From Lua 5.2: Add package.searchpath().

Thanks to F. Perrad.

src/lib_package.c

@@ -3,7 +3,7 @@
 ** Copyright (C) 2005-2011 Mike Pall. See Copyright Notice in luajit.h
 **
 ** Major portions taken verbatim or adapted from the Lua interpreter.
-** Copyright (C) 1994-2008 Lua.org, PUC-Rio. See Copyright Notice in lua.h
+** Copyright (C) 1994-2011 Lua.org, PUC-Rio. See Copyright Notice in lua.h
 */
 
 #define lib_package_c
@@ -210,19 +210,14 @@ static const char *pushnexttemplate(lua_State *L, const char *path)
   return l;
 }
 
-static const char *findfile(lua_State *L, const char *name,
-			    const char *pname)
+static const char *searchpath (lua_State *L, const char *name,
+			       const char *path)
 {
-  const char *path;
   name = luaL_gsub(L, name, ".", LUA_DIRSEP);
-  lua_getfield(L, LUA_ENVIRONINDEX, pname);
-  path = lua_tostring(L, -1);
-  if (path == NULL)
-    luaL_error(L, LUA_QL("package.%s") " must be a string", pname);
   lua_pushliteral(L, "");  /* error accumulator */
   while ((path = pushnexttemplate(L, path)) != NULL) {
-    const char *filename;
-    filename = luaL_gsub(L, lua_tostring(L, -1), LUA_PATH_MARK, name);
+    const char *filename = luaL_gsub(L, lua_tostring(L, -1),
+                                     LUA_PATH_MARK, name);
     lua_remove(L, -2);  /* remove path template */
     if (readable(filename))  /* does file exist and is readable? */
       return filename;  /* return that file name */
@@ -233,6 +228,29 @@ static const char *findfile(lua_State *L, const char *name,
   return NULL;  /* not found */
 }
 
+static int lj_cf_package_searchpath(lua_State *L)
+{
+  const char *f = searchpath(L, luaL_checkstring(L, 1), luaL_checkstring(L, 2));
+  if (f != NULL) {
+    return 1;
+  } else {  /* error message is on top of the stack */
+    lua_pushnil(L);
+    lua_insert(L, -2);
+    return 2;  /* return nil + error message */
+  }
+}
+
+static const char *findfile(lua_State *L, const char *name,
+			    const char *pname)
+{
+  const char *path;
+  lua_getfield(L, LUA_ENVIRONINDEX, pname);
+  path = lua_tostring(L, -1);
+  if (path == NULL)
+    luaL_error(L, LUA_QL("package.%s") " must be a string", pname);
+  return searchpath(L, name, path);
+}
+
 static void loaderror(lua_State *L, const char *filename)
 {
   luaL_error(L, "error loading module " LUA_QS " from file " LUA_QS ":\n\t%s",
@@ -459,6 +477,7 @@ static void setpath(lua_State *L, const char *fieldname, const char *envname,
 
 static const luaL_Reg package_lib[] = {
   { "loadlib",	lj_cf_package_loadlib },
+  { "searchpath",  lj_cf_package_searchpath },
   { "seeall",	lj_cf_package_seeall },
   { NULL, NULL }
 };