Make multiple_unsafe_ops_per_block ignore await desugaring

The await desugaring contains two calls (`Poll::new_unchecked` and
`get_context`) inside a single unsafe block. That violates the lint.

clippy_lints/src/multiple_unsafe_ops_per_block.rs

@@ -9,7 +9,7 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
-use rustc_span::Span;
+use rustc_span::{DesugaringKind, Span};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -64,7 +64,10 @@ declare_lint_pass!(MultipleUnsafeOpsPerBlock => [MULTIPLE_UNSAFE_OPS_PER_BLOCK])
 
 impl<'tcx> LateLintPass<'tcx> for MultipleUnsafeOpsPerBlock {
     fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
-        if !matches!(block.rules, BlockCheckMode::UnsafeBlock(_)) || in_external_macro(cx.tcx.sess, block.span) {
+        if !matches!(block.rules, BlockCheckMode::UnsafeBlock(_))
+            || in_external_macro(cx.tcx.sess, block.span)
+            || block.span.is_desugaring(DesugaringKind::Await)
+        {
             return;
         }
         let mut unsafe_ops = vec![];

tests/ui/multiple_unsafe_ops_per_block.rs

@@ -147,4 +147,11 @@ fn _field_fn_ptr(x: unsafe fn()) {
     }
 }
 
+// await expands to an unsafe block with several operations, but this is fine.: #11312
+async fn await_desugaring_silent() {
+    async fn helper() {}
+
+    helper().await;
+}
+
 fn main() {}