You would need at least a bridging layer (of Objective-C) to so that your app code could use the system frameworks and respond to events (user input, network, sensors, etc).
Objective-C shares calling conventions and struct layout with C, so theoretically you could directly call the system frameworks from Rust via extern "C" functions.
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If I'm reading it right, it lets you build Rust libraries so you can use them in iOS programs.
You can already build for iOS, just not apple tv or watch without bitcode. For building for iphone this is not needed.
Libraries only, or can you write native iOS apps 100% in Rust, no Swift?
You would need at least a bridging layer (of Objective-C) to so that your app code could use the system frameworks and respond to events (user input, network, sensors, etc).
Objective-C shares calling conventions and struct layout with C, so theoretically you could directly call the system frameworks from Rust via extern "C" functions.
Not even theoretically, the bindings for the runtime are out there [1] with some nifty helper macros.
[1] https://github.com/SSheldon/rust-objc
It'd be super cool to see a 100% Rust (with extern "C" calls) Hello, world! iOS compatible app.