Add ObjectRef:is_valid method

doc/lua_api.md

@@ -7815,6 +7815,10 @@ child will follow movement and rotation of that bone.
 
 ### Methods
 
+* `is_valid()`: returns whether the object is valid.
+   Objects may be invalidated either through explicit removal,
+   or implicitly between server steps by the engine.
+   **The below methods should only be called for valid objects.**
 * `get_pos()`: returns position as vector `{x=num, y=num, z=num}`
 * `set_pos(pos)`:
     * Sets the position of the object.

games/devtest/mods/unittests/entity.lua

@@ -71,13 +71,13 @@ local function test_entity_lifecycle(_, pos)
 
 	-- with binary in staticdata
 	local obj = core.add_entity(pos, "unittests:callbacks", "abc\000def")
+	assert(obj:is_valid())
 	check_log({"on_activate(7)"})
 
 	obj:set_hp(0)
 	check_log({"on_death(nil)", "on_deactivate(true)"})
 
-	-- objectref must be invalid now
-	assert(obj:get_velocity() == nil)
+	assert(not obj:is_valid())
 end
 unittests.register("test_entity_lifecycle", test_entity_lifecycle, {map=true})
 

src/script/lua_api/l_object.cpp

@@ -19,6 +19,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #include "lua_api/l_object.h"
 #include <cmath>
+#include <lua.h>
 #include "lua_api/l_internal.h"
 #include "lua_api/l_inventory.h"
 #include "lua_api/l_item.h"
@@ -106,6 +107,13 @@ int ObjectRef::l_remove(lua_State *L)
 	return 0;
 }
 
+// is_valid(self)
+int ObjectRef::l_is_valid(lua_State *L)
+{
+	lua_pushboolean(L, getobject(checkObject<ObjectRef>(L, 1)) != nullptr);
+	return 1;
+}
+
 // get_pos(self)
 int ObjectRef::l_get_pos(lua_State *L)
 {
@@ -2646,6 +2654,7 @@ const char ObjectRef::className[] = "ObjectRef";
 luaL_Reg ObjectRef::methods[] = {
 	// ServerActiveObject
 	luamethod(ObjectRef, remove),
+	luamethod(ObjectRef, is_valid),
 	luamethod_aliased(ObjectRef, get_pos, getpos),
 	luamethod_aliased(ObjectRef, set_pos, setpos),
 	luamethod(ObjectRef, add_pos),

src/script/lua_api/l_object.h

@@ -67,6 +67,9 @@ class ObjectRef : public ModApiBase {
 	// remove(self)
 	static int l_remove(lua_State *L);
 
+	// is_valid(self)
+	static int l_is_valid(lua_State *L);
+
 	// get_pos(self)
 	static int l_get_pos(lua_State *L);