How to Contribute¶
Policies¶
We'd love to accept your patches and contributions to this project. There are just a few small guidelines you need to follow.
Contributor License Agreement¶
Contributions to this project must be accompanied by a Contributor License Agreement. You (or your employer) retain the copyright to your contribution; this simply gives us permission to use and redistribute your contributions as part of the project. Head over to https://cla.developers.google.com/ to see your current agreements on file or to sign a new one.
You generally only need to submit a CLA once, so if you've already submitted one (even if it was for a different project), you probably don't need to do it again.
Code reviews¶
All submissions, including submissions by project members, require review. We use GitHub pull requests for this purpose. Consult GitHub Help for more information on using pull requests.
Unlike many GitHub projects (but like many VCS projects), we care more about the contents of commits than about the contents of PRs. We review each commit separately, and we don't squash-merge the PR (so please manually squash any fixup commits before sending for review).
Each commit should ideally do one thing. For example, if you need to refactor a
function in order to add a new feature cleanly, put the refactoring in one
commit and the new feature in a different commit. If the refactoring itself
consists of many parts, try to separate out those into separate commits. You can
use jj split
to do it if you didn't realize ahead of time how it should be
split up. Include tests and documentation in the same commit as the code the
test and document. The commit message should describe the changes in the commit;
the PR description can even be empty, but feel free to include a personal
message.
When you address comments on a PR, don't make the changes in a commit on top (as
is typical on GitHub). Instead, please make the changes in the appropriate
commit. You can do that by checking out the commit (jj checkout/new <commit>
)
and then squash in the changes when you're done (jj squash
). jj git push
will automatically force-push the branch.
When your first PR has been approved, we typically give you contributor access, so you can address any remaining minor comments and then merge the PR yourself when you're ready. If you realize that some comments require non-trivial changes, please ask your reviewer to take another look.
To avoid conflicts of interest, please don't merge a PR that has only been approved by someone from the same organization. Similarly, as a reviewer, there is no need to approve your coworkers' PRs, since the author should await an approval from someone else anyway. It is of course still appreciated if you review and comment on their PRs. Also, if the PR seems completely unrelated to your company's interests, do feel free to approve it.
Community Guidelines¶
This project follows Google's Open Source Community Guidelines.
Contributing to the documentation¶
We appreciate bug
reports
about any problems, however small, lurking in our documentation
website or in the jj help
<command>
docs. If a part of the bug report template does not apply, you can
just delete it.
Before reporting a problem with the documentation website, we'd appreciate it if
you could check that the problem still exists in the "prerelease" version of the
documentation (as opposed to the docs for one of the released versions of jj
).
You can use the version switcher in the top-left of the website to do so.
If you are willing to make a PR fixing a documentation problem, even better!
The documentation website sources are Markdown files located in the docs/
directory. You do not need to
know Rust to work with them. See below for instructions on how to preview the
HTML docs as you edit the Markdown files.
Doing so is optional, but recommended.
The jj help
docs are sourced from the "docstring" comments inside the Rust
sources, currently from the cli/src/commands
directory. Working
on them requires setting up a Rust development environment, as described
below, and may occasionally require adjusting a test.
Learning Rust¶
In addition to the Rust Book and the other excellent resources at https://www.rust-lang.org/learn, we recommend the "Comprehensive Rust" mini-course for an overview, especially if you are familiar with C++.
Setting up a development environment¶
To develop jj
, the mandatory steps are simply
to install Rust (the default
installer options are fine), clone the repository, and use cargo build
, cargo fmt
,
cargo clippy --workspace --all-targets
, and
cargo test --workspace
. If you are preparing a PR, there are some additional
recommended steps.
You will probably also want to make the gh-pages
branch immutable (and thereby
hidden from the default jj log
output) by running the following in your repo:
jj config set --repo "revset-aliases.immutable_heads()" "main@origin | gh-pages@origin"
Summary¶
One-time setup:
rustup toolchain add nightly # wanted for 'rustfmt'
rustup toolchain add 1.76 # also specified in Cargo.toml
cargo install cargo-insta
cargo install cargo-watch
cargo install cargo-nextest
During development (adapt according to your preference):
cargo watch --ignore '.jj/**' -s \
'cargo clippy --workspace --all-targets \
&& cargo +1.76 check --workspace --all-targets'
cargo +nightly fmt # Occasionally
cargo nextest run --workspace # Occasionally
cargo insta test --workspace --test-runner nextest # Occasionally
WARNING: Build artifacts from debug builds and especially from repeated
invocations of cargo test
can quickly take up 10s of GB of disk space.
