Merge pull request #402 from DolceTriade/cross_ex

crosscompile: Add an example for cross compiling

.github/workflows/workflow.yaml

@@ -109,9 +109,16 @@ jobs:
           for dir in "${with_nix[@]}"; do
               pushd "$dir"
               echo
-              echo "::group::Running $(head -n1 README.md) with Nix"
-              nix-shell --command 'bazel run --config=nix :hello'
-              # TODO: all toolchains should run without Nixpkgs
+              example_name="$(head -n1 README.md) with Nix"
+              if [[ -f skip-on-ci ]]; then
+                  echo "Skipping $example_name"
+                  popd
+                  continue
+              else
+                  echo "::group::Running $example_name"
+                  nix-shell --command 'bazel run --config=nix :hello'
+                  # TODO: all toolchains should run without Nixpkgs
+              fi
               popd
           done
           for dir in "${without_nix[@]}"; do

examples/toolchains/cc_cross_osx_to_linux_amd64/.bazeliskrc

@@ -0,0 +1 @@
+USE_BAZEL_VERSION=6.x

examples/toolchains/cc_cross_osx_to_linux_amd64/.bazelrc

@@ -0,0 +1,6 @@
+build --incompatible_enable_cc_toolchain_resolution
+build:nix --host_platform=@io_tweag_rules_nixpkgs//nixpkgs/platforms:host
+build:nix --crosstool_top=@nixpkgs_config_cc//:toolchain
+build:cross --host_platform=@io_tweag_rules_nixpkgs//nixpkgs/platforms:host
+build:cross --host_crosstool_top=@nixpkgs_config_cc//:toolchain
+build:cross --cpu=k8 --crosstool_top=@nixpkgs_cross_cc//:toolchain --platforms=//toolchains:linux_x86_64

examples/toolchains/cc_cross_osx_to_linux_amd64/BUILD

@@ -0,0 +1,40 @@
+load("@rules_cc//cc:defs.bzl", "cc_binary")
+load("@rules_oci//oci:defs.bzl", "oci_image", "oci_tarball")
+load("@rules_pkg//:pkg.bzl", "pkg_tar")
+load("//toolchains:runfiles.bzl", "runfiles")
+
+cc_binary(
+    name = "hello",
+    srcs = ["hello.cc"],
+    deps = [
+        "@boost.dev//:boost",
+        "@zlib.dev//:zlib",
+    ],
+)
+
+runfiles(
+    name = "hello_runfiles",
+    binary = ":hello",
+    root = "/app"
+)
+
+pkg_tar(
+    name = "hello_tar",
+    srcs = [":hello_runfiles"],
+)
+
+oci_image(
+    name = "hello_image",
+    base = "@alpine",
+    tars = [
+        ":hello_tar",
+        "@nixdeps//:closure.tar",
+    ],
+    entrypoint = ["/app/hello"],
+)
+
+oci_tarball(
+    name = "hello_image_tarball",
+    image = ":hello_image",
+    repo_tags = ["cross_example:latest"],
+)

examples/toolchains/cc_cross_osx_to_linux_amd64/README.md

@@ -0,0 +1,13 @@
+C++ With Dependencies Toolchain Example
+=======================================
+
+This is an example C++ project with dependencies that uses `rules_cc`.
+
+This example uses the Nix package manager to provide C++ dependencies, and as such only works with Nix installed. Demonstrating other methods of providing C++ dependencies is out of scope of this example.
+
+# Usage
+
+To run the example with Nix, issue the following command:
+```
+nix-shell --command 'bazel run --config=cross:hello'
+```

