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| 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. |
| 4 | +// |
| 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. |
| 10 | + |
| 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 |
| 14 | +// general routines. |
| 15 | + |
1 | 16 | use dep_graph::{DepGraph, DepNode, DepTrackingMap, DepTrackingMapConfig}; |
2 | 17 | use hir::def_id::DefId; |
| 18 | +use infer::TransNormalize; |
3 | 19 | use std::cell::RefCell; |
4 | 20 | use std::marker::PhantomData; |
5 | | -use traits::Vtable; |
6 | | -use ty::{self, Ty}; |
| 21 | +use syntax::ast; |
| 22 | +use syntax_pos::Span; |
| 23 | +use traits::{FulfillmentContext, Obligation, ObligationCause, Reveal, SelectionContext, Vtable}; |
| 24 | +use ty::{self, Ty, TyCtxt}; |
| 25 | +use ty::subst::{Subst, Substs}; |
| 26 | +use ty::fold::{TypeFoldable, TypeFolder}; |
| 27 | +use util::common::MemoizationMap; |
| 28 | + |
| 29 | +impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> { |
| 30 | + /// Attempts to resolve an obligation to a vtable.. The result is |
| 31 | + /// a shallow vtable resolution -- meaning that we do not |
| 32 | + /// (necessarily) resolve all nested obligations on the impl. Note |
| 33 | + /// that type check should guarantee to us that all nested |
| 34 | + /// obligations *could be* resolved if we wanted to. |
| 35 | + pub fn trans_fulfill_obligation(self, |
| 36 | + span: Span, |
| 37 | + trait_ref: ty::PolyTraitRef<'tcx>) |
| 38 | + -> Vtable<'tcx, ()> |
| 39 | + { |
| 40 | + // Remove any references to regions; this helps improve caching. |
| 41 | + let trait_ref = self.erase_regions(&trait_ref); |
| 42 | + |
| 43 | + self.trans_trait_caches.trait_cache.memoize(trait_ref, || { |
| 44 | + debug!("trans::fulfill_obligation(trait_ref={:?}, def_id={:?})", |
| 45 | + trait_ref, trait_ref.def_id()); |
| 46 | + |
| 47 | + // Do the initial selection for the obligation. This yields the |
| 48 | + // shallow result we are looking for -- that is, what specific impl. |
| 49 | + self.infer_ctxt((), Reveal::All).enter(|infcx| { |
| 50 | + let mut selcx = SelectionContext::new(&infcx); |
| 51 | + |
| 52 | + let obligation_cause = ObligationCause::misc(span, |
| 53 | + ast::DUMMY_NODE_ID); |
| 54 | + let obligation = Obligation::new(obligation_cause, |
| 55 | + trait_ref.to_poly_trait_predicate()); |
| 56 | + |
| 57 | + let selection = match selcx.select(&obligation) { |
| 58 | + Ok(Some(selection)) => selection, |
| 59 | + Ok(None) => { |
| 60 | + // Ambiguity can happen when monomorphizing during trans |
| 61 | + // expands to some humongo type that never occurred |
| 62 | + // statically -- this humongo type can then overflow, |
| 63 | + // leading to an ambiguous result. So report this as an |
| 64 | + // overflow bug, since I believe this is the only case |
| 65 | + // where ambiguity can result. |
| 66 | + debug!("Encountered ambiguity selecting `{:?}` during trans, \ |
| 67 | + presuming due to overflow", |
| 68 | + trait_ref); |
| 69 | + self.sess.span_fatal(span, |
| 70 | + "reached the recursion limit during monomorphization \ |
| 71 | + (selection ambiguity)"); |
| 72 | + } |
| 73 | + Err(e) => { |
| 74 | + span_bug!(span, "Encountered error `{:?}` selecting `{:?}` during trans", |
| 75 | + e, trait_ref) |
| 76 | + } |
| 77 | + }; |
| 78 | + |
