Got my NixOS flake to run under WSL!

profiles/wsl/nixos-wsl/modules/interop.nix

@@ -0,0 +1,88 @@
+{ lib, pkgs, config, ... }:
+
+with builtins; with lib;
+{
+  imports = [
+    (mkRenamedOptionModule [ "wsl" "compatibility" "interopPreserveArgvZero" ] [ "wsl" "interop" "preserveArgvZero" ])
+  ];
+
+  options.wsl.interop = with types; {
+    register = mkOption {
+      type = bool;
+      default = false; # Use the existing registration by default
+      description = "Explicitly register the binfmt_misc handler for Windows executables";
+    };
+
+    includePath = mkOption {
+      type = bool;
+      default = true;
+      description = "Include Windows PATH in WSL PATH";
+    };
+
+    preserveArgvZero = mkOption {
+      type = nullOr bool;
+      default = null;
+      description = ''
+        Register binfmt interpreter for Windows executables with 'preserves argv[0]' flag.
+
+        Default (null): autodetect, at some performance cost.
+        To avoid the performance cost, set this to true for WSL Preview 0.58 and up,
+        or to false for any older versions, including pre-Microsoft Store and Windows 10.
+      '';
+    };
+  };
+
+  config =
+    let
+      cfg = config.wsl.interop;
+    in
+    mkIf config.wsl.enable {
+
+      boot.binfmt.registrations = mkIf cfg.register {
+        WSLInterop =
+          let
+            compat = cfg.preserveArgvZero;
+
+            # WSL Preview 0.58 and up registers the /init binfmt interp for Windows executable
+            # with the "preserve argv[0]" flag, so if you run `./foo.exe`, the interp gets invoked
+            # as `/init foo.exe ./foo.exe`.
+            #   argv[0] --^        ^-- actual path
+            #
+            # Older versions expect to be called without the argv[0] bit, simply as `/init ./foo.exe`.
+            #
+            # We detect that by running `/init /known-not-existing-path.exe` and checking the exit code:
+            # the new style interp expects at least two arguments, so exits with exit code 1,
+            # presumably meaning "parsing error"; the old style interp attempts to actually run
+            # the executable, fails to find it, and exits with 255.
+            compatWrapper = pkgs.writeShellScript "nixos-wsl-binfmt-hack" ''
+              /init /nixos-wsl-does-not-exist.exe
+              [ $? -eq 255 ] && shift
+              exec /init "$@"
+            '';
+
+            # use the autodetect hack if unset, otherwise call /init directly
+            interpreter = if compat == null then compatWrapper else "/init";
+
+            # enable for the wrapper and autodetect hack
+            preserveArgvZero = if compat == false then false else true;
+          in
+          {
+            magicOrExtension = "MZ";
+            fixBinary = true;
+            wrapInterpreterInShell = false;
+            inherit interpreter preserveArgvZero;
+          };
+      };
+
+      # Include Windows %PATH% in Linux $PATH.
+      environment.extraInit = mkIf cfg.includePath ''PATH="$PATH:$WSLPATH"'';
+
+      warnings =
+        let
+          registrations = config.boot.binfmt.registrations;
+        in
+        optional (!(registrations ? WSLInterop) && (length (attrNames config.boot.binfmt.registrations)) != 0) "Having any binfmt registrations without re-registering WSLInterop (wsl.interop.register) will break running .exe files from WSL2";
+    };
+
+
+}