Add core.obejcts_by_guid table, doc and test for it.

builtin/game/features.lua

@@ -35,6 +35,7 @@ core.features = {
 	wallmounted_rotate = true,
 	item_specific_pointabilities = true,
 	blocking_pointability_type = true,
+	have_guids = true,
 }
 
 function core.has_feature(arg)

doc/lua_api.md

@@ -5302,6 +5302,8 @@ Utilities
       item_specific_pointabilities = true,
       -- Nodes `pointable` property can be `"blocking"` (5.9.0)
       blocking_pointability_type = true,
+      -- objects have get_guid method and lua entities alse set_guid method (5.9.0)
+      have_guids = true,
   }
   ```
 
@@ -7022,6 +7024,8 @@ Global tables
       as they are only read when spawning.
 * `minetest.object_refs`
     * Map of object references, indexed by active object id
+* `minetest.objects_by_guid`
+    * Map of object references, indexed by active object GUID
 * `minetest.luaentities`
     * Map of Lua entities, indexed by active object id
 * `minetest.registered_abms`

games/devtest/mods/unittests/entity.lua

@@ -158,10 +158,12 @@ local function test_entity_guid(_, pos)
 	obj:remove()
 	check_log({"on_deactivate(true)"})
 
+	assert(core.objects_by_guid["@UNITTEST"]==nil)
 	obj = core.add_entity(pos, "unittests:guid")
 	check_log({"on_activate(0)"})
 
 	assert(obj:get_guid()=="@UNITTEST")
+	assert(core.objects_by_guid["@UNITTEST"]~=nil)
 
 	obj:remove()
 end

src/script/cpp_api/s_base.cpp

@@ -399,11 +399,12 @@ void ScriptApiBase::setOriginFromTableRaw(int index, const char *fxn)
 /*
  * How ObjectRefs are handled in Lua:
  * When an active object is created, an ObjectRef is created on the Lua side
- * and stored in core.object_refs[id].
+ * and stored in core.object_refs[id] and in core.objects_by_guids[[GUID].
  * Methods that require an ObjectRef to a certain object retrieve it from that
  * table instead of creating their own.(*)
  * When an active object is removed, the existing ObjectRef is invalidated
- * using ::set_null() and removed from the core.object_refs table.
+ * using ::set_null() and removed from the core.object_refs and
+ * core.object_by_guids tables.
  * (*) An exception to this are NULL ObjectRefs and anonymous ObjectRefs
  *     for objects without ID.
  *     It's unclear what the latter are needed for and their use is problematic
@@ -431,13 +432,35 @@ void ScriptApiBase::addObjectReference(ServerActiveObject *cobj)
 	lua_settable(L, objectstable);
 }
 
+void ScriptApiBase::addObjectByGuid(ServerActiveObject *cobj)
+{
+	SCRIPTAPI_PRECHECKHEADER
+	assert(getType() == ScriptingType::Server);
+
+	// Create object on stack
+	ObjectRef::create(L, cobj); // Puts ObjectRef (as userdata) on stack
+	int object = lua_gettop(L);
+
+	// Get core.objects_by_guid table
+	lua_getglobal(L, "core");
+	lua_getfield(L, -1, "objects_by_guid");
+	luaL_checktype(L, -1, LUA_TTABLE);
+	int objectstable = lua_gettop(L);
+
+	// objects_by_guid[GUID] = object
+	lua_pushstring(L, cobj->getGuid().c_str()); // Push GUID
+	lua_pushvalue(L, object); // Copy object to top of stack
+	lua_settable(L, objectstable);
+}
+
 void ScriptApiBase::removeObjectReference(ServerActiveObject *cobj)
 {
 	SCRIPTAPI_PRECHECKHEADER
 	assert(getType() == ScriptingType::Server);
 
 	// Get core.object_refs table
 	lua_getglobal(L, "core");
+	int core = lua_gettop(L);
 	lua_getfield(L, -1, "object_refs");
 	luaL_checktype(L, -1, LUA_TTABLE);
 	int objectstable = lua_gettop(L);
@@ -450,7 +473,17 @@ void ScriptApiBase::removeObjectReference(ServerActiveObject *cobj)
 	lua_pop(L, 1); // pop object
 
 	// Set object_refs[id] = nil
-	lua_pushnumber(L, cobj->getId()); // Push id
+	lua_pushnumber(L, cobj->getId()); // Push GUID
+	lua_pushnil(L);
+	lua_settable(L, objectstable);
+
+	// Get core.objects_by_guid
+	lua_getfield(L, core, "objects_by_guid");
+	luaL_checktype(L, -1, LUA_TTABLE);
+	objectstable = lua_gettop(L);
+
+	// Set objects_by_guid[GUID] = nil
+	lua_pushstring(L, cobj->getGuid().c_str()); // Push GUID
 	lua_pushnil(L);
 	lua_settable(L, objectstable);
 }

src/script/cpp_api/s_base.h

@@ -98,6 +98,7 @@ class ScriptApiBase : protected LuaHelper {
 
 	/* object */
 	void addObjectReference(ServerActiveObject *cobj);
+	void addObjectByGuid(ServerActiveObject *cobj);
 	void removeObjectReference(ServerActiveObject *cobj);
 
 	ScriptingType getType() { return m_type; }

src/script/scripting_server.cpp

@@ -75,6 +75,9 @@ ServerScripting::ServerScripting(Server* server):
 	lua_newtable(L);
 	lua_setfield(L, -2, "object_refs");
 
+	lua_newtable(L);
+	lua_setfield(L, -2, "objects_by_guid");
+
 	lua_newtable(L);
 	lua_setfield(L, -2, "luaentities");
 

src/serverenvironment.cpp

@@ -1906,6 +1906,8 @@ u16 ServerEnvironment::addActiveObjectRaw(std::unique_ptr<ServerActiveObject> ob
 	m_script->addObjectReference(object);
 	// Post-initialize object
 	object->addedToEnvironment(dtime_s);
+	// After post-initialize, GUID is known
+	m_script->addObjectByGuid(object);
 
 	// Add static data to block
 	if (object->isStaticAllowed()) {