Fixed inadvertent ID creation in rb_iv_get

ext/-test-/symbol/init.c

@@ -20,6 +20,13 @@ sym_pinneddown_p(VALUE dummy, VALUE sym)
 #endif
 }
 
+static VALUE
+sym_iv_get(VALUE dummy, VALUE obj, VALUE name)
+{
+    const char *n = StringValueCStr(name);
+    return rb_iv_get(obj, n);
+}
+
 void
 Init_symbol(void)
 {
@@ -27,5 +34,6 @@ Init_symbol(void)
     VALUE klass = rb_define_class_under(mBug, "Symbol", rb_cSymbol);
     rb_define_singleton_method(klass, "find", sym_find, 1);
     rb_define_singleton_method(klass, "pinneddown?", sym_pinneddown_p, 1);
+    rb_define_singleton_method(klass, "iv_get", sym_iv_get, 2);
     TEST_INIT_FUNCS(init);
 }

test/-ext-/symbol/test_inadvertent_creation.rb

@@ -482,5 +482,14 @@ module Test_Symbol
         foo.call(name.to_sym => 42)
       end
     end
+
+    def test_iv_get
+      obj = Object.new
+      assert_warning(/not initialized/) do
+        assert_no_immortal_symbol_created("rb_iv_get") do |name|
+          Bug::Symbol.iv_get(obj, name)
+        end
+      end
+    end
   end
 end

variable.c

@@ -3361,8 +3361,13 @@ rb_mod_remove_cvar(VALUE mod, VALUE name)
 VALUE
 rb_iv_get(VALUE obj, const char *name)
 {
-    ID id = rb_intern(name);
+    ID id = rb_check_id_cstr(name, strlen(name), rb_usascii_encoding());
 
+    if (!id) {
+	if (RTEST(ruby_verbose))
+	    rb_warning("instance variable %s not initialized", name);
+	return Qnil;
+    }
     return rb_ivar_get(obj, id);
 }