aarch64-darwin: Improve error message when trying to do a x86_64-darwin build and Rosetta is not installed

[edolstra]

Is your feature request related to a problem?

Currently you just get

% nix build nix#hydraJobs.build.nix-functional-tests.x86_64-darwin
error: a 'x86_64-darwin' with features {} is required to build '/nix/store/07c6yy8wamq9707ja3bvdr60kjhaxli3-nix-2.26.0pre20250121_b8c296f.drv', but I am a 'aarch64-darwin' with features {apple-virt, benchmark, big-parallel, nixos-test}

Proposed solution

Ideally it would tell you to run /usr/sbin/softwareupdate --install-rosetta --agree-to-license to enable x86_64-darwin support.

Alternative solutions

Additional context

Checklist

• checked latest Nix manual (source)
• checked open feature issues and pull requests for possible duplicates

---

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[aidenfoxivey]

I presume this is coming from src/libstore/unix/build/local-derivation-goal.cc

Would something like

    /* Right platform? */
    if (!parsedDrv->canBuildLocally(worker.store)) {
        // since aarch64-darwin has Rosetta 2, this user can actually run x86_64-darwin on their hardware - we should tell them to run the command to install Darwin 2
        if (drv->platform == "x86_64-darwin" && setttings.thisSystem == "aarch64-darwin") {
            throw Error("run `/usr/sbin/softwareupdate --install-rosetta --agree-to-license` to enable your %s to run programs for %s", settings.thisSystem, drv->platform);
        } else {
            throw Error("a '%s' with features {%s} is required to build '%s', but I am a '%s' with features {%s}",
                drv->platform,
                concatStringsSep(", ", parsedDrv->getRequiredSystemFeatures()),
                worker.store.printStorePath(drvPath),
                settings.thisSystem,
                concatStringsSep<StringSet>(", ", worker.store.systemFeatures));
        }
}

be what you're looking for?

[tomberek]

It's on the right track. There might be a function to check if Rosetta is enabled in settings::getDefaultExtraPlatforms.

[aidenfoxivey]

Sounds good! I'll poke around and modify my solution.

[aidenfoxivey]

Hmm, so checking whether Rosetta is enabled should be done within canBuildLocally I feel. If it returns true, then it shouldn't even have an error.

That way, if it returns false (and we have the condition I wrote earlier as being on a compatible platform) we can instead prompt the user to run the appropriate command. Does that seem reasonable?

[aidenfoxivey]

Oh okay, I see that's already a thing - awesome

[aidenfoxivey]

Yeah it seems like Settings::getDefaultExtraPlatforms() should already be called by the time that we get to canBuildLocally which then calls

    if (std::string{SYSTEM} == "aarch64-darwin" &&
        runProgram(RunOptions {.program = "arch", .args = {"-arch", "x86_64", "/usr/bin/true"}, .mergeStderrToStdout = true}).first == 0)
        extraPlatforms.insert("x86_64-darwin");

This is then called in

Setting<StringSet> extraPlatforms{
        this,
        getDefaultExtraPlatforms(),

When canBuildLocally is called,

bool ParsedDerivation::canBuildLocally(Store & localStore) const
{
    if (drv.platform != settings.thisSystem.get()
        && !settings.extraPlatforms.get().count(drv.platform)
        && !drv.isBuiltin())
        return false;

    if (settings.maxBuildJobs.get() == 0
        && !drv.isBuiltin())
        return false;

    for (auto & feature : getRequiredSystemFeatures())
        if (!localStore.systemFeatures.get().count(feature)) return false;

    return true;
}

my suspicion is that extraPlatforms should contain the right information.

Thus, I think it's enough to assume Rosetta 2 isn't enabled by the time that we get into the if statement. I feel like from there we can just compare the drv->platform and settings.thisSystem as I did above.

That's just my thoughts though - is there something I'm missing here?