lsp: Check server provider capabilities (#3554)

Language Servers may signal that they do not support a method in
the initialization result (server capabilities). We can check these
when making LSP requests and hint in the status line when a method
is not supported by the server. This can also prevent crashes in
servers which assume that clients do not send requests for methods
which are disabled in the server capabilities.

There is an existing pattern the LSP client module where a method
returns `Option<impl Future<Output = Result<_>>>` with `None` signaling
no support in the server. This change extends this pattern to the rest
of the client functions. And we log an error to the statusline for
manually triggered LSP calls which return `None`.

helix-lsp/src/client.rs

@@ -4,7 +4,6 @@ use crate::{
     Call, Error, OffsetEncoding, Result,
 };
 
-use anyhow::anyhow;
 use helix_core::{find_root, ChangeSet, Rope};
 use lsp_types as lsp;
 use serde::Deserialize;
@@ -546,16 +545,17 @@ impl Client {
         new_text: &Rope,
         changes: &ChangeSet,
     ) -> Option<impl Future<Output = Result<()>>> {
-        // figure out what kind of sync the server supports
-
         let capabilities = self.capabilities.get().unwrap();
 
+        // Return early if the server does not support document sync.
         let sync_capabilities = match capabilities.text_document_sync {
-            Some(lsp::TextDocumentSyncCapability::Kind(kind))
+            Some(
-            | Some(lsp::TextDocumentSyncCapability::Options(lsp::TextDocumentSyncOptions {
+                lsp::TextDocumentSyncCapability::Kind(kind)
+                | lsp::TextDocumentSyncCapability::Options(lsp::TextDocumentSyncOptions {
                     change: Some(kind),
                     ..
-            })) => kind,
+                }),
+            ) => kind,
             // None | SyncOptions { changes: None }
             _ => return None,
         };
@@ -631,8 +631,12 @@ impl Client {
         text_document: lsp::TextDocumentIdentifier,
         position: lsp::Position,
         work_done_token: Option<lsp::ProgressToken>,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
-        // ) -> Result<Vec<lsp::CompletionItem>> {
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support completion.
+        capabilities.completion_provider.as_ref()?;
+
         let params = lsp::CompletionParams {
             text_document_position: lsp::TextDocumentPositionParams {
                 text_document,
@@ -647,14 +651,25 @@ impl Client {
             // lsp::CompletionContext { trigger_kind: , trigger_character: Some(), }
         };
 
-        self.call::<lsp::request::Completion>(params)
+        Some(self.call::<lsp::request::Completion>(params))
     }
 
     pub fn resolve_completion_item(
         &self,
         completion_item: lsp::CompletionItem,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
-        self.call::<lsp::request::ResolveCompletionItem>(completion_item)
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support resolving completion items.
+        match capabilities.completion_provider {
+            Some(lsp::CompletionOptions {
+                resolve_provider: Some(true),
+                ..
+            }) => (),
+            _ => return None,
+        }
+
+        Some(self.call::<lsp::request::ResolveCompletionItem>(completion_item))
     }
 
     pub fn text_document_signature_help(
@@ -665,7 +680,7 @@ impl Client {
     ) -> Option<impl Future<Output = Result<Value>>> {
         let capabilities = self.capabilities.get().unwrap();
 
-        // Return early if signature help is not supported
+        // Return early if the server does not support signature help.
         capabilities.signature_help_provider.as_ref()?;
 
         let params = lsp::SignatureHelpParams {
@@ -686,7 +701,18 @@ impl Client {
         text_document: lsp::TextDocumentIdentifier,
         position: lsp::Position,
         work_done_token: Option<lsp::ProgressToken>,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support hover.
+        match capabilities.hover_provider {
+            Some(
+                lsp::HoverProviderCapability::Simple(true)
+                | lsp::HoverProviderCapability::Options(_),
+            ) => (),
+            _ => return None,
+        }
+
         let params = lsp::HoverParams {
             text_document_position_params: lsp::TextDocumentPositionParams {
                 text_document,
@@ -696,7 +722,7 @@ impl Client {
             // lsp::SignatureHelpContext
         };
 
