Vim: report error on a single line - vim

Question

When an error is raised inside a Vimscript function, Vim reports an error in the following format:
Error detected while processing function <SNR>My_Function:
line X:
EXXX: Error Message Here
This is very distracting. Ideally, I would like this to be formatted in some way to fit on a single line, but if that's not possible, then I just want the last EXXX line with the actual error. Is it possible to change this?

Answer 1

I don't like that behavior neither, but it is how it is, and cannot be changed.
Your functions need to :catch any errors, and convert this into the desired one-line error message:
function! s:My_Function()
try
" commands here
catch /^Vim\%((\a\+)\)\=:/
echohl ErrorMsg
echomsg substitute(v:exception, '^\CVim\%((\a\+)\)\=:', '', '')
echohl None
endtry
endfunction
This is how most plugins handle it. The behavior isn't completely like that of built-in commands, though: The error is effectively "swallowed", and subsequent commands (e.g. in a sequence cmd1 | call <SID>My_Function() | cmd3) will be executed despite the error. For most uses this is okay, and most users probably are even unaware of this.
better alternative
To make the custom command behave like a built-in one, the error message needs to be returned to the custom command or mapping, and :echoerr'd there. In my ingo-library plugin, I have corresponding helper functions:
function! s:My_Function()
try
" commands here
return 1 " Success
catch /^Vim\%((\a\+)\)\=:/
call ingo#err#SetVimException()
return 0 " Failure, use stored error message.
endif
endfunction
if ! <SID>My_Function() | echoerr ingo#err#Get() | endif

Answer 2

There is another approach to the problem: error messages can be decoded.
In my lh-vim-lib, I've defined a function that decodes the last error message and displays the result in the qf-window.
Given lh-vim-lib is installed, you've to add something like
command! WTF call lh#exception#say_what()
to your .vimrc.
The feature by itself has been inspired from https://github.com/tweekmonster/exception.vim, the difference is that I've used stuff I've already implemented in my library plugin in order to:
support localized messages
support autoloaded functions, even when # isn't in &isk (which is possible depending on the settings associated to the current filetype/buffer)
have as few loops as possible
factorize code with my logging, and unit testing, and DbC frameworks.
Near the end of the screencast I've recorded to demonstrate my Dbc framework, I've used :WTF to display the last error in a human friendly manner.