EventName::mask() recursed forever for the three internal leaf events
(ObjectRemovedAbortMultipartUpload, ObjectCreatedCreateMultipartUpload,
ObjectRemovedDeleteObjects): their discriminants fall past
LAST_SINGLE_TYPE_VALUE so mask() took the compound branch, but expand()
returns vec![*self] for them, so mask() called itself with the same
value and overflowed the stack.
Detect the self-expanding leaf case (expand() yields exactly self) and
give it a dedicated bit derived from its discriminant. Those bits sit
above the single-type bits, so they never collide with each other or
with any compound 'All' mask.
Add exhaustive regression tests: every variant's mask() terminates, the
three internal masks are non-zero and mutually distinct and disjoint
from the single-type bits, and Everything covers all single-type bits.
Refs: https://github.com/rustfs/backlog/issues/965
Zhengchao An
976a5d9713