com.google.devtools.build.lib.syntax.compiler.NewObject.java Source code

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Here is the source code for com.google.devtools.build.lib.syntax.compiler.NewObject.java

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// Copyright 2015 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.syntax.compiler;

import net.bytebuddy.description.method.MethodDescription.ForLoadedConstructor;
import net.bytebuddy.implementation.Implementation.Context;
import net.bytebuddy.implementation.bytecode.Duplication;
import net.bytebuddy.implementation.bytecode.StackManipulation;
import net.bytebuddy.implementation.bytecode.member.MethodInvocation;

import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

import java.util.List;

/**
 * Builds byte code for new object creation from constructor calls.
 *
 * <p>Java byte code for new object creation looks like the following pseudo code:
 * <pre>
 * NEW
 * DUP
 * ...load constructor parameters...
 * INVOKESPECIAL constructor
 * </pre>
 * This is because a constructor is actually called on the reference to the object itself, which
 * is left on the stack by NEW.
 *
 * This class helps with wrapping the parameter loading with this structure.
 */
public class NewObject implements StackManipulation {

    private final ForLoadedConstructor constructor;
    private final StackManipulation arguments;

    /**
     * Intermediate state builder for new object construction with missing constructor argument
     * loading.
     */
    public static final class NewObjectBuilder {
        private final ForLoadedConstructor constructor;

        private NewObjectBuilder(ForLoadedConstructor constructor) {
            this.constructor = constructor;
        }

        /**
         * Adds the argument loading in the correct for new object construction.
         */
        public NewObject arguments(StackManipulation... arguments) {
            return new NewObject(constructor, new StackManipulation.Compound(arguments));
        }

        /**
         * Adds the argument loading in the correct for new object construction.
         */
        public NewObject arguments(List<StackManipulation> arguments) {
            return new NewObject(constructor, new StackManipulation.Compound(arguments));
        }
    }

    private NewObject(ForLoadedConstructor constructor, StackManipulation arguments) {
        this.constructor = constructor;
        this.arguments = arguments;
    }

    /**
     * Looks for a constructor in the class with the given parameter types and returns an
     * intermediate builder.
     */
    public static NewObjectBuilder fromConstructor(Class<?> clazz, Class<?>... parameterTypes) {
        return new NewObjectBuilder(ReflectionUtils.getConstructor(clazz, parameterTypes));
    }

    @Override
    public boolean isValid() {
        return true;
    }

    @Override
    public Size apply(MethodVisitor methodVisitor, Context implementationContext) {
        methodVisitor.visitTypeInsn(Opcodes.NEW, constructor.getDeclaringType().getInternalName());
        return new StackManipulation.Compound(Duplication.SINGLE, arguments, MethodInvocation.invoke(constructor))
                .apply(methodVisitor, implementationContext);
    }

    @Override
    public String toString() {
        return "NewObject(" + constructor + ", " + arguments + ")";
    }
}