Issue #21565 has been updated by k0kubun (Takashi Kokubun). We've modified the assertion failure message https://github.com/ruby/ruby/pull/14480 to debug this further. I'll release Ruby 3.4.6 early next week with that patch, so it'd be nice to see an updated error report once you encounter that with the new Ruby version. ---------------------------------------- Bug #21565: YJIT has panicked in rails https://bugs.ruby-lang.org/issues/21565#change-114525 * Author: eiskrenkov (Egor Iskrenkov) * Status: Assigned * Assignee: jit * ruby -v: ruby 3.4.5 (2025-07-16 revision 20cda200d3) +PRISM [arm64-darwin24] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- I've got YJIT has panicked crash in rails app locally on my M1 Pro Mac Book pro for 2 times for last 2 weeks ``` Started GET "/api/admin/environments/13/edit" for ::1 at 2025-09-08 18:32:17 +0200 Processing by Api::Admin::EnvironmentsController#edit as JSON Parameters: {"id" => "13", "environment" => {}} ruby: YJIT has panicked. More info to follow... thread '<unnamed>' panicked at ./yjit/src/codegen.rs:5031:9: assertion failed: !val_type.is_imm() stack backtrace: 0: _rust_begin_unwind 1: core::panicking::panic_fmt 2: core::panicking::panic 3: yjit::codegen::jit_guard_known_klass 4: yjit::codegen::gen_equality_specialized 5: yjit::codegen::gen_opt_eq 6: yjit::codegen::gen_single_block 7: yjit::core::gen_block_series 8: yjit::core::branch_stub_hit_body 9: yjit::stats::with_compile_time 10: yjit::cruby::with_vm_lock 11: yjit::core::branch_stub_hit note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. /Users/eiskrenkov/.local/share/mise/installs/ruby/3.4.5/lib/ruby/gems/3.4.0/gems/actionpack-8.0.2.1/lib/action_dispatch/request/session.rb:118: [BUG] YJIT: panicked at ./yjit/src/codegen.rs:5031:9: assertion failed: !val_type.is_imm() ruby 3.4.5 (2025-07-16 revision 20cda200d3) +YJIT +PRISM [arm64-darwin24] ``` It happens randomly, I couldn't find reproduction steps sadly ---Files-------------------------------- ruby-2025-09-08-183231.ips (45.3 KB) -- https://bugs.ruby-lang.org/