Bug #11205: Problem with __dir__ or it's description

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN

[gam3 (Allen Morris)]

Kernel#__dir__

Returns the canonicalized absolute path of the directory of the file from which this method is called. It means symlinks in the path is resolved. If __FILE__ is nil, it returns nil. The return value equals to File.dirname(File.realpath(__FILE__)).

Here is a script that shows the problem.

def mytest(&block)
  ret = block.binding.eval( '[ __FILE__, __dir__ ]' )
  assert_equal("bill", __dir__)
end
dir = __dir__
eval(%q(
  ret = mytest { }
  ret[0] == '/bill/bill'
  ret[1] == dir          # where it shoudl == '/bill'
  # 
), nil, '/bill/bill', 1)

Even without the binding problem it is clear from the current ruby tests that
__dir__ is not equal to File.realpath(__FILE__).

  def test___dir__
    assert_instance_of String, __dir__
    assert_equal(File.dirname(File.realpath(__FILE__)), __dir__)
    bug8436 = '[ruby-core:55123] [Bug #8436]'
    assert_equal(__dir__, eval("__dir__", binding), bug8436)
    bug8662 = '[ruby-core:56099] [Bug #8662]'
    assert_equal("arbitrary", eval("__dir__", binding, "arbitrary/file.rb"), bug8662)
    assert_equal("arbitrary", Object.new.instance_eval("__dir__", "arbitrary/file.rb"), bug8662)
  end

possible solution:
Fix eval so that it never affects Kernel#__dir__ and add a Kernel#__file__ method and rewrite the description as:

Kernel#__dir__

Returns the canonicalized absolute path of the directory of the file from which this method is called. It means symlinks in the path is resolved. The return value equals to File.dirname(File.realpath(__file__)).

And a definition for __file__

Kernel#__file__

Returns the canonicalized absolute path of the directory of the file from which this method is called. It means symlinks in the path is resolved. The return value equals to File.dirname(File.realpath(__file__)).
Note: __file__ is equal to __FILE__ except inside of #eval and #eval_instance.

This assumes that the purpose of __dir__ is to find files in the current filesystem, and not for the purpose of debugging.

[gam3 (Allen Morris)]

• Assignee set to core

[gam3 (Allen Morris)]

Note that require_relative uses __dir__ as the base to generate an absolute path.

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

[naruse (Yui NARUSE)]

• Assignee deleted (core)

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed

I don't think this is a bug in __dir__. It's just that __FILE__ inside eval depends on either the binding or file argument given to eval (in Ruby 3, it will only depend on the file argument, see #4352).

If you rewrite your example to correctly set __FILE__ inside the call to eval in mytest:

def mytest(&block)
  block.binding.eval( '[ __FILE__, __dir__ ]', block.binding.local_variable_get('f'))
end
eval(%q( f = __FILE__; p mytest {}), nil, '/bill/bill', 1)

You can see that __dir__ is accurate, as the output of the program is:

["/bill/bill", "/bill"]