/*
* Copyright 2012 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.ERROR;
import static com.google.errorprone.matchers.Matchers.staticMethod;
import static com.sun.source.tree.Tree.Kind.CLASS;
import static com.sun.source.tree.Tree.Kind.IDENTIFIER;
import static com.sun.source.tree.Tree.Kind.MEMBER_SELECT;
import static com.sun.source.tree.Tree.Kind.METHOD;
import static com.sun.source.tree.Tree.Kind.METHOD_INVOCATION;
import static com.sun.source.tree.Tree.Kind.VARIABLE;
import static javax.lang.model.element.Modifier.STATIC;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.AssignmentTreeMatcher;
import com.google.errorprone.bugpatterns.BugChecker.VariableTreeMatcher;
import com.google.errorprone.fixes.Fix;
import com.google.errorprone.fixes.SuggestedFix;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.names.LevenshteinEditDistance;
import com.google.errorprone.util.ASTHelpers;
import com.sun.source.tree.AssignmentTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.MemberSelectTree;
import com.sun.source.tree.MethodInvocationTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.VariableTree;
import com.sun.source.util.TreePath;
import com.sun.tools.javac.code.Flags;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.tree.JCTree;
import com.sun.tools.javac.tree.JCTree.JCClassDecl;
import com.sun.tools.javac.tree.JCTree.JCFieldAccess;
import com.sun.tools.javac.tree.JCTree.JCIdent;
import com.sun.tools.javac.tree.JCTree.JCMethodDecl;
import com.sun.tools.javac.tree.JCTree.JCVariableDecl;
import java.util.Objects;
/**
* TODO(eaftan): Consider cases where the parent is not a statement or there is no parent?
*
* @author eaftan@google.com (Eddie Aftandilian)
* @author scottjohnson@google.com (Scott Johnson)
*/
@BugPattern(
name = "SelfAssignment",
summary = "Variable assigned to itself",
category = JDK,
severity = ERROR
)
public class SelfAssignment extends BugChecker
implements AssignmentTreeMatcher, VariableTreeMatcher {
@Override
public Description matchAssignment(AssignmentTree tree, VisitorState state) {
ExpressionTree expression = stripCheckNotNull(tree.getExpression(), state);
if (ASTHelpers.sameVariable(tree.getVariable(), expression)) {
return describeForAssignment(tree, state);
}
return Description.NO_MATCH;
}
@Override
public Description matchVariable(VariableTree tree, VisitorState state) {
ExpressionTree initializer = stripCheckNotNull(tree.getInitializer(), state);
Tree parent = state.getPath().getParentPath().getLeaf();
// must be a static class variable with member select initializer
if (initializer == null || initializer.getKind() != MEMBER_SELECT || parent.getKind() != CLASS
|| !tree.getModifiers().getFlags().contains(STATIC)) {
return Description.NO_MATCH;
}
MemberSelectTree rhs = (MemberSelectTree) initializer;
Symbol rhsClass = ASTHelpers.getSymbol(rhs.getExpression());
Symbol lhsClass = ASTHelpers.getSymbol(parent);
if (rhsClass != null && lhsClass != null
&& rhsClass.equals(lhsClass) && rhs.getIdentifier().contentEquals(tree.getName())) {
return describeForVarDecl(tree, state);
}
return Description.NO_MATCH;
}
/**
* If the given expression is a call to checkNotNull(x), returns x.
* Otherwise, returns the given expression.
*
* TODO(eaftan): Also match calls to Java 7's Objects.requireNonNull() method.
*/
private ExpressionTree stripCheckNotNull(ExpressionTree expression, VisitorState state) {
if (expression != null
&& expression.getKind() == METHOD_INVOCATION
&& staticMethod().onClass("com.google.common.base.Preconditions").named("checkNotNull")
.matches(expression, state)) {
return ((MethodInvocationTree) expression).getArguments().get(0);
}
return expression;
}
public Description describeForVarDecl(VariableTree tree, VisitorState state) {
String varDeclStr = tree.toString();
int equalsIndex = varDeclStr.indexOf('=');
if (equalsIndex < 0) {
throw new IllegalStateException(
"Expected variable declaration to have an initializer: " + tree);
}
varDeclStr = varDeclStr.substring(0, equalsIndex - 1) + ";";
// Delete the initializer but still declare the variable.
return describeMatch(tree, SuggestedFix.replace(tree, varDeclStr));
}
/**
* We expect that the lhs is a field and the rhs is an identifier, specifically
* a parameter to the method. We base our suggested fixes on this expectation.
