run const_eval_raw with root_span

src/librustc_mir/interpret/eval_context.rs

@@ -891,7 +891,7 @@ pub fn const_eval_raw(
         // FIXME: We can hit delay_span_bug if this is an invalid const, interning finds
         // that problem, but we never run validation to show an error. Can we ensure
         // this does not happen?
-        let val = self.tcx.at(self.cur_span()).const_eval_raw(param_env.and(gid))?;
+        let val = self.tcx_at().const_eval_raw(param_env.and(gid))?;
         self.raw_const_to_mplace(val)
     }
 

src/test/ui/infinite/infinite-recursion-const-fn.stderr

 error[E0391]: cycle detected when const-evaluating `a`
-  --> $DIR/infinite-recursion-const-fn.rs:3:25
+  --> $DIR/infinite-recursion-const-fn.rs:3:1
    |
 LL | const fn a() -> usize { b() }
-   |                         ^^^
+   | ^^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires const-evaluating `b`...
-  --> $DIR/infinite-recursion-const-fn.rs:4:25
+  --> $DIR/infinite-recursion-const-fn.rs:4:1
    |
 LL | const fn b() -> usize { a() }
-   |                         ^^^
+   | ^^^^^^^^^^^^^^^^^^^^^
    = note: ...which again requires const-evaluating `a`, completing the cycle
 note: cycle used when const-evaluating `ARR::{{constant}}#0`
   --> $DIR/infinite-recursion-const-fn.rs:5:18