Cross compiling ruby pulls in host package despite it being in nativeBuildInputs

[expipiplus1]

Describe the bug

A clear and concise description of what the bug is.

To Reproduce

• run nix-build -A pkgsCross.armv7l-hf-multiplatform.ruby on an x86_64 system

• Observe that it fails trying to run an arm binary of bison

• Observe that that derivation lists the wrong architecture bison in nativebuildInputs(!)

  , ( "nativeBuildInputs"
    , "/nix/store/p8frky3amk07n2illsnqbn1k8lhy6mci-hook /nix/store/ppb9620xh5gri16lgf6f9sn46mdv2xyk-bison-3.5.4-armv7l-unknown-linux-gnueabihf /nix/store/dbjqx0r50sf5sanmsb0lgyq9zf3vck2k-groff-1.22.4 /nix/store/33nr5mknv9wc75f7lbgnck0z3xipya6s-ruby-2.6.6"
    )
  

• Remove the bison override for ruby in all-packages.nix

• Observe that the native bison is used and present in the derivation (although the build fails with this version of bison as expected)

Additional context

I conjecture that bison_3_5 overridesAttrs is somehow interfering with getting the native derivation when it is passed to nativeBuildInputs

Notify maintainers

@FRidh I think you added this override.

@vrthra @manveru maintainers for ruby.

Metadata

 - system: `"x86_64-linux"`
 - host os: `Linux 5.4.42, NixOS, 20.03.git.48723f48ab9M (Markhor)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.6`
 - nixpkgs: `/home/j/src/nixpkgs2`

Maintainer information:

attribute:
  - pkgsCross.armv7l-hf-multiplatform.ruby

[expipiplus1]

This certainly doesn't seem like a problem specific to ruby btw.

[FRidh]

fixed with 7bf20d7

[FRidh]

This certainly doesn't seem like a problem specific to ruby btw.

Many expressions have not been written with cross-compilation in mind, and so don't separate native build inputs from host inputs.

[expipiplus1]

Thanks @FRidh! Is there a short reason why the usual nativeBuildInputs machinery didn't do this already? It seems to work when one has bison=bison

[FRidh]

When you use callPackage, the splicing automatically passes it the correct version (buildPackages or not). However, if you pass in something explicitly, you need to choose. Have a look at #68967 (comment).

[expipiplus1]

Thanks again, makes sense!