neovim/CONTRIBUTING.md

Contributing to Neovim
======================

Getting started
---------------

If you want to help but don't know where to start, here are some
low-risk/isolated tasks:

- [Merge a Vim patch].
- Try a [good first issue](../../labels/good-first-issue) or [complexity:low] issue.
- Fix bugs found by [Clang](#clang-scan-build), [PVS](#pvs-studio) or
  [Coverity](#coverity).
- [Improve documentation][wiki-contribute-help]

Reporting problems
------------------

- [Check the FAQ][wiki-faq].
- [Search existing issues][github-issues] (including closed!)
- Update Neovim to the latest version to see if your problem persists.
- [Bisect](https://neovim.io/doc/user/starting.html#bisect) your config: disable plugins incrementally, to narrow down the cause of the issue.
- [Bisect][git-bisect] Neovim's source code to find the cause of a regression, if you can. This is _extremely_ helpful.
- When reporting a crash, [include a stacktrace](https://github.com/neovim/neovim/wiki/FAQ#backtrace-linux).
- Use [ASAN/UBSAN](#clang-sanitizers-asan-and-ubsan) to get detailed errors for segfaults and undefined behavior.
- Check the logs. `:edit $NVIM_LOG_FILE`
- Include `cmake --system-information` for build-related issues.

Developer guidelines
--------------------

- Nvim developers should read `:help dev`.
- External UI developers should read `:help dev-ui`.
- API client developers should read `:help dev-api-client`.
- Nvim developers are _strongly encouraged_ to install `ninja` for faster builds.
  ```
  sudo apt-get install ninja-build
  make distclean
  make  # Nvim build system uses ninja automatically, if available.
  ```

Pull requests (PRs)
---------------------

- To avoid duplicate work, create a draft pull request.
- Your PR must include [test coverage][run-tests].
- Avoid cosmetic changes to unrelated files in the same commit.
- Use a [feature branch][git-feature-branch] instead of the master branch.
- Use a **rebase workflow** for small PRs.
  - After addressing review comments, it's fine to rebase and force-push.
- Use a **merge workflow** for big, high-risk PRs.
  - Merge `master` into your PR when there are conflicts or when master
    introduces breaking changes.
  - Use the `ri` git alias:
    ```
    [alias]
    ri = "!sh -c 't=\"${1:-master}\"; s=\"${2:-HEAD}\"; mb=\"$(git merge-base \"$t\" \"$s\")\"; if test \"x$mb\" = x ; then o=\"$t\"; else lm=\"$(git log -n1 --merges \"$t..$s\" --pretty=%H)\"; if test \"x$lm\" = x ; then o=\"$mb\"; else o=\"$lm\"; fi; fi; test $# -gt 0 && shift; test $# -gt 0 && shift; git rebase --interactive \"$o\" \"$@\"'"
    ```
    This avoids unnecessary rebases yet still allows you to combine related
    commits, separate monolithic commits, etc.
  - Do not edit commits that come before the merge commit.
- During a squash/fixup, use `exec make -C build unittest` between each
  pick/edit/reword.

### Stages: Draft and Ready for review

Pull requests have two stages: Draft and Ready for review.

1. [Create a Draft PR][pr-draft] while you are _not_ requesting feedback as
  you are still working on the PR.
    - You can skip this if your PR is ready for review.
2. [Change your PR to ready][pr-ready] when the PR is ready for review.
    - You can convert back to Draft at any time.

Do __not__ add labels like `[RFC]` or `[WIP]` in the title to indicate the
state of your PR: this just adds noise. Non-Draft PRs are assumed to be open
for comments; if you want feedback from specific people, `@`-mention them in
a comment.

