Update marker save compatibility, wrapper for TAG_MAJOR_VERSION.

2 files changed, 34 insertions, 0 deletions

diff --git a/crawl-ref/docs/develop/save_compatibility.txt b/crawl-ref/docs/develop/save_compatibility.txt
index c2f976632b..e9a69ec35e 100644
--- a/crawl-ref/docs/develop/save_compatibility.txt
+++ b/crawl-ref/docs/develop/save_compatibility.txt
@@ -134,3 +134,30 @@ on, we should add placeholder tiles before the official release, that can
 later be replaced without affecting saved games.
 
 Johanna
+
+
+A few comments on map caches and Lua markers
+--------------------------------------------
+Map and vault definitions are read from the relevant .des files and are stored
+in a binary format to prevent slow-down every time crawl starts. If new
+attributes or properties are added to vault definitions, save-compatibility
+needs to be ensured in much the same way as for normal saves. Until recently,
+the .des cache used a different version number to the main major/minor system.
+In theory, all that needs to be done now is to bump the minor version, which
+will cause the being-loaded .des cache file to be considered invalid, and thus
+rebuilt.
+
+When modifying a Lua marker, specifically when adding new options, etc, you'll
+need to likewise ensure save compatibility. The minor version is currently
+accessible by calling file.minor_version(reader). This will return a numeric
+value that has to be manually compared to the relevant minor tag.
+
+The current major version of the software is accessible by calling
+file.major_version(). There's no need to pass the reader in, as if the major
+version of a file mis-matches, the game won't attempt to load it, and you will
+never get to a stage of being able to look for it.
+
+All Lua markers will need to be checked for minor-version checks when updating
+the major version.
+
+due
diff --git a/crawl-ref/source/l_file.cc b/crawl-ref/source/l_file.cc
index e5169c942d..dbb73b7ab8 100644
--- a/crawl-ref/source/l_file.cc
+++ b/crawl-ref/source/l_file.cc
@@ -50,6 +50,12 @@ static int file_minor_version(lua_State *ls)
     return (1);
 }
 
+static int file_major_version(lua_State *ls)
+{
+    lua_pushnumber(ls, TAG_MAJOR_VERSION);
+    return (1);
+}
+
 static int file_unmarshall_boolean(lua_State *ls)
 {
     if (lua_gettop(ls) != 1)
@@ -209,6 +215,7 @@ static const struct luaL_reg file_dlib[] =
     { "datadir_files", _file_datadir_files },
     { "datadir_files_recursive", _file_datadir_files_recursive },
     { "minor_version", file_minor_version },
+    { "major_version", file_major_version },
     { NULL, NULL }
 };