Improve table and userdata conversions

* add convert_fallback and convert_max_attempts to global settings
* if no __lanesconvert is available, use convert_fallback (can be useful for externally provided full userdata with fixed metatables)
* only try conversion on non-deep and non-clonable userdata
* conversion can be applied recursively, up to convert_max_attempts times
* plus all the relevant unit tests of course

1 files changed, 3 insertions, 0 deletions

diff --git a/src/lanes.cpp b/src/lanes.cpp
index 4373aee..024ac67 100644
--- a/src/lanes.cpp
+++ b/src/lanes.cpp
@@ -907,6 +907,9 @@ LANES_API int luaopen_lanes_core(lua_State* const L_)
         // will do nothing on first invocation, as we haven't stored settings in the registry yet
         lua_setfield(L_, -3, "settings");                                                          // L_: M LG_configure()
         lua_setfield(L_, -2, "configure");                                                         // L_: M
+        // lanes.null can be used for some configure settings, expose it now
+        kNilSentinel.pushKey(L_);                                                                  // L_: M kNilSentinel
+        lua_setfield(L_, -2, "null");                                                              // L_: M
     }
 
     STACK_CHECK(L_, 1);