Consider the following class:

 

class Debugging {
public static void main(String[] args) {
  a:
if (args.length > 0) {
   b: println
"args"
 
}
}
}

 

And let’s say that I run the program with no arguments, and I put IntelliJ debugger to break on line a. Now when I “step next” I see it highlight line b, then step next and the program ends. The line b clearly did not run. Is this a problem with IntelliJ or the bytecode? Below is the bytecode for the method. I’m assuming the issue is that L2 is before the return, and at the return bytecode we see before it LINENUMBER 4. If the return was annotated with a linenumber 5 or 6, I assume the debugger would step to the closing brace of the if statement (or of the method itself, depending on what was preferred). Is this an issue with the IntelliJ debugger, or is it really a limitation of the Groovy bytecode generation? A workaround is if I put an empty return statement at the end of main, the debugger works, but strangely in bytecode I see two returns.

 

  public static transient varargs main([Ljava/lang/String;)V

   L0

    INVOKESTATIC Debugging.$getCallSiteArray ()[Lorg/codehaus/groovy/runtime/callsite/CallSite;

    ASTORE 1

   L1

    LINENUMBER 3 L1

    ALOAD 1

    LDC 0

    AALOAD

    ALOAD 0

    INVOKEINTERFACE org/codehaus/groovy/runtime/callsite/CallSite.callGetProperty (Ljava/lang/Object;)Ljava/lang/Object;

    ICONST_0

    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;

    INVOKESTATIC org/codehaus/groovy/runtime/ScriptBytecodeAdapter.compareGreaterThan (Ljava/lang/Object;Ljava/lang/Object;)Z

    IFEQ L2

   L3

    LINENUMBER 4 L3

    ALOAD 1

    LDC 1

    AALOAD

    LDC LDebugging;.class

    LDC "args"

    INVOKEINTERFACE org/codehaus/groovy/runtime/callsite/CallSite.callStatic (Ljava/lang/Class;Ljava/lang/Object;)Ljava/lang/Object;

    POP

   L2

    RETURN

    LOCALVARIABLE args [Ljava/lang/String; L0 L2 0

    MAXSTACK = 3

    MAXLOCALS = 2

 

Jason Winnebeck

 

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