…y annotation

Co-authored-by: Ralf Jung <post@ralfj.de>

The recursive check of `try_print_visible_def_path` did not properly handle
the Rust 2018 case of crate-paths without 'extern crate'. Instead, it returned
a "not found" via (false, self).

This fixes issue rust-lang#56175.

The thread that recovers the unique access to Arc inner value (e.g., drop
when ref-count strong reaches zero, successful try_unwrap), ensures that
other operations on Arc inner value happened before by synchronizing
with release operations performed when decrementing the reference counter.

When try_unwrap succeeds, the current thread recovers the unique access
to Arc inner value, so release is unnecessary.

Co-authored-by: varkor <github@varkor.com>

added .collect() into String from Box<str>

I have not created an rfc, because i felt like this is a very minor change.

i have just set a random feature name and rust version as stability attribute, i expect to have to change that, i just don't know what the policy on that is. all guides i could find focused on contributing to the compiler, not contributing to the standard library.

drawbacks: more code in the standard library, could be replaced with specialization: base-implementation for AsRef\<str> and specialization for String and Cow. i can write that code if ppl want it.

advantages: using "real strings" i.e. Box\<str> is as ergonomic as string slices (&str) and string buffers (String) with iterators.

Add unstable docs for rustc_attrs

r? @RalfJung

…-morse

Some refactoring around intrinsic type checking

So... This PR went a bit overboard. I wanted to make the `rustc_peek` intrinsic safe (cc @ecstatic-morse ), and remembered a long-standing itch of mine. So I made that huge `&str` match for the intrinsic name a match on `Symbol`s (so basically `u32`s). This is unlikely to have a positive perf effect, even if it likely has better codegen (intrinsics are used rarely, mostly once in their wrapper), so it's mostly a consistency thing since other places actually match on the symbol name of the intrinsics.

…r=petrochenkov

Fix try_print_visible_def_path for Rust 2018

The recursive check of `try_print_visible_def_path` did not properly handle the Rust 2018 case of crate-paths without 'extern crate'. Instead, it returned a "not found" via (false, self).

 This fixes rust-lang#56175.

…, r=varkor

Explain exhaustive matching on {usize,isize} maximum values

The wording is taken from https://github.com/rust-lang/rfcs/blob/master/text/2591-exhaustive-integer-pattern-matching.md#reference-level-explanation.
Fixes rust-lang#73919

r? @varkor

Use `Span`s to identify unreachable subpatterns in or-patterns

Fixes rust-lang#71977

…arkor

add `lazy_normalization_consts` feature gate

In rust-lang#71973 I underestimated the amount of code which is influenced by lazy normalization of consts
and decided against having a separate feature flag for this.

Looking a bit more into this, the following issues are already working with lazy norm in its current state rust-lang#47814 rust-lang#57739 rust-lang#73980

I therefore think it is worth it to enable lazy norm separately. Note that `#![feature(const_generics)]` still automatically activates
this feature, so using `#![feature(const_generics, lazy_normalization_consts)]` is redundant.

r? @varkor @nikomatsakis

Remove unnecessary release from Arc::try_unwrap

The thread that recovers the unique access to Arc inner value (e.g., drop
when ref-count strong reaches zero, successful try_unwrap), ensures that
other operations on Arc inner value happened before by synchronizing
with release operations performed when decrementing the reference counter.

When try_unwrap succeeds, the current thread recovers the unique access
to Arc inner value, so release is unnecessary.

r? @Amanieu

Convert more `DefId`s to `LocalDefId`s

Fix spacing in Iterator fold doc

expected_found `&T` -> `T`

…=kennytm

variant_count: avoid incorrect dummy implementation

This also avoids a stage 0 doctest failure.