Preserve # prefix for unresolved cross-references

When `#name` doesn't resolve to a method, the cross-reference handler
was stripping the `#` and returning just the name. Now the original
text including `#` is restored when the lookup fails.

This fixes rendering of text like `#no-space-heading` in Markdown
paragraphs, where the `#` was silently dropped in the final HTML.

Author: st0012

lib/rdoc/markup/to_html_crossref.rb

@@ -61,6 +61,7 @@ def init_link_notation_regexp_handlings
   def cross_reference(name, text = nil, code = true, rdoc_ref: false)
     lookup = name
 
+    display_name = name
     name = name[1..-1] unless @show_hash if name[0, 1] == '#'
 
     if !name.end_with?('+@', '-@') && match = name.match(/(.*[^#:])?@(.*)/)
@@ -73,7 +74,15 @@ def cross_reference(name, text = nil, code = true, rdoc_ref: false)
       text ||= name
     end
 
-    link lookup, text, code, rdoc_ref: rdoc_ref
+    result = link lookup, text, code, rdoc_ref: rdoc_ref
+
+    # If the cross-reference didn't resolve to a link, restore the original
+    # text including the '#' prefix that was stripped above.
+    if result == text && display_name != name && !text.start_with?('#')
+      display_name
+    else
+      result
+    end
   end
 
   ##

test/rdoc/markup/to_html_crossref_test.rb

@@ -435,6 +435,13 @@ def hyper(reference)
     "rdoc-ref:#{reference}"
   end
 
+  def test_handle_regexp_CROSSREF_hash_preserved_for_unresolved
+    @to.show_hash = false
+
+    # #no should not lose its '#' when it doesn't resolve to a method
+    assert_equal "#no", REGEXP_HANDLING('#no')
+  end
+
   def tidy(reference)
     "{tidy}[rdoc-ref:#{reference}]"
   end