#[must_use] for fns returning a list of errors

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -175,10 +175,12 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
             .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
     }
 
+    #[must_use]
     pub fn select_where_possible(&self) -> Vec<FulfillmentError<'tcx>> {
         self.engine.borrow_mut().select_where_possible(self.infcx)
     }
 
+    #[must_use]
     pub fn select_all_or_error(&self) -> Vec<FulfillmentError<'tcx>> {
         self.engine.borrow_mut().select_all_or_error(self.infcx)
     }

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

@@ -1763,7 +1763,9 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
                 // constrain inference variables a bit more to nested obligations from normalize so
                 // we can have more helpful errors.
-                ocx.select_where_possible();
+                //
+                // we intentionally errors from normalization here.
+                let _ = ocx.select_where_possible();
 
                 if let Err(new_err) = ocx.eq_exp(
                     &obligation.cause,