The heading style for `std::prelude` is to be consistent with the
headings for `std` and `core`: `# The Rust Standard Library` and
`# The Rust Core Library`, respectively.

- Don't add backticks for the reason a lint was removed. This is almost
never a code block, and when it is the backticks should be in the reason
itself.
- Don't assume clippy is the only tool that needs to be checked for
backwards compatibility

No functional changes intended

As it was suggested in rust-lang#81037 `SpecFromIter` is not
in the scope and therefore (even it should fail),
we get a warning when we try do document private
intems in `rust/library/alloc/`.

This fixes rust-lang#81037 by adding the trait in the scope
and also adding an `allow(unused_imports)` flag so that
the compiler does not complain, Since the trait is not used
per se in the code, it's just needed to have properly documented
docs.

It's called at the same time and in the same place as `after_krate`, so
they can be combined.

formating -> formatting

Fixes rust-lang#80742

This was already implied because Any: 'static, but this makes it
explicit.

…ct, r=steveklabnik

Use consistent punctuation for 'Prelude contents' docs

…mar, r=m-ou-se

Improve grammar in documentation of format strings

The docs previously were
* using some weird `<` and `>` around some nonterminals
  * _correct me if these **did** have any meaning_
* using of a (not explicitly defined) `text` nonterminal that didn’t explicitly disallow productions containing `'{'` or `'}'`
* incorrect in not allowing for `x?` and `X?` productions of `type`
* unnecessarily ambiguous, both
  * allowing `type` to be `''`, and
  * using an optional `[type]`
* using inconsistent underscore/hyphenation style between `format_string` and `format_spec` vs `maybe-format`

_Rendered:_
![Screenshot_20210101_230901](https://user-images.githubusercontent.com/3986214/103447038-69d7a180-4c86-11eb-8fa0-0a6160a7ff7a.png)
_(current docs: https://doc.rust-lang.org/nightly/std/fmt/#syntax)_

`@rustbot` modify labels: T-doc

…ebank

Improve unknown external crate error

This improves error messages when unknown items in the crate root are encountered.

Fixes rust-lang#63799

r? `@estebank`

Fix formatting for removed lints

- Don't add backticks for the reason a lint was removed. This is almost
never a code block, and when it is the backticks should be in the reason
itself.
- Don't assume clippy is the only tool that needs to be checked for
backwards compatibility

I split this out of rust-lang#80527 because it kept causing tests to fail, and it's a good change to have anyway.

r? `@flip1995`

Fix intersperse_fold

Here is a standalone playground link in case anybody wants to modify code: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=626b4d044fb74f044a36098ad907e40f

Fixes rust-lang#81145

cc rust-lang#79479 `@jonas-schievink`

Visit only terminators when removing landing pads

No functional changes intended

…n514

Fix broken links with `--document-private-items` in the standard library

As it was suggested in rust-lang#81037 `SpecFromIter` is not
in the scope and therefore we get a warning when we try to
do document private intems in `rust/library/alloc/`.

This addresses rust-lang#81037 by adding the trait in the scope as `@jyn514`
suggested and also adding an `allow(unused_imports)` flag so that
the compiler does not complain, Since the trait is not used
per se in the code, it's just needed to have properly documented
docs.

Remove unnecessary `after_run` function

It's called at the same time and in the same place as `after_krate`, so
they can be combined.

Fix ICE in mir when evaluating SizeOf on unsized type

Not quite ready yet. This tries to fix rust-lang#80742 as discussed on [Zulip topic][1],
by using `delay_span_bug`.

I don't understand what `delay_span_bug` does. It seems like my error message
is never used. With this patch, in this program:

```rust
#![allow(incomplete_features)]
#![feature(const_evaluatable_checked)]
#![feature(const_generics)]

use std::fmt::Debug;
use std::marker::PhantomData;
use std::mem::size_of;

struct Inline<T>
where
    [u8; size_of::<T>() + 1]: ,
{
    _phantom: PhantomData<T>,
    buf: [u8; size_of::<T>() + 1],
}

impl<T> Inline<T>
where
    [u8; size_of::<T>() + 1]: ,
{
    pub fn new(val: T) -> Inline<T> {
        todo!()
    }
}

fn main() {
    let dst = Inline::<dyn Debug>::new(0); // line 27
}
```

these errors are printed, both for line 27 (annotated line above):

- "no function or associated item named `new` found for struct `Inline<dyn
  Debug>` in the current scope"
- "the size for values of type `dyn Debug` cannot be known at compilation time"

Second error makes sense, but I'm not sure about the first one and why it's
even printed.

Finally, I'm not sure about the span passing in `const_eval`.

[1]: https://rust-lang.zulipchat.com/#narrow/stream/269128-miri/topic/Help.20fixing.20.2380742

Fix typo in counters.rs

formating -> formatting

Stabilize std::panic::panic_any.

This stabilizes `std::panic::panic_any`.