WORKSPACE snippet to use gcc-toolchain

[tetsuok]

It seems a WORKSPACE snippet to set up gcc-toolchain is missing from the current documentation. It would be nice to include the WORKSPACE snippet in documentation or the release page so that users can start using gcc-toolchain without troubles by copying the WORKSPACE snippet into their WORKSPACE files.

Based on this repo's WORKSPACE, below is an example of the WORKSPACE snippet and .bazelrc to use gcc-toolchain v0.4.2 to build binaries for x86_64. It would be great to confirm that there is something wrong or redundant with the snippet. I mentioned this because unusual configs, --action_env=BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN=1 and --incompatible_enable_cc_toolchain_resolution were required to add to .bazelrc so that Bazel can use the C/C++ toolchain managed by gcc-toolchain. If these configs are required indeed, I think it worth noting it in the documentation because these configs not so obvious for non-Bazel experts.

WORKSPACE:

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

# Skylib
# gcc-toolchain depends on bazel-skylib
http_archive(
    name = "bazel_skylib",
    sha256 = "f7be3474d42aae265405a592bb7da8e171919d74c16f082a5457840f06054728",
    urls = [
        "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.2.1/bazel-skylib-1.2.1.tar.gz",
        "https://github.com/bazelbuild/bazel-skylib/releases/download/1.2.1/bazel-skylib-1.2.1.tar.gz",
    ],
)

load("@bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")

bazel_skylib_workspace()

http_archive(
    name = "aspect_gcc_toolchain",
    sha256 = "3341394b1376fb96a87ac3ca01c582f7f18e7dc5e16e8cf40880a31dd7ac0e1e",
    strip_prefix = "gcc-toolchain-0.4.2",
    url = "https://github.com/aspect-build/gcc-toolchain/archive/refs/tags/0.4.2.tar.gz",
)

load("@aspect_gcc_toolchain//toolchain:defs.bzl", "ARCHS", "gcc_register_toolchain")

gcc_register_toolchain(
    name = "gcc_toolchain_x86_64",
    gcc_version = "10.3.0",
    sysroot_variant = "x86_64",
    target_arch = ARCHS.x86_64,
)

.bazelrc:

# Required to use the C/C++ toolchain managed by gcc-toolchain
build --action_env=BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN=1
build --incompatible_enable_cc_toolchain_resolution

# optional, but preferred for performance as per https://github.com/aspect-build/gcc-toolchain/issues/85
build --experimental_reuse_sandbox_directories

[f0rmiga]

This is probably the missing piece of #75 after adding bcc2a04 (which triggered the blog post https://blog.aspect.dev/hermetic-c-toolchain).

I'm tempted to just add this snippet as part of the releases with the top-level README.md pointing to the link of the latest release.

[f0rmiga]

I agree we should be clear about the extra flags required, they are indeed non-obvious. Before finding BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN buried somewhere deep into the source code, I used to set CC=/bin/false to ensure the toolchain resolution was being enforced, but it started to break some IDEs based on other users reporting directly to me (I haven't experienced it myself).

[tetsuok]

I'm tempted to just add this snippet as part of the releases with the top-level README.md pointing to the link of the latest release.

That sounds good to me.