From 3ff0a1e772bb5382fbb11d066c1148e334bfc439 Mon Sep 17 00:00:00 2001
From: Igor Froehner <igoor.sf14@gmail.com>
Date: Mon, 30 Mar 2026 23:30:21 -0300
Subject: [PATCH 1/2] Return MethodNotFound (-32601) for unrecognized LSP
 requests

The process_message case statement had no else clause, so requests for
unsupported methods were silently dropped. This caused clients to hang
indefinitely waiting for a response. The LSP spec requires servers to
respond with error code -32601 for unsupported methods.

Fixes #3981
---
 lib/ruby_lsp/server.rb |  6 ++++++
 test/server_test.rb    | 12 ++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/lib/ruby_lsp/server.rb b/lib/ruby_lsp/server.rb
index 170c755da..30819246b 100644
--- a/lib/ruby_lsp/server.rb
+++ b/lib/ruby_lsp/server.rb
@@ -120,6 +120,12 @@ def process_message(message)
         @global_state.synchronize { @cancelled_requests << message[:params][:id] }
       when nil
         process_response(message) if message[:result]
+      else
+        send_message(Error.new(
+          id: message[:id],
+          code: -32601,
+          message: "Method not found: #{message[:method]}",
+        )) if message[:id]
       end
     rescue DelegateRequestError
       send_message(Error.new(id: message[:id], code: DelegateRequestError::CODE, message: "DELEGATE_REQUEST"))
diff --git a/test/server_test.rb b/test/server_test.rb
index f38c20fba..2b126a51f 100644
--- a/test/server_test.rb
+++ b/test/server_test.rb
@@ -1726,6 +1726,18 @@ def test_launch_bundle_compose_forwards_argv_to_launcher
     ARGV.replace(original_argv)
   end
 
+  def test_unrecognized_request_returns_method_not_found
+    @server.process_message({
+      id: 1,
+      method: "textDocument/nonExistentMethod",
+      params: {},
+    })
+
+    error = find_message(RubyLsp::Error)
+    assert_equal(-32601, error.code)
+    assert_equal("Method not found: textDocument/nonExistentMethod", error.message)
+  end
+
   private
 
   def run_initialize_server_with_setup_error(error)

From 8a8da0c1a9dc2cdddf32f39b2e1d3fa8676b40fa Mon Sep 17 00:00:00 2001
From: Igor Froehner <igoor.sf14@gmail.com>
Date: Tue, 31 Mar 2026 16:27:21 -0300
Subject: [PATCH 2/2] Use a constant error code

---
 lib/ruby_lsp/server.rb | 14 +++++++++-----
 test/server_test.rb    |  7 ++++---
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/lib/ruby_lsp/server.rb b/lib/ruby_lsp/server.rb
index 30819246b..6a1956d2c 100644
--- a/lib/ruby_lsp/server.rb
+++ b/lib/ruby_lsp/server.rb
@@ -121,11 +121,15 @@ def process_message(message)
       when nil
         process_response(message) if message[:result]
       else
-        send_message(Error.new(
-          id: message[:id],
-          code: -32601,
-          message: "Method not found: #{message[:method]}",
-        )) if message[:id]
+        id = message[:id]
+
+        if id
+          send_message(Error.new(
+            id: id,
+            code: Constant::ErrorCodes::METHOD_NOT_FOUND,
+            message: "Method not found: #{message[:method]}",
+          ))
+        end
       end
     rescue DelegateRequestError
       send_message(Error.new(id: message[:id], code: DelegateRequestError::CODE, message: "DELEGATE_REQUEST"))
diff --git a/test/server_test.rb b/test/server_test.rb
index 2b126a51f..12b6a0e5a 100644
--- a/test/server_test.rb
+++ b/test/server_test.rb
@@ -1727,15 +1727,16 @@ def test_launch_bundle_compose_forwards_argv_to_launcher
   end
 
   def test_unrecognized_request_returns_method_not_found
+    non_existent_method = "textDocument/nonExistentMethod"
     @server.process_message({
       id: 1,
-      method: "textDocument/nonExistentMethod",
+      method: non_existent_method,
       params: {},
     })
 
     error = find_message(RubyLsp::Error)
-    assert_equal(-32601, error.code)
-    assert_equal("Method not found: textDocument/nonExistentMethod", error.message)
+    assert_equal(Constant::ErrorCodes::METHOD_NOT_FOUND, error.code)
+    assert_equal("Method not found: #{non_existent_method}", error.message)
   end
 
   private