Fix rustdoc and fulldeps tests

enforce user annotations in closure signatures

Not *quite* ready yet but I'm opening anyway. Still have to finish running tests locally.

Fixes #54692
Fixes #54124

r? @matthewjasper

This fixes `issue-28848.rs` -- it also handles another case that the
AST region checker gets wrong (`wf-self-type.rs`).  I don't actually
think that this is the *right way* to be enforcing this constraint --
I think we should probably do it more generally, perhaps by editing
`predicates_of` for the impl itself. The chalk-style implied bounds
setup ought to fix this.

Revert "rustc: Fix (again) simd vectors by-val in ABI"

This reverts commit 3cc8f738.

#45829 when a renamed import conflict with a previous import

Fix the suggestion when a renamed import conflict.

It check if the snipped contains `" as "`, and if so uses everything before for the suggestion.

This reverts commit 3cc8f738.

Stabilize impl_header_lifetime_elision in 2015

~~This is currently blocked on https://github.com/rust-lang/rust/issues/54902; it should be good after that~~

It's already stable in 2018; this finishes the stabilization.

FCP completed (https://github.com/rust-lang/rust/issues/15872#issuecomment-417953153), proposal (https://github.com/rust-lang/rust/issues/15872#issuecomment-412759783).

Tracking issue: https://github.com/rust-lang/rust/issues/15872
Usage examples (from libcore): https://github.com/rust-lang/rust/pull/54687

pick a reference issue for absolute-paths future incompatibility info

It would be kind of embarrassing to ship with the "issue TBD" message!

In particular, after the first for a given region variable. This
suppresses a lot of duplicate errors.

Fixes #54124

Use a keyword in raw identifier example

That's a very small documentation fix. The text says "you can now use keywords as identifiers" but example didn't use a keyword and would work without raw identifiers.

improve search tabs look

Fixes #55056.

![screenshot from 2018-10-16 19-06-48](https://user-images.githubusercontent.com/3050060/47034247-1e08b280-d177-11e8-9c1e-c7320af9b561.png)

![screenshot from 2018-10-16 19-09-39](https://user-images.githubusercontent.com/3050060/47034255-2365fd00-d177-11e8-8686-4765d3e56ff5.png)

With this, I think it'll be more obvious.

cc @memoryruins

r? @QuietMisdreavus

Give OpTy access to locals for priroda

r? @oli-obk

Move parse-fail tests to UI

cc https://github.com/rust-lang/rust/issues/53353

r? @davidtwco

Replace CanonicalVar with DebruijnIndex

Close #49887

Also make `layout_of_local` accept any `Frame`

[NLL] Use new region infer errors when explaining borrows

Use the new free region infer errors for explaining borrows

This gives at least some explanation for why a borrow is expected to
last for a certain free region. Also:

* Reports E0373: "closure may outlive the current function" with NLL.
* Special cases the case of returning a reference to (or value referencing) a local variable or temporary (E0515).
* Special case assigning a reference to a local variable in a closure to a captured variable. (E0521)

Closes #51026 - `regions-nested-fns-2.rs` isn't changed to that diagnostic, since that would not be the correct error here.
Closes #51169
cc #53882 - The error is (IMO) better now, but it could be better when we trace lifetimes in these error messages.

r? @nikomatsakis cc @pnkfelix

This gives at least some explanation for why a borrow is expected to
last for a certain free region. Also:

* Reports E0373: "closure may outlive the current function" with NLL.
* Special cases the case of returning a reference to (or value
  referencing) a local variable or temporary (E0515).
* Special case assigning a reference to a local variable in a closure
  to a captured variable.

Enable one fully ignored test

Except those testing parsing during macro expansion