Make it clearer which code is specific to the default revset codepath

Cc: https://github.com/martinvonz/jj/pull/2935#discussion_r1477184743,
thanks to @yuja for the suggestion.

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.

It tries to push all deleted branches, but can only succeed for tracked
branches.

Closes #2946, as there's probably no need to have `--deleted --tracked`
that would only be different in that the warnings wouldn't be printed.
Thanks to @yuja for pointing this out.

New users often want to know how to just see what `git log` would show.
Putting it in the FAQ isn’t perfect but might help a bit.

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.

When the user doesn't have a configured default command, we show a
hint saying to set `ui.default-command`. I think the user is very
likely to want to set that in the user-wide config, so let's include
the command in the hint.

Bumps the cargo-dependencies group with 1 update: [tempfile](https://github.com/Stebalien/tempfile).


Updates `tempfile` from 3.9.0 to 3.10.0
- [Changelog](https://github.com/Stebalien/tempfile/blob/master/CHANGELOG.md)
- [Commits](https://github.com/Stebalien/tempfile/compare/v3.9.0...v3.10.0)

---
updated-dependencies:
- dependency-name: tempfile
dependency-type: direct:production
update-type: version-update:semver-minor
dependency-group: cargo-dependencies
...

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Bumps the github-dependencies group with 1 update: [actions/upload-artifact](https://github.com/actions/upload-artifact).


Updates `actions/upload-artifact` from 4.3.0 to 4.3.1
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/26f96dfa697d77e81fd5907df203aa23a56210a8...5d5d22a31266ced268874388b861e4b58bb5c2f3)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
dependency-type: direct:production
update-type: version-update:semver-patch
dependency-group: github-dependencies
...

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I'll probably add infix logical operators later, but the surround() function
is still useful because we don't have to repeat the condition:

if(x || y, "<" ++ separate(" ", x, y) ++ ">")
surround("<", ">", separate(" ", x, y))

It can't be used if we want to add placeholder text, though:

if(x || y, "<" ++ separate(" ", x, y) ++ ">", "(none)")

Closes #2924

This reimplements the change 9faa4670d53f "cli: on init, import git refs prior
to importing HEAD." Initialization is special because the HEAD ref isn't
available to jj yet, and there is an empty working-copy commit.

The initialization function could be refactored to go through the common code
path, but I think doing that would make future improvement harder. We might
want to initialize tracking branches based on .git/config for example.

Fixes #2942

Working with Gerrit requires directly invoking git commands, which is awkward
without a co-located repo. Add a hint to use a co-located repo.

Bumps the github-dependencies group with 1 update: [EmbarkStudios/cargo-deny-action](https://github.com/embarkstudios/cargo-deny-action).


Updates `EmbarkStudios/cargo-deny-action` from 1.5.12 to 1.5.13
- [Release notes](https://github.com/embarkstudios/cargo-deny-action/releases)
- [Commits](https://github.com/embarkstudios/cargo-deny-action/compare/748857f070c53667b2b8de8bdf468ac75a6b757c...5def368d93be6684ad20a0fdec5f23c8ea11e022)

---
updated-dependencies:
- dependency-name: EmbarkStudios/cargo-deny-action
dependency-type: direct:production
update-type: version-update:semver-patch
dependency-group: github-dependencies
...

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Bumps the cargo-dependencies group with 3 updates: [clap_complete](https://github.com/clap-rs/clap), [pest](https://github.com/pest-parser/pest) and [pest_derive](https://github.com/pest-parser/pest).


Updates `clap_complete` from 4.4.9 to 4.4.10
- [Release notes](https://github.com/clap-rs/clap/releases)
- [Changelog](https://github.com/clap-rs/clap/blob/master/CHANGELOG.md)
- [Commits](https://github.com/clap-rs/clap/compare/clap_complete-v4.4.9...clap_complete-v4.4.10)

Updates `pest` from 2.7.6 to 2.7.7
- [Release notes](https://github.com/pest-parser/pest/releases)
- [Commits](https://github.com/pest-parser/pest/compare/v2.7.6...v2.7.7)

Updates `pest_derive` from 2.7.6 to 2.7.7
- [Release notes](https://github.com/pest-parser/pest/releases)
- [Commits](https://github.com/pest-parser/pest/compare/v2.7.6...v2.7.7)

---
updated-dependencies:
- dependency-name: clap_complete
dependency-type: direct:production
update-type: version-update:semver-patch
dependency-group: cargo-dependencies
- dependency-name: pest
dependency-type: direct:production
update-type: version-update:semver-patch
dependency-group: cargo-dependencies
- dependency-name: pest_derive
dependency-type: direct:production
update-type: version-update:semver-patch
dependency-group: cargo-dependencies
...

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This initializes a git backed repo.

* It does the same thing as `jj init --git` except that it
has a --colocated flag to explicitly specify that we want
the .git repo to be side-by-side the .jj repo in the working
directory.
* `jj init --git` will keep the current behaviour and will not
be able to create colocated git backed repos.
* Update test snapshots.

A few minor updates after 0f27152 AKA #2945

Specifically, I tried to change the help text so that it looks better as
Markdown. I also reworded the deprecation warning and added a hint.

this has two main advantages:
- it makes it clear that the shells are mutually exclusive
- it allows us to extend the command with shell-specific options in the future if necessary
as a happy accident, it also adds support for `elvish` and `powershell`.

for backwards compatibility, this also keeps the existing options as hidden flags.

i am not super happy with how the new help looks; the instructions for setting up the shell are
squished together and IMO a little harder to read. i'm open to suggestions.

it's somewhat confusing to me that the `--bash` flag exists at all, since it does nothing - maybe it makes sense to give a hard error? or just remove the flag?
but in any case, it seems good to document the existing behavior.

previously, `jj diff` would show the full contents of binary files such as images.
after this change, it instead shows "(binary)". it still shows the filename and metadata so that
users can open the file in the viewer of their choce.

future work could involve showing binary files as Sixel or similar; finding a way to compare large
non-binary files without filling up the screen; or extending the data backends to avoid having to
read the whole file contents into memory.

