Add lua_setlightuserdataname and lua_getlightuserdataname

VM/include/lua.h

@@ -325,6 +325,9 @@ typedef void (*lua_Destructor)(lua_State* L, void* userdata);
 LUA_API void lua_setuserdatadtor(lua_State* L, int tag, lua_Destructor dtor);
 LUA_API lua_Destructor lua_getuserdatadtor(lua_State* L, int tag);
 
+LUA_API void lua_setlightuserdataname(lua_State* L, int tag, const char* name);
+LUA_API const char* lua_getlightuserdataname(lua_State* L, int tag);
+
 LUA_API void lua_clonefunction(lua_State* L, int idx);
 
 LUA_API void lua_cleartable(lua_State* L, int idx);

VM/include/luaconf.h

@@ -101,6 +101,11 @@
 #define LUA_UTAG_LIMIT 128
 #endif
 
+// number of valid Lua lightuserdata tags
+#ifndef LUA_LUTAG_LIMIT
+#define LUA_LUTAG_LIMIT 128
+#endif
+
 // upper bound for number of size classes used by page allocator
 #ifndef LUA_SIZECLASSES
 #define LUA_SIZECLASSES 32

VM/src/lapi.cpp

@@ -681,6 +681,7 @@ void lua_pushboolean(lua_State* L, int b)
 
 void lua_pushlightuserdatatagged(lua_State* L, void* p, int tag)
 {
+    api_check(L, unsigned(tag) < LUA_LUTAG_LIMIT);
     setpvalue(L->top, p);
     L->top->extra[0] = tag;
     api_incr_top(L);
@@ -1427,6 +1428,24 @@ lua_Destructor lua_getuserdatadtor(lua_State* L, int tag)
     return L->global->udatagc[tag];
 }
 
+void lua_setlightuserdataname(lua_State* L, int tag, const char* name)
+{
+    api_check(L, unsigned(tag) < LUA_LUTAG_LIMIT);
+    api_check(L, !L->global->lightuserdataname[tag]); // renaming not supported
+    if (!L->global->lightuserdataname[tag])
+    {
+        L->global->lightuserdataname[tag] = luaS_new(L, name);
+        luaS_fix(L->global->lightuserdataname[tag]); // never collect these names
+    }
+}
+
+const char* lua_getlightuserdataname(lua_State* L, int tag)
+{
+    api_check(L, unsigned(tag) < LUA_LUTAG_LIMIT);
+    const TString* name = L->global->lightuserdataname[tag];
+    return name ? getstr(name) : nullptr;
+}
+
 void lua_clonefunction(lua_State* L, int idx)
 {
     luaC_checkGC(L);

VM/src/lstate.cpp

@@ -210,6 +210,8 @@ lua_State* lua_newstate(lua_Alloc f, void* ud)
         g->mt[i] = NULL;
     for (i = 0; i < LUA_UTAG_LIMIT; i++)
         g->udatagc[i] = NULL;
+    for (i = 0; i < LUA_LUTAG_LIMIT; i++)
+        g->lightuserdataname[i] = NULL;
     for (i = 0; i < LUA_MEMORY_CATEGORIES; i++)
         g->memcatbytes[i] = 0;
 

VM/src/lstate.h

@@ -197,6 +197,7 @@ typedef struct global_State
     struct Table* mt[LUA_T_COUNT];                   // metatables for basic types
     TString* ttname[LUA_T_COUNT];       // names for basic types
     TString* tmname[TM_N];             // array with tag-method names
+    TString* lightuserdataname[LUA_LUTAG_LIMIT]; // names for tagged lightuserdata
 
     TValue pseudotemp; // storage for temporary values used in pseudo2addr
 

VM/src/ltm.cpp

@@ -129,6 +129,13 @@ const TString* luaT_objtypenamestr(lua_State* L, const TValue* o)
         if (ttisstring(type))
             return tsvalue(type);
     }
+    if (ttislightuserdata(o) && o->extra[0] != 0)
+    {
+        const TString* name = L->global->lightuserdataname[o->extra[0]];
+
+        if (name)
+            return name;
+    }
     else if (Table* mt = L->global->mt[ttype(o)])
     {
         const TValue* type = luaH_getstr(mt, L->global->tmname[TM_TYPE]);

tests/Conformance.test.cpp

@@ -1684,6 +1684,11 @@ TEST_CASE("LightuserdataApi")
     CHECK(lua_tolightuserdatatagged(L, -1, 0) == nullptr);
     CHECK(lua_tolightuserdatatagged(L, -1, 1) == value);
 
+    lua_setlightuserdataname(L, 1, "id");
+    CHECK(!lua_getlightuserdataname(L, 0));
+    CHECK(strcmp(lua_getlightuserdataname(L, 1), "id") == 0);
+    CHECK(strcmp(luaL_typename(L, -1), "id") == 0);
+
     globalState.reset();
 }