From c229ed597f939eacfe1e9b7113e2a082fe93a3ae Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Wed, 16 Jul 2014 11:51:36 -0300
Subject: 'requiref' checks 'package.loaded' before loading a module

---
 lauxlib.c | 26 +++++++++++++++-----------
 ltests.c  |  9 +++++++--
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/lauxlib.c b/lauxlib.c
index 0ad4cc59..563362e5 100644
--- a/lauxlib.c
+++ b/lauxlib.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lauxlib.c,v 1.263 2014/05/12 21:44:17 roberto Exp roberto $
+** $Id: lauxlib.c,v 1.264 2014/06/26 17:25:11 roberto Exp roberto $
 ** Auxiliary functions for building Lua libraries
 ** See Copyright Notice in lua.h
 */
@@ -883,22 +883,26 @@ LUALIB_API int luaL_getsubtable (lua_State *L, int idx, const char *fname) {
 
 
 /*
-** stripped-down 'require'. Calls 'openf' to open a module,
-** registers the result in 'package.loaded' table and, if 'glb'
-** is true, also registers the result in the global table.
+** Stripped-down 'require': After checking "loaded" table, calls 'openf'
+** to open a module, registers the result in 'package.loaded' table and,
+** if 'glb' is true, also registers the result in the global table.
 ** Leaves resulting module on the top.
 */
 LUALIB_API void luaL_requiref (lua_State *L, const char *modname,
                                lua_CFunction openf, int glb) {
-  lua_pushcfunction(L, openf);
-  lua_pushstring(L, modname);  /* argument to open function */
-  lua_call(L, 1, 1);  /* open module */
   luaL_getsubtable(L, LUA_REGISTRYINDEX, "_LOADED");
-  lua_pushvalue(L, -2);  /* make copy of module (call result) */
-  lua_setfield(L, -2, modname);  /* _LOADED[modname] = module */
-  lua_pop(L, 1);  /* remove _LOADED table */
+  lua_getfield(L, -1, modname);  /* _LOADED[modname] */
+  if (!lua_toboolean(L, -1)) {  /* package not already loaded? */
+    lua_pop(L, 1);  /* remove field */
+    lua_pushcfunction(L, openf);
+    lua_pushstring(L, modname);  /* argument to open function */
+    lua_call(L, 1, 1);  /* call 'openf' to open module */
+    lua_pushvalue(L, -1);  /* make copy of module (call result) */
+    lua_setfield(L, -3, modname);  /* _LOADED[modname] = module */
+  }
+  lua_remove(L, -2);  /* remove _LOADED table */
   if (glb) {
-    lua_pushvalue(L, -1);  /* copy of 'mod' */
+    lua_pushvalue(L, -1);  /* copy of module */
     lua_setglobal(L, modname);  /* _G[modname] = module */
   }
 }
diff --git a/ltests.c b/ltests.c
index f72d413c..d6474335 100644
--- a/ltests.c
+++ b/ltests.c
@@ -1,5 +1,5 @@
 /*
-** $Id: ltests.c,v 2.173 2014/06/19 18:29:30 roberto Exp roberto $
+** $Id: ltests.c,v 2.174 2014/06/26 17:25:11 roberto Exp roberto $
 ** Internal Module for Debugging of the Lua Implementation
 ** See Copyright Notice in lua.h
 */
@@ -839,7 +839,12 @@ static int loadlib (lua_State *L) {
   };
   lua_State *L1 = getstate(L);
   int i;
-  luaL_requiref(L1, "package", luaopen_package, 1);
+  luaL_requiref(L1, "package", luaopen_package, 0);
+  lua_assert(lua_type(L1, -1) == LUA_TTABLE);
+  /* 'requiref' should not reload module already loaded... */
+  luaL_requiref(L1, "package", NULL, 1);  /* seg. fault if it reloads */
+  /* ...but should return the same module */
+  lua_assert(lua_compare(L1, -1, -2, LUA_OPEQ));
   luaL_getsubtable(L1, LUA_REGISTRYINDEX, "_PRELOAD");
   for (i = 0; libs[i].name; i++) {
     lua_pushcfunction(L1, libs[i].func);
-- 
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