swift234

Use a bit to avoid performing early declaration attribute validation more than once.

Attribute validation is not naturally idempotent, and we shouldn’t need to make it so. Rather, we should only do the validation once. This fixes an immediate issue with @NSManaged in multi-file situations (<rdar://problem/16879162>) and avoids some redundant work.

Longer term, we have a ton of redundant visitation that needs to be addressed <rdar://problem/16905199>.

Swift SVN r18039