Make ExprKind::Closure a struct variant.

compiler/rustc_passes/src/upvars.rs

@@ -75,7 +75,7 @@ impl<'tcx> Visitor<'tcx> for CaptureCollector<'_, 'tcx> {
     }
 
     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
-        if let hir::ExprKind::Closure(..) = expr.kind {
+        if let hir::ExprKind::Closure { .. } = expr.kind {
             let closure_def_id = self.tcx.hir().local_def_id(expr.hir_id);
             if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
                 // Every capture of a closure expression is a local in scope,