rustdoc: Use diagnostics for error when including sources

This error probably almost never happens, but we should still use the
diagnostic infrastructure. My guess is that the error was added back
before rustdoc used the rustc diagnostic infrastructure (it was all
`println!` and `eprintln!` back then!) and since it likely rarely occurs
and this code doesn't change that much, no one thought to transition it
to using diagnostics.

Note that the old error was actually a warning (it didn't stop the rest
of doc building). It seems very unlikely that this would fail without
the rest of the doc build failing, so it makes more sense for it to be a
hard error.

The error looks like this:

    error: failed to render source code for `src/test/rustdoc/smart-punct.rs`: "bar": foo
      --> src/test/rustdoc/smart-punct.rs:3:1
       |
    3  | / #![crate_name = "foo"]
    4  | |
    5  | | //! This is the "start" of the 'document'! How'd you know that "it's" ...
    6  | | //!
    ...  |
    22 | | //! I say "don't smart-punct me -- please!"
    23 | | //! ```
       | |_______^

I wasn't sure how to trigger the error, so to create that message I
temporarily made rustdoc always emit it. That's also why it says "bar"
and "foo" instead of a real error message.

Note that the span of the diagnostic starts at line 3 because line 1 of
that file is a (non-doc) comment and line 2 is a blank line.

Add function core::iter::zip

This makes it a little easier to `zip` iterators:

```rust
for (x, y) in zip(xs, ys) {}
// vs.
for (x, y) in xs.into_iter().zip(ys) {}
```

You can `zip(&mut xs, &ys)` for the conventional `iter_mut()` and
`iter()`, respectively. This can also support arbitrary nesting, where
it's easier to see the item layout than with arbitrary `zip` chains:

```rust
for ((x, y), z) in zip(zip(xs, ys), zs) {}
for (x, (y, z)) in zip(xs, zip(ys, zs)) {}
// vs.
for ((x, y), z) in xs.into_iter().zip(ys).zip(xz) {}
for (x, (y, z)) in xs.into_iter().zip((ys.into_iter().zip(xz)) {}
```

It may also format more nicely, especially when the first iterator is a
longer chain of methods -- for example:

```rust
    iter::zip(
        trait_ref.substs.types().skip(1),
        impl_trait_ref.substs.types().skip(1),
    )
    // vs.
    trait_ref
        .substs
        .types()
        .skip(1)
        .zip(impl_trait_ref.substs.types().skip(1))
```

This replaces the tuple-pair `IntoIterator` in #78204.
There is prior art for the utility of this in [`itertools::zip`].

[`itertools::zip`]: https://docs.rs/itertools/0.10.0/itertools/fn.zip.html

update array missing `IntoIterator` msg

fixes #82602

r? ```@estebank``` do you know whether we can use the expr span in `rustc_on_unimplemented`? The label isn't too great rn

make unaligned_references future-incompat lint warn-by-default

and also remove the safe_packed_borrows lint that it replaces.

`std::ptr::addr_of!` has hit beta now and will hit stable in a month, so I propose we start fixing https://github.com/rust-lang/rust/issues/27060 for real: creating a reference to a field of a packed struct needs to eventually become a hard error; this PR makes it a warn-by-default future-incompat lint. (The lint already existed, this just raises its default level.) At the same time I removed the corresponding code from unsafety checking; really there's no reason an `unsafe` block should make any difference here.

For references to packed fields outside `unsafe` blocks, this means `unaligned_refereces` replaces the previous `safe_packed_borrows` warning with a link to https://github.com/rust-lang/rust/issues/82523 (and no more talk about unsafe blocks making any difference). So behavior barely changes, the warning is just worded differently. For references to packed fields inside `unsafe` blocks, this PR shows a new future-incompat warning.

Closes https://github.com/rust-lang/rust/issues/46043 because that lint no longer exists.

combine: stop eagerly evaluating consts

`super_relate_consts` eagerly evaluates constants which doesn't seem too great.

I now also finally understand why all of the unused substs test passed. The reason being
that we just evaluated the constants in `super_relate_consts` 😆

While this change isn't strictly necessary as evaluating consts here doesn't hurt, it still feels a lot cleaner to do it this way

r? `@oli-obk` `@nikomatsakis`

Rollup of 10 pull requests

Successful merges:

 - #79399 (Use detailed and shorter fs error explaination)
 - #83348 (format macro argument parsing fix)
 - #83462 (ExitStatus: print "exit status: {}" rather than "exit code: {}" on unix)
 - #83526 (lazily calls some fns)
 - #83558 (Use DebugStruct::finish_non_exhaustive() in std.)
 - #83559 (Fix Debug implementation for RwLock{Read,Write}Guard.)
 - #83560 (Derive Debug for io::Chain instead of manually implementing it.)
 - #83561 (Improve Debug implementations of Mutex and RwLock.)
 - #83567 (Update rustup cross-compilation docs link)
 - #83569 (Add regression tests for #56445)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Add regression tests for #56445

Closes #56445.

