Add default_mapgen game setting (#16238)

Author: Xeno333

builtin/mainmenu/dlg_create_world.lua

@@ -96,6 +96,8 @@ local function create_world_formspec(dialogdata)
 	if game ~= nil then
 		local gameconfig = Settings(game.path.."/game.conf")
 
+		current_mg = current_mg or gameconfig:get("default_mapgen") or core.settings:get("mg_name")
+
 		local allowed_mapgens = (gameconfig:get("allowed_mapgens") or ""):split()
 		for key, value in pairs(allowed_mapgens) do
 			allowed_mapgens[key] = value:trim()
@@ -456,7 +458,6 @@ function create_create_world_dlg()
 		worldname = "",
 		-- settings the world is created with:
 		seed = core.settings:get("fixed_map_seed") or "",
-		mg = core.settings:get("mg_name"),
 		flags = {
 			main = core.settings:get_flags("mg_flags"),
 			v5 = core.settings:get_flags("mgv5_spflags"),

doc/lua_api.md

@@ -84,6 +84,9 @@ The game directory can contain the following files:
       When both `allowed_mapgens` and `disallowed_mapgens` are
       specified, `allowed_mapgens` is applied before
       `disallowed_mapgens`.
+    * `default_mapgen`
+      e.g. `default_mapgen = valleys`
+      Set default mapgen for game, this will be the default selection when creating a new world.
     * `disallowed_mapgen_settings= <comma-separated mapgen settings>`
       e.g. `disallowed_mapgen_settings = mgv5_spflags`
       These mapgen settings are hidden for this game in the world creation