/*
* Copyright 2008 Google Inc.
*
* 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.gwt.dev.jjs.impl;
import com.google.gwt.dev.jjs.ast.Context;
import com.google.gwt.dev.jjs.ast.JBinaryOperation;
import com.google.gwt.dev.jjs.ast.JBinaryOperator;
import com.google.gwt.dev.jjs.ast.JCastOperation;
import com.google.gwt.dev.jjs.ast.JClassType;
import com.google.gwt.dev.jjs.ast.JExpression;
import com.google.gwt.dev.jjs.ast.JModVisitor;
import com.google.gwt.dev.jjs.ast.JPostfixOperation;
import com.google.gwt.dev.jjs.ast.JPrefixOperation;
import com.google.gwt.dev.jjs.ast.JProgram;
/**
* Most autoboxing is handled by {@link GenerateJavaAST}. The only cases it
* does not handle are <code>++</code>, <code>--</code>, and compound
* assignment operations (<code>+=</code>, etc.) when applied to a boxed
* type. This class fixes such cases in two steps. First, an internal subclass
* of {@link CompoundAssignmentNormalizer} simplifies such expressions to a
* simple assignment expression. Second, this visitor replaces an assignment to
* an unboxing method (<code>unbox(x) = unbox(x) + 1</code>) with an
* assignment to the underlying box (<code>x = box(unbox(x) + 1)</code>).
*
* <p>
* Update: GenerateJavaAST can also leave invalid AST structures of the form
* <code>(Foo) x = foo</code> due to the way generics are handled. This can
* happen when assigning into a field of a generic type. We'll go ahead and
* resolve that case here as well.
* </p>
*/
public class FixAssignmentToUnbox extends JModVisitor {
/**
* Normalize compound assignments where the lhs is an unbox operation.
*/
private static class CompoundAssignmentToUnboxNormalizer extends
CompoundAssignmentNormalizer {
private final AutoboxUtils autoboxUtils;
protected CompoundAssignmentToUnboxNormalizer(JProgram program) {
super(program, false);
autoboxUtils = new AutoboxUtils(program);
}
/**
* If the lhs is an unbox operation, then return the box rather than the
* original value.
*/
@Override
protected JExpression expressionToReturn(JExpression lhs) {
JExpression boxed = autoboxUtils.undoUnbox(lhs);
if (boxed != null) {
return boxed;
}
return lhs;
}
@Override
protected String getTempPrefix() {
return "$tunbox";
}
@Override
protected boolean shouldBreakUp(JBinaryOperation x) {
return isUnboxExpression(x.getLhs());
}
@Override
protected boolean shouldBreakUp(JPostfixOperation x) {
return isUnboxExpression(x.getArg());
}
@Override
protected boolean shouldBreakUp(JPrefixOperation x) {
return isUnboxExpression(x.getArg());
}
private boolean isUnboxExpression(JExpression x) {
return (autoboxUtils.undoUnbox(x) != null);
}
}
public static void exec(JProgram program) {
(new CompoundAssignmentToUnboxNormalizer(program)).breakUpAssignments();
(new FixAssignmentToUnbox(program)).accept(program);
}
private final AutoboxUtils autoboxUtils;
private FixAssignmentToUnbox(JProgram program) {
this.autoboxUtils = new AutoboxUtils(program);
}
@Override
public void endVisit(JBinaryOperation x, Context ctx) {
if (x.getOp() != JBinaryOperator.ASG) {
return;
}
JExpression lhs = x.getLhs();
JExpression boxed = autoboxUtils.undoUnbox(lhs);
if (boxed != null) {
// Assignment-to-unbox, e.g.
// unbox(x) = foo -> x = box(foo)
JClassType boxedType = (JClassType) boxed.getType();
ctx.replaceMe(new JBinaryOperation(x.getSourceInfo(), boxedType,
JBinaryOperator.ASG, boxed, autoboxUtils.box(x.getRhs(), boxedType)));
return;
}
if (lhs instanceof JCastOperation) {
// Assignment-to-cast-operation, e.g.
// (Foo) x = foo -> x = foo
JCastOperation cast = (JCastOperation) lhs;
JBinaryOperation newAsg = new JBinaryOperation(x.getSourceInfo(),
x.getType(), JBinaryOperator.ASG, cast.getExpr(), x.getRhs());
ctx.replaceMe(newAsg);
}
}
}