introduce, but do not use, `free_region_relation` computation

This duplicates, effectively, existing code in the universal regions
computation.

src/librustc_mir/borrow_check/nll/mod.rs

@@ -104,6 +104,8 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
         None
     };
 
+    let universal_regions = Rc::new(universal_regions);
+
     let elements = &Rc::new(RegionValueElements::new(mir));
 
     // Run the MIR type-checker.

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

@@ -206,15 +206,13 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// of constraints produced by the MIR type check.
     pub(crate) fn new(
         var_infos: VarInfos,
-        universal_regions: UniversalRegions<'tcx>,
+        universal_regions: Rc<UniversalRegions<'tcx>>,
         _mir: &Mir<'tcx>,
         outlives_constraints: ConstraintSet,
         type_tests: Vec<TypeTest<'tcx>>,
         liveness_constraints: LivenessValues<RegionVid>,
         elements: &Rc<RegionValueElements>,
     ) -> Self {
-        let universal_regions = Rc::new(universal_regions);
-
         // Create a RegionDefinition for each inference variable.
         let definitions: IndexVec<_, _> = var_infos
             .into_iter()

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

+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use borrow_check::location::LocationTable;
+use borrow_check::nll::facts::AllFacts;
+use borrow_check::nll::universal_regions::UniversalRegions;
+use borrow_check::nll::type_check::constraint_conversion;
+use borrow_check::nll::type_check::{Locations, MirTypeckRegionConstraints};
+use rustc::hir::def_id::DefId;
+use rustc::infer::region_constraints::GenericKind;
+use rustc::infer::InferCtxt;
+use rustc::traits::query::outlives_bounds::{self, OutlivesBound};
+use rustc::traits::query::type_op::{self, TypeOp};
+use rustc::ty::{self, RegionVid, Ty};
+use rustc_data_structures::transitive_relation::TransitiveRelation;
+use std::rc::Rc;
+use syntax::ast;
+
+#[derive(Debug)]
+crate struct UniversalRegionRelations<'tcx> {
+    universal_regions: Rc<UniversalRegions<'tcx>>,
+
+    /// Each RBP `('a, GK)` indicates that `GK: 'a` can be assumed to
+    /// be true. These encode relationships like `T: 'a` that are
+    /// added via implicit bounds.
+    ///
+    /// Each region here is guaranteed to be a key in the `indices`
+    /// map.  We use the "original" regions (i.e., the keys from the
+    /// map, and not the values) because the code in
+    /// `process_registered_region_obligations` has some special-cased
+    /// logic expecting to see (e.g.) `ReStatic`, and if we supplied
+    /// our special inference variable there, we would mess that up.
+    crate region_bound_pairs: Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>,
+
+    /// Stores the outlives relations that are known to hold from the
+    /// implied bounds, in-scope where clauses, and that sort of
+    /// thing.
+    outlives: TransitiveRelation<RegionVid>,
+
+    /// This is the `<=` relation; that is, if `a: b`, then `b <= a`,
+    /// and we store that here. This is useful when figuring out how
+    /// to express some local region in terms of external regions our
+    /// caller will understand.
+    inverse_outlives: TransitiveRelation<RegionVid>,
+}
+
+impl UniversalRegionRelations<'tcx> {
+    crate fn create(
+        infcx: &InferCtxt<'_, '_, 'tcx>,
+        mir_def_id: DefId,
+        param_env: ty::ParamEnv<'tcx>,
+        location_table: &LocationTable,
+        implicit_region_bound: Option<ty::Region<'tcx>>,
+        universal_regions: &Rc<UniversalRegions<'tcx>>,
+        constraints: &mut MirTypeckRegionConstraints<'tcx>,
+        all_facts: &mut Option<AllFacts>,
+    ) -> Self {
+        let mir_node_id = infcx.tcx.hir.as_local_node_id(mir_def_id).unwrap();
+        UniversalRegionRelationsBuilder {
+            infcx,
+            mir_def_id,
+            mir_node_id,
+            param_env,
+            implicit_region_bound,
+            constraints,
+            location_table,
+            all_facts,
+            universal_regions: universal_regions.clone(),
+            relations: UniversalRegionRelations {
+                universal_regions: universal_regions.clone(),
+                region_bound_pairs: Vec::new(),
+                outlives: TransitiveRelation::new(),
+                inverse_outlives: TransitiveRelation::new(),
+            },
+        }.create()
+    }
+
+    /// Records in the `outlives_relation` (and
+    /// `inverse_outlives_relation`) that `fr_a: fr_b`. Invoked by the
+    /// builder below.
+    fn relate_universal_regions(&mut self, fr_a: RegionVid, fr_b: RegionVid) {
+        debug!(
+            "relate_universal_regions: fr_a={:?} outlives fr_b={:?}",
+            fr_a, fr_b
+        );
+        self.outlives.add(fr_a, fr_b);
+        self.inverse_outlives.add(fr_b, fr_a);
+    }
+}
+
+struct UniversalRegionRelationsBuilder<'this, 'gcx: 'tcx, 'tcx: 'this> {
+    infcx: &'this InferCtxt<'this, 'gcx, 'tcx>,
+    mir_def_id: DefId,
+    mir_node_id: ast::NodeId,
+    param_env: ty::ParamEnv<'tcx>,
+    location_table: &'this LocationTable,
