MacOS - how to stop ghc source builds?

From what I’m aware if I’m on nixpkgs-20.09-darwin channel, then I should of had access to pre built ghc versions. (I’ve also tried nixpkgs-unstable)

But what is actually happening is that I’m having to build ghc from source locally and this takes 6-8 hours through nix :cry:

The version I just tried it on is ghc8102 which is available from what I gather as shown here

How do people get around this?

I’m aware of the great project that is happening Recurring funding for making macOS first-class citizen in Nix ecosystem but looking for an intermediary solution :smile_cat:

First of all, confirm you actually have in your nix config with nix show-config | grep substituters.

Otherwise, maybe it wasn’t cached when you first tried but now it is? Because it’s definitely there. Try rm ~/.cache/nix/binary-cache-*

@ElvishJerricco yeah I have substituters =
Would cachix automatically use

Just trying to work out why it’s always building ghc locally for me, is it potentially how I’m setting up my .nix file, like this one.

There must be something different about your ghc derivation. Did you change one of ghc’s build inputs in an overlay or something?

No overlays this is just using niv, but saying that I use:

"nixpkgs": {
        "branch": "nixpkgs-unstable",
        "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",
        "homepage": "",
        "owner": "NixOS",
        "repo": "nixpkgs",
        "rev": "e5b478271ea0af7b75d53c92cfa98bdb126b44a7",
        "sha256": "06hmxvnx2swk63i15zp1q70axf53x04f7ywwlnxlcfkk0prrmwbh",
        "type": "tarball",
        "url": "",
        "url_template": "<owner>/<repo>/archive/<rev>.tar.gz"

Not sure if using niv get’s the right information, plus it’s also pointing a the branch nixpkgs-unstable maybe it should be nixpkgs-20.09-darwin ?