*
* Case 1: If lhs is a field and rhs is an identifier, find a method parameter
* of the same type and similar name and suggest it as the rhs. (Guess that they
* have misspelled the identifier.)
*
* Case 2: If lhs is a field and rhs is not an identifier, find a method parameter
* of the same type and similar name and suggest it as the rhs.
*
* Case 3: If lhs is not a field and rhs is an identifier, find a class field
* of the same type and similar name and suggest it as the lhs.
*
* Case 4: Otherwise suggest deleting the assignment.
*/
public Description describeForAssignment(AssignmentTree assignmentTree, VisitorState state) {
// the statement that is the parent of the self-assignment expression
Tree parent = state.getPath().getParentPath().getLeaf();
// default fix is to delete assignment
Fix fix = SuggestedFix.delete(parent);
ExpressionTree lhs = assignmentTree.getVariable();
ExpressionTree rhs = assignmentTree.getExpression();
// if this is a method invocation, they must be calling checkNotNull()
if (assignmentTree.getExpression().getKind() == METHOD_INVOCATION) {
// change the default fix to be "checkNotNull(x)" instead of "x = checkNotNull(x)"
fix = SuggestedFix.replace(assignmentTree, rhs.toString());
// new rhs is first argument to checkNotNull()
rhs = stripCheckNotNull(rhs, state);
}
if (lhs.getKind() == MEMBER_SELECT) {
// find a method parameter of the same type and similar name and suggest it
// as the rhs
// rhs should be either identifier or field access
assert(rhs.getKind() == IDENTIFIER || rhs.getKind() == MEMBER_SELECT);
// get current name of rhs
String rhsName = null;
if (rhs.getKind() == IDENTIFIER) {
rhsName = ((JCIdent) rhs).name.toString();
} else if (rhs.getKind() == MEMBER_SELECT) {
rhsName = ((JCFieldAccess) rhs).name.toString();
}
// find method parameters of the same type
Type type = ((JCFieldAccess) lhs).type;
TreePath path = state.getPath();
while (path != null && path.getLeaf().getKind() != METHOD) {
path = path.getParentPath();
}
JCMethodDecl method = (JCMethodDecl) path.getLeaf();
int minEditDistance = Integer.MAX_VALUE;
String replacement = null;
for (JCVariableDecl var : method.params) {
if (Objects.equals(var.type, type)) {
int editDistance = LevenshteinEditDistance.getEditDistance(rhsName, var.name.toString());
if (editDistance < minEditDistance) {
// pick one with minimum edit distance
minEditDistance = editDistance;
replacement = var.name.toString();
}
}
}
if (replacement != null) {
// suggest replacing rhs with the parameter
fix = SuggestedFix.replace(rhs, replacement);
}
} else if (rhs.getKind() == IDENTIFIER) {
// find a field of the same type and similar name and suggest it as the lhs
// lhs should be identifier
assert(lhs.getKind() == IDENTIFIER);
// get current name of lhs
String lhsName = ((JCIdent) rhs).name.toString();
// find class instance fields of the same type
Type type = ((JCIdent) lhs).type;
TreePath path = state.getPath();
while (path != null && !(path.getLeaf() instanceof JCClassDecl)) {
path = path.getParentPath();
}
if (path == null) {
throw new IllegalStateException("Expected to find an enclosing class declaration");
}
JCClassDecl klass = (JCClassDecl) path.getLeaf();
int minEditDistance = Integer.MAX_VALUE;
String replacement = null;
for (JCTree member : klass.getMembers()) {
if (member.getKind() == VARIABLE) {
JCVariableDecl var = (JCVariableDecl) member;
if (!Flags.isStatic(var.sym) && Objects.equals(var.type, type)) {
int editDistance =
LevenshteinEditDistance.getEditDistance(lhsName, var.name.toString());
if (editDistance < minEditDistance) {
// pick one with minimum edit distance
minEditDistance = editDistance;
replacement = var.name.toString();
}
}
}
}
if (replacement != null) {
// suggest replacing lhs with the field
fix = SuggestedFix.replace(lhs, "this." + replacement);
}
}
return describeMatch(assignmentTree, fix);
}
}