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`.

3 files changed, 125 insertions, 36 deletions

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 5b44775b..8af5a7e3 100644
--- a/helix-term/src/commands.rs
+++ b/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(|| {
-        helix_lsp::block_on(language_server.text_document_range_formatting(
-            doc.identifier(),
-            range,
-            lsp::FormattingOptions::default(),
-            None,
-        ))
-    })
-    .unwrap_or_default();
+    let request = match language_server.text_document_range_formatting(
+        doc.identifier(),
+        range,
+        lsp::FormattingOptions::default(),
+        None,
+    ) {
+        Some(future) => future,
+        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;
 
diff --git a/helix-term/src/commands/lsp.rs b/helix-term/src/commands/lsp.rs
index dcabfab1..8faf1d08 100644
--- a/helix-term/src/commands/lsp.rs
+++ b/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());
-            match block_on(task) {
+            let future =
+                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,
diff --git a/helix-term/src/ui/completion.rs b/helix-term/src/ui/completion.rs
index 4e6ee424..ebb4fb46 100644
--- a/helix-term/src/ui/completion.rs
+++ b/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,