When parsing `let x: i8 += 1` the compiler interprets `i8` as a trait
which makes it more complicated to do error recovery. More advanced
error recovery is not implemented in this commit.

Do not suggest new type param when encountering a missing type in an ADT
field with generic parameters.

Fix rust-lang#72640.

re rust-lang#72380 (comment)

Given the toy code

```rust
fn is_positive(n: usize) {
  n > -1_isize;
}
```

We currently get a type mismatch error like the following:

```
error[E0308]: mismatched types
 --> src/main.rs:2:9
  |
2 |     n > -1_isize;
  |         ^^^^^^^^ expected `usize`, found `isize`
  |
help: you can convert an `isize` to `usize` and panic if the converted value wouldn't fit
  |
2 |     n > (-1_isize).try_into().unwrap();
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

But clearly, `-1` can never fit into a `usize`, so the suggestion will
always panic. A more useful message would tell the user that the value
can never fit in the expected type:

```
error[E0308]: mismatched types
 --> test.rs:2:9
  |
2 |     n > -1_isize;
  |         ^^^^^^^^ expected `usize`, found `isize`
  |
note: `-1_isize` can never fit into `usize`
 --> test.rs:2:9
  |
2 |     n > -1_isize;
  |         ^^^^^^^^
```

Which is what this commit implements.

I only added this check for negative literals because

- Currently we can only perform such a check for literals (constant
  value propagation is outside the scope of the typechecker at this
  point)
- A lint error for out-of-range numeric literals is already emitted

IMO it makes more sense to put this check in librustc_lint, but as far
as I can tell the typecheck pass happens before the lint pass, so I've
added it here.

r? @estebank

`crt-static` is a rust specific target feature that's absent from llvm feature table, adding it there.

…s between OS

… return types

Fix rust-lang#70968, partially address rust-lang#66523.

Co-authored-by: lzutao <[email protected]>

Suggest new type parameter on single char uppercase ident even if it
doesn't appear in a field's type parameter.

Address comment in rust-lang#72641.

Separate target features from rust ones with a blank line

Co-authored-by: Josh Stone <[email protected]>

Make all uses of ty::Error delay a span bug

r? @eddyb

A second attempt at rust-lang#70245

resolves rust-lang#70866

…komatsakis

Expand "recursive opaque type" diagnostic

Fix rust-lang#70968, partially address rust-lang#66523.

Improve diagnostics for `let x += 1`

Fixes(?) rust-lang#66736

The code responsible for the `E0404` errors is [here](https://github.com/rust-lang/rust/blob/master/src/librustc_parse/parser/ty.rs#L399-L424) which I don't think can be easily modified to prevent emitting an error in one specific case. Because of this I couldn't get rid of `E0404` and instead added `E0067` along with a help message which will fix the problem.

r? @estebank

tag/niche terminology cleanup

The term "discriminant" was used in two ways throughout the compiler:
* every enum variant has a corresponding discriminant, that can be given explicitly with `Variant = N`.
* that discriminant is then encoded in memory to store which variant is active -- but this encoded form of the discriminant was also often called "discriminant", even though it is conceptually quite different (e.g., it can be smaller in size, or even use niche-filling).

After discussion with @eddyb, this renames the second term to "tag". The way the tag is encoded can be either `TagEncoding::Direct` (formerly `DiscriminantKind::Tag`) or `TagEncoding::Niche` (formerly `DiscrimianntKind::Niche`).

This finally resolves some long-standing confusion I had about the handling of variant indices and discriminants, which surfaced in rust-lang#72419.

(There is also a `DiscriminantKind` type in libcore, it remains unaffected. I think this corresponds to the discriminant, not the tag, so that seems all right.)

r? @eddyb

…epmaster

Add tests for 'impl Default for [T; N]'

Related: rust-lang#71690.
This pull request adds two tests:
- Even it T::default() panics, no leaks occur.
- [T; 0] is Default even if T is not.

I believe at some moment `Default` impl for arrays will be rewritten to use const generics instead of macros, and these tests will help to prevent behavior changes.

Added io forwarding methods to the stdio structs

Added methods to forward the `io::Read` and `io::Write` methods of the myriad wrapper structs in `stdio.rs` to their underlying readers / writers. This is especially important for the structs on the outside of a locking boundary, to ensure that the lock isn't being dropped and re-acquired in a loop.

…, r=nikomatsakis

Further tweak lifetime errors involving `dyn Trait` and `impl Trait` in return position

* Suggest substituting `'static` lifetime in impl/dyn `Trait + 'static` instead of `Trait + 'static + '_`
* When `'static` is explicit, also suggest constraining argument with it
* Reduce verbosity of suggestion message and mention lifetime in label
* Tweak output for overlapping required/captured spans
* Give these errors an error code

Follow up to rust-lang#72543.

r? @nikomatsakis

…i-obk

remove visit_terminator_kind from MIR visitor

For some reason, we had both `visit_terminator` and `visit_terminator_kind`. In contrast, for `Statement` we just have `visit_statement`. So this cleans things up by removing `visit_terminator_kind` and porting its users to `visit_terminator`.

…ies, r=shepmaster

Complete the std::time documentation to warn about the inconsistencies between OS

Fixes rust-lang#48980.

I put the new documentation in `src/libstd/time.rs` at the module-level because it affects all types, even the one that are not directly system dependents if they are used with affected types, but there may be a better place for it.

…llaumeGomez

Only highlight doc search results via mouseover if mouse has moved

## What happens

- Go to https://doc.rust-lang.org/stable/std/index.html
- Put your mouse cursor somewhere in the middle where search results will appear and then don't move the mouse
- Press 's' to focus the search box
- Type a query that brings up enough search results to go under where your mouse cursor is
- Press the down arrow
- The search result that is one below where your mouse cursor is will be highlighted.

## What I expected

When not currently using the mouse, I expect doing a search and then pressing the down arrow to always highlight the first search result immediately below the search box.

## The fix

This feels a bit hacky to me; I'm open to other solutions. This introduces a global JS var that keeps track of whether the person searching has moved their mouse after doing a search or not, and only uses the mouse position to highlight search results if the person HAS moved the mouse AFTER doing a search.

…matthewjasper

Export `#[inline]` fns with extern indicators

In ancient history (rust-lang#36280) we stopped `#[inline]` fns being codegened if they weren't used. However,

- rust-lang#72944
- rust-lang#72463

observe that when writing something like

