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Bug #12340
closedWindows: File.truncate has two string encoding issues
    Bug #12340:
    Windows: File.truncate has two string encoding issues
  
Description
File.truncate calls rb_str_encode_ospath() which returns a UTF-8 encoded Ruby string.
Then it passes a pointer to the underlying C string to truncate() aka rb_w32_truncate().
At last the UTF-8 string is passed to CreateFile() aka CreateFileA() (ANSI).
This also means it doesn't support Unicode unlike (hopefully all) other File singleton methods.
s = "\u2603"
IO.write(s, '123')
File.truncate(s, 0)  # Errno::ENOENT: No such file or directory @ rb_file_s_truncate - ☃
A possible fix is attached. I'm not sure about the test code. I also couldn't find any similar tests. The actual fix should be fine however.
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