"My experience with generated code is "all is well until the first bugreport". Usually the bugreport mentions parts (stack traces, line numbers, etc.) from the generated code - how do you get back from that to the code you've written?"
that is exactly why:
2) i went to all the trouble to create pyjamas-desktop, so that you would be able to run the exact same application under the standard python interpreter.
"Not to mention that the code generating can introduce errors on its own."
this is a matter of trust. you place your trust in the tool that it is going to do the job. just as you trust any other tool to do its job. to back up that trust, we always add a regression test whenever a new feature is added, and i've been pushing to have regression tests added whenever someone reports a bug, too, to demonstrate the missing feature.
"Nowadays I spend most of my time chasing bugs in (open source) infrastructure code that should work (but doesn't), so I'd be cautious about adding any extra layers..."
welcome to free software! did you pay money for any of that infrastructure? so - you got what you paid for.
pyjamas, like any free software project, does the job that the people who are *working on it* want it to do. everyone else who is NOT contributing is getting the [free] benefits of their efforts and expertise.
you should be grateful that google released GWT as free software; grateful that james tauber did the port to python, and grateful that the current developers continue to maintain it and release their contributions to the wider world.