From da46eeac88ea24c8c7b5d78c5ac4e0fe681ef13e Mon Sep 17 00:00:00 2001
From: Yuki OKUSHI <huyuumi.dev@gmail.com>
Date: Tue, 30 Apr 2019 20:43:03 +0900
Subject: [PATCH] Add error for existential types

---
 src/librustc_passes/ast_validation.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/librustc_passes/ast_validation.rs b/src/librustc_passes/ast_validation.rs
index 9dd8a7050fd..a482f60897b 100644
--- a/src/librustc_passes/ast_validation.rs
+++ b/src/librustc_passes/ast_validation.rs
@@ -679,6 +679,12 @@ fn visit_item(&mut self, item: &'a Item) {
                                                 "unions cannot have zero fields");
                 }
             }
+            ItemKind::Existential(ref bounds, _) => {
+                if !bounds.iter()
+                          .any(|b| if let GenericBound::Trait(..) = *b { true } else { false }) {
+                    self.err_handler().span_err(item.span, "at least one trait must be specified");
+                }
+            }
             _ => {}
         }
 
-- 
2.44.0