shelve: add utility to abort current transaction but keep dirstate "hg shelve" and "hg unshelve" use aborting a current transaction to discard temporary changes while (un)shelving. This assumes that dirstate changes in a transaction scope are kept even after aborting it. But this assumption will be broken by "transactional dirstate". See the wiki page below for detail about it. https://mercurial.selenic.com/wiki/DirstateTransactionPlan This patch adds utility function "_aborttransaction()" to abort current transaction but keep dirstate changes for (un)shelving. 'dirstate.invalidate()' just after aborting a transaction should be removed soon by subsequent patch, which writes or discards in-memory dirstate changes at releasing transaction according to the result of it. BTW, there are some other ways below, which (seem to, at first glance) resolve this issue. But this patch chose straightforward way for ease of review and future refactorring. - commit transaction at first, and then rollback it It causes unintentional "dirty read" of running transaction to other processes at committing it. - use dirstateguard to save and restore shelved dirstate After DirstateTransactionPlan, making 'dirstate.write()' write in-memory changes into actual file requires 'transaction.writepending()' while transaction running. It causes meaningless writing other in-memory changes out, even though they are never referred. In addition to it, it isn't desirable that scope of dirstateguard and transaction intersects each other. - get list of files changed from the parent, keep it in memory, and emulate that changes after aborting transaction This additional memory consumption may block aborting transaction in large repository (on small resource environment).