-        self.call::<lsp::request::HoverRequest>(params)
+        Some(self.call::<lsp::request::HoverRequest>(params))
     }
 
     // formatting
@@ -709,13 +735,11 @@ impl Client {
     ) -> Option<impl Future<Output = Result<Vec<lsp::TextEdit>>>> {
         let capabilities = self.capabilities.get().unwrap();
 
-        // check if we're able to format
+        // Return early if the server does not support formatting.
         match capabilities.document_formatting_provider {
-            Some(lsp::OneOf::Left(true)) | Some(lsp::OneOf::Right(_)) => (),
+            Some(lsp::OneOf::Left(true) | lsp::OneOf::Right(_)) => (),
-            // None | Some(false)
             _ => return None,
         };
-        // TODO: return err::unavailable so we can fall back to tree sitter formatting
 
         // merge FormattingOptions with 'config.format'
         let config_format = self
@@ -750,22 +774,20 @@ impl Client {
         })
     }
 
-    pub async fn text_document_range_formatting(
+    pub fn text_document_range_formatting(
         &self,
         text_document: lsp::TextDocumentIdentifier,
         range: lsp::Range,
         options: lsp::FormattingOptions,
         work_done_token: Option<lsp::ProgressToken>,
-    ) -> anyhow::Result<Vec<lsp::TextEdit>> {
+    ) -> Option<impl Future<Output = Result<Vec<lsp::TextEdit>>>> {
         let capabilities = self.capabilities.get().unwrap();
 
-        // check if we're able to format
+        // Return early if the server does not support range formatting.
         match capabilities.document_range_formatting_provider {
-            Some(lsp::OneOf::Left(true)) | Some(lsp::OneOf::Right(_)) => (),
+            Some(lsp::OneOf::Left(true) | lsp::OneOf::Right(_)) => (),
-            // None | Some(false)
+            _ => return None,
-            _ => return Ok(Vec::new()),
         };
-        // TODO: return err::unavailable so we can fall back to tree sitter formatting
 
         let params = lsp::DocumentRangeFormattingParams {
             text_document,
@@ -774,11 +796,13 @@ impl Client {
             work_done_progress_params: lsp::WorkDoneProgressParams { work_done_token },
         };
 
-        let response = self
+        let request = self.call::<lsp::request::RangeFormatting>(params);
-            .request::<lsp::request::RangeFormatting>(params)
-            .await?;
 
+        Some(async move {
+            let json = request.await?;
+            let response: Option<Vec<lsp::TextEdit>> = serde_json::from_value(json)?;
             Ok(response.unwrap_or_default())
+        })
     }
 
     pub fn text_document_document_highlight(
@@ -786,7 +810,15 @@ impl Client {
         text_document: lsp::TextDocumentIdentifier,
         position: lsp::Position,
         work_done_token: Option<lsp::ProgressToken>,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support document highlight.
+        match capabilities.document_highlight_provider {
+            Some(lsp::OneOf::Left(true) | lsp::OneOf::Right(_)) => (),
+            _ => return None,
+        }
+
         let params = lsp::DocumentHighlightParams {
             text_document_position_params: lsp::TextDocumentPositionParams {
                 text_document,
@@ -798,7 +830,7 @@ impl Client {
             },
         };
 
-        self.call::<lsp::request::DocumentHighlightRequest>(params)
+        Some(self.call::<lsp::request::DocumentHighlightRequest>(params))
     }
 
     fn goto_request<
@@ -831,8 +863,20 @@ impl Client {
         text_document: lsp::TextDocumentIdentifier,
         position: lsp::Position,
         work_done_token: Option<lsp::ProgressToken>,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
-        self.goto_request::<lsp::request::GotoDefinition>(text_document, position, work_done_token)
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support goto-definition.
+        match capabilities.definition_provider {
+            Some(lsp::OneOf::Left(true) | lsp::OneOf::Right(_)) => (),
+            _ => return None,
+        }
+
+        Some(self.goto_request::<lsp::request::GotoDefinition>(
+            text_document,
+            position,
+            work_done_token,
+        ))
     }
 
