carbon-lang/docs/project/contribution_tools.md

Contribution tools

The Carbon language project has a number of tools used to assist in preparing contributions.

Table of contents

• Setup commands
  • Debian or Ubuntu
  • macOS
• Tools
  • Main tools
    • Running pre-commit
  • Optional tools
  • Manually building Clang and LLVM (not recommended)
• Troubleshooting build issues
  • Old LLVM versions
  • Asking for help
• Troubleshooting debug issues
  • Debugging on MacOS

Setup commands

These commands should help set up a development environment on your machine.

Debian or Ubuntu

# Update apt.
sudo apt update

# Check that the `clang` version is at least 16, our minimum version. That needs
# the number of the `:` in the output to be over 16. For example, `1:16.0-57`.
apt-cache show clang | grep 'Version:'

# Install tools.
sudo apt install \
  bazel \
  clang \
  gh \
  libc++-dev \
  libc++abi-dev \
  lld \
  python3 \
  pipx

# Install pre-commit.
pipx install pre-commit

# Set up git.
# If you don't already have a fork:
gh repo fork --clone carbon-language/carbon-lang
cd carbon-lang
pre-commit install

# Run tests.
bazel test //...:all

If the version of clang is earlier than 16, you may still have version 16 available. You can use the following install instead:

# Install explicitly versioned Clang tools.
sudo apt install \
  clang-16 \
  libc++-16-dev \
  libc++abi-16-dev \
  lld-16

# In your Carbon checkout, tell Bazel where to find `clang`. You can also
# export this path as the `CC` environment variable, or add it directly to
# your `PATH`.
echo "build --repo_env=CC=$(readlink -f $(which clang-16))" >> user.bazelrc

NOTE: Most LLVM 16+ installs should build Carbon. If you're having issues, see troubleshooting build issues.

NOTE: If you don't have a bazel package, see Bazel's install instructions for help.

macOS

# Install Hombrew.
/bin/bash -c "$(curl -fsSL \
  https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

# IMPORTANT: Make sure `brew` is added to the PATH!

# Install Homebrew tools.
brew install \
  bazelisk \
  gh \
  llvm \
  python@3.10 \
  pre-commit

# IMPORTANT: Make sure `llvm` is added to the PATH! It's separate from `brew`.

# Set up git.
gh repo fork --clone carbon-language/carbon-lang
cd carbon-lang
pre-commit install

# Run tests.
bazel test //...:all

NOTE: On macOS, you should end up adding rc file lines similar to:

> # For `brew`, `gh`, and other tools:
> export PATH="${HOME}/.brew/bin:${PATH}"
> # For `llvm`:
> export PATH="$(brew --prefix llvm)/bin:${PATH}"
> ```

<!-- google-doc-style-resume -->

## Tools

### Main tools

These tools are essential for work on Carbon.

-   Package managers
    -   `apt` (for Debian or Ubuntu)
        -   To upgrade versions of `apt` packages, it will be necessary to
            periodically run `sudo apt update && sudo apt upgrade`.
    -   [Homebrew](https://brew.sh/) (for macOS)
        -   To upgrade versions of `brew` packages, it will be necessary to
            periodically run `brew upgrade`.
    -   [`python3` and `pip3`](https://python.org)
        -   Carbon requires Python 3.9 or newer.
        -   To upgrade versions of `pip3` packages, it will be necessary to
            periodically run `pip3 list --outdated`, then
            `pip3 install -U <package>` to upgrade desired packages.
        -   When upgrading, version dependencies may mean packages _should_ be
            outdated, and not be upgraded.
-   Main tools
    -   [Bazel](https://www.bazel.build/)
        -   NOTE: See [the bazelisk config](/.bazeliskrc) for a supported
            version.
    -   [Bazelisk](https://docs.bazel.build/versions/master/install-bazelisk.html)
        (for macOS): Handles Bazel versions.
    -   [Clang](https://clang.llvm.org/) and [LLVM](https://llvm.org/)
        -   NOTE: Most LLVM 14+ installs should build Carbon. If you're having
            issues, see
            [troubleshooting build issues](#troubleshooting-build-issues).
    -   [gh CLI](https://github.com/cli/cli): Helps with GitHub.
    -   [pre-commit](https://pre-commit.com): Validates and cleans up git
        commits.

#### Running pre-commit

[pre-commit](https://pre-commit.com) is typically set up using
`pre-commit install`. When set up in this mode, it will check for issues when
`git commit` is run. A typical commit workflow looks like:

1.  `git commit` to try committing files. This automatically executes
    `pre-commit run`, which may fail and leave files modified for cleanup.
2.  `git add .` to add the automatically modifications done by `pre-commit`.
3.  `git commit` again.

You can also use `pre-commit run` to check pending changes without `git commit`,
or `pre-commit run -a` to run on all files in the repository.

> NOTE: Some developers prefer to run `pre-commit` on `git push` instead of
> `git commit` because they want to commit files as originally authored instead
> of with pre-commit modifications. To switch, run
> `pre-commit uninstall && pre-commit install -t pre-push`.

### Optional tools

These tools aren't necessary to contribute to Carbon, but can be worth
considering if they fit your workflow.

