D-Programming-Language/dmd — pull request #2872 by 9rnsr (2013-11-24 07:40:53+00:00)
Title: Issue 11563 - Module dependency cycle causes unrelated template instantiations to fail

https://d.puremagic.com/issues/show_bug.cgi?id=11563

Using `!b->base->symtab` seems an old way to detect forward reference of base interfaces. Instead use `b->base->scope` for that.