Check if key is already bound in vimscript / Map key only if not mapped already

Question

I'm wondering if it is possible to check in vimscript if a key (or key combination) is already bound?

I know about the :map command which lets me see visually which keys are bound to what actions, but what I am looking for is a way to check it programmatically and perform actions conditionally.

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My concrete scenario is the following: I like the the possibility to dynamically/manually map <leader><leader> to what I need in different cases. (eg. while programming python: run the script. Or compile while programming c++). I usually do it by typing :nmap <leader><leader> :!make && run program manually while editing.

Now I want to check in my .vimrc if the combination is already bound (by a plugin, or manually) and if not map it to a default action.

In short words: How can I map a key only if it is not already bound?

Answer 1

You've got:

• :h maparg()
• :h mapcheck()

that, respectively permit to:

• get the exact mapping bound to the exact keybinding passed as parameter
• check whether there is any mapping bound to a keybinding starting as the parameter

On the other way around (get which keybinding could be bound to an action), so far I've only found the following

function! lh#mapping#who_maps(rhs, mode) abort
  " lh#askvim#execute  =~ split(execute(...), "\n")
  let maps = filter(lh#askvim#execute(a:mode . 'map'), 'v:val =~ a:rhs."$"')
  " Unfortunatelly, knowing exactly what mapping is associated to a
  " keybinding, it's best to use maparg()
  let lhs_list = map(maps, 'split(v:val)[1]')
  let mappings = map(lhs_list, 'maparg(v:val, a:mode, 0, 1)')
  call filter(mappings, 'v:val.rhs == a:rhs')
  return mappings
endfunction