+    universal_regions: Rc<UniversalRegions<'tcx>>,
+    relations: UniversalRegionRelations<'tcx>,
+    implicit_region_bound: Option<ty::Region<'tcx>>,
+    constraints: &'this mut MirTypeckRegionConstraints<'tcx>,
+    all_facts: &'this mut Option<AllFacts>,
+}
+
+impl UniversalRegionRelationsBuilder<'cx, 'gcx, 'tcx> {
+    crate fn create(mut self) -> UniversalRegionRelations<'tcx> {
+        let unnormalized_input_output_tys = self
+            .universal_regions
+            .unnormalized_input_tys
+            .iter()
+            .cloned()
+            .chain(Some(self.universal_regions.unnormalized_output_ty));
+
+        // For each of the input/output types:
+        // - Normalize the type. This will create some region
+        //   constraints, which we buffer up because we are
+        //   not ready to process them yet.
+        // - Then compute the implied bounds. This will adjust
+        //   the `relations.region_bound_pairs` and so forth.
+        // - After this is done, we'll process the constraints, once
+        //   the `relations` is built.
+        let constraint_sets: Vec<_> = unnormalized_input_output_tys
+            .flat_map(|ty| {
+                debug!("build: input_or_output={:?}", ty);
+                let (ty, constraints) = self
+                    .param_env
+                    .and(type_op::normalize::Normalize::new(ty))
+                    .fully_perform(self.infcx)
+                    .unwrap_or_else(|_| bug!("failed to normalize {:?}", ty));
+                self.add_implied_bounds(ty);
+                constraints
+            })
+            .collect();
+
+        // Insert the facts we know from the predicates. Why? Why not.
+        let param_env = self.param_env;
+        self.add_outlives_bounds(outlives_bounds::explicit_outlives_bounds(param_env));
+
+        // Finally:
+        // - outlives is reflexive, so `'r: 'r` for every region `'r`
+        // - `'static: 'r` for every region `'r`
+        // - `'r: 'fn_body` for every (other) universally quantified
+        //   region `'r`, all of which are provided by our caller
+        let fr_static = self.universal_regions.fr_static;
+        let fr_fn_body = self.universal_regions.fr_fn_body;
+        for fr in self.universal_regions.universal_regions() {
+            debug!(
+                "build: relating free region {:?} to itself and to 'static",
+                fr
+            );
+            self.relations.relate_universal_regions(fr, fr);
+            self.relations.relate_universal_regions(fr_static, fr);
+            self.relations.relate_universal_regions(fr, fr_fn_body);
+        }
+
+        for data in constraint_sets {
+            constraint_conversion::ConstraintConversion::new(
+                self.infcx.tcx,
+                &self.universal_regions,
+                &self.location_table,
+                &self.relations.region_bound_pairs,
+                self.implicit_region_bound,
+                self.param_env,
+                Locations::All,
+                &mut self.constraints.outlives_constraints,
+                &mut self.constraints.type_tests,
+                &mut self.all_facts,
+            ).convert_all(&data);
+        }
+
+        self.relations
+    }
+
+    /// Update the type of a single local, which should represent
+    /// either the return type of the MIR or one of its arguments. At
+    /// the same time, compute and add any implied bounds that come
+    /// from this local.
+    fn add_implied_bounds(&mut self, ty: Ty<'tcx>) {
+        debug!("add_implied_bounds(ty={:?})", ty);
+        let span = self.infcx.tcx.def_span(self.mir_def_id);
+        let bounds = self
+            .infcx
+            .implied_outlives_bounds(self.param_env, self.mir_node_id, ty, span);
+        self.add_outlives_bounds(bounds);
+    }
+
+    /// Registers the `OutlivesBound` items from `outlives_bounds` in
+    /// the outlives relation as well as the region-bound pairs
+    /// listing.
+    fn add_outlives_bounds<I>(&mut self, outlives_bounds: I)
+    where
+        I: IntoIterator<Item = OutlivesBound<'tcx>>,
+    {
+        for outlives_bound in outlives_bounds {
+            debug!("add_outlives_bounds(bound={:?})", outlives_bound);
+
+            match outlives_bound {
+                OutlivesBound::RegionSubRegion(r1, r2) => {
+                    // The bound says that `r1 <= r2`; we store `r2: r1`.
+                    let r1 = self.universal_regions.to_region_vid(r1);
+                    let r2 = self.universal_regions.to_region_vid(r2);
+                    self.relations.relate_universal_regions(r2, r1);
+                }
+
+                OutlivesBound::RegionSubParam(r_a, param_b) => {
+                    self.relations
+                        .region_bound_pairs
+                        .push((r_a, GenericKind::Param(param_b)));
+                }
+
+                OutlivesBound::RegionSubProjection(r_a, projection_b) => {
+                    self.relations
+                        .region_bound_pairs
+                        .push((r_a, GenericKind::Projection(projection_b)));
+                }
+            }
+        }
+    }
+}

