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 or complexity:low issue.
• Fix bugs found by Clang, PVS or Coverity.

Reporting problems

• Check the FAQ.
• Search existing 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.
• Use ASAN/UBSAN to get detailed errors for segfaults and undefined behavior.
• 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.
  

• Improve documentation

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.
• Avoid cosmetic changes to unrelated files in the same commit.
• Use a 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).

1. [RFC] is assumed by default, do not put "RFC" in the PR title (it adds noise to merge commit messages).
2. Add [WIP] to the PR title if you are not requesting feedback and the work is still in flux.
3. Add [RDY] to the PR title if you are done and only waiting on merge.

Commit messages

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

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

[optional body]

[optional footer(s)]

• Prefix the commit subject with one of the following types:

  • build: all changes related to the build system (involving scripts, configurations or tools) and package dependencies.
  • ci: all changes related to the continuous integration and deployment system - involving scripts, configurations or tools.
  • docs: all documentation changes. This includes both external documentation intended for end users as well as internal documentation intended for developers.
  • feat: new abilities or functionality.
  • fix: a bug fix.
  • perf: performance improvements.
  • refactor: modification of the code base which neither adds a feature nor fixes a bug - such as removing redundant code, simplifying the code, renaming variables, etc.
  • revert: revert previous commits.
  • test: all changes related to tests such as refactoring existing tests or adding new tests.
  • vim-patch: all patches from upstream Vim. The commit messages for patches has slightly different rules as not to interfere with existing scripts.
  • chore: Lastly, if none of the types above fits you may use chore as the type.

• Append optional scope to type if possible: (lsp), (treesitter) or (float/windows).

• Try to keep the first line under 72 characters.

• A blank line must separate the subject from the description.

• A breaking API change must be indicated by appending ! after the type/scope and at the very beginning of the footer with a BREAKING CHANGE.

  Example:

  refactor(provider)!: drop support for Python 2
  
  BREAKING CHANGE: refactor to use Python 3 features since Python 2 is no longer supported.
  

• 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, sourcehut and AppVeyor.

• CI builds are compiled with -Werror, so compiler warnings will fail the build.
• If any tests fail, the build will fail. See test/README.md#running-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 build checks modified lines and their immediate neighbors, to encourage incrementally updating the legacy style to meet our style. (See #3174 for background.)
• CI for freebsd and openbsd runs on sourcehut.
  • To get a backtrace on freebsd (after connecting via ssh):

    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 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 to see potential bugs found by 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 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)):

  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

• Use universal-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.

Reviewing

To help review pull requests, start with this checklist.

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

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

Use git log -p master..FETCH_HEAD 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.