remove dummy UniverseInfo causes from type checker fully_perform_op

This was backfilling causes for new universes that may have been created
by an op, when there was no error info to use for improved
diagnostics. We don't need to do that anymore: `other()` is the default when
there is no registered universe cause.

Author: lqd

compiler/rustc_borrowck/src/type_check/canonical.rs

@@ -9,7 +9,7 @@ use rustc_span::Span;
 use rustc_trait_selection::traits::query::type_op::{self, TypeOpOutput};
 use rustc_trait_selection::traits::ObligationCause;
 
-use crate::diagnostics::{ToUniverseInfo, UniverseInfo};
+use crate::diagnostics::ToUniverseInfo;
 
 use super::{Locations, NormalizeLocation, TypeChecker};
 
@@ -46,13 +46,11 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             self.push_region_constraints(locations, category, data);
         }
 
+        // If the query has created new universes and errors are going to be emitted, register the
+        // cause of these new universes for improved diagnostics.
         let universe = self.infcx.universe();
-
-        if old_universe != universe {
-            let universe_info = match error_info {
-                Some(error_info) => error_info.to_universe_info(old_universe),
-                None => UniverseInfo::other(),
-            };
+        if old_universe != universe && let Some(error_info) = error_info {
+            let universe_info = error_info.to_universe_info(old_universe);
             for u in (old_universe + 1)..=universe {
                 self.borrowck_context.constraints.universe_causes.insert(u, universe_info.clone());
             }