universe transition

Remove the leak-check and its associated machinery. Replace with
making the solver aware of universes.

Author: nikomatsakis

src/librustc/infer/higher_ranked/mod.rs

@@ -215,23 +215,41 @@ impl<'cx, 'gcx, 'tcx> LexicalResolver<'cx, 'gcx, 'tcx> {
     ) -> bool {
         debug!("expand_node({:?}, {:?} == {:?})", a_region, b_vid, b_data);
 
-        // Check if this relationship is implied by a given.
         match *a_region {
+            // Check if this relationship is implied by a given.
             ty::ReEarlyBound(_) | ty::ReFree(_) => if self.data.givens.contains(&(a_region, b_vid))
             {
                 debug!("given");
                 return false;
             },
+
             _ => {}
         }
 
+
         match *b_data {
             VarValue::Value(cur_region) => {
-                let lub = self.lub_concrete_regions(a_region, cur_region);
+                let mut lub = self.lub_concrete_regions(a_region, cur_region);
                 if lub == cur_region {
                     return false;
                 }
 
+                // Watch out for `'b: !1` relationships, where the
+                // universe of `'b` can't name the placeholder `!1`. In
+                // that case, we have to grow `'b` to be `'static` for the
+                // relationship to hold. This is obviously a kind of sub-optimal
+                // choice -- in the future, when we incorporate a knowledge
+                // of the parameter environment, we might be able to find a
+                // tighter bound than `'static`.
+                //
+                // (This might e.g. arise from being asked to prove `for<'a> { 'b: 'a }`.)
+                let b_universe = self.var_infos[b_vid].universe;
+                if let ty::RePlaceholder(p) = lub {
+                    if b_universe.cannot_name(p.universe) {
+                        lub = self.tcx().types.re_static;
+                    }
+                }
+
                 debug!(
                     "Expanding value of {:?} from {:?} to {:?}",
                     b_vid, cur_region, lub
@@ -554,10 +572,22 @@ impl<'cx, 'gcx, 'tcx> LexicalResolver<'cx, 'gcx, 'tcx> {
         lower_bounds.sort_by_key(region_order_key);
         upper_bounds.sort_by_key(region_order_key);
 
+        let node_universe = self.var_infos[node_idx].universe;
+
         for lower_bound in &lower_bounds {
+            let effective_lower_bound = if let ty::RePlaceholder(p) = lower_bound.region {
+                if node_universe.cannot_name(p.universe) {
+                    self.tcx().types.re_static
+                } else {
+                    lower_bound.region
+                }
+            } else {
+                lower_bound.region
+            };
+
             for upper_bound in &upper_bounds {
                 if !self.region_rels
-                    .is_subregion_of(lower_bound.region, upper_bound.region)
+                    .is_subregion_of(effective_lower_bound, upper_bound.region)
                 {
                     let origin = self.var_infos[node_idx].origin.clone();
                     debug!(
@@ -580,9 +610,10 @@ impl<'cx, 'gcx, 'tcx> LexicalResolver<'cx, 'gcx, 'tcx> {
         span_bug!(
             self.var_infos[node_idx].origin.span(),
             "collect_error_for_expanding_node() could not find \
-             error for var {:?}, lower_bounds={:?}, \
-             upper_bounds={:?}",
+             error for var {:?} in universe {:?}, lower_bounds={:#?}, \
+             upper_bounds={:#?}",
             node_idx,
+            node_universe,
             lower_bounds,
             upper_bounds
         );

src/librustc/infer/lexical_region_resolve/mod.rs

@@ -32,7 +32,6 @@ use ty::{FloatVid, IntVid, TyVid};
 use util::nodemap::FxHashMap;
 
 use self::combine::CombineFields;
-use self::higher_ranked::HrMatchResult;
 use self::lexical_region_resolve::LexicalRegionResolutions;
 use self::outlives::env::OutlivesEnvironment;
 use self::region_constraints::{GenericKind, RegionConstraintData, VarInfos, VerifyBound};
@@ -948,39 +947,32 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             return None;
         }
 
