Make TypeChecker::known_type_outlives_obligations owned.

This avoids the need to arena allocate it. `ConstraintConversion` needs
some simple lifetime adjustments to allow this.

Author: nnethercote

compiler/rustc_borrowck/src/type_check/constraint_conversion.rs

@@ -37,7 +37,7 @@ pub(crate) struct ConstraintConversion<'a, 'tcx> {
     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
     implicit_region_bound: ty::Region<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
+    known_type_outlives_obligations: &'a [ty::PolyTypeOutlivesPredicate<'tcx>],
     locations: Locations,
     span: Span,
     category: ConstraintCategory<'tcx>,
@@ -52,7 +52,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
         implicit_region_bound: ty::Region<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
-        known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
+        known_type_outlives_obligations: &'a [ty::PolyTypeOutlivesPredicate<'tcx>],
         locations: Locations,
         span: Span,
         category: ConstraintCategory<'tcx>,

compiler/rustc_borrowck/src/type_check/free_region_relations.rs

@@ -46,7 +46,7 @@ type NormalizedInputsAndOutput<'tcx> = Vec<Ty<'tcx>>;
 pub(crate) struct CreateResult<'tcx> {
     pub(crate) universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
     pub(crate) region_bound_pairs: RegionBoundPairs<'tcx>,
-    pub(crate) known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
+    pub(crate) known_type_outlives_obligations: Vec<ty::PolyTypeOutlivesPredicate<'tcx>>,
     pub(crate) normalized_inputs_and_output: NormalizedInputsAndOutput<'tcx>,
 }
 
@@ -250,8 +250,6 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
 
             known_type_outlives_obligations.push(outlives);
         }
-        let known_type_outlives_obligations =
-            self.infcx.tcx.arena.alloc_slice(&known_type_outlives_obligations);
 
         let unnormalized_input_output_tys = self
             .universal_regions
@@ -340,7 +338,7 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
                 &self.region_bound_pairs,
                 self.implicit_region_bound,
                 param_env,
-                known_type_outlives_obligations,
+                &known_type_outlives_obligations,
                 Locations::All(span),
                 span,
                 ConstraintCategory::Internal,

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -844,7 +844,7 @@ struct TypeChecker<'a, 'tcx> {
     /// all of the promoted items.
     user_type_annotations: &'a CanonicalUserTypeAnnotations<'tcx>,
     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
-    known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
+    known_type_outlives_obligations: Vec<ty::PolyTypeOutlivesPredicate<'tcx>>,
     implicit_region_bound: ty::Region<'tcx>,
     reported_errors: FxIndexSet<(Ty<'tcx>, Span)>,
     universal_regions: &'a UniversalRegions<'tcx>,
@@ -1028,7 +1028,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             self.region_bound_pairs,
             self.implicit_region_bound,
             self.param_env,
-            self.known_type_outlives_obligations,
+            &self.known_type_outlives_obligations,
             locations,
             locations.span(self.body),
             category,
@@ -2788,7 +2788,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 self.region_bound_pairs,
                 self.implicit_region_bound,
                 self.param_env,
-                self.known_type_outlives_obligations,
+                &self.known_type_outlives_obligations,
                 locations,
                 self.body.span,             // irrelevant; will be overridden.
                 ConstraintCategory::Boring, // same as above.