fix(mcp): a late diagnostics publication for an older text version isn't fresh

check_files counted any publication after the last text change as an
answer for the current text, but a server may publish late for the
version before it. A publication tagged with a version older than the
document's is still shown, but no longer counts as fresh.

crates/ide-lsp/src/handler.rs

@@ -250,7 +250,14 @@ impl ClientHandler {
         {
             return;
         }
-        let shown = self.server.set_diagnostics(path.clone(), params.diagnostics);
+        // A late answer for an older version of the text is shown, but isn't fresh (`check_files`).
+        let obsolete =
+            params.version.is_some_and(|v| mgr.docs.lock().values().any(|d| d.path == path && d.version > v));
+        let shown = if obsolete {
+            self.server.set_obsolete_diagnostics(path.clone(), params.diagnostics)
+        } else {
+            self.server.set_diagnostics(path.clone(), params.diagnostics)
+        };
         mgr.emit_diagnostics(&self.server, path, shown, self.encoding());
     }
 

crates/ide-lsp/src/server.rs

@@ -770,6 +770,20 @@ impl Server {
         self.combine(path)
     }
 
+    /// [`Server::set_diagnostics`] for a publication tagged with a document version older than
+    /// the text the server has now: shown, but not an answer for the current text, so
+    /// [`Server::last_published`] keeps its time.
+    pub fn set_obsolete_diagnostics(&self, path: PathBuf, items: Vec<lsp::Diagnostic>) -> Vec<lsp::Diagnostic> {
+        let before = self.last_published(&path);
+        let shown = self.set_diagnostics(path.clone(), items);
+        let mut published = self.published.lock();
+        match before {
+            Some(at) => published.insert(path, at),
+            None => published.remove(&path),
+        };
+        shown
+    }
+
     /// Records a pulled report for `path` (`None` items: unchanged since `result_id`'s
     /// predecessor); returns what the file now shows.
     pub fn set_pulled(

crates/ide-lsp/tests/mock_server.rs

@@ -2210,6 +2210,19 @@ async fn checking_a_document_saves_it_and_waits_for_fresh_diagnostics() {
     h.mgr.did_change(doc, 2, &[change(rng(0, 0, 0, 3), "good")], &|| "good\n".to_owned());
     let reloaded = h.mgr.check_document(doc, None, Duration::from_millis(800), &cancel).await.unwrap();
     assert!(reloaded.servers[0].incomplete, "{:?}", reloaded.servers);
+
+    // A late publication tagged with the old version is no answer for the current text.
+    s.peer()
+        .notify("textDocument/publishDiagnostics", json!({ "uri": uri_of(&path), "version": 1, "diagnostics": [] }))
+        .unwrap();
+    let late = h.mgr.check_document(doc, None, Duration::from_millis(800), &cancel).await.unwrap();
+    assert!(late.servers[0].incomplete, "{:?}", late.servers);
+    // One for the current version is.
+    s.peer()
+        .notify("textDocument/publishDiagnostics", json!({ "uri": uri_of(&path), "version": 2, "diagnostics": [] }))
+        .unwrap();
+    let fresh = h.mgr.check_document(doc, None, Duration::from_secs(5), &cancel).await.unwrap();
+    assert!(fresh.servers[0].checked && !fresh.servers[0].incomplete, "{:?}", fresh.servers);
 }
 
 #[tokio::test(flavor = "multi_thread")]