Possible to get better error handling for invalid enum parameter to stored program?

[David Karr]

If I define an enum parameter for a stored program, and the calling code
sends an invalid value, they get the less than useful "data truncated"
error.  Is it possible to define the stored program to produce better error
handling for that kind of error?

This is probably a FAQ, but in general, it appears that error diagnostics in
stored programs are very primitive. Are there any plans in a roadmap to
improve this?