3 files changed, 12 insertions, 9 deletions
diff --git a/tvix/eval/src/builtins/impure.rs b/tvix/eval/src/builtins/impure.rs
index cf3186ce5087..e01c642e0a4f 100644
--- a/tvix/eval/src/builtins/impure.rs
+++ b/tvix/eval/src/builtins/impure.rs
@@ -38,7 +38,8 @@ mod impure_builtins {
         let dir = generators::request_read_dir(&co, path).await;
         let res = dir.into_iter().map(|(name, ftype)| {
             (
-                NixString::from(name.as_str()),
+                // TODO: propagate Vec<u8> into NixString.
+                NixString::from(String::from_utf8(name).expect("parsing file name as string")),
                 Value::String(
                     match ftype {
                         FileType::Directory => "directory",
diff --git a/tvix/eval/src/io.rs b/tvix/eval/src/io.rs
index 708c36153c47..de3da9ebe8ec 100644
--- a/tvix/eval/src/io.rs
+++ b/tvix/eval/src/io.rs
@@ -15,12 +15,14 @@
 //! In the context of Nix builds, callers also use this interface to determine
 //! how store paths are opened and so on.
 
-use smol_str::SmolStr;
 use std::{
     io,
     path::{Path, PathBuf},
 };
 
+#[cfg(target_family = "unix")]
+use std::os::unix::ffi::OsStringExt;
+
 /// Types of files as represented by `builtins.readDir` in Nix.
 #[derive(Debug)]
 pub enum FileType {
@@ -40,7 +42,7 @@ pub trait EvalIO {
 
     /// Read the directory at the specified path and return the names
     /// of its entries associated with their [`FileType`].
-    fn read_dir(&self, path: &Path) -> Result<Vec<(SmolStr, FileType)>, io::Error>;
+    fn read_dir(&self, path: &Path) -> Result<Vec<(Vec<u8>, FileType)>, io::Error>;
 
     /// Import the given path. What this means depends on the
     /// implementation, for example for a `std::io`-based
@@ -63,6 +65,7 @@ pub trait EvalIO {
 #[cfg(feature = "impure")]
 pub struct StdIO;
 
+// TODO: we might want to make this whole impl to be target_family = "unix".
 #[cfg(feature = "impure")]
 impl EvalIO for StdIO {
     fn path_exists(&self, path: &Path) -> Result<bool, io::Error> {
@@ -73,7 +76,7 @@ impl EvalIO for StdIO {
         std::fs::read_to_string(&path)
     }
 
-    fn read_dir(&self, path: &Path) -> Result<Vec<(SmolStr, FileType)>, io::Error> {
+    fn read_dir(&self, path: &Path) -> Result<Vec<(Vec<u8>, FileType)>, io::Error> {
         let mut result = vec![];
 
         for entry in path.read_dir()? {
@@ -90,7 +93,7 @@ impl EvalIO for StdIO {
                 FileType::Unknown
             };
 
-            result.push((SmolStr::new(entry.file_name().to_string_lossy()), val));
+            result.push((entry.file_name().into_vec(), val))
         }
 
         Ok(result)
@@ -122,7 +125,7 @@ impl EvalIO for DummyIO {
         ))
     }
 
-    fn read_dir(&self, _: &Path) -> Result<Vec<(SmolStr, FileType)>, io::Error> {
+    fn read_dir(&self, _: &Path) -> Result<Vec<(Vec<u8>, FileType)>, io::Error> {
         Err(io::Error::new(
             io::ErrorKind::Unsupported,
             "I/O methods are not implemented in DummyIO",
diff --git a/tvix/eval/src/vm/generators.rs b/tvix/eval/src/vm/generators.rs
index fb60a45f20cc..3437136bde63 100644
--- a/tvix/eval/src/vm/generators.rs
+++ b/tvix/eval/src/vm/generators.rs
@@ -10,7 +10,6 @@
 use core::pin::Pin;
 use genawaiter::rc::Co;
 pub use genawaiter::rc::Gen;
-use smol_str::SmolStr;
 use std::fmt::Display;
 use std::future::Future;
 
@@ -187,7 +186,7 @@ pub enum VMResponse {
     Path(PathBuf),
 
     /// VM response with the contents of a directory.
-    Directory(Vec<(SmolStr, FileType)>),
+    Directory(Vec<(Vec<u8>, FileType)>),
 
     /// VM response with a span to use at the current point.
     Span(LightSpan),
@@ -736,7 +735,7 @@ pub(crate) async fn request_path_exists(co: &GenCo, path: PathBuf) -> Value {
     }
 }
 
-pub(crate) async fn request_read_dir(co: &GenCo, path: PathBuf) -> Vec<(SmolStr, FileType)> {
+pub(crate) async fn request_read_dir(co: &GenCo, path: PathBuf) -> Vec<(Vec<u8>, FileType)> {
     match co.yield_(VMRequest::ReadDir(path)).await {
         VMResponse::Directory(dir) => dir,
         msg => panic!(