…from HRTB

Improve Markdown styling in README

Update Readme to use consistent line lengths. Also update some formatting and links. (Followup to rust-lang#105553).

r? ``@workingjubilee``

…tebank

Add 'static lifetime suggestion when GAT implied 'static requirement from HRTB

Fix for issue rust-lang#105507

The problem:
When generic associated types (GATs) are from higher-ranked trait bounds (HRTB), they are implied 'static requirement (see
[Implied 'static requirement from higher-ranked trait bounds](https://blog.rust-lang.org/2022/10/28/gats-stabilization.html#implied-static-requirement-from-higher-ranked-trait-bounds) for more details). If the user did not explicitly specify the `'static` lifetime when using the GAT, the current error message will only point out the type `does not live long enough` where the type is used, but not where the GAT is specified and how to fix the problem.

The solution:
Add notes at the span where the problematic GATs are specified and suggestions of how to fix the problem by adding `'static` lifetime at the right spans.

…piler-errors

dont randomly use `_` to print out const generic arguments

const generics seem to get printed out as `_` for no reason a lot of the time, as someone who spends a lot of time with const generics this has gotten ✨ very annoying ✨. Latest example would be rust-lang#106423 where the ICE messaged formatted a `ty::Const` containing no infer vars, as `_`.

For some reason printing of the const argument on arrays was custom instead of using the existing logic for printing `ty::Const`. Additionally the existing logic for printing `ty::Const` would print out `_` for anon consts that are in a separate crate leading to weird diagnostics (see second commit). There ought to be less cases of consts randomly getting printed as `_` hiding valuable info now.

…thomcc

Remove unused `#![feature(box_syntax)]` in `alloc`

…est, r=cuviper

bump failing assembly & codegen tests from LLVM 14 to LLVM 15

These tests need LLVM 15.

Found by ```@Robert-Cunningham``` in rust-lang#100601 (comment)

Passed tests at 006506e93fc80318ebfd7939fe1fd4dc19ecd8cb in https://github.com/rust-lang/rust/actions/runs/3942442730/jobs/6746104740.

…div, r=GuillaumeGomez

rustdoc: instead of `.setting-name { width: 100% }`, use default div CSS

This has no discernible change in appearance.

Add heapsort fallback in `select_nth_unstable`

Addresses rust-lang#102451 and rust-lang#106933.

`slice::select_nth_unstable` uses a quick select implementation based on the same pattern defeating quicksort algorithm that `slice::sort_unstable` uses. `slice::sort_unstable` uses a recursion limit and falls back to heapsort if there were too many bad pivot choices, to ensure O(n log n) worst case running time (known as introsort). However, `slice::select_nth_unstable` does not have such a fallback strategy, which leads to it having a worst case running time of O(n²) instead. rust-lang#102451 links to a playground which generates pathological inputs that show this quadratic behavior. On my machine, a randomly generated slice of length `1 << 19` takes ~200µs to calculate its median, whereas a pathological input of the same length takes over 2.5s. This PR adds an iteration limit to `select_nth_unstable`, falling back to heapsort, which ensures an O(n log n) worst case running time (introselect). With this change, there was no noticable slowdown for the random input, but the same pathological input now takes only ~1.2ms. In the future it might be worth implementing something like Median of Medians or Fast Deterministic Selection instead, which guarantee O(n) running time for all possible inputs. I've left this as a `FIXME` for now and only implemented the heapsort fallback to minimize the needed code changes.

I still think we should clarify in the `select_nth_unstable` docs that the worst case running time isn't currently O(n) (the original reason that rust-lang#102451 was opened), but I think it's a lot better to be able to guarantee O(n log n) instead of O(n²) for the worst case.