Auto merge of #33333 - birkenfeld:issue-30318, r=Manishearth

parser: show a helpful note on unexpected inner comment

Fixes: #30318.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/libsyntax/parse/attr.rs b/src/libsyntax/parse/attr.rs
index 3aac12d76ff..db643eb0df0 100644
--- a/src/libsyntax/parse/attr.rs
+++ b/src/libsyntax/parse/attr.rs
@@ -35,7 +35,10 @@ impl<'a> Parser<'a> {
                     self.span.hi
                 );
                     if attr.node.style != ast::AttrStyle::Outer {
-                        return Err(self.fatal("expected outer comment"));
+                        let mut err = self.fatal("expected outer doc comment");
+                        err.note("inner doc comments like this (starting with \
+                                  `//!` or `/*!`) can only appear before items");
+                        return Err(err);
                     }
                     attrs.push(attr);
                     self.bump();