From e87009f5b278dec0213b6f1ed33a422f55e4ef48 Mon Sep 17 00:00:00 2001
From: Alex Orlenko <zxteam@protonmail.com>
Date: Thu, 14 Jul 2022 20:00:37 +0100
Subject: [PATCH] Add lua_setuserdatatag to update userdata tags (#588)

---
 VM/include/lua.h           | 5 +++--
 VM/src/lapi.cpp            | 8 ++++++++
 tests/Conformance.test.cpp | 4 ++++
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/VM/include/lua.h b/VM/include/lua.h
index 7f9647c8..72edb4a6 100644
--- a/VM/include/lua.h
+++ b/VM/include/lua.h
@@ -64,14 +64,14 @@ enum lua_Type
     LUA_TNIL = 0,     /* must be 0 due to lua_isnoneornil */
     LUA_TBOOLEAN = 1, /* must be 1 due to l_isfalse */
 
-    
+
     LUA_TLIGHTUSERDATA,
     LUA_TNUMBER,
     LUA_TVECTOR,
 
     LUA_TSTRING, /* all types above this must be value types, all types below this must be GC types - see iscollectable */
 
-    
+
     LUA_TTABLE,
     LUA_TFUNCTION,
     LUA_TUSERDATA,
@@ -300,6 +300,7 @@ LUA_API uintptr_t lua_encodepointer(lua_State* L, uintptr_t p);
 
 LUA_API double lua_clock();
 
+LUA_API void lua_setuserdatatag(lua_State* L, int idx, int tag);
 LUA_API void lua_setuserdatadtor(lua_State* L, int tag, void (*dtor)(lua_State*, void*));
 
 LUA_API void lua_clonefunction(lua_State* L, int idx);
diff --git a/VM/src/lapi.cpp b/VM/src/lapi.cpp
index 3c3b7bd0..c2b790ad 100644
--- a/VM/src/lapi.cpp
+++ b/VM/src/lapi.cpp
@@ -1305,6 +1305,14 @@ void lua_unref(lua_State* L, int ref)
     return;
 }
 
+void lua_setuserdatatag(lua_State* L, int idx, int tag)
+{
+    api_check(L, unsigned(tag) < LUA_UTAG_LIMIT);
+    StkId o = index2addr(L, idx);
+    api_check(L, ttisuserdata(o));
+    uvalue(o)->tag = uint8_t(tag);
+}
+
 void lua_setuserdatadtor(lua_State* L, int tag, void (*dtor)(lua_State*, void*))
 {
     api_check(L, unsigned(tag) < LUA_UTAG_LIMIT);
diff --git a/tests/Conformance.test.cpp b/tests/Conformance.test.cpp
index 3f415149..d2311348 100644
--- a/tests/Conformance.test.cpp
+++ b/tests/Conformance.test.cpp
@@ -1152,6 +1152,10 @@ TEST_CASE("UserdataApi")
     CHECK(lua_touserdatatagged(L, -1, 41) == nullptr);
     CHECK(lua_userdatatag(L, -1) == 42);
 
+    lua_setuserdatatag(L, -1, 43);
+    CHECK(lua_userdatatag(L, -1) == 43);
+    lua_setuserdatatag(L, -1, 42);
+
     // user data with inline dtor
     void* ud3 = lua_newuserdatadtor(L, 4, [](void* data) {
         dtorhits += *(int*)data;