Warn when using non-native host tooling on macOS?

[madsmtm]

Problem you are trying to solve

macOS has the capability to transparently run x86 binaries on Aarch64 using Rosetta. This allows things like rustup default stable-x86_64-apple-darwin --force-non-host to work.

Unfortunately, it is also a lot slower, and it can be hard to know that something is wrong.

Rustup already helps a lot with this with the --force-non-host flag, and I'm unsure of the exact reasons why people are still hitting this, but anecdotally, I've helped people both in-person and online run rustup default stable-aarch64-apple-darwin and resolve a lot of problems that way.

It might happen if they've migrated their .rustup folder from an Intel Macbook? Or if they configured their setup before the stuff in #3438 / #3068 / #3972 was implemented?

Solution you'd like

It would be nice if Rustup could warn when the default toolchain is set to an x86_64 variant on a Aarch64 machine.

I am unsure exactly when it would make sense for such a warning to trigger, but probably when running rustup default, and at the end of rustup update.

And maybe rustup show, rustup check and rustup toolchain list?

[rami3l]

@madsmtm Many thanks for your report and the thorrough investigation beforehand!

It might happen if they've migrated their .rustup folder from an Intel Macbook? Or if they configured their setup before the stuff in #3438 / #3068 / #3972 was implemented?

This case is already covered by #4064. Combined with the previous patches that you have mentioned, I don't think a regular user will hit that case very often, so I am currently reluctant to add more stuff related an old target that is moving towards a lower tier.

Also, this is for practical reasons as well, as we are currently running the full test suite for x64 macOS under Rosetta 2 and we are already using a lot of hacks to ensure the E2E tests still pass, thus, we might not want to adjust them further unless the costs are properly justified.

Many thanks in advance for your comprehension 🙏

[madsmtm]

I am currently reluctant to add more stuff related an old target that is moving towards a lower tier.

I think that's the wrong way of looking at it; rather, the fact that x86_64-apple-darwin is moving towards tier 2 should be more motivation to get people to stop using that as their host target.

Also, this is for practical reasons as well

Totally fair, feel free to close the issue if you don't think it's worthwhile.

[rami3l]

I think that's the wrong way of looking at it; rather, the fact that x86_64-apple-darwin is moving towards tier 2 should be more motivation to get people to stop using that as their host target.

Thank you, and I believe I understand what you are trying to say.

Sorry for not being clear enough previously, but I rather wanted to point out the fact that since the host platform itself is losing popularity, there will be fewer people getting this kind of host toolchain without receiving a warning by, say, migrating from an old machine.

In conclusion, I am closing this issue given that this case has been largely covered by #3438 #3068 #3972 #4064, and for those who want to use an old toolchain before ARM64 macOS was made available on GitHub Actions, they should know what they are doing.

If there is another loophole preventing the warning from being received, it belongs to a new issue where it is clarified.