give a helpful diagnostic even when the next struct field has an attribute

compiler/rustc_parse/src/parser/item.rs

@@ -1539,8 +1539,12 @@ impl<'a> Parser<'a> {
                     }
                 }
 
-                if self.token.is_ident() {
-                    // This is likely another field; emit the diagnostic and keep going
+                if self.token.is_ident()
+                    || (self.token.kind == TokenKind::Pound
+                        && (self.look_ahead(1, |t| t == &token::OpenDelim(Delimiter::Bracket))))
+                {
+                    // This is likely another field, TokenKind::Pound is used for `#[..]` attribute for next field,
+                    // emit the diagnostic and keep going
                     err.span_suggestion(
                         sp,
                         "try adding a comma",

src/test/ui/parser/struct-filed-with-attr.fixed

@@ -0,0 +1,18 @@
+// Issue: 100461, Try to give a helpful diagnostic even when the next struct field has an attribute.
+// run-rustfix
+
+struct Feelings {
+    owo: bool,
+    //~^ ERROR expected `,`, or `}`, found `#`
+    #[allow(unused)]
+    uwu: bool,
+}
+
+impl Feelings {
+    #[allow(unused)]
+    fn hmm(&self) -> bool {
+        self.owo
+    }
+}
+
+fn main() { }

src/test/ui/parser/struct-filed-with-attr.rs

@@ -0,0 +1,18 @@
+// Issue: 100461, Try to give a helpful diagnostic even when the next struct field has an attribute.
+// run-rustfix
+
+struct Feelings {
+    owo: bool
+    //~^ ERROR expected `,`, or `}`, found `#`
+    #[allow(unused)]
+    uwu: bool,
+}
+
+impl Feelings {
+    #[allow(unused)]
+    fn hmm(&self) -> bool {
+        self.owo
+    }
+}
+
+fn main() { }

src/test/ui/parser/struct-filed-with-attr.stderr

@@ -0,0 +1,8 @@
+error: expected `,`, or `}`, found `#`
+  --> $DIR/struct-filed-with-attr.rs:5:14
+   |
+LL |     owo: bool
+   |              ^ help: try adding a comma: `,`
+
+error: aborting due to previous error
+