Make inductive cycles in coherence ambiguous always

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

@@ -239,20 +239,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
     }
 
-    // Sets the `TreatInductiveCycleAs` mode temporarily in the selection context
-    pub fn with_treat_inductive_cycle_as<T>(
-        &mut self,
-        treat_inductive_cycle: TreatInductiveCycleAs,
-        f: impl FnOnce(&mut Self) -> T,
-    ) -> T {
+    pub fn with_treat_inductive_cycle_as_ambig(
+        infcx: &'cx InferCtxt<'tcx>,
+    ) -> SelectionContext<'cx, 'tcx> {
         // Should be executed in a context where caching is disabled,
         // otherwise the cache is poisoned with the temporary result.
-        assert!(self.is_intercrate());
-        let treat_inductive_cycle =
-            std::mem::replace(&mut self.treat_inductive_cycle, treat_inductive_cycle);
-        let value = f(self);
-        self.treat_inductive_cycle = treat_inductive_cycle;
-        value
+        assert!(infcx.intercrate);
+        SelectionContext {
+            treat_inductive_cycle: TreatInductiveCycleAs::Ambig,
+            ..SelectionContext::new(infcx)
+        }
     }
 
     pub fn with_query_mode(