### Commit messages

Follow the [conventional commits guidelines][conventional_commits] to *make reviews easier* and to make
the VCS/git logs more valuable. The general structure of a commit message is:

```
<type>([optional scope]): <description>

[optional body]

[optional footer(s)]
```

- Prefix the commit subject with one of these [_types_](https://github.com/commitizen/conventional-commit-types/blob/master/index.json):
    - `build`, `ci`, `docs`, `feat`, `fix`, `perf`, `refactor`, `revert`, `test`, `vim-patch`, `chore`
    - You can **ignore this for "fixup" commits** or any commits you expect to be squashed.
- Append optional scope to _type_ such as `(lsp)`, `(treesitter)`, `(float)`, …
- _Description_ shouldn't start with a capital letter or end in a period.
- Use the _imperative voice_: "Fix bug" rather than "Fixed bug" or "Fixes bug."
- Try to keep the first line under 72 characters.
- A blank line must follow the subject.
- Breaking API changes must be indicated by
    1. "!" after the type/scope, and
    2. a "BREAKING CHANGE" footer describing the change.
       Example:
       ```
       refactor(provider)!: drop support for Python 2

       BREAKING CHANGE: refactor to use Python 3 features since Python 2 is no longer supported.
       ```

### Automated builds (CI)

Each pull request must pass the automated builds on [sourcehut] and [GitHub Actions].

- CI builds are compiled with [`-Werror`][gcc-warnings], so compiler warnings
  will fail the build.
- If any tests fail, the build will fail.
  See [test/README.md#running-tests][run-tests] to run tests locally.
  Passing locally doesn't guarantee passing the CI build, because of the
  different compilers and platforms tested against.
- CI runs [ASan] and other analyzers.
    - To run valgrind locally: `VALGRIND=1 make test`
    - To run Clang ASan/UBSan locally: `CC=clang make CMAKE_FLAGS="-DCLANG_ASAN_UBSAN=ON"`
- The [lint](#lint) build checks modified lines _and their immediate
  neighbors_, to encourage incrementally updating the legacy style to meet our
  [style](#style). (See [#3174][3174] for background.)
- CI for freebsd and openbsd runs on [sourcehut].
    - To get a backtrace on freebsd (after connecting via ssh):
      ```sh
      sudo pkg install tmux  # If you want tmux.
      lldb build/bin/nvim -c nvim.core

      # To get a full backtrace:
      #   1. Rebuild with debug info.
      rm -rf nvim.core build
      gmake CMAKE_BUILD_TYPE=RelWithDebInfo CMAKE_EXTRA_FLAGS="-DCI_BUILD=ON -DMIN_LOG_LEVEL=3" nvim
      #   2. Run the failing test to generate a new core file.
      TEST_FILE=test/functional/foo.lua gmake functionaltest
      lldb build/bin/nvim -c nvim.core
      ```

### Clang scan-build

View the [Clang report] to see potential bugs found by the Clang
[scan-build](https://clang-analyzer.llvm.org/scan-build.html) analyzer.

- Search the Neovim commit history to find examples:
  ```
  git log --oneline --no-merges --grep clang
  ```
- To verify a fix locally, run `scan-build` like this:
  ```
  rm -rf build/
  scan-build --use-analyzer=/usr/bin/clang make
  ```

### PVS-Studio

View the [PVS report](https://neovim.io/doc/reports/pvs/PVS-studio.html.d/) to
see potential bugs found by [PVS Studio](https://www.viva64.com/en/pvs-studio/).

- Use this format for commit messages (where `{id}` is the PVS warning-id)):
  ```
  PVS/V{id}: {description}
  ```
- Search the Neovim commit history to find examples:
  ```
  git log --oneline --no-merges --grep PVS
  ```
- Try `./scripts/pvscheck.sh` to run PVS locally.

### Coverity

[Coverity](https://scan.coverity.com/projects/neovim-neovim) runs against the
master build. To view the defects, just request access; you will be approved.

- Use this format for commit messages (where `{id}` is the CID (Coverity ID);
  ([example](https://github.com/neovim/neovim/pull/804))):
  ```
  coverity/{id}: {description}
  ```
- Search the Neovim commit history to find examples:
  ```
  git log --oneline --no-merges --grep coverity
  ```

### Clang sanitizers (ASAN and UBSAN)

  ASAN/UBSAN can be used to detect memory errors and other common forms of undefined behavior at runtime in debug builds.

