Fixes rust-lang#73836

Make the following methods unstable const under the `const_pin` feature:
- `new`
- `new_unchecked`
- `into_inner`
- `into_inner_unchecked`
- `get_ref`
- `into_ref`

Also adds tests for these methods in a const context.

Tracking issue: rust-lang#76654

Only insert StorageDeads if we actually removed one.
Fixes an issue where we added StorageDead to a place with no StorageLive

Otherwise, we may not have a standard library built for the native "host" target
of the rustc being run.

This isn't an issue for most folks who use x.py dist, which will directly depend
on this. But for x.py build, if we don't properly set target here rustdoc will
not be built.

Currently, there is not a default-on step for generating a rustc for a given
target either, so we will fail to build a rustc as well.

Make the following methods unstable const under the `const_pin` feature:
- `into_ref`
- `get_mut`
- `get_unchecked_mut`

…d reduce nesting (clippy::single_match)

Co-authored-by: David Tolnay <dtolnay@gmail.com>

See
https://internals.rust-lang.org/t/need-for-controlling-drop-order-of-fields/12914/21
for the discussion.

TL;DR: ManuallyDrop is unsafe and footguny, but you can just ask the
compiler to do all the work for you by re-ordering declarations.

- Add a changelog and instructions for updating it
- Use `changelog-seen` in `config.toml` and `VERSION` in bootstrap to determine whether the changelog has been read
- Nag people if they haven't read the x.py changelog
  + Print message twice to make sure it's seen
- Give different error messages depending on whether the version needs to be updated or added

The case shouldn't be necessary and implicitly truncating BytePos is not
desirable.

If the right-hand iterator has exactly one more element than the
left-hand iterator, then both iterators will be fully consumed, but
the extra element will never be compared.

This is heavily dependent on MIR inlining running to actually see the drop statement

Co-authored-by: Andreas Jonson <andjo403@users.noreply.github.com>

Don't use `zip` to compare iterators during pretty-print hack

If the right-hand iterator has exactly one more element than the
left-hand iterator, then both iterators will be fully consumed, but
the extra element will never be compared.

Split out from rust-lang#76130

Don't recommend ManuallyDrop to customize drop order

See
https://internals.rust-lang.org/t/need-for-controlling-drop-order-of-fields/12914/21
for the discussion.

TL;DR: ManuallyDrop is unsafe and footguny, but you can just ask the compiler to do all the work for you by re-ordering declarations.

Specifically, the original example from the docs is much better written as

```rust
struct Peach;
struct Banana;
struct Melon;
struct FruitBox {
    melon: Melon,
    // XXX: mind the relative drop order of the fields below
    peach: Peach,
    banana: Banana,
}
```

…73836, r=dtolnay

Implementation of Write for some immutable ref structs

Fixes  rust-lang#73836

…6, r=jyn514

Add explanation for E0756

r? @pickfire

do not ICE on bound variables, return `TooGeneric` instead

fixes rust-lang#73260, fixes rust-lang#74634, fixes rust-lang#76595

r? @nikomatsakis

…acrum

Add a changelog for x.py and nag contributors until they read it

Add a changelog for x.py

- Add a changelog and instructions for updating it
- Use `changelog-seen` in `config.toml` and `VERSION` in bootstrap to determine whether the changelog has been read.  There's no way to tie reading the changelog to updating the version, so unfortunately they still have to update `config.toml` manually. Actually reading the changelog is optional, anyone can set `changelog-seen = N` without reading (although it's not recommended).
- Nag people if they haven't read the x.py changelog
  + Print message twice to make sure it's seen
- Give different error messages depending on whether the version needs to be updated or added

Closes rust-lang#76617
r? @Mark-Simulacrum

Make some methods of `Pin` unstable const

Make the following methods unstable const under the `const_pin` feature:
- `new`
- `new_unchecked`
- `into_inner`
- `into_inner_unchecked`
- `get_ref`
- `into_ref`
- `get_mut`
- `get_unchecked_mut`

Of these, `into_inner` and `into_inner_unchecked` require the unstable `const_precise_live_drops`.

Also adds tests for these methods in a const context.

Tracking issue: rust-lang#76654

r? @ecstatic-morse

SimplifyComparisonIntegral: fix miscompilation

Fixes rust-lang#76432
Only insert StorageDeads if we actually removed one.
Fixes an issue where we added StorageDead to a place with no StorageLive

r? @oli-obk

…r=oli-obk

MIR pass to remove unneeded drops on types not needing drop

This is heavily dependent on MIR inlining running to actually see the drop statement.

Do we want to special case replacing a call to std::mem::drop with a goto aswell?

Only get ImplKind::Impl once

With this, the code panics in one place instead of two.

…ist, r=alexcrichton

Fix cross compiling dist/build invocations

I am uncertain why the first commit is not affecting CI. I suspect it's because we pass --disable-docs on most of our cross-compilation builders. The second commit doesn't affect CI because CI runs x.py dist, not x.py build.

Both commits are standalone; together they should resolve rust-lang#76733. The first commit doesn't really fix that issue but rather just fixes cross-compiled x.py dist, resolving a bug introduced in rust-lang#76549.

… r=Dylan-DPC

use if let instead of single match arm expressions

use if let instead of single match arm expressions to compact code and reduce nesting (clippy::single_match)

Reduce boilerplate for BytePos and CharPos

Reduces boilerplate code for BytePos and CharPos by using a macro to implement shared traits.