Transition librustdoc to Rust 2018

#58099

Rollup of 17 pull requests

Successful merges:

 - #57656 (Deprecate the unstable Vec::resize_default)
 - #58059 (deprecate before_exec in favor of unsafe pre_exec)
 - #58064 (override `VecDeque::try_rfold`, also update iterator)
 - #58198 (Suggest removing parentheses surrounding lifetimes)
 - #58431 (fix overlapping references in BTree)
 - #58555 (Add a note about 2018e if someone uses `try {` in 2015e)
 - #58588 (remove a bit of dead code)
 - #58589 (cleanup macro after 2018 transition)
 - #58591 (Dedup a rustdoc diagnostic construction)
 - #58600 (fix small documentation typo)
 - #58601 (Search for target_triple.json only if builtin target not found)
 - #58606 (Docs: put Future trait into spotlight)
 - #58607 (Fixes #58586: Make E0505 erronous example fail for the 2018 edition)
 - #58615 (miri: explain why we use static alignment in ref-to-place conversion)
 - #58620 (introduce benchmarks of BTreeSet.intersection)
 - #58621 (Update miri links)
 - #58632 (Make std feature list sorted)

Failed merges:

r? @ghost

Make std feature list sorted

This helps to avoid merge conflicts when concurrent PRs append features to the end of the list.

Update miri links

Miri has been moved to `rust-lang` a couple of days ago.

introduce benchmarks of BTreeSet.intersection

16 tests combining 4 kinds of contents with different sizes exposing edge cases.
The ones with asymmetric sizes are addressed by https://github.com/rust-lang/rust/pull/58577.
The pos_vs_neg cases seems (are were meant to be) the same as the neg_vs_pos case (same thing, reverse order) but reality shows a surprsing 25% difference.

miri: explain why we use static alignment in ref-to-place conversion

@EddyB @oli-obk do you think this makes sense? Or should we use the run-time alignment (`align_of_val`)? I am a bit worried about custom DSTs, but that affects way more areas of Miri so I'd ignore them for now.

r? @oli-obk

Fixes #58586: Make E0505 erronous example fail for the 2018 edition

The original example worked for 2015, but not the 2018 edition of Rust.

Borrowing the moved value after ownership is transferred seems required for 2018.

[this](https://github.com/rust-lang/rust/compare/rust-lang:f66e469...gurgalex:b2a02c8#diff-4ca866aea4a6efecd732f1975faaad88R1564) line though is correct for 2018, but not for the 2015 edition.

Fix #58586

Docs: put Future trait into spotlight

If a function returns a type that implements `Future`, there should be a small "i" symbol next to it indicating the return type implements an important trait.

Search for target_triple.json only if builtin target not found

Before this commit, if the builtin target was found, but an error
happened when instantiating it (e.g. validating the target
specification file failed, etc.), then we ignored those errors
and proceeded to try to find a `target_triple.json` file, and if
that failed, reported that as an error.

With this commit, if rustc is supposed to provide the builtin target,
and something fails while instantiating it, that error will
get properly propagated.

r? @oli-obk

fix small documentation typo

Thanks to @stjepang for catching my mistake.

Dedup a rustdoc diagnostic construction

None

cleanup macro after 2018 transition

We can now use `?`

remove a bit of dead code

[Six years](https://github.com/rust-lang/rust/commit/5dc5efefd47527067ab5b7862d89a99da4824f49) seem to be a long enough transition period 🤣

Add a note about 2018e if someone uses `try {` in 2015e

Inspired by https://github.com/rust-lang/rust/issues/58491, where a `try_blocks` example was accidentally run in 2015, which of course produces a bunch of errors.

What's the philosophy about gating for this?  The keyword is stably a keyword in 2018, so I haven't gated it for now but am not mentioning what the keyword _does_.  Let me know if I should do differently.

Resolves #53672

fix overlapping references in BTree

This fixes two kinds of overlapping references in BTree (both found by running the BTree test suite in Miri).

In `into_slices_mut`, we did `k.into_key_slice_mut()` followed by `self.into_val_slice_mut()` (where `k` is a copy of `self`). Calling `into_val_slice_mut` calls `self.len()`, which creates a shared reference to `NodeHeader`, which unfortunately (due to padding) overlaps with the mutable reference returned by `into_key_slice_mut`.  Hence the key slice got (partially) invalidated.  The fix is to avoid creating an `&NodeHeader` after the first slice got created.

