Only lookup types in one interner

Rename the 2018 edition lint names

* `rust_2018_breakage` -> `rust_2018_compatibility` - the lint for ensuring
  that your code, in the 2015 edition, is compatible with the 2018 edition's
  semantics. This is required to pass *before* you enable the 2018 edition.
* `rust_2018_migration` -> `rust_2018_idioms` - the lint for writing idiomatic
  code after you've already enabled the 2018 edition

Remove `nll` from `rust_2018_preview`

NLL isn't quite ready yet so gonna hold off on inserting it into the preview.

Improve single-use and zero-use lifetime lints

The code now correctly identifies *when* to lint -- or more correctly, anyhow -- but it doesn't yet offer suggestions for how to fix.

(I just remembered when writing this I had meant to go back over some of these cases around e.g. impl Trait and double check that everything is right...)

cc #44752

r? @cramertj

Rollup of 18 pull requests

Successful merges:

 - #49423 (Extend tests for RFC1598 (GAT))
 - #50010 (Give SliceIndex impls a test suite of girth befitting the implementation (and fix a UTF8 boundary check))
 - #50447 (Fix update-references for tests within subdirectories.)
 - #50514 (Pull in a wasm fix from LLVM upstream)
 - #50524 (Make DepGraph::previous_work_products immutable)
 - #50532 (Don't use Lock for heavily accessed CrateMetadata::cnum_map.)
 - #50538 ( Make CrateNum allocation more thread-safe. )
 - #50564 (Inline `Span` methods.)
 - #50565 (Use SmallVec for DepNodeIndex within dep_graph.)
 - #50569 (Allow for specifying a linker plugin for cross-language LTO)
 - #50572 (Clarify in the docs that `mul_add` is not always faster.)
 - #50574 (add fn `into_inner(self) -> (Idx, Idx)` to RangeInclusive (#49022))
 - #50575 (std: Avoid `ptr::copy` if unnecessary in `vec::Drain`)
 - #50588 (Move "See also" disambiguation links for primitive types to top)
 - #50590 (Fix tuple struct field spans)
 - #50591 (Restore RawVec::reserve* documentation)
 - #50598 (Remove unnecessary mutable borrow and resizing in DepGraph::serialize)
 - #50606 (Retry when downloading the Docker cache.)

Failed merges:

 - #50161 (added missing implementation hint)
 - #50558 (Remove all reference to DepGraph::work_products)

Attempting to fix https://travis-ci.org/rust-lang/rust/jobs/377407894 via some
selective ignoring tests

Map the stack guard page with max protection on NetBSD

On NetBSD the initial mmap() protection of a mapping can not be made
less restrictive with mprotect().

So when mapping a stack guard page, use the maximum protection
we ever want to use, then mprotect() it to the permission we
want it to have initially.

Fixes #50313

* `rust_2018_breakage` -> `rust_2018_compatibility` - the lint for ensuring
  that your code, in the 2015 edition, is compatible with the 2018 edition's
  semantics. This is required to pass *before* you enable the 2018 edition.
* `rust_2018_migration` -> `rust_2018_idioms` - the lint for writing idiomatic
  code after you've already enabled the 2018 edition

Retry when downloading the Docker cache.

As a safety measure, prevent spuriously needing to rebuild the docker image in case the network was reset while downloading.

Also, adjusted the retry function to insert a sleep between retries, because retrying immediately will often just hit the same issue.

Remove unnecessary mutable borrow and resizing in DepGraph::serialize

I might be mistaken, but I noticed this whilst in this file for something else. It appears that this mutable borrow is unnecessary and since it's locking it should be removed. The resizing looks redundant since nothing additional is added to the fingerprints in this function, so that can also be removed.

Restore RawVec::reserve* documentation

When the RawVec::try_reserve* methods were added, they took the place of
the ::reserve* methods in the source file, and new ::reserve* methods
wrapping the new try_reserve* methods were created. But the
documentation didn't move along, such that:
 - reserve_* methods are barely documented.
 - try_reserve_* methods have unmodified documentation from reserve_*,
   such that their documentation indicate they are panicking/aborting.

This moves the documentation back to the right methods, with a
placeholder documentation for the try_reserve* methods.

Fix tuple struct field spans

Fix #50578. Will have a merge conflict with #50536.

