Here are some tips on how to debug what is happening on the transition from groovy source code into the generated bytecode.

artifact	transformation	artifact
source (hello.groovy)	GroovyLexer	antlr tokens
antlr tokens	GroovyRecognizer	antlr ast
antlr ast	AntlrParserPlugin	groovy ast
groovy ast	AsmClassGenerator	bytecode (hello.class)

Note1 groovy.g is used to generate GroovyLexer and GroovyRecognizer

Note2 GroovyRecognizer is sometimes easier to understand in its syntax diagram form

Note3 AntlrParserPlugin source available.

Example

For these examples let's assume the file hello.groovy contains

GroovyLexer (viewing Antlr Tokens)

To view the antlr tokens that the source code has been broken into you need to do the following in groovy-core subdirectory

GroovyRecognizer (viewing Antlr AST)

To view the antlr AST that the recognized tokens have built

AntlrParserPlugin (viewing Groovy AST)

To view the Groovy AST that is one step closer to the generated bytecode you can generate hello.groovy.xml using these unix commands.

This can be generated by changing the groovy.ast system property. By doing this we can diff the generated Groovy AST artifacts for debugging and migration purposes.

Viewing Bytecode

One interesting bytecode viewer is jclasslib which renders hello.class in this manner...

Decompiling bytecode back to Java

If, however, you are bamboozled by bytecode... The easiest to grok mechanism for reading the compiled code is to use a tool like JAD to decompile the hello.class into a readable hello.java

From source code to bytecode