revert(nix): back to the runCommand solution

package.nix

@@ -1,82 +1,81 @@
 {
   stdenv,
   lib,
+  runCommand,
   writeShellApplication,
   tree-sitter-nu ? fetchGit "https://github.com/nushell/tree-sitter-nu",
   topiary,
   nushell,
-  writeText,
   callPackage,
-  symlinkJoin,
 }:
-symlinkJoin {
-  name = "topiary-nushell";
-  paths = [
-    (writeShellApplication (
-      let
-        libtree-sitter-nu = callPackage (
-          {
-            lib,
-            stdenv,
-          }:
-          stdenv.mkDerivation (finalAttrs: {
-            pname = "tree-sitter-nu";
-            version = tree-sitter-nu.rev;
+writeShellApplication (
+  let
+    libtree-sitter-nu = callPackage (
+      {
+        lib,
+        stdenv,
+      }:
+      stdenv.mkDerivation (finalAttrs: {
+        pname = "tree-sitter-nu";
+        version = tree-sitter-nu.rev;
+
+        src = tree-sitter-nu;
+
+        makeFlags = [
+          # The PREFIX var isn't picking up from stdenv.
+          "PREFIX=$(out)"
+        ];
 
-            src = tree-sitter-nu;
+        meta = with lib; {
+          description = "A tree-sitter grammar for nu-lang, the language of nushell";
+          homepage = "https://github.com/nushell/tree-sitter-nu";
+          license = licenses.mit;
+        };
+      })
+    ) { };
+
+    extension =
+      with stdenv;
+      if isLinux then
+        ".so"
+      else if isDarwin then
+        ".dylib"
+      else
+        throw "Unsupported system: ${system}";
 
-            makeFlags = [
-              # The PREFIX var isn't picking up from stdenv.
-              "PREFIX=$(out)"
-            ];
+    # Create a directory holding ALL runtime config files
+    # This makes a single path for GC root.
+    topiaryConfigDir = runCommand "topiary-nushell-config" { } ''
+      local_config_dir="$out"
 
-            meta = with lib; {
-              description = "A tree-sitter grammar for nu-lang, the language of nushell";
-              homepage = "https://github.com/nushell/tree-sitter-nu";
-              license = licenses.mit;
-            };
-          })
-        ) { };
+      # 1. Copy the nu.scm language directory
+      mkdir -p $local_config_dir/languages
+      cp ${./languages/nu.scm} $local_config_dir/languages/nu.scm
 
-        extension =
-          with stdenv;
-          if isLinux then
-            ".so"
-          else if isDarwin then
-            ".dylib"
-          else
-            throw "Unsupported system: ${system}";
-      in
+      cat > $local_config_dir/languages.ncl <<EOF
       {
-        name = "topiary-nushell";
-        runtimeInputs = [
-          nushell
-          topiary
-        ];
-        runtimeEnv = {
-          TOPIARY_CONFIG_FILE = writeText "languages.ncl" ''
-            {
-              languages = {
-                nu = {
-                  extensions = ["nu"],
-                  grammar.source.path = "${libtree-sitter-nu}/lib/libtree-sitter-nu${extension}",
-                },
-              },
-            }
-          '';
-          TOPIARY_LANGUAGE_DIR = ./languages;
-        };
-        text = ''
-          ${lib.getExe topiary} "$@"
-        '';
+        languages = {
+          nu = {
+            extensions = ["nu"],
+            grammar.source.path = "${libtree-sitter-nu}/lib/libtree-sitter-nu${extension}",
+          },
+        },
       }
-    ))
-    ./.
-  ];
-  meta = with lib; {
-    description = "topiary formatter for nushell";
-    homepage = "https://github.com/blindFS/topiary-nushell";
-    license = licenses.mit;
-    mainProgram = "topiary-nushell";
-  };
-}
+      EOF
+    '';
+  in
+  {
+    name = "topiary-nushell";
+    runtimeInputs = [
+      nushell
+      topiary
+    ];
+    runtimeEnv = {
+      TOPIARY_CONFIG_FILE = "${topiaryConfigDir}/languages.ncl";
+      TOPIARY_LANGUAGE_DIR = "${topiaryConfigDir}/languages";
+    };
+    text = ''
+      ${lib.getExe topiary} "$@"
+    '';
+  }
+)