variable.c: handle cleared fields_obj in genfields cache

[Bug #21547]

Followup: ruby#14201

When adding an instance variable and the IMEMO/fields need to be
larger, we allocate a new one and clear the old one.

Since the old one may still be in other ec's cache, on a hit we must
check the IMEMO/fields isn't a stale one.

Author: byroot

depend

@@ -6306,6 +6306,7 @@ imemo.$(OBJEXT): $(top_srcdir)/internal/compilers.h
 imemo.$(OBJEXT): $(top_srcdir)/internal/gc.h
 imemo.$(OBJEXT): $(top_srcdir)/internal/imemo.h
 imemo.$(OBJEXT): $(top_srcdir)/internal/namespace.h
+imemo.$(OBJEXT): $(top_srcdir)/internal/object.h
 imemo.$(OBJEXT): $(top_srcdir)/internal/sanitizers.h
 imemo.$(OBJEXT): $(top_srcdir)/internal/serial.h
 imemo.$(OBJEXT): $(top_srcdir)/internal/set_table.h
@@ -7159,7 +7160,6 @@ iseq.$(OBJEXT): $(top_srcdir)/prism/pack.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/parser.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/prettyprint.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/prism.h
-iseq.$(OBJEXT): $(top_srcdir)/prism/prism.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/regexp.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/static_literals.h
 iseq.$(OBJEXT): $(top_srcdir)/prism/util/pm_buffer.h
@@ -11676,7 +11676,6 @@ prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
 prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
 prism/prism.$(OBJEXT): $(top_srcdir)/prism/util/pm_strpbrk.h
 prism/prism.$(OBJEXT): $(top_srcdir)/prism/version.h
-prism/prism.$(OBJEXT): $(top_srcdir)/prism/version.h
 prism/regexp.$(OBJEXT): $(top_srcdir)/prism/ast.h
 prism/regexp.$(OBJEXT): $(top_srcdir)/prism/defines.h
 prism/regexp.$(OBJEXT): $(top_srcdir)/prism/encoding.h

imemo.c

@@ -3,6 +3,7 @@
 #include "id_table.h"
 #include "internal.h"
 #include "internal/imemo.h"
+#include "internal/object.h"
 #include "internal/st.h"
 #include "vm_callinfo.h"
 
@@ -208,6 +209,8 @@ rb_imemo_fields_clear(VALUE fields_obj)
     else {
         RBASIC_SET_SHAPE_ID(fields_obj, ROOT_SHAPE_ID);
     }
+    // Invalidate the ec->gen_fields_cache.
+    RBASIC_CLEAR_CLASS(fields_obj);
 }
 
 /* =========================================================================

test/ruby/test_variable.rb

@@ -447,6 +447,19 @@ def test_local_variables_encoding
     assert_equal(%i[α b], b.local_variables)
   end
 
+  def test_genivar_cache
+    bug21547 = '[Bug #21547]'
+    klass = Class.new(Array)
+    instance = klass.new
+    instance.instance_variable_set(:@a1, 1)
+    instance.instance_variable_set(:@a2, 2)
+    Fiber.new do
+      instance.instance_variable_set(:@a3, 3)
+      instance.instance_variable_set(:@a4, 4)
+    end.resume
+    assert_equal 4, instance.instance_variable_get(:@a4)
+  end
+
   private
   def with_kwargs_11(v1:, v2:, v3:, v4:, v5:, v6:, v7:, v8:, v9:, v10:, v11:)
     local_variables

variable.c

@@ -1247,7 +1247,7 @@ rb_obj_fields(VALUE obj, ID field_name)
           generic_fields:
             {
                 rb_execution_context_t *ec = GET_EC();
-                if (ec->gen_fields_cache.obj == obj) {
+                if (ec->gen_fields_cache.obj == obj && rb_imemo_fields_owner(ec->gen_fields_cache.fields_obj) == obj) {
                     fields_obj = ec->gen_fields_cache.fields_obj;
                 }
                 else {