/*
* Copyright 2016 Google Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.errorprone.bugpatterns;
import static com.google.errorprone.BugPattern.Category.JDK;
import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
import static com.google.errorprone.matchers.Description.NO_MATCH;
import static com.google.errorprone.util.ASTHelpers.getSymbol;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.ImmutableSetMultimap;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.CompilationUnitTreeMatcher;
import com.google.errorprone.bugpatterns.StaticImports.StaticImportInfo;
import com.google.errorprone.fixes.SuggestedFix;
import com.google.errorprone.matchers.Description;
import com.sun.source.doctree.DocCommentTree;
import com.sun.source.doctree.ReferenceTree;
import com.sun.source.tree.CompilationUnitTree;
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.ImportTree;
import com.sun.source.tree.Tree;
import com.sun.source.util.DocTreePath;
import com.sun.source.util.DocTreePathScanner;
import com.sun.source.util.TreePathScanner;
import com.sun.tools.javac.api.JavacTrees;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symbol.MethodSymbol;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.code.Type.ArrayType;
import com.sun.tools.javac.code.Types;
import com.sun.tools.javac.code.Types.SimpleVisitor;
import com.sun.tools.javac.tree.DCTree.DCReference;
import com.sun.tools.javac.tree.JCTree;
import com.sun.tools.javac.tree.JCTree.JCFieldAccess;
import com.sun.tools.javac.tree.JCTree.JCIdent;
import java.util.HashSet;
import java.util.Set;
import javax.annotation.Nullable;
/** @author gak@google.com (Gregory Kick) */
@BugPattern(
name = "RemoveUnusedImports",
summary = "Unused imports",
explanation = "This import is unused.",
category = JDK,
severity = SUGGESTION,
documentSuppression = false
)
public final class RemoveUnusedImports extends BugChecker implements CompilationUnitTreeMatcher {
@Override
public Description matchCompilationUnit(
CompilationUnitTree compilationUnitTree, VisitorState state) {
final ImmutableSetMultimap<ImportTree, Symbol> importedSymbols =
getImportedSymbols(compilationUnitTree, state);
if (importedSymbols.isEmpty()) {
return NO_MATCH;
}
final Set<ImportTree> unusedImports = new HashSet<>(importedSymbols.keySet());
new TreeSymbolScanner(JavacTrees.instance(state.context), state.getTypes())
.scan(
compilationUnitTree,
new SymbolSink() {
@Override
public boolean keepScanning() {
return !unusedImports.isEmpty();
}
@Override
public void accept(Symbol symbol) {
unusedImports.removeAll(importedSymbols.inverse().get(symbol));
}
});
if (unusedImports.isEmpty()) {
return NO_MATCH;
}
SuggestedFix.Builder fixBuilder = SuggestedFix.builder();
for (ImportTree unusedImport : unusedImports) {
fixBuilder.delete(unusedImport);
}
return describeMatch(unusedImports.iterator().next(), fixBuilder.build());
}
/**
* A callback that provides actions for whenever you encounter a {@link Symbol}. Also provides a
* hook by which you can stop scanning.
*/
private interface SymbolSink {
boolean keepScanning();
void accept(Symbol symbol);
}
private static final class TreeSymbolScanner extends TreePathScanner<Void, SymbolSink> {
final DocTreeSymbolScanner docTreeSymbolScanner;
final JavacTrees trees;
final Types types;
private TreeSymbolScanner(JavacTrees trees, Types types) {
this.types = types;
this.docTreeSymbolScanner = new DocTreeSymbolScanner();
this.trees = trees;
}
/** Skip the imports themselves when checking for usage. */
@Override
public Void visitImport(ImportTree importTree, SymbolSink usedSymbols) {
return null;
}
@Override
public Void visitIdentifier(IdentifierTree tree, SymbolSink sink) {
if (tree == null) {
return null;
}
Symbol symbol = getSymbol(tree);
if (symbol == null) {
return null;
}
sink.accept(symbol.baseSymbol());
return null;
}
@Override
public Void scan(Tree tree, SymbolSink sink) {
if (!sink.keepScanning()) {
return null;
}
if (tree == null) {
return null;
}
scanJavadoc(sink);
return super.scan(tree, sink);
}
private void scanJavadoc(SymbolSink sink) {
if (getCurrentPath() == null) {
return;
}
DocCommentTree commentTree = trees.getDocCommentTree(getCurrentPath());
if (commentTree == null) {
return;
}
docTreeSymbolScanner.scan(new DocTreePath(getCurrentPath(), commentTree), sink);
}
/**
* For the time being, this will just report any symbol referenced from javadoc as a usage.
* TODO(gak): improve this so that we can remove imports used only from javadoc and replace the
* usages with fully-qualified names.
*/
final class DocTreeSymbolScanner extends DocTreePathScanner<Void, SymbolSink> {
@Override
public Void visitReference(ReferenceTree referenceTree, SymbolSink sink) {
// do this first, it attributes the referenceTree as a side-effect
Symbol symbolForReference = (Symbol) trees.getElement(getCurrentPath());
JCTree base = ((DCReference) referenceTree).qualifierExpression;
// Only the base type in a qualified name needs to be imported.
// e.g. `Map.Entry` is a use of `Map`, `java.util.List` does not require an import
while (base instanceof JCFieldAccess) {
base = ((JCFieldAccess) base).selected;
}
if (base instanceof JCIdent) {
sink.accept(((JCIdent) base).sym);
}
// Record uses inside method parameters.
if (symbolForReference instanceof MethodSymbol) {
for (VarSymbol parameter : ((MethodSymbol) symbolForReference).getParameters()) {
parameter.type.accept(
new SimpleVisitor<Void, Void>() {
@Override
public Void visitArrayType(ArrayType type, Void unused) {
type.getComponentType().accept(this, null);
return null;
}
@Override
public Void visitType(Type type, Void unused) {
sink.accept(types.erasure(type).tsym);
return null;
}
},
null);
}
}
return null;
}
}
}
private static ImmutableSetMultimap<ImportTree, Symbol> getImportedSymbols(
CompilationUnitTree compilationUnitTree, VisitorState state) {
ImmutableSetMultimap.Builder<ImportTree, Symbol> builder = ImmutableSetMultimap.builder();
for (ImportTree importTree : compilationUnitTree.getImports()) {
builder.putAll(importTree, getImportedSymbols(importTree, state));
}
return builder.build();
}
private static ImmutableSet<Symbol> getImportedSymbols(
ImportTree importTree, VisitorState state) {
if (importTree.isStatic()) {
StaticImportInfo staticImportInfo = StaticImports.tryCreate(importTree, state);
return staticImportInfo == null ? ImmutableSet.<Symbol>of() : staticImportInfo.members();
} else {
@Nullable Symbol importedSymbol = getSymbol(importTree.getQualifiedIdentifier());
return importedSymbol == null ? ImmutableSet.<Symbol>of() : ImmutableSet.of(importedSymbol);
}
}
}