Don't generate cross-reference links to non-text source files

RDoc's cross-reference system generates links to files like
`array_c.html` when it encounters C filenames in documentation text.
However, non-text source files (C, Ruby, etc.) are not meant to have
their own documentation pages, so these links are always broken.

Filter out non-text `TopLevel` references in `CrossReference#resolve`
and `Store#page` so that only files whose parser includes
`RDoc::Parser::Text` (markdown, rdoc, txt, etc.) produce links.

Author: st0012

lib/rdoc/cross_reference.rb

@@ -211,6 +211,10 @@ def resolve(name, text)
 
     ref = nil if RDoc::Alias === ref # external alias, can't link to it
 
+    # Non-text source files (C, Ruby, etc.) don't get HTML pages generated,
+    # so don't create links that would point to non-existent pages.
+    ref = nil if RDoc::TopLevel === ref && !ref.text?
+
     out = if name == '\\' then
             name
           elsif name =~ /^\\/ then

lib/rdoc/store.rb

@@ -839,7 +839,7 @@ def modules_hash
 
   def page(name)
     @files_hash.each_value.find do |file|
-      file.page_name == name or file.base_name == name
+      file.text? and (file.page_name == name or file.base_name == name)
     end
   end
 

test/rdoc/markup/to_html_crossref_test.rb

@@ -387,6 +387,16 @@ def test_to_html_CROSSREF_email_hyperlink_all
     assert_equal 'first.last@example.com', result
   end
 
+  def test_convert_CROSSREF_c_file_not_linked
+    # C files are not text files, so they don't get HTML pages generated.
+    # Cross-references to them should not produce links.
+    c_file = @store.add_file 'array.c'
+    c_file.parser = RDoc::Parser::C
+
+    result = @to.convert 'array.c'
+    assert_equal para("array.c"), result
+  end
+
   def test_link
     assert_equal 'n', @to.link('n', 'n')
 

test/rdoc/rdoc_cross_reference_test.rb

@@ -115,7 +115,13 @@ def test_resolve_class
   end
 
   def test_resolve_file
-    assert_ref @top_level, 'xref_data.rb'
+    # Non-text source files don't get HTML pages generated,
+    # so they should not be cross-referenced
+    refute_ref 'xref_data.rb'
+  end
+
+  def test_resolve_text_file
+    assert_ref @example_md, 'EXAMPLE.md'
   end
 
   def test_resolve_method