preliminary integration of "pick constraints" into nll solver

src/librustc/infer/error_reporting/mod.rs

@@ -385,13 +385,13 @@ pub fn report_region_errors(
                         option_regions: _,
                     } => {
                         let hidden_ty = self.resolve_vars_if_possible(&hidden_ty);
-                        opaque_types::report_unexpected_hidden_region(
+                        opaque_types::unexpected_hidden_region_diagnostic(
                             self.tcx,
                             Some(region_scope_tree),
                             opaque_type_def_id,
                             hidden_ty,
                             pick_region,
-                        );
+                        ).emit();
                     }
                 }
             }

src/librustc/infer/opaque_types/mod.rs

@@ -9,6 +9,7 @@
 use crate::ty::subst::{InternalSubsts, Kind, SubstsRef, UnpackedKind};
 use crate::ty::{self, GenericParamDefKind, Ty, TyCtxt};
 use crate::util::nodemap::DefIdMap;
+use errors::DiagnosticBuilder;
 use rustc_data_structures::fx::FxHashMap;
 use std::rc::Rc;
 
@@ -499,13 +500,13 @@ pub fn infer_opaque_definition_from_instantiation(
     }
 }
 
-pub fn report_unexpected_hidden_region(
+pub fn unexpected_hidden_region_diagnostic(
     tcx: TyCtxt<'tcx>,
     region_scope_tree: Option<&region::ScopeTree>,
     opaque_type_def_id: DefId,
     hidden_ty: Ty<'tcx>,
     hidden_region: ty::Region<'tcx>,
-) {
+) -> DiagnosticBuilder<'tcx> {
     let span = tcx.def_span(opaque_type_def_id);
     let mut err = struct_span_err!(
         tcx.sess,
@@ -573,7 +574,7 @@ pub fn report_unexpected_hidden_region(
         }
     }
 
-    err.emit();
+    err
 }
 
 // Visitor that requires that (almost) all regions in the type visited outlive
@@ -724,13 +725,13 @@ fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
             None => {
                 if !self.map_missing_regions_to_empty && !self.tainted_by_errors {
                     if let Some(hidden_ty) = self.hidden_ty.take() {
-                        report_unexpected_hidden_region(
+                        unexpected_hidden_region_diagnostic(
                             self.tcx,
                             None,
                             self.opaque_type_def_id,
                             hidden_ty,
                             r,
-                        );
+                        ).emit();
                     }
                 }
                 self.tcx.lifetimes.re_empty

src/librustc_mir/borrow_check/nll/pick_constraints.rs

@@ -71,10 +71,12 @@ impl<'tcx> PickConstraintSet<'tcx, ty::RegionVid> {
         p_c: &PickConstraint<'tcx>,
         mut to_region_vid: impl FnMut(ty::Region<'tcx>) -> ty::RegionVid,
     ) {
+        debug!("push_constraint(p_c={:?})", p_c);
         let pick_region_vid: ty::RegionVid = to_region_vid(p_c.pick_region);
         let next_constraint = self.first_constraints.get(&pick_region_vid).cloned();
         let start_index = self.option_regions.len();
         let end_index = start_index + p_c.option_regions.len();
+        debug!("push_constraint: pick_region_vid={:?}", pick_region_vid);
         let constraint_index = self.constraints.push(NllPickConstraint {
             next_constraint,
             pick_region_vid,
@@ -136,6 +138,12 @@ impl<'tcx, R> PickConstraintSet<'tcx, R>
 where
     R: Copy + Hash + Eq,
 {
+    crate fn all_indices(
+        &self,
+    ) -> impl Iterator<Item = NllPickConstraintIndex> {
+        self.constraints.indices()
+    }
+
     /// Iterate down the constraint indices associated with a given
     /// peek-region.  You can then use `option_regions` and other
     /// methods to access data.

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

@@ -51,6 +51,8 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
     }
 
     pub(super) fn convert_all(&mut self, query_constraints: &QueryRegionConstraints<'tcx>) {
+        debug!("convert_all(query_constraints={:#?})", query_constraints);
+
         let QueryRegionConstraints { outlives, pick_constraints } = query_constraints;
 
         // Annoying: to invoke `self.to_region_vid`, we need access to