Source code

001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2019 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 * Check for ensuring that for loop control variables are not modified
038 * inside the for block. An example is:
039 *
040 * <pre>
041 * {@code
042 * for (int i = 0; i &lt; 1; i++) {
043 *     i++;//violation
044 * }
045 * }
046 * </pre>
047 * Rationale: If the control variable is modified inside the loop
048 * body, the program flow becomes more difficult to follow.<br>
049 * See <a href="https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.14">
050 * FOR statement</a> specification for more details.
051 * <p>Examples:</p>
052 *
053 * <pre>
054 * &lt;module name=&quot;ModifiedControlVariable&quot;&gt;
055 * &lt;/module&gt;
056 * </pre>
057 *
058 * <p>Such loop would be suppressed:
059 *
060 * <pre>
061 * {@code
062 * for(int i=0; i &lt; 10;) {
063 *     i++;
064 * }
065 * }
066 * </pre>
067 *
068 * <p>
069 * By default, This Check validates
070 *  <a href = "https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.14.2">
071 * Enhanced For-Loop</a>.
072 * </p>
073 * <p>
074 * Option 'skipEnhancedForLoopVariable' could be used to skip check of variable
075 *  from Enhanced For Loop.
076 * </p>
077 * <p>
078 * An example of how to configure the check so that it skips enhanced For Loop Variable is:
079 * </p>
080 * <pre>
081 * &lt;module name="ModifiedControlVariable"&gt;
082 *     &lt;property name="skipEnhancedForLoopVariable" value="true"/&gt;
083 * &lt;/module&gt;
084 * </pre>
085 * <p>Example:</p>
086 *
087 * <pre>
088 * {@code
089 * for (String line: lines) {
090 *     line = line.trim();   // it will skip this violation
091 * }
092 * }
093 * </pre>
094 *
095 *
096 */
097@FileStatefulCheck
098public final class ModifiedControlVariableCheck extends AbstractCheck {
099
100    /**
101     * A key is pointing to the warning message text in "messages.properties"
102     * file.
103     */
104    public static final String MSG_KEY = "modified.control.variable";
105
106    /**
107     * Message thrown with IllegalStateException.
108     */
109    private static final String ILLEGAL_TYPE_OF_TOKEN = "Illegal type of token: ";
110
111    /** Operations which can change control variable in update part of the loop. */
112    private static final Set<Integer> MUTATION_OPERATIONS =
113        Arrays.stream(new Integer[] {
114            TokenTypes.POST_INC,
115            TokenTypes.POST_DEC,
116            TokenTypes.DEC,
117            TokenTypes.INC,
118            TokenTypes.ASSIGN,
119        }).collect(Collectors.toSet());
120
121    /** Stack of block parameters. */
122    private final Deque<Deque<String>> variableStack = new ArrayDeque<>();
123
124    /** Controls whether to skip enhanced for-loop variable. */
125    private boolean skipEnhancedForLoopVariable;
126
127    /**
128     * Whether to skip enhanced for-loop variable or not.
129     * @param skipEnhancedForLoopVariable whether to skip enhanced for-loop variable
130     */
131    public void setSkipEnhancedForLoopVariable(boolean skipEnhancedForLoopVariable) {
132        this.skipEnhancedForLoopVariable = skipEnhancedForLoopVariable;
133    }
134
135    @Override
136    public int[] getDefaultTokens() {
137        return getRequiredTokens();
138    }
139
140    @Override
141    public int[] getRequiredTokens() {
142        return new int[] {
143            TokenTypes.OBJBLOCK,
144            TokenTypes.LITERAL_FOR,
145            TokenTypes.FOR_ITERATOR,
146            TokenTypes.FOR_EACH_CLAUSE,
147            TokenTypes.ASSIGN,
148            TokenTypes.PLUS_ASSIGN,
149            TokenTypes.MINUS_ASSIGN,
150            TokenTypes.STAR_ASSIGN,
151            TokenTypes.DIV_ASSIGN,
152            TokenTypes.MOD_ASSIGN,
153            TokenTypes.SR_ASSIGN,
154            TokenTypes.BSR_ASSIGN,
155            TokenTypes.SL_ASSIGN,
156            TokenTypes.BAND_ASSIGN,
157            TokenTypes.BXOR_ASSIGN,
158            TokenTypes.BOR_ASSIGN,
159            TokenTypes.INC,
160            TokenTypes.POST_INC,
161            TokenTypes.DEC,
162            TokenTypes.POST_DEC,
163        };
164    }
165
166    @Override
167    public int[] getAcceptableTokens() {
168        return getRequiredTokens();
169    }
170
171    @Override
172    public void beginTree(DetailAST rootAST) {
173        // clear data
174        variableStack.clear();
175    }
176
177    @Override
178    public void visitToken(DetailAST ast) {
179        switch (ast.getType()) {
180            case TokenTypes.OBJBLOCK:
