Avoid query in cases where it will probably be region-dependent

Author: Aaron1011

compiler/rustc_middle/src/ty/fold.rs

@@ -116,6 +116,9 @@ pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
     fn has_free_regions(&self) -> bool {
         self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
     }
+    fn has_free_local_regions(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_REGIONS)
+    }
 
     fn has_erased_regions(&self) -> bool {
         self.has_type_flags(TypeFlags::HAS_RE_ERASED)

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -619,7 +619,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
         stalled_on: &mut Vec<TyOrConstInferVar<'tcx>>,
     ) -> ProcessResult<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>> {
         let infcx = self.selcx.infcx();
-        if !obligation.predicate.needs_infer() {
+        if !obligation.predicate.needs_infer() && !obligation.predicate.has_free_local_regions() {
             // no type variables present, can use evaluation for better caching.
             // FIXME: consider caching errors too.
             if infcx.predicate_must_hold_considering_regions(obligation) {
@@ -628,6 +628,8 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
                     obligation.recursion_depth
                 );
                 return ProcessResult::Changed(vec![]);
+            } else {
+                debug!("Eager eval failed: {:?}", obligation);
             }
         }