Allow overriding username

More specifically, this assists with the Steam Deck.

flake.lock

@@ -7,11 +7,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1705169127,
-        "narHash": "sha256-j9OEtNxOIPWZWjbECVMkI1TO17SzlpHMm0LnVWKOR/g=",
+        "lastModified": 1706080884,
+        "narHash": "sha256-qhxisCrSraN5YWVb0lNCFH8ovqnCw5W9ldac4Dzr0Nw=",
         "owner": "nix-community",
         "repo": "home-manager",
-        "rev": "f2942f3385f1b35cc8a1abb03a45e29c9cb4d3c8",
+        "rev": "6b28ab2d798c1c84e24053d95f4ee1dd9d81e2fb",
         "type": "github"
       },
       "original": {
@@ -22,11 +22,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1705133751,
-        "narHash": "sha256-rCIsyE80jgiOU78gCWN3A0wE0tR2GI5nH6MlS+HaaSQ=",
+        "lastModified": 1705856552,
+        "narHash": "sha256-JXfnuEf5Yd6bhMs/uvM67/joxYKoysyE3M2k6T3eWbg=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "9b19f5e77dd906cb52dade0b7bd280339d2a1f3d",
+        "rev": "612f97239e2cc474c13c9dafa0df378058c5ad8d",
         "type": "github"
       },
       "original": {

flake.nix

@@ -51,6 +51,16 @@
             gpg = true;
           };
         };
+
+        # For a special case: with the Steam Deck, we have to assume the user
+        # is named `deck` due to its immutable system image.
+        x86_64-linux.homeConfigurations.deck = homeManager {
+          system = "x86_64-linux";
+          specialArgs = {
+            gpg = true;
+            username = "deck";
+          };
+        };
       };
 
       nixosModules.default = {

home/home.nix

@@ -8,22 +8,26 @@ let
 
   # Whether to configure various programs to leverage GPG.
   gpg = specialArgs.gpg or false;
-in
-{
+
   # It's standard convention that Darwin has the username
-  # "spot" - "spotlight" was reserved by the system at some point.
+  # "spot" - regretfully, "spotlight" is reserved by the system.
   # (Sigh... the downsides of sharing a namesake.)
-  home.username =
+  nativeUsername =
     if pkgs.stdenv.isDarwin then
       "spot"
     else
       "spotlight";
 
+  username = specialArgs.username or nativeUsername;
+in
+{
+  home.username = username;
+
   home.homeDirectory =
     if pkgs.stdenv.isDarwin then
-      "/Users/spot"
+      "/Users/" + username
     else
-      "/home/spotlight";
+      "/home/" + username;
 
   # Git
   programs.git = {