Nixpkgs rules for Bazel

Use Nix and the Nixpkgs package set to import external dependencies (like system packages) into Bazel hermetically. If the version of any dependency changes, Bazel will correctly rebuild targets, and only those targets that use the external dependencies that changed.

Links:

• Nix + Bazel = fully reproducible, incremental builds (blog post)
• Nix + Bazel (lightning talk)

Rules

• nixpkgs_git_repository
• nixpkgs_local_repository
• nixpkgs_package
• nixpkgs_cc_configure
• nixpkgs_cc_configure_deprecated
• nixpkgs_java_configure
• nixpkgs_python_configure
• nixpkgs_go_configure
• nixpkgs_rust_configure
• nixpkgs_sh_posix_configure

Setup

Add the following to your WORKSPACE file, and select a $COMMIT accordingly.

http_archive(
    name = "io_tweag_rules_nixpkgs",
    strip_prefix = "rules_nixpkgs-$COMMIT",
    urls = ["https://github.com/tweag/rules_nixpkgs/archive/$COMMIT.tar.gz"],
)

load("@io_tweag_rules_nixpkgs//nixpkgs:repositories.bzl", "rules_nixpkgs_dependencies")
rules_nixpkgs_dependencies()

load("@io_tweag_rules_nixpkgs//nixpkgs:nixpkgs.bzl", "nixpkgs_git_repository", "nixpkgs_package", "nixpkgs_cc_configure")

load("@io_tweag_rules_nixpkgs//nixpkgs:toolchains/go.bzl", "nixpkgs_go_configure") # optional

If you use rules_nixpkgs to configure a toolchain, then you will also need to configure the build platform to include the @io_tweag_rules_nixpkgs//nixpkgs/constraints:support_nix constraint. For example by adding the following to .bazelrc:

build --host_platform=@io_tweag_rules_nixpkgs//nixpkgs/platforms:host

Example

nixpkgs_git_repository(
    name = "nixpkgs",
    revision = "17.09", # Any tag or commit hash
    sha256 = "" # optional sha to verify package integrity!
)

nixpkgs_package(
    name = "hello",
    repositories = { "nixpkgs": "@nixpkgs//:default.nix" }
)

Migration from older releases

path Attribute (removed in 0.3)

path was an attribute from the early days of rules_nixpkgs, and its ability to reference arbitrary paths is a danger to build hermeticity.

Replace it with either nixpkgs_git_repository if you need a specific version of nixpkgs. If you absolutely must depend on a local folder, use Bazel's local_repository workspace rule. Both approaches work well with the repositories attribute of nixpkgs_package.

local_repository(
  name = "local-nixpkgs",
  path = "/path/to/nixpkgs",
)

nixpkgs_package(
  name = "somepackage",
  repositories = {
    "nixpkgs": "@local-nixpkgs//:default.nix",
  },
)

Reference documentation

nixpkgs_git_repository

nixpkgs_git_repository(name, remote, revision, sha256)

Name a specific revision of Nixpkgs on GitHub or a local checkout.

Attributes

name	Name; required A unique name for this repository.
remote	String; optional The URI of the remote Git repository. This must be a HTTP URL. There is currently no support for authentication. Defaults to upstream nixpkgs.
revision	String; required Git commit hash or tag identifying the version of Nixpkgs to use.
sha256	String; optional The SHA256 used to verify the integrity of the repository.

nixpkgs_local_repository

nixpkgs_local_repository(name, nix_file, nix_file_content, nix_file_deps)

Create an external repository representing the content of Nixpkgs, based on a Nix expression stored locally or provided inline. One of nix_file or nix_file_content must be provided.

Attributes

name	Name; required A unique name for this repository.
nix_file	Label; optional A file containing an expression for a Nix derivation.
nix_file_content	String; optional An expression for a Nix derivation.
nix_file_deps	List of labels; optional Dependencies of nix_file if any.

nixpkgs_cc_configure

nixpkgs_cc_configure(name, attribute_path, nix_file, nix_file_content, nix_file_deps, repositories,
                     repository, nixopts, quiet, fail_not_supported, exec_constraints,
                     target_constraints, register)

Use a CC toolchain from Nixpkgs. No-op if not a nix-based platform.

