Merge pull request #487 from pietroalbini/reducing-support-for-apple-32bit

[main blog] Reducing support for 32-bit Apple targets

Author: pietroalbini

posts/2020-01-03-reducing-support-for-32-bit-apple-targets.md

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+---
+layout: post
+title: "Reducing support for 32-bit Apple targets"
+author: Pietro Albini
+---
+
+The Rust team regrets to announce that Rust 1.41.0 (to be released on January
+30th, 2020) will be the last release with the current level of support for
+32-bit Apple targets. Starting from Rust 1.42.0, those targets will be demoted
+to Tier 3.
+
+The decision was made on [RFC 2837], and was accepted by the compiler and
+release teams. This post explains what the change means, why we did it, and how
+your project is affected.
+
+[RFC 2837]: https://github.com/rust-lang/rfcs/pull/2837
+
+# What’s a support tier?
+
+The Rust compiler can build code targeting [a lot of
+platforms][platform-support] (also called “targets”), but the team doesn't have
+the resources or manpower to provide the same level of support and testing for
+each of them.
+To make our commitments clear, we follow a tiered support policy (currently
+being formalized and revised in [RFC 2803]), explaining what we guarantee:
+
+- Tier 1 targets can be downloaded through rustup and are fully tested
+  during the project’s automated builds. A bug or a regression affecting one of
+  these targets is usually prioritized more than bugs only affecting platforms
+  in other tiers.
+
+- Tier 2 targets can also be downloaded through rustup, but our
+  automated builds don’t execute the test suite for them. While we guarantee a
+  standard library build (and for some of them a full compiler build) will be
+  available, we don’t ensure it will actually work without bugs (or even work
+  at all).
+
+- Tier 3 targets are not available for download through rustup, and are
+  ignored during our automated builds. You can still build their standard
+  library for cross-compiling (or the full compiler in some cases) from source
+  on your own, but you might encounter build errors, bugs, or missing features.
+
+[platform-support]: https://forge.rust-lang.org/release/platform-support.html
+[RFC 2803]: https://github.com/rust-lang/rfcs/pull/2803
+
+# Which targets are affected?
+
+The main target affected by this change is 32-bit macOS (`i686-apple-darwin`),
+which will be demoted from Tier 1 to Tier 3. This will affect both using the
+compiler on 32-bit Mac hardware, and cross-compiling 32-bit macOS binaries from
+any other platform.
+
+Additionally, the following 32-bit iOS targets will be demoted from Tier 2 to
+Tier 3:
+
+* `armv7-apple-ios`
+* `armv7s-apple-ios`
+* `i386-apple-ios`
+
+We will continue to provide the current level of support for all Apple 64bit
+targets.
+
+# Why are those targets being demoted?
+
+Apple dropped support for running 32-bit binaries starting from [macOS
+10.15][deprecate-macos] and [iOS 11][deprecate-ios]. They also prevented all
+developers from cross-compiling 32-bit programs and apps starting from Xcode 10
+(the platform’s IDE, containing the SDKs).
+
+Due to those decisions from Apple, the targets are no longer useful to our users,
+and their choice to prevent cross-compiling makes it hard for the
+project to continue supporting the 32-bit platform in the long term.
+
+[deprecate-macos]: https://support.apple.com/en-us/HT208436
+[deprecate-ios]: https://developer.apple.com/documentation/uikit/app_and_environment/updating_your_app_from_32-bit_to_64-bit_architecture
+
+# How will this affect my project?
+
+If you don’t build 32-bit Apple binaries this change won’t affect you at all.
+
+If you still need to build them, you’ll be able to continue using Rust 1.41.0
+without issues. As usual the Rust project will provide critical bugfixes and
+security patches until the next stable version is released (on March 12th,
+2020), and we plan to keep the release available for download for the
+foreseeable future (as we do with all the releases shipped so far).
+
+The code implementing the targets won’t be removed from the compiler codebase,
+so you’ll also be able to build future releases from source on your own
+(keeping in mind they might have bugs or be broken, as that code will be
+completly untested).
+
+# What about the nightly channel?
+
+We will demote the targets on the nightly channel soon, but we don't have an
+exact date for when that will happen. We recommend pinning a nightly version
+beforehand though, to prevent `rustup toolchain install` from failing once we
+apply the demotion.
+
+To pin a nightly version you need to use "nightly" followed by the day the
+nightly was released, as the toolchain name. For example, to install the nightly
+released on December 1st, 2019 and to use it you can run:
+
+```plain
+rustup toolchain install nightly-2019-12-01
+
+# Default to this nightly system-wide...
+rustup default nightly-2019-12-01
+
+# ...or use this nightly for a single build
+cargo +nightly-2019-12-01 build
+```