feat(all-formats.nix): add formatConfigs

While the `all-formats.nix` module allows to import all formats at once, it lacks an interface to customize formats or add formats.

This is fixed by adding the top-level option `formatConfigs` (attrsOf deferredModule).

All format modules created under `config.formatConfigs` are mapped so their outputs are available under `config.formats` which has also been moved to the top-level (previously `config.system.formats`).

Done:
- add option `formatConfigs`
- move option `system.formats` -> `formats`
- add test for customizing a format

all-formats.nix

@@ -1,8 +1,13 @@
 {
+  config,
   lib,
   extendModules,
   ...
 }: let
+  inherit
+    (lib)
+    types
+    ;
   # attrs of all format modules from ./formats
   formatModules =
     lib.flip lib.mapAttrs' (builtins.readDir ./formats)
@@ -21,7 +26,7 @@
     };
 
   # evaluated configs for all formats
-  allConfigs = lib.mapAttrs (formatName: evalFormat) formatModules;
+  allConfigs = lib.mapAttrs (formatName: evalFormat) config.formatConfigs;
 
   # attrset of formats to be exposed under config.system.formats
   formats = lib.flip lib.mapAttrs allConfigs (
@@ -37,13 +42,22 @@ in {
   key = "github:nix-community/nixos-generators/all-formats.nix";
 
   # declare option for exposing all formats
-  options.system.formats = lib.mkOption {
+  options.formats = lib.mkOption {
     type = lib.types.lazyAttrsOf lib.types.raw;
     description = ''
       Different target formats generated for this NixOS configuratation.
     '';
   };
 
+  options.formatConfigs = lib.mkOption {
+    type = types.attrsOf types.deferredModule;
+  };
+
   # expose all formats
-  config.system = {inherit formats;};
+  config.formats = formats;
+
+  #
+  config.formatConfigs = lib.flip lib.mapAttrs formatModules (name: module: {
+    imports = [module];
+  });
 }

checks/test-all-formats.nix

@@ -28,6 +28,6 @@
   testedFormats =
     lib.filterAttrs
     (name: _: ! exclude ? ${name})
-    conf.config.system.formats;
+    conf.config.formats;
 in
   testedFormats

checks/test-customize-format.nix

@@ -0,0 +1,27 @@
+{
+  nixpkgs ? <nixpkgs>,
+  system ? builtins.currentSystem,
+  lib ? import (nixpkgs + /lib),
+}: let
+  nixosSystem = import (nixpkgs + /nixos/lib/eval-config.nix);
+
+  userModule1 = {...}: {
+    formatConfigs.amazon.amazonImage.name = "xyz";
+  };
+
+  userModule2 = {...}: {
+    formatConfigs.amazon.amazonImage.name = lib.mkForce "custom-name";
+  };
+
+  conf = nixosSystem {
+    inherit system;
+    modules = [
+      ../configuration.nix
+      ../all-formats.nix
+      userModule1
+      userModule2
+    ];
+  };
+in
+  assert lib.hasInfix "custom-name" "${conf.config.formats.amazon}";
+    conf.config.formats.amazon

flake.nix

@@ -11,8 +11,23 @@
     self,
     nixpkgs,
     nixlib,
-  }:
-  # Library modules (depend on nixlib)
+  }: let
+    lib = nixpkgs.lib;
+
+    # Ensures a derivation's name can be accessed without evaluating it deeply.
+    # Prevents `nix flake show` from being very slow.
+    makeLazyDrv = name: drv: {
+      inherit name;
+      inherit
+        (drv)
+        drvPath
+        outPath
+        outputName
+        ;
+      type = "derivation";
+    };
+  in
+    # Library modules (depend on nixlib)
     {
       # export all generator formats in ./formats
       nixosModules = nixlib.lib.mapAttrs' (file: _: {
@@ -109,23 +124,31 @@
         });
 
         checks =
-          nixpkgs.lib.genAttrs ["x86_64-linux" "aarch64-linux"]
+          lib.genAttrs ["x86_64-linux" "aarch64-linux"]
           (
             system: let
               allFormats = import ./checks/test-all-formats.nix {
                 inherit nixpkgs system;
               };
+              test-customize-format = import ./checks/test-customize-format.nix {
+                inherit nixpkgs system;
+              };
             in
-              {
-                inherit
-                  (self.packages.${system})
-                  nixos-generate
-                  ;
-                is-formatted = import ./checks/is-formatted.nix {
-                  pkgs = nixpkgs.legacyPackages.${system};
-                };
-              }
-              // allFormats
+              lib.mapAttrs makeLazyDrv (
+                {
+                  inherit
+                    (self.packages.${system})
+                    nixos-generate
+                    ;
+
+                  inherit test-customize-format;
+
+                  is-formatted = import ./checks/is-formatted.nix {
+                    pkgs = nixpkgs.legacyPackages.${system};
+                  };
+                }
+                // allFormats
+              )
           );
 
         devShells = forAllSystems (system: let