We haven't used custom Git commit headers for two main reasons:
1. I don't want commits created by jj to be different from any other
commits. I don't want Git projects to get annoyed by such commit
and reject them.
2. I've been concerned that tools don't know how to handle such
headers, perhaps even resulting in crashes.
The first argument doesn't apply to commits with conflicts because
such commits would never be accepted by a project whether or not they
use custom commit headers. The second argument is less relevant for
conflicted commits because most tools will be confused by such commits
anyway.
Storing conflict information in commit headers means that we can
transfer them via the regular Git wire protocol. We already include
the tree objects nested inside the root-level tree, so they will also
be transferred.
So, let's start by writing the information redundantly to the commit
header and to the existing storage. That way we can roll it back if we
realize there's a problem with using commit headers.
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.
I have used the tree-level conflict format for several weeks without
problem (after the fix in 51b5d168ae). Now - right after the 0.10.0
release - seems like a good time to enable the config by default.
I enabled the config in our default configs in the CLI crate to reduce
impact on tests (compared to changing the default in `settings.rs`).
When we start writing tree-level conflicts in an existing repo, we
don't want commits that change the format to be non-empty if they
don't change any content. This patch updates `MergeTreeId::eq()` to
consider two resolved trees equal even if only their `MergedTreeId`
variant is different (one is path-level and one is tree-level).
I think I've gone through all places we compare tree ids and checked
that it's safe to compare them this way. One consequence is that
rebasing a commit without changing the parents (typically
auto-rebasing after `jj describe`) will not lead to the tree id
getting upgraded, due to an optimization we have for that case. I
don't think that's serious enough to handle specially; we'll have to
support the old format for existing repos for a while regardless of a
few commits not getting upgraded right away.
The number of failing tests with the config option enabled drop from
108 to 11 with this patch.
We're finally ready to start writing trees using the new format where
we represent conflicts by having multiple trees in the commit instead
of having a single tree with multiple entries at a path. This patch
adds a config option for that. It's not ready to be used yet, so I
haven't updated the release notes or other documentation.
I added only a simple CLI test for testing what happens when the
config is enabled in an existing repo. 108 tests currently fail if we
flip the default.
