOR_ITERATOR,
156            TokenTypes.FOR_EACH_CLAUSE,
157            TokenTypes.ASSIGN,
158            TokenTypes.PLUS_ASSIGN,
159            TokenTypes.MINUS_ASSIGN,
160            TokenTypes.STAR_ASSIGN,
161            TokenTypes.DIV_ASSIGN,
162            TokenTypes.MOD_ASSIGN,
163            TokenTypes.SR_ASSIGN,
164            TokenTypes.BSR_ASSIGN,
165            TokenTypes.SL_ASSIGN,
166            TokenTypes.BAND_ASSIGN,
167            TokenTypes.BXOR_ASSIGN,
168            TokenTypes.BOR_ASSIGN,
169            TokenTypes.INC,
170            TokenTypes.POST_INC,
171            TokenTypes.DEC,
172            TokenTypes.POST_DEC,
173        };
174    }
175
176    @Override
177    public int[] getAcceptableTokens() {
178        return getRequiredTokens();
179    }
180
181    @Override
182    public void beginTree(DetailAST rootAST) {
183        // clear data
184        variableStack.clear();
185    }
186
187    @Override
188    public void visitToken(DetailAST ast) {
189        switch (ast.getType()) {
190            case TokenTypes.OBJBLOCK:
191                enterBlock();
192                break;
193            case TokenTypes.LITERAL_FOR:
194            case TokenTypes.FOR_ITERATOR:
195            case TokenTypes.FOR_EACH_CLAUSE:
196                //we need that Tokens only at leaveToken()
197                break;
198            case TokenTypes.ASSIGN:
199            case TokenTypes.PLUS_ASSIGN:
200            case TokenTypes.MINUS_ASSIGN:
201            case TokenTypes.STAR_ASSIGN:
202            case TokenTypes.DIV_ASSIGN:
203            case TokenTypes.MOD_ASSIGN:
204            case TokenTypes.SR_ASSIGN:
205            case TokenTypes.BSR_ASSIGN:
206            case TokenTypes.SL_ASSIGN:
207            case TokenTypes.BAND_ASSIGN:
208            case TokenTypes.BXOR_ASSIGN:
209            case TokenTypes.BOR_ASSIGN:
210            case TokenTypes.INC:
211            case TokenTypes.POST_INC:
212            case TokenTypes.DEC:
213            case TokenTypes.POST_DEC:
214                checkIdent(ast);
215                break;
216            default:
217                throw new IllegalStateException(ILLEGAL_TYPE_OF_TOKEN + ast);
218        }
219    }
220
221    @Override
222    public void leaveToken(DetailAST ast) {
223        switch (ast.getType()) {
224            case TokenTypes.FOR_ITERATOR:
225                leaveForIter(ast.getParent());
226                break;
227            case TokenTypes.FOR_EACH_CLAUSE:
228                if (!skipEnhancedForLoopVariable) {
229                    final DetailAST paramDef = ast.findFirstToken(TokenTypes.VARIABLE_DEF);
230                    leaveForEach(paramDef);
231                }
232                break;
233            case TokenTypes.LITERAL_FOR:
234                leaveForDef(ast);
235                break;
236            case TokenTypes.OBJBLOCK:
237                exitBlock();
238                break;
239            case TokenTypes.ASSIGN:
240            case TokenTypes.PLUS_ASSIGN:
241            case TokenTypes.MINUS_ASSIGN:
242            case TokenTypes.STAR_ASSIGN:
243            case TokenTypes.DIV_ASSIGN:
244            case TokenTypes.MOD_ASSIGN:
245            case TokenTypes.SR_ASSIGN:
246            case TokenTypes.BSR_ASSIGN:
247            case TokenTypes.SL_ASSIGN:
248            case TokenTypes.BAND_ASSIGN:
249            case TokenTypes.BXOR_ASSIGN:
250            case TokenTypes.BOR_ASSIGN:
251            case TokenTypes.INC:
252            case TokenTypes.POST_INC:
253            case TokenTypes.DEC:
254            case TokenTypes.POST_DEC:
255                //we need that Tokens only at visitToken()
256                break;
257            default:
258                throw new IllegalStateException(ILLEGAL_TYPE_OF_TOKEN + ast);
259        }
260    }
261
262    /**
263     * Enters an inner class, which requires a new variable set.
264     */
265    private void enterBlock() {
266        variableStack.push(new ArrayDeque<>());
267    }
268
269    /**
270     * Leave an inner class, so restore variable set.
271     */
272    private void exitBlock() {
273        variableStack.pop();
274    }
275
276    /**
277     * Get current variable stack.
278     * @return current variable stack
279     */
280    private Deque<String> getCurrentVariables() {
281        return variableStack.peek();
282    }
283
284    /**
285     * Check if ident is parameter.
286     * @param ast ident to check.
287     */
288    private void checkIdent(DetailAST ast) {
289        final Deque<String> currentVariables = getCurrentVariables();
290        final DetailAST identAST = ast.getFirstChild();
291
292        if (identAST != null && identAST.getType() == TokenTypes.IDENT
293            && currentVariables.contains(identAST.getText())) {
294            log(ast, MSG_KEY, identAST.getText());
295        }
296    }
297
298    /**
299     * Push current variables to the stack.
