com.puppycrawl.tools.checkstyle.checks.imports.UnusedImportsCheck Maven / Gradle / Ivy
///////////////////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
// Copyright (C) 2001-2023 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
///////////////////////////////////////////////////////////////////////////////////////////////
package com.puppycrawl.tools.checkstyle.checks.imports;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.FileContents;
import com.puppycrawl.tools.checkstyle.api.FullIdent;
import com.puppycrawl.tools.checkstyle.api.TextBlock;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
import com.puppycrawl.tools.checkstyle.checks.javadoc.JavadocTag;
import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
import com.puppycrawl.tools.checkstyle.utils.JavadocUtil;
import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
/**
*
* Checks for unused import statements. An import statement
* is considered unused if:
*
*
* -
* It is not referenced in the file. The algorithm does not support wild-card
* imports like {@code import java.io.*;}. Most IDE's provide very sophisticated
* checks for imports that handle wild-card imports.
*
* -
* The class imported is from the {@code java.lang} package. For example
* importing {@code java.lang.String}.
*
* -
* The class imported is from the same package.
*
* -
* Optionally: it is referenced in Javadoc comments. This check is on by
* default, but it is considered bad practice to introduce a compile-time
* dependency for documentation purposes only. As an example, the import
* {@code java.util.List} would be considered referenced with the Javadoc
* comment {@code {@link List}}. The alternative to avoid introducing a compile-time
* dependency would be to write the Javadoc comment as {@code {@link java.util.List}}.
*
*
*
* The main limitation of this check is handling the cases where:
*
*
* -
* An imported type has the same name as a declaration, such as a member variable.
*
* -
* There are two or more static imports with the same method name
* (javac can distinguish imports with same name but different parameters, but checkstyle can not
* due to limitation.)
*
*
*
* -
* Property {@code processJavadoc} - Control whether to process Javadoc comments.
* Type is {@code boolean}.
* Default value is {@code true}.
*
*
*
* Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
*
*
* Violation Message Keys:
*
*
* -
* {@code import.unused}
*
*
*
* @since 3.0
*/
@FileStatefulCheck
public class UnusedImportsCheck extends AbstractCheck {
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_KEY = "import.unused";
/** Regex to match class names. */
private static final Pattern CLASS_NAME = CommonUtil.createPattern(
"((:?[\\p{L}_$][\\p{L}\\p{N}_$]*\\.)*[\\p{L}_$][\\p{L}\\p{N}_$]*)");
/** Regex to match the first class name. */
private static final Pattern FIRST_CLASS_NAME = CommonUtil.createPattern(
"^" + CLASS_NAME);
/** Regex to match argument names. */
private static final Pattern ARGUMENT_NAME = CommonUtil.createPattern(
"[(,]\\s*" + CLASS_NAME.pattern());
/** Regexp pattern to match java.lang package. */
private static final Pattern JAVA_LANG_PACKAGE_PATTERN =
CommonUtil.createPattern("^java\\.lang\\.[a-zA-Z]+$");
/** Suffix for the star import. */
private static final String STAR_IMPORT_SUFFIX = ".*";
/** Set of the imports. */
private final Set imports = new HashSet<>();
/** Flag to indicate when time to start collecting references. */
private boolean collect;
/** Control whether to process Javadoc comments. */
private boolean processJavadoc = true;
/**
* The scope is being processed.
* Types declared in a scope can shadow imported types.
*/
private Frame currentFrame;
/**
* Setter to control whether to process Javadoc comments.
*
* @param value Flag for processing Javadoc comments.
* @since 5.4
*/
public void setProcessJavadoc(boolean value) {
processJavadoc = value;
}
@Override
public void beginTree(DetailAST rootAST) {
collect = false;
currentFrame = Frame.compilationUnit();
imports.clear();
}
@Override
public void finishTree(DetailAST rootAST) {
currentFrame.finish();
// loop over all the imports to see if referenced.
imports.stream()
.filter(imprt -> isUnusedImport(imprt.getText()))
.forEach(imprt -> log(imprt.getDetailAst(), MSG_KEY, imprt.getText()));
}
@Override
public int[] getDefaultTokens() {
return getRequiredTokens();
}
@Override
public int[] getRequiredTokens() {
return new int[] {
TokenTypes.IDENT,
TokenTypes.IMPORT,
TokenTypes.STATIC_IMPORT,
// Definitions that may contain Javadoc...
