instance method set_root_path!

# File railties/lib/initializer.rb, line 890
    def set_root_path!
      raise 'RAILS_ROOT is not set' unless defined?(::RAILS_ROOT)
      raise 'RAILS_ROOT is not a directory' unless File.directory?(::RAILS_ROOT)

      @root_path =
        # Pathname is incompatible with Windows, but Windows doesn't have
        # real symlinks so File.expand_path is safe.
        if RUBY_PLATFORM =~ /(:?mswin|mingw)/
          File.expand_path(::RAILS_ROOT)

        # Otherwise use Pathname#realpath which respects symlinks.
        else
          Pathname.new(::RAILS_ROOT).realpath.to_s
        end

      Object.const_set(:RELATIVE_RAILS_ROOT, ::RAILS_ROOT.dup) unless defined?(::RELATIVE_RAILS_ROOT)
      ::RAILS_ROOT.replace @root_path
    end