examples/toolchains/cc_cross_osx_to_linux_amd64/WORKSPACE

@@ -0,0 +1,180 @@
+# Replace with http_archive: https://github.com/tweag/rules_nixpkgs/#setup
+local_repository(
+    name = "io_tweag_rules_nixpkgs",
+    path = "../../../",
+)
+
+load("@io_tweag_rules_nixpkgs//nixpkgs:repositories.bzl", "rules_nixpkgs_dependencies")
+
+rules_nixpkgs_dependencies()
+
+load(
+    "@io_tweag_rules_nixpkgs//nixpkgs:nixpkgs.bzl",
+    "nixpkgs_cc_configure",
+    "nixpkgs_local_repository",
+)
+
+nixpkgs_local_repository(
+    name = "nixpkgs",
+    nix_file = "//:nixpkgs.nix",
+    nix_file_deps = ["//:nixpkgs.json"],
+)
+
+nixpkgs_cc_configure(
+    name = "nixpkgs_config_cc",
+    nix_file = "//toolchains:cc.nix",
+    repository = "@nixpkgs",
+)
+
+nixpkgs_cc_configure(
+    name = "nixpkgs_cross_cc",
+    cross_cpu = "k8",
+    exec_constraints = [
+        "@platforms//os:osx",
+        "@platforms//cpu:arm64",
+    ],
+    nix_file = "//toolchains:osxcross_cc.nix",
+    nixopts = [
+        "--arg",
+        "ccPkgs",
+        "import <nixpkgs> { crossSystem = \"x86_64-linux\";}",
+        "--show-trace",
+    ],
+    repository = "@nixpkgs",
+    target_constraints = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:linux",
+        "@rules_nixpkgs_core//constraints:support_nix",
+    ],
+)
+
+load("@io_tweag_rules_nixpkgs//nixpkgs:nixpkgs.bzl", "nixpkgs_package")
+
+# We would probably want a select or something to make this work with OSX as well, for a more
+# production set up.
+nixpkgs_package(
+    name = "boost",
+    attribute_path = "boost175",
+    nix_file_content = """import <nixpkgs> { config = {}; overlays = []; system = "x86_64-linux"; }""",
+    repository = "@nixpkgs",
+)
+
+nixpkgs_package(
+    name = "boost.dev",
+    attribute_path = "boost175.dev",
+    build_file_content = """\
+load("@rules_cc//cc:defs.bzl", "cc_library")
+filegroup(
+    name = "include",
+    srcs = glob(["include/**/*.h", "include/**/*.hpp"]),
+    visibility = ["//visibility:public"],
+)
+cc_library(
+    name = "boost",
+    srcs = ["@boost//:lib"],
+    hdrs = [":include"],
+    strip_include_prefix = "include",
+    visibility = ["//visibility:public"],
+)
+""",
+    nix_file_content = """import <nixpkgs> { config = {}; overlays = []; system = "x86_64-linux"; }""",
+    repository = "@nixpkgs",
+)
+
+nixpkgs_package(
+    name = "zlib",
+    attribute_path = "zlib",
+    nix_file_content = """import <nixpkgs> { config = {}; overlays = []; system = "x86_64-linux"; }""",
+    repository = "@nixpkgs",
+)
+
+nixpkgs_package(
+    name = "zlib.dev",
+    attribute_path = "zlib.dev",
+    build_file_content = """\
+load("@rules_cc//cc:defs.bzl", "cc_library")
+filegroup(
+    name = "include",
+    srcs = glob(["include/**/*.h"]),
+    visibility = ["//visibility:public"],
+)
+cc_library(
+    name = "zlib",
+    srcs = ["@zlib//:lib"],
+    hdrs = [":include"],
+    strip_include_prefix = "include",
+    visibility = ["//visibility:public"],
+)
+""",
+    nix_file_content = """import <nixpkgs> { config = {}; overlays = []; system = "x86_64-linux"; }""",
+    repository = "@nixpkgs",
+)
+
+nixpkgs_package(
+    name = "nixdeps",
+    build_file_content = """\
+exports_files(["closure.tar"])
+""",
+    nix_file = "//toolchains:tarenv.nix",
+    repository = "@nixpkgs",
+)
+
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "rules_oci",
+    sha256 = "a3b6f4c0051938940ccf251a7bdcdf7ac5a93ae00e63ad107c9c6d3bfe20885b",
+    strip_prefix = "rules_oci-1.3.1",
+    url = "https://github.com/bazel-contrib/rules_oci/releases/download/v1.3.1/rules_oci-v1.3.1.tar.gz",
+)
+
+load("@rules_oci//oci:dependencies.bzl", "rules_oci_dependencies")
+
+rules_oci_dependencies()
+
+load("@rules_oci//oci:repositories.bzl", "LATEST_CRANE_VERSION", "LATEST_ZOT_VERSION", "oci_register_toolchains")
+
+oci_register_toolchains(
+    name = "oci",
+    crane_version = LATEST_CRANE_VERSION,
+    # Uncommenting the zot toolchain will cause it to be used instead of crane for some tasks.
+    # Note that it does not support docker-format images.
+    # zot_version = LATEST_ZOT_VERSION,
+)
+
+# You can pull your base images using oci_pull like this:
+load("@rules_oci//oci:pull.bzl", "oci_pull")
+
+oci_pull(
+    name = "distroless_base",
+    digest = "sha256:ccaef5ee2f1850270d453fdf700a5392534f8d1a8ca2acda391fbb6a06b81c86",
+    image = "gcr.io/distroless/base",
+    platforms = [
+        "linux/amd64",
+        "linux/arm64",
+    ],
+)
+
+oci_pull(
+    name = "alpine",
+    digest = "sha256:7144f7bab3d4c2648d7e59409f15ec52a18006a128c733fcff20d3a4a54ba44a",
+    image = "https://index.docker.io/library/alpine",
+    platforms = [
+        "linux/amd64",
+    ],
+)
+
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "rules_pkg",
+    sha256 = "8f9ee2dc10c1ae514ee599a8b42ed99fa262b757058f65ad3c384289ff70c4b8",
+    urls = [
+        "https://mirror.bazel.build/github.com/bazelbuild/rules_pkg/releases/download/0.9.1/rules_pkg-0.9.1.tar.gz",
+        "https://github.com/bazelbuild/rules_pkg/releases/download/0.9.1/rules_pkg-0.9.1.tar.gz",
+    ],
+)
+
+load("@rules_pkg//:deps.bzl", "rules_pkg_dependencies")
+
+rules_pkg_dependencies()

