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 [complexity:low] issue.
- Fix bugs found by [Clang](#clang-scan-build), [PVS](#pvs-studio) or
  [Coverity](#coverity).

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.
- Disable plugins incrementally, to narrow down the cause of the issue.
- When reporting a crash, [include a stacktrace](https://github.com/neovim/neovim/wiki/FAQ#backtrace-linux).
- [Bisect][git-bisect] to the cause of a regression, if you are able. This is _extremely_ helpful.
- Check `$NVIM_LOG_FILE`, if it exists.
- Include `cmake --system-information` for build-related issues.

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

- Nvim contributors 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 `[WIP]` pull request as soon as possible.
- Your PR must include **test coverage.** See [test/README.md][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: WIP, RFC, RDY

Pull requests have three stages: `[WIP]` (Work In Progress), `[RFC]` (Request
For Comment) and `[RDY]` (Ready).

- `[RFC]` is assumed by default, i.e. you are requesting a review.
- Add `[WIP]` to the PR title if you are _not_ requesting feedback and the work
  is still in flux.
- Add `[RDY]` if you are _done_ and only waiting on merge.

### Commit messages

Follow [commit message hygiene][hygiene] to *make reviews easier* and to make
the VCS/git logs more valuable.

- Try to keep the first line under 72 characters.
- **Prefix the commit subject with a _scope_:** `doc:`, `test:`, `foo.c:`,
  `runtime:`, ...
    - Subject line for commits with only style/lint changes can be a single
      word: `style` or `lint`.
- A blank line must separate the subject from the description.
- Use the _imperative voice_: "Fix bug" rather than "Fixed bug" or "Fixes bug."

### Automated builds (CI)

Each pull request must pass the automated builds on [Travis CI], [QuickBuild]
and [AppVeyor].

- 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.)
- [How to investigate QuickBuild failures](https://github.com/neovim/neovim/pull/4718#issuecomment-217631350)
    - QuickBuild uses this invocation:
      ```
      mkdir -p build/${params.get("buildType")} \
      && cd build/${params.get("buildType")} \
      && cmake -G "Unix Makefiles" -DBUSTED_OUTPUT_TYPE=TAP -DCMAKE_BUILD_TYPE=${params.get("buildType")}
      -DTRAVIS_CI_BUILD=ON ../.. && ${node.getAttribute("make", "make")}
      VERBOSE=1 nvim unittest-prereqs functionaltest-prereqs
      ```

### 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
  ```


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

- 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/
[hygiene]: http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html
[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
[Travis CI]: https://travis-ci.org/neovim/neovim
[QuickBuild]: http://neovim-qb.szakmeister.net/dashboard
[AppVeyor]: https://ci.appveyor.com/project/neovim/neovim
[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