interop: enable preserveArgvZero

Fixes interop with latest WSL versions

Author: K900

modules/wsl-distro.nix

@@ -42,6 +42,20 @@ with builtins; with lib;
           description = "Include Windows PATH in WSL PATH";
         };
       };
+
+      compatibility = {
+        interopPreserveArgvZero = 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 older versions (including pre-Microsoft Store).
+          '';
+        };
+      };
     };
 
   config =
@@ -65,10 +79,35 @@ with builtins; with lib;
         isContainer = true;
 
         binfmt.registrations = mkIf cfg.interop.register {
-          WSLInterop = {
+          WSLInterop = let
+            compat = cfg.compatibility.interopPreserveArgvZero;
+
+            # 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";
-            interpreter = "/init";
             fixBinary = true;
+            inherit interpreter preserveArgvZero;
           };
         };
       };