enable Xp::FetchTree by default

README.md

@@ -25,6 +25,7 @@ The following experimental features are enabled by default:
 - `flakes` (`Xp::Flakes`)
 - `nix-command` (`Xp::NixCommand`)
 - `repl-flake` (`Xp::ReplFlake`)
+- `fetch-tree` (`Xp::FetchTree`)
 
 ### Full thunk evaluation in `flake.nix`
 

src/libutil/config.cc

@@ -510,6 +510,7 @@ bool ExperimentalFeatureSettings::isEnabled(const ExperimentalFeature & feature)
     case ExperimentalFeature::Flakes:
     case ExperimentalFeature::NixCommand:
     case ExperimentalFeature::ReplFlake:
+    case ExperimentalFeature::FetchTree:
         return true;
     default:
         break;