Better error debugging for generation

[mperham]

I'm trying to figure out why JSON is blowing up when generating the JSON for a big ole Hash of stuff. It raises a GeneratorError, but with no context so I can't easily tell where my bad data is. The line in question is here:

json/ext/json/ext/generator/generator.c

Line 912 in 55015fa

rb_raise(rb_path2class("JSON::GeneratorError"), "source sequence is illegal/malformed utf-8");

I would suggest this error include the relevant object at fault. Something like:

class JSON::GeneratorError
  attr_reader :invalid_element
end

[byroot]

Makes sense. Wouldn't be too hard to implement.

[mperham]

Thank you, it worked great.

Should it emit the invalid object as part of message? That's extremely useful context that most people won't know exists. Is the attribute in the RDoc?

[byroot]

The object may be huge, that's why it's included in detailed_message and not just message, to avoid things like: https://bugs.ruby-lang.org/issues/18285

[mperham]

TIL about #detailed_message! I think I could roll this into Sidekiq's debugging output: turn on debugging => get detailed_message logged which will solve my need.

https://docs.ruby-lang.org/en/master/Exception.html#method-i-detailed_message