-        Some(self.commit_if_ok(|snapshot| {
-            let (
-                ty::SubtypePredicate {
-                    a_is_expected,
-                    a,
-                    b,
-                },
-                placeholder_map,
-            ) = self.replace_bound_vars_with_placeholders(predicate);
+        let (
+            ty::SubtypePredicate {
+                a_is_expected,
+                a,
+                b,
+            },
+            _,
+        ) = self.replace_bound_vars_with_placeholders(predicate);
 
-            let cause_span = cause.span;
-            let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
-            self.leak_check(false, cause_span, &placeholder_map, snapshot)?;
-            self.pop_placeholders(placeholder_map, snapshot);
-            Ok(ok.unit())
-        }))
+        Some(
+            self.at(cause, param_env)
+                .sub_exp(a_is_expected, a, b)
+                .map(|ok| ok.unit()),
+        )
     }
 
     pub fn region_outlives_predicate(
         &self,
         cause: &traits::ObligationCause<'tcx>,
         predicate: &ty::PolyRegionOutlivesPredicate<'tcx>,
-    ) -> UnitResult<'tcx> {
-        self.commit_if_ok(|snapshot| {
-            let (ty::OutlivesPredicate(r_a, r_b), placeholder_map) =
-                self.replace_bound_vars_with_placeholders(predicate);
-            let origin = SubregionOrigin::from_obligation_cause(cause, || {
-                RelateRegionParamBound(cause.span)
-            });
-            self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
-            self.leak_check(false, cause.span, &placeholder_map, snapshot)?;
-            Ok(self.pop_placeholders(placeholder_map, snapshot))
-        })
+    ) {
+        let (ty::OutlivesPredicate(r_a, r_b), _) =
+            self.replace_bound_vars_with_placeholders(predicate);
+        let origin =
+            SubregionOrigin::from_obligation_cause(cause, || RelateRegionParamBound(cause.span));
+        self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
     }
 
     pub fn next_ty_var_id(&self, diverging: bool, origin: TypeVariableOrigin) -> TyVid {
@@ -1389,46 +1381,6 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.tcx.replace_bound_vars(value, fld_r, fld_t)
     }
 
-    /// Given a higher-ranked projection predicate like:
-    ///
-    ///     for<'a> <T as Fn<&'a u32>>::Output = &'a u32
-    ///
-    /// and a target trait-ref like:
-    ///
-    ///     <T as Fn<&'x u32>>
-    ///
-    /// find a substitution `S` for the higher-ranked regions (here,
-    /// `['a => 'x]`) such that the predicate matches the trait-ref,
-    /// and then return the value (here, `&'a u32`) but with the
-    /// substitution applied (hence, `&'x u32`).
-    ///
-    /// See `higher_ranked_match` in `higher_ranked/mod.rs` for more
-    /// details.
-    pub fn match_poly_projection_predicate(
-        &self,
-        cause: ObligationCause<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        match_a: ty::PolyProjectionPredicate<'tcx>,
-        match_b: ty::TraitRef<'tcx>,
-    ) -> InferResult<'tcx, HrMatchResult<Ty<'tcx>>> {
-        let match_pair = match_a.map_bound(|p| (p.projection_ty.trait_ref(self.tcx), p.ty));
-        let trace = TypeTrace {
-            cause,
-            values: TraitRefs(ExpectedFound::new(
-                true,
-                match_pair.skip_binder().0,
-                match_b,
-            )),
-        };
-
-        let mut combine = self.combine_fields(trace, param_env);
-        let result = combine.higher_ranked_match(&match_pair, &match_b, true)?;
-        Ok(InferOk {
-            value: result,
-            obligations: combine.obligations,
-        })
-    }
-
     /// See `verify_generic_bound` method in `region_constraints`
     pub fn verify_generic_bound(
         &self,

src/librustc/infer/mod.rs

@@ -17,8 +17,6 @@ use ty::{Region, RegionVid};
 use std::collections::BTreeMap;
 use std::{cmp, fmt, mem, u32};
 
