example: nix cross compiling

.bazelci/presubmit.yml

@@ -587,6 +587,12 @@ tasks:
   #   working_directory: examples/zig_cross_compiling
   #   build_targets:
   #     - "//..."
+  nix_cross_compiling:
+    name: Nix cross compiling test
+    platform: ubuntu2004
+    working_directory: examples/nix_cross_compiling
+    build_targets:
+      - "//..."
 
 buildifier:
   version: latest

examples/nix_cross_compiling/.bazelrc

@@ -0,0 +1,15 @@
+# Sensible Defaults
+build --sandbox_default_allow_network=false
+build --incompatible_strict_action_env
+build --action_env=BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN=1
+build --incompatible_enable_cc_toolchain_resolution=true
+
+# Require Platform Transitions
+## This works by setting the targte platform to an invalid platform
+## and each `x_binary()` and `x_library()` rule unfortunately needs
+## to tag itself with `platform_missing` to get excluded from glob
+## builds like `build //...` but still have a way to include them
+## by removing the filter line for things like Rust Analyzer.
+build --host_platform=//bazel/platforms:host
+build --platforms=//bazel/platforms:missing
+build --build_tag_filters=-platform_missing

examples/nix_cross_compiling/.envrc

@@ -0,0 +1 @@
+use flake

examples/nix_cross_compiling/.gitignore

@@ -0,0 +1 @@
+/bazel-*

examples/nix_cross_compiling/BUILD.bazel

@@ -0,0 +1,139 @@
+load("@aspect_bazel_lib//lib:transitions.bzl", "platform_transition_binary")
+
+# Disabled targets need the user to supply a sysroot in `flake.nix` first.
+
+"""
+platform_transition_binary(
+    name = "cc_binary_aarch64-apple-darwin",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:aarch64-apple-darwin",
+)
+"""
+
+"""
+platform_transition_binary(
+    name = "cc_binary_aarch64-apple-ios",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:aarch64-apple-ios",
+)
+"""
+
+platform_transition_binary(
+    name = "cc_binary_aarch64-linux-android",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:aarch64-linux-android",
+)
+
+platform_transition_binary(
+    name = "cc_binary_aarch64-unknown-linux-gnu",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:aarch64-unknown-linux-gnu",
+)
+
+platform_transition_binary(
+    name = "cc_binary_wasm32-unknown-unknown",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:wasm32-unknown-unknown",
+)
+
+platform_transition_binary(
+    name = "cc_binary_wasm32-wasi",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:wasm32-wasi",
+)
+
+"""
+platform_transition_binary(
+    name = "cc_binary_x86_64-apple-darwin",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:x86_64-apple-darwin",
+)
+"""
+
+"""
+platform_transition_binary(
+    name = "cc_binary_x86_64-pc-windows-msvc",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:x86_64-pc-windows-msvc",
+)
+"""
+
+platform_transition_binary(
+    name = "cc_binary_x86_64-unknown-linux-gnu",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:x86_64-unknown-linux-gnu",
+)
+
+platform_transition_binary(
+    name = "cc_binary_x86_64-unknown-nixos-gnu",
+    binary = "//cc_binary",
+    target_platform = "//bazel/platforms:x86_64-unknown-nixos-gnu",
+)
+
+"""
+platform_transition_binary(
+    name = "rust_binary_aarch64-apple-darwin",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:aarch64-apple-darwin",
+)
+"""
+
+"""
+platform_transition_binary(
+    name = "rust_binary_aarch64-apple-ios",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:aarch64-apple-ios",
+)
+"""
+
+platform_transition_binary(
+    name = "rust_binary_aarch64-linux-android",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:aarch64-linux-android",
+)
+
+platform_transition_binary(
+    name = "rust_binary_aarch64-unknown-linux-gnu",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:aarch64-unknown-linux-gnu",
+)
+
+platform_transition_binary(
+    name = "rust_binary_wasm32-unknown-unknown",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:wasm32-unknown-unknown",
+)
+
+platform_transition_binary(
+    name = "rust_binary_wasm32-wasi",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:wasm32-wasi",
+)
+
+"""
+platform_transition_binary(
+    name = "rust_binary_x86_64-apple-darwin",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:x86_64-apple-darwin",
+)
+"""
+
+"""
+platform_transition_binary(
+    name = "rust_binary_x86_64-pc-windows-msvc",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:x86_64-pc-windows-msvc",
+)
+"""
+
+platform_transition_binary(
+    name = "rust_binary_x86_64-unknown-linux-gnu",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:x86_64-unknown-linux-gnu",
+)
+
+platform_transition_binary(
+    name = "rust_binary_x86_64-unknown-nixos-gnu",
+    binary = "//rust_binary",
+    target_platform = "//bazel/platforms:x86_64-unknown-nixos-gnu",
+)

