ruff server: Support publish diagnostics as a fallback when pull diagnostics aren't supported (#11092)

## Summary

Fixes #11059 

Several major editors don't support [pull
diagnostics](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_pullDiagnostics),
a method of sending diagnostics to the client that was introduced in
version `0.3.17` of the specification. Until now, `ruff server` has only
used pull diagnostics, which resulted in diagnostics not being available
on Neovim and Helix, which don't support pull diagnostics yet (though
Neovim `10.0` will have support for this).

`ruff server` will now utilize the older method of sending diagnostics,
known as 'publish diagnostics', when pull diagnostics aren't supported
by the client. This involves re-linting a document every time it is
opened or modified, and then sending the diagnostics generated from that
lint to the client via the `textDocument/publishDiagnostics`
notification.

## Test Plan

The easiest way to test that this PR works is to check if diagnostics
show up on Neovim `<=0.9`.

crates/ruff_server/src/server/api.rs

@@ -1,6 +1,7 @@
 use crate::{server::schedule::Task, session::Session};
 use lsp_server as server;
 
+mod diagnostics;
 mod notifications;
 mod requests;
 mod traits;

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

@@ -0,0 +1,34 @@
+use crate::{server::client::Notifier, session::DocumentSnapshot};
+
+use super::LSPResult;
+
+pub(super) fn generate_diagnostics(snapshot: &DocumentSnapshot) -> Vec<lsp_types::Diagnostic> {
+    if snapshot.client_settings().lint() {
+        crate::lint::check(
+            snapshot.document(),
+            &snapshot.settings().linter,
+            snapshot.encoding(),
+        )
+    } else {
+        vec![]
+    }
+}
+
+pub(super) fn publish_diagnostics_for_document(
+    snapshot: &DocumentSnapshot,
+    notifier: &Notifier,
+) -> crate::server::Result<()> {
+    let diagnostics = generate_diagnostics(snapshot);
+
+    notifier
+        .notify::<lsp_types::notification::PublishDiagnostics>(
+            lsp_types::PublishDiagnosticsParams {
+                uri: snapshot.url().clone(),
+                diagnostics,
+                version: Some(snapshot.document().version()),
+            },
+        )
+        .with_failure_code(lsp_server::ErrorCode::InternalError)?;
+
+    Ok(())
+}

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

@@ -1,3 +1,4 @@
+use crate::server::api::diagnostics::publish_diagnostics_for_document;
 use crate::server::api::LSPResult;
 use crate::server::client::{Notifier, Requester};
 use crate::server::Result;
@@ -15,7 +16,7 @@ impl super::SyncNotificationHandler for DidChange {
     #[tracing::instrument(skip_all, fields(file=%uri))]
     fn run(
         session: &mut Session,
-        _notifier: Notifier,
+        notifier: Notifier,
         _requester: &mut Requester,
         types::DidChangeTextDocumentParams {
             text_document:
@@ -40,6 +41,12 @@ impl super::SyncNotificationHandler for DidChange {
             .make_mut()
             .apply_changes(content_changes, new_version, encoding);
 
+        // Publish diagnostics if the client doesnt support pull diagnostics
+        if !session.resolved_client_capabilities().pull_diagnostics {
+            let snapshot = session.take_snapshot(&uri).unwrap();
+            publish_diagnostics_for_document(&snapshot, &notifier)?;
+        }
+
         Ok(())
     }
 }

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

@@ -1,3 +1,5 @@
+use crate::server::api::diagnostics::publish_diagnostics_for_document;
+use crate::server::api::LSPResult;
 use crate::server::client::{Notifier, Requester};
 use crate::server::Result;
 use crate::session::Session;
@@ -14,7 +16,7 @@ impl super::SyncNotificationHandler for DidOpen {
     #[tracing::instrument(skip_all, fields(file=%url))]
     fn run(
         session: &mut Session,
-        _notifier: Notifier,
+        notifier: Notifier,
         _requester: &mut Requester,
         types::DidOpenTextDocumentParams {
             text_document:
@@ -27,6 +29,18 @@ impl super::SyncNotificationHandler for DidOpen {
         }: types::DidOpenTextDocumentParams,
     ) -> Result<()> {
         session.open_document(url, text, version);
+
+        // Publish diagnostics if the client doesnt support pull diagnostics
+        if !session.resolved_client_capabilities().pull_diagnostics {
+            let snapshot = session
+                .take_snapshot(url)
+                .ok_or_else(|| {
+                    anyhow::anyhow!("Unable to take snapshot for document with URL {url}")
+                })
+                .with_failure_code(lsp_server::ErrorCode::InternalError)?;
+            publish_diagnostics_for_document(&snapshot, &notifier)?;
+        }
+
         Ok(())
     }
 }

crates/ruff_server/src/server/api/requests/diagnostic.rs

@@ -1,3 +1,4 @@
+use crate::server::api::diagnostics::generate_diagnostics;
 use crate::server::{client::Notifier, Result};
 use crate::session::DocumentSnapshot;
 use lsp_types::{self as types, request as req};
@@ -19,23 +20,13 @@ impl super::BackgroundDocumentRequestHandler for DocumentDiagnostic {
         _notifier: Notifier,
         _params: types::DocumentDiagnosticParams,
     ) -> Result<DocumentDiagnosticReportResult> {
-        let diagnostics = if snapshot.client_settings().lint() {
-            crate::lint::check(
-                snapshot.document(),
-                &snapshot.settings().linter,
-                snapshot.encoding(),
-            )
-        } else {
-            vec![]
-        };
-
         Ok(DocumentDiagnosticReportResult::Report(
             types::DocumentDiagnosticReport::Full(RelatedFullDocumentDiagnosticReport {
                 related_documents: None,
                 full_document_diagnostic_report: FullDocumentDiagnosticReport {
                     // TODO(jane): eventually this will be important for caching diagnostic information.
                     result_id: None,
-                    items: diagnostics,
+                    items: generate_diagnostics(&snapshot),
                 },
             }),
         ))

crates/ruff_server/src/session/capabilities.rs

@@ -7,6 +7,7 @@ pub(crate) struct ResolvedClientCapabilities {
     pub(crate) apply_edit: bool,
     pub(crate) document_changes: bool,
     pub(crate) workspace_refresh: bool,
+    pub(crate) pull_diagnostics: bool,
 }
 
 impl ResolvedClientCapabilities {
@@ -48,12 +49,19 @@ impl ResolvedClientCapabilities {
             .unwrap_or_default();
         */
 
+        let pull_diagnostics = client_capabilities
+            .text_document
+            .as_ref()
+            .and_then(|text_document| text_document.diagnostic.as_ref())
+            .is_some();
+
         Self {
             code_action_deferred_edit_resolution: code_action_data_support
                 && code_action_edit_resolution,
             apply_edit,
             document_changes,
             workspace_refresh,
+            pull_diagnostics,
         }
     }
 }