Fix Ractor sharing for too complex generic ivars

ractor.c

@@ -2739,6 +2739,19 @@ obj_traverse_rec(struct obj_traverse_data *data)
     return data->rec;
 }
 
+static int
+obj_traverse_ivar_foreach_i(ID key, VALUE val, st_data_t ptr)
+{
+    struct obj_traverse_callback_data *d = (struct obj_traverse_callback_data *)ptr;
+
+    if (obj_traverse_i(val, d->data)) {
+        d->stop = true;
+        return ST_STOP;
+    }
+
+    return ST_CONTINUE;
+}
+
 static int
 obj_traverse_i(VALUE obj, struct obj_traverse_data *data)
 {
@@ -2755,14 +2768,12 @@ obj_traverse_i(VALUE obj, struct obj_traverse_data *data)
         return 0;
     }
 
-    if (UNLIKELY(FL_TEST_RAW(obj, FL_EXIVAR))) {
+    struct obj_traverse_callback_data d = {
-        struct gen_ivtbl *ivtbl;
+        .stop = false,
-        rb_ivar_generic_ivtbl_lookup(obj, &ivtbl);
+        .data = data,
-        for (uint32_t i = 0; i < ivtbl->as.shape.numiv; i++) {
+    };
-            VALUE val = ivtbl->as.shape.ivptr[i];
+    rb_ivar_foreach(obj, obj_traverse_ivar_foreach_i, (st_data_t)&d);
-            if (!UNDEF_P(val) && obj_traverse_i(val, data)) return 1;
+    if (d.stop) return 1;
-        }
-    }
 
     switch (BUILTIN_TYPE(obj)) {
       // no child node
@@ -3229,12 +3240,29 @@ obj_traverse_replace_i(VALUE obj, struct obj_traverse_replace_data *data)
     if (UNLIKELY(FL_TEST_RAW(obj, FL_EXIVAR))) {
         struct gen_ivtbl *ivtbl;
         rb_ivar_generic_ivtbl_lookup(obj, &ivtbl);
+
+        if (UNLIKELY(rb_shape_obj_too_complex(obj))) {
+            struct obj_traverse_replace_callback_data d = {
+                .stop = false,
+                .data = data,
+                .src = obj,
+            };
+            rb_st_foreach_with_replace(
+                ivtbl->as.complex.table,
+                obj_iv_hash_traverse_replace_foreach_i,
+                obj_iv_hash_traverse_replace_i,
+                (st_data_t)&d
+            );
+            if (d.stop) return 1;
+        }
+        else {
             for (uint32_t i = 0; i < ivtbl->as.shape.numiv; i++) {
                 if (!UNDEF_P(ivtbl->as.shape.ivptr[i])) {
                     CHECK_AND_REPLACE(ivtbl->as.shape.ivptr[i]);
                 }
             }
         }
+    }
 
     switch (BUILTIN_TYPE(obj)) {
       // no child node

test/ruby/test_shapes.rb

@@ -621,6 +621,24 @@ class TestShapes < Test::Unit::TestCase
     end;
   end
 
+  def test_too_complex_generic_ivar_ractor_share
+    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      $VERBOSE = nil
+
+      RubyVM::Shape.exhaust_shapes
+
+      r = Ractor.new do
+        o = []
+        o.instance_variable_set(:@a, "hello")
+        Ractor.yield(o)
+      end
+
+      o = r.take
+      assert_equal "hello", o.instance_variable_get(:@a)
+    end;
+  end
+
   def test_read_iv_after_complex
     ensure_complex