darwin.darling.src: fix build on case-sensitive filesystems

[veprbl]

Motivation for this change

Fix #91480 as discussed in #101799 (comment)

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[veprbl]

@GrahamcOfBorg build darling.src

[veprbl]

@GrahamcOfBorg build darwin.darling.src

[thefloweringash]

Thanks for working on this. I think there are two things that need to be handled. The first is with case-sensitive filesystems in which the directories are split, and the second is with case-insensitive filesystems where the result is non-deterministic (the canonical name is either lowercase or camelcase). Maybe something like this. It seems to work on my case-insensitive macOS and my case-sensitive linux.

fetchzip {
  url = "https://github.com/darlinghq/darling/archive/d2cc5fa748003aaa70ad4180fff0a9a85dc65e9b.tar.gz";
  sha256 = "0000000000000000000000000000000000000000000000000000"; # for testing
  postFetch = ''
    # Get rid of case conflicts
    mkdir $out

    # The archive contains both `src/opendirectory` and `src/OpenDirectory`,
    # pre-create the directory to choose the canonical case on
    # case-insensitive filesystems.
    mkdir -p $out/src/OpenDirectory

    cd $out
    tar -xzf $downloadedFile --strip-components=1
    rm -r $out/src/libm

    # If `src/opendirectory` and `src/OpenDirectory` refer to different
    # things, then combine them into `src/OpenDirectory` to match the result
    # on case-insensitive filesystems.
    if [ "$(stat -c %i src/opendirectory)" != "$(stat -c %i src/OpenDirectory)" ]; then
      mv src/opendirectory/* src/OpenDirectory/
      rmdir src/opendirectory
    fi
  '';
}

[holymonson]

@veprbl this has been fixed on upstream darlinghq/darling@ea5f07d , should we use an updated source instead of fixing it here? We need darling to update xnu and Libsystem.