```rust
#![crate_type = "cdylib"]

#[no_mangle]
#[inline]
pub extern "C" fn foo() {
    // ...
}
```

we really _do_ want `foo` to be codegened. This change makes this the case.

Resolves rust-lang#72944, resolves rust-lang#72463 (and maybe some more)

…, r=kinnison

Clean up some weird command strings

r? @kinnison

…vidtwco

Make new type param suggestion more targetted

Do not suggest new type param when encountering a missing type in an ADT
field with generic parameters.

Fix rust-lang#72640.

…r=estebank

Note numeric literals that can never fit in an expected type

re rust-lang#72380 (comment)

Given the toy code

```rust
fn is_positive(n: usize) {
  n > -1_isize;
}
```

We currently get a type mismatch error like the following:

```
error[E0308]: mismatched types
 --> src/main.rs:2:9
  |
2 |     n > -1_isize;
  |         ^^^^^^^^ expected `usize`, found `isize`
  |
help: you can convert an `isize` to `usize` and panic if the converted value wouldn't fit
  |
2 |     n > (-1_isize).try_into().unwrap();
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

But clearly, `-1` can never fit into a `usize`, so the suggestion will
always panic. A more useful message would tell the user that the value
can never fit in the expected type:

```
error[E0308]: mismatched types
 --> test.rs:2:9
  |
2 |     n > -1_isize;
  |         ^^^^^^^^ expected `usize`, found `isize`
  |
note: `-1_isize` can never fit into `usize`
 --> test.rs:2:9
  |
2 |     n > -1_isize;
  |         ^^^^^^^^
```

Which is what this commit implements.

I only added this check for negative literals because

- Currently we can only perform such a check for literals (constant
  value propagation is outside the scope of the typechecker at this
  point)
- A lint error for out-of-range numeric literals is already emitted

IMO it makes more sense to put this check in librustc_lint, but as far
as I can tell the typecheck pass happens before the lint pass, so I've
added it here.

r? @estebank

Add rust specific features to print target features

Fixes rust-lang#71583

`crt-static` is a rust specific target feature that's absent from llvm feature table, adding it there so that it shows under `rustc --print target-features`.

Probably the most native implementation I could think of, would love to get feedback.

… r=jonas-schievink

Document format correction

Minor amendments to the document.

r? @steveklabnik

Add specialization of `ToString for char`

Closes rust-lang#73462