_G is now equivalent to std for Lua version used to run Luacheck

src/luacheck/builtin_standards.lua

@@ -266,6 +266,22 @@ for name, def in pairs(lua_defs) do
    builtin_standards[name] = def_to_std(def)
 end
 
+local function detect_default_std()
+   if rawget(_G, "jit") then
+      return "luajit"
+   elseif _VERSION == "Lua 5.1" then
+      return "lua51c"
+   elseif _VERSION == "Lua 5.2" then
+      return "lua52c"
+   elseif _VERSION == "Lua 5.3" then
+      return "lua53c"
+   else
+      return "max"
+   end
+end
+
+builtin_standards._G = builtin_standards[detect_default_std()]
+
 builtin_standards.busted = {
    read_globals = {
       "describe", "insulate", "expose", "it", "pending", "before_each", "after_each",
@@ -281,30 +297,6 @@ builtin_standards.rockspec = {
    }
 }
 
-local function make_globals_std()
-   local globals_std = {globals = {}, read_globals = {}}
-
-   for global in pairs(_G) do
-      if global == "_G" or global == "package" then
-         table.insert(globals_std.globals, global)
-      else
-         table.insert(globals_std.read_globals, global)
-      end
-   end
-
-   local function has_env()
-      local _ENV = {} -- luacheck: ignore
-      return not _G
-   end
-
-   if has_env() then
-      table.insert(globals_std.globals, "_ENV")
-   end
-
-   return globals_std
-end
-
-builtin_standards._G = make_globals_std()
 builtin_standards.none = {}
 
 return builtin_standards

src/luacheck/main.lua

@@ -1,5 +1,6 @@
 local luacheck = require "luacheck"
 local argparse = require "luacheck.argparse"
+local builtin_standards = require "luacheck.builtin_standards"
 local config = require "luacheck.config"
 local options = require "luacheck.options"
 local expand_rockspec = require "luacheck.expand_rockspec"
@@ -47,27 +48,39 @@ together with used ones.]]):target("unused_secondaries"):action("store_false")
       parser:flag("--no-self", "Filter out warnings related to implicit self argument.")
          :target("self"):action("store_false")
 
-      parser:option("--std", [[Set standard globals. <std> can be one of:
-   _G (default) - globals of the current Lua
-      interpreter;
+      local default_std_name = "max"
+
+      for _, name in ipairs({"lua51c", "lua52c", "lua53c", "luajit"}) do
+         if builtin_standards._G == builtin_standards[name] then
+            default_std_name = name
+            break
+         end
+      end
+
+      parser:option("--std", ([[Set standard globals, default is _G.
+<std> can be one of:
    lua51 - globals of Lua 5.1 without deprecated ones;
-   lua5c - globals of Lua 5.1;
+   lua51c - globals of Lua 5.1;
    lua52 - globals of Lua 5.2;
    lua52c - globals of Lua 5.2 with LUA_COMPAT_ALL;
    lua53 - globals of Lua 5.3;
    lua53c - globals of Lua 5.3 with LUA_COMPAT_5_2;
    luajit - globals of LuaJIT 2.0;
    ngx_lua - globals of Openresty lua-nginx-module
       with LuaJIT 2.0;
-   rockspec - globals allowed in rockspecs;
    min - intersection of globals of Lua 5.1, Lua 5.2,
       Lua 5.3 and LuaJIT 2.0;
    max - union of globals of Lua 5.1, Lua 5.2, Lua 5.3
       and LuaJIT 2.0;
+   _G - same as lua51c, lua52c, lua53c, or luajit
+      depending on version of Lua used to run luacheck
+      or same as max if couldn't detect the version.
+      Currently %s;
    busted - globals added by Busted 2.0;
+   rockspec - globals allowed in rockspecs;
    none - no standard globals.
 
-   Sets can be combined using "+".]])
+   Sets can be combined using "+".]]):format(default_std_name))
       parser:option("--globals", "Add custom globals on top of standard ones.")
          :args "*"
          :count "*"