Previously, `jj git push; jj git push` would tell the user that "No
branches point to the specified revisions.". I found this confusing,
even though strictly speaking it is correct (as the default revset only
considers revisions that haven't been pushed to the remote).

Closes #2241

There are many minor bugs that are difficult to fix in the short-term.

See also the commit message for a197409b2b

minor fix.

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

Summary: Put both notices together at once, for ease of reading and
understanding.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Change-Id: I2aedb42fdab346b21990a106433512d7ec119ad4

Summary: As discussed in Discord, on GitHub, and elsewhere, this change
deprecates the use of `jj merge` and suggests users use `jj new` exclusively
instead. `merge` isn't completely unfit as a name; but we think it obscures
the generality of `new` and we want people to use it instead.

To further drive the bit home, by default, `jj merge` is now hidden. This will
hopefully stop new users from running into it.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Change-Id: I94938aca9d3e2aa12d1394a5fbc58acce3185b56

Summary: As discussed in Discord, on GitHub, and elsewhere, this change
deprecates the use of `jj checkout` and suggests users use `jj new` exclusively
instead. The verb `checkout` is a relic of a bygone era the — days of RCS
file locking, before 3-way merge — and is not a good, fitting name for the
functionality it provides.

To further drive the bit home, by default, `jj checkout` (and `jj co`) is now
hidden. This will hopefully stop new users from running into it.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Change-Id: I7a1adfc9168fce1f25cf5d4c4c313304769e41a1

These didn't really need to use `jj checkout`, and it will be deprecated in a
future change anyway. Move them out of there and into `new`.

Ideally this would go into `test_conflicts.rs`, but that exists in `jj-lib`, so
it doesn't have `TestEnvironment` available to it.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Change-Id: If0173b27ab4d1f6036a4ec632ec77b6824f310c3

* Move git_init() to cli/src/commands/git.rs and call it from there.
* Move print_trackable_remote_branches into cli_util since it's not git specific,
but would apply to any backend that supports remote branches.
* A no-op change. A follow up PR will make use of this.

* Create a git_init() function in cli/src/commands/init.rs where all git related work is done.
This function will be moved to cli/src/commands/git.rs in a subsequent PR.

* Add file_util::create_or_reuse_dir() which is needed by all init
functionality regardless of the backend.

This changes the intro section to recommend using `jj config edit` to
edit the config instead of looking for the files manually.

Bumps the cargo-dependencies group with 1 update: [tokio](https://github.com/tokio-rs/tokio).


Updates `tokio` from 1.35.1 to 1.36.0
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](https://github.com/tokio-rs/tokio/compare/tokio-1.35.1...tokio-1.36.0)

---
updated-dependencies:
- dependency-name: tokio
dependency-type: direct:production
update-type: version-update:semver-minor
dependency-group: cargo-dependencies
...

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Bumps the github-dependencies group with 1 update: [DeterminateSystems/magic-nix-cache-action](https://github.com/determinatesystems/magic-nix-cache-action).


Updates `DeterminateSystems/magic-nix-cache-action` from 1402a2dd8f56a6a6306c015089c5086f5e1ca3ef to eeabdb06718ac63a7021c6132129679a8e22d0c7
- [Release notes](https://github.com/determinatesystems/magic-nix-cache-action/releases)
- [Commits](https://github.com/determinatesystems/magic-nix-cache-action/compare/1402a2dd8f56a6a6306c015089c5086f5e1ca3ef...eeabdb06718ac63a7021c6132129679a8e22d0c7)

---
updated-dependencies:
- dependency-name: DeterminateSystems/magic-nix-cache-action
dependency-type: direct:production
dependency-group: github-dependencies
...

Signed-off-by: dependabot[bot] <support@github.com>

Kicks off work on issue #1896

The inner error message is now printed by default.

It doesn't add much context, and looks worse with the new error formatting.

"Caused by" lines are inserted before the hint because they are more strongly
related to the error.

Bumps the cargo-dependencies group with 3 updates: [indexmap](https://github.com/indexmap-rs/indexmap), [libc](https://github.com/rust-lang/libc) and [rustix](https://github.com/bytecodealliance/rustix).


Updates `indexmap` from 2.2.1 to 2.2.2
- [Changelog](https://github.com/indexmap-rs/indexmap/blob/master/RELEASES.md)
- [Commits](https://github.com/indexmap-rs/indexmap/compare/2.2.1...2.2.2)

Updates `libc` from 0.2.152 to 0.2.153
- [Release notes](https://github.com/rust-lang/libc/releases)
- [Commits](https://github.com/rust-lang/libc/compare/0.2.152...0.2.153)

Updates `rustix` from 0.38.30 to 0.38.31
- [Release notes](https://github.com/bytecodealliance/rustix/releases)
- [Commits](https://github.com/bytecodealliance/rustix/compare/v0.38.30...v0.38.31)

---
updated-dependencies:
- dependency-name: indexmap
dependency-type: direct:production
update-type: version-update:semver-patch
dependency-group: cargo-dependencies
- dependency-name: libc
dependency-type: direct:production
update-type: version-update:semver-patch
dependency-group: cargo-dependencies
- dependency-name: rustix
dependency-type: direct:production
update-type: version-update:semver-patch
dependency-group: cargo-dependencies
...

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The error message suggests that BackendError isn't a user error.

Multi-line output should be easier to follow than lengthy line separated by
colon.