Closes rust-lang#58692

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

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

Prior art:

`rust_analyzer` uses
[`Parser::eat`](https://github.com/rust-analyzer/rust-analyzer/blob/50f4ae798b7c54d417ee88455b87fd0477473150/crates/ra_parser/src/parser.rs#L94), which is `next_if` specialized to
`|y| next_if(|x| x == y)`.

Basically every other parser I've run into in Rust has an equivalent of
Parser::eat; see for example

- [cranelift](https://github.com/bytecodealliance/wasmtime/blob/94190d57244b26baf36629c88104b0ba516510cf/cranelift/reader/src/parser.rs#L498)
- [rcc](https://github.com/jyn514/rcc/blob/a8159c3904a0c950fbba817bf9109023fad69033/src/parse/mod.rs#L231)
- [crunch](https://github.com/Kixiron/crunch-lang/blob/8521874fab8a7d62bfa7dea8bd1da94b63e31be8/crates/crunch-parser/src/parser/mod.rs#L213-L241)

Add Peekable::next_if

Prior art:

`rust_analyzer` uses [`Parser::eat`](https://github.com/rust-analyzer/rust-analyzer/blob/50f4ae798b7c54d417ee88455b87fd0477473150/crates/ra_parser/src/parser.rs#L94), which is `next_if` specialized to `|y| self.next_if(|x| x == y)`.

Basically every other parser I've run into in Rust has an equivalent of `Parser::eat`; see for example

- [cranelift](https://github.com/bytecodealliance/wasmtime/blob/94190d57244b26baf36629c88104b0ba516510cf/cranelift/reader/src/parser.rs#L498)
- [rcc](https://github.com/jyn514/rcc/blob/a8159c3904a0c950fbba817bf9109023fad69033/src/parse/mod.rs#L231)
- [crunch](https://github.com/Kixiron/crunch-lang/blob/8521874fab8a7d62bfa7dea8bd1da94b63e31be8/crates/crunch-parser/src/parser/mod.rs#L213-L241)

Possible extensions: A specialization of `next_if` to using `Eq::eq`. The only difficulty here is the naming - maybe `next_if_eq`?

Alternatives:
- Instead of `func: impl FnOnce(&I::Item) -> bool`, use `func: impl FnOnce(I::Item) -> Option<I::Item>`. This has the advantage that `func` can move the value if necessary, but means that there is no guarantee `func` will return the same value it was given.
- Instead of `fn next_if(...) -> Option<I::Item>`, use `fn next_if(...) -> bool`. This makes the common case of `iter.next_if(f).is_some()` easier, but makes the unusual case impossible.

Bikeshedding on naming:
- `next_if` could be renamed to `consume_if` (to match `eat`, but a little more formally)
- `next_if_eq` could be renamed to `consume`. This is more concise but less self-explanatory if you haven't written a lot of parsers.
- Both of the above, but with `consume` replaced by `eat`.

Added a codegen test for a recent optimization for overflow-checks=on

Closes rust-lang#58692

… r=sfackler

Implement total_cmp for f32, f64

# Overview
* Implements method `total_cmp` on `f32` and `f64`. This method implements a float comparison that, unlike the standard `partial_cmp`, is total (defined on all values) in accordance to the IEEE 754 (rev 2008) §5.10 `totalOrder` predicate.
* The method has an API similar to `cmp`: `pub fn total_cmp(&self, other: &Self) -> crate::cmp::Ordering { ... }`.
* Implements tests.
* Has documentation.

# Justification for the API
* Total ordering for `f32` and `f64` has been discussed many time before:
  * https://internals.rust-lang.org/t/pre-pre-rfc-range-restricting-wrappers-for-floating-point-types/6701
  * rust-lang/rfcs#1249
  * rust-lang#53938
  * rust-lang#5585
* The lack of total ordering leads to frequent complaints, especially from people new to Rust.
  * This is an ergonomics issue that needs to be addressed.
  * However, the default behaviour of implementing only `PartialOrd` is intentional, as relaxing it might lead to correctness issues.
* Most earlier implementations and discussions have been focusing on a wrapper type that implements trait `Ord`. Such a wrapper type is, however not easy to add because of the large API surface added.
* As a minimal step that hopefully proves uncontroversial, we can implement a stand-alone method `total_cmp` on floating point types.
  * I expect adding such methods should be uncontroversial because...
    * Similar methods on `f32` and `f64` would be warranted even in case stdlib would provide a wrapper type that implements `Ord` some day.
    * It implements functionality that is standardised. (IEEE 754, 2008 rev. §5.10 Note, that the 2019 revision relaxes the ordering. The way we do ordering in this method conforms to the stricter 2008 standard.)
* With stdlib APIs such as `slice::sort_by` and `slice::binary_search_by` that allow users to provide a custom ordering criterion, providing additional helper methods is a minimal way of adding ordering functionality.
  * Not also does it allow easily using aforementioned APIs, it also provides an easy and well-tested primitive for the users and library authors to implement an `Ord`-implementing wrapper, if needed.

…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.

Add myself to .mailmap