Why my plugin keeps adding an extra line to a script source?

I am working on a plugin that helps you edit and fix your code.

I made a 'replace keyword' system but when a keyword is replaced in another script source, an extra line comes in the source.

local rptext = ui.Frame.Replace.Text
local withtext = ui.Frame.With.Text
	

local lines = {}
	
for line in string.gmatch(item.Source, "[^\n]*") do
	if string.find(line,rptext) then
		local modifiedline = string.gsub(line,rptext,withtext)
			
		table.insert(lines, modifiedline)

	else
		table.insert(lines, line)

	end
		
end
	
	
item.Source = table.concat(lines,'\n')
	

i was trying to find the cause of the issue for a long time but it's kind of hard, i will make an update if i find out about it. what i could find out was that it seems to match some character after some non-empty newlines which returns nil when put into string.byte.

the solution for your case is to just string.split, there really is no need for gmatch, split the string by newlines:

local rptext = ui.Frame.Replace.Text
local withtext = ui.Frame.With.Text

local lines = string.split(item.Source, "\n")

for i, line in ipairs(lines) do
	lines[i] = string.gsub(line, rptext, withtext)
end

item.Source = table.concat(lines, "\n")

notice there is no reason to check if string.find finds something, gsub won't replace anything if it's not found, you are redundantly doing 2 pattern searches.

now let's get to feedback part, your plugin is absolute trash... like who can't just click Ctrl + H you self appointed programmer ;-;