workspace: Fix last removed folder from workspace used to reopen on Zed startup (#34925)

Closes #34924

Now, when `local_paths` are empty, we detach `session_id` from that
workspace serialization item. This way, when we restore it using the
default "last_session", we don't restore this workspace back. This is
same as when we use `cmd-w` to close window, which also sets
`session_id` to `None` before serialization.

Release Notes:

- Fixed an issue where last removed folder from workspace used to reopen
on Zed startup.

crates/workspace/src/workspace.rs

@@ -1016,6 +1016,15 @@ pub enum OpenVisible {
     OnlyDirectories,
 }
 
+enum WorkspaceLocation {
+    // Valid local paths or SSH project to serialize
+    Location(SerializedWorkspaceLocation),
+    // No valid location found hence clear session id
+    DetachFromSession,
+    // No valid location found to serialize
+    None,
+}
+
 type PromptForNewPath = Box<
     dyn Fn(
         &mut Workspace,
@@ -1135,7 +1144,6 @@ impl Workspace {
                     this.update_window_title(window, cx);
                     this.serialize_workspace(window, cx);
                     // This event could be triggered by `AddFolderToProject` or `RemoveFromProject`.
-                    // So we need to update the history.
                     this.update_history(cx);
                 }
 
@@ -5218,48 +5226,58 @@ impl Workspace {
             }
         }
 
-        if let Some(location) = self.serialize_workspace_location(cx) {
-            let breakpoints = self.project.update(cx, |project, cx| {
-                project
-                    .breakpoint_store()
-                    .read(cx)
-                    .all_source_breakpoints(cx)
-            });
+        match self.serialize_workspace_location(cx) {
+            WorkspaceLocation::Location(location) => {
+                let breakpoints = self.project.update(cx, |project, cx| {
+                    project
+                        .breakpoint_store()
+                        .read(cx)
+                        .all_source_breakpoints(cx)
+                });
 
-            let center_group = build_serialized_pane_group(&self.center.root, window, cx);
-            let docks = build_serialized_docks(self, window, cx);
-            let window_bounds = Some(SerializedWindowBounds(window.window_bounds()));
-            let serialized_workspace = SerializedWorkspace {
-                id: database_id,
-                location,
-                center_group,
-                window_bounds,
-                display: Default::default(),
-                docks,
-                centered_layout: self.centered_layout,
-                session_id: self.session_id.clone(),
-                breakpoints,
-                window_id: Some(window.window_handle().window_id().as_u64()),
-            };
+                let center_group = build_serialized_pane_group(&self.center.root, window, cx);
+                let docks = build_serialized_docks(self, window, cx);
+                let window_bounds = Some(SerializedWindowBounds(window.window_bounds()));
+                let serialized_workspace = SerializedWorkspace {
+                    id: database_id,
+                    location,
+                    center_group,
+                    window_bounds,
+                    display: Default::default(),
+                    docks,
+                    centered_layout: self.centered_layout,
+                    session_id: self.session_id.clone(),
+                    breakpoints,
+                    window_id: Some(window.window_handle().window_id().as_u64()),
+                };
 
-            return window.spawn(cx, async move |_| {
-                persistence::DB.save_workspace(serialized_workspace).await;
-            });
+                window.spawn(cx, async move |_| {
+                    persistence::DB.save_workspace(serialized_workspace).await;
+                })
+            }
+            WorkspaceLocation::DetachFromSession => window.spawn(cx, async move |_| {
+                persistence::DB
+                    .set_session_id(database_id, None)
+                    .await
+                    .log_err();
+            }),
+            WorkspaceLocation::None => Task::ready(()),
         }
-        Task::ready(())
     }
 
-    fn serialize_workspace_location(&self, cx: &App) -> Option<SerializedWorkspaceLocation> {
+    fn serialize_workspace_location(&self, cx: &App) -> WorkspaceLocation {
         if let Some(ssh_project) = &self.serialized_ssh_project {
-            Some(SerializedWorkspaceLocation::Ssh(ssh_project.clone()))
+            WorkspaceLocation::Location(SerializedWorkspaceLocation::Ssh(ssh_project.clone()))
         } else if let Some(local_paths) = self.local_paths(cx) {
             if !local_paths.is_empty() {
-                Some(SerializedWorkspaceLocation::from_local_paths(local_paths))
+                WorkspaceLocation::Location(SerializedWorkspaceLocation::from_local_paths(
+                    local_paths,
+                ))
             } else {
-                None
+                WorkspaceLocation::DetachFromSession
             }
         } else {
-            None
+            WorkspaceLocation::None
         }
     }
 
@@ -5267,8 +5285,9 @@ impl Workspace {
         let Some(id) = self.database_id() else {
             return;
         };
-        let Some(location) = self.serialize_workspace_location(cx) else {
-            return;
+        let location = match self.serialize_workspace_location(cx) {
+            WorkspaceLocation::Location(location) => location,
+            _ => return,
         };
         if let Some(manager) = HistoryManager::global(cx) {
             manager.update(cx, |this, cx| {