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// Copyright 2016 The Bazel Authors. 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.devtools.build.lib.query2.engine;
import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.Argument;
/**
* Performs an arbitrary contextual transformation of a {@link QueryExpression}.
*
* <p>For each subclass of {@link QueryExpression}, there's a corresponding {@link #visit} overload
* that transforms a node of that type. By default, this method recursively applies this {@link
* QueryExpressionMapper}'s transformation in a structure-preserving manner (trying to maintain
* reference-equality, as an optimization). Subclasses of {@link QueryExpressionMapper} can override
* these methods in order to implement an arbitrary transformation.
*/
public abstract class QueryExpressionMapper<C>
implements QueryExpressionVisitor<QueryExpression, C> {
@Override
public QueryExpression visit(TargetLiteral targetLiteral, C context) {
return targetLiteral;
}
@Override
public QueryExpression visit(BinaryOperatorExpression binaryOperatorExpression, C context) {
boolean changed = false;
ImmutableList.Builder<QueryExpression> mappedOperandsBuilder = ImmutableList.builder();
for (QueryExpression operand : binaryOperatorExpression.getOperands()) {
QueryExpression mappedOperand = operand.accept(this, context);
if (mappedOperand != operand) {
changed = true;
}
mappedOperandsBuilder.add(mappedOperand);
}
return changed
? new BinaryOperatorExpression(
binaryOperatorExpression.getOperator(), mappedOperandsBuilder.build())
: binaryOperatorExpression;
}
@Override
public QueryExpression visit(FunctionExpression functionExpression, C context) {
boolean changed = false;
ImmutableList.Builder<Argument> mappedArgumentBuilder = ImmutableList.builder();
for (Argument argument : functionExpression.getArgs()) {
switch (argument.getType()) {
case EXPRESSION:
{
QueryExpression expr = argument.getExpression();
QueryExpression mappedExpression = expr.accept(this, context);
mappedArgumentBuilder.add(Argument.of(mappedExpression));
if (expr != mappedExpression) {
changed = true;
}
break;
}
default:
mappedArgumentBuilder.add(argument);
break;
}
}
return changed
? new FunctionExpression(functionExpression.getFunction(), mappedArgumentBuilder.build())
: functionExpression;
}
@Override
public QueryExpression visit(LetExpression letExpression, C context) {
boolean changed = false;
QueryExpression mappedVarExpr = letExpression.getVarExpr().accept(this, context);
if (mappedVarExpr != letExpression.getVarExpr()) {
changed = true;
}
QueryExpression mappedBodyExpr = letExpression.getBodyExpr().accept(this, context);
if (mappedBodyExpr != letExpression.getBodyExpr()) {
changed = true;
}
return changed
? new LetExpression(letExpression.getVarName(), mappedVarExpr, mappedBodyExpr)
: letExpression;
}
@Override
public QueryExpression visit(SetExpression setExpression, C context) {
return setExpression;
}
public static QueryExpressionMapper identity() {
return IdentityMapper.INSTANCE;
}
/**
* Returns a {@link QueryExpressionMapper} which applies all the mappings provided by {@code
* mappers}, in the reverse order of mapper array.
*/
public static <C> QueryExpressionMapper<C> compose(QueryExpressionMapper<C>... mappers) {
return new ComposedQueryExpressionMapper(mappers);
}
private static class ComposedQueryExpressionMapper<C> extends QueryExpressionMapper<C> {
private final QueryExpressionMapper<C>[] mappers;
private ComposedQueryExpressionMapper(QueryExpressionMapper... mappers) {
this.mappers = mappers;
}
@Override
public QueryExpression visit(TargetLiteral targetLiteral, C context) {
return mapAll(targetLiteral, mappers, context);
}
@Override
public QueryExpression visit(BinaryOperatorExpression binaryOperatorExpression, C context) {
return mapAll(binaryOperatorExpression, mappers, context);
}
@Override
public QueryExpression visit(FunctionExpression functionExpression, C context) {
return mapAll(functionExpression, mappers, context);
}
@Override
public QueryExpression visit(LetExpression letExpression, C context) {
return mapAll(letExpression, mappers, context);
}
@Override
public QueryExpression visit(SetExpression setExpression, C context) {
return mapAll(setExpression, mappers, context);
}
private static <C> QueryExpression mapAll(
QueryExpression expression,
QueryExpressionMapper<C>[] mappers,
C context) {
QueryExpression expr = expression;
for (int i = mappers.length - 1; i >= 0; i--) {
expr = expr.accept(mappers[i], context);
}
return expr;
}
}
private static class IdentityMapper extends QueryExpressionMapper<Void> {
private static final IdentityMapper INSTANCE = new IdentityMapper();
private IdentityMapper() {
}
@Override
public QueryExpression visit(TargetLiteral targetLiteral, Void context) {
return targetLiteral;
}
@Override
public QueryExpression visit(BinaryOperatorExpression binaryOperatorExpression, Void context) {
return binaryOperatorExpression;
}
@Override
public QueryExpression visit(FunctionExpression functionExpression, Void context) {
return functionExpression;
}
@Override
public QueryExpression visit(LetExpression letExpression, Void context) {
return letExpression;
}
@Override
public QueryExpression visit(SetExpression setExpression, Void context) {
return setExpression;
}
}
}
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