feat(tvix/eval): add file_type method r/8304

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>

3 files changed, 51 insertions, 0 deletions

diff --git a/tvix/eval/src/io.rs b/tvix/eval/src/io.rs
index 58586030aa08..9acfd6eeba02 100644
--- a/tvix/eval/src/io.rs
+++ b/tvix/eval/src/io.rs
@@ -54,6 +54,10 @@ pub trait EvalIO {
     /// Open the file at the specified path to a `io::Read`.
     fn open(&self, path: &Path) -> io::Result<Box<dyn io::Read>>;
 
+    /// Return the [FileType] of the given path, or an error if it doesn't
+    /// exist.
+    fn file_type(&self, path: &Path) -> io::Result<FileType>;
+
     /// Read the directory at the specified path and return the names
     /// of its entries associated with their [`FileType`].
     ///
@@ -101,6 +105,20 @@ impl EvalIO for StdIO {
         Ok(Box::new(File::open(path)?))
     }
 
+    fn file_type(&self, path: &Path) -> io::Result<FileType> {
+        let file_type = File::open(path)?.metadata()?.file_type();
+
+        Ok(if file_type.is_dir() {
+            FileType::Directory
+        } else if file_type.is_file() {
+            FileType::Regular
+        } else if file_type.is_symlink() {
+            FileType::Symlink
+        } else {
+            FileType::Unknown
+        })
+    }
+
     fn read_dir(&self, path: &Path) -> io::Result<Vec<(bytes::Bytes, FileType)>> {
         let mut result = vec![];
 
@@ -150,6 +168,13 @@ impl EvalIO for DummyIO {
         ))
     }
 
+    fn file_type(&self, _: &Path) -> io::Result<FileType> {
+        Err(io::Error::new(
+            io::ErrorKind::Unsupported,
+            "I/O methods are not implemented in DummyIO",
+        ))
+    }
+
     fn read_dir(&self, _: &Path) -> io::Result<Vec<(bytes::Bytes, FileType)>> {
         Err(io::Error::new(
             io::ErrorKind::Unsupported,
diff --git a/tvix/glue/src/tvix_io.rs b/tvix/glue/src/tvix_io.rs
index 0e5f23b99093..db0c2cef77aa 100644
--- a/tvix/glue/src/tvix_io.rs
+++ b/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)
     }
diff --git a/tvix/glue/src/tvix_store_io.rs b/tvix/glue/src/tvix_store_io.rs
index 489f020436c7..dd034d74bf3e 100644
--- a/tvix/glue/src/tvix_store_io.rs
+++ b/tvix/glue/src/tvix_store_io.rs
@@ -532,6 +532,28 @@ 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)) =
             StorePath::from_absolute_path_full(&path.to_string_lossy())