repository_ctx.os.name.lower() inappropriate when remote build.

[kekxv]

local os : macos
remote os : linux

It's supposed to download for Linux, but instead it downloads for macos

https://github.com/uber/hermetic_cc_toolchain/blob/cddeaa4c7173f8bf8bd5c14914670af352a68d89/toolchain/defs.bzl#L102C21-L107

[motiejus]

I don't have/use RBE environment -- can you send a suggestion/PR that fixes it?

[mattyclarkson]

I'm hitting the same issue: download is for arm64 but the remote executor is amd64.

This is caused because @zig_sdk is downloaded for the local execution host and then registered to be executable with all platforms, i.e. it does not have exec_compatible_with set here.

What should happen is that we have repositories for each Zig host, arm64-linux, amd64-darwin, etc and register each of those with exec_compatible_with set to the correct constraints. Then Bazel will download and use the correct Zig for the execution platform.

Currently, any remote execution that is not the same constraints as the local executor fails with an "exec format error".

The solution would be something akin to the following in the extension:

load("@hermetic_cc_toolchain//toolchain:defs.bzl", "toolchain")

_HOSTS = (
    "amd64-linux",
    "arm64-linux",
    "...etc...",
)

def _toolchains_impl(ctx):
    for host in _HOSTS:
        toolchain(host = HOST)  # Creates `@amd64-linux-zig_sdk`, etc repositories

    return ctx.extension_metadata(
        ctx,
        root_module_direct_deps = ["{}-zig_sdk".format(h) for h in _HOSTS],
        root_module_direct_dev_deps = (),
        reproducible = True,
    )

toolchains = module_extension(implementation = _toolchains_impl)

Then in the MODULE.bazel we register all the toolchains for the different execution hosts.