Building

PureDarwin is built with Nix. Everything the project produces, from a single library to a bootable disk image, is a flake output: components, kernel collections, disk images and the QEMU runners that boot them. The short version, on a Linux host:

nix build .#image-minimal
nix run .#vm

Under the Nix layer, the Darwin sources are compiled with CMake. That CMake tree exists because Apple’s Xcode projects had to be ported to something, and Nix drives it. Configuring it by hand is not supported. Both layers use cross toolchains the project builds for itself, and an SDK the project assembles from open source headers. Those topics get a page each:

• The Nix Flake covers the outputs, how they are organised and the dev shell.
• The CMake Tree covers what CMake does here, and why it is not a supported entry point on its own.
• Host Tools and Toolchains covers the cross compilers, the real ld64 and the bootstrap sequence that produces them.
• The SDK covers how the build gets its headers without Apple’s proprietary SDK.

Two Traps

Untracked files are invisible. The flake is read as a git+file:// source, so a file you have not added with git add does not exist as far as the build is concerned. The build does not fail. It quietly uses the old state, and your change seems to do nothing. Stage before you build.

CMake is not an entry point. Nix drives it. The dev shell is for working on a single component. It does not produce a system. Read The CMake Tree before reaching for it.