Patch Homebrew to embed version number

homebrew-bundle now depends on $HOMEBREW_VERSION, which is set by
`brew.sh` using the output of `git describe`. We don't have a git
repo, so let's embed the version directly.

Fixes #19.

flake.nix

@@ -14,6 +14,9 @@
   outputs = { self, nixpkgs, nix-darwin, flake-utils, brew-src, ... } @ inputs: let
     # System types to support.
     supportedSystems = [ "x86_64-darwin" "aarch64-darwin" ];
+
+    flakeLock = builtins.fromJSON (builtins.readFile ./flake.lock);
+    brewVersion = flakeLock.nodes.brew-src.original.ref;
   in flake-utils.lib.eachSystem supportedSystems (system: let
     pkgs = nixpkgs.legacyPackages.${system};
   in {
@@ -32,7 +35,10 @@
         imports = [
           ./modules
         ];
-        nix-homebrew.package = lib.mkOptionDefault brew-src.outPath;
+        nix-homebrew.package = lib.mkOptionDefault (brew-src // {
+          name = "brew-${brewVersion}";
+          version = brewVersion;
+        });
       };
     };
     darwinConfigurations = {

modules/default.nix

@@ -287,7 +287,7 @@ let
 
   patchBrew = brew: let
     pinnedRuby = "${pkgs.ruby}/bin/ruby";
-  in pkgs.runCommandLocal "${brew.name or "brew"}-patched" {} ''
+  in pkgs.runCommandLocal "${brew.name or "brew"}-patched" {} (''
     cp -r "${brew}" "$out"
     chmod u+w "$out" "$out/Library/Homebrew/cmd"
 
@@ -301,7 +301,12 @@ let
       chmod u+w "$ruby_sh"
       echo -e "setup-ruby-path() { export HOMEBREW_RUBY_PATH=\"${pinnedRuby}\"; }" >>"$ruby_sh"
     fi
-  '';
+  '' + lib.optionalString (brew ? version) ''
+    # Embed version number instead of checking with git
+    brew_sh="$out/Library/Homebrew/brew.sh"
+    chmod u+w "$out/Library/Homebrew" "$brew_sh"
+    sed -i -e 's/^HOMEBREW_VERSION=.*/HOMEBREW_VERSION="${brew.version}"/g' "$brew_sh"
+  '');
 in {
   options = {
     nix-homebrew = {