     pub fn goto_type_definition(
@@ -840,12 +884,23 @@ impl Client {
         text_document: lsp::TextDocumentIdentifier,
         position: lsp::Position,
         work_done_token: Option<lsp::ProgressToken>,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
-        self.goto_request::<lsp::request::GotoTypeDefinition>(
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support goto-type-definition.
+        match capabilities.type_definition_provider {
+            Some(
+                lsp::TypeDefinitionProviderCapability::Simple(true)
+                | lsp::TypeDefinitionProviderCapability::Options(_),
+            ) => (),
+            _ => return None,
+        }
+
+        Some(self.goto_request::<lsp::request::GotoTypeDefinition>(
             text_document,
             position,
             work_done_token,
-        )
+        ))
     }
 
     pub fn goto_implementation(
@@ -853,12 +908,23 @@ impl Client {
         text_document: lsp::TextDocumentIdentifier,
         position: lsp::Position,
         work_done_token: Option<lsp::ProgressToken>,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
-        self.goto_request::<lsp::request::GotoImplementation>(
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support goto-definition.
+        match capabilities.implementation_provider {
+            Some(
+                lsp::ImplementationProviderCapability::Simple(true)
+                | lsp::ImplementationProviderCapability::Options(_),
+            ) => (),
+            _ => return None,
+        }
+
+        Some(self.goto_request::<lsp::request::GotoImplementation>(
             text_document,
             position,
             work_done_token,
-        )
+        ))
     }
 
     pub fn goto_reference(
@@ -866,7 +932,15 @@ impl Client {
         text_document: lsp::TextDocumentIdentifier,
         position: lsp::Position,
         work_done_token: Option<lsp::ProgressToken>,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support goto-reference.
+        match capabilities.references_provider {
+            Some(lsp::OneOf::Left(true) | lsp::OneOf::Right(_)) => (),
+            _ => return None,
+        }
+
         let params = lsp::ReferenceParams {
             text_document_position: lsp::TextDocumentPositionParams {
                 text_document,
@@ -881,31 +955,47 @@ impl Client {
             },
         };
 
-        self.call::<lsp::request::References>(params)
+        Some(self.call::<lsp::request::References>(params))
     }
 
     pub fn document_symbols(
         &self,
         text_document: lsp::TextDocumentIdentifier,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support document symbols.
+        match capabilities.document_symbol_provider {
+            Some(lsp::OneOf::Left(true) | lsp::OneOf::Right(_)) => (),
+            _ => return None,
+        }
+
         let params = lsp::DocumentSymbolParams {
             text_document,
             work_done_progress_params: lsp::WorkDoneProgressParams::default(),
             partial_result_params: lsp::PartialResultParams::default(),
         };
 
-        self.call::<lsp::request::DocumentSymbolRequest>(params)
+        Some(self.call::<lsp::request::DocumentSymbolRequest>(params))
     }
 
     // empty string to get all symbols
-    pub fn workspace_symbols(&self, query: String) -> impl Future<Output = Result<Value>> {
+    pub fn workspace_symbols(&self, query: String) -> Option<impl Future<Output = Result<Value>>> {
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support workspace symbols.
+        match capabilities.workspace_symbol_provider {
+            Some(lsp::OneOf::Left(true) | lsp::OneOf::Right(_)) => (),
+            _ => return None,
+        }
+
         let params = lsp::WorkspaceSymbolParams {
             query,
             work_done_progress_params: lsp::WorkDoneProgressParams::default(),
             partial_result_params: lsp::PartialResultParams::default(),
         };
 