TokenTypes.PACKAGE_DEF,
TokenTypes.ANNOTATION_DEF,
TokenTypes.ANNOTATION_FIELD_DEF,
TokenTypes.ENUM_DEF,
TokenTypes.ENUM_CONSTANT_DEF,
TokenTypes.CLASS_DEF,
TokenTypes.INTERFACE_DEF,
TokenTypes.METHOD_DEF,
TokenTypes.CTOR_DEF,
TokenTypes.VARIABLE_DEF,
TokenTypes.RECORD_DEF,
TokenTypes.COMPACT_CTOR_DEF,
// Tokens for creating a new frame
TokenTypes.OBJBLOCK,
TokenTypes.SLIST,
};
}
@Override
public int[] getAcceptableTokens() {
return getRequiredTokens();
}
@Override
public void visitToken(DetailAST ast) {
switch (ast.getType()) {
case TokenTypes.IDENT:
if (collect) {
processIdent(ast);
}
break;
case TokenTypes.IMPORT:
processImport(ast);
break;
case TokenTypes.STATIC_IMPORT:
processStaticImport(ast);
break;
case TokenTypes.OBJBLOCK:
case TokenTypes.SLIST:
currentFrame = currentFrame.push();
break;
default:
collect = true;
if (processJavadoc) {
collectReferencesFromJavadoc(ast);
}
break;
}
}
@Override
public void leaveToken(DetailAST ast) {
if (TokenUtil.isOfType(ast, TokenTypes.OBJBLOCK, TokenTypes.SLIST)) {
currentFrame = currentFrame.pop();
}
}
/**
* Checks whether an import is unused.
*
* @param imprt an import.
* @return true if an import is unused.
*/
private boolean isUnusedImport(String imprt) {
final Matcher javaLangPackageMatcher = JAVA_LANG_PACKAGE_PATTERN.matcher(imprt);
return !currentFrame.isReferencedType(CommonUtil.baseClassName(imprt))
|| javaLangPackageMatcher.matches();
}
/**
* Collects references made by IDENT.
*
* @param ast the IDENT node to process
*/
private void processIdent(DetailAST ast) {
final DetailAST parent = ast.getParent();
final int parentType = parent.getType();
final boolean isPossibleDotClassOrInMethod = parentType == TokenTypes.DOT
|| parentType == TokenTypes.METHOD_DEF;
final boolean isQualifiedIdent = parentType == TokenTypes.DOT
&& !TokenUtil.isOfType(ast.getPreviousSibling(), TokenTypes.DOT)
&& ast.getNextSibling() != null;
if (TokenUtil.isTypeDeclaration(parentType)) {
currentFrame.addDeclaredType(ast.getText());
}
else if (!isPossibleDotClassOrInMethod || isQualifiedIdent) {
currentFrame.addReferencedType(ast.getText());
}
}
/**
* Collects the details of imports.
*
* @param ast node containing the import details
*/
private void processImport(DetailAST ast) {
final FullIdent name = FullIdent.createFullIdentBelow(ast);
if (!name.getText().endsWith(STAR_IMPORT_SUFFIX)) {
imports.add(name);
}
}
/**
* Collects the details of static imports.
*
* @param ast node containing the static import details
*/
private void processStaticImport(DetailAST ast) {
final FullIdent name =
FullIdent.createFullIdent(
ast.getFirstChild().getNextSibling());
if (!name.getText().endsWith(STAR_IMPORT_SUFFIX)) {
imports.add(name);
}
}
/**
* Collects references made in Javadoc comments.
*
* @param ast node to inspect for Javadoc
*/
// suppress deprecation until https://github.com/checkstyle/checkstyle/issues/11166
@SuppressWarnings("deprecation")
private void collectReferencesFromJavadoc(DetailAST ast) {
final FileContents contents = getFileContents();
final int lineNo = ast.getLineNo();
final TextBlock textBlock = contents.getJavadocBefore(lineNo);
if (textBlock != null) {
currentFrame.addReferencedTypes(collectReferencesFromJavadoc(textBlock));
}
}
/**
* Process a javadoc {@link TextBlock} and return the set of classes
* referenced within.
