@AtLine 应用在 arthas 中，@Binding.LocalVars 不生效

[lotabout]

背景

在尝试为 arthas 添加 @AtLine 的支持，用于打印出方法运行时，局部变量的信息。
当前有了一个 MVP 的版本(commit: lotabout/arthas@5536242#diff-060c8feafaa130cf1bf5dad5a84703d46db28aa09e78fe2088b8d49288005949R48)

在自测时，发现 @AtLine 返回的 LocalVars 和 LocalVarName 都是空。

问题复现

测试类如下：

public class Hello {

  public static void main(String[] args) throws InterruptedException {
    Sample sample = new Sample();
    for (int i = 0; i < 10000; i++) {
      System.out.println(sample.hello());
      Thread.sleep(1000);
    }
  }


  private static class Sample {
    private int i = 0;

    public String hello() {
      int x = i * 2;
      String y = String.format("hello %d", x);
      return y;
    }
  }
}

启动测试类：

javac Hello.java
java Hello

随后有添加 AtLine 版本的 arthas 进行 attach

java -jar arthas-boot.jar
# 其中 `-l` 新 patch 后新加的参数
$ watch Hello$Sample hello '{varNames, vars}' -l

在 arthas 的 Enhancer 中已经加了 log 逻辑，打印出 transform 后的代码，如下：

/*
 * Decompiled with CFR.
 *
 * Could not load the following classes:
 *  java.arthas.SpyAPI
 */
import java.arthas.SpyAPI;

private static class Hello.Sample {
    private int i = 0;

    public String hello() {
        Object[] objectArray = new Object[]{};
        String string = "hello|()Ljava/lang/String;";
        Class<Hello.Sample> clazz = Hello.Sample.class;
        Hello.Sample sample = this;
        SpyAPI.atEnter(clazz, (String)string, (Object)sample, (Object[])objectArray);
        try {
            String string2;
            String[] stringArray = new String[]{};
            Object[] objectArray2 = new Object[]{};
            int n = 16;
            Object[] objectArray3 = new Object[]{};
            String string3 = "hello|()Ljava/lang/String;";
            Class<Hello.Sample> clazz2 = Hello.Sample.class;
            Hello.Sample sample2 = this;
            SpyAPI.atLine(clazz2, (String)string3, (Object)sample2, (Object[])objectArray3, (int)n, (String[])stringArray, (Object[])objectArray2);
            int n2 = this.i * 2;
            String[] stringArray2 = new String[]{};
            Object[] objectArray4 = new Object[]{};
            int n3 = 17;
            Object[] objectArray5 = new Object[]{};
            String string4 = "hello|()Ljava/lang/String;";
            Class<Hello.Sample> clazz3 = Hello.Sample.class;
            Hello.Sample sample3 = this;
            SpyAPI.atLine(clazz3, (String)string4, (Object)sample3, (Object[])objectArray5, (int)n3, (String[])stringArray2, (Object[])objectArray4);
            String string5 = String.format("hello %d", n2);
            String[] stringArray3 = new String[]{};
            Object[] objectArray6 = new Object[]{};
            int n4 = 18;
            Object[] objectArray7 = new Object[]{};
            String string6 = "hello|()Ljava/lang/String;";
            Class<Hello.Sample> clazz4 = Hello.Sample.class;
            Hello.Sample sample4 = this;
            SpyAPI.atLine(clazz4, (String)string6, (Object)sample4, (Object[])objectArray7, (int)n4, (String[])stringArray3, (Object[])objectArray6);
            String string7 = string2 = string5;
            Object[] objectArray8 = new Object[]{};
            String string8 = "hello|()Ljava/lang/String;";
            Class<Hello.Sample> clazz5 = Hello.Sample.class;
            Hello.Sample sample5 = this;
            SpyAPI.atExit(clazz5, (String)string8, (Object)sample5, (Object[])objectArray8, (Object)string7);
            return string2;
        }
        catch (Throwable throwable) {
            Throwable throwable2 = throwable;
            Object[] objectArray9 = new Object[]{};
            String string9 = "hello|()Ljava/lang/String;";
            Class<Hello.Sample> clazz6 = Hello.Sample.class;
            Hello.Sample sample6 = this;
            SpyAPI.atExceptionExit(clazz6, (String)string9, (Object)sample6, (Object[])objectArray9, (Throwable)throwable2);
            throw throwable;
        }
    }

    private Hello.Sample() {
    }
}

发现其中 atLine 的最后两个参数 varName 和 vars 都是空数组。

环境信息

分别使用 JDK 1.8 和 JDK 11 进行测试，都有这个问题。

另外，单独运行 bytekit 的 unit test，是能正确 transform 的，下面是 UT 的一些中间输出

vars: [com.alibaba.bytekit.asm.interceptor.AtLineTest$Sample@5b3c56e0, 101, 100, 100100]
varNames: [this, i, s, abc]
method: methodtestLine|(I)I
atLine: thiscom.alibaba.bytekit.asm.interceptor.AtLineTest$Sample@5b3c56e0
line: 29
args: [10202]
argNames: [i]
vars: [com.alibaba.bytekit.asm.interceptor.AtLineTest$Sample@5b3c56e0, 10202, 100, 100100]
varNames: [this, i, s, abc]
method: methodtestLine|(I)I
atLine: thiscom.alibaba.bytekit.asm.interceptor.AtLineTest$Sample@5b3c56e0
line: 30
args: [10211]
argNames: [i]
vars: [com.alibaba.bytekit.asm.interceptor.AtLineTest$Sample@5b3c56e0, 10211, 100]
varNames: [this, i, s]
method: methodtestLine|(I)I
atLine: thiscom.alibaba.bytekit.asm.interceptor.AtLineTest$Sample@5b3c56e0
line: 41
args: [10211]
argNames: [i]
vars: [com.alibaba.bytekit.asm.interceptor.AtLineTest$Sample@5b3c56e0, 10211, 100]
varNames: [this, i, s]

[lotabout]

定位到是 AsmUtils.loadClass 与 AsmUtils.toClassNode 的差异，loadClass 生成的 ClassNode 缺少 localVariables 信息。
并发现 javac 后的 bytecode 就缺少了 localVariableTable。