By default, Bazel auto-configures a CC toolchain from commands (e.g. gcc) available in the environment. To make builds more hermetic, use this rule to specify explicitly which commands the toolchain should use.

Specifically, it builds a Nix derivation that provides the CC toolchain tools in the bin/ path and constructs a CC toolchain that uses those tools. Tools that aren't found are replaced by ${coreutils}/bin/false. You can inspect the resulting @<name>_info//:CC_TOOLCHAIN_INFO to see which tools were discovered.

This rule depends on rules_cc.

Note: You need to configure --crosstool_top=@<name>//:toolchain to activate this toolchain.

Parameters

name	optional. default is "local_config_cc"
attribute_path	optional. default is "" optional, string, Obtain the toolchain from the Nix expression under this attribute path. Requires nix_file or nix_file_content.
nix_file	optional. default is None optional, Label, Obtain the toolchain from the Nix expression defined in this file. Specify only one of nix_file or nix_file_content.
nix_file_content	optional. default is "" optional, string, Obtain the toolchain from the given Nix expression. Specify only one of nix_file or nix_file_content.
nix_file_deps	optional. default is [] optional, list of Label, Additional files that the Nix expression depends on.
repositories	optional. default is {} dict of Label to string, Provides <nixpkgs> and other repositories. Specify one of repositories or repository.
repository	optional. default is None Label, Provides <nixpkgs>. Specify one of repositories or repository.
nixopts	optional. default is [] optional, list of string, Extra flags to pass when calling Nix. Subject to location expansion, any instance of $(location LABEL) will be replaced by the path to the file ferenced by LABEL relative to the workspace root.
quiet	optional. default is False bool, Whether to hide nix-build output.
fail_not_supported	optional. default is True bool, Whether to fail if nix-build is not available.
exec_constraints	optional. default is None Constraints for the execution platform.
target_constraints	optional. default is None Constraints for the target platform.
register	optional. default is True bool, enabled by default, Whether to register (with register_toolchains) the generated toolchain and install it as the default cc_toolchain.

nixpkgs_cc_configure_deprecated

nixpkgs_cc_configure_deprecated(repository, repositories, nix_file, nix_file_deps, nix_file_content,
                                nixopts)

Use a CC toolchain from Nixpkgs. No-op if not a nix-based platform.

Tells Bazel to use compilers and linkers from Nixpkgs for the CC toolchain. By default, Bazel auto-configures a CC toolchain from commands available in the environment (e.g. gcc). Overriding this autodetection makes builds more hermetic and is considered a best practice.

Example

nixpkgs_cc_configure(repository = "@nixpkgs//:default.nix")

Parameters

repository	optional. default is None A repository label identifying which Nixpkgs to use. Equivalent to repositories = { "nixpkgs": ...}.
repositories	optional. default is {} A dictionary mapping NIX_PATH entries to repository labels. Setting it to repositories = { "myrepo" : "//:myrepo" } for example would replace all instances of <myrepo> in the called nix code by the path to the target "//:myrepo". See the relevant section in the nix manual for more information. Specify one of repository or repositories.
nix_file	optional. default is None An expression for a Nix environment derivation. The environment should expose all the commands that make up a CC toolchain (cc, ld etc). Exposes all commands in stdenv.cc and binutils by default.
nix_file_deps	optional. default is None Dependencies of nix_file if any.
nix_file_content	optional. default is None An expression for a Nix environment derivation.
nixopts	optional. default is [] Options to forward to the nix command.

nixpkgs_java_configure

nixpkgs_java_configure(name, attribute_path, java_home_path, repository, repositories, nix_file,
                       nix_file_content, nix_file_deps, nixopts, fail_not_supported, quiet, toolchain,
                       toolchain_name, toolchain_version, exec_constraints, target_constraints)

Define a Java runtime provided by nixpkgs.