- To build Neovim with sanitizers enabled, use
  ```
  rm -rf build && CMAKE_EXTRA_FLAGS="-DCMAKE_C_COMPILER=clang -DCLANG_ASAN_UBSAN=1" make
  ```
- When running Neovim, use
  ```
  UBSAN_OPTIONS=print_stacktrace=1 ASAN_OPTIONS=log_path=/tmp/nvim_asan nvim args...
  ```
- If Neovim exits unexpectedly, check `/tmp/nvim_asan.{PID}` (or your preferred `log_path`) for log files with error messages.


Coding
------

### Lint

You can run the linter locally by:

    make lint

The lint step downloads the [master error list] and excludes them, so only lint
errors related to the local changes are reported.

You can lint a single file (but this will _not_ exclude legacy errors):

    ./src/clint.py src/nvim/ops.c

### Style

The repo includes a `.clang-format` config file which (mostly) matches the
[style-guide].  You can use `clang-format` to format code with the `gq`
operator in Nvim:

    if !empty(findfile('.clang-format', ';'))
      setlocal formatprg=clang-format\ -style=file
    endif

### Navigate

- Set `blame.ignoreRevsFile` to ignore [noise commits](https://github.com/neovim/neovim/commit/2d240024acbd68c2d3f82bc72cb12b1a4928c6bf) in git blame:
  ```
  git config blame.ignoreRevsFile .git-blame-ignore-revs
  ```
- Use **[universal-ctags](https://github.com/universal-ctags/ctags).**
  ("Exuberant ctags", the typical `ctags` binary provided by your distro, is
  unmaintained and won't recognize many function signatures in Neovim source.)
- Explore the source code [on the web](https://sourcegraph.com/github.com/neovim/neovim).


Reviewing
---------

To help review pull requests, start with [this checklist][review-checklist].

Reviewing can be done on GitHub, but you may find it easier to do locally.
Using [`hub`][hub], you can create a new branch with the contents of a pull
request, e.g. [#1820][1820]:

    hub checkout https://github.com/neovim/neovim/pull/1820

Use [`git log -p master..FETCH_HEAD`][git-history-filtering] to list all
commits in the feature branch which aren't in the `master` branch; `-p`
shows each commit's diff. To show the whole surrounding function of a change
as context, use the `-W` argument as well.

[gcc-warnings]: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
[git-bisect]: http://git-scm.com/book/en/v2/Git-Tools-Debugging-with-Git
[git-feature-branch]: https://www.atlassian.com/git/tutorials/comparing-workflows
[git-history-filtering]: https://www.atlassian.com/git/tutorials/git-log/filtering-the-commit-history
[git-history-rewriting]: http://git-scm.com/book/en/v2/Git-Tools-Rewriting-History
[git-rebasing]: http://git-scm.com/book/en/v2/Git-Branching-Rebasing
[github-issues]: https://github.com/neovim/neovim/issues
[1820]: https://github.com/neovim/neovim/pull/1820
[hub]: https://hub.github.com/
[conventional_commits]: https://www.conventionalcommits.org
[style-guide]: http://neovim.io/develop/style-guide.xml
[ASan]: http://clang.llvm.org/docs/AddressSanitizer.html
[run-tests]: https://github.com/neovim/neovim/blob/master/test/README.md#running-tests
[wiki-faq]: https://github.com/neovim/neovim/wiki/FAQ
[review-checklist]: https://github.com/neovim/neovim/wiki/Code-review-checklist
[3174]: https://github.com/neovim/neovim/issues/3174
[sourcehut]: https://builds.sr.ht/~jmk
[GitHub Actions]: https://github.com/neovim/neovim/actions
[Merge a Vim patch]: https://github.com/neovim/neovim/wiki/Merging-patches-from-upstream-Vim
[Clang report]: https://neovim.io/doc/reports/clang/
[complexity:low]: https://github.com/neovim/neovim/issues?q=is%3Aopen+is%3Aissue+label%3Acomplexity%3Alow
[master error list]: https://raw.githubusercontent.com/neovim/doc/gh-pages/reports/clint/errors.json
[wiki-contribute-help]: https://github.com/neovim/neovim/wiki/contribute-%3Ahelp
[pr-draft]: https://docs.github.com/en/github/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request
[pr-ready]: https://docs.github.com/en/github/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-stage-of-a-pull-request