Issue #22341 has been updated by dug (Doug E). I opened https://github.com/ruby/ruby/pull/19267, which removes the assertion as suggested in #note-1. Debug builds now raise `TypeError` ("uninitialized class") like release builds do, and there's a regression test in `TestClass#test_uninitialized`. It doesn't make `include` raise on an uninitialized class. I'm happy to do that in a follow-up, if desired. ---------------------------------------- Bug #22341: Class#superclass can crash the interpreter in debug build https://bugs.ruby-lang.org/issues/22341#change-119400 * Author: tekknolagi (Maxwell Bernstein) * Status: Open * Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- While implementing this in ZJIT, @nirvdrum reported, and I investigated, a potential interpreter crash: module M; end C = Class.allocate C.include M C.superclass In a debug build, this crashes: plum% ./build-dev/miniruby crash.rb ../object.c:2398: Assertion Failed: rb_class_superclass:!RCLASS_SUPER(klass) ruby 4.1.0dev (2026-09-22T14:09:58Z mb-class-superclass 05c0248e3a) +PRISM [arm64-darwin25] -- Crash Report log information -------------------------------------------- See Crash Report log file in one of the following locations: * ~/Library/Logs/DiagnosticReports * /Library/Logs/DiagnosticReports for more details. Don't forget to include the above Crash Report log file in bug reports. -- Control frame information ----------------------------------------------- c:0003 p:---- s:0010 e:000009 l:y b:0001 r:0x0 CFUNC :superclass c:0002 p:0027 s:0006 e:000005 l:n b:---- r:0x0 EVAL crash.rb:4 [FINISH] c:0001 p:0000 s:0003 E:001fc8 l:y b:---- r:0x0 DUMMY [FINISH] -- Ruby level backtrace information ---------------------------------------- crash.rb:4:in '<main>' crash.rb:4:in 'superclass' -- Threading information --------------------------------------------------- Total ractor count: 1 Ruby thread count for this ractor: 1 -- C level backtrace information ------------------------------------------- /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_print_backtrace+0x24) [0x100b210c4] /Users/emacs/Documents/code/ruby/build-dev/../vm_dump.c:1113 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_print_backtrace) (null):0 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_vm_bugreport+0x3ac) [0x100b21490] /Users/emacs/Documents/code/ruby/build-dev/../vm_dump.c:1479 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_assert_failure_detail+0x138) [0x10079c6b4] /Users/emacs/Documents/code/ruby/build-dev/../error.c:1258 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_assert_failure_detail+0x0) [0x10079c57c] /Users/emacs/Documents/code/ruby/build-dev/../error.c:1234 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_assert_failure) (null):0 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_class_superclass+0x254) [0x1008b1d18] /Users/emacs/Documents/code/ruby/build-dev/../object.c:2398 /Users/emacs/Documents/code/ruby/build-dev/miniruby(ractor_safe_call_cfunc_0+0x30) [0x100b0a8bc] ../vm_insnhelper.c:3720 /Users/emacs/Documents/code/ruby/build-dev/miniruby(vm_call_cfunc_with_frame_+0x290) [0x100af8900] ../vm_insnhelper.c:3904 /Users/emacs/Documents/code/ruby/build-dev/miniruby(vm_call_cfunc_with_frame+0x6c) [0x100af8bfc] ../vm_insnhelper.c:3950 /Users/emacs/Documents/code/ruby/build-dev/miniruby(vm_call_cfunc_other+0x38c) [0x100af84d0] ../vm_insnhelper.c:3976 /Users/emacs/Documents/code/ruby/build-dev/miniruby(vm_call_cfunc+0x128) [0x100aede50] ../vm_insnhelper.c:4058 /Users/emacs/Documents/code/ruby/build-dev/miniruby(vm_call_method_each_type+0x200) [0x100aecf90] ../vm_insnhelper.c:4896 /Users/emacs/Documents/code/ruby/build-dev/miniruby(vm_call_method+0xe8) [0x100aecba4] ../vm_insnhelper.c:5022 /Users/emacs/Documents/code/ruby/build-dev/miniruby(vm_call_general+0x28) [0x100a9b1f8] ../vm_insnhelper.c:5066 /Users/emacs/Documents/code/ruby/build-dev/miniruby(vm_sendish+0x708) [0x100ab4424] ../vm_insnhelper.c:6283 /Users/emacs/Documents/code/ruby/build-dev/miniruby(vm_exec_core) ../insns.def:911 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_vm_exec+0x118) [0x100a9c92c] /Users/emacs/Documents/code/ruby/build-dev/../vm.c:2901 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_iseq_eval_main+0x34) [0x100adef20] /Users/emacs/Documents/code/ruby/build-dev/../vm.c:3254 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_ec_exec_node+0x100) [0x1007ac1f8] /Users/emacs/Documents/code/ruby/build-dev/../eval.c:300 /Users/emacs/Documents/code/ruby/build-dev/miniruby(ruby_run_node+0x94) [0x1007ac0ac] /Users/emacs/Documents/code/ruby/build-dev/../eval.c:338 /Users/emacs/Documents/code/ruby/build-dev/miniruby(rb_main+0x40) [0x10067ca2c] /Users/emacs/Documents/code/ruby/build-dev/../main.c:42 /Users/emacs/Documents/code/ruby/build-dev/miniruby(main+0x70) [0x10067c9b8] /Users/emacs/Documents/code/ruby/build-dev/../main.c:62 -- https://bugs.ruby-lang.org/