lua: complete-word: use internal regex for splitting words

Internally vis supports unicode just fine. Instead of relying on
external programs utilize vis' own features.

Thanks to Florian Fischer for the correct regex!

lua/plugins/complete-word.lua

@@ -5,18 +5,32 @@ vis:map(vis.modes.INSERT, "<C-n>", function()
 	local file = win.file
 	local pos = win.selection.pos
 	if not pos then return end
+
 	local range = file:text_object_word(pos > 0 and pos-1 or pos);
 	if not range then return end
 	if range.finish > pos then range.finish = pos end
 	if range.start == range.finish then return end
 	local prefix = file:content(range)
 	if not prefix then return end
-	local cmd = string.format("vis-complete --word '%s'", prefix:gsub("'", "'\\''"))
-	local status, out, err = vis:pipe(file, { start = 0, finish = file.size }, cmd)
+
+	vis:feedkeys("<vis-selections-save><Escape><Escape>")
+	-- collect words starting with prefix
+	vis:command("x/\\b" .. prefix .. "\\w+/")
+	local candidates = {}
+	for sel in win:selections_iterator() do
+		table.insert(candidates, file:content(sel.range))
+	end
+	vis:feedkeys("<Escape><Escape><vis-selections-restore>")
+	if #candidates == 1 and candidates[1] == "\n" then return end
+	candidates = table.concat(candidates, "\n")
+
+	local cmd = "printf '" .. candidates .. "' | sort -u | vis-menu"
+	local status, out, err = vis:pipe(cmd)
 	if status ~= 0 or not out then
 		if err then vis:info(err) end
 		return
 	end
+	out = out:sub(#prefix + 1, #out - 1)
 	file:insert(pos, out)
 	win.selection.pos = pos + #out
 end, "Complete word in file")