fstring: don't assume FL_EXIVAR mean there are ivars.

Author: byroot

string.c

@@ -45,6 +45,7 @@
 #include "ruby/thread.h"
 #include "ruby/util.h"
 #include "ruby_assert.h"
+#include "shape.h"
 #include "vm_sync.h"
 
 #if defined HAVE_CRYPT_R
@@ -383,7 +384,16 @@ fstring_hash(VALUE str)
 #define fstring_hash rb_str_hash
 #endif
 
-#define BARE_STRING_P(str) (!FL_ANY_RAW(str, FL_EXIVAR) && RBASIC_CLASS(str) == rb_cString)
+static inline bool
+BARE_STRING_P(VALUE str)
+{
+    if (RBASIC_CLASS(str) != rb_cString) return false;
+
+    if (FL_TEST_RAW(str, FL_EXIVAR)) {
+        return rb_ivar_count(str) == 0;
+    }
+    return true;
+}
 
 static inline st_index_t
 str_do_hash(VALUE str)
@@ -872,7 +882,6 @@ register_fstring(VALUE str, bool copy, bool force_precompute_hash)
     RUBY_ASSERT(RB_TYPE_P(result, T_STRING));
     RUBY_ASSERT(OBJ_FROZEN(result));
     RUBY_ASSERT(!FL_TEST_RAW(result, STR_FAKESTR));
-    RUBY_ASSERT(!FL_TEST_RAW(result, FL_EXIVAR));
     RUBY_ASSERT(RBASIC_CLASS(result) == rb_cString);
 
     return result;

variable.c

@@ -2301,23 +2301,31 @@ rb_ivar_count(VALUE obj)
 {
     if (SPECIAL_CONST_P(obj)) return 0;
 
+    st_index_t iv_count = 0;
     switch (BUILTIN_TYPE(obj)) {
       case T_OBJECT:
-        return ROBJECT_IV_COUNT(obj);
+        iv_count = ROBJECT_IV_COUNT(obj);
+        break;
       case T_CLASS:
       case T_MODULE:
-        return RCLASS_IV_COUNT(obj);
+        iv_count = RCLASS_IV_COUNT(obj);
+        break;
       default:
         if (FL_TEST(obj, FL_EXIVAR)) {
             struct gen_ivtbl *ivtbl;
 
             if (rb_gen_ivtbl_get(obj, 0, &ivtbl)) {
-                return gen_ivtbl_count(obj, ivtbl);
+                iv_count = gen_ivtbl_count(obj, ivtbl);
             }
         }
         break;
     }
-    return 0;
+
+    if (FL_TEST_RAW(obj, FL_SEEN_OBJ_ID)) {
+        iv_count--;
+    }
+
+    return iv_count;
 }
 
 static int