Issue #6324 has been reported by jrochkind (jonathan rochkind).

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Bug #6324: Spurious/incorrect warning on File.open with internal_encoding specified in string mode to duplicate external_encoding
https://bugs.ruby-lang.org/issues/6324

Author: jrochkind (jonathan rochkind)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: ruby 1.9.3p125 (2012-02-16 revision 34643) [x86_64-linux]


Normally, if you open a File specifying an internal_encoding equivalent to an external_encoding, using the string method, it gives you a warning. _Normally_ this warning is possibly appropriate and accurate:



   irb(main):018:0* f = File.open("test", "r:cp866:cp866")
   (irb):18: warning: Ignoring internal encoding cp866: it is identical to external encoding cp866

However, there is a case where it is NOT. If you have set your Encoding.default_internal

   irb(main):019:0> Encoding.default_internal = "UTF-8"
   irb(main):020:0> f = File.open("test", "r:cp866:cp866")
   (irb):20: warning: Ignoring internal encoding cp866: it is identical to external encoding cp866

In this case, it is neccesary to set the internal_encoding to override the non-nil Encoding.default_internal

The functionality in fact _works_ here, we HAVE succesfully over-ridden the default_internal:

   irb(main):022:0> p f.internal_encoding
   => nil
   irb(main):023:0> f.read.encoding
   => #<Encoding:IBM866>

So the warning is in fact _wrong_, the :internal_encoding was NOT ignored, it was used as desired. The warning is also unneccesary, what was being done here makes perfect sense, there's no need for a warning. 

Note that the named argument approach works differnetly, no warning is output (whether or not you've set Encoding.default_internal). 


    irb(main):024:0> f = File.open("foo", :external_encoding => "cp866", :internal_encoding => "cp866")
    => #<File:foo>  # NO WARNING OUTPUT
    irb(main):025:0> f.internal_encoding
    => nil # CORRECT
    irb(main):026:0> f.read.encoding
    => #<Encoding:IBM866> # CORRECT

Both the named argument and the permission-string method seem to work properly and equivalently. But only the permission-string argument method gives you an incorrect warning. 




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