Allow opening non-extant files (#9256)

Fixes #7400



Release Notes:

- Improved the `zed` command to not create files until you save them in
the editor ([#7400](https://github.com/zed-industries/zed/issues/7400)).

crates/fs/src/fs.rs

@@ -56,6 +56,7 @@ pub trait Fs: Send + Sync {
     async fn save(&self, path: &Path, text: &Rope, line_ending: LineEnding) -> Result<()>;
     async fn canonicalize(&self, path: &Path) -> Result<PathBuf>;
     async fn is_file(&self, path: &Path) -> bool;
+    async fn is_dir(&self, path: &Path) -> bool;
     async fn metadata(&self, path: &Path) -> Result<Option<Metadata>>;
     async fn read_link(&self, path: &Path) -> Result<PathBuf>;
     async fn read_dir(
@@ -264,6 +265,12 @@ impl Fs for RealFs {
             .map_or(false, |metadata| metadata.is_file())
     }
 
+    async fn is_dir(&self, path: &Path) -> bool {
+        smol::fs::metadata(path)
+            .await
+            .map_or(false, |metadata| metadata.is_dir())
+    }
+
     async fn metadata(&self, path: &Path) -> Result<Option<Metadata>> {
         let symlink_metadata = match smol::fs::symlink_metadata(path).await {
             Ok(metadata) => metadata,
@@ -500,7 +507,12 @@ impl FakeFsState {
     fn read_path(&self, target: &Path) -> Result<Arc<Mutex<FakeFsEntry>>> {
         Ok(self
             .try_read_path(target, true)
-            .ok_or_else(|| anyhow!("path does not exist: {}", target.display()))?
+            .ok_or_else(|| {
+                anyhow!(io::Error::new(
+                    io::ErrorKind::NotFound,
+                    format!("not found: {}", target.display())
+                ))
+            })?
             .0)
     }
 
@@ -1260,6 +1272,12 @@ impl Fs for FakeFs {
         }
     }
 
+    async fn is_dir(&self, path: &Path) -> bool {
+        self.metadata(path)
+            .await
+            .is_ok_and(|metadata| metadata.is_some_and(|metadata| metadata.is_dir))
+    }
+
     async fn metadata(&self, path: &Path) -> Result<Option<Metadata>> {
         self.simulate_random_delay().await;
         let path = normalize_path(path);