-   [GitHub Desktop](https://desktop.github.com/): A UI for managing GitHub
    repositories.
-   `rs-git-fsmonitor` and Watchman: Helps make `git` run faster on large
    repositories.
    -   **WARNING**: Bugs in `rs-git-fsmonitor` and/or Watchman can result in
        `pre-commit` deleting files. If you see files being deleted, disable
        `rs-git-fsmonitor` with `git config --unset core.fsmonitor`.
-   [vim-prettier](https://github.com/prettier/vim-prettier): A vim integration
    for [Prettier](https://prettier.io/), which we use for formatting.
-   [Visual Studio Code](https://code.visualstudio.com/): A code editor.
    -   We provide [recommended extensions](/.vscode/extensions.json) to assist
        Carbon development. Some settings changes must be made separately:
        -   Python › Formatting: Provider: `black`
    -   **WARNING:** Visual Studio Code modifies the `PATH` environment
        variable, particularly in the terminals it creates. The `PATH`
        difference can cause `bazel` to detect different startup options,
        discarding its build cache. As a consequence, it's recommended to use
        **either** normal terminals **or** Visual Studio Code to run `bazel`,
        not both in combination. Visual Studio Code can still be used for other
        purposes, such as editing files, without interfering with `bazel`.
    -   [DevContainers](https://code.visualstudio.com/docs/remote/containers): A
        way to use Docker for build environments.
        -   After following the
            [installation instructions](https://code.visualstudio.com/docs/remote/containers#_installation),
            you should be prompted to use Carbon's
            [devcontainer](/.devcontainer/devcontainer.json) with "Reopen in
            container".

### Manually building Clang and LLVM (not recommended)

We primarily test against [apt.llvm.org](https://apt.llvm.org) and Homebrew
installations. However, you can build and install LLVM yourself if you feel more
comfortable with it. The essential CMake options to pass in order for this to
work reliably include:

-DLLVM_ENABLE_PROJECTS=clang;clang-tools-extra;lld -DLLVM_ENABLE_RUNTIMES=compiler-rt;libcxx;libcxxabi;libunwind -DRUNTIMES_CMAKE_ARGS=-DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=OFF;-DCMAKE_POSITION_INDEPENDENT_CODE=ON;-DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=ON;-DLIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY=OFF;-DLIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY=ON;-DLIBCXX_USE_COMPILER_RT=ON;-DLIBCXXABI_USE_COMPILER_RT=ON;-DLIBCXXABI_USE_LLVM_UNWINDER=ON

## Troubleshooting build issues

### Old LLVM versions

Many build issues result from the particular options `clang` and `llvm` have
been built with, particularly when it comes to system-installed versions. If you
run `clang --version`, you should see at least version 16. If you see an older
version, please update, or use the special `clang-16` instructions above.

System installs of macOS typically won't work, for example being an old LLVM
version or missing llvm-ar; [setup commands](#setup-commands) includes LLVM from
Homebrew for this reason.

It may be necessary to run `bazel clean` after updating versions in order to
clean up cached state.

### Asking for help

If you're having trouble resolving issues, please ask on
[#build-help](https://discord.com/channels/655572317891461132/824137170032787467),
providing the output of the following diagnostic commands:

```shell
echo $CC
which clang
which clang-16
clang --version
grep llvm_bindir $(bazel info workspace)/bazel-execroot/external/bazel_cc_toolchain/clang_detected_variables.bzl

# If on macOS:
brew --prefix llvm

These commands will help diagnose potential build issues by showing which tooling is in use.

Troubleshooting debug issues

Pass -c dbg to bazel build in order to compile with debugging enabled. For example:

bazel build -c dbg //toolchain/driver:carbon

Then debugging works with GDB:

gdb bazel-bin/toolchain/driver/carbon

Note that LLVM uses DWARF v5 debug symbols, which means that GDB version 10.1 or newer is required. If you see an error like this:

Dwarf Error: DW_FORM_strx1 found in non-DWO CU

It means that the version of GDB used is too old, and does not support the DWARF v5 format.

Debugging on MacOS

Bazel sandboxes builds, which on MacOS makes it hard for the debugger to locate symbols on linked binaries when debugging. See this Bazel issue for more information. To workaround, provide the --spawn_strategy=local option to Bazel for the debug build, like:

bazel build --spawn_strategy=local -c dbg //toolchain/driver:carbon

You should then be able to debug with lldb.

If this build command doesn't seem to produce a debuggable binary you might need to both clear the build disk cache and clean the build. Running scripts/clean_disk_cache.sh may not be enough, you might try deleting all the files within the disk cache, typically located at ~/.cache/carbon-lang-build-cache. Deleting the disk cache, followed by a bazel clean should allow your next rebuild, with the recommended options, to supply the symbols for debugging.

For debugging on MacOS using VSCode, some people have had success using the CodeLLDB extension. In order for LLDB to connect the project source files with the symbols you will need to add a "sourceMap": { ".": "${workspaceRoot}" } line to the CodeLLDB launch.json configuration, for example:

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "explorer",
            "type": "lldb",
            "request": "launch",
            "program": "${workspaceRoot}/bazel-bin/explorer/explorer",
            "args": [],
            "cwd": "${workspaceRoot}",
            "sourceMap": {
                ".": "${workspaceRoot}"
            }
        }
    ]
}