Don't add message that will never be shown to users

It will still be used in json, as seen by the ui test changes

Author: oli-obk

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

@@ -2445,12 +2445,12 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             (Ok(l), Ok(r)) => l.line == r.line,
                             _ => true,
                         };
-                    if !ident.span.overlaps(span) && !same_line {
+                    if !ident.span.is_dummy() && !ident.span.overlaps(span) && !same_line {
                         multispan.push_span_label(ident.span, "required by a bound in this");
                     }
                 }
                 let descr = format!("required by a bound in `{}`", item_name);
-                if span != DUMMY_SP {
+                if !span.is_dummy() {
                     let msg = format!("required by this bound in `{}`", item_name);
                     multispan.push_span_label(span, msg);
                     err.span_note(multispan, &descr);

src/test/ui/iterators/collect-into-array.rs

@@ -1,5 +1,4 @@
 fn main() {
-    //~^ NOTE required by a bound in this
     let whatever: [u32; 10] = (0..10).collect();
     //~^ ERROR an array of type `[u32; 10]` cannot be built directly from an iterator
     //~| NOTE try collecting into a `Vec<{integer}>`, then using `.try_into()`

src/test/ui/iterators/collect-into-array.stderr

@@ -1,5 +1,5 @@
 error[E0277]: an array of type `[u32; 10]` cannot be built directly from an iterator
-  --> $DIR/collect-into-array.rs:3:31
+  --> $DIR/collect-into-array.rs:2:31
    |
 LL |     let whatever: [u32; 10] = (0..10).collect();
    |                               ^^^^^^^ ------- required by a bound introduced by this call

src/test/ui/iterators/collect-into-slice.rs

@@ -1,6 +1,4 @@
 fn process_slice(data: &[i32]) {
-    //~^ NOTE required by a bound in this
-    //~| NOTE required by a bound in this
     todo!()
 }
 

src/test/ui/iterators/collect-into-slice.stderr

@@ -1,5 +1,5 @@
 error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
-  --> $DIR/collect-into-slice.rs:8:9
+  --> $DIR/collect-into-slice.rs:6:9
    |
 LL |     let some_generated_vec = (0..10).collect();
    |         ^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
@@ -9,7 +9,7 @@ LL |     let some_generated_vec = (0..10).collect();
    = help: unsized locals are gated as an unstable feature
 
 error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
-  --> $DIR/collect-into-slice.rs:8:38
+  --> $DIR/collect-into-slice.rs:6:38
    |
 LL |     let some_generated_vec = (0..10).collect();
    |                                      ^^^^^^^ doesn't have a size known at compile-time
@@ -22,7 +22,7 @@ LL |     fn collect<B: FromIterator<Self::Item>>(self) -> B
    |                ^ required by this bound in `collect`
 
 error[E0277]: a slice of type `[i32]` cannot be built since `[i32]` has no definite size
-  --> $DIR/collect-into-slice.rs:8:30
+  --> $DIR/collect-into-slice.rs:6:30
    |
 LL |     let some_generated_vec = (0..10).collect();
    |                              ^^^^^^^ ------- required by a bound introduced by this call