From: "naruse (Yui NARUSE)" <noreply@...>
Date: 2022-11-21T12:22:19+00:00
Subject: [ruby-core:110832] [Ruby master Bug#18899] Inconsistent argument handling in IO#set_encoding

Issue #18899 has been updated by naruse (Yui NARUSE).


I think your example needs to be as follows:
```ruby
#!/usr/bin/env ruby

def show(io, args)
  printf(
    "args: %-50s  external encoding: %-25s  internal encoding: %-25s\n",
    args.inspect,
    io.external_encoding.inspect,
    io.internal_encoding.inspect
  )
end

File.open('/dev/null', 'r:binary:utf-8') do |f|
  args = ['r:binary:utf-8']
  show(f, args)

  args = ['binary:utf-8']
  f.set_encoding(*args)
  show(f, args)

  args = ['binary', 'utf-8']
  f.set_encoding(*args)
  show(f, args)

  args = [Encoding.find('binary'), Encoding.find('utf-8')]
  f.set_encoding(*args)
  show(f, args)
end
```
The result will be
```
args: ["r:binary:utf-8"]                                  external encoding: #<Encoding:ASCII-8BIT>     internal encoding: nil
args: ["binary:utf-8"]                                    external encoding: #<Encoding:ASCII-8BIT>     internal encoding: nil
args: ["binary", "utf-8"]                                 external encoding: #<Encoding:ASCII-8BIT>     internal encoding: #<Encoding:UTF-8>
args: [#<Encoding:ASCII-8BIT>, #<Encoding:UTF-8>]         external encoding: #<Encoding:ASCII-8BIT>     internal encoding: #<Encoding:UTF-8>
```

----------------------------------------
Bug #18899: Inconsistent argument handling in IO#set_encoding
https://bugs.ruby-lang.org/issues/18899#change-100190

* Author: javanthropus (Jeremy Bopp)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`IO#set_encoding` behaves differently when processing a single String argument than it does when processing 2 arguments (whether Strings or Encodings) in the case where the external encoding is being set to binary and the internal encoding is being set to any other encoding.

This script demonstrates the resulting values of the external and internal encodings for an IO instance given different ways to equivalently call `#set_encoding`:

```ruby
#!/usr/bin/env ruby


def show(io, args)
  printf(
    "args: %-50s  external encoding: %-25s  internal encoding: %-25s\n",
    args.inspect,
    io.external_encoding.inspect,
    io.internal_encoding.inspect
  )
end

File.open('/dev/null') do |f|
  args = ['binary:utf-8']
  f.set_encoding(*args)
  show(f, args)

  args = ['binary', 'utf-8']
  f.set_encoding(*args)
  show(f, args)

  args = [Encoding.find('binary'), Encoding.find('utf-8')]
  f.set_encoding(*args)
  show(f, args)
end
```

This behavior is the same from Ruby 2.7.0 to 3.1.2.



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