ssh remoting: Show error message if project path does not exist (#18343)

This now shows an error message if you try open a project over SSH that
doesn't exist. If it's a possible file-path though, it acts like Zed's
`cli` and opens the file so that it can be created.

- Works: `cargo run ssh://127.0.0.1/~/folder-exists/file-does-not-exist`
— this will open `file-does-not-exist`
- Shows error: `cargo run
ssh://127.0.0.1/~/folder-does-not-exist/file-does-not-exist` — this will
show an error

Release Notes:

- N/A

Co-authored-by: Bennet <bennet@zed.dev>
Co-authored-by: Conrad <conrad@zed.dev>

crates/remote_server/Cargo.toml

@@ -22,6 +22,7 @@ test-support = ["fs/test-support"]
 
 [dependencies]
 anyhow.workspace = true
+client.workspace = true
 env_logger.workspace = true
 fs.workspace = true
 futures.workspace = true

crates/remote_server/src/headless_project.rs

@@ -189,11 +189,34 @@ impl HeadlessProject {
         message: TypedEnvelope<proto::AddWorktree>,
         mut cx: AsyncAppContext,
     ) -> Result<proto::AddWorktreeResponse> {
+        use client::ErrorCodeExt;
         let path = shellexpand::tilde(&message.payload.path).to_string();
+
+        let fs = this.read_with(&mut cx, |this, _| this.fs.clone())?;
+        let path = PathBuf::from(path);
+
+        let canonicalized = match fs.canonicalize(&path).await {
+            Ok(path) => path,
+            Err(e) => {
+                let mut parent = path
+                    .parent()
+                    .ok_or(e)
+                    .map_err(|_| anyhow!("{:?} does not exist", path))?;
+                if parent == Path::new("") {
+                    parent = util::paths::home_dir();
+                }
+                let parent = fs.canonicalize(parent).await.map_err(|_| {
+                    anyhow!(proto::ErrorCode::DevServerProjectPathDoesNotExist
+                        .with_tag("path", &path.to_string_lossy().as_ref()))
+                })?;
+                parent.join(path.file_name().unwrap())
+            }
+        };
+
         let worktree = this
             .update(&mut cx.clone(), |this, _| {
                 Worktree::local(
-                    Path::new(&path),
+                    Arc::from(canonicalized),
                     true,
                     this.fs.clone(),
                     this.next_entry_id.clone(),