181                enterBlock();
182                break;
183            case TokenTypes.LITERAL_FOR:
184            case TokenTypes.FOR_ITERATOR:
185            case TokenTypes.FOR_EACH_CLAUSE:
186                //we need that Tokens only at leaveToken()
187                break;
188            case TokenTypes.ASSIGN:
189            case TokenTypes.PLUS_ASSIGN:
190            case TokenTypes.MINUS_ASSIGN:
191            case TokenTypes.STAR_ASSIGN:
192            case TokenTypes.DIV_ASSIGN:
193            case TokenTypes.MOD_ASSIGN:
194            case TokenTypes.SR_ASSIGN:
195            case TokenTypes.BSR_ASSIGN:
196            case TokenTypes.SL_ASSIGN:
197            case TokenTypes.BAND_ASSIGN:
198            case TokenTypes.BXOR_ASSIGN:
199            case TokenTypes.BOR_ASSIGN:
200            case TokenTypes.INC:
201            case TokenTypes.POST_INC:
202            case TokenTypes.DEC:
203            case TokenTypes.POST_DEC:
204                checkIdent(ast);
205                break;
206            default:
207                throw new IllegalStateException(ILLEGAL_TYPE_OF_TOKEN + ast);
208        }
209    }
210
211    @Override
212    public void leaveToken(DetailAST ast) {
213        switch (ast.getType()) {
214            case TokenTypes.FOR_ITERATOR:
215                leaveForIter(ast.getParent());
216                break;
217            case TokenTypes.FOR_EACH_CLAUSE:
218                if (!skipEnhancedForLoopVariable) {
219                    final DetailAST paramDef = ast.findFirstToken(TokenTypes.VARIABLE_DEF);
220                    leaveForEach(paramDef);
221                }
222                break;
223            case TokenTypes.LITERAL_FOR:
224                if (!getCurrentVariables().isEmpty()) {
225                    leaveForDef(ast);
226                }
227                break;
228            case TokenTypes.OBJBLOCK:
229                exitBlock();
230                break;
231            case TokenTypes.ASSIGN:
232            case TokenTypes.PLUS_ASSIGN:
233            case TokenTypes.MINUS_ASSIGN:
234            case TokenTypes.STAR_ASSIGN:
235            case TokenTypes.DIV_ASSIGN:
236            case TokenTypes.MOD_ASSIGN:
237            case TokenTypes.SR_ASSIGN:
238            case TokenTypes.BSR_ASSIGN:
239            case TokenTypes.SL_ASSIGN:
240            case TokenTypes.BAND_ASSIGN:
241            case TokenTypes.BXOR_ASSIGN:
242            case TokenTypes.BOR_ASSIGN:
243            case TokenTypes.INC:
244            case TokenTypes.POST_INC:
245            case TokenTypes.DEC:
246            case TokenTypes.POST_DEC:
247                //we need that Tokens only at visitToken()
248                break;
249            default:
250                throw new IllegalStateException(ILLEGAL_TYPE_OF_TOKEN + ast);
251        }
252    }
253
254    /**
255     * Enters an inner class, which requires a new variable set.
256     */
257    private void enterBlock() {
258        variableStack.push(new ArrayDeque<>());
259    }
260
261    /**
262     * Leave an inner class, so restore variable set.
263     */
264    private void exitBlock() {
265        variableStack.pop();
266    }
267
268    /**
269     * Get current variable stack.
270     * @return current variable stack
271     */
272    private Deque<String> getCurrentVariables() {
273        return variableStack.peek();
274    }
275
276    /**
277     * Check if ident is parameter.
278     * @param ast ident to check.
279     */
280    private void checkIdent(DetailAST ast) {
281        final Deque<String> currentVariables = getCurrentVariables();
282        if (currentVariables != null && !currentVariables.isEmpty()) {
283            final DetailAST identAST = ast.getFirstChild();
284
285            if (identAST != null && identAST.getType() == TokenTypes.IDENT
286                && getCurrentVariables().contains(identAST.getText())) {
287                log(ast, MSG_KEY, identAST.getText());
288            }
289        }
290    }
291
292    /**
293     * Push current variables to the stack.
294     * @param ast a for definition.
295     */
296    private void leaveForIter(DetailAST ast) {
297        final Set<String> variablesToPutInScope = getVariablesManagedByForLoop(ast);
298        for (String variableName : variablesToPutInScope) {
299            getCurrentVariables().push(variableName);
300        }
301    }
302
303    /**
304     * Determines which variable are specific to for loop and should not be
305     * change by inner loop body.