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

@@ -71,6 +71,7 @@
 }
 
 mod constraint_conversion;
+mod free_region_relations;
 mod input_output;
 mod liveness;
 mod relate_tys;
@@ -110,7 +111,7 @@ pub(crate) fn type_check<'gcx, 'tcx>(
     param_env: ty::ParamEnv<'gcx>,
     mir: &Mir<'tcx>,
     mir_def_id: DefId,
-    universal_regions: &UniversalRegions<'tcx>,
+    universal_regions: &Rc<UniversalRegions<'tcx>>,
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
     liveness: &LivenessResults<LocalWithRegion>,
@@ -127,6 +128,17 @@ pub(crate) fn type_check<'gcx, 'tcx>(
         type_tests: Vec::default(),
     };
 
+    let _urr = free_region_relations::UniversalRegionRelations::create(
+        infcx,
+        mir_def_id,
+        param_env,
+        location_table,
+        Some(implicit_region_bound),
+        universal_regions,
+        &mut constraints,
+        all_facts,
+    );
+
     {
         let mut borrowck_context = BorrowCheckContext {
             universal_regions,

src/librustc_mir/lib.rs

@@ -14,6 +14,8 @@
 
 */
 
+#![feature(infer_outlives_requirements)]
+#![feature(in_band_lifetimes)]
 #![feature(slice_patterns)]
 #![feature(slice_sort_by_cached_key)]
 #![feature(from_ref)]