Do not suggest impl traits as type arguments

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1603,6 +1603,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
                     let generics = self.tcx.generics_of(*def_id);
                     if generics.params.iter().any(|p| p.name != kw::SelfUpper)
                         && !snippet.ends_with('>')
+                        && !generics.has_impl_trait()
                     {
                         // FIXME: To avoid spurious suggestions in functions where type arguments
                         // where already supplied, we check the snippet to make sure it doesn't