An extended undefined variable checker for Lua 5.1 using bytecode analysis based on David Manura's globalplus.lua http://lua-users.org/wiki/DetectingUndefinedVariables

globalsplus.lua

-- globalsplus.lua
-- Like globals.lua in Lua 5.1.4 -- globalsplus.lua
-- Like globals.lua in Lua 5.1.4 but records fields in global tables too.
-- Probably works but not well tested.  Could be extended even further.
--
-- usage: lua globalsplus.lua example.lua
--
-- D.Manura, 2010-07, public domain
--
-- See http://lua-users.org/wiki/DetectingUndefinedVariables
-- extended by Steve Donovan, 2013 with tolerant mode and explicit extra whitelist

local append = table.insert
local lua52 = _VERSION:match '5%.2$'

local load,luac = load
if not lua52 then
     function load(str,src,mode,env)
        local chunk,err = loadstring(str,src)
        if err then return nil,err end
        setfenv(chunk, env)
        return chunk
    end
    luac = 'luac'
else
    luac = 'luac52'
end

local function exists (file)
    local f = io.open(file)
    if not f then
        return nil
    else
        f:close()
        return file
    end
end

local function contents (file)
    local f = io.open(file)
    local res = f:read '*a'
    f:close()
    return res
end

local function parse(line)
    local idx,linenum,opname,arga,argb,extra =
    line:match('^%s+(%d+)%s+%[(%d+)%]%s+(%w+)%s+([-%d]+)%s+([-%d]+)%s*(.*)')
    if idx then
        idx = tonumber(idx)
        linenum = tonumber(linenum)
        arga = tonumber(arga)
        argb = tonumber(argb)
    end
    local argc, const
    if extra then
        local extra2
        argc, extra2 = extra:match('^([-%d]+)%s*(.*)')
        if argc then argc = tonumber(argc); extra = extra2 end
    end
    if extra then
        const = extra:match('^; (.+)')
    end
    return {idx=idx,linenum=linenum,opname=opname,arga=arga,argb=argb,argc=argc,const=const}
end

local function stripq (const)
    return const:match('"(.*)"')
end

local function getname (const)
    if lua52 then
        if const:match '^_ENV ' then
            return stripq(const)
        end
    else
        return const
    end
end

local function getglobals(fh,line)
    local globals, requires = {},{}
    local last
    while line do
        local data = parse(line)
        local opname = data.opname
        if opname == 'GETGLOBAL' or opname == 'GETTABUP' then
            local name = getname(data.const)
            if name then
                data.gname = name
                last = data
                append(globals, {linenum=last.linenum, name=name, isset=false})
            end
         elseif opname == 'SETGLOBAL' or opname == 'SETTABUP' then
            local name = getname(data.const)
            if name then
                append(globals, {linenum=data.linenum, name=name, isset=true})
            end
        elseif (opname == 'GETTABLE' or opname == 'SETTABLE') and last and data.const
               and last.gname and (data.idx - last.idx <= 2) and last.arga == data.arga
        then
            local name = stripq(data.const)
            if name then
                data.gname = last.gname .. '.' .. name
                append(globals, {linenum=last.linenum, name=data.gname, isset=data.opname=='SETTABLE'})
                last = nil
            end
        elseif data.opname == 'LOADK' then
            if last and last.const == 'require' then
                append(requires,{linenum=last.linenum,name=stripq(data.const)})
            else
                last = nil
            end
        elseif next(data) == nil then -- end of function disassembly --
            last = nil
        end
        line = fh:read()
    end
    return globals, requires
end

local function rindex(t, name)
    local top,last_t,ok = t
    for part in name:gmatch('[%w_]+') do
        last_t = t
        ok,t = pcall(function() return t[part] end)
        if not ok or t == nil then return nil, last_t ~= top end
    end
    return t
end

local function load_whitelist (file)
    local res = {}
    local chunk,err = load(contents(file),'tmp','t',res)
    if err then
        print("whitelist compilation error",err)
        return nil
    end
    local ok,err = pcall(chunk)
    if not ok then
        print("whitelist runtime error",err)
        return nil
    end
    return res
end

local whitelist = _G

if #arg == 0 then
    print [[
    usage: [-t] [-w whitelist] <script>
      where t means "tolerant"; required modules are loaded, defined globals are ok
      -w loads a whitelist, which is a file containing symbol={entries..} lines
      If globals.whitelist exists, use that implicitly.
      Unless tolerant, warn about altering known globals.
    ]]
    return
end
local tolerant, extra_whitelist = false, nil
local idx = 1
if arg[idx] == '-t' then
    tolerant = true
    idx = idx + 1
end
if arg[idx] == '-w' then
    extra_whitelist = load_whitelist(arg[idx+1])
    idx = idx + 2
end
local file = arg[idx]
if not file then
    print 'no file provided!'
    return
end

if exists('global.whitelist') then
    extra_whitelist = load_whitelist 'global.whitelist'
end

local inf = io.popen(luac..' -p -l '..file)
local line = inf:read()
if not line then -- we hit
    return
end
local globals, requires = getglobals(inf,line)
inf:close()

if tolerant and requires then
    for _,item in ipairs(requires) do
        if not pcall(require,item.name) then
            io.write('warning: could not require "',item.name,'"\n')
        end
    end
end

if extra_whitelist then
    for k,v in pairs(extra_whitelist) do
        whitelist[k] = v
    end
end

if tolerant then
    for k,v in pairs(globals) do
        if v.isset then
            whitelist[v.name] = {}
        end
    end
end

table.sort(globals, function(a,b) return a.linenum < b.linenum end)

for i,v in ipairs(globals) do
    if v.name == nil then print(v.linenum) end
    local found, found_root = rindex(whitelist, v.name)
    if not tolerant and (found or found_root) and v.isset then
        io.write('globals: ',file,':',v.linenum,': redefining global ',v.name,'\n')
    elseif not found then
        io.write('globals: ',file,':',v.linenum,': undefined ',v.isset and 'set' or 'get',' ',v.name,'\n')
    end
end