Add channel to notify project when languages are added

crates/project/src/project_tests.rs

@@ -122,11 +122,46 @@ async fn test_managing_language_servers(cx: &mut gpui::TestAppContext) {
     .await;
 
     let project = Project::test(fs.clone(), ["/the-root".as_ref()], cx).await;
-    project.update(cx, |project, _| {
-        project.languages.add(Arc::new(rust_language));
+
+    // Open a buffer before languages have been added
+    let json_buffer = project
+        .update(cx, |project, cx| {
+            project.open_local_buffer("/the-root/package.json", cx)
+        })
+        .await
+        .unwrap();
+
+    // Assert that this buffer does not have a language
+    assert!(json_buffer.read_with(cx, |buffer, _| { buffer.language().is_none() }));
+
+    // Now we add the languages to the project, and subscribe to the watcher
+    project.update(cx, |project, cx| {
+        // Get a handle to the channel and clear out default item
+        let mut recv = project.languages.subscribe();
+        recv.blocking_recv();
+
+        // Add, then wait to be notified that JSON has been added
         project.languages.add(Arc::new(json_language));
+        recv.blocking_recv();
+
+        // Add, then wait to be notified that Rust has been added
+        project.languages.add(Arc::new(rust_language));
+        recv.blocking_recv();
+        // Uncommenting this would cause the thread to block indefinitely:
+        // recv.blocking_recv();
+
+        // Force the assignment, we know the watcher has been notified
+        // but have no way to wait for the watcher to assign to the project
+        project.assign_language_to_buffer(&json_buffer, cx);
     });
 
+    // Assert that the opened buffer does have a language, and that it is JSON
+    let name = json_buffer.read_with(cx, |buffer, _| buffer.language().map(|l| l.name()));
+    assert_eq!(name, Some("JSON".into()));
+
+    // Close the JSON buffer we opened
+    cx.update(|_| drop(json_buffer));
+
     // Open a buffer without an associated language server.
     let toml_buffer = project
         .update(cx, |project, cx| {