If the operation corresponding to a workspace is missing for some reason
(the specific situation in the test in this commit is that an operation
was abandoned and garbage-collected from another workspace), currently,
jj fails with a 255 error code. Teach jj a way to recover from this
situation.
When jj detects such a situation, it prints a message and stops
operation, similar to when a workspace is stale. The message tells the
user what command to run.
When that command is run, jj loads the repo at the @ operation (instead
of the operation of the workspace), creates a new commit on the @
commit with an empty tree, and then proceeds as usual - in particular,
including the auto-snapshotting of the working tree, which creates
another commit that obsoletes the newly created commit.
There are several design points I considered.
1) Whether the recovery should be automatic, or (as in this commit)
manual in that the user should be prompted to run a command. The user
might prefer to recover in another way (e.g. by simply deleting the
workspace) and this situation is (hopefully) rare enough that I think
it's better to prompt the user.
2) Which command the user should be prompted to run (and thus, which
command should be taught to perform the recovery). I chose "workspace
update-stale" because the circumstances are very similar to it: it's
symptom is that the regular jj operation is blocked somewhere at the
beginning, and "workspace update-stale" already does some special work
before the blockage (this commit adds more of such special work). But it
might be better for something more explicitly named, or even a sequence
of commands (e.g. "create a new operation that becomes @ that no
workspace points to", "low-level command that makes a workspace point to
the operation @") but I can see how this can be unnecessarily confusing
for the user.
3) How we recover. I can think of several ways:
a) Always create a commit, and allow the automatic snapshotting to
create another commit that obsoletes this commit.
b) Create a commit but somehow teach the automatic snapshotting to
replace the created commit in-place (so it has no predecessor, as viewed
in "obslog").
c) Do either a) or b), with the added improvement that if there is no
diff between the newly created commit and the former @, to behave as if
no new commit was created (@ remains as the former @).
I chose a) since it was the simplest and most easily reasoned about,
which I think is the best way to go when recovering from a rare
situation.
this greatly speeds up the time to run all tests, at the cost of slightly larger recompile times for individual tests.
this unfortunately adds the requirement that all tests are listed in `runner.rs` for the crate.
to avoid forgetting, i've added a new test that ensures the directory is in sync with the file.
## benchmarks
before this change, recompiling all tests took 32-50 seconds and running a single test took 3.5 seconds:
```
; hyperfine 'touch lib/src/lib.rs && cargo t --test test_working_copy'
Time (mean ± σ): 3.543 s ± 0.168 s [User: 2.597 s, System: 1.262 s]
Range (min … max): 3.400 s … 3.847 s 10 runs
```
after this change, recompiling all tests take 4 seconds:
```
; hyperfine 'touch lib/src/lib.rs ; cargo t --test runner --no-run'
Time (mean ± σ): 4.055 s ± 0.123 s [User: 3.591 s, System: 1.593 s]
Range (min … max): 3.804 s … 4.159 s 10 runs
```
and running a single test takes about the same:
```
; hyperfine 'touch lib/src/lib.rs && cargo t --test runner -- test_working_copy'
Time (mean ± σ): 4.129 s ± 0.120 s [User: 3.636 s, System: 1.593 s]
Range (min … max): 3.933 s … 4.346 s 10 runs
```
about 1.4 seconds of that is the time for the runner, of which .4 is the time for the linker. so
there may be room for further improving the times.
Mostly, I was a bit confused that some of these functions return a
`TrackingRefPair` but don't seem to take into account whether the remote
branch is being tracked or not.
Our virtual file system at Google (CitC) would like to know the commit
so it can scan backwards and find the closest mainline tree based on
it. Since we always record an operation id (which resolves to a
working-copy commit) when we write the working-copy state, it doesn't
seem like a restriction to require a commit.
The error output gets more verbose because all gix error sources are printed.
Maybe we'll need a better formatting, but changing to multi-line output doesn't
look nice either.
These error types are special because the message is embedded in ASCII art. I
think it would be a source of bugs if some error types had ": {source}" but
others don't. So I'm going to remove all ": {source}"s, and let the callers
concatenate them when needed.
This mostly reverts https://github.com/martinvonz/jj/pull/2901 as well as its
fixup https://github.com/martinvonz/jj/pull/2903. The related bug is reopened,
see https://github.com/martinvonz/jj/issues/2869#issuecomment-1920367932.
The problem is that while the fix did fix#2869 in most cases, it did
reintroduce the more severe bug https://github.com/martinvonz/jj/issues/2760
in one case, if the working copy is the commit being rebased.
For example, suppose you have the tree
```
root -> A -> B -> @ (empty) -> C
```
### Before this commit
#### Case 1
`jj rebase -s B -d root --skip-empty` would work perfectly before this
commit, resulting in
```
root -> A
\-------B -> C
\- @ (new, empty)
```
#### Case 2
Unfortunately, if you run `jj rebase -s @ -d A --skip-empty`, you'd have the
following result (before this commit), which shows the reintroduction of #2760:
```
root -> A @ -> C
\-- B
```
with the working copy at `A`. The reason for this is explained in
https://github.com/martinvonz/jj/pull/2901#issuecomment-1920043560.
### After this commit
After this commit, both case 1 and case 2 will be wrong in the sense of #2869,
but it will no longer exhibit the worse bug #2760 in the second case.
