diff --git a/Library/Homebrew/migrator.rb b/Library/Homebrew/migrator.rb
new file mode 100644
index 0000000000..5bd3c6c57a
--- /dev/null
+++ b/Library/Homebrew/migrator.rb
@@ -0,0 +1,303 @@
+require "formula"
+require "keg"
+require "tab"
+require "tap_migrations"
+
+class Migrator
+  class MigratorNoOldnameError < RuntimeError
+    def initialize(formula)
+      super "#{formula.name} doesn't replace any formula."
+    end
+  end
+
+  class MigratorNoOldpathError < RuntimeError
+    def initialize(formula)
+      super "#{HOMEBREW_CELLAR/formula.oldname} doesn't exist."
+    end
+  end
+
+  class MigratorDifferentTapsError < RuntimeError
+    def initialize(formula, tap)
+      if tap.nil?
+        super <<-EOS.undent
+        #{formula.name} from #{formula.tap} is given, but old name #{formula.oldname} wasn't installed from taps or core formulae
+
+        You can try `brew migrate --force #{formula.oldname}`.
+        EOS
+      else
+        user, repo = tap.split("/")
+        repo.sub!("homebrew-", "")
+        name = "fully-qualified #{user}/#{repo}/#{formula.oldname}"
+        name = formula.oldname if tap == "Homebrew/homebrew"
+        super <<-EOS.undent
+        #{formula.name} from #{formula.tap} is given, but old name #{formula.oldname} was installed from #{tap}
+
+        Please try to use #{name} to refer the formula
+        EOS
+      end
+    end
+  end
+
+  attr_reader :formula
+  attr_reader :oldname, :oldpath, :old_pin_record, :old_opt_record
+  attr_reader :old_linked_keg_record, :oldkeg, :old_tabs, :old_tap
+  attr_reader :newname, :newpath, :new_pin_record
+  attr_reader :old_pin_link_record
+
+  def initialize(formula)
+    @oldname = formula.oldname
+    @newname = formula.name
+    raise MigratorNoOldnameError.new(formula) unless oldname
+
+    @formula = formula
+    @oldpath = HOMEBREW_CELLAR/formula.oldname
+    raise MigratorNoOldpathError.new(formula) unless oldpath.exist?
+
+    @old_tabs = oldpath.subdirs.each.map { |d| Tab.for_keg(Keg.new(d)) }
+    @old_tap = old_tabs.first.tap
+    raise MigratorDifferentTapsError.new(formula, old_tap) unless from_same_taps?
+
+    @newpath = HOMEBREW_CELLAR/formula.name
+
+    if @oldkeg = get_linked_oldkeg
+      @old_linked_keg_record = oldkeg.linked_keg_record if oldkeg.linked?
+      @old_opt_record = oldkeg.opt_record if oldkeg.optlinked?
+    end
+
+    @old_pin_record = HOMEBREW_LIBRARY/"PinnedKegs"/oldname
+    @new_pin_record = HOMEBREW_LIBRARY/"PinnedKegs"/newname
+    @pinned = old_pin_record.symlink?
+    @old_pin_link_record = old_pin_record.readlink if @pinned
+  end
+
+  # Fix INSTALL_RECEIPTS for tap-migrated formula.
+  def fix_tabs
+    old_tabs.each do |tab|
+      tab.source["tap"] = formula.tap
+      tab.write
+    end
+  end
+
+  def from_same_taps?
+    if old_tap == nil && formula.core_formula? && ARGV.force?
+      true
+    elsif formula.tap == old_tap
+      true
+    # Homebrew didn't use to update tabs while performing tap-migrations,
+    # so there can be INSTALL_RECEIPT's containing wrong information about
+    # tap (tap is Homebrew/homebrew if installed formula migrates to a tap), so
+    # we check if there is an entry about oldname migrated to tap and if
+    # newname's tap is the same as tap to which oldname migrated, then we
+    # can perform migrations and the taps for oldname and newname are the same.
+    elsif TAP_MIGRATIONS && (rec = TAP_MIGRATIONS[formula.oldname]) \
+          && rec == formula.tap.sub("homebrew-", "")
+      fix_tabs
+      true
+    elsif formula.tap
+      false
+    end
+  end
+
+  def get_linked_oldkeg
+    kegs = oldpath.subdirs.map { |d| Keg.new(d) }
+    kegs.detect(&:linked?) || kegs.detect(&:optlinked?)
+  end
+
+  def pinned?
+    @pinned
+  end
+
+  def oldkeg_linked?
+    !!oldkeg
+  end
+
+  def migrate
+    if newpath.exist?
+      onoe "#{newpath} already exists; remove it manually and run brew migrate #{oldname}."
+      return
+    end
+
+    begin
+      oh1 "Migrating #{Tty.green}#{oldname}#{Tty.white} to #{Tty.green}#{newname}#{Tty.reset}"
+      unlink_oldname
+      move_to_new_directory
+      repin
+      link_newname
+      link_oldname_opt
+      link_oldname_cellar
+      update_tabs
+    rescue Interrupt
+      ignore_interrupts { backup_oldname }
+    rescue Exception => e
+      onoe "error occured while migrating."
+      puts e if ARGV.debug?
+      puts "Backuping..."
+      ignore_interrupts { backup_oldname }
+    end
+  end
+
+  # move everything from Cellar/oldname to Cellar/newname
+  def move_to_new_directory
+    puts "Moving to: #{newpath}"
+    FileUtils.mv(oldpath, newpath)
+  end
+
+  def repin
+    if pinned?
