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.design;
021
022import java.util.Arrays;
023import java.util.Optional;
024import java.util.Set;
025import java.util.function.Predicate;
026import java.util.stream.Collectors;
027
028import com.puppycrawl.tools.checkstyle.StatelessCheck;
029import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
030import com.puppycrawl.tools.checkstyle.api.DetailAST;
031import com.puppycrawl.tools.checkstyle.api.Scope;
032import com.puppycrawl.tools.checkstyle.api.TokenTypes;
033import com.puppycrawl.tools.checkstyle.utils.ScopeUtils;
034import com.puppycrawl.tools.checkstyle.utils.TokenUtils;
035
036/**
037 * The check finds classes that are designed for extension (subclass creation).
038 *
039 * <p>
040 * Nothing wrong could be with founded classes.
041 * This check makes sense only for library projects (not application projects)
042 * which care of ideal OOP-design to make sure that class works in all cases even misusage.
043 * Even in library projects this check most likely will find classes that are designed for extension
044 * by somebody. User needs to use suppressions extensively to got a benefit from this check,
045 * and keep in suppressions all confirmed/known classes that are deigned for inheritance
046 * intentionally to let the check catch only new classes, and bring this to team/user attention.
047 * </p>
048 *
049 * <p>
050 * ATTENTION: Only user can decide whether a class is designed for extension or not.
051 * The check just shows all classes which are possibly designed for extension.
052 * If smth inappropriate is found please use suppression.
053 * </p>
054 *
055 * <p>
056 * ATTENTION: If the method which can be overridden in a subclass has a javadoc comment
057 * (a good practice is to explain its self-use of overridable methods) the check will not
058 * rise a violation. The violation can also be skipped if the method which can be overridden
059 * in a subclass has one or more annotations that are specified in ignoredAnnotations
060 * option. Note, that by default @Override annotation is not included in the
061 * ignoredAnnotations set as in a subclass the method which has the annotation can also be
062 * overridden in its subclass.
063 * </p>
064 *
065 * <p>
066 * More specifically, the check enforces a programming style where superclasses provide empty
067 * "hooks" that can be implemented by subclasses.
068 * </p>
069 *
070 * <p>
071 * The check finds classes that have overridable methods (public or protected methods
072 * that are non-static, not-final, non-abstract) and have non-empty implementation.
073 * </p>
074 *
075 * <p>
076 * This protects superclasses against being broken by subclasses. The downside is that subclasses
077 * are limited in their flexibility, in particular, they cannot prevent execution of code in the
078 * superclass, but that also means that subclasses cannot forget to call their super method.
079 * </p>
080 *
081 * <p>
082 * The check has the following options:
083 * </p>
084 * <ul>
085 * <li>
086 * ignoredAnnotations - annotations which allow the check to skip the method from validation.
087 * Default value is <b>Test, Before, After, BeforeClass, AfterClass</b>.
088 * </li>
089 * </ul>
090 *
091 * @author lkuehne
092 * @author Andrei Selkin
093 */
094@StatelessCheck
095public class DesignForExtensionCheck extends AbstractCheck {
096
097    /**
098     * A key is pointing to the warning message text in "messages.properties"
099     * file.
100     */
101    public static final String MSG_KEY = "design.forExtension";
102
103    /**
104     * A set of annotations which allow the check to skip the method from validation.
105     */
106    private Set<String> ignoredAnnotations = Arrays.stream(new String[] {"Test", "Before", "After",
107        "BeforeClass", "AfterClass", }).collect(Collectors.toSet());
108
109    /**
110     * Sets annotations which allow the check to skip the method from validation.
111     * @param ignoredAnnotations method annotations.
112     */
113    public void setIgnoredAnnotations(String... ignoredAnnotations) {
114        this.ignoredAnnotations = Arrays.stream(ignoredAnnotations).collect(Collectors.toSet());
115    }
116
117    @Override
118    public int[] getDefaultTokens() {
119        return getRequiredTokens();
120    }
121
122    @Override
123    public int[] getAcceptableTokens() {
124        return getRequiredTokens();
125    }
126
127    @Override
128    public int[] getRequiredTokens() {
129        // The check does not subscribe to CLASS_DEF token as now it is stateless. If the check
130        // subscribes to CLASS_DEF token it will become stateful, since we need to have additional
131        // stack to hold CLASS_DEF tokens.
