Build iOS applications on Linux

Once can cross-compile native Apple libraries, frameworks, applications, and executables on Linux using Swift and xtool's Darwin SDK. Compilation, linking, resource packaging, and ad-hoc signing remain declared Once actions, with the same caching and memory-budgeted scheduling as other builds.

Linux iOS device builds default to ARM64, including on x86_64 hosts. Once uses the active Swift toolchain's Clang, the SDK's Mach-O linker and archiver, omarchy-apple-dev's installed resource compatibility tools, and rcodesign. You supply the Apple SDK through xtool; Once does not redistribute it.

A Linux application starter is available through target-kind discovery:

once edit materialize-example apple_application apple-application-linux
once build Hello

The output is ad-hoc signed, not provisioned for device installation or App Store submission. Simulator execution, Apple test runtimes, Xcode and Swift package workspace resolution, and Xcode app thinning still require macOS. See Build iOS Applications on Linux for setup, SDK repair after toolchain switches, and deployment boundaries.