buildinput inconsistent treating of nested lists

[alexarice]

Issue description

If buildInputs is given a list that contains list e.g.
buildInputs = [ [a] b c ]
it sometimes successfully passes in the inputs and sometimes doesn't
i have seen this occur in cases such as
buildInputs = [ a b ] ++ lib.optional buildDocs [ builddocdep ]
(although this is probably incorrect I expect it may happen a couple of times in nixpkgs)

Steps to reproduce

• clone nixpkgs repository
• run nix-build -A grim
• It builds
• go into the repository and change buildInputs in grim to

  buildInputs = [
    [cairo]
    libjpeg
    wayland
    wayland-protocols
  ];

• build fails with something like this https://gist.github.com/alexarice/0028eb89577489d5c15ffd07e8e9ddec#file-grim-build-singleton-cairo
• change build inputs to this

  buildInputs = [
    cairo
    libjpeg
    [wayland]
    wayland-protocols
  ];

• build succeeds with something like this https://gist.github.com/alexarice/0028eb89577489d5c15ffd07e8e9ddec#file-build-with-wrapped-wayland

Technical details

• system: "x86_64-linux"
• host os: Linux 4.19.36, NixOS, 19.09pre177249.dfd8f84aef1 (Loris)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.2.2
• channels(alex): ""
• channels(root): "nixos-19.09pre177249.dfd8f84aef1"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

[alexarice]

Feel it is worth adding that grim does not build without the wayland buildInput

[stale]

Thank you for your contributions.

This has been automatically marked as stale because it has had no activity for 180 days.

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[alexarice]

I believe this is still relevant though I haven't investigated in ages

[stale]

I marked this as stale due to inactivity. → More info