…ode base.

This also tests for the ICE in rust-lang#71734

`slice::fill`: use `T` instead of generic arg

implements rust-lang#70758 (comment)

As the discussion in rust-lang#70758 has shifted, I now use `T` instead of `&T`.

Implement RFC 2523, `#[cfg(version(..))]`

Hi! This is my first contribution to rust, I hope I didn't miss anything. I tried to implement this feature so that `#[cfg(version(1.44.0))]` works but the parser was printing an error that I wasn't sure how to fix so I just opted for implementing `#[cfg(version("1.44.0"))]` (note the quotes).

Tracking issue: rust-lang#64796

…chenkov

Implement `confusable_idents` lint.

This collects all identifier symbols into `ParseSession` and examines them within the non-ascii-idents lint.

The skeleton generation part needs to be added to `unicode-security` crate. Will update this PR when the crate is updated.

r? @petrochenkov

EDIT: also included the `concat_idents` part.

typo

Decode qualifs for associated const defaults

Fixes rust-lang#71734.

We encode qualifs for associated constants, but never expected to decode the qualifs for defaulted associated consts. Fix this, and test that associated const defaults have the correct qualifs cross-crate.

r? @tmandry