300     * @param ast a for definition.
301     */
302    private void leaveForIter(DetailAST ast) {
303        final Set<String> variablesToPutInScope = getVariablesManagedByForLoop(ast);
304        for (String variableName : variablesToPutInScope) {
305            getCurrentVariables().push(variableName);
306        }
307    }
308
309    /**
310     * Determines which variable are specific to for loop and should not be
311     * change by inner loop body.
312     * @param ast For Loop
313     * @return Set of Variable Name which are managed by for
314     */
315    private static Set<String> getVariablesManagedByForLoop(DetailAST ast) {
316        final Set<String> initializedVariables = getForInitVariables(ast);
317        final Set<String> iteratingVariables = getForIteratorVariables(ast);
318        return initializedVariables.stream().filter(iteratingVariables::contains)
319            .collect(Collectors.toSet());
320    }
321
322    /**
323     * Push current variables to the stack.
324     * @param paramDef a for-each clause variable
325     */
326    private void leaveForEach(DetailAST paramDef) {
327        final DetailAST paramName = paramDef.findFirstToken(TokenTypes.IDENT);
328        getCurrentVariables().push(paramName.getText());
329    }
330
331    /**
332     * Pops the variables from the stack.
333     * @param ast a for definition.
334     */
335    private void leaveForDef(DetailAST ast) {
336        final DetailAST forInitAST = ast.findFirstToken(TokenTypes.FOR_INIT);
337        if (forInitAST == null) {
338            if (!skipEnhancedForLoopVariable) {
339                // this is for-each loop, just pop variables
340                getCurrentVariables().pop();
341            }
342        }
343        else {
344            final Set<String> variablesManagedByForLoop = getVariablesManagedByForLoop(ast);
345            popCurrentVariables(variablesManagedByForLoop.size());
346        }
347    }
348
349    /**
350     * Pops given number of variables from currentVariables.
351     * @param count Count of variables to be popped from currentVariables
352     */
353    private void popCurrentVariables(int count) {
354        for (int i = 0; i < count; i++) {
355            getCurrentVariables().pop();
356        }
357    }
358
359    /**
360     * Get all variables initialized In init part of for loop.
361     * @param ast for loop token
362     * @return set of variables initialized in for loop
363     */
364    private static Set<String> getForInitVariables(DetailAST ast) {
365        final Set<String> initializedVariables = new HashSet<>();
366        final DetailAST forInitAST = ast.findFirstToken(TokenTypes.FOR_INIT);
367
368        for (DetailAST parameterDefAST = forInitAST.findFirstToken(TokenTypes.VARIABLE_DEF);
369             parameterDefAST != null;
370             parameterDefAST = parameterDefAST.getNextSibling()) {
371            if (parameterDefAST.getType() == TokenTypes.VARIABLE_DEF) {
372                final DetailAST param =
373                        parameterDefAST.findFirstToken(TokenTypes.IDENT);
374
375                initializedVariables.add(param.getText());
376            }
377        }
378        return initializedVariables;
379    }
380
381    /**
382     * Get all variables which for loop iterating part change in every loop.
383     * @param ast for loop literal(TokenTypes.LITERAL_FOR)
384     * @return names of variables change in iterating part of for
385     */
386    private static Set<String> getForIteratorVariables(DetailAST ast) {
387        final Set<String> iteratorVariables = new HashSet<>();
388        final DetailAST forIteratorAST = ast.findFirstToken(TokenTypes.FOR_ITERATOR);
389        final DetailAST forUpdateListAST = forIteratorAST.findFirstToken(TokenTypes.ELIST);
390
391        findChildrenOfExpressionType(forUpdateListAST).stream()
392            .filter(iteratingExpressionAST -> {
393                return MUTATION_OPERATIONS.contains(iteratingExpressionAST.getType());
394            }).forEach(iteratingExpressionAST -> {
395                final DetailAST oneVariableOperatorChild = iteratingExpressionAST.getFirstChild();
396                iteratorVariables.add(oneVariableOperatorChild.getText());
397            });
398
399        return iteratorVariables;
400    }
401
402    /**
403     * Find all child of given AST of type TokenType.EXPR
404     * @param ast parent of expressions to find
405     * @return all child of given ast
406     */
407    private static List<DetailAST> findChildrenOfExpressionType(DetailAST ast) {
408        final List<DetailAST> foundExpressions = new LinkedList<>();
409        if (ast != null) {
410            for (DetailAST iteratingExpressionAST = ast.findFirstToken(TokenTypes.EXPR);
411                 iteratingExpressionAST != null;
412                 iteratingExpressionAST = iteratingExpressionAST.getNextSibling()) {
413                if (iteratingExpressionAST.getType() == TokenTypes.EXPR) {
414                    foundExpressions.add(iteratingExpressionAST.getFirstChild());
415                }
416            }
417        }
418        return foundExpressions;
419    }
420
421}