a.lua

local a = function ()
   print("i am a")
end

error("no")

return a

b.lua

local a = require('a')
local b = {}

function b.begin()
   a()
end

builder.lua

local input = arg

-- This line defines the addition of a chunk to a preload entry.

local function fpreload(mod, func, strip)
   local s = 'package.preload["%s"] = load(%q)();'
   return s:format(mod, string.dump(func, strip))
end

local function fload(func, strip)
   local s = 'load(%q)();'
   return s:format(string.dump(func, strip))
end

local preloads = {}

for ix, mod in ipairs(arg) do
   local file = mod .. ".lua"
   local chunk = assert(loadfile(file))

   local s
   if ix < #arg then
      s = fpreload(mod, chunk, false)
   else
      s = fload(chunk, false)
   end
   table.insert(preloads, s)
end

local final = table.concat(preloads, "\n")
local out = io.open("../out.luac", "w")

-- Dump the combined preload chunk. Strip debugging information out of
-- this final piece. User-defined files above maintain their debugging
-- information for now.
out:write(string.dump(assert(load(final)), true))

Example usage:

$ lua-5.3 builder.lua a b
$ cd ..
$ lua-5.3 out.luac
lua: a.lua:5: no
stack traceback:
    [C]: in function 'error'
    a.lua:5: in main chunk  <--- notice it saw the error in the combined file at the right place
    ?: in main chunk
    [C]: in ?