rippled/docs/build/nix.md

Using Nix Development Shell for xrpld Development

This guide explains how to use Nix to set up a reproducible development environment for xrpld. Using Nix eliminates the need to manually install utilities and ensures consistent tooling across different machines.

The Nix development shell is the recommended way to develop xrpld. It unifies the development environment for everyone and synchronizes updates: the same tooling and compiler versions are used both here and in CI. Any custom environment (Homebrew packages or anything else) will continue to work, but then it is up to you to keep it in sync with the environment used in CI.

Benefits of Using Nix

• Reproducible environment: Everyone gets the same versions of tools and compilers
• Matches CI: The Linux CI runs in Docker images built from this exact Nix environment
• No system pollution: Dependencies are isolated and don't affect your system packages
• Consistent compilers: The GCC and Clang shells use the same versions as CI
• Quick setup: Get started with a single command
• Works on Linux and macOS: Consistent experience across platforms

Install Nix

Please follow the official installation instructions of nix package manager for your system.

Entering the Development Shell

Basic Usage

From the root of the xrpld repository, enter the default development shell:

nix --experimental-features 'nix-command flakes' develop

This will:

• Download and set up all required development tools (CMake, Ninja, Conan, etc.)
• Configure the appropriate compiler for your platform:
  • Linux: GCC (provided by Nix)
  • macOS: Clang (provided by Nix)

The first time you run this command, it will take a few minutes to download and build the environment. Subsequent runs will be much faster.

Platform notes

• Linux: nix develop gives you a shell with all the tooling necessary to develop xrpld and with the same GCC/glibc toolchain that Nix builds for CI. See Choosing a different compiler for the custom-vs-plain toolchain trade-off.
• macOS: nix develop gives you a full environment too, with Clang (and every other tool, including Conan) provided by Nix. To use your system-wide Apple Clang instead, enter nix develop .#apple-clang. Conan has no binary in the Nix cache for macOS, so it is built from source the first time you enter the shell, which makes the initial setup slower (this is handled automatically; see nix/devshell.nix).

Tip

To avoid typing --experimental-features 'nix-command flakes' every time, you can permanently enable flakes by creating ~/.config/nix/nix.conf:

mkdir -p ~/.config/nix
echo "experimental-features = nix-command flakes" >> ~/.config/nix/nix.conf

After this, you can simply use nix develop instead.

Note

The examples below assume you've enabled flakes in your config. If you haven't, add --experimental-features 'nix-command flakes' after each nix command.

Choosing a different compiler

A compiler can be chosen by providing its name with the .# prefix, e.g. nix develop .#clang.

On Linux, .#gcc and .#clang provide the exact toolchain CI uses: the compiler (pinned in nix/packages.nix) rebuilt against the pinned custom glibc (see nix/compilers.nix). Building that toolchain the first time is slow unless it is fetched from a Nix binary cache. If you don't need the custom glibc, the Linux-only .#gcc-plain and .#clang-plain give you the stock nixpkgs compilers of the same versions. On macOS there is no custom glibc, so .#gcc and .#clang are already the plain nixpkgs toolchain, and the -plain variants do not exist.

Use nix flake show to see all the available development shells.

Use nix develop .#no-compiler to use the compiler from your system.

Example Usage

# Use GCC — same toolchain as CI (custom glibc on Linux)
nix develop .#gcc

# Use Clang — same toolchain as CI (custom glibc on Linux)
nix develop .#clang

# Use default for your platform
nix develop

# Stock nixpkgs GCC/Clang, Linux only — skips the custom-glibc build, but does not match CI
nix develop .#gcc-plain
nix develop .#clang-plain

Using a different shell

nix develop opens bash by default. To use another shell, pass it with the -c flag — this works with any shell, e.g. zsh or fish:

# Use zsh
nix develop -c zsh

# Use fish
nix develop -c fish

# Use your login shell
nix develop -c "$SHELL"

Warning

Your shell's interactive startup files (e.g. config.fish, .zshrc) may prepend other directories — most commonly Homebrew — to $PATH, which can shadow the tools provided by the Nix shell. After entering, verify that tools resolve into the Nix store:

command -v cmake   # should print a /nix/store/... path

If it doesn't, either adjust your shell configuration so it doesn't override $PATH, or use direnv (below), which loads the environment after your shell config and so takes precedence regardless of the shell you use.

Building xrpld with Nix

Once inside the Nix development shell, follow the standard build instructions. The Nix shell provides all necessary tools (CMake, Ninja, Conan, etc.).

Coverage builds (-Dcoverage=ON) work in the gcc shell (and gcc-plain on Linux): each ships a gcov matching its compiler, since Nix's cc-wrapper does not expose one. The clang shells do not include llvm-cov, so use a gcc shell for coverage.

Automatic Activation with direnv

direnv or nix-direnv can automatically activate the Nix development shell when you enter the repository directory.

This is also the most robust way to use the environment from any shell (bash, zsh, fish, …): direnv stays in your current shell and loads the environment after your shell's startup files have run, so the Nix-provided tools take precedence over anything your shell configuration adds to $PATH.

The repository already ships an .envrc at its root that activates the Nix flake development shell, so you don't need to create one. To use it:

1. Install direnv and hook it into your shell (bash, zsh, fish, …). Installing nix-direnv as well is recommended: it caches the shell so that activation is near-instant after the first run.
2. Run direnv allow once in the repository root. direnv will then load (and reload) the Nix development shell automatically whenever you enter the directory.

Note

direnv only caches the .direnv directory (already listed in .gitignore); no other repository files are affected.

Conan and Prebuilt Packages

Please note that there is no guarantee that binaries from conan cache will work when using nix. If you encounter any errors, please use --build '*' to force conan to compile everything from source:

conan install .. --output-folder . --build '*' --settings build_type=Release

Updating flake.lock file

To update flake.lock to the latest revision use nix flake update command.

Tooling snapshots

The tool versions in each Nix environment are recorded in nix/check-tools/ and verified by CI. If you change the environment (bump the CI image tag, update flake.lock, or edit the tool list in bin/check-tools.sh), CI fails until you regenerate and commit the affected snapshot — see nix/check-tools/README.md.

Troubleshooting

See Troubleshooting Nix problems for common issues, such as nix develop failing inside Git worktrees.