Move "See also" disambiguation links for primitive types to top

Closes #50384.

<details>
<summary>Images</summary>

![rust-slice](https://user-images.githubusercontent.com/1411280/39843148-caa41c3e-53b7-11e8-8123-b57c25a4d9e0.png)

![rust-isize](https://user-images.githubusercontent.com/1411280/39843146-ca94b384-53b7-11e8-85f3-3f5e5d353a05.png)

</details>

r? @steveklabnik

std: Avoid `ptr::copy` if unnecessary in `vec::Drain`

This commit is spawned out of a performance regression investigation in #50496.
In tracking down this regression it turned out that the `expand_statements`
function in the compiler was taking quite a long time. Further investigation
showed two key properties:

* The function was "fast" on glibc 2.24 and slow on glibc 2.23
* The hottest function was memmove from glibc

Combined together it looked like glibc gained an optimization to the memmove
function in 2.24. Ideally we don't want to rely on this optimization, so I
wanted to dig further to see what was happening.

The hottest part of `expand_statements` was `Drop for Drain` in the call to
`splice` where we insert new statements into the original vector. This *should*
be a cheap operation because we're draining and replacing iterators of the exact
same length, but under the hood memmove was being called a lot, causing a
slowdown on glibc 2.23.

It turns out that at least one of the optimizations in glibc 2.24 was that
`memmove` where the src/dst are equal becomes much faster. [This program][prog]
executes in ~2.5s against glibc 2.23 and ~0.3s against glibc 2.24, exhibiting
how glibc 2.24 is optimizing `memmove` if the src/dst are equal.

And all that brings us to what this commit itself is doing. The change here is
purely to `Drop for Drain` to avoid the call to `ptr::copy` if the region being
copied doesn't actually need to be copied. For normal usage of just `Drain`
itself this check isn't really necessary, but because `Splice` internally
contains `Drain` this provides a nice speed boost on glibc 2.23. Overall this
should fix the regression seen in #50496 on glibc 2.23 and also fix the
regression on Windows where `memmove` looks to not have this optimization.

Note that the way `splice` was called in `expand_statements` would cause a
quadratic number of elements to be copied via `memmove` which is likely why the
tuple-stress benchmark showed such a severe regression.

Closes #50496

[prog]: https://gist.github.com/alexcrichton/c05bc51c6771bba5ae5b57561a6c1cd3

add fn `into_inner(self) -> (Idx, Idx)` to RangeInclusive (#49022)

adds `into_inner(self) -> (Idx, Idx)` to RangeInclusive
https://github.com/rust-lang/rust/issues/49022#issuecomment-387645176

Clarify in the docs that `mul_add` is not always faster.

Fixes https://github.com/rust-lang/rust/issues/49842.

Other resources:

- https://users.rust-lang.org/t/why-does-the-mul-add-method-produce-a-more-accurate-result-with-better-performance/1626
- https://en.wikipedia.org/wiki/Multiply%E2%80%93accumulate_operation

Allow for specifying a linker plugin for cross-language LTO

This PR makes the `-Zcross-lang-lto` flag optionally take the path to the `LLVMgold.so` linker plugin. If this path is specified, `rustc` will invoke the linker with the correct arguments (i.e. `-plugin` and various `-plugin-opt`s).

This can be used to ergonomically enable cross-language LTO for Rust programs with C/C++ dependencies:
```
clang -O2 test.c -otest.o -c -flto=thin
llvm-ar -rv libxxx.a test.o
rustc -L. main.rs -Zcross-lang-lto=/usr/lib64/LLVMgold.so -O -Clink-arg=-fuse-ld=gold
```

- Note that in theory this should work with Gold, LLD, and newer versions of binutils' LD but on my current system I could only get it to work with Gold.
- Also note that this will work best if the Clang version and Rust's LLVM version are close enough. Clang 6.0 works well with the current nightly.

r? @alexcrichton

Use SmallVec for DepNodeIndex within dep_graph.

This avoids a decent number of allocations, enough to speed up
incremental runs of many rustc-benchmarks, the best by 2%.

