Issue #21561 has been updated by byroot (Jean Boussier). Backport changed from 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN to 3.2: WONTFIX, 3.3: REQUIRED, 3.4: REQUIRED

The source problem is the encoding US-ASCII for "."

Yes, but `File.expand_path` behavior is also suspicious. Either way, I think returning a different encoding in a special case isn't a good idea. So I'm in favor of always using the same logic for the encoding selection: https://github.com/ruby/ruby/pull/14472 ---------------------------------------- Bug #21561: Wrong encoding for File.dirname result on Windows https://bugs.ruby-lang.org/issues/21561#change-114519 * Author: thyresias (Thierry Lambert) * Status: Open * ruby -v: ruby 3.4.5 (2025-07-16 revision 20cda200d3) +PRISM [x64-mingw-ucrt] * Backport: 3.2: WONTFIX, 3.3: REQUIRED, 3.4: REQUIRED ---------------------------------------- I placed the file containing the code below in a directory named "à_signaler" to show the effect on non-ascii characters: ```ruby def dirname_encoding(file) h = { "file" => file, "File.dirname(file)" => File.dirname(file), "File.expand_path(file)" => File.expand_path(file), "File.expand_path(File.dirname(file))" => File.expand_path(File.dirname(file)), "File.dirname(File.expand_path(file))" => File.dirname(File.expand_path(file)), } puts h.each do |name, value| puts "#{name} = #{value.inspect} (#{value.encoding})" end end dirname_encoding "foo.bar" dirname_encoding "foo/bar" ``` The result: ``` file = "foo.bar" (UTF-8) File.dirname(file) = "." (US-ASCII) File.expand_path(file) = "D:/à_signaler/foo.bar" (UTF-8) File.expand_path(File.dirname(file)) = "D:/\xE0_signaler" (US-ASCII) File.dirname(File.expand_path(file)) = "D:/à_signaler" (UTF-8) file = "foo/bar" (UTF-8) File.dirname(file) = "foo" (UTF-8) File.expand_path(file) = "D:/à_signaler/foo/bar" (UTF-8) File.expand_path(File.dirname(file)) = "D:/à_signaler/foo" (UTF-8) File.dirname(File.expand_path(file)) = "D:/à_signaler/foo" (UTF-8) ``` The source problem is the encoding US-ASCII for "." This may be linked to Bug #20699. -- https://bugs.ruby-lang.org/