Fixes for Lua 5.2+ (neovim#43)

Author: blueyed

nvim/_compat.lua

@@ -0,0 +1,12 @@
+-- Lua 5.1 forward-compatibility layer.
+-- For background see https://github.com/neovim/neovim/pull/9280
+--
+-- Reference the lua-compat-5.2 project for hints:
+--    https://github.com/keplerproject/lua-compat-5.2/blob/c164c8f339b95451b572d6b4b4d11e944dc7169d/compat52/mstrict.lua
+--    https://github.com/keplerproject/lua-compat-5.2/blob/c164c8f339b95451b572d6b4b4d11e944dc7169d/tests/test.lua
+
+local lua_version = _VERSION:sub(-3)
+
+if lua_version >= "5.2" then
+  unpack = table.unpack  -- luacheck: ignore 121 143
+end

nvim/native.c

@@ -15,7 +15,7 @@ static int pid_wait(lua_State *L) {
 
 static int pid_wait(lua_State *L) {
   int status;
-  pid_t pid = luaL_checkint(L, 1);
+  pid_t pid = (pid_t)luaL_checkinteger(L, 1);
   /* Work around libuv bug that leaves defunct children:
    * https://github.com/libuv/libuv/issues/154 */
   while (!kill(pid, 0)) waitpid(pid, &status, WNOHANG);

nvim/session.lua

@@ -1,6 +1,7 @@
 local coxpcall = require('coxpcall')
 local uv = require('luv')
 local MsgpackRpcStream = require('nvim.msgpack_rpc_stream')
+require('nvim._compat')
 
 
 local Session = {}

test/session_spec.lua

@@ -4,6 +4,7 @@ local SocketStream = require('nvim.socket_stream')
 local Session = require('nvim.session')
 local coxpcall = require('coxpcall')
 local busted = require('busted')
+require('nvim._compat')
 
 local nvim_prog = os.getenv('NVIM_PROG') or 'nvim'
 local child_session