Address closure-related review

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -750,6 +750,15 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
  }
  }
  }
+ } else if let PatKind::Deref(subpattern) = pat.kind {
+ // A deref pattern is a bit special: the binding mode of its inner bindings
+ // determines whether to borrow *at the level of the deref pattern* rather than
+ // borrowing the bound place (since that inner place is inside the temporary that
+ // stores the result of calling `deref()`/`deref_mut()` so can't be captured).
+ let mutable = mc.typeck_results.pat_has_ref_mut_binding(subpattern);
+ let mutability = if mutable { hir::Mutability::Mut } else { hir::Mutability::Not };
+ let bk = ty::BorrowKind::from_mutbl(mutability);
+ delegate.borrow(place, discr_place.hir_id, bk);
  }
  }));
  }

compiler/rustc_hir_typeck/src/mem_categorization.rs

@@ -719,7 +719,11 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
  self.cat_pattern_(subplace, subpat, op)?;
  }
  PatKind::Deref(subpat) => {
+ let mutable = self.typeck_results.pat_has_ref_mut_binding(subpat);
+ let mutability = if mutable { hir::Mutability::Mut } else { hir::Mutability::Not };
+ let re_erased = self.tcx().lifetimes.re_erased;
  let ty = self.pat_ty_adjusted(subpat)?;
+ let ty = Ty::new_ref(self.tcx(), re_erased, ty, mutability);
  // A deref pattern generates a temporary.
  let place = self.cat_rvalue(pat.hir_id, ty);
  self.cat_pattern_(place, subpat, op)?;

compiler/rustc_middle/src/ty/typeck_results.rs

@@ -451,7 +451,7 @@ impl<'tcx> TypeckResults<'tcx> {
  /// This is computed from the typeck results since we want to make
  /// sure to apply any match-ergonomics adjustments, which we cannot
  /// determine from the HIR alone.
- pub fn pat_has_ref_mut_binding(&self, pat: &'tcx hir::Pat<'tcx>) -> bool {
+ pub fn pat_has_ref_mut_binding(&self, pat: &hir::Pat<'_>) -> bool {
  let mut has_ref_mut = false;
  pat.walk(|pat| {
  if let hir::PatKind::Binding(_, id, _, _) = pat.kind

tests/ui/pattern/deref-patterns/closure_capture.rs

@@ -0,0 +1,21 @@
+//@ run-pass
+#![feature(deref_patterns)]
+#![allow(incomplete_features)]
+
+fn main() {
+ let b = Box::new("aaa".to_string());
+ let f = || {
+ let deref!(ref s) = b else { unreachable!() };
+ assert_eq!(s.len(), 3);
+ };
+ assert_eq!(b.len(), 3);
+ f();
+
+ let mut b = Box::new("aaa".to_string());
+ let mut f = || {
+ let deref!(ref mut s) = b else { unreachable!() };
+ s.push_str("aa");
+ };
+ f();
+ assert_eq!(b.len(), 5);
+}