localrepo: make journal.dirstate contain in-memory changes before transaction

Before this patch, in-memory dirstate changes aren't written out at
opening transaction, even though 'journal.dirstate' is created
directly from '.hg/dirstate'.

Therefore, subsequent 'hg rollback' uses incomplete 'undo.dirstate' to
restore dirstate, if dirstate is changed and isn't written out before
opening transaction.

In cases below, the condition "dirstate is changed and isn't written
out before opening transaction" isn't satisfied and this problem
doesn't appear:

  - "wlock scope" and "transaction scope" are almost equivalent

    e.g. 'commit --amend', 'import' and so on

  - dirstate changes are written out before opening transaction

    e.g. 'rebase' (via 'dirstateguard') and 'commit -A' (by separated
    wlock scopes)

On the other hand, 'backout' may satisfy the condition above.

To make 'journal.dirstate' contain in-memory changes before opening
transaction, this patch explicitly invokes 'dirstate.write()' in
'localrepository.transaction()'.

'dirstate.write()' is placed before not "writing journal files out"
but "invoking pretxnopen hooks" for visibility of dirstate changes to
external hook processes.

BTW, in the test script, 'touch -t 200001010000' and 'hg status' are
invoked to make file 'c' surely clean in dirstate, because "clean but
unsure" files indirectly cause 'dirstate.write()' at 'repo.status()'
in 'repo.commit()' (see fe03f522dda9 for detail) and prevents from
certainly reproducing the issue.

mercurial/localrepo.py

@@ -968,6 +968,9 b' class localrepository(object):'
                 _("abandoned transaction found"),
                 hint=_("run 'hg recover' to clean up transaction"))
 
+        # make journal.dirstate contain in-memory changes at this point
+        self.dirstate.write()
+
         idbase = "%.40f#%f" % (random.random(), time.time())
         txnid = 'TXN:' + util.sha1(idbase).hexdigest()
         self.hook('pretxnopen', throw=True, txnname=desc, txnid=txnid)

tests/test-backout.t

@@ -130,6 +130,34 b' backout of backout is as if nothing happ'
   update: (current)
   phases: 4 draft
 
+Test that 'hg rollback' restores dirstate just before opening
+transaction: in-memory dirstate changes should be written into
+'.hg/journal.dirstate' as expected.
+
+  $ echo 'removed soon' > b
+  $ hg commit -A -d '4 0' -m 'prepare for subsequent removing'
+  adding b
+  $ echo 'newly added' > c
+  $ hg add c
+  $ hg remove b
+  $ hg commit -d '5 0' -m 'prepare for subsequent backout'
+  $ touch -t 200001010000 c
+  $ hg status -A
+  C c
+  $ hg debugstate --nodates
+  n 644         12 set                 c
+  $ hg backout -d '6 0' -m 'to be rollback-ed soon' -r .
+  adding b
+  removing c
+  changeset 6:4bfec048029d backs out changeset 5:fac0b729a654
+  $ hg rollback -q
+  $ hg status -A
+  A b
+  R c
+  $ hg debugstate --nodates
+  a   0         -1 unset               b
+  r   0          0 set                 c
+
 across branch
 
   $ cd ..