Use normal method instead of ban ver. for String

Ruby 2.2 or earlier only has String#force_encoding for changing
character encoding set without encode byte sequence, it changes receiver
itself. Ruby 2.3 or later has frozen_striing_literal magic comment and
String#new can take encoding keyword parameter for character encoding
set without encode byte sequence.

So implements RDoc::Encoding.change_encoding and RDoc::Comment#encode!
to disguise difference between #force_encoding and encoding keyword
parameter of #new on String.

lib/rdoc/any_method.rb

@@ -244,9 +244,9 @@ def param_list
     if @block_params then
       # If this method has explicit block parameters, remove any explicit
       # &block
-      params.sub!(/,?\s*&\w+/, '')
+      params = params.sub(/,?\s*&\w+/, '')
     else
-      params.sub!(/\&(\w+)/, '\1')
+      params = params.sub(/\&(\w+)/, '\1')
     end
 
     params = params.gsub(/\s+/, '').split(',').reject(&:empty?)
@@ -274,11 +274,11 @@ def param_seq
     if @block_params then
       # If this method has explicit block parameters, remove any explicit
       # &block
-      params.sub!(/,?\s*&\w+/, '')
+      params = params.sub(/,?\s*&\w+/, '')
 
       block = @block_params.tr_s("\n ", " ")
       if block[0] == ?(
-        block.sub!(/^\(/, '').sub!(/\)/, '')
+        block = block.sub(/^\(/, '').sub(/\)/, '')
       end
       params << " { |#{block}| ... }"
     end

lib/rdoc/code_object.rb

@@ -144,7 +144,7 @@ def comment=(comment)
                    # HACK correct fix is to have #initialize create @comment
                    #      with the correct encoding
                    if String === @comment and @comment.empty? then
-                     @comment.force_encoding comment.encoding
+                     @comment = RDoc::Encoding.change_encoding @comment, comment.encoding
                    end
                    @comment
                  end

lib/rdoc/comment.rb

@@ -45,7 +45,7 @@ class RDoc::Comment
 
   def initialize text = nil, location = nil
     @location = location
-    @text     = text
+    @text     = text.nil? ? nil : text.dup
 
     @document   = nil
     @format     = 'rdoc'
@@ -114,10 +114,14 @@ def extract_call_seq method
 
       method.call_seq = seq.chomp
 
-    elsif @text.sub!(/^\s*:?call-seq:(.*?)(^\s*$|\z)/m, '') then
-      seq = $1
-      seq.gsub!(/^\s*/, '')
-      method.call_seq = seq
+    else
+      regexp = /^\s*:?call-seq:(.*?)(^\s*$|\z)/m
+      if regexp =~ @text then
+        @text = @text.sub(regexp, '')
+        seq = $1
+        seq.gsub!(/^\s*/, '')
+        method.call_seq = seq
+      end
     end
 
     method
@@ -133,8 +137,14 @@ def empty?
   ##
   # HACK dubious
 
-  def force_encoding encoding
-    @text.force_encoding encoding
+  def encode! encoding
+    # TODO: Remove this condition after Ruby 2.2 EOL
+    if RUBY_VERSION < '2.3.0'
+      @text = @text.force_encoding encoding
+    else
+      @text = String.new @text, encoding: encoding
+    end
+    self
   end
 
   ##
@@ -200,7 +210,7 @@ def parse
   def remove_private
     # Workaround for gsub encoding for Ruby 1.9.2 and earlier
     empty = ''
-    empty.force_encoding @text.encoding
+    empty = RDoc::Encoding.change_encoding empty, @text.encoding
 
     @text = @text.gsub(%r%^\s*([#*]?)--.*?^\s*(\1)\+\+\n?%m, empty)
     @text = @text.sub(%r%^\s*[#*]?--.*%m, '')
@@ -216,7 +226,7 @@ def text= text
       @text.nil? and @document
 
     @document = nil
-    @text = text
+    @text = text.nil? ? nil : text.dup
   end
 
   ##

lib/rdoc/context.rb

@@ -239,7 +239,7 @@ def add_attribute attribute
 
       if known then
         known.comment = attribute.comment if known.comment.empty?
-      elsif registered = @methods_hash[attribute.pretty_name << '='] and
+      elsif registered = @methods_hash[attribute.pretty_name + '='] and
             RDoc::Attr === registered then
         registered.rw = 'RW'
       else
@@ -249,7 +249,7 @@ def add_attribute attribute
     end
 
     if attribute.rw.index 'W' then
-      key = attribute.pretty_name << '='
+      key = attribute.pretty_name + '='
       known = @methods_hash[key]
 
       if known then

lib/rdoc/context/section.rb

@@ -43,7 +43,7 @@ def initialize parent, title, comment
     @parent = parent
     @title = title ? title.strip : title
 
