ruff server: In 'publish diagnostics' mode, document diagnostics are cleared properly when a file is closed (#11137)

## Summary

Fixes #11114. 

As part of the `onClose` handler, we publish an empty array of
diagnostics for the document being closed, similar to
[`ruff-lsp`](https://github.com/astral-sh/ruff-lsp/blob/187d7790be0783b9ac41ce025a724cf389bf575c/ruff_lsp/server.py#L459-L464).
This prevent phantom diagnostics from lingering after a document is
closed. We'll only do this if the client doesn't support pull
diagnostics, because otherwise clearing diagnostics is their
responsibility.

## Test Plan

Diagnostics should no longer appear for a document in the Problems tab
after the document is closed.

Author: snowsignal

crates/ruff_server/src/server/api/diagnostics.rs

@@ -32,3 +32,20 @@ pub(super) fn publish_diagnostics_for_document(
 
     Ok(())
 }
+
+pub(super) fn clear_diagnostics_for_document(
+    snapshot: &DocumentSnapshot,
+    notifier: &Notifier,
+) -> crate::server::Result<()> {
+    notifier
+        .notify::<lsp_types::notification::PublishDiagnostics>(
+            lsp_types::PublishDiagnosticsParams {
+                uri: snapshot.url().clone(),
+                diagnostics: vec![],
+                version: Some(snapshot.document().version()),
+            },
+        )
+        .with_failure_code(lsp_server::ErrorCode::InternalError)?;
+
+    Ok(())
+}

crates/ruff_server/src/server/api/notifications/did_close.rs

@@ -1,3 +1,4 @@
+use crate::server::api::diagnostics::clear_diagnostics_for_document;
 use crate::server::api::LSPResult;
 use crate::server::client::{Notifier, Requester};
 use crate::server::Result;
@@ -15,12 +16,24 @@ impl super::SyncNotificationHandler for DidClose {
     #[tracing::instrument(skip_all, fields(file=%uri))]
     fn run(
         session: &mut Session,
-        _notifier: Notifier,
+        notifier: Notifier,
         _requester: &mut Requester,
         types::DidCloseTextDocumentParams {
             text_document: types::TextDocumentIdentifier { uri },
         }: types::DidCloseTextDocumentParams,
     ) -> Result<()> {
+        // Publish an empty diagnostic report for the document if the client does not support pull diagnostics.
+        // This will de-register any existing diagnostics.
+        if !session.resolved_client_capabilities().pull_diagnostics {
+            let snapshot = session
+                .take_snapshot(&uri)
+                .ok_or_else(|| {
+                    anyhow::anyhow!("Unable to take snapshot for document with URL {uri}")
+                })
+                .with_failure_code(lsp_server::ErrorCode::InternalError)?;
+            clear_diagnostics_for_document(&snapshot, &notifier)?;
+        }
+
         session
             .close_document(&uri)
             .with_failure_code(lsp_server::ErrorCode::InternalError)