How to format with `gq` using the same settings as when editing the text

Question

I have the following options set (in ~/.config/vim/ftplugin/asciidoc.vim):

setlocal wrap
setlocal textwidth=0
setlocal wrapmargin=0
setlocal formatoptions=l

And when I'm writing text, it's not hard-wrapped automatically at all.

However, when I need to reformat an existing paragraph, and press gqap, it's hard-wrapped to fit 79 columns.

From help gq:

Format the lines that {motion} moves over.
Formatting is done with one of three methods:

In the third case the 'textwidth' option controls the
length of each formatted line (see below).
If the 'textwidth' option is 0, the formatted line
length is the screen width (with a maximum width of
79).

Is there a way to work around this 79 columns limitation?

VIM 8.1.

Answer 1

It turns out a negative value for wrapmargin helps:

setlocal wrapmargin=-1000

As per :help wrapmargin:

Number of characters from the right window border where wrapping
starts.

So it seems that the :help gq docs are not entirely correct, and with textwidth=0, wrapmargin is also considered when picking a column to wrap at.