Proper span for new generic param suggestion

Author: Stoozy

compiler/rustc_resolve/src/late/lifetimes.rs

@@ -1333,11 +1333,16 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
                                         );
 
                                         diag.span_label(lifetime_ref.span, "expected named lifetime parameter");
-
                                         diag.multipart_suggestion("consider introducing a named lifetime parameter",
                                                                   vec![
                                                                     (lifetime_ref.span.shrink_to_hi(), "'a ".to_owned()),
-                                                                    (generics.span, "<'a>".to_owned())
+                                                                    match generics.span_for_param_suggestion() {
+                                                                        Some(_) => {
+                                                                            (self.tcx.sess.source_map().span_through_char(generics.span, '<').shrink_to_hi(), "'a, ".to_owned())
+                                                                        }
+                                                                        None => (generics.span, "<'a>".to_owned()),
+
+                                                                    }
                                                                   ], rustc_errors::Applicability::MaybeIncorrect);
                                         diag.emit();
 

src/test/ui/suggestions/impl-trait-missing-lifetime-gated.stderr

@@ -26,17 +26,25 @@ error[E0658]: anonymous lifetimes in `impl Trait` are unstable
   --> $DIR/impl-trait-missing-lifetime-gated.rs:5:31
    |
 LL | fn f(_: impl Iterator<Item = &'_ ()>) {}
-   |                               ^^
+   |                               ^^ expected named lifetime parameter
    |
    = help: add `#![feature(anonymous_lifetime_in_impl_trait)]` to the crate attributes to enable
+help: consider introducing a named lifetime parameter
+   |
+LL | fn f<'a>(_: impl Iterator<Item = &'_'a  ()>) {}
+   |     ++++                            ++
 
 error[E0658]: anonymous lifetimes in `impl Trait` are unstable
   --> $DIR/impl-trait-missing-lifetime-gated.rs:8:31
    |
 LL | fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
-   |                               ^^
+   |                               ^^ expected named lifetime parameter
    |
    = help: add `#![feature(anonymous_lifetime_in_impl_trait)]` to the crate attributes to enable
+help: consider introducing a named lifetime parameter
+   |
+LL | fn g<'a>(x: impl Iterator<Item = &'_'a  ()>) -> Option<&'_ ()> { x.next() }
+   |     ++++                            ++
 
 error: aborting due to 4 previous errors