| 79 | + debug!("fulfill_obligation: selection={:?}", selection); |
| 80 | + |
| 81 | + // Currently, we use a fulfillment context to completely resolve |
| 82 | + // all nested obligations. This is because they can inform the |
| 83 | + // inference of the impl's type parameters. |
| 84 | + let mut fulfill_cx = FulfillmentContext::new(); |
| 85 | + let vtable = selection.map(|predicate| { |
| 86 | + debug!("fulfill_obligation: register_predicate_obligation {:?}", predicate); |
| 87 | + fulfill_cx.register_predicate_obligation(&infcx, predicate); |
| 88 | + }); |
| 89 | + let vtable = infcx.drain_fulfillment_cx_or_panic(span, &mut fulfill_cx, &vtable); |
| 90 | + |
| 91 | + info!("Cache miss: {:?} => {:?}", trait_ref, vtable); |
| 92 | + vtable |
| 93 | + }) |
| 94 | + }) |
| 95 | + } |
| 96 | + |
| 97 | + /// Monomorphizes a type from the AST by first applying the in-scope |
| 98 | + /// substitutions and then normalizing any associated types. |
| 99 | + pub fn trans_apply_param_substs<T>(self, |
| 100 | + param_substs: &Substs<'tcx>, |
| 101 | + value: &T) |
| 102 | + -> T |
| 103 | + where T: TransNormalize<'tcx> |
| 104 | + { |
| 105 | + debug!("apply_param_substs(param_substs={:?}, value={:?})", param_substs, value); |
| 106 | + let substituted = value.subst(self, param_substs); |
| 107 | + let substituted = self.erase_regions(&substituted); |
| 108 | + AssociatedTypeNormalizer::new(self).fold(&substituted) |
| 109 | + } |
| 110 | +} |
| 111 | + |
| 112 | +struct AssociatedTypeNormalizer<'a, 'gcx: 'a> { |
| 113 | + tcx: TyCtxt<'a, 'gcx, 'gcx>, |
| 114 | +} |
| 115 | + |
| 116 | +impl<'a, 'gcx> AssociatedTypeNormalizer<'a, 'gcx> { |
| 117 | + fn new(tcx: TyCtxt<'a, 'gcx, 'gcx>) -> Self { |
| 118 | + AssociatedTypeNormalizer { tcx } |
| 119 | + } |
| 120 | + |
| 121 | + fn fold<T:TypeFoldable<'gcx>>(&mut self, value: &T) -> T { |
| 122 | + if !value.has_projection_types() { |
| 123 | + value.clone() |
| 124 | + } else { |
| 125 | + value.fold_with(self) |
| 126 | + } |
| 127 | + } |
| 128 | +} |
| 129 | + |
| 130 | +impl<'a, 'gcx> TypeFolder<'gcx, 'gcx> for AssociatedTypeNormalizer<'a, 'gcx> { |
| 131 | + fn tcx<'c>(&'c self) -> TyCtxt<'c, 'gcx, 'gcx> { |
| 132 | + self.tcx |
| 133 | + } |
| 134 | + |
| 135 | + fn fold_ty(&mut self, ty: Ty<'gcx>) -> Ty<'gcx> { |
| 136 | + if !ty.has_projection_types() { |
| 137 | + ty |
| 138 | + } else { |
| 139 | + self.tcx.trans_trait_caches.project_cache.memoize(ty, || { |
| 140 | + debug!("AssociatedTypeNormalizer: ty={:?}", ty); |
| 141 | + self.tcx.normalize_associated_type(&ty) |
| 142 | + }) |
| 143 | + } |
| 144 | + } |
| 145 | +} |
7 | 146 |
|
8 | 147 | /// Specializes caches used in trans -- in particular, they assume all |
9 | 148 | /// types are fully monomorphized and that free regions can be erased. |
10 | 149 | pub struct TransTraitCaches<'tcx> { |
11 | | - pub trait_cache: RefCell<DepTrackingMap<TraitSelectionCache<'tcx>>>, |
12 | | - pub project_cache: RefCell<DepTrackingMap<ProjectionCache<'tcx>>>, |
| 150 | + trait_cache: RefCell<DepTrackingMap<TraitSelectionCache<'tcx>>>, |
| 151 | + project_cache: RefCell<DepTrackingMap<ProjectionCache<'tcx>>>, |
13 | 152 | } |
14 | 153 |
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15 | 154 | impl<'tcx> TransTraitCaches<'tcx> { |
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