feat(tvix/eval): add file_type method

This allows peeking of the type at a given path.

It's necessary, as an open() might not fail until you try to read()
from it, and generally, stat'ing can be faster in some cases.

Change-Id: Ib002da3194a3546ca286de49aac8d1022ec5560f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11871
Tested-by: BuildkiteCI
Reviewed-by: Ilan Joselevich <personal@ilanjoselevich.com>
Reviewed-by: Connor Brewster <cbrewster@hey.com>

tvix/glue/src/tvix_io.rs

@@ -60,6 +60,10 @@ where
         self.actual.as_ref().open(path)
     }
 
+    fn file_type(&self, path: &Path) -> io::Result<FileType> {
+        self.actual.as_ref().file_type(path)
+    }
+
     fn read_dir(&self, path: &Path) -> io::Result<Vec<(bytes::Bytes, FileType)>> {
         self.actual.as_ref().read_dir(path)
     }

tvix/glue/src/tvix_store_io.rs

@@ -531,6 +531,28 @@ impl EvalIO for TvixStoreIO {
         }
     }
 
+    #[instrument(skip(self), ret(level = Level::TRACE), err)]
+    fn file_type(&self, path: &Path) -> io::Result<FileType> {
+        if let Ok((store_path, sub_path)) =
+            StorePath::from_absolute_path_full(&path.to_string_lossy())
+        {
+            if let Some(node) = self
+                .tokio_handle
+                .block_on(async { self.store_path_to_node(&store_path, &sub_path).await })?
+            {
+                match node {
+                    Node::Directory(_) => Ok(FileType::Directory),
+                    Node::File(_) => Ok(FileType::Regular),
+                    Node::Symlink(_) => Ok(FileType::Symlink),
+                }
+            } else {
+                self.std_io.file_type(path)
+            }
+        } else {
+            self.std_io.file_type(path)
+        }
+    }
+
     #[instrument(skip(self), ret(level = Level::TRACE), err)]
     fn read_dir(&self, path: &Path) -> io::Result<Vec<(bytes::Bytes, FileType)>> {
         if let Ok((store_path, sub_path)) =