Rename Session::span_diagnostic as Session::dcx.

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

@@ -3395,7 +3395,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         };
 
         if let Some(diag) =
-            self.tcx.sess.diagnostic().steal_diagnostic(self.tcx.def_span(def_id), StashKey::Cycle)
+            self.tcx.sess.dcx().steal_diagnostic(self.tcx.def_span(def_id), StashKey::Cycle)
         {
             diag.cancel();
         }

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -594,9 +594,7 @@ fn virtual_call_violations_for_method<'tcx>(
             // would already have reported an error at the definition of the
             // auto trait.
             if pred_trait_ref.args.len() != 1 {
-                tcx.sess
-                    .diagnostic()
-                    .span_delayed_bug(span, "auto traits cannot have generic parameters");
+                tcx.sess.dcx().span_delayed_bug(span, "auto traits cannot have generic parameters");
             }
             return false;
         }