Rollup of 6 pull requests

- Successful merges: #32383, #32387, #32440, #32470, #32478, #32492
- Failed merges:

Avoid page reload upon hitting "S" when browsing documentation in local mode

The problem seems to have been introduced with commit 2910c002

Add note on `str` being an unsized type in strings section of book

The book section on Rust strings mentions `&str` and `String` but does not address why `str` is not used directly. This adds a short blurb and a link to the unsized types chapter. The second draft of the book will go more in-depth on this, but this should help a bit for now. Thanks #rust for clarifying this point, and let me know if it needs rewording or different placement 😄.

CC @steveklabnik @Kimundi

remove broken config

Fixes #32412

doc: remove needless bindings

The extra syntax is more noise than help in simple examples like this

std: Add regression test for #32074

Just to make sure we don't accidentally break this in the future.

Document heap allocation location guarantee

```
14:25 < aidanhs> is there any guarantee that boxes will not move the value on the heap when they are moved?
14:26 <@steveklabnik> aidanhs: ... i'm not sure if it's a guarantee, but it follows, generally
14:26 <@steveklabnik> aidanhs: moves mean memcpy, so you're memcpying the structure of the box itself, which is copying the pointer
14:26 <@steveklabnik> so the pointer won't be updated
14:26 <@steveklabnik> moves cannot do complex things like move the memory around on the heap
14:26 <@kmc> aidanhs: I would say it's guaranteed
14:27 < aidanhs> steveklabnik: yeah, that's what I was thinking, it'd be pretty strange for rust to do something, but I couldn't find any docs one way or the other
14:27 <@steveklabnik> kmc: aidanhs yeah, it's like a borderline thing that we don't explicitly guanratee but i think IS guaranteed by our other guarantees
14:27 <@steveklabnik> mostly that move == memcpy
14:28 < aidanhs> kmc: steveklabnik great thanks! would a PR to the rust reference along these lines be ok?
14:28 < jmesmon> aidanhs: I believe owning_ref has some discussion of that (stable references)
14:29 <@steveklabnik> aidanhs: i would probably take that, yeah
14:29 < aidanhs> jmesmon: thanks, I'll take a look at that
```
https://botbot.me/mozilla/rust/2016-02-22/?msg=60657619&page=18

r? @steveklabnik

Fix the name of the 'check-cargotest' step

configure: update required LLVM version

Rust 1.7.0 and newer appears to require LLVM 3.6.0 or newer when
building against a version that's out of the tree with the --llvm-root
flag.
Signed-off-by: NDoug Goldstein <cardoe@cardoe.com>

Rollup of 11 pull requests

- Successful merges: #32131, #32199, #32257, #32325, #32435, #32447, #32448, #32456, #32469, #32476, #32482
- Failed merges: #32240

use new visitor to erase regions

r? @nagisa

Fix unsound behaviour with null characters in thread names (issue #32475)

Previously, the thread name (&str) was converted to a CString in the
new thread, but outside unwind::try, causing a panic to continue into FFI.

This patch changes that behaviour, so that the panic instead happens
in the parent thread (where panic infrastructure is properly set up),
not the new thread.

This could potentially be a breaking change for architectures who don't
support thread names.

make available monomorphizations shared by CGU

The current setup means that all generics are local to a codegen-unit,
which means massive duplication.

Hardcode accepting 0 as a valid str char boundary

If we check explicitly for index == 0, that removes the need to read the
byte at index 0, so it avoids a trip to the string's memory, and it
optimizes out the slicing index' bounds check whenever it is (a constant) zero.

Add augmented assignment operator impls for time types

r? @alexcrichton

Remove ungrammatical dots from the error index.

They were probably meant as a shorthand for omitted code.

Part of #32446 but there should be a separate fix for the issue.

Some fixes for error recovery in the compiler

std: Fix inheriting stdin on status()

This regression was accidentally introduced in #31618, and it's just flipping a
boolean!

