From 32005fe1957fc163036fbe0da8b12d39a9fb54cb Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Sat, 25 Jan 2020 02:28:41 +0100
Subject: [PATCH] Allow 0 or 1 explicit generator parameters

---
 src/librustc_ast_lowering/expr.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/librustc_ast_lowering/expr.rs b/src/librustc_ast_lowering/expr.rs
index 5dc855e935c..0c4cfa1f650 100644
--- a/src/librustc_ast_lowering/expr.rs
+++ b/src/librustc_ast_lowering/expr.rs
@@ -688,12 +688,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ) -> Option<hir::Movability> {
         match generator_kind {
             Some(hir::GeneratorKind::Gen) => {
-                if !decl.inputs.is_empty() {
+                if decl.inputs.len() > 1 {
                     struct_span_err!(
                         self.sess,
                         fn_decl_span,
                         E0628,
-                        "generators cannot have explicit parameters"
+                        "too many parameters for generator (expected 0 or 1 parameters)"
                     )
                     .emit();
                 }