Do not suggest adding a bound to a opaque type

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -273,13 +273,17 @@ impl<'tcx> BorrowExplanation<'tcx> {
             _ => {}
         }
     }
-    pub(crate) fn add_lifetime_bound_suggestion_to_diagnostic(
+
+    fn add_lifetime_bound_suggestion_to_diagnostic(
         &self,
         err: &mut Diagnostic,
         category: &ConstraintCategory<'tcx>,
         span: Span,
         region_name: &RegionName,
     ) {
+        if !span.is_desugaring(DesugaringKind::OpaqueTy) {
+            return;
+        }
         if let ConstraintCategory::OpaqueType = category {
             let suggestable_name =
                 if region_name.was_named() { region_name.name } else { kw::UnderscoreLifetime };

src/test/ui/regions/do-not-suggest-adding-bound-to-opaque-type.rs

@@ -0,0 +1,12 @@
+pub trait T {}
+
+struct S<'a>(&'a ());
+
+impl<'a> T for S<'a> {}
+
+fn foo() -> impl T {
+    let x = ();
+    S(&x) //~ ERROR `x` does not live long enough
+}
+
+fn main() {}

src/test/ui/regions/do-not-suggest-adding-bound-to-opaque-type.stderr

@@ -0,0 +1,14 @@
+error[E0597]: `x` does not live long enough
+  --> $DIR/do-not-suggest-adding-bound-to-opaque-type.rs:9:7
+   |
+LL |     S(&x)
+   |     --^^-
+   |     | |
+   |     | borrowed value does not live long enough
+   |     opaque type requires that `x` is borrowed for `'static`
+LL | }
+   | - `x` dropped here while still borrowed
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0597`.