Only show "same type from differnt version" note when relevant

Author: estebank

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

@@ -1750,6 +1750,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 {
  span.push_span_label(sp, label);
 }
+letmut points_at_type = false;
 ifletSome(found_type) = found_type {
  span.push_span_label(
 self.tcx.def_span(found_type),
@@ -1772,6 +1773,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
  candidate_span,
 "this type implements the required trait",
 );
+ points_at_type = true;
 }
 }
 }
@@ -1783,14 +1785,20 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 StringPart::highlighted(format!("{crate_name}")),
 StringPart::normal("` in the dependency graph\n".to_string()),
 ]);
- err.highlighted_note(vec![
-StringPart::normal(
-"two types coming from two different versions of the same crate are \
+if points_at_type {
+// We only clarify that the same type from different crate versions are not the
+// same when we *find* the same type coming from different crate versions, otherwise
+// it could be that it was a type provided by a different crate than the one that
+// provides the trait, and mentioning this adds verbosity without clarification.
+ err.highlighted_note(vec![
+StringPart::normal(
+"two types coming from two different versions of the same crate are \
  different types "
-.to_string(),
-),
-StringPart::highlighted("even if they look the same".to_string()),
-]);
+.to_string(),
+),
+StringPart::highlighted("even if they look the same".to_string()),
+]);
+}
  err.highlighted_help(vec![
 StringPart::normal("you can use `".to_string()),
 StringPart::highlighted("cargo tree".to_string()),