-        self.call::<lsp::request::WorkspaceSymbol>(params)
+        Some(self.call::<lsp::request::WorkspaceSymbol>(params))
     }
 
     pub fn code_actions(
@@ -913,7 +1003,18 @@ impl Client {
         text_document: lsp::TextDocumentIdentifier,
         range: lsp::Range,
         context: lsp::CodeActionContext,
-    ) -> impl Future<Output = Result<Value>> {
+    ) -> Option<impl Future<Output = Result<Value>>> {
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the server does not support code actions.
+        match capabilities.code_action_provider {
+            Some(
+                lsp::CodeActionProviderCapability::Simple(true)
+                | lsp::CodeActionProviderCapability::Options(_),
+            ) => (),
+            _ => return None,
+        }
+
         let params = lsp::CodeActionParams {
             text_document,
             range,
@@ -922,26 +1023,22 @@ impl Client {
             partial_result_params: lsp::PartialResultParams::default(),
         };
 
-        self.call::<lsp::request::CodeActionRequest>(params)
+        Some(self.call::<lsp::request::CodeActionRequest>(params))
     }
 
-    pub async fn rename_symbol(
+    pub fn rename_symbol(
         &self,
         text_document: lsp::TextDocumentIdentifier,
         position: lsp::Position,
         new_name: String,
-    ) -> anyhow::Result<lsp::WorkspaceEdit> {
+    ) -> Option<impl Future<Output = Result<lsp::WorkspaceEdit>>> {
         let capabilities = self.capabilities.get().unwrap();
 
-        // check if we're able to rename
+        // Return early if the language server does not support renaming.
         match capabilities.rename_provider {
             Some(lsp::OneOf::Left(true)) | Some(lsp::OneOf::Right(_)) => (),
             // None | Some(false)
-            _ => {
+            _ => return None,
-                log::warn!("rename_symbol failed: The server does not support rename");
-                let err = "The server does not support rename";
-                return Err(anyhow!(err));
-            }
         };
 
         let params = lsp::RenameParams {
@@ -955,11 +1052,21 @@ impl Client {
             },
         };
 
-        let response = self.request::<lsp::request::Rename>(params).await?;
+        let request = self.call::<lsp::request::Rename>(params);
+
+        Some(async move {
+            let json = request.await?;
+            let response: Option<lsp::WorkspaceEdit> = serde_json::from_value(json)?;
             Ok(response.unwrap_or_default())
+        })
     }
 
-    pub fn command(&self, command: lsp::Command) -> impl Future<Output = Result<Value>> {
+    pub fn command(&self, command: lsp::Command) -> Option<impl Future<Output = Result<Value>>> {
+        let capabilities = self.capabilities.get().unwrap();
+
+        // Return early if the language server does not support executing commands.
+        capabilities.execute_command_provider.as_ref()?;
+
         let params = lsp::ExecuteCommandParams {
             command: command.command,
             arguments: command.arguments.unwrap_or_default(),
@@ -968,6 +1075,6 @@ impl Client {
             },
         };
 
-        self.call::<lsp::request::ExecuteCommand>(params)
+        Some(self.call::<lsp::request::ExecuteCommand>(params))
     }
 }

helix-term/src/commands.rs

@@ -3801,15 +3801,21 @@ fn format_selections(cx: &mut Context) {
 
     let range = ranges[0];
 
-    let edits = tokio::task::block_in_place(|| {
+    let request = match language_server.text_document_range_formatting(
-        helix_lsp::block_on(language_server.text_document_range_formatting(
         doc.identifier(),
         range,
         lsp::FormattingOptions::default(),
         None,
-        ))
+    ) {
-    })
+        Some(future) => future,
-    .unwrap_or_default();
+        None => {
+            cx.editor
+                .set_error("Language server does not support range formatting");
+            return;
+        }
+    };
+
+    let edits = tokio::task::block_in_place(|| helix_lsp::block_on(request)).unwrap_or_default();
 
     let transaction = helix_lsp::util::generate_transaction_from_edits(
         doc.text(),
@@ -3953,7 +3959,10 @@ pub fn completion(cx: &mut Context) {
 
     let pos = pos_to_lsp_pos(doc.text(), cursor, offset_encoding);
 
