Move lifetimes before the *first* type argument

src/libsyntax/parse/parser.rs

@@ -5229,7 +5229,9 @@ fn parse_trait_item_assoc_ty(&mut self)
             } else if self.check_ident() {
                 // Parse type parameter.
                 params.push(self.parse_ty_param(attrs)?);
-                seen_ty_param = Some(self.prev_span);
+                if seen_ty_param.is_none() {
+                    seen_ty_param = Some(self.prev_span);
+                }
             } else {
                 // Check for trailing attributes and stop parsing.
                 if !attrs.is_empty() {

src/test/ui/suggestions/suggest-move-lifetimes.stderr

@@ -25,8 +25,8 @@ LL | struct C<T, U, 'a> {
    |                ^^
 help: move the lifetime parameter prior to the first type parameter
    |
-LL | struct C<T, 'a, U> {
-   |             ^^^ --
+LL | struct C<'a, T, U> {
+   |          ^^^    --
 
 error: aborting due to 3 previous errors