Build default trace modes as late as possible

lib/graphql/schema.rb

@@ -170,9 +170,9 @@ def trace_class(new_class = nil)
       end
 
       # @return [Class] Return the trace class to use for this mode, looking one up on the superclass if this Schema doesn't have one defined.
-      def trace_class_for(mode, build: false)
+      def trace_class_for(mode)
         own_trace_modes[mode] ||
-          (superclass.respond_to?(:trace_class_for) ? superclass.trace_class_for(mode) : nil)
+          (superclass.respond_to?(:trace_class_for) ? superclass.trace_class_for(mode) : (own_trace_modes[mode] = build_trace_mode(mode)))
       end
 
       # Configure `trace_class` to be used whenever `context: { trace_mode: mode_name }` is requested.
@@ -921,7 +921,6 @@ def resolve_type(type, obj, ctx)
 
       def inherited(child_class)
         if self == GraphQL::Schema
-          child_class.own_trace_modes[:default] = child_class.build_trace_mode(:default)
           child_class.directives(default_directives.values)
         end
         # Make sure the child class has these built out, so that

spec/graphql/tracing/trace_modes_spec.rb

@@ -116,14 +116,17 @@ def execute_query(query:)
 
       # Initialize the trace class, make sure no legacy tracers are present at this point:
       refute_includes child_class.trace_class_for(:default).ancestors, GraphQL::Tracing::CallLegacyTracers
-
+      tracer_class = Class.new
       # add a legacy tracer
-      GraphQL::Schema.tracer(Class.new)
+      GraphQL::Schema.tracer(tracer_class)
       # A newly created child class gets the right setup:
       new_child_class = Class.new(GraphQL::Schema)
       assert_includes new_child_class.trace_class_for(:default).ancestors, GraphQL::Tracing::CallLegacyTracers
       # But what about an already-created child class?
       assert_includes child_class.trace_class_for(:default).ancestors, GraphQL::Tracing::CallLegacyTracers
+    ensure
+      GraphQL::Schema.send(:own_tracers).delete(tracer_class)
+      GraphQL::Schema.own_trace_modes.delete(:default)
     end
   end