-    let future = language_server.completion(doc.identifier(), pos, None);
+    let future = match language_server.completion(doc.identifier(), pos, None) {
+        Some(future) => future,
+        None => return,
+    };
 
     let trigger_offset = cursor;
 

helix-term/src/commands/lsp.rs

@@ -333,7 +333,14 @@ pub fn symbol_picker(cx: &mut Context) {
     let current_url = doc.url();
     let offset_encoding = language_server.offset_encoding();
 
-    let future = language_server.document_symbols(doc.identifier());
+    let future = match language_server.document_symbols(doc.identifier()) {
+        Some(future) => future,
+        None => {
+            cx.editor
+                .set_error("Language server does not support document symbols");
+            return;
+        }
+    };
 
     cx.callback(
         future,
@@ -365,7 +372,14 @@ pub fn workspace_symbol_picker(cx: &mut Context) {
     let current_url = doc.url();
     let language_server = language_server!(cx.editor, doc);
     let offset_encoding = language_server.offset_encoding();
-    let future = language_server.workspace_symbols("".to_string());
+    let future = match language_server.workspace_symbols("".to_string()) {
+        Some(future) => future,
+        None => {
+            cx.editor
+                .set_error("Language server does not support workspace symbols");
+            return;
+        }
+    };
 
     cx.callback(
         future,
@@ -493,7 +507,7 @@ pub fn code_action(cx: &mut Context) {
 
     let range = range_to_lsp_range(doc.text(), selection_range, offset_encoding);
 
-    let future = language_server.code_actions(
+    let future = match language_server.code_actions(
         doc.identifier(),
         range,
         // Filter and convert overlapping diagnostics
@@ -509,7 +523,14 @@ pub fn code_action(cx: &mut Context) {
                 .collect(),
             only: None,
         },
-    );
+    ) {
+        Some(future) => future,
+        None => {
+            cx.editor
+                .set_error("Language server does not support code actions");
+            return;
+        }
+    };
 
     cx.callback(
         future,
@@ -617,9 +638,16 @@ pub fn execute_lsp_command(editor: &mut Editor, cmd: lsp::Command) {
 
     // the command is executed on the server and communicated back
     // to the client asynchronously using workspace edits
-    let command_future = language_server.command(cmd);
+    let future = match language_server.command(cmd) {
+        Some(future) => future,
+        None => {
+            editor.set_error("Language server does not support executing commands");
+            return;
+        }
+    };
+
     tokio::spawn(async move {
-        let res = command_future.await;
+        let res = future.await;
 
         if let Err(e) = res {
             log::error!("execute LSP command: {}", e);
@@ -853,7 +881,14 @@ pub fn goto_definition(cx: &mut Context) {
 
     let pos = doc.position(view.id, offset_encoding);
 
-    let future = language_server.goto_definition(doc.identifier(), pos, None);
+    let future = match language_server.goto_definition(doc.identifier(), pos, None) {
+        Some(future) => future,
+        None => {
+            cx.editor
+                .set_error("Language server does not support goto-definition");
+            return;
+        }
+    };
 
     cx.callback(
         future,
@@ -871,7 +906,14 @@ pub fn goto_type_definition(cx: &mut Context) {
 
     let pos = doc.position(view.id, offset_encoding);
 
-    let future = language_server.goto_type_definition(doc.identifier(), pos, None);
+    let future = match language_server.goto_type_definition(doc.identifier(), pos, None) {
+        Some(future) => future,
+        None => {
+            cx.editor
+                .set_error("Language server does not support goto-type-definition");
+            return;
+        }
+    };
 
     cx.callback(
         future,
@@ -889,7 +931,14 @@ pub fn goto_implementation(cx: &mut Context) {
 
     let pos = doc.position(view.id, offset_encoding);
 
-    let future = language_server.goto_implementation(doc.identifier(), pos, None);
+    let future = match language_server.goto_implementation(doc.identifier(), pos, None) {
+        Some(future) => future,
+        None => {
+            cx.editor
+                .set_error("Language server does not support goto-implementation");
+            return;
+        }
+    };
 
     cx.callback(
         future,
@@ -907,7 +956,14 @@ pub fn goto_reference(cx: &mut Context) {
 
     let pos = doc.position(view.id, offset_encoding);
 
