YJIT: Abort expandarray optimization if method_missing is defined

Author: rwstauner

bootstraptest/test_yjit.rb

@@ -2680,6 +2680,22 @@ def expandarray_redefined_nilclass
   expandarray_redefined_nilclass
 }
 
+assert_equal 'not_array', %q{
+  def expandarray_not_array(obj)
+    a, = obj
+    a
+  end
+
+  obj = Object.new
+  def obj.method_missing(m, *args, &block)
+    return [:not_array] if m == :to_ary
+    super
+  end
+
+  expandarray_not_array(obj)
+  expandarray_not_array(obj)
+}
+
 assert_equal '[1, 2, nil]', %q{
   def expandarray_rhs_too_small
     a, b, c = [1, 2]

yjit/src/codegen.rs

@@ -2270,6 +2270,13 @@ fn gen_expandarray(
             return None;
         }
 
+        // If method_missing is overridden, the object might respond to to_ary
+        // so we can't assume to_ary won't be called.
+        if !assume_method_basic_definition(jit, asm, comptime_recv.class_of(), ID!(method_missing)) {
+            gen_counter_incr(jit, asm, Counter::expandarray_to_ary);
+            return None;
+        }
+
         // invalidate compile block if to_ary is later defined
         jit.assume_method_lookup_stable(asm, target_cme);
 

yjit/src/cruby.rs

@@ -816,6 +816,7 @@ pub(crate) mod ids {
     def_ids! {
         name: NULL               content: b""
         name: respond_to_missing content: b"respond_to_missing?"
+        name: method_missing     content: b"method_missing"
         name: to_ary             content: b"to_ary"
         name: to_s               content: b"to_s"
         name: eq                 content: b"=="