Merge pull request #4977 from myk002/myk_unionize

[Lua] add _union=true field to union types

Author: myk002

docs/dev/Lua API.rst

@@ -315,6 +315,10 @@ All types and the global object have the following features:
 
 All compound types (structs, classes, unions, and the global object) support:
 
+* ``type._union``
+
+  ``true`` if the type represents a union, otherwise ``nil``.
+
 * ``type._fields``
 
   Contains a table mapping field names to descriptions of the type's fields,

library/LuaWrapper.cpp

@@ -1638,8 +1638,11 @@ static void RenderType(lua_State *state, const compound_identity *node)
 
     switch (node->type())
     {
-    case IDTYPE_STRUCT:
     case IDTYPE_UNION: // TODO: change this to union-type? what relies on this?
+        lua_pushboolean(state, true);
+        lua_setfield(state, ftable, "_union");
+        // fall through
+    case IDTYPE_STRUCT:
         lua_pushstring(state, "struct-type");
         lua_setfield(state, ftable, "_kind");
         IndexStatics(state, ix_meta, ftable, (struct_identity*)node);