*
* @param textBlock The javadoc block to parse
* @return a set of classes referenced in the javadoc block
*/
private static Set collectReferencesFromJavadoc(TextBlock textBlock) {
final List tags = new ArrayList<>();
// gather all the inline tags, like @link
// INLINE tags inside BLOCKs get hidden when using ALL
tags.addAll(getValidTags(textBlock, JavadocUtil.JavadocTagType.INLINE));
// gather all the block-level tags, like @throws and @see
tags.addAll(getValidTags(textBlock, JavadocUtil.JavadocTagType.BLOCK));
final Set references = new HashSet<>();
tags.stream()
.filter(JavadocTag::canReferenceImports)
.forEach(tag -> references.addAll(processJavadocTag(tag)));
return references;
}
/**
* Returns the list of valid tags found in a javadoc {@link TextBlock}.
*
* @param cmt The javadoc block to parse
* @param tagType The type of tags we're interested in
* @return the list of tags
*/
private static List getValidTags(TextBlock cmt,
JavadocUtil.JavadocTagType tagType) {
return JavadocUtil.getJavadocTags(cmt, tagType).getValidTags();
}
/**
* Returns a list of references that found in a javadoc {@link JavadocTag}.
*
* @param tag The javadoc tag to parse
* @return A list of references that found in this tag
*/
private static Set processJavadocTag(JavadocTag tag) {
final Set references = new HashSet<>();
final String identifier = tag.getFirstArg();
for (Pattern pattern : new Pattern[]
{FIRST_CLASS_NAME, ARGUMENT_NAME}) {
references.addAll(matchPattern(identifier, pattern));
}
return references;
}
/**
* Extracts a set of texts matching a {@link Pattern} from a
* {@link String}.
*
* @param identifier The String to match the pattern against
* @param pattern The Pattern used to extract the texts
* @return A set of texts which matched the pattern
*/
private static Set matchPattern(String identifier, Pattern pattern) {
final Set references = new HashSet<>();
final Matcher matcher = pattern.matcher(identifier);
while (matcher.find()) {
references.add(topLevelType(matcher.group(1)));
}
return references;
}
/**
* If the given type string contains "." (e.g. "Map.Entry"), returns the
* top level type (e.g. "Map"), as that is what must be imported for the
* type to resolve. Otherwise, returns the type as-is.
*
* @param type A possibly qualified type name
* @return The simple name of the top level type
*/
private static String topLevelType(String type) {
final String topLevelType;
final int dotIndex = type.indexOf('.');
if (dotIndex == -1) {
topLevelType = type;
}
else {
topLevelType = type.substring(0, dotIndex);
}
return topLevelType;
}
/**
* Holds the names of referenced types and names of declared inner types.
*/
private static final class Frame {
/** Parent frame. */
private final Frame parent;
/** Nested types declared in the current scope. */
private final Set declaredTypes;
/** Set of references - possibly to imports or locally declared types. */
private final Set referencedTypes;
/**
* Private constructor. Use {@link #compilationUnit()} to create a new top-level frame.
*
* @param parent the parent frame
*/
private Frame(Frame parent) {
this.parent = parent;
declaredTypes = new HashSet<>();
referencedTypes = new HashSet<>();
}
/**
* Adds new inner type.
*
* @param type the type name
*/
public void addDeclaredType(String type) {
declaredTypes.add(type);
}
/**
* Adds new type reference to the current frame.
*
* @param type the type name
*/
public void addReferencedType(String type) {
referencedTypes.add(type);
}
/**
* Adds new inner types.
*
* @param types the type names
*/
public void addReferencedTypes(Collection types) {
referencedTypes.addAll(types);
}
/**
* Filters out all references to locally defined types.
*
*/
public void finish() {
referencedTypes.removeAll(declaredTypes);
}
/**
* Creates new inner frame.
*
* @return a new frame.
*/
public Frame push() {
return new Frame(this);
}
/**
* Pulls all referenced types up, except those that are declared in this scope.
*
* @return the parent frame
*/
public Frame pop() {
finish();
parent.addReferencedTypes(referencedTypes);
return parent;
}
/**
* Checks whether this type name is used in this frame.
*
* @param type the type name
* @return {@code true} if the type is used
*/
public boolean isReferencedType(String type) {
return referencedTypes.contains(type);
}
/**
* Creates a new top-level frame for the compilation unit.
*
* @return a new frame.
*/
public static Frame compilationUnit() {
return new Frame(null);
}
}
}
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