From Lua 5.2: debug.getinfo(..., "u") returns nparams and isvararg.

src/Makefile.dep

@@ -8,7 +8,7 @@ lib_base.o: lib_base.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h \
 lib_bit.o: lib_bit.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h lj_def.h \
  lj_arch.h lj_err.h lj_errmsg.h lj_str.h lj_lib.h lj_libdef.h
 lib_debug.o: lib_debug.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h \
- lj_def.h lj_arch.h lj_err.h lj_errmsg.h lj_lib.h lj_libdef.h
+ lj_def.h lj_arch.h lj_err.h lj_errmsg.h lj_debug.h lj_lib.h lj_libdef.h
 lib_ffi.o: lib_ffi.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h lj_def.h \
  lj_arch.h lj_gc.h lj_err.h lj_errmsg.h lj_str.h lj_tab.h lj_meta.h \
  lj_ctype.h lj_cparse.h lj_cdata.h lj_cconv.h lj_carith.h lj_ccall.h \

src/lib_debug.c

@@ -15,6 +15,7 @@
 
 #include "lj_obj.h"
 #include "lj_err.h"
+#include "lj_debug.h"
 #include "lj_lib.h"
 
 /* ------------------------------------------------------------------------ */
@@ -77,6 +78,12 @@ static void settabsi(lua_State *L, const char *i, int v)
   lua_setfield(L, -2, i);
 }
 
+static void settabsb(lua_State *L, const char *i, int v)
+{
+  lua_pushboolean(L, v);
+  lua_setfield(L, -2, i);
+}
+
 static lua_State *getthread(lua_State *L, int *arg)
 {
   if (L->base < L->top && tvisthread(L->base)) {
@@ -101,12 +108,12 @@ static void treatstackoption(lua_State *L, lua_State *L1, const char *fname)
 
 LJLIB_CF(debug_getinfo)
 {
-  lua_Debug ar;
+  lj_Debug ar;
   int arg, opt_f = 0, opt_L = 0;
   lua_State *L1 = getthread(L, &arg);
   const char *options = luaL_optstring(L, arg+2, "flnSu");
   if (lua_isnumber(L, arg+1)) {
-    if (!lua_getstack(L1, (int)lua_tointeger(L, arg+1), &ar)) {
+    if (!lua_getstack(L1, (int)lua_tointeger(L, arg+1), (lua_Debug *)&ar)) {
       setnilV(L->top-1);
       return 1;
     }
@@ -116,7 +123,7 @@ LJLIB_CF(debug_getinfo)
   } else {
     lj_err_arg(L, arg+1, LJ_ERR_NOFUNCL);
   }
-  if (!lua_getinfo(L1, options, &ar))
+  if (!lj_debug_getinfo(L1, options, &ar, 1))
     lj_err_arg(L, arg+2, LJ_ERR_INVOPT);
   lua_createtable(L, 0, 16);  /* Create result table. */
   for (; *options; options++) {
@@ -133,6 +140,8 @@ LJLIB_CF(debug_getinfo)
       break;
     case 'u':
       settabsi(L, "nups", ar.nups);
+      settabsi(L, "nparams", ar.nparams);
+      settabsb(L, "isvararg", ar.isvararg);
       break;
     case 'n':
       settabss(L, "name", ar.name);

src/lj_debug.c

@@ -423,7 +423,7 @@ LUA_API const char *lua_setlocal(lua_State *L, const lua_Debug *ar, int n)
   return name;
 }
 
-LUA_API int lua_getinfo(lua_State *L, const char *what, lua_Debug *ar)
+int lj_debug_getinfo(lua_State *L, const char *what, lj_Debug *ar, int ext)
 {
   int opt_f = 0, opt_L = 0;
   TValue *frame = NULL;
@@ -471,6 +471,16 @@ LUA_API int lua_getinfo(lua_State *L, const char *what, lua_Debug *ar)
       ar->currentline = frame ? debug_frameline(L, fn, nextframe) : -1;
     } else if (*what == 'u') {
       ar->nups = fn->c.nupvalues;
+      if (ext) {
+	if (isluafunc(fn)) {
+	  GCproto *pt = funcproto(fn);
+	  ar->nparams = pt->numparams;
+	  ar->isvararg = !!(pt->flags & PROTO_VARARG);
+	} else {
+	  ar->nparams = 0;
+	  ar->isvararg = 1;
+	}
+      }
     } else if (*what == 'n') {
       ar->namewhat = frame ? lj_debug_funcname(L, frame, &ar->name) : NULL;
       if (ar->namewhat == NULL) {
@@ -515,6 +525,11 @@ LUA_API int lua_getinfo(lua_State *L, const char *what, lua_Debug *ar)
   return 1;  /* Ok. */
 }
 
+LUA_API int lua_getinfo(lua_State *L, const char *what, lua_Debug *ar)
+{
+  return lj_debug_getinfo(L, what, (lj_Debug *)ar, 0);
+}
+
 LUA_API int lua_getstack(lua_State *L, int level, lua_Debug *ar)
 {
   int size;

src/lj_debug.h

@@ -8,6 +8,24 @@
 
 #include "lj_obj.h"
 
+typedef struct lj_Debug {
+  /* Common fields. Must be in the same order as in lua.h. */
+  int event;
+  const char *name;
+  const char *namewhat;
+  const char *what;
+  const char *source;
+  int currentline;
+  int nups;
+  int linedefined;
+  int lastlinedefined;
+  char short_src[LUA_IDSIZE];
+  int i_ci;
+  /* Extended fields. Only valid if lj_debug_getinfo() is called with ext = 1.*/
+  int nparams;
+  int isvararg;
+} lj_Debug;
+
 LJ_FUNC cTValue *lj_debug_frame(lua_State *L, int level, int *size);
 LJ_FUNC BCLine LJ_FASTCALL lj_debug_line(GCproto *pt, BCPos pc);
 LJ_FUNC const char *lj_debug_uvname(GCproto *pt, uint32_t idx);
@@ -20,6 +38,8 @@ LJ_FUNC void lj_debug_shortname(char *out, GCstr *str);
 LJ_FUNC void lj_debug_addloc(lua_State *L, const char *msg,
 			     cTValue *frame, cTValue *nextframe);
 LJ_FUNC void lj_debug_pushloc(lua_State *L, GCproto *pt, BCPos pc);
+LJ_FUNC int lj_debug_getinfo(lua_State *L, const char *what, lj_Debug *ar,
+			     int ext);
 
 /* Fixed internal variable names. */
 #define VARNAMEDEF(_) \