How to properly filter output with errorformat

[MarcelRobitaille]

I have everything set up so that if I call :make and then :copen, I only see errors in my quickfix list.

vim.opt.makeprg = '~/path/to/custom/script.sh'
vim.opt.errorformat = '%f:%l:%c:\\ %tnfo\\ %n:\\ %m,%-G%.%#'

The second formatter handles this, taken from here.

I want to use Dispatch to run jobs in the background. I thought it would "just work", but if I :Make (or :Make!) and then :Copen, I see all lines output by my script, not only the errors. If I verbose set errorformat, I see:

errorformat=%f:%l:%c:\ %tnfo\ %n:\ %m,
        Last set from ~/.local/share/nvim/site/pack/packer/start/vim-dispatch/autoload/dispatch.vim line 1387

I read through :help dispatch, and thought maybe I needed to configure a compiler with its own errorformat, and that dispatch would set errorformat to what I have configured for that compiler. I read :help :CompilerSet, and created ~/.config/nvim/after/compiler/custom.vim with the contents:

CompilerSet makeprg=~/path/to/custom/script.sh errorformat=%f:%l:%c:\ %tnfo\ %n:\ %m,%-G%.%#

I also tried in two lines like in :help :CompilerSet:

CompilerSet makeprg=~/path/to/custom/script.sh
CompilerSet errorformat=%f:%l:%c:\ %tnfo\ %n:\ %m,%-G%.%#

However, if I :compiler custom, :Make, and :Copen, same thing. My errorformat is incorrectly set on line 1387 again.

How do I configure Dispatch's errorformat? I read through :help dispatch and the readme, but I only see one reference to errorformat and it doesn't really tell me how to configure it. I don't see anything about Dispatch mutating errorformat on me.

:Dispatch[!] [options] {program} [arguments]
                        Find a compiler plugin that sets 'makeprg' to
                        {program} and use its 'errorformat' to dispatch a
                        |:Make| for the given {program} and [arguments].  If
                        no compiler plugin is found, the generic format
                        %+I%.%# is used.

I tried to read the Dispatch source code, but I don't know vimscript well at all.

I am using NVIM v0.10.0-dev-737+gdf2f5e391 and Debian 11

[MarcelRobitaille]

To be clear, it still correctly matches the actual errors, it just also shows non-matches. If anyone knows a better way to show non-matches, I would also accept that solution.