Remove a now-unused trait

compiler/rustc_borrowck/src/type_check/free_region_relations.rs

@@ -1,20 +1,18 @@
 use rustc_data_structures::frozen::Frozen;
 use rustc_data_structures::transitive_relation::TransitiveRelation;
 use rustc_infer::infer::canonical::QueryRegionConstraints;
-use rustc_infer::infer::free_regions::FreeRegionRelations;
 use rustc_infer::infer::outlives;
 use rustc_infer::infer::region_constraints::GenericKind;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::traits::query::OutlivesBound;
-use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt};
+use rustc_middle::ty::{self, RegionVid, Ty};
 use rustc_span::DUMMY_SP;
 use rustc_trait_selection::traits::query::type_op::{self, TypeOp};
 use std::rc::Rc;
 use type_op::TypeOpOutput;
 
 use crate::{
-    nll::ToRegionVid,
     type_check::constraint_conversion,
     type_check::{Locations, MirTypeckRegionConstraints},
     universal_regions::UniversalRegions,
@@ -383,21 +381,3 @@ impl UniversalRegionRelationsBuilder<'cx, 'tcx> {
         }
     }
 }
-
-/// This trait is used by the `impl-trait` constraint code to abstract
-/// over the `FreeRegionMap` from lexical regions and
-/// `UniversalRegions` (from NLL)`.
-impl<'tcx> FreeRegionRelations<'tcx> for UniversalRegionRelations<'tcx> {
-    fn sub_free_regions(
-        &self,
-        _tcx: TyCtxt<'tcx>,
-        shorter: ty::Region<'tcx>,
-        longer: ty::Region<'tcx>,
-    ) -> bool {
-        let shorter = shorter.to_region_vid();
-        assert!(self.universal_regions.is_universal_region(shorter));
-        let longer = longer.to_region_vid();
-        assert!(self.universal_regions.is_universal_region(longer));
-        self.outlives(longer, shorter)
-    }
-}

compiler/rustc_infer/src/infer/free_regions.rs

@@ -66,8 +66,6 @@ impl<'tcx> FreeRegionMap<'tcx> {
     /// follows. If we know that `r_b: 'static`, then this function
     /// will return true, even though we don't know anything that
     /// directly relates `r_a` and `r_b`.
-    ///
-    /// Also available through the `FreeRegionRelations` trait below.
     pub fn sub_free_regions(
         &self,
         tcx: TyCtxt<'tcx>,
@@ -131,27 +129,6 @@ impl<'tcx> FreeRegionMap<'tcx> {
     }
 }
 
-/// The NLL region handling code represents free region relations in a
-/// slightly different way; this trait allows functions to be abstract
-/// over which version is in use.
-pub trait FreeRegionRelations<'tcx> {
-    /// Tests whether `r_a <= r_b`. Both must be free regions or
-    /// `'static`.
-    fn sub_free_regions(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        shorter: ty::Region<'tcx>,
-        longer: ty::Region<'tcx>,
-    ) -> bool;
-}
-
-impl<'tcx> FreeRegionRelations<'tcx> for FreeRegionMap<'tcx> {
-    fn sub_free_regions(&self, tcx: TyCtxt<'tcx>, r_a: Region<'tcx>, r_b: Region<'tcx>) -> bool {
-        // invoke the "inherent method"
-        self.sub_free_regions(tcx, r_a, r_b)
-    }
-}
-
 impl<'a, 'tcx> Lift<'tcx> for FreeRegionMap<'a> {
     type Lifted = FreeRegionMap<'tcx>;
     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<FreeRegionMap<'tcx>> {