fix(app): close a project window without blocking the UI thread (#1610)

close_project was a synchronous command, so it ran on the UI thread and dropped the project there: stopping its file watcher and index worker waits for the batch of file events they are applying, many while a build or rust-analyzer writes output. The command now runs off the main thread, and the project is dropped on the project shutdown thread, which a project opened next still waits for (the index database is released first). The window Destroyed path gets the same.

crates/ide-host/src/lib.rs

@@ -245,6 +245,7 @@ impl Host {
             project.kotlin_bridge.iter().cloned().collect(),
             Some(project.lsp.clone()),
             Some((self.debugger.clone(), window.to_owned())),
+            Some(project),
         ))
     }
 
@@ -257,6 +258,7 @@ impl Host {
         bridges: Vec<Arc<kotlin_bridge::KotlinBridge>>,
         lsp: Option<Arc<ide_lsp::LspManager>>,
         debug: Option<(Arc<ide_dap::DebugManager>, String)>,
+        retired: Option<Arc<Project>>,
     ) -> std::thread::JoinHandle<()> {
         for bridge in &bridges {
             bridge.stop();
@@ -266,6 +268,10 @@ impl Host {
         }
         let runtime = self.runtime.clone();
         std::thread::spawn(move || {
+            // Dropping the project stops its file watcher and index worker, which first finish the
+            // batch they are applying (many file events while a build writes its output), so it
+            // isn't done on the closing caller's thread (the UI thread for a window close).
+            let retired = retired.map(|project| std::thread::spawn(move || drop(project)));
             runtime.block_on(async move {
                 for bridge in bridges {
                     bridge.shutdown().await;
@@ -280,6 +286,9 @@ impl Host {
                     debug.stop_key(&key).await;
                 }
             });
+            if let Some(retired) = retired {
+                let _ = retired.join();
+            }
         })
     }
 
@@ -319,6 +328,7 @@ impl Host {
             projects.iter().filter_map(|project| project.kotlin_bridge.clone()).collect(),
             None,
             None,
+            None,
         ));
         let deadline = std::time::Instant::now() + EXIT_SHUTDOWN_WAIT;
         while pending.iter().any(|handle| !handle.is_finished()) {
@@ -422,3 +432,37 @@ impl Host {
         self.projects.write().insert(window.to_owned(), project);
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn detached_close_releases_the_project_before_a_reopen() {
+        let temp = tempfile::tempdir().unwrap();
+        let base = dunce::canonicalize(temp.path()).unwrap();
+        let root = base.join("project");
+        std::fs::create_dir(&root).unwrap();
+        std::fs::write(root.join("main.rs"), "fn main() {}\n").unwrap();
+        let host = Host::new(HostConfig {
+            config_dir: base.join("config"),
+            data_dir: base.join("data"),
+            local_data_dir: base.join("local"),
+            languages: Arc::new(ide_language::LanguageRegistry::load(None).unwrap()),
+            syntax: Arc::default(),
+            sink_for: Box::new(|_| Arc::new(|_| {})),
+            owner: |w| w,
+            runtime: tokio::runtime::Handle::current(),
+            project_environment: false,
+        });
+        let project = Arc::downgrade(&host.open_project("main", &root).unwrap());
+        host.close_project_detached("main");
+        assert!(host.project("main").is_err());
+        // The project (its file watcher and index database) is dropped off the closing thread, but
+        // before opening a project waits out the close.
+        host.wait_detached_closes();
+        assert!(project.upgrade().is_none(), "the closed project is dropped");
+        host.open_project("main", &root).unwrap();
+        host.close_project("main");
+    }
+}

src-tauri/src/commands/app.rs

@@ -129,7 +129,8 @@ pub fn project_rename(window: Window, state: State<'_, AppState>, name: String)
     Ok(project_info(&project))
 }
 
-#[tauri::command]
+// Not on the main thread: closing stops the project's language servers, runs and file watcher.
+#[tauri::command(async)]
 #[specta::specta]
 pub fn close_project(window: Window, state: State<'_, AppState>) {
     crate::windows::close_auxiliary_windows(window.app_handle(), window.label());