Make LspAdapter::process_diagnostics synchronous (#2829)

When editing rust code, the project diagnostics view sometimes fails to
update, so that you have to close the view and re-open it to see the
correct state.

This PR fixes one possible cause of that problem. There was an async
step in between *receiving* diagnostics from the language server and
updating the diagnostics, due to an async call to
`LspAdapter::process_diagnostics`. This could cause the following
sequence of events to happen:

1. Rust-analyzer sends us new diagnostics for a file `a.rs`
2. We call `process_diagnostics` with those diagnostics
3. Rust-analyzer sends us a `WorkDoneProgress` message, indicating that
the "flycheck" (aka `cargo check`) process has completed
4. We update the project diagnostics view due to this message.
5. The `process_diagnostics` call for `a.rs` completes
6. 💥 We have the new diagnostics for `a.rs`, but do not update the
project diagnostics view again.

This PR fixes this bug by simply making `process_diagnostics`
synchronous. There is no I/O or expensive computation happening in that
method. If we need to make it asynchronous in the future, we need to
introduce a queue that ensures that `publishDiagnostics` and
`workDoneProgress` messages are processed serially.

Release Notes:

- Fixed a bug where the project diagnostics view would sometimes fail to
update properly when using Rust-analyzer.

crates/language/src/language.rs

@@ -182,8 +182,8 @@ impl CachedLspAdapter {
         self.adapter.workspace_configuration(cx)
     }
 
-    pub async fn process_diagnostics(&self, params: &mut lsp::PublishDiagnosticsParams) {
-        self.adapter.process_diagnostics(params).await
+    pub fn process_diagnostics(&self, params: &mut lsp::PublishDiagnosticsParams) {
+        self.adapter.process_diagnostics(params)
     }
 
     pub async fn process_completion(&self, completion_item: &mut lsp::CompletionItem) {
@@ -262,7 +262,7 @@ pub trait LspAdapter: 'static + Send + Sync {
         container_dir: PathBuf,
     ) -> Option<LanguageServerBinary>;
 
-    async fn process_diagnostics(&self, _: &mut lsp::PublishDiagnosticsParams) {}
+    fn process_diagnostics(&self, _: &mut lsp::PublishDiagnosticsParams) {}
 
     async fn process_completion(&self, _: &mut lsp::CompletionItem) {}
 
@@ -1487,12 +1487,6 @@ impl Language {
         None
     }
 
-    pub async fn process_diagnostics(&self, diagnostics: &mut lsp::PublishDiagnosticsParams) {
-        for adapter in &self.adapters {
-            adapter.process_diagnostics(diagnostics).await;
-        }
-    }
-
     pub async fn process_completion(self: &Arc<Self>, completion: &mut lsp::CompletionItem) {
         for adapter in &self.adapters {
             adapter.process_completion(completion).await;
@@ -1756,7 +1750,7 @@ impl LspAdapter for Arc<FakeLspAdapter> {
         unreachable!();
     }
 
-    async fn process_diagnostics(&self, _: &mut lsp::PublishDiagnosticsParams) {}
+    fn process_diagnostics(&self, _: &mut lsp::PublishDiagnosticsParams) {}
 
     async fn disk_based_diagnostic_sources(&self) -> Vec<String> {
         self.disk_based_diagnostics_sources.clone()

crates/project/src/project.rs

@@ -2769,24 +2769,21 @@ impl Project {
         language_server
             .on_notification::<lsp::notification::PublishDiagnostics, _>({
                 let adapter = adapter.clone();
-                move |mut params, cx| {
+                move |mut params, mut cx| {
                     let this = this;
                     let adapter = adapter.clone();
-                    cx.spawn(|mut cx| async move {
-                        adapter.process_diagnostics(&mut params).await;
-                        if let Some(this) = this.upgrade(&cx) {
-                            this.update(&mut cx, |this, cx| {
-                                this.update_diagnostics(
-                                    server_id,
-                                    params,
-                                    &adapter.disk_based_diagnostic_sources,
-                                    cx,
-                                )
-                                .log_err();
-                            });
-                        }
-                    })
-                    .detach();
+                    adapter.process_diagnostics(&mut params);
+                    if let Some(this) = this.upgrade(&cx) {
+                        this.update(&mut cx, |this, cx| {
+                            this.update_diagnostics(
+                                server_id,
+                                params,
+                                &adapter.disk_based_diagnostic_sources,
+                                cx,
+                            )
+                            .log_err();
+                        });
+                    }
                 }
             })
             .detach();

crates/zed/src/languages/rust.rs

@@ -102,7 +102,7 @@ impl LspAdapter for RustLspAdapter {
         Some("rust-analyzer/flycheck".into())
     }
 
-    async fn process_diagnostics(&self, params: &mut lsp::PublishDiagnosticsParams) {
+    fn process_diagnostics(&self, params: &mut lsp::PublishDiagnosticsParams) {
         lazy_static! {
             static ref REGEX: Regex = Regex::new("(?m)`([^`]+)\n`$").unwrap();
         }
@@ -310,7 +310,7 @@ mod tests {
                 },
             ],
         };
-        RustLspAdapter.process_diagnostics(&mut params).await;
+        RustLspAdapter.process_diagnostics(&mut params);
 
         assert_eq!(params.diagnostics[0].message, "use of moved value `a`");