First of all, I talk about debugging. Unfortunately, there's no particularly easy way of doing it, but one useful possibility is to run make and spit the output into a file and then:
:let &makeprg="cat ~/outputfile.log"
:make
Regarding making the errorformat, this does require a bit of trial and error. You can use %A, %C and %Z for multiline messages and you can use %-G to ignore stuff. The order is very important and note that sometimes the %C or even %Z come before the %A! In your case, you may be able to get somewhere with the efm below. I tend to use let &efm =
and let &efm .=
rather than set as you don't have to escape every space or quotation mark and you can build it up gradually. It's also much more readable.
" Start of the multi-line error message (%A),
" %p^ means a string of spaces and then a ^ to
" get the column number
let &efm = '%A%p^' . ','
" Next is the main bit: continuation of the error line (%C)
" followed by the filename in quotes, a comma (\,)
" then the rest of the details
let &efm .= '%C"%f"\, line %l: error(%n): %m' . ','
" Next is the last line of the error message, any number
" of spaces (' %#': equivalent to ' *') followed by a bit
" more error message
let &efm .= '%Z %#%m' . ','
" This just ignores any other lines (must be last!)
let &efm .= '%-G%.%#'