Here are the rustc-perf benchmarks that showed an improvement of at least 1% on one run:
```
unused-warnings-check
	avg: -1.7%	min: -2.4%	max: 0.0%
unused-warnings-opt
	avg: -1.4%	min: -2.0%	max: 0.0%
unused-warnings
	avg: -1.4%	min: -2.0%	max: -0.0%
tokio-webpush-simple-check
	avg: -1.0%	min: -1.7%	max: 0.0%
futures-opt
	avg: -0.9%	min: -1.6%	max: 0.0%
encoding
	avg: -1.2%	min: -1.6%	max: -0.6%
encoding-check
	avg: -0.9%	min: -1.6%	max: 0.0%
encoding-opt
	avg: -0.8%	min: -1.6%	max: -0.1%
futures
	avg: -0.9%	min: -1.5%	max: 0.0%
futures-check
	avg: -0.9%	min: -1.5%	max: 0.1%
regression-31157-check
	avg: -0.9%	min: -1.5%	max: 0.0%
regex
	avg: -0.6%	min: -1.4%	max: 0.0%
regression-31157-opt
	avg: -0.5%	min: -1.4%	max: 0.1%
regression-31157
	avg: -0.7%	min: -1.4%	max: 0.2%
regex-opt
	avg: -0.6%	min: -1.4%	max: 0.1%
hyper-check
	avg: -0.8%	min: -1.4%	max: -0.1%
regex-check
	avg: -1.0%	min: -1.4%	max: 0.0%
hyper-opt
	avg: -0.7%	min: -1.4%	max: -0.1%
hyper
	avg: -0.7%	min: -1.3%	max: 0.1%
piston-image-opt
	avg: -0.4%	min: -1.3%	max: 0.0%
tokio-webpush-simple-opt
	avg: -0.3%	min: -1.3%	max: 0.0%
piston-image-check
	avg: -0.5%	min: -1.3%	max: -0.0%
syn-opt
	avg: -0.5%	min: -1.3%	max: 0.0%
clap-rs-check
	avg: -0.3%	min: -1.3%	max: 0.2%
piston-image
	avg: -0.5%	min: -1.2%	max: 0.1%
syn
	avg: -0.5%	min: -1.2%	max: 0.1%
syn-check
	avg: -0.6%	min: -1.2%	max: -0.1%
issue-46449-opt
	avg: -0.4%	min: -1.2%	max: -0.1%
parser-check
	avg: -0.7%	min: -1.2%	max: 0.1%
issue-46449
	avg: -0.5%	min: -1.2%	max: -0.0%
```

Inline `Span` methods.

Because they are simple and hot.

This change speeds up some incremental runs of a few rustc-perf
benchmarks, the best by 3%.

Here are the ones with a speedup of at least 1%:
```
coercions
        avg: -1.1%      min: -3.4%      max: -0.2%
html5ever-opt
        avg: -0.8%      min: -1.7%      max: -0.2%
clap-rs-check
        avg: -0.3%      min: -1.4%      max: 0.7%
html5ever
        avg: -0.7%      min: -1.2%      max: -0.4%
html5ever-check
        avg: -0.9%      min: -1.1%      max: -0.8%
clap-rs
        avg: -0.4%      min: -1.1%      max: -0.1%
crates.io-check
        avg: -0.8%      min: -1.0%      max: -0.6%
serde-opt
        avg: -0.6%      min: -1.0%      max: -0.3%
```

 Make CrateNum allocation more thread-safe.

This PR makes sure that we can't have race conditions when assigning CrateNums. It's a slight improvement but a larger refactoring of the CrateStore/CrateLoader infrastructure would be good, I think.

r? @Zoxc

Don't use Lock for heavily accessed CrateMetadata::cnum_map.

The `cnum_map` in `CrateMetadata` is used for two things:
1. to map `CrateNums` between crates (used a lot during decoding)
2. to construct the (reverse) post order of the crate graph

For the second case, we need to modify the map after the fact, which is why the map is wrapped in a `Lock`. This is bad for the first case, which does not need the modification and does lots of small reads from the map.

This PR splits case (2) out into a separate `dependencies` field. This allows to make the `cnum_map` immutable (and shifts the interior mutability to a less busy data structure).

Fixes #50502

r? @Zoxc

Make DepGraph::previous_work_products immutable

Fixes #50501

r? @michaelwoerister

Pull in a wasm fix from LLVM upstream

This pulls in a fix for https://bugs.llvm.org/show_bug.cgi?id=36564 which has
already landed in upstream LLVM and should...

