refactor(registry): add stable uid registry

lib/registry.nix

@@ -1,16 +1,68 @@
 { lib, self }:
 let
   inherit (lib)
+    all
+    concatLists
+    concatMapStringsSep
+    filter
     filterAttrs
+    foldl'
+    hasAttr
     hasSuffix
     mapAttrs
     mapAttrs'
+    mapAttrsToList
     mkOption
     nameValuePair
     removeSuffix
     types
     ;
 
+  assertionType = types.submodule {
+    options = {
+      assertion = mkOption {
+        type = types.bool;
+        description = ''
+          Whether this registry validation assertion passed.
+        '';
+      };
+
+      message = mkOption {
+        type = types.str;
+        description = ''
+          Error message shown when this registry validation assertion fails.
+        '';
+      };
+    };
+  };
+
+  registryDefinitionModule = {
+    options = {
+      type = mkOption {
+        type = types.raw;
+        description = ''
+          NixOS option type for one registry entry.
+        '';
+      };
+
+      replicate = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Whether collected entries are merged and published under every host key.
+        '';
+      };
+
+      validate = mkOption {
+        type = types.functionTo (types.listOf assertionType);
+        default = _entries: [ ];
+        description = ''
+          Validate this registry's flattened collected entries.
+        '';
+      };
+    };
+  };
+
   registryName = fileName: removeSuffix ".nix" fileName;
 
   registryOption = registry: mkOption {
@@ -21,13 +73,96 @@ let
     '';
   };
 
+  mkRegistry = path:
+    let
+      evaluated = lib.evalModules {
+        specialArgs = { inherit lib; };
+        modules = [
+          registryDefinitionModule
+          path
+        ];
+      };
+    in
+    {
+      inherit (evaluated.config) type replicate validate;
+    };
+
   definitions = mapAttrs' (
     name: type:
     let
       path = self + "/registry/${name}";
     in
-    nameValuePair (registryName name) (import path { inherit lib; })
+    nameValuePair (registryName name) (mkRegistry path)
   ) (filterAttrs (name: type: type == "regular" && hasSuffix ".nix" name) (builtins.readDir (self + "/registry")));
+
+  flattenRegistryEntries = registryName: data:
+    concatLists (
+      mapAttrsToList (
+        host: entries:
+        mapAttrsToList (entry: value: {
+          path = "registry.${registryName}.${host}.${entry}";
+          inherit host entry value;
+        }) entries
+      ) data
+    );
+
+  rawDeclarations = registryName: hosts:
+    mapAttrs (_hostName: host: host.config.registry.${registryName} or { }) hosts;
+
+  replicatedEntries = registryName: raw:
+    let
+      entries = concatLists (
+        concatLists (
+          mapAttrsToList (
+            _evalHost: hostDeclarations:
+            mapAttrsToList (
+              hostName: declarations:
+              mapAttrsToList (entryName: value: {
+                path = "registry.${registryName}.${hostName}.${entryName}";
+                inherit entryName value;
+              }) declarations
+            ) hostDeclarations
+          ) raw
+        )
+      );
+    in
+    foldl' (
+      acc: entry:
+      if hasAttr entry.entryName acc then
+        if acc.${entry.entryName}.value == entry.value then
+          acc
+        else
+          throw "conflicting replicated registry entry ${entry.path} does not match ${acc.${entry.entryName}.path}"
+      else
+        acc // {
+          ${entry.entryName} = entry;
+        }
+    ) { } entries;
+
+  replicatedData = registryName: hosts: raw:
+    let
+      entries = mapAttrs (_entryName: entry: entry.value) (replicatedEntries registryName raw);
+    in
+    mapAttrs (_hostName: _host: entries) hosts;
+
+  validationAssertions = data:
+    concatLists (
+      mapAttrsToList (
+        registryName: registry:
+        registry.validate (flattenRegistryEntries registryName data.${registryName})
+      ) definitions
+    );
+
+  assertValid = data:
+    let
+      assertions = validationAssertions data;
+      failures = filter (assertion: !assertion.assertion) assertions;
+    in
+    assert lib.assertMsg (all (assertion: assertion.assertion) assertions) (
+      concatMapStringsSep "\n" (assertion: assertion.message) failures
+    );
+    data;
+
   join = registry: host: entry:
     filterAttrs (_name: value: value != null) (
       mapAttrs (registryName: _registry: (registry.${registryName}.${host} or { }).${entry} or null) definitions
@@ -35,10 +170,17 @@ let
 
   collectData =
     { hosts }:
-    mapAttrs (
-      registryName: _registry:
-      mapAttrs (hostName: host: host.config.registry.${registryName}.${hostName} or { }) hosts
-    ) definitions;
+    let
+      raw = mapAttrs (registryName: _registry: rawDeclarations registryName hosts) definitions;
+      data = mapAttrs (
+        registryName: registry:
+        if registry.replicate or false then
+          replicatedData registryName hosts raw.${registryName}
+        else
+          mapAttrs (hostName: host: host.config.registry.${registryName}.${hostName} or { }) hosts
+      ) definitions;
+    in
+    assertValid data;
 
   withOperations = registry:
     registry