rebase: use one dirstateguard for when using rebase.singletransaction
This was previously landed as
2519994d25ca but backed out in
b63351f6a2 because
it broke hooks mid-rebase and caused conflict resolution data loss in the event
of unexpected exceptions. This new version adds the behavior back but behind a
config flag, since the performance improvement is notable in large repositories.
The old commit message was:
Recently we switched rebases to run the entire rebase inside a single
transaction, which dramatically improved the speed of rebases in repos with
large working copies. Let's also move the dirstate into a single dirstateguard
to get the same benefits. This let's us avoid serializing the dirstate after
each commit.
In a large repo, rebasing 27 commits is sped up by about 20%.
I believe the test changes are because us touching the dirstate gave the
transaction something to actually rollback.
(grafted from
9e3dc3a1638b9754b58a0cb26aaa75d868058109)
(grafted from
7d38b41d2266d9a02a15c64229fae0da5738dcec)
Differential Revision: https://phab.mercurial-scm.org/D135
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