Vimscript: fetch list of keymappings containing a prefix?

Question

I'm adding a buffer-local mapping to close netrw windows:

" ~/.vim/ftplugin/netrw.vim
nnoremap <buffer> q <C-W>c

It works, but it hesitates because Netrw has created other mappings with a q prefix, namely qb, qf, qF, and qL, so it waits for the duration of 'timeoutlen' before executing my mapping.

I want my q mapping to be instantaneous, so I've unmapped the other q-sequences:

nunmap <buffer> qb
nunmap <buffer> qf
nunmap <buffer> qF
nunmap <buffer> qL

But rather than hard-code these and have to update them if netrw adds more q mappings, I'd like to programmatically fetch a list of the keys my netrw buffer has mapped to sequences beginning with q and use that to drive the unmappings.

I suppose I could parse the output of :nmap, but that seems like a kludge. Is this information more directly accessible?

UPDATE

The answer provided below worked perfectly. It turns out, however, there's a way I can avoid the need to fetch these keybindings in the first place:

:help map-nowait

I came across this when reading through the dirvish plugin. So rather then perform any nunmaps, I just changed my ftplugin file to:

nnoremap <nowait> <buffer> q <C-W>c

and it works right away!

Answer 1

EDIT: My mistake: Neither getcompletion() nor the old trick (see my lh#command#matchging_askvim() function) are able to return buffer-local mappings.

This means: I'm not aware of any way other than parsing execute('nmap q') result. This means you'll may need to decrypt @ and *. From execute() result, I'll simply extract the keybindings. Then, I'll use maparg() to have more precise information.

let keybindings = map(split(execute('nmap q'), '\n'), 'split(v:val, "\\W\\+")[1]')
let mappings =  map(copy(keybindings), 'maparg(v:val, "n", 0, 1)')

NB: in lh-vim-lib, I have other functions able to obtain mapping states and to restore them eventually. See lh#on#exit().restore_mapping_and_clear_now()