Issue #18995 has been updated by javanthropus (Jeremy Bopp). @nobu, may I ask you to take a look at this? ---------------------------------------- Bug #18995: IO#set_encoding sometimes set an IO's internal encoding to the default external encoding https://bugs.ruby-lang.org/issues/18995#change-117891 * Author: javanthropus (Jeremy Bopp) * Status: Open * ruby -v: ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux] * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN ---------------------------------------- This script demonstrates the behavior: ```ruby def show(io) printf( "external encoding: %-25p internal encoding: %-25p\n", io.external_encoding, io.internal_encoding ) end Encoding.default_external = 'iso-8859-1' Encoding.default_internal = 'iso-8859-2' File.open('/dev/null') do |f| f.set_encoding('utf-8', nil) show(f) # f.internal_encoding is iso-8859-2, as expected f.set_encoding('utf-8', 'invalid') show(f) # f.internal_encoding is now iso-8859-1! Encoding.default_external = 'iso-8859-3' Encoding.default_internal = 'iso-8859-4' show(f) # f.internal_encoding is now iso-8859-3! end ``` In the 1st case, we see that the IO's internal encoding is set to the current setting of Encoding.default_internal. In the 2nd case, the IO's internal encoding is set to Encoding.default_external instead. The 3rd case is more interesting because it shows that the IO's internal encoding is actually following the current setting of Encoding.default_external. It didn't just copy it when #set_encoding was called. It changes whenever Encoding.default_external changes. What should the correct behavior be? -- https://bugs.ruby-lang.org/