Fix :stopdoc: directive being undone for C-defined classes

After parsing, `parse_file` resets `done_documenting = false` on all
classes in `top_level.classes_or_modules`. The `done_documenting=`
setter unconditionally sets `document_self = !value`, which overrides
the `document_self = false` state set by `:stopdoc:`.

This became visible after `add_to_classes_or_modules` was added to the
C parser's `handle_class_module`, causing C-defined classes to appear
in `top_level.classes_or_modules` for the first time.

Fix by tracking when `:stopdoc:` is explicitly used via a `@stopped_doc`
flag. The `done_documenting=` setter skips the `document_self` override
when this flag is set. The flag is:
- Set only when the `:stopdoc:` directive is processed
- Cleared by `:startdoc:`
- NOT set by `suppress` (which calls `stop_doc` internally but should
  remain reversible via `done_documenting = false`)

Author: st0012

lib/rdoc/code_object.rb

@@ -125,6 +125,7 @@ def initialize_visibility # :nodoc:
     @received_nodoc      = false
     @ignored             = false
     @suppressed          = false
+    @stopped_doc         = false
     @track_visibility    = true
   end
 
@@ -205,8 +206,10 @@ def documented?
   def done_documenting=(value)
     return unless @track_visibility
     @done_documenting  = value
-    @document_self     = !value
-    @document_children = @document_self
+    unless @stopped_doc
+      @document_self     = !value
+      @document_children = @document_self
+    end
   end
 
   ##
@@ -343,16 +346,18 @@ def start_doc
     @document_children = true
     @ignored    = false
     @suppressed = false
+    @stopped_doc = false
   end
 
   ##
   # Disable capture of documentation
 
-  def stop_doc
+  def stop_doc(from_directive: false)
     return unless @track_visibility
 
     @document_self = false
     @document_children = false
+    @stopped_doc = true if from_directive
   end
 
   ##

lib/rdoc/markup/pre_process.rb

@@ -231,7 +231,7 @@ def handle_directive(prefix, directive, param, code_object = nil,
     when 'stopdoc' then
       return blankline unless code_object
 
-      code_object.stop_doc
+      code_object.stop_doc(from_directive: true)
 
       blankline
     when 'yield', 'yields' then

test/rdoc/parser/c_test.rb

@@ -2292,6 +2292,32 @@ def test_reparse_c_file_no_duplicates
     assert_include method_names, 'baz'
   end
 
+  def test_stopdoc_class_display
+    content = <<~C
+      /* Document-class: Parent
+       * This is the Parent class
+       */
+      VALUE rb_cParent = rb_define_class("Parent", rb_cObject);
+
+      /* :stopdoc: */
+      VALUE cInternal = rb_define_class_under(rb_cParent, "Internal", rb_cObject);
+      /* :startdoc: */
+    C
+
+    util_get_class content, 'cInternal'
+
+    # Simulate parse_file's done_documenting reset
+    @top_level.classes_or_modules.each do |cm|
+      cm.done_documenting = false
+    end
+
+    parent = @store.find_class_named 'Parent'
+    internal = @store.find_class_named 'Parent::Internal'
+
+    assert parent.display?, 'Parent should be displayed'
+    refute internal.display?, 'stopdoc class should not be displayed'
+  end
+
   def util_get_class(content, name = nil)
     @parser = util_parser content
     @parser.scan