132        return new int[] {TokenTypes.METHOD_DEF};
133    }
134
135    @Override
136    public boolean isCommentNodesRequired() {
137        return true;
138    }
139
140    @Override
141    public void visitToken(DetailAST ast) {
142        if (!hasJavadocComment(ast)
143                && canBeOverridden(ast)
144                && (isNativeMethod(ast)
145                    || !hasEmptyImplementation(ast))
146                && !hasIgnoredAnnotation(ast, ignoredAnnotations)) {
147
148            final DetailAST classDef = getNearestClassOrEnumDefinition(ast);
149            if (canBeSubclassed(classDef)) {
150                final String className = classDef.findFirstToken(TokenTypes.IDENT).getText();
151                final String methodName = ast.findFirstToken(TokenTypes.IDENT).getText();
152                log(ast.getLineNo(), ast.getColumnNo(), MSG_KEY, className, methodName);
153            }
154        }
155    }
156
157    /**
158     * Checks whether a method has a javadoc comment.
159     * @param methodDef method definition token.
160     * @return true if a method has a javadoc comment.
161     */
162    private static boolean hasJavadocComment(DetailAST methodDef) {
163        final DetailAST modifiers = methodDef.findFirstToken(TokenTypes.MODIFIERS);
164        return modifiers.branchContains(TokenTypes.BLOCK_COMMENT_BEGIN);
165    }
166
167    /**
168     * Checks whether a methods is native.
169     * @param ast method definition token.
170     * @return true if a methods is native.
171     */
172    private static boolean isNativeMethod(DetailAST ast) {
173        final DetailAST mods = ast.findFirstToken(TokenTypes.MODIFIERS);
174        return mods.findFirstToken(TokenTypes.LITERAL_NATIVE) != null;
175    }
176
177    /**
178     * Checks whether a method has only comments in the body (has an empty implementation).
179     * Method is OK if its implementation is empty.
180     * @param ast method definition token.
181     * @return true if a method has only comments in the body.
182     */
183    private static boolean hasEmptyImplementation(DetailAST ast) {
184        boolean hasEmptyBody = true;
185        final DetailAST methodImplOpenBrace = ast.findFirstToken(TokenTypes.SLIST);
186        final DetailAST methodImplCloseBrace = methodImplOpenBrace.getLastChild();
187        final Predicate<DetailAST> predicate = currentNode -> {
188            return currentNode != methodImplCloseBrace
189                && !TokenUtils.isCommentType(currentNode.getType());
190        };
191        final Optional<DetailAST> methodBody =
192            TokenUtils.findFirstTokenByPredicate(methodImplOpenBrace, predicate);
193        if (methodBody.isPresent()) {
194            hasEmptyBody = false;
195        }
196        return hasEmptyBody;
197    }
198
199    /**
200     * Checks whether a method can be overridden.
201     * Method can be overridden if it is not private, abstract, final or static.
202     * Note that the check has nothing to do for interfaces.
203     * @param methodDef method definition token.
204     * @return true if a method can be overridden in a subclass.
205     */
206    private static boolean canBeOverridden(DetailAST methodDef) {
207        final DetailAST modifiers = methodDef.findFirstToken(TokenTypes.MODIFIERS);
208        return ScopeUtils.getSurroundingScope(methodDef).isIn(Scope.PROTECTED)
209            && !ScopeUtils.isInInterfaceOrAnnotationBlock(methodDef)
210            && modifiers.findFirstToken(TokenTypes.LITERAL_PRIVATE) == null
211            && modifiers.findFirstToken(TokenTypes.ABSTRACT) == null
212            && modifiers.findFirstToken(TokenTypes.FINAL) == null
213            && modifiers.findFirstToken(TokenTypes.LITERAL_STATIC) == null;
214    }
215
216    /**
217     * Checks whether a method has any of ignored annotations.
