refactor: simplify host composition and shared feature config

modules/features/meta.nix

@@ -1,5 +1,7 @@
 { lib, ... }:
 let
+  nonEmptyStrType = lib.types.addCheck lib.types.str (value: lib.stringLength value > 0);
+
   mkNullableOption =
     type:
     lib.mkOption {
@@ -10,9 +12,26 @@ let
   hasSinglePrimaryEmail =
     user: builtins.length (lib.filter (email: email.primary) (builtins.attrValues user.emails)) == 1;
 
+  scopeEmailCount =
+    scope: user:
+    builtins.length (lib.filter (email: email.scope == scope) (builtins.attrValues user.emails));
+
+  hasAtMostOneScopedEmail = scope: user: scopeEmailCount scope user <= 1;
+
+  requiredSourceControlScopes =
+    user:
+    lib.unique [
+      "personal"
+      user.sourceControl.projectScope
+    ];
+
+  hasRequiredScopedEmail =
+    scope: user: scopeEmailCount scope user == 1;
+
   primaryEmailFallback = {
     address = "";
     primary = false;
+    scope = null;
     type = "";
   };
 
@@ -53,6 +72,8 @@ let
         type = lib.mkOption {
           type = lib.types.str;
         };
+
+        scope = mkNullableOption sourceControlScopeType;
       };
     }
   );
@@ -62,13 +83,11 @@ let
     {
       options = {
         publicKey = lib.mkOption {
-          type = lib.types.str;
-        };
-
-        privateKeyPath = lib.mkOption {
-          type = lib.types.nullOr lib.types.str;
+          type = lib.types.nullOr nonEmptyStrType;
           default = null;
         };
+
+        privateKeyPath = mkNullableOption nonEmptyStrType;
       };
     }
   );
@@ -93,22 +112,10 @@ let
     }
   );
 
-  sourceControlProfileType = lib.types.submodule (
-    { ... }:
-    {
-      options = { };
-    }
-  );
-
   sourceControlType = lib.types.submodule (
     { ... }:
     {
       options = {
-        profiles = lib.mkOption {
-          type = lib.types.attrsOf sourceControlProfileType;
-          default = { };
-        };
-
         projectScope = lib.mkOption {
           type = sourceControlScopeType;
           default = "personal";
@@ -305,7 +312,22 @@ in
       config.assertions = lib.mapAttrsToList (userName: user: {
         assertion = hasSinglePrimaryEmail user;
         message = "User `${userName}` must define exactly one primary email entry.";
-      }) config.meta.host.users;
+      }) config.meta.host.users
+      ++ lib.flatten (
+        lib.mapAttrsToList (userName: user:
+          (map (scope: {
+            assertion = hasAtMostOneScopedEmail scope user;
+            message = "User `${userName}` may define at most one `${scope}` scoped email entry.";
+          }) [
+            "personal"
+            "work"
+          ])
+          ++ map (scope: {
+            assertion = hasRequiredScopedEmail scope user;
+            message = "User `${userName}` must define exactly one `${scope}` scoped email entry.";
+          }) (requiredSourceControlScopes user)
+        ) config.meta.host.users
+      );
     };
 
   flake.modules.homeManager.meta =
@@ -326,6 +348,19 @@ in
       config.assertions = lib.optional (config.meta.user != null) {
         assertion = hasSinglePrimaryEmail config.meta.user;
         message = "User `${config.meta.user.name}` must define exactly one primary email entry.";
-      };
+      }
+      ++ lib.optionals (config.meta.user != null) (
+        (map (scope: {
+          assertion = hasAtMostOneScopedEmail scope config.meta.user;
+          message = "User `${config.meta.user.name}` may define at most one `${scope}` scoped email entry.";
+        }) [
+          "personal"
+          "work"
+        ])
+        ++ map (scope: {
+          assertion = hasRequiredScopedEmail scope config.meta.user;
+          message = "User `${config.meta.user.name}` must define exactly one `${scope}` scoped email entry.";
+        }) (requiredSourceControlScopes config.meta.user)
+      );
     };
 }