Always perform discr read for never pattern in EUV

Author: compiler-errors

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -943,6 +943,10 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 let mutability = if mutable { hir::Mutability::Mut } else { hir::Mutability::Not };
                 let bk = ty::BorrowKind::from_mutbl(mutability);
                 self.delegate.borrow_mut().borrow(place, discr_place.hir_id, bk);
+            } else if let PatKind::Never = pat.kind {
+                // A `!` pattern always counts as an immutable read of the discriminant,
+                // even in an irrefutable pattern.
+                self.delegate.borrow_mut().borrow(place, discr_place.hir_id, BorrowKind::Immutable);
             }
 
             Ok(())

tests/ui/rfcs/rfc-0000-never_patterns/always-read-in-closure-capture.rs

@@ -0,0 +1,16 @@
+//@ check-pass
+
+// Make sure that the closure captures `s` so it can perform a read of `s`.
+
+#![feature(never_patterns)]
+#![allow(incomplete_features)]
+
+enum Void {}
+
+fn by_value(s: Void) {
+    move || {
+        let ! = s;
+    };
+}
+
+fn main() {}