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

Closes rust-lang#32254

closes rust-lang#31804

Closes rust-lang#31994

They were probably meant as a shorthand for omitted code.

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

Signed-off-by: NODA, Kai <nodakai@gmail.com>

Index 0 must be a valid char boundary (invariant of str that it contains
valid UTF-8 data).

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 zero.

With this change, the following examples all change from having a read of
the byte at 0 and a branch to possibly panicing, to having the bounds
checking optimized away.

```rust
pub fn split(s: &str) -> (&str, &str) {
    s.split_at(0)
}

pub fn both(s: &str) -> &str {
    &s[0..s.len()]
}

pub fn first(s: &str) -> &str {
    &s[..0]
}

pub fn last(s: &str) -> &str {
    &s[0..]
}
```

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

+ Fix a comment and add a test based on it

…t-lang#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.

Signed-off-by: David Henningsson <diwic@ubuntu.com>

to careful use of the span from deriving, we
can permit it in stable code if it derives from
deriving (not-even-a-pun intended)

this was required to preserve the span from
the #[structural_match] attribute -- but honestly
I am not 100% sure if it makes sense.

This is a [breaking-change]: according to RFC rust-lang#1445, constants used as
patterns must be of a type that *derives* `Eq`. 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 rust-lang#1445 for more details.

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

…patterns-2, r=pnkfelix

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 rust-lang#1445 for more details.

cc rust-lang#31434

r? @pnkfelix

…uron

std: Fix inheriting stdin on status()

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

Closes rust-lang#32254

Some fixes for error recovery in the compiler

Remove ungrammatical dots from the error index.

They were probably meant as a shorthand for omitted code.

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

… r=alexcrichton

Add augmented assignment operator impls for time types

r? @alexcrichton

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.

make available monomorphizations shared by CGU

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

…ichton

Fix unsound behaviour with null characters in thread names (issue rust-lang#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.

…agisa

use new visitor to erase regions

r? @nagisa