1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 // This file contains various trait resolution methods used by trans.
12 // They all assume regions can be erased and monomorphic types. It
13 // seems likely that they should eventually be merged into more
16 use dep_graph::{DepGraph, DepNode, DepTrackingMap, DepTrackingMapConfig,
18 use hir::def_id::DefId;
19 use infer::TransNormalize;
20 use std::cell::RefCell;
21 use std::marker::PhantomData;
24 use traits::{FulfillmentContext, Obligation, ObligationCause, Reveal, SelectionContext, Vtable};
25 use ty::{self, Ty, TyCtxt};
26 use ty::subst::{Subst, Substs};
27 use ty::fold::{TypeFoldable, TypeFolder};
28 use util::common::MemoizationMap;
30 impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
31 /// Attempts to resolve an obligation to a vtable.. The result is
32 /// a shallow vtable resolution -- meaning that we do not
33 /// (necessarily) resolve all nested obligations on the impl. Note
34 /// that type check should guarantee to us that all nested
35 /// obligations *could be* resolved if we wanted to.
36 pub fn trans_fulfill_obligation(self,
38 trait_ref: ty::PolyTraitRef<'tcx>)
41 // Remove any references to regions; this helps improve caching.
42 let trait_ref = self.erase_regions(&trait_ref);
44 self.trans_trait_caches.trait_cache.memoize(self, trait_ref, || {
45 debug!("trans::fulfill_obligation(trait_ref={:?}, def_id={:?})",
46 trait_ref, trait_ref.def_id());
48 // Do the initial selection for the obligation. This yields the
49 // shallow result we are looking for -- that is, what specific impl.
50 self.infer_ctxt().enter(|infcx| {
51 let mut selcx = SelectionContext::new(&infcx);
53 let param_env = ty::ParamEnv::empty(Reveal::All);
54 let obligation_cause = ObligationCause::misc(span,
56 let obligation = Obligation::new(obligation_cause,
58 trait_ref.to_poly_trait_predicate());
60 let selection = match selcx.select(&obligation) {
61 Ok(Some(selection)) => selection,
63 // Ambiguity can happen when monomorphizing during trans
64 // expands to some humongo type that never occurred
65 // statically -- this humongo type can then overflow,
66 // leading to an ambiguous result. So report this as an
67 // overflow bug, since I believe this is the only case
68 // where ambiguity can result.
69 debug!("Encountered ambiguity selecting `{:?}` during trans, \
70 presuming due to overflow",
72 self.sess.span_fatal(span,
73 "reached the recursion limit during monomorphization \
74 (selection ambiguity)");
77 span_bug!(span, "Encountered error `{:?}` selecting `{:?}` during trans",
82 debug!("fulfill_obligation: selection={:?}", selection);
84 // Currently, we use a fulfillment context to completely resolve
85 // all nested obligations. This is because they can inform the
86 // inference of the impl's type parameters.
87 let mut fulfill_cx = FulfillmentContext::new();
88 let vtable = selection.map(|predicate| {
89 debug!("fulfill_obligation: register_predicate_obligation {:?}", predicate);
90 fulfill_cx.register_predicate_obligation(&infcx, predicate);
92 let vtable = infcx.drain_fulfillment_cx_or_panic(span, &mut fulfill_cx, &vtable);
94 info!("Cache miss: {:?} => {:?}", trait_ref, vtable);
100 /// Monomorphizes a type from the AST by first applying the in-scope
101 /// substitutions and then normalizing any associated types.