Update rustup cross-compilation docs link

Improve Debug implementations of Mutex and RwLock.

This improves the Debug implementations of Mutex and RwLock.

They now show the poison flag and use debug_non_exhaustive. (See #67364.)

Derive Debug for io::Chain instead of manually implementing it.

This derives Debug for io::Chain instead of manually implementing it.

The manual implementation has the same bounds, so I don't think there's any reason for a manual implementation. The names used in the derive implementation are even nicer (`first`/`second`) than the manual implementation (`t`/`u`), and include the `done_first` field too.

Fix Debug implementation for RwLock{Read,Write}Guard.

This would attempt to print the Debug representation of the lock that the guard has locked, which will try to lock again, fail, and just print `"<locked>"` unhelpfully.

After this change, this just prints the contents of the mutex, like the other smart pointers (and MutexGuard) do.

MutexGuard had this problem too: https://github.com/rust-lang/rust/issues/57702

Use DebugStruct::finish_non_exhaustive() in std.

See https://github.com/rust-lang/rust/issues/67364

lazily calls some fns

Replaced some fn's with it's lazy variants.

ExitStatus: print "exit status: {}" rather than "exit code: {}" on unix

Proper Unix terminology is "exit status" (vs "wait status").  "exit
code" is imprecise on Unix and therefore unclear.  (As far as I can
tell, "exit code" is correct terminology on Windows.)

This new wording is unfortunately inconsistent with the identifier
names in the Rust stdlib.

It is the identifier names that are wrong, as discussed at length in eg
  https://doc.rust-lang.org/nightly/std/process/struct.ExitStatus.html
  https://doc.rust-lang.org/nightly/std/os/unix/process/trait.ExitStatusExt.html

Unfortunately for API stability reasons it would be a lot of work, and
a lot of disruption, to change the names in the stdlib (eg to rename
`std::process::ExitStatus` to `std::process::ChildStatus` or
something), but we should fix the message output.  Many (probably
most) readers of these messages about exit statuses will be users and
system administrators, not programmers, who won't even know that Rust
has this wrong terminology.

So I think the right thing is to fix the documentation (as I have
already done) and, now, the terminology in the implementation.

This is a user-visible change to the behaviour of all Rust programs
which run Unix subprocesses.  Hopefully no-one is matching against the
exit status string, except perhaps in tests.

format macro argument parsing fix

When the character next to `{}` is "shifted" (when mapping a byte index
in the format string to span) we should avoid shifting the span end
index, so first map the index of `}` to span, then bump the span,
instead of first mapping the next byte index to a span (which causes
bumping the end span too much).

Regression test added.

Fixes #83344

---

r? ```@estebank```

Use detailed and shorter fs error explaination

Includes suggestion from `@the8472` https://github.com/rust-lang/rust/issues/79390#issuecomment-733263336

make unaligned_refereces future-incompat lint warn-by-default, and remove the safe_packed_borrows lint that it replaces

Closes #56445.

Generalize and inline slice::fill specializations

This makes the memset specialization applicable to more types. And since the code now lives in a generic method it is also eligible for cross-crate inlining which  should fix #83235

Includes suggestion from the8472 https://github.com/rust-lang/rust/issues/79390#issuecomment-733263336

More detail error explanation in fs doc

They now show the poison flag and use debug_non_exhaustive.

The manual implementation has the same bounds, so I don't think there's
any reason for a manual implementation. The names used in the derive
implementation are even nicer (`first`/`second`) than the manual
implementation (`t`/`u`), and include the `done_first` field too.

This would attempt to print the Debug representation of the lock that
the guard has locked, which will try to lock again, fail, and just print
"<locked>" unhelpfully.

After this change, this just prints the contents of the mutex, like the
other smart pointers (and MutexGuard) do.

Add IEEE 754 compliant fmt/parse of -0, infinity, NaN

This pull request improves the Rust float formatting/parsing libraries to comply with IEEE 754's formatting expectations around certain special values, namely signed zero, the infinities, and NaN. It also adds IEEE 754 compliance tests that, while less stringent in certain places than many of the existing flt2dec/dec2flt capability tests, are intended to serve as the beginning of a roadmap to future compliance with the standard. Some relevant documentation is also adjusted with clarifying remarks.

This PR follows from discussion in https://github.com/rust-lang/rfcs/issues/1074, and closes #24623.

