lsp/python: Temporarily report just a singular workspace folder instead of all of the roots (#35243)

Temporarily fixes #29133

Co-authored-by: Cole <cole@zed.dev>

Release Notes:

- python: Zed now reports a slightly different set of workspace folders
for Python projects to work around quirks in handling of multi-lsp
projects with virtual environment. This behavior will be revisited in a
near future.

Co-authored-by: Cole <cole@zed.dev>

crates/lsp/src/lsp.rs

@@ -29,7 +29,7 @@ use std::{
     ffi::{OsStr, OsString},
     fmt,
     io::Write,
-    ops::{Deref, DerefMut},
+    ops::DerefMut,
     path::PathBuf,
     pin::Pin,
     sync::{
@@ -100,7 +100,7 @@ pub struct LanguageServer {
     io_tasks: Mutex<Option<(Task<Option<()>>, Task<Option<()>>)>>,
     output_done_rx: Mutex<Option<barrier::Receiver>>,
     server: Arc<Mutex<Option<Child>>>,
-    workspace_folders: Arc<Mutex<BTreeSet<Url>>>,
+    workspace_folders: Option<Arc<Mutex<BTreeSet<Url>>>>,
     root_uri: Url,
 }
 
@@ -307,7 +307,7 @@ impl LanguageServer {
         binary: LanguageServerBinary,
         root_path: &Path,
         code_action_kinds: Option<Vec<CodeActionKind>>,
-        workspace_folders: Arc<Mutex<BTreeSet<Url>>>,
+        workspace_folders: Option<Arc<Mutex<BTreeSet<Url>>>>,
         cx: &mut AsyncApp,
     ) -> Result<Self> {
         let working_dir = if root_path.is_dir() {
@@ -381,7 +381,7 @@ impl LanguageServer {
         code_action_kinds: Option<Vec<CodeActionKind>>,
         binary: LanguageServerBinary,
         root_uri: Url,
-        workspace_folders: Arc<Mutex<BTreeSet<Url>>>,
+        workspace_folders: Option<Arc<Mutex<BTreeSet<Url>>>>,
         cx: &mut AsyncApp,
         on_unhandled_notification: F,
     ) -> Self
@@ -595,16 +595,26 @@ impl LanguageServer {
     }
 
     pub fn default_initialize_params(&self, pull_diagnostics: bool, cx: &App) -> InitializeParams {
-        let workspace_folders = self
-            .workspace_folders
-            .lock()
-            .iter()
-            .cloned()
-            .map(|uri| WorkspaceFolder {
-                name: Default::default(),
-                uri,
-            })
-            .collect::<Vec<_>>();
+        let workspace_folders = self.workspace_folders.as_ref().map_or_else(
+            || {
+                vec![WorkspaceFolder {
+                    name: Default::default(),
+                    uri: self.root_uri.clone(),
+                }]
+            },
+            |folders| {
+                folders
+                    .lock()
+                    .iter()
+                    .cloned()
+                    .map(|uri| WorkspaceFolder {
+                        name: Default::default(),
+                        uri,
+                    })
+                    .collect()
+            },
+        );
+
         #[allow(deprecated)]
         InitializeParams {
             process_id: None,
@@ -1315,7 +1325,10 @@ impl LanguageServer {
             return;
         }
 
-        let is_new_folder = self.workspace_folders.lock().insert(uri.clone());
+        let Some(workspace_folders) = self.workspace_folders.as_ref() else {
+            return;
+        };
+        let is_new_folder = workspace_folders.lock().insert(uri.clone());
         if is_new_folder {
             let params = DidChangeWorkspaceFoldersParams {
                 event: WorkspaceFoldersChangeEvent {
@@ -1345,7 +1358,10 @@ impl LanguageServer {
         {
             return;
         }
-        let was_removed = self.workspace_folders.lock().remove(&uri);
+        let Some(workspace_folders) = self.workspace_folders.as_ref() else {
+            return;
+        };
+        let was_removed = workspace_folders.lock().remove(&uri);
         if was_removed {
             let params = DidChangeWorkspaceFoldersParams {
                 event: WorkspaceFoldersChangeEvent {
@@ -1360,7 +1376,10 @@ impl LanguageServer {
         }
     }
     pub fn set_workspace_folders(&self, folders: BTreeSet<Url>) {
-        let mut workspace_folders = self.workspace_folders.lock();
+        let Some(workspace_folders) = self.workspace_folders.as_ref() else {
+            return;
+        };
+        let mut workspace_folders = workspace_folders.lock();
 
         let old_workspace_folders = std::mem::take(&mut *workspace_folders);
         let added: Vec<_> = folders
@@ -1389,8 +1408,11 @@ impl LanguageServer {
         }
     }
 
-    pub fn workspace_folders(&self) -> impl Deref<Target = BTreeSet<Url>> + '_ {
-        self.workspace_folders.lock()
+    pub fn workspace_folders(&self) -> BTreeSet<Url> {
+        self.workspace_folders.as_ref().map_or_else(
+            || BTreeSet::from_iter([self.root_uri.clone()]),
+            |folders| folders.lock().clone(),
+        )
     }
 
     pub fn register_buffer(
@@ -1535,7 +1557,7 @@ impl FakeLanguageServer {
             None,
             binary.clone(),
             root,
-            workspace_folders.clone(),
+            Some(workspace_folders.clone()),
             cx,
             |_| {},
         );
@@ -1554,7 +1576,7 @@ impl FakeLanguageServer {
                     None,
                     binary,
                     Self::root_path(),
-                    workspace_folders,
+                    Some(workspace_folders),
                     cx,
                     move |msg| {
                         notifications_tx