Use kw::Empty for elided lifetimes in path.

compiler/rustc_middle/src/ty/generics.rs

@@ -3,7 +3,7 @@ use crate::ty::{EarlyBinder, SubstsRef};
 use rustc_ast as ast;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def_id::DefId;
-use rustc_span::symbol::Symbol;
+use rustc_span::symbol::{kw, Symbol};
 use rustc_span::Span;
 
 use super::{EarlyBoundRegion, InstantiatedPredicates, ParamConst, ParamTy, Predicate, TyCtxt};
@@ -78,6 +78,15 @@ impl GenericParamDef {
         }
     }
 
+    pub fn is_anonymous_lifetime(&self) -> bool {
+        match self.kind {
+            GenericParamDefKind::Lifetime => {
+                self.name == kw::UnderscoreLifetime || self.name == kw::Empty
+            }
+            _ => false,
+        }
+    }
+
     pub fn default_value<'tcx>(
         &self,
         tcx: TyCtxt<'tcx>,