Enable cross reference in code

Some people like to mark up method names in MarkDown style block
quotes, like this: ruby/ruby#12333.
Currently, no links are created in the code in the RDoc, but such
words most likely refer to methods.
This PR makes a word a code cross-reference if the whole word can be
resolved as a reference.

Author: nobu

lib/rdoc/markup/formatter.rb

@@ -195,32 +195,39 @@ def in_tt?
     @in_tt > 0
   end
 
+  def tt_tag? attr_mask, reverse = false
+    each_attr_tag(attr_mask, reverse) do |tag|
+      return true if tt? tag
+    end
+    false
+  end
+
   ##
   # Turns on tags for +item+ on +res+
 
   def on_tags res, item
-    attr_mask = item.turn_on
-    return if attr_mask.zero?
-
-    @attr_tags.each do |tag|
-      if attr_mask & tag.bit != 0 then
-        res << annotate(tag.on)
-        @in_tt += 1 if tt? tag
-      end
+    each_attr_tag(item.turn_on) do |tag|
+      res << annotate(tag.on)
+      @in_tt += 1 if tt? tag
     end
   end
 
   ##
   # Turns off tags for +item+ on +res+
 
   def off_tags res, item
-    attr_mask = item.turn_off
+    each_attr_tag(item.turn_off, true) do |tag|
+      @in_tt -= 1 if tt? tag
+      res << annotate(tag.off)
+    end
+  end
+
+  def each_attr_tag attr_mask, reverse = false
     return if attr_mask.zero?
 
-    @attr_tags.reverse_each do |tag|
+    @attr_tags.public_send(reverse ? :reverse_each : :each) do |tag|
       if attr_mask & tag.bit != 0 then
-        @in_tt -= 1 if tt? tag
-        res << annotate(tag.off)
+        yield tag
       end
     end
   end

lib/rdoc/markup/to_html_crossref.rb

@@ -172,4 +172,43 @@ def link name, text, code = true
     end
   end
 
+  def convert_flow(flow)
+    res = []
+
+    i = 0
+    while i < flow.size
+      item = flow[i]
+      i += 1
+      case item
+      when RDoc::Markup::AttrChanger then
+        # Make "+Class#method+" a cross reference
+        if respond_to?(:cross_reference) and
+          tt_tag?(item.turn_on) and
+          String === (str = flow[i]) and
+          RDoc::Markup::AttrChanger === flow[i+1] and
+          tt_tag?(flow[i+1].turn_off, true) and
+          (text = cross_reference str) != str
+        then
+          text = yield text, res if defined?(yield)
+          res << text
+          i += 2
+          next
+        end
+        off_tags res, item
+        on_tags res, item
+      when String then
+        text = convert_string(item)
+        text = yield text, res if defined?(yield)
+        res << text
+      when RDoc::Markup::RegexpHandling then
+        text = convert_regexp_handling(item)
+        text = yield text, res if defined?(yield)
+        res << text
+      else
+        raise "Unknown flow element: #{item.inspect}"
+      end
+    end
+
+    res.join('')
+  end
 end

test/rdoc/test_rdoc_markup_to_html_crossref.rb

@@ -15,6 +15,10 @@ def test_convert_CROSSREF
     result = @to.convert 'C1'
 
     assert_equal para("<a href=\"C1.html\"><code>C1</code></a>"), result
+
+    result = @to.convert '+C1+'
+
+    assert_equal para("<a href=\"C1.html\"><code>C1</code></a>"), result
   end
 
   def test_convert_CROSSREF_method