Add freeformType to flake option

all-modules.nix

@@ -3,6 +3,7 @@
   imports = [
     ./modules/checks.nix
     ./modules/devShell.nix
+    ./modules/flake.nix
     ./modules/legacyPackages.nix
     ./modules/packages.nix
     ./modules/perSystem.nix

lib.nix

@@ -16,6 +16,17 @@ let
         specialArgs = { inherit self flake-modules-core-lib; } // specialArgs;
         modules = [ ./all-modules.nix module ];
       };
+
+    # For extending options in an already declared submodule.
+    # Workaround for https://github.com/NixOS/nixpkgs/issues/146882
+    mkSubmoduleOptions =
+      options:
+      mkOption {
+        type = types.submoduleWith {
+          modules = [ { inherit options; } ];
+        };
+      };
   };
+
 in
 flake-modules-core-lib

modules/checks.nix

@@ -8,10 +8,13 @@ let
     optionalAttrs
     types
     ;
+  inherit (flake-modules-core-lib)
+    mkSubmoduleOptions
+    ;
 in
 {
   options = {
-    flake = {
+    flake = mkSubmoduleOptions {
       checks = mkOption {
         type = types.lazyAttrsOf (types.lazyAttrsOf types.package);
         default = { };

modules/devShell.nix

@@ -8,10 +8,13 @@ let
     optionalAttrs
     types
     ;
+  inherit (flake-modules-core-lib)
+    mkSubmoduleOptions
+    ;
 in
 {
   options = {
-    flake = {
+    flake = mkSubmoduleOptions {
       devShell = mkOption {
         type = types.lazyAttrsOf types.package;
         default = { };

modules/flake.nix

@@ -0,0 +1,27 @@
+{ config, lib, ... }:
+let
+  inherit (lib)
+    filterAttrs
+    genAttrs
+    mapAttrs
+    mkOption
+    optionalAttrs
+    types
+    ;
+in
+{
+  options = {
+    flake = mkOption {
+      type = types.submoduleWith {
+        modules = [
+          { freeformType = types.lazyAttrsOf types.anything; }
+        ];
+      };
+      description = ''
+        Raw flake attributes. Any attribute can be set here, but some
+        attributes are represented by options, to provide appropriate
+        configuration merging.
+      '';
+    };
+  };
+}

modules/legacyPackages.nix

@@ -8,10 +8,13 @@ let
     optionalAttrs
     types
     ;
+  inherit (flake-modules-core-lib)
+    mkSubmoduleOptions
+    ;
 in
 {
   options = {
-    flake = {
+    flake = mkSubmoduleOptions {
       legacyPackages = mkOption {
         type = types.lazyAttrsOf (types.lazyAttrsOf types.anything);
         default = { };

modules/packages.nix

@@ -8,10 +8,13 @@ let
     optionalAttrs
     types
     ;
+  inherit (flake-modules-core-lib)
+    mkSubmoduleOptions
+    ;
 in
 {
   options = {
-    flake = {
+    flake = mkSubmoduleOptions {
       packages = mkOption {
         type = types.lazyAttrsOf (types.lazyAttrsOf types.package);
         default = { };