julia

5c268621 - types: singleton subtype semantics, typemap guards, datatype.c update

types: singleton subtype semantics, typemap guards, datatype.c update Singleton subtype: types with free typevars are singletons — only themselves and Bottom are subtypes (in jl_subtype_env public API). Typemap guards: add NULL/validity checks in jl_typemap_assoc_by_type tname walk to handle partially-constructed types encountered during recursive type definitions. Without these guards, ConstType dispatch tuples that reference types being constructed could crash in mtcache_hash_lookup. Remove outdated hasuniquerep reference in jl_pointer_egal comment. Restore T54757 recursive type test (now works with the guards). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>