Clean up buffer-local and other dangling callbacks

[wincent]

Was originally thinking of callbacks created via the map() function, for example:

wincent/aspects/nvim/files/.config/nvim/lua/wincent/vim/map.lua

Lines 11 to 41 in 1556492

	if rhs_type == 'function' then
	key = wincent.util.get_key_for_fn(rhs, wincent.g.map_callbacks)
	wincent.g.map_callbacks[key] = rhs
	if opts.expr then
	rhs = 'v:lua.wincent.g.map_callbacks.' .. key .. '()'
	else
	rhs = ':lua wincent.g.map_callbacks.' .. key .. '()<CR>'
	end
	elseif rhs_type ~= 'string' then
	error('map(): unsupported rhs type: ' .. rhs_type)
	end
	local buffer = opts.buffer
	opts.buffer = nil
	if buffer == true then
	vim.api.nvim_buf_set_keymap(0, mode, lhs, rhs, opts)
	else
	vim.api.nvim_set_keymap(mode, lhs, rhs, opts)
	end
	return {
	dispose = function()
	if buffer == true then
	vim.api.nvim_buf_del_keymap(0, mode, lhs)
	else
	vim.api.nvim_del_keymap(mode, lhs)
	end
	if key ~= nil then
	wincent.g.map_callbacks[key] = nil
	end
	end,
	}

But that was removed (migrated to native Neovim API) in fdb2015.

With that API, it was possible for a caller to keep a reference to the returned dispose function and call it in order to clean-up all the book-keeping, including the stored reference to the function, but in practice I didn't actually do that anywhere. It would have been nice if we could have registered an autocmd that would do this clean-up whenever the buffer is destroyed (Vim itself gets rid of the mapping, but we still have that dangling reference to the callback function itself).

Keeping this open though, because there's a similar thing going on with autocmd() callbacks here:

wincent/aspects/nvim/files/.config/nvim/lua/wincent/vim/autocmd.lua

Line 10 in 1556492

wincent.g.autocommand_callbacks[key] = cmd

If the autocmd is set to run only once with once, Vim will clean up the autocmd itself, but our reference to the callback will linger on, forever.

And here's the last one, where we hang on to augroup() callbacks forever:

wincent/aspects/nvim/files/.config/nvim/lua/wincent/vim/augroup.lua

Line 12 in 1556492

wincent.g.augroup_callbacks[name] = callback