Fix diagnostic::on_const label span

Author: mejrs

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

@@ -917,7 +917,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         diag.primary_message(message);
                     }
                     if let Some(label) = label {
-                        diag.span_label(impl_span, label);
+                        diag.span_label(span, label);
                     }
                     for note in notes {
                         diag.note(note);

tests/ui/diagnostic_namespace/on_const/it_works_foreign.rs

@@ -9,6 +9,7 @@ const _: () = {
     let x = X;
     x == x;
     //~^ ERROR: their message
+    //~| NOTE: their label
     //~| NOTE: trait `PartialEq` is implemented but not `const`
     //~| NOTE: their note
     //~| NOTE: their other note

tests/ui/diagnostic_namespace/on_const/it_works_foreign.stderr

@@ -2,12 +2,7 @@ error[E0277]: their message
   --> $DIR/it_works_foreign.rs:10:5
    |
 LL |     x == x;
-   |     ^^^^^^
-   |
-  ::: $DIR/auxiliary/non_const_impl.rs:11:1
-   |
-LL | impl PartialEq for X {
-   | -------------------- their label
+   |     ^^^^^^ their label
    |
 note: trait `PartialEq` is implemented but not `const`
   --> $DIR/auxiliary/non_const_impl.rs:11:1

tests/ui/diagnostic_namespace/on_const/it_works_local.rs

@@ -10,7 +10,6 @@ pub struct X;
     note = "my other note"
 )]
 impl PartialEq for X {
-    //~^NOTE: my label
     fn eq(&self, _other: &X) -> bool {
         true
     }
@@ -20,6 +19,7 @@ const _: () = {
     let x = X;
     x == x;
     //~^ ERROR: my message
+    //~| NOTE: my label
     //~| NOTE: my note
     //~| NOTE: my other note
 };

tests/ui/diagnostic_namespace/on_const/it_works_local.stderr

@@ -1,11 +1,8 @@
 error[E0277]: my message
-  --> $DIR/it_works_local.rs:21:5
+  --> $DIR/it_works_local.rs:20:5
    |
-LL | impl PartialEq for X {
-   | -------------------- my label
-...
 LL |     x == x;
-   |     ^^^^^^
+   |     ^^^^^^ my label
    |
    = note: my note
    = note: my other note