+      # old_pin_record is a relative symlink and when we try to to read it
+      # from <dir> we actually try to find file
+      # <dir>/../<...>/../Cellar/name/version.
+      # To repin formula we need to update the link thus that it points to
+      # the right directory.
+      # NOTE: old_pin_record.realpath.sub(oldname, newname) is unacceptable
+      # here, because it resolves every symlink for old_pin_record and then
+      # substitutes oldname with newname. It breaks things like
+      # Pathname#make_relative_symlink, where Pathname#relative_path_from
+      # is used to find relative path from source to destination parent and
+      # it assumes no symlinks.
+      src_oldname = old_pin_record.dirname.join(old_pin_link_record).expand_path
+      new_pin_record.make_relative_symlink(src_oldname.sub(oldname, newname))
+      old_pin_record.delete
+    end
+  end
+
+  def unlink_oldname
+    oh1 "Unlinking #{Tty.green}#{oldname}#{Tty.reset}"
+    oldpath.subdirs.each do |d|
+      keg = Keg.new(d)
+      keg.unlink
+    end
+  end
+
+  def link_newname
+    oh1 "Linking #{Tty.green}#{newname}#{Tty.reset}"
+    keg = Keg.new(formula.installed_prefix)
+
+    if formula.keg_only?
+      begin
+        keg.optlink
+      rescue Keg::LinkError => e
+        onoe "Failed to create #{formula.opt_prefix}"
+        puts e
+        raise
+      end
+      return
+    end
+
+    keg.remove_linked_keg_record if keg.linked?
+
+    begin
+      keg.link
+    rescue Keg::ConflictError => e
+      onoe "Error while executing `brew link` step on #{newname}"
+      puts e
+      puts
+      puts "Possible conflicting files are:"
+      mode = OpenStruct.new(:dry_run => true, :overwrite => true)
+      keg.link(mode)
+      raise
+    rescue Keg::LinkError => e
+      onoe "Error while linking"
+      puts e
+      puts
+      puts "You can try again using:"
+      puts "  brew link #{formula.name}"
+    rescue Exception => e
+      onoe "An unexpected error occurred during linking"
+      puts e
+      puts e.backtrace
+      ignore_interrupts { keg.unlink }
+      raise e
+    end
+  end
+
+  # Link keg to opt if it was linked before migrating.
+  def link_oldname_opt
+    if old_opt_record
+      old_opt_record.delete if old_opt_record.symlink? || old_opt_record.exist?
+      old_opt_record.make_relative_symlink(formula.installed_prefix)
+    end
+  end
+
+  # After migtaion every INSTALL_RECEIPT.json has wrong path to the formula
+  # so we must update INSTALL_RECEIPTs
+  def update_tabs
+    new_tabs = newpath.subdirs.map { |d| Tab.for_keg(Keg.new(d)) }
+    new_tabs.each do |tab|
+      tab.source["path"] = formula.path.to_s if tab.source["path"]
+      tab.write
+    end
+  end
+
+  # Remove opt/oldname link if it belongs to newname.
+  def unlink_oldname_opt
+    return unless old_opt_record
+    if old_opt_record.symlink? && formula.installed_prefix.exist? \
+              && formula.installed_prefix.realpath == old_opt_record.realpath
+      old_opt_record.unlink
+      old_opt_record.parent.rmdir_if_possible
+    end
+  end
+
+  # Remove oldpath if it exists
+  def link_oldname_cellar
+    oldpath.delete if oldpath.symlink? || oldpath.exist?
+    oldpath.make_relative_symlink(formula.rack)
+  end
+
+  # Remove Cellar/oldname link if it belongs to newname.
+  def unlink_oldname_cellar
+    if (oldpath.symlink? && !oldpath.exist?) || (oldpath.symlink? \
+          && formula.rack.exist? && formula.rack.realpath == oldpath.realpath)
+      oldpath.unlink
+    end
+  end
+
+  # Backup everything if errors occured while migrating.
+  def backup_oldname
+    unlink_oldname_opt
+    unlink_oldname_cellar
+    backup_oldname_cellar
+    backup_old_tabs
+
+    if pinned? && !old_pin_record.symlink?
+      src_oldname = old_pin_record.dirname.join(old_pin_link_record).expand_path
+      old_pin_record.make_relative_symlink(src_oldname)
+      new_pin_record.delete
+    end
+
+    if newpath.exist?
+      newpath.subdirs.each do |d|
+        newname_keg = Keg.new(d)
+        newname_keg.unlink
+        newname_keg.uninstall
+      end
+    end
+
+    if oldkeg_linked?
+      begin
+        # The keg used to be linked  and when we backup everything we restore
+        # Cellar/oldname, the target also gets restored, so we are able to
+        # create a keg using its old path
+        keg = Keg.new(Pathname.new(oldkeg.to_s))
+        keg.link
+      rescue Keg::LinkError
+        keg.unlink
+        raise
+      rescue Keg::AlreadyLinkedError
+        keg.unlink
+        retry
+      end
+    end
+  end
+
+  def backup_oldname_cellar
+    unless oldpath.exist?
+      FileUtils.mv(newpath, oldpath)
+    end
+  end
+
+  def backup_old_tabs
+    old_tabs.each(&:write)
+  end
+end