The Rust language development team plans to reduce the level of support for 32-bit Apple targets. Rust 1.41.0, due January 30, 2020, will be the last version of the language with full support for these targets, according to a bulletin published January 3, 2020.
Starting with Rust 1.42.0, 32-bit Apple targets will be reduced to “Tier 3” status, which means they won’t be available for download via the rustup installer and they will be ignored during automated builds. The main target affected by the team’s declaration is
i686 apple darwin, which is being demoted from Tier 1 to Tier 3. This affects use of the compiler on 32-bit Mac hardware as well as cross-compiling 32-bit MacOS binaries from another platform. Other targets to be demoted include