tests/test-log-exthook.t

sqlitestore: support for storing revisions without their parents

This commit kinda/sorta implements the equivalent of ellipsis nodes for
the SQLite storage backend.

Without implementing full blown ellipsis nodes (and the necessary support for
them in the wire protocol), we instead teach the store to rewrite the p1 and
p2 nodes to nullid when the incoming parent isn't in the local store. This allows
servers to remain dumb and send the real parent and have the clients deal
with the missing parent problem.

This obviously isn't ideal because a benefit of ellipsis nodes is we can
insert a fake parent to ellide missing changesets. But neither solution is
ideal because it drops the original parent from storage. We could probably
teach the SQLite store to retain the original parent and handle missing
parents at read time. However, parent revisions are stored as integers and
it isn't trivial to store an "empty" revision in the store yet, which would
be necessary to represent the "missing" parent.

The store is somewhat intelligent in trying to remove the missing parents
metadata when the revision is re-added. But, revision numbers will be all
messed up in that case, so I'm not sure it is worth it. At some point we'll
likely want to remove the concept of revision numbers from the database and
have the store invent them at index generation time. Or even better, we can
do away with revision numbers from the file storage interface completely.
We'll get there eventually...

Differential Revision: https://phab.mercurial-scm.org/D5168

Test hg log changeset printer external hook
-------------------------------------------

  $ cat > $TESTTMP/logexthook.py <<EOF
  > from __future__ import absolute_import
  > import codecs
  > from mercurial import (
  >   commands,
  >   logcmdutil,
  >   repair,
  > )
  > def rot13description(self, ctx):
  >     summary = codecs.encode("summary", 'rot-13')
  >     description = ctx.description().strip().splitlines()[0].encode('rot13')
  >     self.ui.write("%s:     %s\n" % (summary, description))
  > def reposetup(ui, repo):
  >     logcmdutil.changesetprinter._exthook = rot13description
  > EOF

Prepare the repository

  $ hg init empty
  $ cd empty
  $ touch ROOT
  $ hg commit -A -m "Root" ROOT

  $ touch a b c
  $ hg commit -A -m "Add A, B, C" a b c

Check the log

  $ hg log --config extensions.t=$TESTTMP/logexthook.py
  changeset:   1:70fc82b23320
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  fhzznel:     Nqq N, O, P
  summary:     Add A, B, C
  
  changeset:   0:b00443a54871
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  fhzznel:     Ebbg
  summary:     Root
  
Check that exthook is working with graph log too

  $ hg log -G --config extensions.t=$TESTTMP/logexthook.py
  @  changeset:   1:70fc82b23320
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  fhzznel:     Nqq N, O, P
  |  summary:     Add A, B, C
  |
  o  changeset:   0:b00443a54871
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     fhzznel:     Ebbg
     summary:     Root