The default immutable_heads() includes tags(), which makes sense, but computing
heads(tags()) can be expensive because the tags() set is usually sparse. For
example, "jj bench revset 'heads(tags())'" took 157ms in my linux stable
mirror. We can of course optimize the heads evaluation by using bit set or
segmented index, but the query includes many historical heads if the repository
has per-release branches, which are uninteresting anyway. So, this patch
replaces heads(immutable_heads()) with trunk().
The reason we include heads(immutable_heads()) is to mitigate the following
problem. Suppose trunk() is the branch to be based off, I think using trunk()
here is pretty good.
```
A B
*---*----* trunk() ⊆ immutable_heads()
\
* C
```
https://github.com/martinvonz/jj/pull/2247#discussion_r1335078879
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`).
I think most users who change the set of immutable heads away from
`trunk() | tags()` are going to also want to change the default log
revset to include the newly mutable commit and to exclude the newly
immutable commits. So let's update the default log revset to use
`immutable_heads()` instead.
`test_templater` changed because we have overridden the set of
immutable commits there so `jj log` now includes the remote branch.
This adds a new `revset-aliases.immutable_heads()s` config for
defining the set of immutable commits. The set is defined as the
configured revset, as well as its ancestors, and the root commit
commit (even if the configured set is empty).
This patch also adds enforcement of the config where we already had
checks preventing rewrite of the root commit. The working-copy commit
is implicitly assumed to be writable in most cases. Specifically, we
won't prevent amending the working copy even if the user includes it
in the config but we do prevent `jj edit @` in that case. That seems
good enough to me. Maybe we should emit a warning when the working
copy is in the set of immutable commits.
Maybe we should add support for something more like [Mercurial's
phases](https://wiki.mercurial-scm.org/Phases), which is propagated on
push and pull. There's already some affordance for that in the view
object's `public_heads` field. However, this is simpler, especially
since we can't propagate the phase to Git remotes, and seems like a
good start. Also, it lets you say that commits authored by other users
are immutable, for example.
For now, the functionality is in the CLI library. I'm not sure if we
want to move it into the library crate. I'm leaning towards letting
library users do whatever they want without being restricted by
immutable commits. I do think we should move the functionality into a
future `ui-lib` or `ui-util` crate. That crate would have most of the
functionality in the current `cli_util` module (but in a
non-CLI-specific form).