examples/nix_cross_compiling/README.md

@@ -0,0 +1,3 @@
+# Nix + Bazel Crosspiling
+
+Blog Post: <https://consumingchaos.github.io/posts/nix-bazel-crosspiling/>

examples/nix_cross_compiling/WORKSPACE.bazel

@@ -0,0 +1,64 @@
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+# Aspect Bazel Lib
+http_archive(
+    name = "aspect_bazel_lib",
+    sha256 = "97fa63d95cc9af006c4c7b2123ddd2a91fb8d273012f17648e6423bae2c69470",
+    strip_prefix = "bazel-lib-1.30.2",
+    url = "https://github.com/aspect-build/bazel-lib/releases/download/v1.30.2/bazel-lib-v1.30.2.tar.gz",
+)
+
+load("@aspect_bazel_lib//lib:repositories.bzl", "aspect_bazel_lib_dependencies")
+
+aspect_bazel_lib_dependencies()
+
+# Nix
+http_archive(
+    name = "io_tweag_rules_nixpkgs",
+    sha256 = "657db2e70d933f252735a5a5c9f532c4cd5e77018b9d7256bc9c7b80a01e96b5",
+    strip_prefix = "rules_nixpkgs-816e913f41d161659cbd1e49ff77694853398a3a",
+    urls = ["https://github.com/tweag/rules_nixpkgs/archive/816e913f41d161659cbd1e49ff77694853398a3a.tar.gz"],
+)
+
+load("@io_tweag_rules_nixpkgs//nixpkgs:repositories.bzl", "rules_nixpkgs_dependencies")
+
+rules_nixpkgs_dependencies()
+
+# Rust
+local_repository(
+    name = "rules_rust",
+    path = "../..",
+)
+
+# Nix Toolchains
+load("//bazel:nix_repositories.bzl", "nix_repositories")
+
+nix_repositories()
+
+register_toolchains(
+    "//bazel/toolchains/cc/aarch64-apple-darwin:toolchain",
+    "//bazel/toolchains/cc/aarch64-apple-ios:toolchain",
+    "//bazel/toolchains/cc/aarch64-linux-android:toolchain",
+    "//bazel/toolchains/cc/aarch64-unknown-linux-gnu:toolchain",
+    "//bazel/toolchains/cc/wasm32-unknown-unknown:toolchain",
+    "//bazel/toolchains/cc/wasm32-wasi:toolchain",
+    "//bazel/toolchains/cc/x86_64-apple-darwin:toolchain",
+    "//bazel/toolchains/cc/x86_64-pc-windows-msvc:toolchain",
+    "//bazel/toolchains/cc/x86_64-unknown-linux-gnu:toolchain",
+    "//bazel/toolchains/cc/x86_64-unknown-nixos-gnu:toolchain",
+    "//bazel/toolchains/rust/aarch64-apple-darwin:toolchain",
+    "//bazel/toolchains/rust/aarch64-apple-ios:toolchain",
+    "//bazel/toolchains/rust/aarch64-linux-android:toolchain",
+    "//bazel/toolchains/rust/aarch64-unknown-linux-gnu:toolchain",
+    "//bazel/toolchains/rust/wasm32-unknown-unknown:toolchain",
+    "//bazel/toolchains/rust/wasm32-wasi:toolchain",
+    "//bazel/toolchains/rust/x86_64-apple-darwin:toolchain",
+    "//bazel/toolchains/rust/x86_64-pc-windows-msvc:toolchain",
+    "//bazel/toolchains/rust/x86_64-unknown-linux-gnu:toolchain",
+    "//bazel/toolchains/rust/x86_64-unknown-nixos-gnu:toolchain",
+)
+
+# Rust
+load("@rules_rust//rust:repositories.bzl", "rules_rust_dependencies")
+
+rules_rust_dependencies()