Closes rust-lang-nursery/rust-wasm#168

Fix update-references for tests within subdirectories.

Fixes #50438.

I'll make this more robust later for #49815.

Give SliceIndex impls a test suite of girth befitting the implementation (and fix a UTF8 boundary check)

So one day I was writing something in my codebase that basically amounted to `impl SliceIndex for (Bound<usize>, Bound<usize>)`, and I said to myself:

*Boy, gee, golly!  I never realized bounds checking was so tricky!*

At some point when I had around 60 lines of tests for it, I decided to go see how the standard library does it to see if I missed any edge cases. ...That's when I discovered that libcore only had about 40 lines of tests for slicing altogether, and none of them even used `..=`.

---

This PR includes:

* **Literally the first appearance of the word `get_unchecked_mut` in any directory named `test` or `tests`.**
* Likewise the first appearance of `get_mut` used with _any type of range argument_ in these directories.
* Tests for the panics on overflow with `..=`.
    * I wanted to test on `[(); usize::MAX]` as well but that takes linear time in debug mode </3
* A horrible and ugly test-generating macro for the `should_panic` tests that increases the DRYness by a single order of magnitude (which IMO wasn't enough, but I didn't want to go any further and risk making the tests inaccessible to next guy).
* Same stuff for str!
    * Actually, the existing `str` tests were pretty good. I just helped filled in the holes.
* [A fix for the bug it caught](https://github.com/rust-lang/rust/issues/50002).  (only one ~~sadly~~)

Extend tests for RFC1598 (GAT)

More GAT tests, namely some usage for `Iterable` and `StreamingIterator`, shadowing (lifetimes and type params), `Collection<T>` and `CollectionFamily` from [the series](http://smallcultfollowing.com/babysteps/blog/2016/11/03/associated-type-constructors-part-2-family-traits/) with default associated types. Tracking issue: #44265

r? @nikomatsakis

Wrong GAT argument numbers / kinds and default values are next.

Remove usages of Term::as_str and mark it for removal

Returning references to rustc internal data structures is a bad idea since their lifetimes are unrelated to the lifetimes of proc_macro values.

See https://github.com/rust-lang/rust/pull/46972 and the `Taming thread-local storage` section of https://internals.rust-lang.org/t/parallelizing-rustc-using-rayon/6606

r? @alexcrichton

NLL isn't quite ready yet so gonna hold off on inserting it into the preview.

Optimize layout of TypeVariants

This makes references to `Slice` use thin pointers by storing the slice length in the slice itself. `GeneratorInterior` is replaced by storing the movability of generators in `TyGenerator` and the interior witness is stored in `GeneratorSubsts` (which is just a wrapper around `&'tcx Substs`, like `ClosureSubsts`). Finally the fields of `TypeAndMut` is stored inline in `TyRef`. These changes combine to reduce `TypeVariants` from 48 bytes to 24 bytes on x86_64.

r? @michaelwoerister

This pulls in a fix for https://bugs.llvm.org/show_bug.cgi?id=36564 which has
already landed in upstream LLVM and should...

Closes rust-lang-nursery/rust-wasm#168

Prevent spuriously needing to rebuild the docker image when the network
was down.

Also, adjusted the retry function to insert a sleep between retries,
because retrying immediately will often just hit the same issue.

Compile LLVM with Clang on release builders

Attempting to cache in on some rustc compile time wins mentioned in https://github.com/rust-lang/rust/issues/49879#issuecomment-383602941

Fix rustdoc pathes search

Fixes #50086.

Depends on #50302.

r? @QuietMisdreavus

./x.py test should be able to run individual tests

Allows user to be able to run individual tests by specifying filename i.e `./x.py test src/test/run-pass/foo.rs`

Fixes #48483

When the RawVec::try_reserve* methods were added, they took the place of
the ::reserve* methods in the source file, and new ::reserve* methods
wrapping the new try_reserve* methods were created. But the
documentation didn't move along, such that:
 - reserve_* methods are barely documented.
 - try_reserve_* methods have unmodified documentation from reserve_*,
   such that their documentation indicate they are panicking/aborting.

This moves the documentation back to the right methods, with a
placeholder documentation for the try_reserve* methods.

also make a drive-by typo fix