Auto merge of #24553 - nikomatsakis:issue-22779-overconstrained-impl, r=pnkfelix

Rather than storing the relations between free-regions in a global
table, introduce a `FreeRegionMap` data structure. regionck computes the
`FreeRegionMap` for each fn and stores the result into the tcx so that
borrowck can use it (this could perhaps be refactored to have borrowck
recompute the map, but it's a bid tedious to recompute due to the
interaction of closures and free fns). The main reason to do this is
because of #22779 -- using a global table was incorrect because when
validating impl method signatures, we want to use the free region
relationships from the *trait*, not the impl.

Fixes #22779.

Author: bors

src/librustc/lib.rs

@@ -106,8 +106,10 @@ pub mod middle {
     pub mod entry;
     pub mod expr_use_visitor;
     pub mod fast_reject;
+    pub mod free_region;
     pub mod intrinsicck;
     pub mod infer;
+    pub mod implicator;
     pub mod lang_items;
     pub mod liveness;
     pub mod mem_categorization;

src/librustc/middle/free_region.rs

@@ -0,0 +1,127 @@
+// Copyright 2012-2014 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.
+
+//! This file defines
+
+use middle::implicator::Implication;
+use middle::ty::{self, FreeRegion};
+use util::common::can_reach;
+use util::nodemap::FnvHashMap;
+use util::ppaux::Repr;
+
+#[derive(Clone)]
+pub struct FreeRegionMap {
+    /// `free_region_map` maps from a free region `a` to a list of
+    /// free regions `bs` such that `a <= b for all b in bs`
+    map: FnvHashMap<FreeRegion, Vec<FreeRegion>>,
+}
+
+impl FreeRegionMap {
+    pub fn new() -> FreeRegionMap {
+        FreeRegionMap { map: FnvHashMap() }
+    }
+
+    pub fn relate_free_regions_from_implications<'tcx>(&mut self,
+                                                       tcx: &ty::ctxt<'tcx>,
+                                                       implications: &[Implication<'tcx>])
+    {
+        for implication in implications {
+            debug!("implication: {}", implication.repr(tcx));
+            match *implication {
+                Implication::RegionSubRegion(_, ty::ReFree(free_a), ty::ReFree(free_b)) => {
+                    self.relate_free_regions(free_a, free_b);
+                }
+                Implication::RegionSubRegion(..) |
+                Implication::RegionSubClosure(..) |
+                Implication::RegionSubGeneric(..) |
+                Implication::Predicate(..) => {
+                }
+            }
+        }
+    }
+
+    pub fn relate_free_regions_from_predicates<'tcx>(&mut self,
+                                                     tcx: &ty::ctxt<'tcx>,
+                                                     predicates: &[ty::Predicate<'tcx>]) {
+        debug!("relate_free_regions_from_predicates(predicates={})", predicates.repr(tcx));
+        for predicate in predicates {
+            match *predicate {
+                ty::Predicate::Projection(..) |
+                ty::Predicate::Trait(..) |
+                ty::Predicate::Equate(..) |
+                ty::Predicate::TypeOutlives(..) => {
+                    // No region bounds here
+                }
+                ty::Predicate::RegionOutlives(ty::Binder(ty::OutlivesPredicate(r_a, r_b))) => {
+                    match (r_a, r_b) {
+                        (ty::ReFree(fr_a), ty::ReFree(fr_b)) => {
+                            // Record that `'a:'b`. Or, put another way, `'b <= 'a`.
+                            self.relate_free_regions(fr_b, fr_a);
+                        }
+                        _ => {
+                            // All named regions are instantiated with free regions.
+                            tcx.sess.bug(
+                                &format!("record_region_bounds: non free region: {} / {}",
+                                         r_a.repr(tcx),
+                                         r_b.repr(tcx)));
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    pub fn relate_free_regions(&mut self, sub: FreeRegion, sup: FreeRegion) {
+        let mut sups = self.map.entry(sub).or_insert(Vec::new());
+        if !sups.contains(&sup) {
+            sups.push(sup);
+        }
+    }
+
+    /// Determines whether two free regions have a subregion relationship
+    /// by walking the graph encoded in `map`.  Note that
+    /// it is possible that `sub != sup` and `sub <= sup` and `sup <= sub`
+    /// (that is, the user can give two different names to the same lifetime).
+    pub fn sub_free_region(&self, sub: FreeRegion, sup: FreeRegion) -> bool {
+        can_reach(&self.map, sub, sup)
+    }
+
+    /// Determines whether one region is a subregion of another.  This is intended to run *after
+    /// inference* and sadly the logic is somewhat duplicated with the code in infer.rs.
+    pub fn is_subregion_of(&self,
+                           tcx: &ty::ctxt,
+                           sub_region: ty::Region,
+                           super_region: ty::Region)
+                           -> bool {
+        debug!("is_subregion_of(sub_region={:?}, super_region={:?})",
+               sub_region, super_region);
+
+        sub_region == super_region || {
+            match (sub_region, super_region) {
+                (ty::ReEmpty, _) |
+                (_, ty::ReStatic) =>
+                    true,
+
+                (ty::ReScope(sub_scope), ty::ReScope(super_scope)) =>
+                    tcx.region_maps.is_subscope_of(sub_scope, super_scope),
+
+                (ty::ReScope(sub_scope), ty::ReFree(ref fr)) =>
+                    tcx.region_maps.is_subscope_of(sub_scope, fr.scope.to_code_extent()),
+
+                (ty::ReFree(sub_fr), ty::ReFree(super_fr)) =>
+                    self.sub_free_region(sub_fr, super_fr),
+
+                _ =>
+                    false,
+            }
+        }
+    }
+}
+

