Encode spans relative to their parent.

compiler/rustc_resolve/src/lib.rs

@@ -1114,6 +1114,11 @@ impl ResolverAstLowering for Resolver<'_> {
         }
     }
 
+    #[inline]
+    fn def_span(&self, id: LocalDefId) -> Span {
+        self.definitions.def_span(id)
+    }
+
     fn item_generics_num_lifetimes(&self, def_id: DefId) -> usize {
         if let Some(def_id) = def_id.as_local() {
             self.item_generics_num_lifetimes[&def_id]
@@ -1221,6 +1226,11 @@ impl<'a, 'b> rustc_span::HashStableContext for ExpandHasher<'a, 'b> {
         true
     }
 
+    #[inline]
+    fn def_span(&self, id: LocalDefId) -> Span {
+        self.resolver.def_span(id)
+    }
+
     #[inline]
     fn def_path_hash(&self, def_id: DefId) -> DefPathHash {
         self.resolver.def_path_hash(def_id)