Do not show an anonymous class as a receiver

test/ruby/test_backtrace.rb

@@ -428,4 +428,23 @@ def foo
       enum.next
     end;
   end
+
+  def test_no_receiver_for_anonymous_class
+    err = ["-:2:in 'bar': unhandled exception", # Not '#<Class:0xXXX>.bar'
+           "\tfrom -:3:in '<main>'"]
+    assert_in_out_err([], <<-"end;", [], err)
+    foo = Class.new
+    def foo.bar = raise
+    foo.bar
+    end;
+
+    err = ["-:3:in 'baz': unhandled exception", # Not '#<Class:0xXXX>::Bar.baz'
+           "\tfrom -:4:in '<main>'"]
+    assert_in_out_err([], <<-"end;", [], err)
+    foo = Class.new
+    foo::Bar = Class.new
+    def (foo::Bar).baz = raise
+    foo::Bar.baz
+    end;
+  end
 end

variable.c

@@ -111,6 +111,12 @@ classname(VALUE klass, bool *permanent)
     return classpath;
 }
 
+VALUE
+rb_mod_name0(VALUE klass, bool *permanent)
+{
+    return classname(klass, permanent);
+}
+
 /*
  *  call-seq:
  *     mod.name    -> string

vm_backtrace.c

@@ -191,22 +191,25 @@ location_lineno_m(VALUE self)
     return INT2FIX(location_lineno(location_ptr(self)));
 }
 
+VALUE rb_mod_name0(VALUE klass, bool *permanent);
+
 static VALUE
 gen_method_name(VALUE owner, VALUE name)
 {
+    bool permanent;
     if (RB_TYPE_P(owner, T_CLASS) || RB_TYPE_P(owner, T_MODULE)) {
         if (RBASIC(owner)->flags & FL_SINGLETON) {
             VALUE v = RCLASS_ATTACHED_OBJECT(owner);
             if (RB_TYPE_P(v, T_CLASS) || RB_TYPE_P(v, T_MODULE)) {
-                v = rb_class_path(v);
-                if (!NIL_P(v)) {
+                v = rb_mod_name0(v, &permanent);
+                if (permanent && !NIL_P(v)) {
                     return rb_sprintf("%"PRIsVALUE".%"PRIsVALUE, v, name);
                 }
             }
         }
         else {
-            owner = rb_class_path(owner);
-            if (!NIL_P(owner)) {
+            owner = rb_mod_name0(owner, &permanent);
+            if (permanent && !NIL_P(owner)) {
                 return rb_sprintf("%"PRIsVALUE"#%"PRIsVALUE, owner, name);
             }
         }