From b42c8398ba84437cd6e96cbf6ccaf5ac5eff32b6 Mon Sep 17 00:00:00 2001
From: Max Bernstein <max.bernstein@shopify.com>
Date: Mon, 28 Apr 2025 14:54:39 -0400
Subject: [PATCH] Don't support blockarg in opt_new

We don't calculate the correct argc so the bookkeeping slot is something
else (unexpected) instead of Qnil (expected).
---
 insns.def       | 4 +++-
 prism_compile.c | 3 ++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/insns.def b/insns.def
index b0c74df220..ba71e9f856 100644
--- a/insns.def
+++ b/insns.def
@@ -916,11 +916,13 @@ opt_new
     VALUE argc = vm_ci_argc(cd->ci);
     VALUE val = TOPN(argc);
 
+    // The bookkeeping slot should be empty.
+    RUBY_ASSERT(TOPN(argc + 1) == Qnil);
+
     if (vm_method_cfunc_is(GET_ISEQ(), cd, val, rb_class_new_instance_pass_kw) && !(ruby_vm_event_flags & ISEQ_TRACE_EVENTS)) {
         RB_DEBUG_COUNTER_INC(opt_new_hit);
         val = rb_obj_alloc(val);
         TOPN(argc) = val;
-        RUBY_ASSERT(TOPN(argc + 1) == Qnil);
         TOPN(argc + 1) = val;
     }
     else {
diff --git a/prism_compile.c b/prism_compile.c
index 3688a1e515..71361e9aa9 100644
--- a/prism_compile.c
+++ b/prism_compile.c
@@ -3722,7 +3722,8 @@ pm_compile_call(rb_iseq_t *iseq, const pm_call_node_t *call_node, LINK_ANCHOR *c
 
     bool inline_new = ISEQ_COMPILE_DATA(iseq)->option->specialized_instruction &&
         method_id == rb_intern("new") &&
-        call_node->block == NULL;
+        call_node->block == NULL &&
+        (flags & VM_CALL_ARGS_BLOCKARG) == 0;
 
     if (inline_new) {
         if (LAST_ELEMENT(ret) == opt_new_prelude) {