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Nixpkgs rules for Bazel

Continuous integration

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:

See examples for how to use rules_nixpkgs with different toolchains.

Rules

Setup

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

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

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 @rules_nixpkgs_core//constraints:support_nix constraint. For example by adding the following to .bazelrc:

build --host_platform=@rules_nixpkgs_core//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_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, cc_lang)

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.

If you specify the nix_file or nix_file_content argument, the CC toolchain is discovered by evaluating the corresponding expression. In addition, you may use the attribute_path argument to select an attribute from the result of the expression to use as the CC toolchain (see example below).

If neither the nix_file nor nix_file_content argument is used, the toolchain is discovered from the stdenv.cc and the stdenv.cc.bintools attributes of the given <nixpkgs> repository.

# use GCC 11
nixpkgs_cc_configure(
  repository = "@nixpkgs",
  nix_file_content = "(import <nixpkgs> {}).gcc11",
)
# use GCC 11 (same result as above)
nixpkgs_cc_configure(
  repository = "@nixpkgs",
  attribute_path = "gcc11",
  nix_file_content = "import <nixpkgs> {}",
)
# alternate usage without specifying `nix_file` or `nix_file_content`
nixpkgs_cc_configure(
  repository = "@nixpkgs",
  attribute_path = "gcc11",
)
# use the `stdenv.cc` compiler (the default of the given @nixpkgs repository)
nixpkgs_cc_configure(
  repository = "@nixpkgs",
)

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. Uses default repository if no nix_file or nix_file_content is provided.

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. See nixopts attribute to nixpkgs_package for further details.

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.

cc_lang

optional. default is "c++"

string, "c++" by default. Used to populate CXX_FLAG so the compiler is called in C++ mode. Can be set to "none" together with appropriate copts in the cc_library call: see above.

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_git_repository

nixpkgs_git_repository(name, revision, remote, sha256, kwargs)

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

Parameters

name

required.

String

A unique name for this repository.

revision

required.

String

Git commit hash or tag identifying the version of Nixpkgs to use.

remote

optional. default is "https://github.com/NixOS/nixpkgs"

String

The URI of the remote Git repository. This must be a HTTP URL. There is currently no support for authentication. Defaults to upstream nixpkgs.

sha256

optional. default is None

String

The SHA256 used to verify the integrity of the repository.

kwargs

optional.

Additional arguments to forward to the underlying repository rule.

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,
                       register, 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 a Bazel toolchain based on the Java runtime.

register

optional. default is None

Register the created toolchain. Requires toolchain to be True. Defaults to the value of toolchain.

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_local_repository

nixpkgs_local_repository(name, nix_file, nix_file_deps, nix_file_content, nix_flake_lock_file,
                         kwargs)

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.

Parameters

name

required.

String

A unique name for this repository.

nix_file

optional. default is None

Label

A file containing an expression for a Nix derivation.

nix_file_deps

optional. default is None

List of labels

Dependencies of nix_file if any.

nix_file_content

optional. default is None

String

An expression for a Nix derivation.

nix_flake_lock_file

optional. default is None

String

A flake lock file that can be used on the provided nixpkgs repository.

kwargs

optional.

Additional arguments to forward to the underlying repository rule.

nixpkgs_nodejs_configure

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

Parameters

name

optional. default is "nixpkgs_nodejs"

attribute_path

optional. default is "nodejs"

repository

optional. default is None

repositories

optional. default is {}

nix_platform

optional. default is None

nix_file

optional. default is None

nix_file_content

optional. default is None

nix_file_deps

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

register

optional. default is True

nixpkgs_nodejs_configure_platforms

nixpkgs_nodejs_configure_platforms(name, platforms_mapping, attribute_path, repository,
                                   repositories, nix_platform, nix_file, nix_file_content,
                                   nix_file_deps, nixopts, fail_not_supported, quiet,
                                   exec_constraints, target_constraints, register, kwargs)

Runs nixpkgs_nodejs_configure for each platform.

Since rules_nodejs adds platform suffix to repository name, this can be helpful if one wants to use npm_install and reference js dependencies from npm repo. See the example directory.

Parameters

name

optional. default is "nixpkgs_nodejs"

platforms_mapping

optional. default is {"aarch64-darwin": struct(exec_constraints = ["@platforms//os:macos", "@platforms//cpu:arm64"], rules_nodejs_platform = "darwin_arm64", target_constraints = ["@platforms//os:macos", "@platforms//cpu:arm64"]), "x86_64-linux": struct(exec_constraints = ["@platforms//os:linux", "@platforms//cpu:x86_64"], rules_nodejs_platform = "linux_amd64", target_constraints = ["@platforms//os:linux", "@platforms//cpu:x86_64"]), "x86_64-darwin": struct(exec_constraints = ["@platforms//os:macos", "@platforms//cpu:x86_64"], rules_nodejs_platform = "darwin_amd64", target_constraints = ["@platforms//os:macos", "@platforms//cpu:x86_64"]), "aarch64-linux": struct(exec_constraints = ["@platforms//os:linux", "@platforms//cpu:arm64"], rules_nodejs_platform = "linux_arm64", target_constraints = ["@platforms//os:linux", "@platforms//cpu:arm64"])}

struct describing mapping between nix platform and rules_nodejs bazel platform with target and exec constraints

attribute_path

optional. default is "nodejs"

repository

optional. default is None

repositories

optional. default is {}

nix_platform

optional. default is None

nix_file

optional. default is None

nix_file_content

optional. default is None

nix_file_deps

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

register

optional. default is True

kwargs

optional.

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, .dylib and .a files that can be found in subdirectories of lib/.
:include
All .h, .hh, .hpp and .hxx files that can be found in subdirectories of include/.

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.

Subject to location expansion, any instance of $(location LABEL) will be replaced by the path to the file referenced by LABEL relative to the workspace root.

Note, labels to external workspaces will resolve to paths that contain ~ characters if the Bazel flag --enable_bzlmod is true. Nix does not support ~ characters in path literals at the time of writing, see #7742. Meaning, the result of location expansion may not form a valid Nix path literal. Use ./$${"$(location @for//:example)"} to work around this limitation if you need to pass a path argument via --arg, or pass the resulting path as a string value using --argstr and combine it with an additional --arg workspace_root ./. argument using workspace_root + ("/" + path_str).

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, register)

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.

register

optional. default is True

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, register)

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

register

optional. default is True

nixpkgs_sh_posix_configure

nixpkgs_sh_posix_configure(name, packages, exec_constraints, register, 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.

exec_constraints

optional. default is None

Constraints for the execution platform.

register

optional. default is True

Automatically register the generated toolchain if set to True.

kwargs

optional.

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