Creates a nixpkgs_package for a java_runtime instance. Optionally, you can also create & register a Java toolchain. This only works with Bazel >= 5.0 Bazel can use this instance to run JVM binaries and tests, refer to the Bazel documentation for details.

Example

Bazel 4

Add the following to your WORKSPACE file to import a JDK from nixpkgs:

load("@io_tweag_rules_nixpkgs//nixpkgs:nixpkgs.bzl", "nixpkgs_java_configure")
nixpkgs_java_configure(
    attribute_path = "jdk11.home",
    repository = "@nixpkgs",
)

Add the following configuration to .bazelrc to enable this Java runtime:

build --javabase=@nixpkgs_java_runtime//:runtime
build --host_javabase=@nixpkgs_java_runtime//:runtime
# Adjust this to match the Java version provided by this runtime.
# See `bazel query 'kind(java_toolchain, @bazel_tools//tools/jdk:all)'` for available options.
build --java_toolchain=@bazel_tools//tools/jdk:toolchain_java11
build --host_java_toolchain=@bazel_tools//tools/jdk:toolchain_java11

Bazel 5

Add the following to your WORKSPACE file to import a JDK from nixpkgs:

load("@io_tweag_rules_nixpkgs//nixpkgs:nixpkgs.bzl", "nixpkgs_java_configure")
nixpkgs_java_configure(
    attribute_path = "jdk11.home",
    repository = "@nixpkgs",
    toolchain = True,
    toolchain_name = "nixpkgs_java",
    toolchain_version = "11",
)

Add the following configuration to .bazelrc to enable this Java runtime:

build --host_platform=@io_tweag_rules_nixpkgs//nixpkgs/platforms:host
build --java_runtime_version=nixpkgs_java
build --tool_java_runtime_version=nixpkgs_java

Parameters

name	optional. default is "nixpkgs_java_runtime" The name-prefix for the created external repositories.
attribute_path	optional. default is None string, The nixpkgs attribute path for jdk.home.
java_home_path	optional. default is "" optional, string, The path to JAVA_HOME within the package.
repository	optional. default is None See nixpkgs_package.
repositories	optional. default is {} See nixpkgs_package.
nix_file	optional. default is None optional, Label, Obtain the runtime from the Nix expression defined in this file. Specify only one of nix_file or nix_file_content.
nix_file_content	optional. default is "" optional, string, Obtain the runtime from the given Nix expression. Specify only one of nix_file or nix_file_content.
nix_file_deps	optional. default is None See nixpkgs_package.
nixopts	optional. default is [] See nixpkgs_package.
fail_not_supported	optional. default is True See nixpkgs_package.
quiet	optional. default is False See nixpkgs_package.
toolchain	optional. default is False Create & register a Bazel toolchain based on the Java runtime.
toolchain_name	optional. default is None The name of the toolchain that can be used in --java_runtime_version.
toolchain_version	optional. default is None The version of the toolchain that can be used in --java_runtime_version.
exec_constraints	optional. default is None Constraints for the execution platform.
target_constraints	optional. default is None Constraints for the target platform.

nixpkgs_package

nixpkgs_package(name, attribute_path, nix_file, nix_file_deps, nix_file_content, repository,
                repositories, build_file, build_file_content, nixopts, quiet, fail_not_supported,
                kwargs)

Make the content of a Nixpkgs package available in the Bazel workspace.

If repositories is not specified, you must provide a nixpkgs clone in nix_file or nix_file_content.

