Add snippetTextEdit protocol extension

Author: matklad

crates/rust-analyzer/src/config.rs

@@ -234,6 +234,7 @@ impl Config {
             {
                 self.client_caps.code_action_literals = value;
             }
+
             self.completion.allow_snippets(false);
             if let Some(completion) = &doc_caps.completion {
                 if let Some(completion_item) = &completion.completion_item {
@@ -242,13 +243,19 @@ impl Config {
                     }
                 }
             }
-            self.assist.allow_snippets(false);
         }
 
         if let Some(window_caps) = caps.window.as_ref() {
             if let Some(value) = window_caps.work_done_progress {
                 self.client_caps.work_done_progress = value;
             }
         }
+
+        self.assist.allow_snippets(false);
+        if let Some(experimental) = &caps.experimental {
+            let enable =
+                experimental.get("snippetTextEdit").and_then(|it| it.as_bool()) == Some(true);
+            self.assist.allow_snippets(enable);
+        }
     }
 }

docs/dev/lsp-extensions.md

@@ -0,0 +1,34 @@
+# LSP Extensions
+
+This document describes LSP extensions used by rust-analyzer.
+It's a best effort document, when in doubt, consult the source (and send a PR with clarification ;-) ).
+We aim to upstream all non Rust-specific extensions to the protocol, but this is not a top priority.
+All capabilities are enabled via `experimental` field of `ClientCapabilities`.
+
+## `SnippetTextEdit`
+
+**Capability**
+
+```typescript
+{
+    "snippetTextEdit": boolean
+}
+```
+
+If this capability is set, `WorkspaceEdit`s returned from `codeAction` requests might contain `SnippetTextEdit`s instead of usual `TextEdit`s:
+
+```typescript
+interface SnippetTextEdit extends TextEdit {
+    insertTextFormat?: InsertTextFormat;
+}
+```
+
+```typescript
+export interface TextDocumentEdit {
+	textDocument: VersionedTextDocumentIdentifier;
+	edits: (TextEdit | SnippetTextEdit)[];
+}
+```
+
+When applying such code action, the editor should insert snippet, with tab stops and placeholder.
+At the moment, rust-analyzer guarantees that only a single edit will have `InsertTextFormat.Snippet`.

editors/code/src/client.ts

@@ -35,7 +35,7 @@ export function createClient(serverPath: string, cwd: string): lc.LanguageClient
         } as any
     };
 
-    const res = new lc.LanguageClient(
+    const client = new lc.LanguageClient(
         'rust-analyzer',
         'Rust Analyzer Language Server',
         serverOptions,
@@ -47,8 +47,19 @@ export function createClient(serverPath: string, cwd: string): lc.LanguageClient
     // since they are available on stable.
     // Note that while these features are stable in vscode their LSP protocol
     // implementations are still in the "proposed" category for 3.16.
-    res.registerFeature(new CallHierarchyFeature(res));
-    res.registerFeature(new SemanticTokensFeature(res));
+    client.registerFeature(new CallHierarchyFeature(client));
+    client.registerFeature(new SemanticTokensFeature(client));
+    client.registerFeature(new SnippetTextEditFeature());
 
-    return res;
+    return client;
+}
+
+class SnippetTextEditFeature implements lc.StaticFeature {
+    fillClientCapabilities(capabilities: lc.ClientCapabilities): void {
+        const caps: any = capabilities.experimental ?? {};
+        caps.snippetTextEdit = true;
+        capabilities.experimental = caps
+    }
+    initialize(_capabilities: lc.ServerCapabilities<any>, _documentSelector: lc.DocumentSelector | undefined): void {
+    }
 }