[GROOVY-7644] ExternalizeMethods generates incorrect bytecode for statically compiled nested classes

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4.5
• Fix Version/s: 2.4.6
• Component/s: Static compilation
• Environment: OSX 10.10, JDK 1.8
• Assignee: Cédric Champeau
• Reporter: Shil Sinha
• Created: 23/Oct/15 01:08
• Updated: 22/Feb/16 20:48
• Resolved: 28/Oct/15 00:44

Description

When @AutoExternalize and @CompileStatic are both applied to a nested (static) class, the generated writeExternal and readExternal methods call writeObject/readObject on 'this' rather than on their arguments. This results in IncompatibleClassChange errors at runtime. Example:

class Person {
    @groovy.transform.ToString(includePackage=false)
    @groovy.transform.AutoExternalize
    @groovy.transform.CompileStatic
    static class AddressCS {
        String street, town
    }
}

The bytecode generated for the Person.AddressCS.writeExternal method is:

public writeExternal(Ljava/io/ObjectOutput;)V throws java/io/IOException 
   L0
    ALOAD 0
    ALOAD 0
    GETFIELD Person$AddressCS.street : Ljava/lang/String;
    INVOKEINTERFACE java/io/ObjectOutput.writeObject (Ljava/lang/Object;)V
    ACONST_NULL
    POP
    ALOAD 0
    ALOAD 0
    GETFIELD Person$AddressCS.town : Ljava/lang/String;
    INVOKEINTERFACE java/io/ObjectOutput.writeObject (Ljava/lang/Object;)V
    ACONST_NULL
    POP
   L1
    RETURN
    LOCALVARIABLE this LPerson$AddressCS; L0 L1 0
    LOCALVARIABLE out Ljava/io/ObjectOutput; L0 L1 1
    MAXSTACK = 2
    MAXLOCALS = 2

This seems to occur because the writeObject method call expressions within writeExternal have implicitThis set to true.

The problem is essentially the same for generated readExternal methods.