Use `and_then` instead of while let chain to clarify `iter` scope
diff --git a/compiler/rustc_middle/src/mir/traversal.rs b/compiler/rustc_middle/src/mir/traversal.rs
index cc189a2..28b05f2 100644
--- a/compiler/rustc_middle/src/mir/traversal.rs
+++ b/compiler/rustc_middle/src/mir/traversal.rs
@@ -178,7 +178,7 @@
// When we yield `C` and call `traverse_successor`, we push `B` to the stack, but
// since we've already visited `E`, that child isn't added to the stack. The last
// two iterations yield `B` and finally `A` for a final traversal of [E, D, C, B, A]
- while let Some((_, iter)) = self.visit_stack.last_mut() && let Some(bb) = iter.next_back() {
+ while let Some(bb) = self.visit_stack.last_mut().and_then(|(_, iter)| iter.next_back()) {
if self.visited.insert(bb) {
if let Some(term) = &self.basic_blocks[bb].terminator {
self.visit_stack.push((bb, term.successors()));
