[Fix #9819] Fix a false negative for Style/TopLevelMethodDefinition

Fixes #9819.

This PR fixes a false negative for `Style/TopLevelMethodDefinition`
when defining a top-level method after a class definition.

changelog/fix_false_negative_for_style_top_level_method_definition.md

@@ -0,0 +1 @@
+* [#9819](https://github.com/rubocop/rubocop/issues/9819): Fix a false negative for `Style/TopLevelMethodDefinition` when defining a top-level method after a class definition. ([@koic][])

lib/rubocop/cop/style/top_level_method_definition.rb

@@ -50,21 +50,29 @@ class TopLevelMethodDefinition < Base
         RESTRICT_ON_SEND = %i[define_method].freeze
 
         def on_def(node)
-          return unless node.root?
+          return unless top_level_method_definition?(node)
 
           add_offense(node)
         end
         alias on_defs on_def
         alias on_send on_def
 
         def on_block(node)
-          return unless define_method_block?(node) && node.root?
+          return unless define_method_block?(node) && top_level_method_definition?(node)
 
           add_offense(node)
         end
 
         private
 
+        def top_level_method_definition?(node)
+          if node.parent&.begin_type?
+            node.parent.root?
+          else
+            node.root?
+          end
+        end
+
         # @!method define_method_block?(node)
         def_node_matcher :define_method_block?, <<~PATTERN
           (block (send _ {:define_method} _) ...)

spec/rubocop/cop/style/top_level_method_definition_spec.rb

@@ -40,6 +40,16 @@ def self.foo; end
     end
   end
 
+  it 'registers an offense when defining a top-level method after a class definition' do
+    expect_offense(<<~RUBY)
+      class Foo
+      end
+
+      def foo; end
+      ^^^^^^^^^^^^ Do not define methods at the top-level.
+    RUBY
+  end
+
   it 'does not register an offense when using module' do
     expect_no_offenses(<<~RUBY)
       module Foo