src/librustc_typeck/check/implicator.rs src/librustc/middle/implicator.rs

@@ -10,11 +10,10 @@
 
 // #![warn(deprecated_mode)]
 
-use astconv::object_region_bounds;
 use middle::infer::{InferCtxt, GenericKind};
 use middle::subst::Substs;
 use middle::traits;
-use middle::ty::{self, ToPolyTraitRef, Ty};
+use middle::ty::{self, RegionEscape, ToPolyTraitRef, Ty};
 use middle::ty_fold::{TypeFoldable, TypeFolder};
 
 use std::rc::Rc;
@@ -423,6 +422,39 @@ impl<'a, 'tcx> Implicator<'a, 'tcx> {
     }
 }
 
+/// Given an object type like `SomeTrait+Send`, computes the lifetime
+/// bounds that must hold on the elided self type. These are derived
+/// from the declarations of `SomeTrait`, `Send`, and friends -- if
+/// they declare `trait SomeTrait : 'static`, for example, then
+/// `'static` would appear in the list. The hard work is done by
+/// `ty::required_region_bounds`, see that for more information.
+pub fn object_region_bounds<'tcx>(
+    tcx: &ty::ctxt<'tcx>,
+    principal: &ty::PolyTraitRef<'tcx>,
+    others: ty::BuiltinBounds)
+    -> Vec<ty::Region>
+{
+    // Since we don't actually *know* the self type for an object,
+    // this "open(err)" serves as a kind of dummy standin -- basically
+    // a skolemized type.
+    let open_ty = ty::mk_infer(tcx, ty::FreshTy(0));
+
+    // Note that we preserve the overall binding levels here.
+    assert!(!open_ty.has_escaping_regions());
+    let substs = tcx.mk_substs(principal.0.substs.with_self_ty(open_ty));
+    let trait_refs = vec!(ty::Binder(Rc::new(ty::TraitRef::new(principal.0.def_id, substs))));
+
+    let param_bounds = ty::ParamBounds {
+        region_bounds: Vec::new(),
+        builtin_bounds: others,
+        trait_bounds: trait_refs,
+        projection_bounds: Vec::new(), // not relevant to computing region bounds
+    };
+
+    let predicates = ty::predicates(tcx, open_ty, &param_bounds);
+    ty::required_region_bounds(tcx, open_ty, predicates)
+}
+
 impl<'tcx> Repr<'tcx> for Implication<'tcx> {
     fn repr(&self, tcx: &ty::ctxt<'tcx>) -> String {
         match *self {

src/librustc/middle/infer/mod.rs

@@ -22,6 +22,7 @@ pub use middle::ty::IntVarValue;
 pub use self::freshen::TypeFreshener;
 pub use self::region_inference::GenericKind;
 
+use middle::free_region::FreeRegionMap;
 use middle::subst;
 use middle::subst::Substs;
 use middle::ty::{TyVid, IntVid, FloatVid, RegionVid, UnconstrainedNumeric};
@@ -855,8 +856,10 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         self.region_vars.new_bound(debruijn)
     }
 
-    pub fn resolve_regions_and_report_errors(&self, subject_node_id: ast::NodeId) {
-        let errors = self.region_vars.resolve_regions(subject_node_id);
+    pub fn resolve_regions_and_report_errors(&self,
+                                             free_regions: &FreeRegionMap,
+                                             subject_node_id: ast::NodeId) {
+        let errors = self.region_vars.resolve_regions(free_regions, subject_node_id);
         self.report_region_errors(&errors); // see error_reporting.rs
     }