feat: add function to filter hosts from an attrset by system

flake.nix

@@ -127,6 +127,7 @@
         inherit (generators) mkDeployNodes mkHomeConfigurations ;
         inherit (collectors)
           collectHosts
+          collectHostsOnSystem
         ;
 
         # DEPRECATED - will be removed soon

src/collectors.nix

@@ -1,19 +1,34 @@
 { lib }:
 let
-  collectHosts = nixosHosts: darwinHosts:
+  collectHosts = nixosConfigurations: darwinConfigurations:
     /**
-      Synopsis: hostsOnSystem _hostOutputs_ _system_
+      Synopsis: collectHosts _nixosConfigurations_ _darwinConfigurations_
 
+      Collect all hosts across NixOS and Darwin configurations, validating for
+      unique hostnames to prevent collisions.
       **/
-    (nixosHosts // lib.mapAttrs (name: value:
-        if builtins.hasAttr name nixosHosts
-        then throw ''
-          Hostnames must be unique across all platforms! Found a duplicate host config for '${name}'.
-        ''
+    (nixosConfigurations // lib.mapAttrs
+      (name: value:
+        if builtins.hasAttr name nixosConfigurations
+        then
+          throw ''
+            Hostnames must be unique across all platforms! Found a duplicate host config for '${name}'.
+          ''
         else value
       )
-      darwinHosts);
+      darwinConfigurations);
 in
 {
   inherit collectHosts;
+
+  collectHostsOnSystem = hostConfigurations: system:
+    /**
+      Synopsis: collectHostsOnSystem _hostConfigurations_ _system_
+
+      Filter a set of host configurations to those matching a given system.
+      **/
+    let
+      systemSieve = _: host: host.config.nixpkgs.system == system;
+    in
+    lib.filterAttrs systemSieve hostConfigurations;
 }

src/mkFlake/outputs-builder.nix

@@ -1,5 +1,5 @@
 # constructor dependencies
-{ lib, self, inputs, deploy, devshell, home-manager, flake-utils-plus, tests, ... }:
+{ lib, self, inputs, collectors, deploy, devshell, home-manager, flake-utils-plus, tests, ... }:
 config: channels:
 let
 
@@ -109,8 +109,7 @@ in
         (self.nixosConfigurations != { })
       ) then
         let
-          systemSieve = _: host: host.config.nixpkgs.system == system;
-          hostConfigsOnThisSystem = lib.filterAttrs systemSieve self.nixosConfigurations;
+          hostConfigsOnThisSystem = collectors.collectHostsOnSystem self.nixosConfigurations system;
 
           createCustomTestOp = n: host: test:
             lib.warnIf (!(test ? name)) ''
@@ -145,8 +144,7 @@ in
         (self.darwinConfigurations != { })
       ) then
         let
-          systemSieve = _: host: host.config.nixpkgs.system == system;
-          hostConfigsOnThisSystem = lib.filterAttrs systemSieve self.darwinConfigurations;
+          hostConfigsOnThisSystem = collectors.collectHostsOnSystem self.darwinConfigurations system;
 
           createCustomTestOp = n: host: test:
             lib.warnIf (!(test ? name)) ''