examples/toolchains/cc_cross_osx_to_linux_amd64/hello.cc

@@ -0,0 +1,8 @@
+#include <iostream>
+#include <boost/filesystem/operations.hpp>
+#include <zlib.h>
+
+int main()
+{
+	std::cout << "Hello world!\n";
+}

examples/toolchains/cc_cross_osx_to_linux_amd64/nixpkgs.json

@@ -0,0 +1,7 @@
+{
+  "owner": "NixOS",
+  "repo": "nixpkgs",
+  "branch": "23.05",
+  "rev": "3ad64d9e2d5bf80c877286102355b1625891ae9a",
+  "sha256": "sha256-PuZSAHeq4/9pP/uYH1FcagQ3nLm/DrDrvKi/xC9glvw="
+}

examples/toolchains/cc_cross_osx_to_linux_amd64/nixpkgs.nix

@@ -0,0 +1,8 @@
+let
+  spec = builtins.fromJSON (builtins.readFile ./nixpkgs.json);
+  nixpkgs = fetchTarball {
+    url = "https://github.com/${spec.owner}/${spec.repo}/archive/${spec.rev}.tar.gz";
+    sha256 = spec.sha256;
+  };
+in
+import nixpkgs

examples/toolchains/cc_cross_osx_to_linux_amd64/shell.nix

@@ -0,0 +1,3 @@
+{ pkgs ? import ./nixpkgs.nix { } }:
+
+pkgs.mkShellNoCC { nativeBuildInputs = [ pkgs.bazel_6 ]; }

examples/toolchains/cc_cross_osx_to_linux_amd64/toolchains/BUILD

@@ -0,0 +1,9 @@
+platform(
+    name = "linux_x86_64",
+    constraint_values = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:linux",
+        "@rules_nixpkgs_core//constraints:support_nix",
+    ],
+    visibility = ["//visibility:public"],
+)

