The documentation and the implementation of the two functions
lua.setluaname and lua.getluaname do not match.

Minimal working example (MWE):

% lua.setluaname(42, '@filename') not working
\directlua{
  lua.setluaname(nil, 42, '@filename')
}
\directlua 42 {xxx}
\bye


This is how the parameters should be arranged in the set function:

lua.setluaname(<number> n, <string> s)
<string> s = lua.getluaname(<number> n)

# Patch:

diff --git a/manual/luatex-tex.tex b/manual/luatex-tex.tex
index f8c3d5ac6..e953a1802 100644
--- a/manual/luatex-tex.tex
+++ b/manual/luatex-tex.tex
@@ -96,7 +96,7 @@ If you want to unset a \LUA\ name, you can assign
\type {nil} to it. The functio
 accessors are:

 \startfunctioncall
-lua.setluaname(<string> s,<number> n])
+lua.setluaname(<number> n, <string> s)
 <string> s = lua.getluaname(<number> n)
 \stopfunctioncall

@@ -2747,7 +2747,6 @@ The options match commandline arguments from \type
{kpsewhich}:
 If \type {--output-directory} is specified and the value is a relative
pathname,
 the file is searched first here and then in the standard tree.

-
 \stopsubsection

 \startsubsection[title={\type {init_prog}}]
diff --git a/source/texk/web2c/luatexdir/lua/llualib.c
b/source/texk/web2c/luatexdir/lua/llualib.c
index 0586aba02..d91a9a729 100644
--- a/source/texk/web2c/luatexdir/lua/llualib.c
+++ b/source/texk/web2c/luatexdir/lua/llualib.c
@@ -319,8 +319,8 @@ static int set_luaname(lua_State * L)
 {
     int k;
     const char *s;
-    if (lua_gettop(L) == 3) {
-        k = (int) luaL_checkinteger(L, 2);
+    if (lua_gettop(L) == 2) {
+        k = (int) luaL_checkinteger(L, 1);
         if (k > 65535 || k < 0) {
             /* error */
         } else {
@@ -328,8 +328,8 @@ static int set_luaname(lua_State * L)
                 free(luanames[k]);
                 luanames[k] = NULL;
             }
-            if (lua_type(L,3) == LUA_TSTRING) {
-                s = lua_tostring(L, 3);
+            if (lua_type(L, 2) == LUA_TSTRING) {
+                s = lua_tostring(L, 2);
                 if (s != NULL)
                     luanames[k] = xstrdup(s);
             }
@@ -340,7 +340,7 @@ static int set_luaname(lua_State * L)

 static int get_luaname(lua_State * L)
 {
-    int k = (int) luaL_checkinteger(L, 2);
+    int k = (int) luaL_checkinteger(L, 1);
     if (k > 65535 || k < 0) {
         /* error */
         lua_pushnil(L);