/*
* Copyright 2014 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.WARNING;
import static com.google.errorprone.util.ASTHelpers.getType;
import static com.google.errorprone.util.Signatures.prettyType;
import com.google.common.base.Optional;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.CompoundAssignmentTreeMatcher;
import com.google.errorprone.fixes.Fix;
import com.google.errorprone.fixes.SuggestedFix;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.util.OperatorPrecedence;
import com.sun.source.tree.CompoundAssignmentTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.Tree.Kind;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.code.Types;
import com.sun.tools.javac.tree.JCTree.JCBinary;
/** @author cushon@google.com (Liam Miller-Cushon) */
@BugPattern(
name = "NarrowingCompoundAssignment",
summary = "Compound assignments may hide dangerous casts",
category = JDK,
severity = WARNING
)
public class NarrowingCompoundAssignment extends BugChecker
implements CompoundAssignmentTreeMatcher {
static String assignmentToString(Tree.Kind kind) {
switch (kind) {
case MULTIPLY:
return "*";
case DIVIDE:
return "/";
case REMAINDER:
return "%";
case PLUS:
return "+";
case MINUS:
return "-";
case LEFT_SHIFT:
return "<<";
case AND:
return "&";
case XOR:
return "^";
case OR:
return "|";
case RIGHT_SHIFT:
return ">>";
case UNSIGNED_RIGHT_SHIFT:
return ">>>";
default:
throw new IllegalArgumentException("Unexpected operator assignment kind: " + kind);
}
}
static Kind regularAssignmentFromCompound(Kind kind) {
switch (kind) {
case MULTIPLY_ASSIGNMENT:
return Kind.MULTIPLY;
case DIVIDE_ASSIGNMENT:
return Kind.DIVIDE;
case REMAINDER_ASSIGNMENT:
return Kind.REMAINDER;
case PLUS_ASSIGNMENT:
return Kind.PLUS;
case MINUS_ASSIGNMENT:
return Kind.MINUS;
case LEFT_SHIFT_ASSIGNMENT:
return Kind.LEFT_SHIFT;
case AND_ASSIGNMENT:
return Kind.AND;
case XOR_ASSIGNMENT:
return Kind.XOR;
case OR_ASSIGNMENT:
return Kind.OR;
case RIGHT_SHIFT_ASSIGNMENT:
return Kind.RIGHT_SHIFT;
case UNSIGNED_RIGHT_SHIFT_ASSIGNMENT:
return Kind.UNSIGNED_RIGHT_SHIFT;
default:
throw new IllegalArgumentException("Unexpected compound assignment kind: " + kind);
}
}
@Override
public Description matchCompoundAssignment(CompoundAssignmentTree tree, VisitorState state) {
String message =
identifyBadCast(
getType(tree.getVariable()), getType(tree.getExpression()), state.getTypes());
if (message == null) {
return Description.NO_MATCH;
}
Optional<Fix> fix = rewriteCompoundAssignment(tree, state);
if (!fix.isPresent()) {
return Description.NO_MATCH;
}
return buildDescription(tree).addFix(fix.get()).setMessage(message).build();
}
/** Classifies bad casts. */
private static String identifyBadCast(Type lhs, Type rhs, Types types) {
if (!lhs.isPrimitive()) {
return null;
}
if (types.isConvertible(rhs, lhs)) {
// Exemption if the rhs is convertible to the lhs.
// This allows, e.g.: <byte> &= <byte> since the narrowing conversion can never be
// detected.
// This also allows, for example, char += char, which could overflow, but this is no
// different than any other integral addition.
return null;
}
return String.format(
"Compound assignments from %s to %s hide lossy casts", prettyType(rhs), prettyType(lhs));
}
/** Desugars a compound assignment, making the cast explicit. */
private static Optional<Fix> rewriteCompoundAssignment(
CompoundAssignmentTree tree, VisitorState state) {
CharSequence var = state.getSourceForNode(tree.getVariable());
CharSequence expr = state.getSourceForNode(tree.getExpression());
if (var == null || expr == null) {
return Optional.absent();
}
switch (tree.getKind()) {
case RIGHT_SHIFT_ASSIGNMENT:
// narrowing the result of a signed right shift does not lose information
return Optional.absent();
default:
break;
}
Kind regularAssignmentKind = regularAssignmentFromCompound(tree.getKind());
String op = assignmentToString(regularAssignmentKind);
// Add parens to the rhs if necessary to preserve the current precedence
// e.g. 's -= 1 - 2' -> 's = s - (1 - 2)'
if (tree.getExpression() instanceof JCBinary) {
Kind rhsKind = tree.getExpression().getKind();
if (!OperatorPrecedence.from(rhsKind)
.isHigher(OperatorPrecedence.from(regularAssignmentKind))) {
expr = String.format("(%s)", expr);
}
}
// e.g. 's *= 42' -> 's = (short) (s * 42)'
String castType = getType(tree.getVariable()).toString();
String replacement = String.format("%s = (%s) (%s %s %s)", var, castType, var, op, expr);
return Optional.of(SuggestedFix.replace(tree, replacement));
}
}