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      1 // Copyright 2017 The Bazel Authors. All rights reserved.
      2 //
      3 // Licensed under the Apache License, Version 2.0 (the "License");
      4 // you may not use this file except in compliance with the License.
      5 // You may obtain a copy of the License at
      6 //
      7 //    http://www.apache.org/licenses/LICENSE-2.0
      8 //
      9 // Unless required by applicable law or agreed to in writing, software
     10 // distributed under the License is distributed on an "AS IS" BASIS,
     11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     12 // See the License for the specific language governing permissions and
     13 // limitations under the License.
     14 package com.google.devtools.build.android.desugar;
     15 
     16 import com.google.common.base.Preconditions;
     17 import org.objectweb.asm.ClassVisitor;
     18 import org.objectweb.asm.Label;
     19 import org.objectweb.asm.MethodVisitor;
     20 import org.objectweb.asm.Opcodes;
     21 
     22 /**
     23  * A class scanner to check whether the class has the synthetic method $closeResource(Throwable,
     24  * AutoCloseable).
     25  */
     26 public class CloseResourceMethodScanner extends ClassVisitor {
     27 
     28   private boolean hasCloseResourceMethod;
     29   private String internalName;
     30   private int classFileVersion;
     31 
     32   public CloseResourceMethodScanner() {
     33     super(Opcodes.ASM6);
     34   }
     35 
     36   @Override
     37   public void visit(
     38       int version,
     39       int access,
     40       String name,
     41       String signature,
     42       String superName,
     43       String[] interfaces) {
     44     Preconditions.checkState(internalName == null, "This scanner has been used.");
     45     this.internalName = name;
     46     this.classFileVersion = version;
     47     super.visit(version, access, name, signature, superName, interfaces);
     48   }
     49 
     50   public boolean hasCloseResourceMethod() {
     51     return hasCloseResourceMethod;
     52   }
     53 
     54   @Override
     55   public MethodVisitor visitMethod(
     56       int access, String name, String desc, String signature, String[] exceptions) {
     57     if (classFileVersion <= 50) {
     58       // A Java 6 or below class file should not have $closeResource method.
     59       return null;
     60     }
     61     if (!hasCloseResourceMethod) {
     62       hasCloseResourceMethod =
     63           TryWithResourcesRewriter.isSyntheticCloseResourceMethod(access, name, desc);
     64     }
     65     return new StackMapFrameCollector(name, desc);
     66   }
     67 
     68   private class StackMapFrameCollector extends MethodVisitor {
     69 
     70     private final String methodSignature;
     71     private boolean hasCallToCloseResourceMethod;
     72     private boolean hasJumpInstructions;
     73     private boolean hasStackMapFrame;
     74 
     75     public StackMapFrameCollector(String name, String desc) {
     76       super(Opcodes.ASM6);
     77       methodSignature = internalName + '.' + name + desc;
     78     }
     79 
     80     @Override
     81     public void visitEnd() {
     82       if (!hasCallToCloseResourceMethod) {
     83         return;
     84       }
     85       if (hasJumpInstructions && !hasStackMapFrame) {
     86         throw new UnsupportedOperationException(
     87             "The method "
     88                 + methodSignature
     89                 + " calls $closeResource(Throwable, AutoCloseable), "
     90                 + "and Desugar thus needs to perform type inference for it "
     91                 + "to rewrite $closeResourceMethod. "
     92                 + "However, this method has jump instructions, but does not have stack map frames. "
     93                 + "Please recompile this class with stack map frames.");
     94       }
     95     }
     96 
     97     @Override
     98     public void visitMethodInsn(int opcode, String owner, String name, String desc, boolean itf) {
     99       if (!hasCallToCloseResourceMethod
    100           && TryWithResourcesRewriter.isCallToSyntheticCloseResource(
    101               internalName, opcode, owner, name, desc)) {
    102         hasCallToCloseResourceMethod = true;
    103       }
    104     }
    105 
    106     @Override
    107     public void visitFrame(int type, int nLocal, Object[] local, int nStack, Object[] stack) {
    108       hasStackMapFrame = true;
    109     }
    110 
    111     @Override
    112     public void visitJumpInsn(int opcode, Label label) {
    113       hasJumpInstructions = true;
    114     }
    115   }
    116 }
    117