Parameters

name	required. A unique name for this repository.
attribute_path	optional. default is "" Select an attribute from the top-level Nix expression being evaluated. The attribute path is a sequence of attribute names separated by dots.
nix_file	optional. default is None A file containing an expression for a Nix derivation.
nix_file_deps	optional. default is [] Dependencies of nix_file if any.
nix_file_content	optional. default is "" An expression for a Nix derivation.
repository	optional. default is None A repository label identifying which Nixpkgs to use. Equivalent to repositories = { "nixpkgs": ...}
repositories	optional. default is {} A dictionary mapping NIX_PATH entries to repository labels. Setting it to repositories = { "myrepo" : "//:myrepo" } for example would replace all instances of <myrepo> in the called nix code by the path to the target "//:myrepo". See the relevant section in the nix manual for more information. Specify one of repository or repositories.
build_file	optional. default is None The file to use as the BUILD file for this repository. Its contents are copied copied into the file BUILD in root of the nix output folder. The Label does not need to be named BUILD, but can be. For common use cases we provide filegroups that expose certain files as targets: :bin Everything in the bin/ directory. :lib All .so and .a files that can be found in subdirectories of lib/. :include All .h files that can be found in subdirectories of bin/. If you need different files from the nix package, you can reference them like this: package(default_visibility = [ "//visibility:public" ]) filegroup( name = "our-docs", srcs = glob(["share/doc/ourpackage/**/*"]), ) See the bazel documentation of filegroup and glob.
build_file_content	optional. default is "" Like build_file, but a string of the contents instead of a file name.
nixopts	optional. default is [] Extra flags to pass when calling Nix.
quiet	optional. default is False Whether to hide the output of the Nix command.
fail_not_supported	optional. default is True If set to True (default) this rule will fail on platforms which do not support Nix (e.g. Windows). If set to False calling this rule will succeed but no output will be generated.
kwargs	optional.

nixpkgs_python_configure

nixpkgs_python_configure(name, python2_attribute_path, python2_bin_path, python3_attribute_path,
                         python3_bin_path, repository, repositories, nix_file_deps, nixopts,
                         fail_not_supported, quiet, exec_constraints, target_constraints)

Define and register a Python toolchain provided by nixpkgs.

Creates nixpkgs_packages for Python 2 or 3 py_runtime instances and a corresponding py_runtime_pair and toolchain. The toolchain is automatically registered and uses the constraint:

"@io_tweag_rules_nixpkgs//nixpkgs/constraints:support_nix"

Parameters

name	optional. default is "nixpkgs_python_toolchain" The name-prefix for the created external repositories.
python2_attribute_path	optional. default is None The nixpkgs attribute path for python2.
python2_bin_path	optional. default is "bin/python" The path to the interpreter within the package.
python3_attribute_path	optional. default is "python3" The nixpkgs attribute path for python3.
python3_bin_path	optional. default is "bin/python" The path to the interpreter within the package.
repository	optional. default is None See nixpkgs_package.
repositories	optional. default is {} See nixpkgs_package.
nix_file_deps	optional. default is None See nixpkgs_package.
nixopts	optional. default is [] See nixpkgs_package.
fail_not_supported	optional. default is True See nixpkgs_package.
quiet	optional. default is False See nixpkgs_package.
exec_constraints	optional. default is None Constraints for the execution platform.
target_constraints	optional. default is None Constraints for the target platform.

nixpkgs_rust_configure

nixpkgs_rust_configure(name, default_edition, repository, repositories, nix_file, nix_file_deps,
                       nix_file_content, nixopts, fail_not_supported, quiet, exec_constraints,
                       target_constraints)

Parameters

name	optional. default is "nixpkgs_rust"
default_edition	optional. default is "2018"
repository	optional. default is None
repositories	optional. default is {}
nix_file	optional. default is None
nix_file_deps	optional. default is None
nix_file_content	optional. default is None
nixopts	optional. default is []
fail_not_supported	optional. default is True
quiet	optional. default is False
exec_constraints	optional. default is None
target_constraints	optional. default is None

nixpkgs_sh_posix_configure

nixpkgs_sh_posix_configure(name, packages, kwargs)

Create a POSIX toolchain from nixpkgs.

Loads the given Nix packages, scans them for standard Unix tools, and generates a corresponding sh_posix_toolchain.

Make sure to call nixpkgs_sh_posix_configure before sh_posix_configure, if you use both. Otherwise, the local toolchain will always be chosen in favor of the nixpkgs one.

Parameters

name	optional. default is "nixpkgs_sh_posix_config" Name prefix for the generated repositories.
packages	optional. default is ["stdenv.initialPath"] List of Nix attribute paths to draw Unix tools from.
kwargs	optional.