examples/toolchains/cc_cross_osx_to_linux_amd64/toolchains/cc.nix

@@ -0,0 +1,72 @@
+# We need to write a fancy nix file to handle the CC compiler due to OSX: https://github.com/tweag/rules_nixpkgs/issues/368
+# What this file is basically saying is: if OSX, change the CXX compiler to use a bunch of Apple frameworks, LLVM libs,
+# libc++ instead of libstdc++, and some additional compiler flags to ignore some warnings, otherwise, just use clang11
+let
+  pkgs = import <nixpkgs> {};
+in let
+  clang = pkgs.clang_11;
+  # The original `postLinkSignHook` from nixpkgs assumes `codesign_allocate` is
+  # in the PATH which is not the case when using our cc_wrapper. Set
+  # `CODESIGN_ALLOCATE` to an absolute path here and override the hook for
+  # `darwinCC` below.
+  postLinkSignHook = with pkgs;
+    writeTextFile {
+      name = "post-link-sign-hook";
+      executable = true;
+
+      text = ''
+        CODESIGN_ALLOCATE=${darwin.cctools}/bin/codesign_allocate \
+          ${darwin.sigtool}/bin/codesign -f -s - "$linkerOutput"
+      '';
+    };
+  darwinCC =
+    # Work around https://github.com/NixOS/nixpkgs/issues/42059.
+    # See also https://github.com/NixOS/nixpkgs/pull/41589.
+    pkgs.wrapCCWith rec {
+      cc = clang;
+      bintools = pkgs.stdenv.cc.bintools.override {inherit postLinkSignHook;};
+      extraBuildCommands = with pkgs.darwin.apple_sdk.frameworks; ''
+        echo "-Wno-unused-command-line-argument" >> $out/nix-support/cc-cflags
+        echo "-Wno-elaborated-enum-base" >> $out/nix-support/cc-cflags
+        echo "-isystem ${pkgs.llvmPackages_11.libcxx.dev}/include/c++/v1" >> $out/nix-support/cc-cflags
+        echo "-isystem ${pkgs.llvmPackages_11.clang-unwrapped.lib}/lib/clang/${cc.version}/include" >> $out/nix-support/cc-cflags
+        echo "-F${CoreFoundation}/Library/Frameworks" >> $out/nix-support/cc-cflags
+        echo "-F${CoreServices}/Library/Frameworks" >> $out/nix-support/cc-cflags
+        echo "-F${Security}/Library/Frameworks" >> $out/nix-support/cc-cflags
+        echo "-F${Foundation}/Library/Frameworks" >> $out/nix-support/cc-cflags
+        echo "-L${pkgs.llvmPackages_11.libcxx}/lib" >> $out/nix-support/cc-cflags
+        echo "-L${pkgs.llvmPackages_11.libcxxabi}/lib" >> $out/nix-support/cc-cflags
+        echo "-L${pkgs.libiconv}/lib" >> $out/nix-support/cc-cflags
+        echo "-L${pkgs.darwin.libobjc}/lib" >> $out/nix-support/cc-cflags
+        echo "-resource-dir=${pkgs.stdenv.cc}/resource-root" >> $out/nix-support/cc-cflags
+      '';
+    };
+  linuxCC = pkgs.wrapCCWith rec {
+    cc = clang;
+    bintools = pkgs.stdenv.cc.bintools;
+    extraPackages = [pkgs.glibc.static];
+    extraBuildCommands = ''
+      echo "-isystem ${pkgs.llvmPackages_11.clang-unwrapped.lib}/lib/clang/${cc.version}/include" >> $out/nix-support/cc-cflags
+      echo "-L ${pkgs.glibc.static}/lib" >> $out/nix-support/cc-ldflags
+      echo "-resource-dir=${cc}/resource-root" >> $out/nix-support/cc-cflags
+    '';
+  };
+in
+  pkgs.buildEnv (
+    let
+      cc =
+        if pkgs.stdenv.isDarwin
+        then darwinCC
+        else linuxCC;
+    in {
+      name = "bazel-nixpkgs-cc";
+      # XXX: `gcov` is missing in `/bin`.
+      #   It exists in `stdenv.cc.cc` but that collides with `stdenv.cc`.
+      paths = [cc cc.bintools] ++ pkgs.lib.optional pkgs.stdenv.isDarwin pkgs.darwin.cctools;
+      pathsToLink = ["/bin"];
+      passthru = {
+        inherit (cc) isClang targetPrefix;
+        orignalName = cc.name;
+      };
+    }
+  )