RCR 211: Normalize filenames before requiring them

Consider the following code:

  a.rb:

  puts "a"</pre>
  b.rb:

  require 'a'
  puts "b"</pre>
  test.rb:

  require './a'
  require './b'</pre>

This will print:

  a

  a
  b</pre>

because a.rb is loaded first by the name 'a.rb' and then by the name './a.rb'.
This is probably not what is intended, and the only workarounds are:

• be careful never to require a file by two different names, or
• put require guards inside a.rb (similar to #include guards in C)

The above code is probably not a good idea to begin with (requring files from the current directory is bad, in case the user runs from a different directory than expected), but it is a simple way to demonstrate the problem.

1. Find the file to require by searching the search path
2. Expand the pathanme of the file being required by using File#expand_path
3. Determine if the resulting pathname refers to a symlink; if it does, then read the link and go back to step 2.

def find_file_in_path(file, path=$:, extensions=['', '.so', '.rb'])

  path.each do |dir|
    pathname = File.join(dir, file)
    extensions.each do |ext|
      filename = pathname + ext
      if File.exists?(filename) then
        return File.expand_path(filename)
      end
    end
  end
  return file

end

def realpath(file)

  if not File.respond_to?(:readlink) then
    return file
  end
  total = ''
  File.expand_path(file).split(File::SEPARATOR).each do |piece|
    next if piece == ""
    if File.symlink?(total + File::SEPARATOR + piece) then
      total += File::SEPARATOR + piece
      begin
        total =  File.expand_path(
            File.readlink(total),
            File.dirname(total))
      end while File.symlink?(total)
    else
      total << File::SEPARATOR + piece
    end
  end
  return total

end

$__old_require__ = method(:require)

def require(file)

  file_to_require = find_file_in_path(file)
  $__old_require__.call(realpath(file_to_require))

end