Rollup merge of #58387 - alexreg:fix-trait-alias-2, r=centril

Disallow `auto` trait alias syntax

See https://github.com/rust-lang/rust/issues/41517#issuecomment-462567679.

r? @Centril

CC @topecongiro @nikomatsakis

1 files changed, 7 insertions, 1 deletions

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 50cedc0f8d4..e22047938e5 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -6538,8 +6538,14 @@ impl<'a> Parser<'a> {
             let bounds = self.parse_generic_bounds()?;
             tps.where_clause = self.parse_where_clause()?;
             self.expect(&token::Semi)?;
+            if is_auto == IsAuto::Yes {
+                let msg = "trait aliases cannot be `auto`";
+                self.struct_span_err(self.prev_span, msg)
+                    .span_label(self.prev_span, msg)
+                    .emit();
+            }
             if unsafety != Unsafety::Normal {
-                let msg = "trait aliases cannot be unsafe";
+                let msg = "trait aliases cannot be `unsafe`";
                 self.struct_span_err(self.prev_span, msg)
                     .span_label(self.prev_span, msg)
                     .emit();