[ruby/rdoc] Pull up handle_tab_width to RDoc::Parser

To share with the duplicate code in RDoc::Parser::Ruby#initialize.

https://github.com/ruby/rdoc/commit/27829ac119

lib/rdoc/parser.rb

@@ -266,6 +266,23 @@ class RDoc::Parser
   autoload :RubyTools, "#{__dir__}/parser/ruby_tools"
   autoload :Text,      "#{__dir__}/parser/text"
 
+  ##
+  # Normalizes tabs in +body+
+
+  def handle_tab_width(body)
+    if /\t/ =~ body
+      tab_width = @options.tab_width
+      body.split(/\n/).map do |line|
+        1 while line.gsub!(/\t+/) do
+          b, e = $~.offset(0)
+          ' ' * (tab_width * (e-b) - b % tab_width)
+        end
+        line
+      end.join "\n"
+    else
+      body
+    end
+  end
 end
 
 # simple must come first in order to show up last in the parsers list

lib/rdoc/parser/c.rb

@@ -1057,23 +1057,6 @@ class RDoc::Parser::C < RDoc::Parser
     @singleton_classes[sclass_var] = class_name
   end
 
-  ##
-  # Normalizes tabs in +body+
-
-  def handle_tab_width(body)
-    if /\t/ =~ body
-      tab_width = @options.tab_width
-      body.split(/\n/).map do |line|
-        1 while line.gsub!(/\t+/) do
-          ' ' * (tab_width * $&.length - $`.length % tab_width)
-        end && $~
-        line
-      end.join "\n"
-    else
-      body
-    end
-  end
-
   ##
   # Loads the variable map with the given +name+ from the RDoc::Store, if
   # present.

lib/rdoc/parser/ruby.rb

@@ -164,15 +164,7 @@ class RDoc::Parser::Ruby < RDoc::Parser
   def initialize(top_level, file_name, content, options, stats)
     super
 
-    if /\t/ =~ content then
-      tab_width = @options.tab_width
-      content = content.split(/\n/).map do |line|
-        1 while line.gsub!(/\t+/) {
-          ' ' * (tab_width*$&.length - $`.length % tab_width)
-        }  && $~
-        line
-      end.join("\n")
-    end
+    content = handle_tab_width(content)
 
     @size = 0
     @token_listeners = nil