In the iterators, we used to first create the references that will be returned, and then perform the walk on the tree.  Walking the tree creates references (such as `&mut InternalNode`) that overlap with all of the keys and values stored in a pointer; in particular, they overlap with the references the iterator will later return. This is fixed by reordering the operations of walking the tree and obtaining the inner references.

The test suite still passes (and it passes in Miri now!), but there is a lot of code here that I do not understand...

Suggest removing parentheses surrounding lifetimes

Fixes #57386.

r? @estebank

override `VecDeque::try_rfold`, also update iterator

This keeps the slice based iteration and updates the iterator state after each slice. It also uses a loop to reduce the amount of code.

This uses unsafe code, so some thorough review would be appreciated. Cc @RalfJung

deprecate before_exec in favor of unsafe pre_exec

Fixes https://github.com/rust-lang/rust/issues/39575

As per the [lang team decision](https://github.com/rust-lang/rust/issues/39575#issuecomment-442993358):

> The language team agreed that before_exec should be unsafe, and leaves the details of a transition plan to the libs team.

Cc @alexcrichton @rust-lang/libs how would you like to proceed?

Deprecate the unstable Vec::resize_default

As a way to either get additional feedback to stabilize or help move nightly users off it.

Tracking issue: https://github.com/rust-lang/rust/issues/41758#issuecomment-449719961

r? @SimonSapin

Wrap write_bytes in a function. Move docs

This will allow us to add debug assertions.
See issue #53871.

This helps to avoid merge conflicts when concurrent PRs append
features to the end of the list.

Erroneous loop diagnostic in nll

Closes #53773

r? @nikomatsakis

improve Pin documentation

Incorporates a bunch of the documentation-related comments that came up when discussing `Pin` stabilization.

Cc @alexcrichton @withoutboats @cramertj @jonhoo

Fixes https://github.com/rust-lang/rust/issues/58130

Destabilize fixed-width const defined atomic integers

With this PR version 1.34.0 onwards const declarations of atomic integers will be unstable.

* Closes https://github.com/rust-lang/rust/issues/58089
* Reverts partially: https://github.com/rust-lang/rust/pull/57425

Re-implement leak check in terms of universes

This PR temporarily restores the leak-check, but implemented in terms of universes. This is not because the leak check behavior was necessarily **correct**, but because (a) we may want to have a transition period and because (b) we want to have more breathing room to work through the full implications of handling higher-ranked types correctly. Note that this PR builds atop https://github.com/rust-lang/rust/pull/58056.

Fixes #58451
Fixes #46989
Fixes #57639

r? @aturon
cc @arielb1, @lqd

~~Temporary note: I've not finished running `./x.py test` locally -- I'm confident a lot of error messages in tests will need updating. I sort of expect them to revert to the older, (imo) less good error messages, which is mildly unfortunate. There might be a way to preserve the new error messages, not sure.~~

Miri has been moved to `rust-lang` a couple of days ago.

This preserves the error you currently get on stable for the
old-lub-glb-object.rs test.

Update cargo

9 commits in 865cb70106a6b1171a500ff68f93ab52eea56e72..b33ce7fc9092962b0657b4c25354984b5e5c47e4
2019-02-10 15:49:37 +0000 to 2019-02-19 18:42:50 +0000
- Don't retry invalid credentials from git credential helpers (rust-lang/cargo#6681)
- Fix some typos in resolver tests (rust-lang/cargo#6682)
- Add an unstable option to build proc macros for both the host and the target (rust-lang/cargo#6547)
- Test cases proving RUSTC_WRAPPER can be a relative path (rust-lang/cargo#6638)
- Add support for Azure DevOps (rust-lang/cargo#6264)
- Update docs for removed `patch` restriction. (rust-lang/cargo#6663)
- Fix incorrect help message (rust-lang/cargo#6555)
- Stabilize Alternative Registries (rust-lang/cargo#6654)
- Having a [patch] section when publishing is not an error (rust-lang/cargo#6535)

One surprise: old-lub-glb-object.rs, may indicate a bug

This set of diffs was produced by combing through
b68fad67 and seeing where the
`leak_check` used to be invoked and how.