Cargo will happily use up your entire hard drive. If this happens, run
cargo clean
.
Explanation¶
These are listed roughly in order of decreasing importance.
-
Nearly any change to
jj
's CLI will require writing or updating snapshot tests that use theinsta
crate. To make this convenient, install thecargo-insta
binary. Usecargo insta test --workspace
to run tests, andcargo insta review --workspace
to update the snapshot tests. The--workspace
flag is needed to run the tests on all crates; by default, only the crate in the current directory is tested. -
GitHub CI checks require that the code is formatted with the nightly version of
rustfmt
. To do this on your computer, install the nightly toolchain and usecargo +nightly fmt
. -
Your code will be rejected if it cannot be compiled with the minimal supported version of Rust ("MSRV"). Currently,
jj
follows a rather casual MSRV policy: "The currentrustc
stable version, minus one." As of this writing, that version is 1.76.0. -
Your code needs to pass
cargo clippy
. You can also usecargo +nightly clippy
if you wish to see more warnings. -
You may also want to install and use
cargo-watch
. In this case, you should exclude.jj
. directory from the filesystem watcher, as it gets updated on everyjj log
. -
To run tests more quickly, use
cargo nextest run --workspace
. To usenextest
withinsta
, usecargo insta test --workspace --test-runner nextest
.On Linux, you may be able to speed up
nextest
even further by using themold
linker, as explained below.
Using mold
for faster tests on Linux¶
On a machine with a multi-core CPU, one way to speed up
cargo nextest
on Linux is to use the multi-threaded mold
linker. This linker may help
if, currently, your CPU is underused while Rust is linking test
binaries. Before proceeding with mold
, you can check whether this is
an issue worth solving using a system monitoring tool such as htop
.
mold
is packaged for many distributions. On Debian, for example,
sudo apt install mold
should just work.
A simple way to use mold
is via the -run
option, e.g.:
mold -run cargo insta test --workspace --test-runner nextest
There will be no indication that a different linker is used, except for
higher CPU usage while linking and, hopefully, faster completion. You
can verify that mold
was indeed used by running
readelf -p .comment target/debug/jj
.
There are also ways of having Rust use mold
by default, see the "How
to use" instructions.
On recent versions of MacOS, the default linker Rust uses is already multi-threaded. It should use all the CPU cores without any configuration.
Previewing the HTML documentation¶
The documentation for jj
is automatically published to the website at
https://martinvonz.github.io/jj/.
When editing documentation, we'd appreciate it if you checked that the result will look as expected when published to the website.
Setting up the prerequisites¶
To build the website, you must have Python and poetry
installed. If
your distribution packages poetry
, something like apt install
python3-poetry
is likely the best way to install it. Otherwise, you
can download Python from https://python.org or follow the Python
installation instructions. Finally, follow the Poetry installation
instructions.
Once you have poetry
installed, you should ask it to install the rest
of the required tools into a virtual environment as follows:
# --no-root avoids a harmless error message starting with Poetry 1.7
poetry install --no-root
You may get requests to "unlock a keyring", an error messages about failing to
do so, or, in the case of
Poetry 1.7, it may simply hang
indefinitely. The
workaround is to either to unlock the keyring or to run the following, and then
to try poetry install --no-root
again:
# For sh-compatible shells or recent versions of `fish`
export PYTHON_KEYRING_BACKEND=keyring.backends.fail.Keyring
Building the HTML docs locally (with live reload)¶
The HTML docs are built with MkDocs. After following the above steps, you should be able to view the docs by running
# Note: this and all the commands below should be run from the root of
# the `jj` source tree.
poetry run -- mkdocs serve
and opening http://127.0.0.1:8000 in your browser.
As you edit the md
files, the website should be rebuilt and reloaded in your
browser automatically, unless build errors occur.
