Triggered by a discussion on wg-unsafe-code-guidelines about which layouts of
`Option<T>` one can guarantee are optimised to a single pointer.

Co-authored-by: Ralf Jung <[email protected]>

Co-authored-by: Ralf Jung <[email protected]>

…stead of whole format string

The main use case of TrustedLen is allowing APIs to specialize on it,
but no use of it uses that specialization. Instead, only the .len()
function provided by ExactSizeIterator is used, which is already
required to be accurate.

Thus, the TrustedLen requirement on BuilderMethods::switch is redundant.

This refactors handling of `Rvalue::{Unary,Binary}Op` in the
const-checker. Now we `span_bug` if there's an unexpected type in a
primitive operation. This also allows unary negation on
`char` values through the const-checker because it makes the code a bit
cleaner. `char` does not actually support these operations, and if it
did, we could evaluate them at compile-time.

It's called `span` elsewhere in the compiler and `span` is also less
surprising. `whence` is whimsical, but not super clear :)

…es, r=dtolnay

Explicitly document the size guarantees that Option makes.

Triggered by a discussion on wg-unsafe-code-guidelines about which layouts of `Option<T>` one can guarantee are optimised to a single pointer.

CC @RalfJung

…r=davidtwco

Point at named argument not found when using `format_args_capture` instead of whole format string

…s-slice-iter, r=Dylan-DPC

Add missing code examples on slice iter types

r? @Dylan-DPC

…r=varkor

merge `need_type_info_err(_const)`

I hoped that this would automatically solve rust-lang#76737 but it doesn't quite seem like it

fixes rust-lang#77092

r? @varkor

… r=RalfJung,oli-obk

Add `#![feature(const_fn_floating_point_arithmetic)]`

cc rust-lang#76618

This is a template for splitting up `const_fn` into granular feature gates. I think this will make it easier, both for us and for users, to track stabilization of each individual feature. We don't *have* to do this, however. We could also keep stabilizing things out from under `const_fn`.

cc @rust-lang/wg-const-eval
r? @oli-obk

…petrochenkov

Remove TrustedLen requirement from BuilderMethods::switch

The main use case of TrustedLen is allowing APIs to specialize on it,
but no use of it uses that specialization. Instead, only the .len()
function provided by ExactSizeIterator is used, which is already
required to be accurate.

Thus, the TrustedLen requirement on BuilderMethods::switch is redundant.

update Miri

Fixes rust-lang#77130

Remove stray word from `ClosureKind::extends` docs

Rename `whence` to `span`

It's called `span` elsewhere in the compiler and `span` is also less
surprising. `whence` is whimsical, but not super clear :)

See [this Discord conversation](https://discord.com/channels/442252698964721669/459149231702278154/758731658689511444) for more.

r? @jyn514

Remove unused #[allow(...)] statements from compiler/