Add flake schema for epoch

flake.nix

@@ -3,22 +3,34 @@
     nixpkgs.url = "https://flakehub.com/f/nixos/nixpkgs/0.1.*";
     determinate.url = "https://flakehub.com/f/DeterminateSystems/determinate/*";
     fh.url = "https://flakehub.com/f/DeterminateSystems/fh/0.1.*";
-    flake-schemas.url = "https://flakehub.com/f/DeterminateSystems/flake-schemas/0.1.5";
     nixos-amis.url = "https://flakehub.com/f/NixOS/amis/0.1.*";
+    flake-schemas.url = "https://flakehub.com/f/DeterminateSystems/flake-schemas/0.1";
   };
 
-  outputs = { self, ... }@inputs:
+  outputs =
+    { self, ... }@inputs:
     let
-      linuxSystems = [ "x86_64-linux" "aarch64-linux" ];
-      allSystems = linuxSystems ++ [ "x86_64-darwin" "aarch64-darwin" ];
+      linuxSystems = [
+        "x86_64-linux"
+        "aarch64-linux"
+      ];
+      allSystems = linuxSystems ++ [
+        "x86_64-darwin"
+        "aarch64-darwin"
+      ];
 
-      forSystems = systems: f: inputs.nixpkgs.lib.genAttrs systems (system: f {
-        inherit system;
-        pkgs = import inputs.nixpkgs {
-          inherit system;
-        };
-        lib = inputs.nixpkgs.lib;
-      });
+      forSystems =
+        systems: f:
+        inputs.nixpkgs.lib.genAttrs systems (
+          system:
+          f {
+            inherit system;
+            pkgs = import inputs.nixpkgs {
+              inherit system;
+            };
+            lib = inputs.nixpkgs.lib;
+          }
+        );
 
       forLinuxSystems = forSystems linuxSystems;
       forAllSystems = forSystems allSystems;
@@ -27,61 +39,96 @@
       # Update this, and the changelog *and* usage examples in the README, for breaking changes to the AMIs
       epoch = builtins.toString 1;
 
-      nixosConfigurations = forLinuxSystems ({ system, pkgs, lib, ... }: lib.nixosSystem {
-        inherit system;
-        modules = [
-          "${inputs.nixpkgs}/nixos/maintainers/scripts/ec2/amazon-image.nix"
-          inputs.determinate.nixosModules.default
-          ({ config, ... }: {
+      nixosConfigurations = forLinuxSystems (
+        {
+          system,
+          pkgs,
+          lib,
+          ...
+        }:
+        lib.nixosSystem {
+          inherit system;
+          modules = [
+            "${inputs.nixpkgs}/nixos/maintainers/scripts/ec2/amazon-image.nix"
+            inputs.determinate.nixosModules.default
+            (
+              { config, ... }:
+              {
 
-            system.nixos.tags = lib.mkForce [ ];
-            environment.systemPackages = [
-              inputs.fh.packages.${system}.default
-              pkgs.git
-            ];
+                system.nixos.tags = lib.mkForce [ ];
+                environment.systemPackages = [
+                  inputs.fh.packages.${system}.default
+                  pkgs.git
+                ];
 
-            virtualisation.diskSize = lib.mkForce (4 * 1024);
+                virtualisation.diskSize = lib.mkForce (4 * 1024);
 
-            assertions =
-              [{
-                assertion = ((
-                  builtins.match
-                    "^[0-9][0-9]\.[0-9][0-9]\..*"
-                    config.system.nixos.label
-                ) != null);
-                message = "nixos image label is incorrect";
-              }];
-          })
-        ];
-      });
+                assertions = [
+                  {
+                    assertion = ((builtins.match "^[0-9][0-9]\.[0-9][0-9]\..*" config.system.nixos.label) != null);
+                    message = "nixos image label is incorrect";
+                  }
+                ];
+              }
+            )
+          ];
+        }
+      );
 
-      diskImages = forLinuxSystems ({ system, ... }: {
-        aws = self.nixosConfigurations.${system}.config.system.build.amazonImage;
-      });
+      diskImages = forLinuxSystems (
+        { system, ... }:
+        {
+          aws = self.nixosConfigurations.${system}.config.system.build.amazonImage;
+        }
+      );
 
-      devShells = forAllSystems ({ system, pkgs, lib, ... }: {
-        default = pkgs.mkShell {
-          packages = with pkgs; [
-            lychee
-            nixpkgs-fmt
-          ] ++ lib.optionals (builtins.elem system linuxSystems) [
-            inputs.nixos-amis.packages.${system}.upload-ami
-          ];
-        };
-      });
+      devShells = forAllSystems (
+        {
+          system,
+          pkgs,
+          lib,
+          ...
+        }:
+        {
+          default = pkgs.mkShell {
+            packages =
+              with pkgs;
+              [
+                lychee
+                nixpkgs-fmt
+              ]
+              ++ lib.optionals (builtins.elem system linuxSystems) [
+                inputs.nixos-amis.packages.${system}.upload-ami
+              ];
+          };
+        }
+      );
 
-      apps = forLinuxSystems ({ system, ... }: {
-        smoke-test = inputs.nixos-amis.apps.${system}.smoke-test;
-      });
+      apps = forLinuxSystems (
+        { system, ... }:
+        {
+          smoke-test = inputs.nixos-amis.apps.${system}.smoke-test;
+        }
+      );
 
-      schemas = inputs.flake-schemas.schemas // {
+      schemas = {
         diskImages = {
           version = 1;
           doc = ''
             The `diskImages` flake output contains derivations that build disk images for various execution environments.
           '';
           inventory = inputs.flake-schemas.lib.derivationsInventory "Disk image" false;
         };
+
+        epoch = {
+          version = 1;
+          doc = "The `epoch` output provides a simple string value that's meant to be updated whenever there are breaking changes to the AMIs.";
+          inventory = output: {
+            what = "Epoch string";
+            shortDescription = "A string representing the epoch value: ${output}";
+            evalChecks.isString = e: builtins.isString e;
+          };
+        };
       };
     };
 }