-mod taint;
-
 #[derive(Default)]
 pub struct RegionConstraintCollector<'tcx> {
     /// For each `RegionVid`, the corresponding `RegionVariableOrigin`.
@@ -826,35 +824,6 @@ impl<'tcx> RegionConstraintCollector<'tcx> {
             .collect()
     }
 
-    /// Computes all regions that have been related to `r0` since the
-    /// mark `mark` was made---`r0` itself will be the first
-    /// entry. The `directions` parameter controls what kind of
-    /// relations are considered. For example, one can say that only
-    /// "incoming" edges to `r0` are desired, in which case one will
-    /// get the set of regions `{r|r <= r0}`. This is used when
-    /// checking whether placeholder regions are being improperly
-    /// related to other regions.
-    pub fn tainted(
-        &self,
-        tcx: TyCtxt<'_, '_, 'tcx>,
-        mark: &RegionSnapshot,
-        r0: Region<'tcx>,
-        directions: TaintDirections,
-    ) -> FxHashSet<ty::Region<'tcx>> {
-        debug!(
-            "tainted(mark={:?}, r0={:?}, directions={:?})",
-            mark, r0, directions
-        );
-
-        // `result_set` acts as a worklist: we explore all outgoing
-        // edges and add any new regions we find to result_set.  This
-        // is not a terribly efficient implementation.
-        let mut taint_set = taint::TaintSet::new(directions, r0);
-        taint_set.fixed_point(tcx, &self.undo_log[mark.length..], &self.data.verifys);
-        debug!("tainted: result={:?}", taint_set);
-        return taint_set.into_set();
-    }
-
     pub fn region_constraints_added_in_snapshot(&self, mark: &RegionSnapshot) -> bool {
         self.undo_log[mark.length..]
             .iter()

src/librustc/infer/region_constraints/mod.rs

@@ -771,13 +771,7 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
                     }
                 }
                 &ty::Predicate::RegionOutlives(ref binder) => {
-                    if select
-                        .infcx()
-                        .region_outlives_predicate(&dummy_cause, binder)
-                        .is_err()
-                    {
-                        return false;
-                    }
+                    let () = select.infcx().region_outlives_predicate(&dummy_cause, binder);
                 }
                 &ty::Predicate::TypeOutlives(ref binder) => {
                     match (

src/librustc/infer/region_constraints/taint.rs

@@ -728,12 +728,9 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     }
 
                     ty::Predicate::RegionOutlives(ref predicate) => {
-                        let predicate = self.resolve_type_vars_if_possible(predicate);
-                        let err = self.region_outlives_predicate(&obligation.cause,
-                                                                 &predicate).err().unwrap();
-                        struct_span_err!(self.tcx.sess, span, E0279,
-                            "the requirement `{}` is not satisfied (`{}`)",
-                            predicate, err)
+                        // These errors should show up as region
+                        // inference failures.
+                        panic!("region outlives {:?} failed", predicate);
                     }
 
                     ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {

src/librustc/traits/auto_trait.rs

@@ -331,10 +331,8 @@ impl<'a, 'b, 'gcx, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'gcx,
             }
 
             ty::Predicate::RegionOutlives(ref binder) => {
-                match self.selcx.infcx().region_outlives_predicate(&obligation.cause, binder) {
-                    Ok(()) => ProcessResult::Changed(vec![]),
-                    Err(_) => ProcessResult::Error(CodeSelectionError(Unimplemented)),
-                }
+                let () = self.selcx.infcx().region_outlives_predicate(&obligation.cause, binder);
+                ProcessResult::Changed(vec![])
             }
 
             ty::Predicate::TypeOutlives(ref binder) => {