The main goal is to avoid having a symlink in our source tree. Currently, there
is no good way to work with the `jj` repo with `jj` on Windows. Currently `jj`
just crashes with symlinks. This is being worked on, see e.g. #2939, but it will
always depend on whether Developer Mode is enabled in Windows or whether
symlinks are materialized as text files with symlinks. Finally, MkDocs has
trouble following symlinks on Windows, so building docs wouldn't work there.
Another advantage is that, previously, we were lucky that MkDocs treats `insta`
header in `cli-reference@.md.snap` as a Markdown header and follows symlinks at
all. Now, we no longer depend on that.
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 am using a very hacky approach, using `insta` to generate the markdown help.
This is based on a lucky coincidence that `insta` chose to use a header
format for snapshot files that MkDocs interprets as a Markdown header (and
ignores).
I considered several other approaches, but I couldn't resist the facts that:
- This doesn't require new developers to install any extra tools or run any
extra commands.
- There is no need for a new CI check.
- There is no need to compile `jj` in the "Make HTML docs" GitHub action,
which is currently very fast and cheap.
Downside: I'm not sure how well MkDocs will work on Windows, unless the
developer explicitly enables symbolic links (which IIUC is not trivial).
### Possible alternatives
My next favorite approaches (which we could switch to later) would be:
#### `xtask`
Set up a CI check and a [Cargo `xtask`] so that `cargo xtask cli-help-to-md`
essentially runs `cargo run -- util markdown-help > docs/cli-reference.md` from
the project root.
Every developer would have to know to run `cargo xtask cli-help-to-md` if
they change the help text.
Eventually, we could have `cargo xtask preflight` that runs `cargo +nightly
fmt; cargo xtask cli-help-to-md; cargo nextest run`, or `cargo insta`.
#### Only generate markdown for CLI help when building the website, don't track it in Git.
I think that having the file in the repo will be nice to preview changes to
docs, and it'll allow people to consult the file on GitHub or in their repo.
The (currently) very fast job of building the website would now require
installing Rust and building `jj`.
#### Same as the `xtask`, but use a shell script instead of an `xtask`
An `xtask` might seem like overkill, since it's Rust instead of a shell script.
However, I don't want this to be a shell script so that new contributors on
Windows can still easily run it ( since this will be necessary for the CI to
pass) without us having to support a batch file.
#### Cargo Alias
My first attempt was to set up a [cargo alias] to run this, but that doesn't
support redirection (so I had to change the `jj util` command to output to a
file) and, worse, is incapable of executing the command *in the project root*
regardless of where in the project the current directory is. Again, this seems
to be too inconvenient for a command that every new PR author would have to run
to pass CI.
Overall, this just seems a bit ugly. I did file
https://github.com/rust-lang/cargo/issues/13348, I'm not really sure that was
worthwhile, though.
**Aside:** For reference, the alias was:
```toml
# .cargo/config.toml
alias.gen-cli-reference = "run -p jj-cli -- util markdown-help docs/cli-reference.md"
```
### Non-alternatives
#### Clap's new feature
`clap` recently obtained a similarly-sounding feature in
https://github.com/clap-rs/clap/pull/5206. However, it only prints short help
for subcommands and can't be triggered by an option AFAICT, so it won't help us
too much.
[Cargo `xtask`]: https://github.com/matklad/cargo-xtask
[cargo alias]: https://doc.rust-lang.org/cargo/reference/config.html#alias
