language-server: Stub out support for some messages we don't handle yet. (#7637)

This suppresses warnings for unhandled messages where we currently have
nothing to do. No functionality change, except for less spam in the VS
Code output tab.

Assisted-by: Claude Code

toolchain/language_server/handle.h

@@ -20,6 +20,11 @@ auto HandleDidCloseTextDocument(
     Context& context, const clang::clangd::DidCloseTextDocumentParams& params)
     -> void;
 
+// Acknowledges that a document was saved.
+auto HandleDidSaveTextDocument(
+    Context& context, const clang::clangd::DidSaveTextDocumentParams& params)
+    -> void;
+
 // Updates the content of already-open documents.
 auto HandleDidOpenTextDocument(
     Context& context, const clang::clangd::DidOpenTextDocumentParams& params)
@@ -39,6 +44,10 @@ auto HandleInitialize(
     llvm::function_ref<auto(llvm::Expected<llvm::json::Object>)->void> on_done)
     -> void;
 
+// Acknowledges that the client finished initializing.
+auto HandleInitialized(Context& context, const clang::clangd::NoParams& params)
+    -> void;
+
 // Prepares LSP for shutdown.
 auto HandleShutdown(
     Context& /*context*/,

toolchain/language_server/handle_initialize.cpp

@@ -19,4 +19,14 @@ auto HandleInitialize(
   on_done(reply);
 }
 
+// Implements `initialized`:
+// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initialized
+auto HandleInitialized(Context& /*context*/,
+                       const clang::clangd::NoParams& /*params*/) -> void {
+  // Nothing to do, but every client sends this, so we handle it rather than
+  // warning about an unsupported notification.
+  // TODO: This is when we would use `client/registerCapability` for any
+  // capabilities we want to register dynamically.
+}
+
 }  // namespace Carbon::LanguageServer

toolchain/language_server/handle_text_document.cpp

@@ -115,6 +115,19 @@ auto HandleDidChangeTextDocument(
   }
 }
 
+// Implements `textDocument/didSave`:
+// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_didSave
+auto HandleDidSaveTextDocument(
+    Context& /*context*/,
+    const clang::clangd::DidSaveTextDocumentParams& /*params*/) -> void {
+  // Saving doesn't change the content we're tracking: we always use the text
+  // provided by the client, which is already up-to-date from `didChange`. We
+  // handle this rather than warning about an unsupported notification.
+  // TODO: Other open files that import this one may now be stale, because they
+  // read it from disk rather than from the client. Re-check them here, or
+  // handle `workspace/didChangeWatchedFiles` instead.
+}
+
 // Implements `textDocument/didClose`:
 // https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_didClose
 auto HandleDidCloseTextDocument(

toolchain/language_server/incoming_messages.cpp

@@ -76,10 +76,12 @@ IncomingMessages::IncomingMessages(clang::clangd::Transport* transport,
   AddCallHandler("textDocument/documentSymbol", &HandleDocumentSymbol);
   AddCallHandler("initialize", &HandleInitialize);
   AddCallHandler("shutdown", &HandleShutdown);
+  AddNotificationHandler("initialized", &HandleInitialized);
   AddNotificationHandler("textDocument/didChange",
                          &HandleDidChangeTextDocument);
   AddNotificationHandler("textDocument/didClose", &HandleDidCloseTextDocument);
   AddNotificationHandler("textDocument/didOpen", &HandleDidOpenTextDocument);
+  AddNotificationHandler("textDocument/didSave", &HandleDidSaveTextDocument);
 }
 
 auto IncomingMessages::onCall(llvm::StringRef name, llvm::json::Value params,
@@ -103,6 +105,14 @@ auto IncomingMessages::onNotify(llvm::StringRef name, llvm::json::Value value)
   if (name == "exit") {
     return false;
   }
+  // Notifications prefixed with `$/` are implementation dependent, and LSP says
+  // a recipient is free to ignore ones it doesn't implement. Note this doesn't
+  // apply to calls, which must be answered with `MethodNotFound`; `onCall`
+  // already does that for anything unhandled.
+  // https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#dollarRequests
+  if (name.starts_with("$/")) {
+    return true;
+  }
   if (auto result = notification_handlers_.Lookup(name)) {
     (result.value())(*context_, std::move(value));
   } else {

toolchain/language_server/testdata/basics/quiet_notifications.carbon

@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/language_server/testdata/basics/quiet_notifications.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/language_server/testdata/basics/quiet_notifications.carbon
+
+// Notifications that we accept without doing anything, and so should produce no
+// output at all. `$/` notifications are ignored whether or not we know them.
+
+// --- STDIN
+[[@LSP-NOTIFY:initialized]]
+[[@LSP-NOTIFY:textDocument/didSave:
+  "textDocument": {"uri": "file:/unknown.carbon"}
+]]
+[[@LSP-NOTIFY:$/cancelRequest:"id": 1]]
+[[@LSP-NOTIFY:$/unknown-notify]]
+[[@LSP-NOTIFY:exit]]
+
+// --- AUTOUPDATE-SPLIT
+
+// CHECK:STDOUT: