How to handle input UFO with bad glyph names?

[belluzj]

When someone tries to compile with fontmake a UFO that has an invalid glyph name (in this case it was "G," with a literal comma in the name), the bad glyph name goes verbatim into the output feature code and fontmake complains about the syntax being wrong. When trying to understand the problem, it's a bit confusing because the original feature only has valid syntax, and the syntax error lies in what ufo2ft writes out.

I have added tests that cover this bug. What do you think we should do?

1. Not care: the bad naming was obviously a mistake, and it doesn't happen often enough to warrant a proper error message
2. Make ufo2ft raise when glyph names are wrong: in my opinion ufo2ft should always output compilable feature code, or raise if that's not possible.
3. @moyogo suggests that this should not be an issue in the first place, and ufo2ft/fontmake should rename glyphs to production names on the fly and don't care about crazy glyph names

[anthrotype]

personally, I'm leaning towards option 1 (not care, bad glyph name as user's mistake).
Option 3 is not straightforward, because the production glyph renaming occurs after we have compiled the features.
If somebody wants to implement option 2 (raise meaningful error on invalid glyph names) you're welcome