fix(aaron): workaround compiler-rt 18 darwin build via overlay#147
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Apple SDK 26.4 ships libc++ 21, which dropped the fallbacks for __builtin_ctzg/__builtin_clzg — builtins Clang 18 does not recognize. nixos-unstable has been stuck at 64c08a7 (2026-05-23) ever since, because Hydra cannot advance past this failure. Mirror NixOS/nixpkgs#523142 with a host-scoped overlay that disables the C++ components (XRAY, LIBFUZZER, MEMPROF, ORC) of compiler-rt 18. Built locally on aarch64-darwin; the overlay propagates through the stdenv-darwin bootstrap via overrideScope. Refs: NixOS/nixpkgs#480849, NixOS/nixpkgs#523142
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May 29, 2026
This was referenced May 29, 2026
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Summary
nixos-unstablehas been stuck at64c08a7(2026-05-23) for almost a week because Apple SDK 26.4 ships libc++ 21, which dropped fallbacks for__builtin_ctzg/__builtin_clzg— builtins Clang 18 does not recognize. This breakscompiler-rt-libc-18.1.8on Darwin and blocks all ournixos-unstableupdates (chore: update flake inputs #141 has been failing aaron since 2026-05-23).overrideScopeso the fix propagates into the darwin stdenv bootstrap.Tracking: NixOS/nixpkgs#480849, NixOS/nixpkgs#523142.
Test plan
nix flake check --no-buildpasses (statix, deadnix, all configurations evaluate)nix build .#darwinConfigurations.aaron.systemsucceeds locally on aaron — the previously-failingcompiler-rt-libc-18.1.8derivation now builds, andclang-wrapper-18.1.8/stdenv-darwin/ full system path all completedarwin-rebuild switchon aaron once merged