Auto merge of #101212 - eholk:dyn-star, r=compiler-errors

Initial implementation of dyn*

This PR adds extremely basic and incomplete support for [dyn*](https://smallcultfollowing.com/babysteps//blog/2022/03/29/dyn-can-we-make-dyn-sized/). The goal is to get something in tree behind a flag to make collaboration easier, and also to make sure the implementation so far is not unreasonable. This PR does quite a few things:

* Introduce `dyn_star` feature flag
* Adds parsing for `dyn* Trait` types
* Defines `dyn* Trait` as a sized type
* Adds support for explicit casts, like `42usize as dyn* Debug`
  * Including const evaluation of such casts
* Adds codegen for drop glue so things are cleaned up properly when a `dyn* Trait` object goes out of scope
* Adds codegen for method calls, at least for methods that take `&self`

Quite a bit is still missing, but this gives us a starting point. Note that this is never intended to become stable surface syntax for Rust, but rather `dyn*` is planned to be used as an implementation detail for async functions in dyn traits.

Joint work with `@nikomatsakis` and `@compiler-errors.`

r? `@bjorn3`

1 files changed, 2 insertions, 2 deletions

diff --git a/src/tools/clippy/clippy_lints/src/transmute/utils.rs b/src/tools/clippy/clippy_lints/src/transmute/utils.rs
index 74927570b40..8bdadf24402 100644
--- a/src/tools/clippy/clippy_lints/src/transmute/utils.rs
+++ b/src/tools/clippy/clippy_lints/src/transmute/utils.rs
@@ -2,7 +2,7 @@ use rustc_hir::Expr;
 use rustc_lint::LateContext;
 use rustc_middle::ty::{cast::CastKind, Ty};
 use rustc_span::DUMMY_SP;
-use rustc_typeck::check::{cast::CastCheck, FnCtxt, Inherited};
+use rustc_typeck::check::{cast::{self, CastCheckResult}, FnCtxt, Inherited};
 
 // check if the component types of the transmuted collection and the result have different ABI,
 // size or alignment
@@ -53,7 +53,7 @@ fn check_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>
             "Newly created FnCtxt contained errors"
         );
 
-        if let Ok(check) = CastCheck::new(
+        if let CastCheckResult::Deferred(check) = cast::check_cast(
             &fn_ctxt, e, from_ty, to_ty,
             // We won't show any error to the user, so we don't care what the span is here.
             DUMMY_SP, DUMMY_SP,