Issue #8445 has been reported by pjmtdw (Haruhiro Yoshimoto).

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Bug #8445: IO.open and IO#set_enconding does not support :fallback option
https://bugs.ruby-lang.org/issues/8445

Author: pjmtdw (Haruhiro Yoshimoto)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: trunk(ruby 2.1.0dev)
Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN


RubyDoc says that IO.open and IO#set_encoding supports optional argument defined in String#encode.
http://ruby-doc.org/core-2.0/IO.html#method-c-new-label-Options
In fact, :invalid, :undef and :replace works as expected.

However, :fallback option does not work neither for IO.open and IO#set_encoding.
Following is the example code which does not work.
f(x) is never called even if hoge.txt contains non convertible character.

File.open("./hoge.txt","r:Shift_JIS:utf-8", :fallback => lambda{|x|f(x)}){|f|
  ...
}
File.open("./hoge.txt"){|f|
  f.set_encoding("Shift_JIS","utf-8",:fallback => lambda{|x|f(x)})
  ...
}

I Think this is because fill_cbuf() in io.c calls rb_econv_convert() from transcode.c directly.
On the other hand, fallback_func is called in transcode_loop(), which is called by str_encode(). 

Since transcode_loop() also calls rb_econv_convert(), I wrote a small patch which moves some codes from
transcode_loop() to rb_econv_convert() to fix the problem.

The attached file is the patch. Hope this helps.



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