Hello folks, I want to PR darwin support for libtree (analysis of linked libraries) and I have questions about tests.

There's a passthru.tests attrset at https://github.com/NixOS/nixpkgs/blob/5e2a59a5b1a82f89f2c7e598302a9cacebb72a67/pkgs/by-name/li/libtree/package.nix#L28-L46 which tests ls from coreutils. On macos, by default, it checks the macOS build of ls, which is not an ELF. I can get it to work properly using pkgsCross, as in the following.

    (libtree.override {
      inherit (pkgsCross.aarch64-multiplatform) coreutils;
    }).overrideAttrs
      (old: {
        meta = lib.recursiveUpdate (old.meta or { }) { platforms = lib.platforms.darwin; };
      })

I presume that in this case libtree should always test the pkgsCross coreutils… but certainly the tests fail on macos without it. What's the idiomatic way of handling this case?

[Edit: I don't mean idiomatic way of implementing the changes, as opposed to the override, I mean the idiomatic way of handling the cross-platform dependency in the tests.]

Yes. There’s an open issue for Mach-O support, but it’s old.

https://github.com/haampie/libtree/issues/22

> nix build -L '.#libtree.tests.checkCoreUtils' --no-link --print-out-paths
/nix/store/40xm11r0sklkl4x5cp8xdckp5sha0yfd-libtree-ls-test

> nix build -L '.#libtree.tests.checkCoreUtils' --no-link --print-out-paths | xargs bat
───────┬──────────────────────────────────────────────────────────────────────────────────────────────
       │ File: /nix/store/40xm11r0sklkl4x5cp8xdckp5sha0yfd-libtree-ls-test
───────┼──────────────────────────────────────────────────────────────────────────────────────────────
   1   │ /nix/store/x2s54dnz7kd4vbslfcv1x3g69p30fz7y-coreutils-aarch64-unknown-linux-gnu-9.7/bin/ls
   2   │ ├── libacl.so.1 [runpath]
   3   │ │   └── libattr.so.1 [runpath]
   4   │ ├── libattr.so.1 [runpath]
   5   │ └── libgmp.so.10 [runpath]
───────┴──────────────────────────────────────────────────────────────────────────────────────────────

> nix build -L '.#libtree.tests.checkCoreUtils' --no-link --print-out-paths
/nix/store/40xm11r0sklkl4x5cp8xdckp5sha0yfd-libtree-ls-test

> nix build -L '.#libtree.tests.checkCoreUtils' --no-link --print-out-paths | xargs bat
───────┬──────────────────────────────────────────────────────────────────────────────────────────────
       │ File: /nix/store/40xm11r0sklkl4x5cp8xdckp5sha0yfd-libtree-ls-test
───────┼──────────────────────────────────────────────────────────────────────────────────────────────
   1   │ /nix/store/x2s54dnz7kd4vbslfcv1x3g69p30fz7y-coreutils-aarch64-unknown-linux-gnu-9.7/bin/ls
   2   │ ├── libacl.so.1 [runpath]
   3   │ │   └── libattr.so.1 [runpath]
   4   │ ├── libattr.so.1 [runpath]
   5   │ └── libgmp.so.10 [runpath]
───────┴──────────────────────────────────────────────────────────────────────────────────────────────

This is the test result, making the above change to use the pkgsCross (but not pkgsStatic!) coreutils.