-    @@sequence.succ!
+    @@sequence = @@sequence.succ
     @sequence = @@sequence.dup
 
     @comments = []

lib/rdoc/encoding.rb

@@ -23,26 +23,26 @@ def self.read_file filename, encoding, force_transcode = false
 
     utf8 = content.sub!(/\A\xef\xbb\xbf/, '')
 
-    RDoc::Encoding.set_encoding content
+    content = RDoc::Encoding.set_encoding content
 
     begin
       encoding ||= Encoding.default_external
       orig_encoding = content.encoding
 
       if not orig_encoding.ascii_compatible? then
-        content.encode! encoding
+        content = content.encode encoding
       elsif utf8 then
-        content.force_encoding Encoding::UTF_8
-        content.encode! encoding
+        content = RDoc::Encoding.change_encoding content, Encoding::UTF_8
+        content = content.encode encoding
       else
         # assume the content is in our output encoding
-        content.force_encoding encoding
+        content = RDoc::Encoding.change_encoding content, encoding
       end
 
       unless content.valid_encoding? then
         # revert and try to transcode
-        content.force_encoding orig_encoding
-        content.encode! encoding
+        content = RDoc::Encoding.change_encoding content, orig_encoding
+        content = content.encode encoding
       end
 
       unless content.valid_encoding? then
@@ -52,10 +52,11 @@ def self.read_file filename, encoding, force_transcode = false
     rescue Encoding::InvalidByteSequenceError,
            Encoding::UndefinedConversionError => e
       if force_transcode then
-        content.force_encoding orig_encoding
-        content.encode!(encoding,
-                        :invalid => :replace, :undef => :replace,
-                        :replace => '?')
+        content = RDoc::Encoding.change_encoding content, orig_encoding
+        content = content.encode(encoding,
+                                 :invalid => :replace,
+                                 :undef => :replace,
+                                 :replace => '?')
         return content
       else
         warn "unable to convert #{e.message} for #{filename}, skipping"
@@ -77,15 +78,17 @@ def self.remove_frozen_string_literal string
     first_line = $1
 
     if first_line =~ /\A# +frozen[-_]string[-_]literal[=:].+$/i
-      string.sub! first_line, ''
+      string = string.sub first_line, ''
     end
+
+    string
   end
 
   ##
   # Sets the encoding of +string+ based on the magic comment
 
   def self.set_encoding string
-    remove_frozen_string_literal string
+    string = remove_frozen_string_literal string
 
     string =~ /\A(?:#!.*\n)?(.*\n)/
 
@@ -94,15 +97,34 @@ def self.set_encoding string
     name = case first_line
            when /^<\?xml[^?]*encoding=(["'])(.*?)\1/ then $2
            when /\b(?:en)?coding[=:]\s*([^\s;]+)/i   then $1
-           else                                           return
+           else                                           return string
            end
 
-    string.sub! first_line, ''
+    string = string.sub first_line, ''
 
-    remove_frozen_string_literal string
+    string = remove_frozen_string_literal string
 
     enc = Encoding.find name
-    string.force_encoding enc if enc
+    string = RDoc::Encoding.change_encoding string, enc if enc
+
+    string
+  end
+
+  ##
+  # Changes encoding based on +encoding+ without converting and returns new
+  # string
+
+  def self.change_encoding text, encoding
+    if text.kind_of? RDoc::Comment
+      text.encode! encoding
+    else
+      # TODO: Remove this condition after Ruby 2.2 EOL
+      if RUBY_VERSION < '2.3.0'
+        text.force_encoding encoding
+      else
+        String.new text, encoding: encoding
+      end
+    end
   end
 
 end

lib/rdoc/generator/pot/po.rb

@@ -29,8 +29,8 @@ def add entry
   def to_s
     po = ''
     sort_entries.each do |entry|
-      po << "\n" unless po.empty?
-      po << entry.to_s
+      po += "\n" unless po.empty?
+      po += entry.to_s
     end
     po
   end

lib/rdoc/generator/pot/po_entry.rb

@@ -40,11 +40,11 @@ def initialize msgid, options = {}
 
   def to_s
     entry = ''
-    entry << format_translator_comment
-    entry << format_extracted_comment
-    entry << format_references
-    entry << format_flags
-    entry << <<-ENTRY
+    entry += format_translator_comment
+    entry += format_extracted_comment
+    entry += format_references
+    entry += format_flags
+    entry += <<-ENTRY
 msgid #{format_message(@msgid)}
 msgstr #{format_message(@msgstr)}
     ENTRY
@@ -75,9 +75,9 @@ def format_comment mark, comment
 
     formatted_comment = ''
     comment.each_line do |line|
-      formatted_comment << "#{mark} #{line}"
+      formatted_comment += "#{mark} #{line}"
     end
-    formatted_comment << "\n" unless formatted_comment.end_with?("\n")
+    formatted_comment += "\n" unless formatted_comment.end_with?("\n")
     formatted_comment
   end
 