The most controversial change here is likely to be that -0 is now printed as -0. Allow me to explain: While there appears to be community support for an opt-in toggle of printing floats as if they exist in the naively expected domain of numbers, i.e. not the extended reals (where floats live), IEEE 754-2019 is clear that a float converted to a string should be capable of being transformed into the original floating point bit-pattern when it satisfies certain conditions (namely, when it is an actual numeric value i.e. not a NaN and the original and destination float width are the same). -0 is given special attention here as a value that should have its sign preserved. In addition, the vast majority of other programming languages not only output `-0` but output `-0.0` here.

While IEEE 754 offers a broad leeway in how to handle producing what it calls a "decimal character sequence", it is clear that the operations a language provides should be capable of round tripping, and it is confusing to advertise the f32 and f64 types as binary32 and binary64 yet have the most basic way of producing a string and then reading it back into a floating point number be non-conformant with the standard. Further, existing documentation suggested that e.g. -0 would be printed with -0 regardless of the presence of the `+` fmt character, but it prints "+0" instead if given such (which was what led to the opening of #24623).

There are other parsing and formatting issues for floating point numbers which prevent Rust from complying with the standard, as well as other well-documented challenges on the arithmetic level, but I hope that this can be the beginning of motion towards solving those challenges.

When the character next to `{}` is "shifted" (when mapping a byte index
in the format string to span) we should avoid shifting the span end
index, so first map the index of `}` to span, then bump the span,
instead of first mapping the next byte index to a span (which causes
bumping the end span too much).

Regression test added.

Fixes #83344

Rollup of 9 pull requests

Successful merges:

 - #83239 (Remove/replace some outdated crates from the dependency tree)
 - #83328 (Fixes to inline assmebly tests)
 - #83343 (Simplify and fix byte skipping in format! string parser)
 - #83388 (Make # pretty print format easier to discover)
 - #83431 (Tell GitHub to highlight `config.toml.example` as TOML)
 - #83508 (Use the direct link to the platform support page)
 - #83511 (compiletest: handle llvm_version with suffix like "12.0.0libcxx")
 - #83524 (Document that the SocketAddr memory representation is not stable)
 - #83525 (fix doc comment for `ty::Dynamic`)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

fix doc comment for `ty::Dynamic`

Document that the SocketAddr memory representation is not stable

Intended to help out with #78802. Work has been put into finding and fixing code that assumes the memory layout of `SocketAddrV4` and `SocketAddrV6`. But it turns out there are cases where new code continues to make the same assumption ([example](https://github.com/spacejam/seaslug/commit/96927dc2b7b918860a79c4eb6336051e52c6137a#diff-917db3d8ca6f862ebf42726b23c72a12b35e584e497ebdb24e474348d7c6ffb6R610-R621)).

The memory layout of a type in `std` is never part of the public API. Unless explicitly stated I guess. But since that is invalidly relied upon by a considerable amount of code for these particular types, it might make sense to explicitly document this. This can be temporary. Once #78802 lands it does not make sense to rely on the layout any longer, and this documentation can also be removed.

compiletest: handle llvm_version with suffix like "12.0.0libcxx"

The previous code only remove the suffix begin with `-`, but Gentoo Linux [define `LLVM_VERSION_SUFFIX="libcxx"`](https://github.com/gentoo/gentoo/blob/604d79f327176eecb05293d7154e24231229cb31/sys-devel/llvm/llvm-11.1.0.ebuild#L378) when llvm is linked to libc++ and lead to a panic:

```
thread 'main' panicked at 'Malformed version component: ParseIntError { kind: InvalidDigit }', src/tools/compiletest/src/header.rs:968:28
```

This new code will handle all suffix not beginning with digit or dot.

Use the direct link to the platform support page

Tell GitHub to highlight `config.toml.example` as TOML

This should be a nice small quality of life improvement when looking at
`config.toml.example` on GitHub or looking at diffs of it in PRs.

Make # pretty print format easier to discover

# Rationale:

I use (cargo cult?) three formats in rust:  `{}`, debug `{:?}`, and pretty-print debug `{:#?}`. I discovered `{:#?}` in some blog post or guide when I started working in Rust. While `#` is documented I think it is hard to discover. So taking the good advice of ```@carols10cents```  I am trying to improve the docs with a PR

As a reminder "pretty print" means that where `{:?}` will print something like
```
foo: { b1: 1, b2: 2}
```

`{:#?}` will prints something like
```
foo {
  b1: 1
  b2: 3
}
```

# Changes
Add an example to `fmt` to try and make it easier to discover `#`

Simplify and fix byte skipping in format! string parser

Fixes '\\' handling in format strings.

Fixes #83340

Fixes to inline assmebly tests

* Join test thread to make assertion effective in sym.rs test case
* Use a single codegen unit to reduce non-determinism in srcloc.rs test #82886