From 99c18c417adc69113002c07e4d7bdfc48be62869 Mon Sep 17 00:00:00 2001
From: Agustin Fernandez <juan.fernandez@opower.com>
Date: Tue, 29 Oct 2019 11:48:14 -0400
Subject: [PATCH] Add more context to `async fn` trait error. Suggest
 `async-trait`.

---
 src/librustc_passes/ast_validation.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/librustc_passes/ast_validation.rs b/src/librustc_passes/ast_validation.rs
index 994e9405fb643..08f6e6fe0e716 100644
--- a/src/librustc_passes/ast_validation.rs
+++ b/src/librustc_passes/ast_validation.rs
@@ -244,7 +244,12 @@ impl<'a> AstValidator<'a> {
     fn check_trait_fn_not_async(&self, span: Span, asyncness: IsAsync) {
         if asyncness.is_async() {
             struct_span_err!(self.session, span, E0706,
-                             "trait fns cannot be declared `async`").emit()
+                             "trait fns cannot be declared `async`")
+                .note("Due to technical restrictions rust does not currently support `async` \
+                       trait fns.")
+                .note("Consider using the `async-trait` crate in the meantime until further \
+                       notice.")
+                .emit();
         }
     }