vscode: add package option and link extensions

modules/programs/vscode.nix

@@ -6,12 +6,22 @@ let
 
   cfg = config.programs.vscode;
 
+  vscodePname = cfg.package.pname;
+
+  configDir = {
+    "vscode" = "Code";
+    "vscode-insiders" = "Code - Insiders";
+    "vscodium" = "Codium";
+  }.${vscodePname};
+
   configFilePath =
     if pkgs.stdenv.hostPlatform.isDarwin then
-      "Library/Application Support/Code/User/settings.json"
+      "Library/Application Support/${configDir}/User/settings.json"
     else
-      "${config.xdg.configHome}/Code/User/settings.json";
+      "${config.xdg.configHome}/${configDir}/User/settings.json";
 
+  # TODO: On Darwin where are the extensions?
+  extensionPath = ".${vscodePname}/extensions";
 in
 
 {
@@ -19,6 +29,15 @@ in
     programs.vscode = {
       enable = mkEnableOption "Visual Studio Code";
 
+      package = mkOption {
+        type = types.package;
+        default = pkgs.vscode;
+        example = literalExample "pkgs.vscodium";
+        description = ''
+          Version of Visual Studio Code to install.
+        '';
+      };
+
       userSettings = mkOption {
         type = types.attrs;
         default = {};
@@ -47,12 +66,24 @@ in
   };
 
   config = mkIf cfg.enable {
-    home.packages = [
-      (pkgs.vscode-with-extensions.override {
-        vscodeExtensions = cfg.extensions;
-      })
-    ];
+    home.packages = [ cfg.package ];
 
-    home.file."${configFilePath}".text = builtins.toJSON cfg.userSettings;
+    # Adapted from https://discourse.nixos.org/t/vscode-extensions-setup/1801/2
+    home.file =
+      let
+        toPaths = p:
+          # Links every dir in p to the extension path.
+          mapAttrsToList (k: v:
+            {
+              "${extensionPath}/${k}".source = "${p}/${k}";
+            }) (builtins.readDir p);
+        toSymlink = concatMap toPaths cfg.extensions;
+      in
+        foldr
+          (a: b: a // b)
+          {
+            "${configFilePath}".text = builtins.toJSON cfg.userSettings;
+          }
+          toSymlink;
   };
 }