Issue #19166 has been reported by alanwu (Alan Wu). ---------------------------------------- Bug #19166: Module#remove_method can change frozen modules when there is a prepended module https://bugs.ruby-lang.org/issues/19166 * Author: alanwu (Alan Wu) * Status: Open * Priority: Normal * ruby -v: 2.7, 3.0, 3.1, dev * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN ---------------------------------------- ```ruby module A prepend Module.new # remove this line and you'd get FrozenError as expected def foo; end freeze remove_method :foo # remove works even though module is frozen! p instance_methods(false) # => [] end ``` Old bug, reproduces in 2.7 through 3.1 and on master. Found while investigating #19164. -- https://bugs.ruby-lang.org/