Oli Scherer

yea we can't use crates.io crates in tests. the only way a test can be added right now is via the following: > we do have tests like [/home/ubuntu/rustc/rust10/tests/ui/proc-macro/derive-b.rs](https://github.com/rust-lang/rust/blob/master/tests/ui/proc-macro/derive-b.rs) so...

Great! Let's land this then @bors r+ rollup

@bors r- I've been told about a possible perf impact that previous attempts have had

@bors try @rust-timer queue

r? @pnkfelix

oh yea, I wasn't done yet XD thus some things weren't marked as resolved yet

Now I got through all the comments. @rustbot ready

This just adds the feature unstably, and thus doesn't need an FCP @bors r+ rollup

We can directly feed the `AnonConst`'s type instead of adding another indirection. Ideally we'd only create the `AnonConst`'s `DefId` right here, but since that can't be done for the other...

> Just out of curiosity I'd to ask if the previous approach was unsound? It fed a hir id query, which we haven't considered yet at all. We could have...