@@ -94,7 +94,7 @@ def format_references
 
     formatted_references = ''
     @references.sort.each do |file, line|
-      formatted_references << "\#: #{file}:#{line}\n"
+      formatted_references += "\#: #{file}:#{line}\n"
     end
     formatted_references
   end
@@ -111,8 +111,8 @@ def format_message message
 
     formatted_message = '""'
     message.each_line do |line|
-      formatted_message << "\n"
-      formatted_message << "\"#{escape(line)}\""
+      formatted_message += "\n"
+      formatted_message += "\"#{escape(line)}\""
     end
     formatted_message
   end

lib/rdoc/i18n/text.rb

@@ -46,9 +46,9 @@ def translate(locale)
     parse do |part|
       case part[:type]
       when :paragraph
-        translated_text << locale.translate(part[:paragraph])
+        translated_text += locale.translate(part[:paragraph])
       when :empty_line
-        translated_text << part[:line]
+        translated_text += part[:line]
       else
         raise "should not reach here: unexpected type: #{type}"
       end
@@ -69,14 +69,14 @@ def parse(&block)
         if paragraph.empty?
           emit_empty_line_event(line, line_no, &block)
         else
-          paragraph << line
+          paragraph += line
           emit_paragraph_event(paragraph, paragraph_start_line, line_no,
                                &block)
           paragraph = ''
         end
       else
         paragraph_start_line = line_no if paragraph.empty?
-        paragraph << line
+        paragraph += line
       end
     end
 

lib/rdoc/markup/attribute_manager.rb

@@ -246,7 +246,7 @@ def add_special pattern, name
   # Processes +str+ converting attributes, HTML and specials
 
   def flow str
-    @str = str
+    @str = str.dup
 
     mask_protected_sequences
 

lib/rdoc/markup/parser.rb

@@ -249,15 +249,15 @@ def build_verbatim margin
 
     min_indent = nil
     generate_leading_spaces = true
-    line = ''
+    line = ''.dup
 
     until @tokens.empty? do
       type, data, column, = get
 
       if type == :NEWLINE then
         line << data
         verbatim << line
-        line = ''
+        line = ''.dup
         generate_leading_spaces = true
         next
       end

lib/rdoc/markup/pre_process.rb

@@ -105,7 +105,7 @@ def handle text, code_object = nil, &block
     # regexp helper (square brackets for optional)
     # $1      $2  $3        $4      $5
     # [prefix][\]:directive:[spaces][param]newline
-    text.gsub!(/^([ \t]*(?:#|\/?\*)?[ \t]*)(\\?):(\w+):([ \t]*)(.+)?(\r?\n|$)/) do
+    text = text.gsub(/^([ \t]*(?:#|\/?\*)?[ \t]*)(\\?):(\w+):([ \t]*)(.+)?(\r?\n|$)/) do
       # skip something like ':toto::'
       next $& if $4.empty? and $5 and $5[0, 1] == ':'
 
@@ -123,7 +123,11 @@ def handle text, code_object = nil, &block
       handle_directive $1, $3, $5, code_object, text.encoding, &block
     end
 
-    comment = text unless comment
+    if comment then
+      comment.text = text
+    else
+      comment = text
+    end
 
     self.class.post_processors.each do |handler|
       handler.call comment, code_object
@@ -212,7 +216,7 @@ def handle_directive prefix, directive, param, code_object = nil,
     when 'yield', 'yields' then
       return blankline unless code_object
       # remove parameter &block
-      code_object.params.sub!(/,?\s*&\w+/, '') if code_object.params
+      code_object.params = code_object.params.sub(/,?\s*&\w+/, '') if code_object.params
 
       code_object.block_params = param
 

lib/rdoc/markup/to_joined_paragraph.rb

@@ -29,7 +29,8 @@ def accept_paragraph paragraph
     paragraph.parts.each do |part|
       if String === part then
         if string then
-          string << part
+          string += part
+          parts[-1] = string
         else
           parts << part
           string = part

lib/rdoc/method_attr.rb

@@ -188,7 +188,7 @@ def find_method_or_attribute name # :nodoc:
       next if String === ancestor
       next if parent == ancestor
 
-      other = ancestor.find_method_named('#' << name) ||
+      other = ancestor.find_method_named('#' + name) ||
               ancestor.find_attribute_named(name)
 
       return other if other