Support macOS

Currently it requires Linux remote builders to be set up to do
anything useful, but soon it will not once we able to initiate
builds directly on the target nodes themselves.

.github/workflows/build.yml

@@ -4,9 +4,11 @@ on:
   push:
 jobs:
   build:
-    runs-on: ubuntu-latest
     strategy:
       matrix:
+        os:
+          - ubuntu-latest
+          - macos-11
         nix:
           - name: 2.4
             url: https://releases.nixos.org/nix/nix-2.4/install
@@ -14,6 +16,7 @@ jobs:
           #  url: https://releases.nixos.org/nix/nix-2.3.16/install
           #- name: 2.5pre
           #  url: https://github.com/numtide/nix-unstable-installer/releases/download/nix-2.5pre20211026_5667822/install
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2.3.5
       - uses: cachix/install-nix-action@v15
@@ -43,9 +46,10 @@ jobs:
         if: ${{ !contains(matrix.nix.name, '2.3') }}
 
   tests:
-    runs-on: ubuntu-latest
     strategy:
       matrix:
+        os:
+          - ubuntu-latest
         nix:
           - name: 2.3.16
             url: https://releases.nixos.org/nix/nix-2.3.16/install
@@ -53,6 +57,7 @@ jobs:
             url: https://releases.nixos.org/nix/nix-2.4/install
           - name: 2.5pre
             url: https://github.com/numtide/nix-unstable-installer/releases/download/nix-2.5pre20211026_5667822/install
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2.3.5
       - uses: cachix/install-nix-action@v15

default.nix

@@ -41,6 +41,6 @@ in rustPlatform.buildRustPackage rec {
     homepage = "https://zhaofengli.github.io/colmena/${passthru.apiVersion}";
     license = licenses.mit;
     maintainers = with maintainers; [ zhaofengli ];
-    platforms = platforms.linux;
+    platforms = platforms.linux ++ platforms.darwin;
   };
 }

flake.nix

@@ -12,8 +12,7 @@
   };
 
   outputs = { self, nixpkgs, utils, ... }: let
-    # We aren't testing against Darwin at the moment
-    supportedSystems = [ "x86_64-linux" "i686-linux" "aarch64-linux" ];
+    supportedSystems = [ "x86_64-linux" "i686-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
   in utils.lib.eachSystem supportedSystems (system: let
     pkgs = import nixpkgs { inherit system; };
   in rec {