I don't know why I made the walk stop at heads instead of indexed
commits before. Perhaps I did it because it's cheap to check in the
set of head. However, it gets very expensive to walk all the way back
to the root if the parents are not in the set of heads.
With tons of groundwork done, wee can now finally keep the index up to
date within a transaction! That means that we can start relying on the
index to always be valid, so we can use it e.g. for finding common
ancestors within a transaction. That should help speed up `jj evolve`
immensely on large repos.
We still don't write the updated index to disk when the transaction
closes. That will come later.
`Transaction::add_head()` currently invalidates the whole evolution
state. We've had support for incrementally updating evolution since
4619942a57. We should start taking advantage of that. Let's add a
fast-path in `Transaction::add_head()` for the common case where we
add a single commit on top of an existing head. That cheap an simple
to check for. However, it won't cover the case of adding a child off
of a non-head. It's still a good start.
I'm about to move the functions from `CompositeIndex` to an new
`Index` trait implemeted by `ReadonlyIndex` and `MutableIndex`. Since
those types already implement `IndexSegment`, the names would conflict
and it would get annoying to have to disambiguate them. This commit
therefore prepares for that by adding a `segment_` prefix to the
functions in `IndexSegment`.
I want to keep the index updated within the transaction. I tried doing
that by adding a `trait Index`, implemented by `ReadonlyIndex` and
`MutableIndex`. However, `ReadonlyRepo::index` is of type
`Mutex<Option<Arc<IndexFile>>>` (because it is lazily initialized),
and we cannot get a `&dyn Index` that lives long enough to be returned
from a `Repo::index()` from that. It seems the best solution is to
instead create an `Index` enum (instead of a trait), with one readonly
and one mutable variant. This commit starts the migration to that
design by replacing the `Repo` trait by an enum. I never intended for
there there to be more implementations of `Repo` than `ReadonlyRepo`
and `MutableRepo` anyway.
I just learned that attaching a git note is not enough to keep a
commit from being GC'd. I had read `git help gc` before but it was
quite misleading (I just sent a patch to clarify it). Since the git
note is not enough, we need to create some other reference. This patch
makes it so we write refs in `refs/jj/keep/` for every commit we
create. We will probably want to remove unnecessary refs (ancestors of
commits pointed to by other refs) once we have a `jj gc` command.
We store conflicts as blobs with JSON data and with a git note
pointing to them to prevent GC. These are stored in the git tree as
regular files. The only thing that distinguishes them is that their
filename ends with `.jjconflict`. Since they are referenced from the
tree, there's no need for the git note to prevent GC (which doesn't
work anyway, as I just learned), and we don't store any additional
data in the note either, so let's just remove it.
Windows doesn't support recording the executable bit in the file
system. Before this commit, the code for reading and writing the
executable wouldn't even compile on Windows. This commit at least
makes it so we preserve whatever bit has been recorded in the repo.
At least I hope that's what it does -- I don't have access to a
Windows machine right now.
The project doesn't currently build on Windows. One reason is because
we had a `unimplemented!()` when trying to write a symlink. Let's
print a warning instead, so the project can start building on
Windows. (The next patch will fix another build problem on Windows.)
When a transaction gets dropped without being committed or explicitly
discarded, we currently raise an assertion error. I added that check
because I kept forgetting to commit transactions. However, it's quite
normal to want to drop transactions in error cases. The current
assertion means that we panic and don't report the actual error to the
user in such cases. We should probably audit the code paths where we
commit transactions and decide for each if we simply want to to
discard the transaction or not. In some cases, we may want to commit
the transaction without integrating it in the operation log
(i.e. without creating a file entry in .jj/views/op_heads/). However,
we can do that later. For now, let's just make sure we don't panic
when dropping the transaction in release builds.
I'm about to move `MutableRepo` to the `repo` module so it becomes
more important to encapsulate access. Besides, the new functions
introduced in this commit reduces some duplication.
There's still one access of `MutableRepo::evolution` in
`Transaction::new()`. I'll address that next by adding a factory
function to `MutableRepo`.
I'm about to add the argument to `jj merge` and `jj close` as
well. For those, I think `--description` would have made more sense
than `--text`, but I don't like the idea of having the short form be
`-d` (sounds too much like `--destination` or `--delete`). It's
unfortunate that `jj describe` set the "commit description" but the
argument is called "message". That still seems better than calling the
command `jj message`.
I've been confused twice that rebasing an open commit so it results in
conflicts doesn't show the conflicts in the log output. That's because
we create a successor instead if a commit with conflicts is open. I
guess I thought it would be expected that a child commit was not
created. Since it seems surprising in practice, let's change it and
we'll see if the new behavior is more or less surprising.
The most annoying remaining bug is that 3-way merge frequently panics
with "unhandled merge case". This commit fixes that by rewriting the
merge code. The new code is based on the algorithm used in Mercurial
(which was in turn copied from Bazaar):
1. Find "sync" regions, which are regions that are the unchanged in
the base and two sides. Note their start end end positions in each
version.
2. Produce the output by taking the sync regions and inserting the
result of merging the regions between the sync regions. These
regions can either be changed on only one side, in which case we
use that version, or it can be changed on both sides, in which
case we indicate a conflict in the output.
It's both more correct and much easier to follow.
We want to be able to be able to do fast `.contains()` checks on the
result, so `Iterator` was a bad type. We probably should hide the
exact type (currently `HashSet` for both readonly and mutable views),
but we can do that later. I actually thought I'd want to use
`.contains()` for indiciting public-phase commits in the log output,
but of course want to also indicate ancestors as public. This still
seem like a step (mostly) in the right direction.
Mercurial's "phase" concept is important for evolution, and it's also
useful for filtering out uninteresting commits from log
output. Commits are typically marked "public" when they are pushed to
a remote. The CLI prevents public commits from being rewritten. Public
commits cannot be obsolete (even if they have a successor, they won't
be considered obsolete like non-public commits would).
This commits just makes space for tracking the public heads in the
View.
All commits in the view are supposed to be reachable from its
heads. If a head is removed and there are git refs pointing to
ancestors of it (or to the removed head itself), we should make that
ancestor a head.
The only invariant we currently enforce is that the set of heads does
not include any ancestors of other commits in the set. I'm about to
make sure that we don't end up with dangling git refs (pointing to
commits no reachable from the heads). It will be useful to have a
single place to enforce that since we'll need to do the same thing
after updating the view as after merging views.
I think it's better to let the caller decide if the parents should be
added. One use case for removing a head is when fetching from a Git
remote where a branch has been rewritten. In that case, it's probably
the best user experience to remove the old head. With the current
semantics of `View::remove_head()`, we would need to walk up the graph
to find a commit that's an ancestor and for each commit we remove as
head, its parents get temporarily added as heads. It's much easier for
callers that want to add the parents as heads to do that.
They're rendered as a single string created by joining the refs by
spaces because we don't have any support in the template language for
rendering a list.
Git refs are important at least for understanding where the remote
branches are. This commit adds support for tracking them in the view
and makes `git::import_refs()` update them.
When merging views (either because of concurrent operations or when
undoing an earlier operation), there can be conflicts between git ref
changes. I ignored that for now and let the later operation win. That
will probably be good enough for a while. It's not hard to detect the
conflicts, but I haven't yet decided how to handle them. I'm leaning
towards representing the conflicting refs in the view just like how we
represent conflicting files in the tree.
This is partly to prepare for merging the operations in order of
transaction-commit time (currently merged in order of operation id),
so we can get a predictable order in tests (assuming transactions are
not committed the same millisecond).
