parboiled-java: assert that debug information (-g:vars) is present

[nornagon]

Perhaps I'm missing something obvious, but Var framing doesn't seem to be working properly. I made a small repro: https://gist.github.com/nornagon/73f6d756f22fc685028bec855eecfd27

The symptom appears to be that Var frames don't get pushed/popped.

To repro:

$ git clone https://gist.github.com/73f6d756f22fc685028bec855eecfd27.git parboiled-repro
$ cd parboiled-repro
$ make

Instead of seeing the value 1 for the Var every time, we see the values 1, 2, 3 and 4. Instead of seeing the level of the Var change when recursing, we see it's always 0.

[nornagon]

I discovered what the issue is here: without debugging info (javac -g), ASM is unable to discover local variable information. Adding -g to the javac command in the Makefile in my above-linked gist fixes the behavior.

Perhaps an assertion could be added to detect whether debugging symbols are present?