Rollup merge of #86517 - camsteffen:unused-unsafe-async, r=LeSeulArtichaut

Fix `unused_unsafe` around `await`

Enables `unused_unsafe` lint for `unsafe { future.await }`.

The existing test for this is `unsafe { println!() }`, so I assume that `println!` used to contain compiler-generated unsafe but this is no longer true, and so the existing test is broken. I replaced the test with `unsafe { ...await }`. I believe `await` is currently the only instance of compiler-generated unsafe.

Reverts some parts of #85421, but the issue predates that PR.

compiler/rustc_middle/src/mir/mod.rs

@@ -494,6 +494,8 @@ impl<'tcx> Body<'tcx> {
 #[derive(Copy, Clone, PartialEq, Eq, Debug, TyEncodable, TyDecodable, HashStable)]
 pub enum Safety {
     Safe,
+    /// Unsafe because of compiler-generated unsafe code, like `await` desugaring
+    BuiltinUnsafe,
     /// Unsafe because of an unsafe fn
     FnUnsafe,
     /// Unsafe because of an `unsafe` block

compiler/rustc_middle/src/thir.rs

@@ -114,6 +114,7 @@ pub struct Adt<'tcx> {
 #[derive(Copy, Clone, Debug, HashStable)]
 pub enum BlockSafety {
     Safe,
+    BuiltinUnsafe,
     ExplicitUnsafe(hir::HirId),
 }