Remove `__call` metamethod for compiled regexp objects

[kmarius]

Pinging @L3MON4D3

I would like to remove the old, undocumented __call metamethod at some point in the future because it duplicates a lot of the matching logic.

As far as I can tell, LuaSnip only uses the begin_ind property and the capture groups of a match. A simple migration step could look like this: when loading jsregexp, check if the __call metamethod exists, and if not set to something like this:

local jsregexp = require("jsregexp")
local meta = getmetatable(jsregexp.compile(""))

meta.__call = function(self, str)
	local match = self:exec(str)
	if not match then
		return {}
	end
	return {
		{
			begin_ind = match.index,
			groups = { unpack(match) },
		},
	}
end

This should work as long as only the first match is needed and the global flag is not set. A full replacement looks more like this (Note that the match object already contains the full match in match[0] which could be used directly by LuaSnip):

meta.__call = function(self, s)
	local jstr = jsregexp.to_jsstring(s)
	self.last_index = 1
	local matches = {}
	while true do
		local match = self:exec(jstr)
		if match == nil then
			break
		end
		table.insert(matches, {
			begin_ind = match.index,
			end_ind = match.index + #match[0] - 1,
			groups = { unpack(match) },
			named_groups = match.groups,
		})
                if not self.global then
                        break
                end
		if #match[0] == 0 then
			self.last_index = self.last_index + 1
		end
	end
	return matches
end

Opinions? I am not planning to release anything until I have the OK, and there is no urgency whatsoever.