construct pick-constraints and give them to region inference

src/librustc_mir/borrow_check/nll/mod.rs

@@ -130,6 +130,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
         placeholder_index_to_region: _,
         mut liveness_constraints,
         outlives_constraints,
+        pick_constraints,
         closure_bounds_mapping,
         type_tests,
     } = constraints;
@@ -151,6 +152,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
         universal_region_relations,
         body,
         outlives_constraints,
+        pick_constraints,
         closure_bounds_mapping,
         type_tests,
         liveness_constraints,

src/librustc_mir/borrow_check/nll/pick_constraints.rs

@@ -55,18 +55,20 @@
     }
 }
 
-impl<'tcx> PickConstraintSet<'tcx, ty::RegionVid> {
-    crate fn new() -> Self {
+impl Default for PickConstraintSet<'tcx, ty::RegionVid> {
+    fn default() -> Self {
         Self {
             first_constraints: Default::default(),
             constraints: Default::default(),
             option_regions: Default::default(),
         }
     }
+}
 
+impl<'tcx> PickConstraintSet<'tcx, ty::RegionVid> {
     crate fn push_constraint(
         &mut self,
-        p_c: PickConstraint<'tcx>,
+        p_c: &PickConstraint<'tcx>,
         mut to_region_vid: impl FnMut(ty::Region<'tcx>) -> ty::RegionVid,
     ) {
         let pick_region_vid: ty::RegionVid = to_region_vid(p_c.pick_region);

src/librustc_mir/borrow_check/nll/region_infer/mod.rs

 use super::universal_regions::UniversalRegions;
 use crate::borrow_check::nll::constraints::graph::NormalConstraintGraph;
 use crate::borrow_check::nll::constraints::{ConstraintSccIndex, OutlivesConstraintSet, OutlivesConstraint};
+use crate::borrow_check::nll::pick_constraints::PickConstraintSet;
 use crate::borrow_check::nll::region_infer::values::{
     PlaceholderIndices, RegionElement, ToElementIndex
 };
@@ -187,6 +188,7 @@ pub(crate) fn new(
         universal_region_relations: Rc<UniversalRegionRelations<'tcx>>,
         _body: &Body<'tcx>,
         outlives_constraints: OutlivesConstraintSet,
+        pick_constraints: PickConstraintSet<'tcx, RegionVid>,
         closure_bounds_mapping: FxHashMap<
             Location,
             FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>,
@@ -218,6 +220,10 @@ pub(crate) fn new(
 
         let scc_representatives = Self::compute_scc_representatives(&constraint_sccs, &definitions);
 
+        let _pick_constraints_scc = pick_constraints.into_mapped( // TODO
+            |r| constraint_sccs.scc(r),
+        );
+
         let mut result = Self {
             definitions,
             liveness_constraints,

src/librustc_mir/borrow_check/nll/type_check/constraint_conversion.rs

@@ -51,7 +51,22 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
     }
 
     pub(super) fn convert_all(&mut self, query_constraints: &QueryRegionConstraints<'tcx>) {
-        for query_constraint in &query_constraints.outlives {
+        let QueryRegionConstraints { outlives, pick_constraints } = query_constraints;
+
+        // Annoying: to invoke `self.to_region_vid`, we need access to
+        // `self.constraints`, but we also want to be mutating
+        // `self.pick_constraints`. For now, just swap out the value
+        // we want and replace at the end.
+        let mut tmp = std::mem::replace(&mut self.constraints.pick_constraints, Default::default());
+        for pick_constraint in pick_constraints {
+            tmp.push_constraint(
+                pick_constraint,
+                |r| self.to_region_vid(r),
+            );
+        }
+        self.constraints.pick_constraints = tmp;
+
+        for query_constraint in outlives {
             self.convert(query_constraint);
         }
     }

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -5,6 +5,7 @@
 use crate::borrow_check::borrow_set::BorrowSet;
 use crate::borrow_check::location::LocationTable;
 use crate::borrow_check::nll::constraints::{OutlivesConstraintSet, OutlivesConstraint};
+use crate::borrow_check::nll::pick_constraints::PickConstraintSet;
 use crate::borrow_check::nll::facts::AllFacts;
 use crate::borrow_check::nll::region_infer::values::LivenessValues;
 use crate::borrow_check::nll::region_infer::values::PlaceholderIndex;
@@ -128,6 +129,7 @@ pub(crate) fn type_check<'tcx>(
         placeholder_index_to_region: IndexVec::default(),
         liveness_constraints: LivenessValues::new(elements.clone()),
         outlives_constraints: OutlivesConstraintSet::default(),
+        pick_constraints: PickConstraintSet::default(),
         closure_bounds_mapping: Default::default(),
         type_tests: Vec::default(),
     };
@@ -886,6 +888,8 @@ struct BorrowCheckContext<'a, 'tcx> {
 
     crate outlives_constraints: OutlivesConstraintSet,
 
+    crate pick_constraints: PickConstraintSet<'tcx, RegionVid>,
+
     crate closure_bounds_mapping:
         FxHashMap<Location, FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>>,