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
Initial setup.
$ hg init repo
$ cd repo
$ touch thefile
$ hg ci -A -m 'Initial commit.'
adding thefile
Create a tag.
$ hg tag branchortag
Create a branch with the same name as the tag.
$ hg branch branchortag
marked working directory as branch branchortag
(branches are permanent and global, did you want a bookmark?)
$ hg ci -m 'Create a branch with the same name as a tag.'
This is what we have:
$ hg log
changeset: 2:10519b3f489a
branch: branchortag
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: Create a branch with the same name as a tag.
changeset: 1:2635c45ca99b
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: Added tag branchortag for changeset f57387372b5d
changeset: 0:f57387372b5d
tag: branchortag
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: Initial commit.
Update to the tag:
$ hg up 'tag(branchortag)'
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg parents
changeset: 0:f57387372b5d
tag: branchortag
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: Initial commit.
Updating to the branch:
$ hg up 'branch(branchortag)'
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg parents
changeset: 2:10519b3f489a
branch: branchortag
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: Create a branch with the same name as a tag.
$ cd ..