fix(lsp): respect Dart's own filesystem watcher (#2350)

crates/ide-lsp/src/lib.rs

@@ -2584,6 +2584,10 @@ impl LspManager {
             let watchers = run.watchers.read();
             let roots = self.server_workspace_roots(&s);
             let changes: Vec<(&PathBuf, Change)> = if watchers.is_empty() {
+                // Dart watches the filesystem itself and rejects this unregistered notification.
+                if s.name == "dart" {
+                    continue;
+                }
                 let languages = s.languages();
                 all.filter(|(p, change)| {
                     roots.iter().any(|root| p.starts_with(root))

crates/ide-lsp/tests/mock_server.rs

@@ -420,6 +420,45 @@ fn change(range: Range, text: &str) -> AppliedChange {
     AppliedChange { range, text: text.into() }
 }
 
+#[tokio::test(flavor = "multi_thread")]
+async fn dart_file_watching_requires_an_explicit_registration() {
+    for (language, extension, name, fallback) in
+        [("dart", "dart", "dart", false), ("dart", "dart", "alternative-dart", true), ("java", "java", "jdtls", true)]
+    {
+        let h = harness_for(language, extension, &[(name, incremental_caps())], &[]);
+        let (doc, _) = h.open(&format!("open.{extension}"), "x");
+        h.wait_status(name, ServerStatus::Ready).await;
+        let s = h.launcher.state(name);
+        let path = h.root.join(format!("closed.{extension}"));
+        let notify = || h.mgr.watched_files_changed(&[], std::slice::from_ref(&path), &[], &[]);
+        notify();
+        h.mgr.hover(doc, Pos::new(0, 0), Default::default()).await.unwrap();
+        assert_eq!(s.notified("workspace/didChangeWatchedFiles").len(), usize::from(fallback), "{name}");
+        s.peer()
+            .request::<_, Value>(
+                "client/registerCapability",
+                json!({ "registrations": [{ "id": "watch", "method": "workspace/didChangeWatchedFiles", "registerOptions": { "watchers": [{ "globPattern": "**/*" }] } }] }),
+                None,
+            )
+            .await
+            .unwrap();
+        notify();
+        eventually(|| s.notified("workspace/didChangeWatchedFiles").len() == usize::from(fallback) + 1).await;
+        s.peer()
+            .request::<_, Value>(
+                "client/unregisterCapability",
+                json!({ "unregisterations": [{ "id": "watch", "method": "workspace/didChangeWatchedFiles" }] }),
+                None,
+            )
+            .await
+            .unwrap();
+        notify();
+        h.mgr.hover(doc, Pos::new(0, 0), Default::default()).await.unwrap();
+        assert_eq!(s.notified("workspace/didChangeWatchedFiles").len(), usize::from(fallback) * 2 + 1, "{name}");
+        h.mgr.shutdown_all().await;
+    }
+}
+
 // ------------------------------------------------------------------ tests
 
 #[tokio::test(flavor = "multi_thread")]