306     * @param ast For Loop
307     * @return Set of Variable Name which are managed by for
308     */
309    private static Set<String> getVariablesManagedByForLoop(DetailAST ast) {
310        final Set<String> initializedVariables = getForInitVariables(ast);
311        final Set<String> iteratingVariables = getForIteratorVariables(ast);
312        return initializedVariables.stream().filter(iteratingVariables::contains)
313            .collect(Collectors.toSet());
314    }
315
316    /**
317     * Push current variables to the stack.
318     * @param paramDef a for-each clause variable
319     */
320    private void leaveForEach(DetailAST paramDef) {
321        final DetailAST paramName = paramDef.findFirstToken(TokenTypes.IDENT);
322        getCurrentVariables().push(paramName.getText());
323    }
324
325    /**
326     * Pops the variables from the stack.
327     * @param ast a for definition.
328     */
329    private void leaveForDef(DetailAST ast) {
330        final DetailAST forInitAST = ast.findFirstToken(TokenTypes.FOR_INIT);
331        if (forInitAST == null) {
332            if (!skipEnhancedForLoopVariable) {
333                // this is for-each loop, just pop variables
334                getCurrentVariables().pop();
335            }
336        }
337        else {
338            final Set<String> variablesManagedByForLoop = getVariablesManagedByForLoop(ast);
339            popCurrentVariables(variablesManagedByForLoop.size());
340        }
341    }
342
343    /**
344     * Pops given number of variables from currentVariables.
345     * @param count Count of variables to be popped from currentVariables
346     */
347    private void popCurrentVariables(int count) {
348        for (int i = 0; i < count; i++) {
349            getCurrentVariables().pop();
350        }
351    }
352
353    /**
354     * Get all variables initialized In init part of for loop.
355     * @param ast for loop token
356     * @return set of variables initialized in for loop
357     */
358    private static Set<String> getForInitVariables(DetailAST ast) {
359        final Set<String> initializedVariables = new HashSet<>();
360        final DetailAST forInitAST = ast.findFirstToken(TokenTypes.FOR_INIT);
361
362        for (DetailAST parameterDefAST = forInitAST.findFirstToken(TokenTypes.VARIABLE_DEF);
363             parameterDefAST != null;
364             parameterDefAST = parameterDefAST.getNextSibling()) {
365            if (parameterDefAST.getType() == TokenTypes.VARIABLE_DEF) {
366                final DetailAST param =
367                        parameterDefAST.findFirstToken(TokenTypes.IDENT);
368
369                initializedVariables.add(param.getText());
370            }
371        }
372        return initializedVariables;
373    }
374
375    /**
376     * Get all variables which for loop iterating part change in every loop.
377     * @param ast for loop literal(TokenTypes.LITERAL_FOR)
378     * @return names of variables change in iterating part of for
379     */
380    private static Set<String> getForIteratorVariables(DetailAST ast) {
381        final Set<String> iteratorVariables = new HashSet<>();
382        final DetailAST forIteratorAST = ast.findFirstToken(TokenTypes.FOR_ITERATOR);
383        final DetailAST forUpdateListAST = forIteratorAST.findFirstToken(TokenTypes.ELIST);
384
385        findChildrenOfExpressionType(forUpdateListAST).stream()
386            .filter(iteratingExpressionAST -> {
387                return MUTATION_OPERATIONS.contains(iteratingExpressionAST.getType());
388            }).forEach(iteratingExpressionAST -> {
389                final DetailAST oneVariableOperatorChild = iteratingExpressionAST.getFirstChild();
390                if (oneVariableOperatorChild.getType() == TokenTypes.IDENT) {
391                    iteratorVariables.add(oneVariableOperatorChild.getText());
392                }
393            });
394
395        return iteratorVariables;
396    }
397
398    /**
399     * Find all child of given AST of type TokenType.EXPR
400     * @param ast parent of expressions to find
401     * @return all child of given ast
402     */
403    private static List<DetailAST> findChildrenOfExpressionType(DetailAST ast) {
404        final List<DetailAST> foundExpressions = new LinkedList<>();
405        if (ast != null) {
406            for (DetailAST iteratingExpressionAST = ast.findFirstToken(TokenTypes.EXPR);
407                 iteratingExpressionAST != null;
408                 iteratingExpressionAST = iteratingExpressionAST.getNextSibling()) {
409                if (iteratingExpressionAST.getType() == TokenTypes.EXPR) {
410                    foundExpressions.add(iteratingExpressionAST.getFirstChild());
411                }
412            }
413        }
414        return foundExpressions;
415    }
416
417}