Set the root_path to RAILS_ROOT and canonicalize it.

Source Code

# File initializer.rb, line 502
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