Closes #32254

Restrict constants in patterns

This implements [RFC 1445](https://github.com/rust-lang/rfcs/blob/master/text/1445-restrict-constants-in-patterns.md). The primary change is to limit the types of constants used in patterns to those that *derive* `Eq` (note that implementing `Eq` is not sufficient). This has two main effects:

1. Floating point constants are linted, and will eventually be disallowed. This is because floating point constants do not implement `Eq` but only `PartialEq`. This check replaces the existing special case code that aimed to detect the use of `NaN`.
2. Structs and enums must derive `Eq` to be usable within a match.

This is a [breaking-change]: if you encounter a problem, you are most likely using a constant in an expression where the type of the constant is some struct that does not currently implement
`Eq`. Something like the following:

```rust
struct SomeType { ... }
const SOME_CONST: SomeType = ...;

match foo {
    SOME_CONST => ...
}
```

The easiest and most future compatible fix is to annotate the type in question with `#[derive(Eq)]` (note that merely *implementing* `Eq` is not enough, it must be *derived*):

```rust
struct SomeType { ... }
const SOME_CONST: SomeType = ...;

match foo {
    SOME_CONST => ...
}
```

Another good option is to rewrite the match arm to use an `if` condition (this is also particularly good for floating point types, which implement `PartialEq` but not `Eq`):

```rust
match foo {
    c if c == SOME_CONST => ...
}
```

Finally, a third alternative is to tag the type with `#[structural_match]`; but this is not recommended, as the attribute is never expected to be stabilized. Please see RFC #1445 for more details.

cc https://github.com/rust-lang/rust/issues/31434

r? @pnkfelix

resolve: Minimize hacks in name resolution of primitive types

When resolving the first unqualified segment in a path with `n` segments and `n - 1` associated item segments, e.g. (`a` or `a::assoc` or `a::assoc::assoc` etc) try to resolve `a` without considering primitive types first. If the "normal" lookup fails or results in a module, then try to resolve `a` as a primitive type as a fallback.

This way backward compatibility is respected, but the restriction from E0317 can be lifted, i.e. primitive names mostly can be shadowed like any other names.

Furthermore, if names of primitive types are [put into prelude](https://github.com/petrochenkov/rust/tree/prim2) (now it's possible to do), then most of names will be resolved in conventional way and amount of code relying on this fallback will be greatly reduced. Although, it's not entirely convenient to put them into prelude right now due to temporary conflicts like `use prelude::v1::*; use usize;` in libcore/libstd, I'd better wait for proper glob shadowing before doing it.
I wish the `no_prelude` attribute were unstable as intended :(

cc @jseyfried @arielb1
r? @EddyB

Revamp symbol names for impls (and make them deterministic, etc)

This builds on @michaelwoerister's epic PR #31539 (note that his PR never landed, so I just incorporated it into this one). The main change here is that we remove the "name" from `DefPathData` for impls, since that name is synthetic and not sufficiently predictable for incr comp. However, just doing that would cause bad symbol names since those are based on the `DefPath`. Therefore, I introduce a new mechanism for getting symbol names (and also paths for user display) called `item_path`. This is kind of simplistic for now (based on strings) but I expect to expand it later to support richer types, hopefully generating C++-mangled names that gdb etc can understand. Along the way I cleaned up how we track the path that leads to an extern crate.

There is still some cleanup left undone here. Notably, I didn't remove the impl names altogether -- that would probably make sense. I also didn't try to remove the `item_symbols` vector. Mostly I want to unblock my other incr. comp. work. =)

r? @EddyB
cc @EddyB @alexcrichton @michaelwoerister

resolve: Refactor how the prelude is handled

This PR refactors how the prelude is handled in `resolve`.

Instead of importing names from the prelude into each module's `resolutions`, this PR adds a new field `prelude: RefCell<Option<Module>>` to `ModuleS` that is set during import resolution but used only when resolving in a lexical scope (i.e. the scope of an initial segment of a relative path).

r? @nikomatsakis

exclude the prelude from `resolve_name(.., allow_private_imports = true)`.