fs: Replace a bunch of uses of smol::fs with manual impls (#40172)

smol::fs uses a separate threadpool, which is a bit yuck.

This PR also added a benchmark you can use to run a full worktree scan
(initial one, that is) for arbitrary worktree.. and refactored worktree
scanner to use async locks, as otherwise tests were deadlocking. :)
I've benchmarked it against Zed, Linux and Chromium and saw a ~60% drop
in initial worktree scan times across the board.
Release Notes:

- Significantly (3.3x speedup over the old implementation) improved
speed of Zed's worktree scanner, that's responsible for synchronizing
the state of your project with the state of files on hard drive.

---------

Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>

crates/fs/src/fs.rs

@@ -7,6 +7,7 @@ pub mod fs_watcher;
 use anyhow::{Context as _, Result, anyhow};
 #[cfg(any(target_os = "linux", target_os = "freebsd"))]
 use ashpd::desktop::trash;
+use futures::stream::iter;
 use gpui::App;
 use gpui::BackgroundExecutor;
 use gpui::Global;
@@ -562,12 +563,17 @@ impl Fs for RealFs {
 
     async fn load(&self, path: &Path) -> Result<String> {
         let path = path.to_path_buf();
-        let text = smol::unblock(|| std::fs::read_to_string(path)).await?;
-        Ok(text)
+        self.executor
+            .spawn(async move { Ok(std::fs::read_to_string(path)?) })
+            .await
     }
+
     async fn load_bytes(&self, path: &Path) -> Result<Vec<u8>> {
         let path = path.to_path_buf();
-        let bytes = smol::unblock(|| std::fs::read(path)).await?;
+        let bytes = self
+            .executor
+            .spawn(async move { std::fs::read(path) })
+            .await?;
         Ok(bytes)
     }
 
@@ -635,30 +641,46 @@ impl Fs for RealFs {
         if let Some(path) = path.parent() {
             self.create_dir(path).await?;
         }
-        smol::fs::write(path, content).await?;
-        Ok(())
+        let path = path.to_owned();
+        let contents = content.to_owned();
+        self.executor
+            .spawn(async move {
+                std::fs::write(path, contents)?;
+                Ok(())
+            })
+            .await
     }
 
     async fn canonicalize(&self, path: &Path) -> Result<PathBuf> {
-        Ok(smol::fs::canonicalize(path)
+        let path = path.to_owned();
+        self.executor
+            .spawn(async move {
+                std::fs::canonicalize(&path).with_context(|| format!("canonicalizing {path:?}"))
+            })
             .await
-            .with_context(|| format!("canonicalizing {path:?}"))?)
     }
 
     async fn is_file(&self, path: &Path) -> bool {
-        smol::fs::metadata(path)
+        let path = path.to_owned();
+        self.executor
+            .spawn(async move { std::fs::metadata(path).is_ok_and(|metadata| metadata.is_file()) })
             .await
-            .is_ok_and(|metadata| metadata.is_file())
     }
 
     async fn is_dir(&self, path: &Path) -> bool {
-        smol::fs::metadata(path)
+        let path = path.to_owned();
+        self.executor
+            .spawn(async move { std::fs::metadata(path).is_ok_and(|metadata| metadata.is_dir()) })
             .await
-            .is_ok_and(|metadata| metadata.is_dir())
     }
 
     async fn metadata(&self, path: &Path) -> Result<Option<Metadata>> {
-        let symlink_metadata = match smol::fs::symlink_metadata(path).await {
+        let path_buf = path.to_owned();
+        let symlink_metadata = match self
+            .executor
+            .spawn(async move { std::fs::symlink_metadata(&path_buf) })
+            .await
+        {
             Ok(metadata) => metadata,
             Err(err) => {
                 return match (err.kind(), err.raw_os_error()) {
@@ -669,19 +691,28 @@ impl Fs for RealFs {
             }
         };
 
-        let path_buf = path.to_path_buf();
-        let path_exists = smol::unblock(move || {
-            path_buf
-                .try_exists()
-                .with_context(|| format!("checking existence for path {path_buf:?}"))
-        })
-        .await?;
         let is_symlink = symlink_metadata.file_type().is_symlink();
-        let metadata = match (is_symlink, path_exists) {
-            (true, true) => smol::fs::metadata(path)
-                .await
-                .with_context(|| "accessing symlink for path {path}")?,
-            _ => symlink_metadata,
+        let metadata = if is_symlink {
+            let path_buf = path.to_path_buf();
+            let path_exists = self
+                .executor
+                .spawn(async move {
+                    path_buf
+                        .try_exists()
+                        .with_context(|| format!("checking existence for path {path_buf:?}"))
+                })
+                .await?;
+            if path_exists {
+                let path_buf = path.to_path_buf();
+                self.executor
+                    .spawn(async move { std::fs::metadata(path_buf) })
+                    .await
+                    .with_context(|| "accessing symlink for path {path}")?
+            } else {
+                symlink_metadata
+            }
+        } else {
+            symlink_metadata
         };
 
         #[cfg(unix)]
@@ -707,7 +738,11 @@ impl Fs for RealFs {
     }
 
     async fn read_link(&self, path: &Path) -> Result<PathBuf> {
-        let path = smol::fs::read_link(path).await?;
+        let path = path.to_owned();
+        let path = self
+            .executor
+            .spawn(async move { std::fs::read_link(&path) })
+            .await?;
         Ok(path)
     }
 
@@ -715,7 +750,13 @@ impl Fs for RealFs {
         &self,
         path: &Path,
     ) -> Result<Pin<Box<dyn Send + Stream<Item = Result<PathBuf>>>>> {
-        let result = smol::fs::read_dir(path).await?.map(|entry| match entry {
+        let path = path.to_owned();
+        let result = iter(
+            self.executor
+                .spawn(async move { std::fs::read_dir(path) })
+                .await?,
+        )
+        .map(|entry| match entry {
             Ok(entry) => Ok(entry.path()),
             Err(error) => Err(anyhow!("failed to read dir entry {error:?}")),
         });