Unreachable code detector using luacheck

dead_code.lua

-- Requires luacheck scm-6
-- Reads a Lua program from stdin, prints warnings for unreachable code in top level closure.
-- Crashes on `break` or `goto` or labels.
local flow = require "luacheck.flow"
local parser = require "metalua.compiler".new()

local src = assert(io.stdin:read("*a"))
local ast = assert(parser:src_to_ast(src))
local intel = {closures = {{stmts = ast}}, gotos = {}}
flow(intel)

local graph = intel.closures[1].flow
local nodes = intel.flow_nodes

local marked = {}

local function mark(node)
   marked[node] = true

   for i=1, #node.nexts do
      if not marked[node.nexts[i]] then
         mark(node.nexts[i])
      end
   end
end

mark(graph)

for i=1, #nodes do
   if not marked[nodes[i]] then
      if nodes[i].ast_node then
         print("Dead code at line "..nodes[i].ast_node.lineinfo.first.line)
         mark(nodes[i])
      end
   end
end