transaction: leave unfinished without crashing when not properly released I think the transaction.__del__ is there just as a last resort in case we (or an extension) forgot to release the transaction. When that happens, the repo can (or will on Python 3?) get deleted before the transaction. This leads to a crash in test-devel-warnings.t on Python 3 because we tried to access repo.dirstate, where repo was retried from a weak reference. There's not much we can do here, but let's at least avoid the crash. The user will have run `hg recover` afterwards regardless. Differential Revision: https://phab.mercurial-scm.org/D6664