Fix singleton class nesting when inside top level reference

lib/ruby_indexer/lib/ruby_indexer/declaration_listener.rb

@@ -152,16 +152,17 @@ def on_singleton_class_node_enter(node)
 
       if current_owner
         expression = node.expression
-        @stack << (expression.is_a?(Prism::SelfNode) ? "<Class:#{@stack.last}>" : "<Class:#{expression.slice}>")
+        name = (expression.is_a?(Prism::SelfNode) ? "<Class:#{@stack.last}>" : "<Class:#{expression.slice}>")
+        real_nesting = actual_nesting(name)
 
-        existing_entries = T.cast(@index[@stack.join("::")], T.nilable(T::Array[Entry::SingletonClass]))
+        existing_entries = T.cast(@index[real_nesting.join("::")], T.nilable(T::Array[Entry::SingletonClass]))
 
         if existing_entries
           entry = T.must(existing_entries.first)
           entry.update_singleton_information(node.location, expression.location, collect_comments(node))
         else
           entry = Entry::SingletonClass.new(
-            @stack,
+            real_nesting,
             @file_path,
             node.location,
             expression.location,
@@ -172,6 +173,7 @@ def on_singleton_class_node_enter(node)
         end
 
         @owner_stack << entry
+        @stack << name
       end
     end
 

lib/ruby_indexer/test/classes_and_modules_test.rb

@@ -564,6 +564,27 @@ class Bar
       assert_entry("Foo::Bar", Entry::Class, "/fake/path/foo.rb:1-2:2-5")
     end
 
+    def test_indexing_singletons_inside_top_level_references
+      index(<<~RUBY)
+        module ::Foo
+          class Bar
+            class << self
+            end
+          end
+        end
+      RUBY
+
+      # We want to explicitly verify that we didn't introduce the leading `::` by accident, but `Index#[]` deletes the
+      # prefix when we use `refute_entry`
+      entries = @index.instance_variable_get(:@entries)
+      refute(entries.key?("::Foo"))
+      refute(entries.key?("::Foo::Bar"))
+      refute(entries.key?("::Foo::Bar::<Class:Bar>"))
+      assert_entry("Foo", Entry::Module, "/fake/path/foo.rb:0-0:5-3")
+      assert_entry("Foo::Bar", Entry::Class, "/fake/path/foo.rb:1-2:4-5")
+      assert_entry("Foo::Bar::<Class:Bar>", Entry::SingletonClass, "/fake/path/foo.rb:2-4:3-7")
+    end
+
     def test_indexing_namespaces_inside_nested_top_level_references
       index(<<~RUBY)
         class Baz