Preserve immortal group for players when damage is disabled

builtin/settingtypes.txt

@@ -1085,7 +1085,7 @@ default_stack_max (Default stack size) int 99
 #    Enable players getting damage and dying.
 enable_damage (Damage) bool false
 
-#    Enable creative mode for new created maps.
+#    Enable creative mode for all players
 creative_mode (Creative) bool false
 
 #    A chosen map seed for a new map, leave empty for random.

doc/lua_api.txt

@@ -1745,8 +1745,9 @@ to games.
 ### `ObjectRef` groups
 
 * `immortal`: Skips all damage and breath handling for an object. This group
-  will also hide the integrated HUD status bars for players, and is
-  automatically set to all players when damage is disabled on the server.
+  will also hide the integrated HUD status bars for players. It is
+  automatically set to all players when damage is disabled on the server and
+  cannot be reset (subject to change).
 * `punch_operable`: For entities; disables the regular damage mechanism for
   players punching it by hand or a non-tool item, so that it can do something
   else than take damage.

src/script/lua_api/l_object.cpp

@@ -355,6 +355,15 @@ int ObjectRef::l_set_armor_groups(lua_State *L)
 	ItemGroupList groups;
 
 	read_groups(L, 2, groups);
+	if (sao->getType() == ACTIVEOBJECT_TYPE_PLAYER) {
+		if (!g_settings->getBool("enable_damage") && !itemgroup_get(groups, "immortal")) {
+			warningstream << "Mod tried to enable damage for a player, but it's "
+				"disabled globally. Ignoring." << std::endl;
+			infostream << script_get_backtrace(L) << std::endl;
+			groups["immortal"] = 1;
+		}
+	}
+
 	sao->setArmorGroups(groups);
 	return 0;
 }

src/server.cpp

@@ -1349,7 +1349,7 @@ void Server::SendPlayerHPOrDie(PlayerSAO *playersao, const PlayerHPChangeReason
 		return;
 
 	session_t peer_id = playersao->getPeerID();
-	bool is_alive = playersao->getHP() > 0;
+	bool is_alive = !playersao->isDead();
 
 	if (is_alive)
 		SendPlayerHP(peer_id);