Only pop namespace stack when the class or module is pushed onto it

Currently, the indexer doesn't index classes and modules that have dynamic
namespace. Similarly, those classes and modules' names are not pushed onto the
namespace stack. However, the stack is currently popped on every class or module
exit, which could lead to an incorrect stack popping.

This commit fixes the issue by only popping the stack when the class or module
name is considered indexable.

lib/ruby_indexer/lib/ruby_indexer/declaration_listener.rb

@@ -70,7 +70,8 @@ def on_class_node_enter(node)
 
     sig { params(node: Prism::ClassNode).void }
     def on_class_node_leave(node)
-      @stack.pop
+      name = node.constant_path.location.slice
+      @stack.pop if /^[A-Z:]/.match?(name)
     end
 
     sig { params(node: Prism::ModuleNode).void }
@@ -86,7 +87,8 @@ def on_module_node_enter(node)
 
     sig { params(node: Prism::ModuleNode).void }
     def on_module_node_leave(node)
-      @stack.pop
+      name = node.constant_path.location.slice
+      @stack.pop if /^[A-Z:]/.match?(name)
     end
 
     sig { params(node: Prism::MultiWriteNode).void }

lib/ruby_indexer/test/classes_and_modules_test.rb

@@ -72,6 +72,22 @@ class self::Bar
       refute_entry("self::Bar")
     end
 
+    def test_dynamically_namespaced_class_doesnt_affect_other_classes
+      index(<<~RUBY)
+        class Foo
+          class self::Bar
+          end
+
+          class Bar
+          end
+        end
+      RUBY
+
+      refute_entry("self::Bar")
+      assert_entry("Foo", Entry::Class, "/fake/path/foo.rb:0-0:6-3")
+      assert_entry("Foo::Bar", Entry::Class, "/fake/path/foo.rb:4-2:5-5")
+    end
+
     def test_empty_statements_module
       index(<<~RUBY)
         module Foo
@@ -127,6 +143,22 @@ module self::Bar
       refute_entry("self::Bar")
     end
 
+    def test_dynamically_namespaced_module_doesnt_affect_other_modules
+      index(<<~RUBY)
+        module Foo
+          class self::Bar
+          end
+
+          module Bar
+          end
+        end
+      RUBY
+
+      refute_entry("self::Bar")
+      assert_entry("Foo", Entry::Module, "/fake/path/foo.rb:0-0:6-3")
+      assert_entry("Foo::Bar", Entry::Module, "/fake/path/foo.rb:4-2:5-5")
+    end
+
     def test_nested_modules_and_classes
       index(<<~RUBY)
         module Foo