You should occasionally check the terminal from which you ran mkdocs serve
for
any build errors or warnings. Warnings about "GET /versions.json HTTP/1.1" code
404
are expected and harmless.
How to build the entire website (not usually necessary)¶
The full jj
website includes the documentation for several jj
versions
(prerelease
, latest release, and the older releases). The top-level
URL https://martinvonz.github.io/jj redirects to
https://martinvonz.github.io/jj/latest, which in turn redirects to
the docs for the last stable version.
The different versions of documentation are managed and deployed with
mike
, which can be run with
poetry run -- mike
.
On a POSIX system or WSL, one way to build the entire website is as follows (on Windows, you'll need to understand and adapt the shell script):
-
Check out
jj
as a co-locatedjj + git
repository (jj clone --colocate
), cloned from your fork ofjj
(e.g.jjfan.github.com/jj
). You can also use a pure Git repo if you prefer. -
Make sure
jjfan.github.com/jj
includes thegh-pages
branch of the jj repo and rungit fetch origin gh-pages
. -
Go to the GitHub repository settings, enable GitHub Pages, and configure them to use the
gh-pages
branch (this is usually the default). -
Run the same
sh
script that is used in GitHub CI (details below):.github/scripts/docs-build-deploy 'https://jjfan.github.io/jj/'\ prerelease main --push
This should build the version of the docs from the current commit, deploy it as a new commit to the
gh-pages
branch, and push thegh-pages
branch to the origin. -
Now, you should be able to see the full website, including your latest changes to the
prerelease
version, athttps://jjfan.github.io/jj/prerelease/
. -
(Optional) The previous steps actually only rebuild
https://jjfan.github.io/jj/prerelease/
and its aliashttps://jjfan.github.io/jj/main/
. If you'd like to test out version switching back and forth, you can also rebuild the docs for the latest release as follows.jj new v1.33.1 # Let's say `jj 1.33.1` is the currently the latest release .github/scripts/docs-build-deploy 'https://jjfan.github.io/jj/'\ v1.33.1 latest --push
-
(Optional) When you are done, you may want to reset the
gh-branches
to the same spot as it is in the upstream. If you configured theupstream
remote, this can be done with:# This will LOSE any changes you made to `gh-pages` jj git fetch --remote upstream jj branch set gh-pages -r gh-pages@upstream jj git push --remote origin --branch gh-pages
If you want to preserve some of the changes you made, you can do
jj branch set my-changes -r gh-pages
BEFORE running the above commands.
Explanation of the docs-build-deploy
script¶
The script sets up the site_url
mkdocs config to
'https://jjfan.github.io/jj/'
. If this config does not match the URL
where you loaded the website, some minor website features (like the
version switching widget) will have reduced functionality.
Then, the script passes the rest of its arguments to potery run -- mike
deploy
, which does the rest of the job. Run poetry run -- mike help deploy
to
find out what the arguments do.
If you need to do something more complicated, you can use poetry run -- mike
...
commands. You can also edit the gh-pages
branch directly, but take care
to avoid files that will be overwritten by future invocations of mike
. Then,
you can submit a PR based on the gh-pages
branch of
https://martinvonz.github.com/jj (instead of the usual main
branch).
Modifying protobuffers (this is not common)¶
Occasionally, you may need to change the .proto
files that define jj's data
storage format. In this case, you will need to add a few steps to the above
workflow.
- Install the
protoc
compiler. This usually means eitherapt-get install protobuf-compiler
or downloading an official release. Theprost
library docs have additional advice. - Run
cargo run -p gen-protos
regularly (or after every edit to a.proto
file). This is the same as runningcargo run
fromlib/gen-protos
. Thegen-protos
binary will use theprost-build
library to compile the.proto
files into.rs
files. - If you are adding a new
.proto
file, you will need to edit the list of these files inlib/gen-protos/src/main.rs
.
The .rs
files generated from .proto
files are included in the repository,
and there is a GitHub CI check that will complain if they do not match.
Profiling¶
One easy-to-use sampling profiler is samply. For example:
cargo install samply
samply record jj diff
Another option is to use the instrumentation we've added manually (using
tracing::instrument
) in various places. For example:
JJ_TRACE=/tmp/trace.json jj diff
https://ui.perfetto.dev/
in Chrome and load /tmp/trace.json
from
there.