Case 1 would result in:
```
root -> A
\-------B -> @ (empty) -> C
```
Case 2 would result in:
```
root -> A -> @ -> C
\-- B
```
with the working copy remaining a descendant of A
`rebase_next()` returns an `Option<RebasedDescendant>`, but the only
way we use it is to decide whether to terminate the loop over
`to_visit`. Let's simplify by making the caller iterate over
`to_visit` instead.
The `edit` argument seems to be true if and only if the
old commit was *not* abandoned. So, I flipped its value
and renamed it to `abandoned_old_commit`.
With my jj repo, the number of jj/keep refs went down from 87887 to 27733.
The .git directory size is halved, but we'll need to clean up extra and index
files to save disk space. "git gc --prune=now && jj debug reindex" passed, so
the repo wouldn't be corrupted.
#12
GitBackend::gc() will need to check if a commit is reachable from any
historical operations. This could be calculated from the view and commit
objects, but the Index will do a better job.
I'm going to make WorkspaceCommandHelper::maybe_snapshot() snapshot the working
copy before importing refs. git::import_some_refs() can rebase the working copy
branch and therefore @ can be moved. git::import_head() doesn't, and it should
be invoked before snapshotting.
git::import_head() is inserted to some of the git:import_refs() callers where
HEAD seems to matter. I feel it's a bit odd that the HEAD ref is imported to
non-colocated repo, but "jj init --git-repo" relies on that, and I think the
existence of HEAD@git is harmless. It's merely a ref to the revision checked
out somewhere else.
This was broken at afa72ff496 "git_backend: inline prevent_gc() to bulk-update
refs." Since no-gc refs are created within a transaction, duplicated edits are
no longer allowed.
We didn't have any tests with negative snapshots (after a `-------`
line). I initially thought we couldn't produce such conflict markers
anymore. I'm not sure we want to render conflicts like the one in the
test like this. I don't think I intended for `add_index` in the code
to be able to be two steps ahead of the remove. Maybe we should
rewrite the algorithm to not do that and thus never produce negative
snapshots.
The count() function in this trait is used by "jj branch" to determine
(and then report) how many commits a certain branch is ahead/behind
another branch. This is currently implemented by walking all commits
in the revset, counting how many were encountered. But this could be
improved: if the number is large, it is probably sufficient to report
"at least N" (instead of walking all the way), and this does not scale
well to jj backends that may not have all commits present locally (which
may prefer to return an estimate, rather than access the network).
Therefore, add a function that is explicitly documented to be O(1)
and that can return a range of values if the backend so chooses.
Also remove count(), as it is not immediately obvious that it is an
expensive call, and callers that are willing to pay the cost can obtain
the exact same functionality through iter().count() anyway. (In this
commit, all users of count() are migrated to iter().count() to preserve
all existing functionality; they will be migrated to count_estimate() in
a subsequent commit.)
"branch" needed to be updated due to this change. Although jj
is currently only available in English, I have attempted to keep
user-visible text from being assembled piece by piece, so that if we
later decide to translate jj into other languages, things will be easier
for translators.
GitBackend::gc() will recreate no-gc refs for the indexed heads. We could
collect all historical heads by traversing operation log, but it isn't enough
because there may be predecessor links to hidden commits, and "git gc" isn't
aware of predecessors.
This also means that we can implement GC without taking care of extra
metadata. I haven't tried, but it wouldn't be easy to keep Git refs and extra
table in sync.
The idea is that GC, if implemented, will clean up objects based on the Index
knowledge. It's probably okay to leave some extra metadata of unreachable
objects, but GC-ed refs should be recreated if the corresponding heads get
reimported. See also the next patch.
This will allow us to issue multiple prevent_gc() requests all at once. It's
not important here, but will be unavoidable when implementing GC. Deleting
tons of refs from packed refs is super slow if the requests were processed one
by one.
* Move canonicalization of the external git repo path into the Workspace::init_git_external().
This keeps necessary code together.
* Add a new variant of WorkspaceInitError for reporting path not found errors. The user error
string is written to pass existing tests.
Because the default index cuts off the traversal at min(generations), including
the root id means all ancestors will be visited. This could be worked around at
the index side, but I think it's the repo/view's responsibility. That being
said, it's not uncommon to pad a revset with "root()", so it might make sense
for the index to special case the root id.
I also removed the redundant .clone().
It seems obvious in hindsight to have a virtual root operation just
like we have a virtual root commit. It removes the same kind of
problems by making sure there's always a common ancestor (or multiple)
between any two commits.
I think the reason I didn't add a root operation from the beginning
was that there used to be a mandatory working-copy commit in the view
(this was before support for multiple workspaces).
Perhaps we should remove the "initialize repo" operation now. The only
difference between their view objects is that the "initialize repo"
operation adds the root commit as a head. We could add that to the
root operation, but then the root operation's value depends on the
commit backend.
We've had the public_heads for as long as we've had the View object,
IIRC (I didn't check), but we still don't use it for anything. I don't
have any concrete plans for using it either. Maybe our config for
immutable commits is good enough, or maybe we'll want something more
generic (like Mercurial's phases). For now, I think we should simplify
by removing it the storage for public heads.
