Summary

This RFC proposes to demote the i686-apple-darwin rustc target from Tier 1 to Tier 3, and to demote the armv7-apple-ios, armv7s-apple-ios and i386-apple-ios rustc targets from Tier 2 to Tier 3.

Motivation

Apple publicly announced that macOS 10.14 Mojave is the last OS supporting the execution of 32bit binaries, and macOS 10.15 (and later) prevents running them at all. It’s been years since the last 32bit Apple hardware was sold, so providing 64bit binaries should cover most of the macOS userbase.

Apple also announced that iOS 10 is the last one supporting the execution of 32bit apps, and they won’t work at all on iOS 11 and later. All iPhones after the iPhone 5 and the iPhone 5C support 64bit apps, which means all the supported ones can run them.

Along with the deprecation, Apple removed support for building 32bit binaries since Xcode 10, and that makes building rustc itself on the project’s CI harder (as we’re limited to providers still offering Xcode 9).

It makes little sense for the Rust team to continue providing support for a platform the upstream vendor abandoned, especially when it requires extra effort from us infrastructure-wise.

Guide-level explanation

The first release after this RFC is merged will be the last one with Tier 1 support for the i686-apple-darwin target and Tier 2 support for the armv7-apple-ios, armv7s-apple-ios and i386-apple-ios targets. The release after that will demote the targets to Tier 3, which means no official build will be available for them, and they will not be tested by CI.

Once this RFC is merged a blog post will be published on the main Rust Blog announcing the change, to alert the users of the target of the demotion. The demotion will also be mentioned in the release announcement for the last release with Tier 1 and Tier 2 support, as well as the first release with Tier 3 support.

This RFC does not propose removing the targets completely from the codebase: that will be decided either by another RFC just for those targets, or by an RFC defining a general policy for Tier 3 target removal.

Once the targets are demoted to Tier 3, users on other platforms with one of those targets’ rust-std installed won’t be able to update the toolchain until they remove that target. Users using an Apple 32bit compiler as their host platforms will instead be prevented from updating at all, as no new binary artifact will be available.

Reference-level explanation

The i686-apple-darwin, armv7-apple-ios, armv7s-apple-ios and i386-apple-ios targets will be considered Tier 3 from the second release after this RFC is merged. The code supporting the target will not be removed from the compiler, even though we won’t guarantee it will continue to work.

The following CI builders will be removed:

  • dist-i686-apple
  • i686-apple

In addition, the armv7-apple-ios, armv7s-apple-ios and i386-apple-ios targets will be removed from the dist-x86_64-apple builder.

Drawbacks

Users might depend on the target, and approving this RFC means they’ll be stuck on an old compiler version forever, unless they build their own compiler and fix the regressions introduced in newer releases themselves.

Rationale and alternatives

Support for building 32bit binaries for Apple targets is shrinking as time goes by: the latest SDKs from Apple don’t support building them at all, and CI providers are slowly starting to upgrade their minimum supported SDK versions:

  • Azure Pipelines (the provider rustc currently use) doesn’t have any public information on when Xcode 9 will be deprecated.
  • GitHub Actions doesn’t support Xcode 9 at all.
  • Travis CI deprecated Xcode older than 9.2 in July 2018.

If this RFC is not accepted, we’ll eventually reach a point when we’ll have to make considerable investments both in terms of money and time to keep building on Apple 32bit.

Prior art

There is no precedent inside the project for the deprecation of Tier 1 targets to Tier 3.

Go is taking a similar approach to us, documenting that the last release supporting Apple 32bit is going to be Go 1.14 (the next one), with support for the target being dropped in Go 1.15.

Unresolved questions

Nothing here.

Future possibilities

Nothing here.