218     * @param methodDef method definition token.
219     * @param annotations a set of ignored annotations.
220     * @return true if a method has any of ignored annotations.
221     */
222    private static boolean hasIgnoredAnnotation(DetailAST methodDef, Set<String> annotations) {
223        final DetailAST modifiers = methodDef.findFirstToken(TokenTypes.MODIFIERS);
224        boolean hasIgnoredAnnotation = false;
225        if (modifiers.findFirstToken(TokenTypes.ANNOTATION) != null) {
226            final Optional<DetailAST> annotation = TokenUtils.findFirstTokenByPredicate(modifiers,
227                currentToken -> {
228                    return currentToken.getType() == TokenTypes.ANNOTATION
229                        && annotations.contains(getAnnotationName(currentToken));
230                });
231            if (annotation.isPresent()) {
232                hasIgnoredAnnotation = true;
233            }
234        }
235        return hasIgnoredAnnotation;
236    }
237
238    /**
239     * Gets the name of the annotation.
240     * @param annotation to get name of.
241     * @return the name of the annotation.
242     */
243    private static String getAnnotationName(DetailAST annotation) {
244        final DetailAST dotAst = annotation.findFirstToken(TokenTypes.DOT);
245        final String name;
246        if (dotAst == null) {
247            name = annotation.findFirstToken(TokenTypes.IDENT).getText();
248        }
249        else {
250            name = dotAst.findFirstToken(TokenTypes.IDENT).getText();
251        }
252        return name;
253    }
254
255    /**
256     * Returns CLASS_DEF or ENUM_DEF token which is the nearest to the given ast node.
257     * Searches the tree towards the root until it finds a CLASS_DEF or ENUM_DEF node.
258     * @param ast the start node for searching.
259     * @return the CLASS_DEF or ENUM_DEF token.
260     */
261    private static DetailAST getNearestClassOrEnumDefinition(DetailAST ast) {
262        DetailAST searchAST = ast;
263        while (searchAST.getType() != TokenTypes.CLASS_DEF
264               && searchAST.getType() != TokenTypes.ENUM_DEF) {
265            searchAST = searchAST.getParent();
266        }
267        return searchAST;
268    }
269
270    /**
271     * Checks if the given class (given CLASS_DEF node) can be subclassed.
272     * @param classDef class definition token.
273     * @return true if the containing class can be subclassed.
274     */
275    private static boolean canBeSubclassed(DetailAST classDef) {
276        final DetailAST modifiers = classDef.findFirstToken(TokenTypes.MODIFIERS);
277        return classDef.getType() != TokenTypes.ENUM_DEF
278            && modifiers.findFirstToken(TokenTypes.FINAL) == null
279            && hasDefaultOrExplicitNonPrivateCtor(classDef);
280    }
281
282    /**
283     * Checks whether a class has default or explicit non-private constructor.
284     * @param classDef class ast token.
285     * @return true if a class has default or explicit non-private constructor.
286     */
287    private static boolean hasDefaultOrExplicitNonPrivateCtor(DetailAST classDef) {
288        // check if subclassing is prevented by having only private ctors
289        final DetailAST objBlock = classDef.findFirstToken(TokenTypes.OBJBLOCK);
290
291        boolean hasDefaultConstructor = true;
292        boolean hasExplicitNonPrivateCtor = false;
293
294        DetailAST candidate = objBlock.getFirstChild();
295
296        while (candidate != null) {
297            if (candidate.getType() == TokenTypes.CTOR_DEF) {
298                hasDefaultConstructor = false;
299
300                final DetailAST ctorMods =
301                        candidate.findFirstToken(TokenTypes.MODIFIERS);
302                if (ctorMods.findFirstToken(TokenTypes.LITERAL_PRIVATE) == null) {
303                    hasExplicitNonPrivateCtor = true;
304                    break;
305                }
306            }
307            candidate = candidate.getNextSibling();
308        }
309
310        return hasDefaultConstructor || hasExplicitNonPrivateCtor;
311    }
312}