Do not parse non-Ruby files as Ruby when :markup: is markdown or tomdoc

lib/rdoc/parser.rb

@@ -228,14 +228,20 @@ def self.remove_modeline(content)
   # appear on the second or third line.
   #
   # Any comment style may be used to hide the markup comment.
+  #
+  # The +tomdoc+ and +markdown+ markups name comment formats rather than
+  # parsers, so no parser is selected for them and RDoc::Parser.for picks one
+  # from the file name instead.
 
   def self.use_markup(content)
     markup = content.lines.first(3).grep(/markup:\s+(\w+)/) { $1 }.first
 
     return unless markup
 
-    # TODO Ruby should be returned only when the filename is correct
-    return RDoc::Parser::Ruby if %w[tomdoc markdown].include? markup
+    # tomdoc and markdown name a comment format, not a parser.  Skipping them
+    # keeps the search below from matching RDoc::Parser::Markdown for a file
+    # that is not markdown.
+    return if %w[tomdoc markdown].include? markup
 
     markup = Regexp.escape markup
 

test/rdoc/parser/parser_test.rb

@@ -227,6 +227,36 @@ def test_class_for_markup
     end
   end
 
+  def test_class_for_markup_markdown_c_file
+    content = <<-CONTENT
+/* file.c */
+/* :markup: markdown */
+
+/* method comment */
+VALUE rb_a_foo(VALUE self) {
+}
+    CONTENT
+
+    file_name = File.join Dir.tmpdir, "file.c"
+    File.write file_name, content
+
+    top_level = @store.add_file file_name
+
+    parser = @RP.for top_level, content, @options, :stats
+
+    assert_kind_of @RP::C, parser
+  ensure
+    File.unlink file_name
+  end
+
+  def test_class_for_markup_markdown_ruby_file
+    with_top_level("file.rb", "# :markup: markdown\n") do |top_level, content|
+      parser = @RP.for top_level, content, @options, nil
+
+      assert_kind_of @RP::Ruby, parser
+    end
+  end
+
   def test_class_use_markup
     content = <<-CONTENT
 # coding: utf-8 markup: rd
@@ -244,7 +274,7 @@ def test_class_use_markup_markdown
 
     parser = @RP.use_markup content
 
-    assert_equal @RP::Ruby, parser
+    assert_nil parser
   end
 
   def test_class_use_markup_modeline
@@ -289,7 +319,7 @@ def test_class_use_markup_tomdoc
 
     parser = @RP.use_markup content
 
-    assert_equal @RP::Ruby, parser
+    assert_nil parser
   end
 
   def test_class_use_markup_none