Add variation_count on classes

Count how many "variations" each class creates. A "variation" is a a
unique ordering of instance variables on a particular class. This can
also be thought of as a branch in the shape tree.

For example, the following Foo class will have 2 variations:

```ruby
class Foo ; end

Foo.new.instance_variable_set(:@a, 1) # case 1: creates one variation
Foo.new.instance_variable_set(:@b, 1) # case 2: creates another variation

foo = Foo.new
foo.instance_variable_set(:@a, 1) # does not create a new variation
foo.instance_variable_set(:@b, 1) # does not create a new variation (a continuation of the variation in case 1)
```

We will use this number to limit the amount of shapes that a class can
create and fallback to using a hash iv lookup.

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/ext/objspace/objspace_dump.c b/ext/objspace/objspace_dump.c
index a4858d44b9..4c261a7a35 100644
--- a/ext/objspace/objspace_dump.c
+++ b/ext/objspace/objspace_dump.c
@@ -15,6 +15,7 @@
 #include "gc.h"
 #include "internal.h"
 #include "internal/array.h"
+#include "internal/class.h"
 #include "internal/hash.h"
 #include "internal/string.h"
 #include "internal/sanitizers.h"
@@ -498,6 +499,9 @@ dump_object(VALUE obj, struct dump_config *dc)
         break;
 
       case T_CLASS:
+        dump_append(dc, ", \"variation_count\":");
+        dump_append_d(dc, RCLASS_EXT(obj)->variation_count);
+
       case T_MODULE:
         if (rb_class_get_superclass(obj)) {
             dump_append(dc, ", \"superclass\":");