Fix diagnostics for async block cloning

Author: wutchzone

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -4,6 +4,7 @@
 #![allow(rustc::untranslatable_diagnostic)]
 
 use either::Either;
+use hir::ClosureKind;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::{codes::*, struct_span_code_err, Applicability, Diag, MultiSpan};
@@ -463,6 +464,15 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 } else if let UseSpans::FnSelfUse { kind: CallKind::Normal { .. }, .. } = move_spans
                 {
                     // We already suggest cloning for these cases in `explain_captures`.
+                } else if let UseSpans::ClosureUse {
+                    closure_kind:
+                        ClosureKind::Coroutine(CoroutineKind::Desugared(_, CoroutineSource::Block)),
+                    args_span: _,
+                    capture_kind_span: _,
+                    path_span,
+                } = move_spans
+                {
+                    self.suggest_cloning(err, ty, expr, path_span);
                 } else if self.suggest_hoisting_call_outside_loop(err, expr) {
                     // The place where the the type moves would be misleading to suggest clone.
                     // #121466

tests/ui/borrowck/cloning-in-async-block-121547.rs

@@ -0,0 +1,11 @@
+//@ edition:2021
+
+async fn clone_async_block(value: String) {
+    for _ in 0..10 {
+        async { //~ ERROR: use of moved value: `value` [E0382]
+            drop(value);
+            //~^ HELP: consider cloning the value if the performance cost is acceptable
+        }.await
+    }
+}
+fn main() {}

tests/ui/borrowck/cloning-in-async-block-121547.stderr

@@ -0,0 +1,22 @@
+error[E0382]: use of moved value: `value`
+  --> $DIR/cloning-in-async-block-121547.rs:5:9
+   |
+LL |   async fn clone_async_block(value: String) {
+   |                              ----- move occurs because `value` has type `String`, which does not implement the `Copy` trait
+LL |       for _ in 0..10 {
+   |       -------------- inside of this loop
+LL | /         async {
+LL | |             drop(value);
+   | |                  ----- use occurs due to use in coroutine
+LL | |
+LL | |         }.await
+   | |_________^ value moved here, in previous iteration of loop
+   |
+help: consider cloning the value if the performance cost is acceptable
+   |
+LL |             drop(value.clone());
+   |                       ++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0382`.