-    let future = language_server.goto_reference(doc.identifier(), pos, None);
+    let future = match language_server.goto_reference(doc.identifier(), pos, None) {
+        Some(future) => future,
+        None => {
+            cx.editor
+                .set_error("Language server does not support goto-reference");
+            return;
+        }
+    };
 
     cx.callback(
         future,
@@ -950,7 +1006,13 @@ pub fn signature_help_impl(cx: &mut Context, invoked: SignatureHelpInvoked) {
 
     let future = match language_server.text_document_signature_help(doc.identifier(), pos, None) {
         Some(f) => f,
-        None => return,
+        None => {
+            if was_manually_invoked {
+                cx.editor
+                    .set_error("Language server does not support signature-help");
+            }
+            return;
+        }
     };
 
     cx.callback(
@@ -1051,7 +1113,14 @@ pub fn hover(cx: &mut Context) {
 
     let pos = doc.position(view.id, offset_encoding);
 
-    let future = language_server.text_document_hover(doc.identifier(), pos, None);
+    let future = match language_server.text_document_hover(doc.identifier(), pos, None) {
+        Some(future) => future,
+        None => {
+            cx.editor
+                .set_error("Language server does not support hover");
+            return;
+        }
+    };
 
     cx.callback(
         future,
@@ -1121,8 +1190,16 @@ pub fn rename_symbol(cx: &mut Context) {
 
             let pos = doc.position(view.id, offset_encoding);
 
-            let task = language_server.rename_symbol(doc.identifier(), pos, input.to_string());
+            let future =
-            match block_on(task) {
+                match language_server.rename_symbol(doc.identifier(), pos, input.to_string()) {
+                    Some(future) => future,
+                    None => {
+                        cx.editor
+                            .set_error("Language server does not support symbol renaming");
+                        return;
+                    }
+                };
+            match block_on(future) {
                 Ok(edits) => apply_workspace_edit(cx.editor, offset_encoding, &edits),
                 Err(err) => cx.editor.set_error(err.to_string()),
             }
@@ -1137,7 +1214,15 @@ pub fn select_references_to_symbol_under_cursor(cx: &mut Context) {
 
     let pos = doc.position(view.id, offset_encoding);
 
-    let future = language_server.text_document_document_highlight(doc.identifier(), pos, None);
+    let future = match language_server.text_document_document_highlight(doc.identifier(), pos, None)
+    {
+        Some(future) => future,
+        None => {
+            cx.editor
+                .set_error("Language server does not support document highlight");
+            return;
+        }
+    };
 
     cx.callback(
         future,

helix-term/src/ui/completion.rs

@@ -245,21 +245,13 @@ impl Completion {
         completion_item: lsp::CompletionItem,
     ) -> Option<CompletionItem> {
         let language_server = doc.language_server()?;
-        let completion_resolve_provider = language_server
-            .capabilities()
-            .completion_provider
-            .as_ref()?
-            .resolve_provider;
-        if completion_resolve_provider != Some(true) {
-            return None;
-        }
 
-        let future = language_server.resolve_completion_item(completion_item);
+        let future = language_server.resolve_completion_item(completion_item)?;
         let response = helix_lsp::block_on(future);
         match response {
             Ok(value) => serde_json::from_value(value).ok(),
             Err(err) => {
-                log::error!("execute LSP command: {}", err);
+                log::error!("Failed to resolve completion item: {}", err);
                 None
             }
         }
@@ -330,7 +322,10 @@ impl Completion {
         };
 
         // This method should not block the compositor so we handle the response asynchronously.
-        let future = language_server.resolve_completion_item(current_item.clone());
+        let future = match language_server.resolve_completion_item(current_item.clone()) {
+            Some(future) => future,
+            None => return false,
+        };
 
         cx.callback(
             future,