Automatically name forked processes based on callers

Author: vinistock

lib/ruby_lsp/ruby_lsp_rails/server.rb

@@ -529,6 +529,32 @@ def database_supports_indexing?(model)
   end
 end
 
+# Patch fork to name processes based on the caller's file path. This is useful for figuring out what is creating more
+# child processes from the runtime server, so that we can optimize and more easily debug orphaned processes
+# @requires_ancestor: Kernel
+module ForkPatch
+  #: () ?{ () -> void } -> Integer?
+  def fork(&block)
+    fork_caller = caller_locations(1, 1)&.first
+
+    # If a block is given, set the child process name and call the original block
+    if block
+      return super do
+        $0 = "ruby-lsp-rails: #{fork_caller&.path}"
+        block.call
+      end
+    end
+
+    # If no block is given, then only set the child process name (when `pid` is `nil`)
+    pid = super
+    $0 = "ruby-lsp-rails: #{fork_caller&.path}" unless pid
+    pid
+  end
+
+  Kernel.prepend(self)
+  Process.singleton_class.prepend(self)
+end
+
 if ARGV.first == "start"
   RubyLsp::Rails::Server.new(capabilities: JSON.parse(ARGV[1], symbolize_names: true)).start
 end

test/ruby_lsp_rails/server_test.rb

@@ -268,6 +268,38 @@ def print_it!
     $> = original_stdout
   end
 
+  test "forked processes are named based on caller" do
+    skip("Fork is not supported on Windows") if Gem.win_platform?
+
+    File.write("my_addon.rb", <<~RUBY)
+      class MyServerAddon < RubyLsp::Rails::ServerAddon
+        def name
+          "MyAddon"
+        end
+
+        def execute(request, params)
+          pid = fork do
+            # We can't directly send a message in theses tests because we're using a StringIO as stdout instead of the
+            # actual pipe, which means that the child process doesn't have access to the same object
+            File.write("process_name.txt", $0)
+          end
+
+          Process.wait(pid)
+          send_message({ process_name: File.read("process_name.txt") })
+          File.delete("process_name.txt")
+        end
+      end
+    RUBY
+
+    addon_path = File.expand_path("my_addon.rb")
+    @server.execute("server_addon/register", server_addon_path: addon_path)
+    @server.execute("server_addon/delegate", server_addon_name: "MyAddon", request_name: "dsl")
+
+    assert_equal(response, { process_name: "ruby-lsp-rails: #{addon_path}" })
+  ensure
+    FileUtils.rm("my_addon.rb")
+  end
+
   private
 
   def response