com.google.devtools.build.android.desugar.CloseResourceMethodScanner.java Source code

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Here is the source code for com.google.devtools.build.android.desugar.CloseResourceMethodScanner.java

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// Copyright 2017 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.android.desugar;

import com.google.common.base.Preconditions;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

/**
 * A class scanner to check whether the class has the synthetic method $closeResource(Throwable,
 * AutoCloseable).
 */
public class CloseResourceMethodScanner extends ClassVisitor {

    private boolean hasCloseResourceMethod;
    private String internalName;
    private int classFileVersion;

    public CloseResourceMethodScanner() {
        super(Opcodes.ASM6);
    }

    @Override
    public void visit(int version, int access, String name, String signature, String superName,
            String[] interfaces) {
        Preconditions.checkState(internalName == null, "This scanner has been used.");
        this.internalName = name;
        this.classFileVersion = version;
        super.visit(version, access, name, signature, superName, interfaces);
    }

    public boolean hasCloseResourceMethod() {
        return hasCloseResourceMethod;
    }

    @Override
    public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
        if (classFileVersion <= 50) {
            // A Java 6 or below class file should not have $closeResource method.
            return null;
        }
        if (!hasCloseResourceMethod) {
            hasCloseResourceMethod = TryWithResourcesRewriter.isSyntheticCloseResourceMethod(access, name, desc);
        }
        return new StackMapFrameCollector(name, desc);
    }

    private class StackMapFrameCollector extends MethodVisitor {

        private final String methodSignature;
        private boolean hasCallToCloseResourceMethod;
        private boolean hasJumpInstructions;
        private boolean hasStackMapFrame;

        public StackMapFrameCollector(String name, String desc) {
            super(Opcodes.ASM6);
            methodSignature = internalName + '.' + name + desc;
        }

        @Override
        public void visitEnd() {
            if (!hasCallToCloseResourceMethod) {
                return;
            }
            if (hasJumpInstructions && !hasStackMapFrame) {
                throw new UnsupportedOperationException(
                        "The method " + methodSignature + " calls $closeResource(Throwable, AutoCloseable), "
                                + "and Desugar thus needs to perform type inference for it "
                                + "to rewrite $closeResourceMethod. "
                                + "However, this method has jump instructions, but does not have stack map frames. "
                                + "Please recompile this class with stack map frames.");
            }
        }

        @Override
        public void visitMethodInsn(int opcode, String owner, String name, String desc, boolean itf) {
            if (!hasCallToCloseResourceMethod && TryWithResourcesRewriter
                    .isCallToSyntheticCloseResource(internalName, opcode, owner, name, desc)) {
                hasCallToCloseResourceMethod = true;
            }
        }

        @Override
        public void visitFrame(int type, int nLocal, Object[] local, int nStack, Object[] stack) {
            hasStackMapFrame = true;
        }

        @Override
        public void visitJumpInsn(int opcode, Label label) {
            hasJumpInstructions = true;
        }
    }
}