… to remove an `unsafe` block.

… to protect against UB in the unlikely case that `idx + 1` overflows.

On SPARC, optimization fuel ends up emitting incorrect load and store
instructions for the transmute() call in blake2b_compress().  If we
force Blake2bCtx to be repr(C), the problem disappears.

Fixes rust-lang#43346

Point at the correct path segment on a import statement where a module
doesn't exist.

New output:

```rust
error[E0432]: unresolved import `std::bar`
 --> <anon>:1:10
  |
1 | use std::bar::{foo1, foo2};
  |          ^^^ Could not find `bar` in `std`
```

instead of:

```rust
error[E0432]: unresolved import `std::bar::foo1`
 --> <anon>:1:16
  |
1 | use std::bar::{foo1, foo2};
  |                ^^^^ Could not find `bar` in `std`

error[E0432]: unresolved import `std::bar::foo2`
 --> <anon>:1:22
  |
1 | use std::bar::{foo1, foo2};
  |                      ^^^^ Could not find `bar` in `std`
```

Make the "main" constructors of NonZero/Shared/Unique return Option

Per discussion in rust-lang#27730 (comment).

This is a breaking change to unstable APIs.

The old behavior is still available under the name `new_unchecked`. Note that only that one can be `const fn`, since `if` is currently not allowed in constant contexts.

In the case of `NonZero` this requires adding a new `is_zero` method to the `Zeroable` trait. I mildly dislike this, but it’s not much worse than having a `Zeroable` trait in the first place. `Zeroable` and `NonZero` are both unstable, this can be reworked later.

Point at path segment on module not found

Point at the correct path segment on a import statement where a module
doesn't exist.

New output:

```rust
error[E0432]: unresolved import `std::bar`
 --> <anon>:1:10
  |
1 | use std::bar::{foo1, foo2};
  |          ^^^ Could not find `bar` in `std`
```

instead of:

```rust
error[E0432]: unresolved import `std::bar::foo1`
 --> <anon>:1:16
  |
1 | use std::bar::{foo1, foo2};
  |                ^^^^ Could not find `bar` in `std`

error[E0432]: unresolved import `std::bar::foo2`
 --> <anon>:1:22
  |
1 | use std::bar::{foo1, foo2};
  |                      ^^^^ Could not find `bar` in `std`
```

Fix rust-lang#43040.

…=steveklabnik

add a note to Vec's Extend<&T> impl about its slice specialization

From the regular documentation view, it's not at all apparent that [this specialization](https://github.com/rust-lang/rust/blob/5669c9988f50788b5ab5dee2d4538519d4e5663d/src/liballoc/vec.rs#L1879-L1891) exists for `slice::Iter`. This adds a documentation blurb to the Extend impl itself to note that this optimization exists.

…chton

std::thread::spawn: Fix grammar in documentation

Closes rust-lang#43435.

Fix printing regions with -Z verbose

When dumping MIR with `-Z verbose`, it would print regions on types, but not in the code. It seems the Rvalue printing code tried to be smart and guessed when the `Display` for `Region` would not possibly print anything.

This PR makes it no longer be smart, and just always use the `Display` like all the other code (e.g. printing types) does.

DNS functions are in libresolv on Solaris, just like on MacOS

Fix the spans of catch blocks to include the `do`

…lacrum

Add tests for issues with the E-needstest label

Fixes rust-lang#19181.
Fixes rust-lang#29516.
Fixes rust-lang#29798.
Fixes rust-lang#33504.
Fixes rust-lang#34780.
Fixes rust-lang#39211.
Fixes rust-lang#39467.
Fixes rust-lang#39720.

Add missing impl and tests for int to int TryFrom impls

These were missing from rust-lang#43248.

r? @nagisa

Constrain the layout of Blake2bCtx for proper SPARC compilation

On SPARC, optimization fuel ends up emitting incorrect load and store
instructions for the transmute() call in blake2b_compress().  If we
force Blake2bCtx to be repr(C), the problem disappears.

Fixes rust-lang#43346