Add Drop impl for linked_list::DrainFilter

This is part of #43244. See https://github.com/rust-lang/rust/issues/43244#issuecomment-349894355

This reverts commit 00acdbd5.

Fixes doc important trait display on mobile

Fixes #46527.

r? @QuietMisdreavus

macros: add test for #44128

Closes #44128.
r? @nrc

Add read, read_string, and write functions to std::fs

New APIs in `std::fs`:

```rust
pub fn read<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> { … }
pub fn read_string<P: AsRef<Path>>(path: P) -> io::Result<String> { … }
pub fn write<P: AsRef<Path>, C: AsRef<[u8]>>(path: P, contents: C) -> io::Result<()> { ... }
```

(`read_string` is based on `read_to_string` and so returns an error on non-UTF-8 content.)

Before:

```rust
use std::fs::File;
use std::io::Read;

let mut bytes = Vec::new();
File::open(filename)?.read_to_end(&mut bytes)?;
do_something_with(bytes)
```

After:

```rust
use std::fs;

do_something_with(fs::read(filename)?)
```

Make CGU-local globals private so they don't show up in the local symbol table.

Should reduce binary sizes. Great find, @EddyB!

r? @alexcrichton
(I have not tested this locally. Better wait for travis to turn green before approving)

Md warnings

Fixes #45365.

r? @QuietMisdreavus

incr.comp.: Enable query result caching for many more queries

Newly cached queries are:
* const_is_rvalue_promotable_to_static
* trans_fulfill_obligation
* optimized_mir
* unsafety_check_result
* borrowck
* mir_borrowck
* mir_const_qualif
* contains_extern_indicator
* def_symbol_name
* symbol_name

This also includes the stricter `Span` hashing first mentioned in #46490, which will lead to more false positives in release builds but overall is more correct -- and necessary for caching MIR. Hopefully we will soon be able to reduce the rate of false positives again by factoring `Span` out of MIR.

r? @nikomatsakis

These were already broken for debug builds.

rustc: Further tweak linkage in ThinLTO

In #46382 the logic around linkage preservation with ThinLTO ws tweaked but the
loop that registered all otherwise exported GUID values as "don't internalize
me please" was erroneously too conservative and only asking "external" linkage
items to not be internalized. Instead we actually want the inversion of that
condition, everything *without* "local" linkage to be internalized.

This commit updates the condition there, adds a test, and...

Closes #46543

Rollup of 5 pull requests

- Successful merges: #46416, #46444, #46526, #46539, #46548
- Failed merges:

Recommends lazily evaluated alternatives for `Option::or` and `Result::or`

Adds language to docs for `Option` and `Result` recommending the use of lazily evaluated alternatives when appropriate. These comments are intended to echo a [clippy lint] on the same topic. The [reddit discussion] may also be of interest.

[clippy lint]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#or_fun_call
[reddit discussion]: https://www.reddit.com/r/rust/comments/7hutqn/perils_of_optionor_and_resultor/

Do not automatically merge `Cargo.lock`

It essentially never does what it's supposed to and often leaves the `Cargo.lock` in a state where it needs manual adjustments or resetting to master/yourbranch. With this setting git will always choose your `Cargo.lock` over the one from master and report a merge error (if both master and your branch touched `Cargo.lock`). Now you can run `./x.py help` and it should normally update the `Cargo.lock` to be one that has everything needed by master and your branch.

Greatly improve sidebar when width < 700px

Fixes #36531.

r? @QuietMisdreavus

A few screenshots:

<img width="1440" alt="screen shot 2017-12-06 at 00 41 36" src="https://user-images.githubusercontent.com/3050060/33636875-6ad8b1a6-da1e-11e7-8d5b-d6d530ea5258.png">
<img width="1440" alt="screen shot 2017-12-06 at 00 41 40" src="https://user-images.githubusercontent.com/3050060/33636876-6af58196-da1e-11e7-82ab-b82768958037.png">

Move colors to main.css

r? @QuietMisdreavus

doc: macro `cfg!` evaluating at compile-time

Modify message for keyword as identifier name

This is a temporary solution to #46311.

The message is generic enough to cover both cases and is probably a fine enough solution to the specific problem described in the task. However, the underlying reason for this to be wrong is that `next_token_inner` returns `Lifetime` even if the token is a label. That's not simple, as the syntax for both can be quite similar and it may need to take a look to the next token to make a decision. I'm not sure I have enough knowledge about the project to be able to solve that (yet!), so I thought I'll fix the immediate problem first.

Allow feature-gate tests to live in ui/ and migrate most of the tests from compile-fail

The PR consists of three commits:

1. change tidy to allow feature-gate tests to live in ui/
2. migrate some feature gate tests to ui/ with renaming only
3. migrate some feature gate tests to ui/ with also removing `// gate-test-...` lines and renaming them to the standard `feature-gate-<feat-name>.rs` format.

closure handling for NLL

This branch overhauls how we handle closures and universally quantified regions in the NLL code. The goal is to lay the groundwork for "region erasure" by the HIR-based type checker, as well as to avoid "crazy hacks" when it comes to closures. This means that when we type-check a closure, we cannot make use of *any* of the precise values of free regions in its signature, since those are inferred by the HIR type-checker. Therefore, the new code handles closures by:

- Creating fresh regions for every free region that appears in the closure's type, which now includes both its signature and the types of all upvars.
    - This means that the closure is type-checked without knowing about the connections.
- When we encounter some region relationship that we can't locally verify, we propagate it to the closure's creator.
- During MIR typeck, the closure creators then validates those relationships.

For a good example and explanation, see e.g. the test `src/test/nll/closure-requirements/propagate-despite-same-free-region.rs`.

Upcoming changes in the next NLL PR (not included in this PR in order to keep it manageable):

- Improvements to the MIR type checker so that it handles a lot of stuff presently overlooked
- Refactor how we store region values to make it more efficient, better encapsulated
- Propagate "type-outlives" relationships like `T: 'a` in a similar fashion to the one covered in this PR (still in the works, but close)
- Improvements to error reporting (still in the works)

r? @arielb1 or @pnkfelix

In #46382 the logic around linkage preservation with ThinLTO ws tweaked but the
loop that registered all otherwise exported GUID values as "don't internalize
me please" was erroneously too conservative and only asking "external" linkage
items to not be internalized. Instead we actually want the inversion of that
condition, everything *without* "local" linkage to be internalized.

This commit updates the condition there, adds a test, and...

Closes #46543

Update fingerprint tests macros

Part of #44924

r? @michaelwoerister

per pnkfelix's suggestion

suggested by arielb1