102 pub fn trans_apply_param_substs<T>(self,
103 param_substs: &Substs<'tcx>,
106 where T: TransNormalize<'tcx>
108 debug!("apply_param_substs(param_substs={:?}, value={:?})", param_substs, value);
109 let substituted = value.subst(self, param_substs);
110 let substituted = self.erase_regions(&substituted);
111 AssociatedTypeNormalizer::new(self).fold(&substituted)
115 struct AssociatedTypeNormalizer<'a, 'gcx: 'a> {
116 tcx: TyCtxt<'a, 'gcx, 'gcx>,
119 impl<'a, 'gcx> AssociatedTypeNormalizer<'a, 'gcx> {
120 fn new(tcx: TyCtxt<'a, 'gcx, 'gcx>) -> Self {
121 AssociatedTypeNormalizer { tcx }
124 fn fold<T:TypeFoldable<'gcx>>(&mut self, value: &T) -> T {
125 if !value.has_projection_types() {
128 value.fold_with(self)
133 impl<'a, 'gcx> TypeFolder<'gcx, 'gcx> for AssociatedTypeNormalizer<'a, 'gcx> {
134 fn tcx<'c>(&'c self) -> TyCtxt<'c, 'gcx, 'gcx> {
138 fn fold_ty(&mut self, ty: Ty<'gcx>) -> Ty<'gcx> {
139 if !ty.has_projection_types() {
142 self.tcx.trans_trait_caches.project_cache.memoize(self.tcx, ty, || {
143 debug!("AssociatedTypeNormalizer: ty={:?}", ty);
144 self.tcx.normalize_associated_type(&ty)
150 /// Specializes caches used in trans -- in particular, they assume all
151 /// types are fully monomorphized and that free regions can be erased.
152 pub struct TransTraitCaches<'tcx> {
153 trait_cache: RefCell<DepTrackingMap<TraitSelectionCache<'tcx>>>,
154 project_cache: RefCell<DepTrackingMap<ProjectionCache<'tcx>>>,
157 impl<'tcx> TransTraitCaches<'tcx> {
158 pub fn new(graph: DepGraph) -> Self {
160 trait_cache: RefCell::new(DepTrackingMap::new(graph.clone())),
161 project_cache: RefCell::new(DepTrackingMap::new(graph)),
166 // Implement DepTrackingMapConfig for `trait_cache`
167 pub struct TraitSelectionCache<'tcx> {
168 data: PhantomData<&'tcx ()>
171 impl<'tcx> DepTrackingMapConfig for TraitSelectionCache<'tcx> {
172 type Key = ty::PolyTraitRef<'tcx>;
173 type Value = Vtable<'tcx, ()>;
174 fn to_dep_node(tcx: TyCtxt, key: &ty::PolyTraitRef<'tcx>) -> DepNode {
175 key.to_poly_trait_predicate().dep_node(tcx)
181 pub struct ProjectionCache<'gcx> {
182 data: PhantomData<&'gcx ()>
185 impl<'gcx> DepTrackingMapConfig for ProjectionCache<'gcx> {
187 type Value = Ty<'gcx>;
188 fn to_dep_node(tcx: TyCtxt, key: &Self::Key) -> DepNode {
189 // Ideally, we'd just put `key` into the dep-node, but we
190 // can't put full types in there. So just collect up all the
191 // def-ids of structs/enums as well as any traits that we
192 // project out of. It doesn't matter so much what we do here,
193 // except that if we are too coarse, we'll create overly
194 // coarse edges between impls and the trans. For example, if
195 // we just used the def-id of things we are projecting out of,
196 // then the key for `<Foo as SomeTrait>::T` and `<Bar as
197 // SomeTrait>::T` would both share a dep-node
198 // (`TraitSelect(SomeTrait)`), and hence the impls for both
199 // `Foo` and `Bar` would be considered inputs. So a change to
200 // `Bar` would affect things that just normalized `Foo`.
201 // Anyway, this heuristic is not ideal, but better than
203 let def_ids: Vec<DefId> =
205 .filter_map(|t| match t.sty {
206 ty::TyAdt(adt_def, _) => Some(adt_def.did),
207 ty::TyProjection(ref proj) => Some(proj.item_def_id),
212 DepNode::new(tcx, DepConstructor::ProjectionCache { def_ids: def_ids })