1 // Copyright 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 //! See `README.md` for high-level documentation
13 use hir::def_id::{DefId, LOCAL_CRATE};
14 use syntax_pos::DUMMY_SP;
15 use traits::{self, Normalized, SelectionContext, Obligation, ObligationCause, Reveal};
16 use traits::select::IntercrateAmbiguityCause;
17 use ty::{self, Ty, TyCtxt};
20 use infer::{InferCtxt, InferOk};
22 #[derive(Copy, Clone)]
23 struct InferIsLocal(bool);
25 pub struct OverlapResult<'tcx> {
26 pub impl_header: ty::ImplHeader<'tcx>,
27 pub intercrate_ambiguity_causes: Vec<IntercrateAmbiguityCause>,
30 /// If there are types that satisfy both impls, returns a suitably-freshened
31 /// `ImplHeader` with those types substituted
32 pub fn overlapping_impls<'cx, 'gcx, 'tcx>(infcx: &InferCtxt<'cx, 'gcx, 'tcx>,
35 -> Option<OverlapResult<'tcx>>
37 debug!("impl_can_satisfy(\
43 let selcx = &mut SelectionContext::intercrate(infcx);
44 overlap(selcx, impl1_def_id, impl2_def_id)
47 fn with_fresh_ty_vars<'cx, 'gcx, 'tcx>(selcx: &mut SelectionContext<'cx, 'gcx, 'tcx>,
48 param_env: ty::ParamEnv<'tcx>,
50 -> ty::ImplHeader<'tcx>
52 let tcx = selcx.tcx();
53 let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
55 let header = ty::ImplHeader {
57 self_ty: tcx.type_of(impl_def_id),
58 trait_ref: tcx.impl_trait_ref(impl_def_id),
59 predicates: tcx.predicates_of(impl_def_id).predicates
60 }.subst(tcx, impl_substs);
62 let Normalized { value: mut header, obligations } =
63 traits::normalize(selcx, param_env, ObligationCause::dummy(), &header);
65 header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
69 /// Can both impl `a` and impl `b` be satisfied by a common type (including
70 /// `where` clauses)? If so, returns an `ImplHeader` that unifies the two impls.
71 fn overlap<'cx, 'gcx, 'tcx>(selcx: &mut SelectionContext<'cx, 'gcx, 'tcx>,
74 -> Option<OverlapResult<'tcx>>
76 debug!("overlap(a_def_id={:?}, b_def_id={:?})",
80 // For the purposes of this check, we don't bring any skolemized
81 // types into scope; instead, we replace the generic types with
82 // fresh type variables, and hence we do our evaluations in an
84 let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
86 let a_impl_header = with_fresh_ty_vars(selcx, param_env, a_def_id);
87 let b_impl_header = with_fresh_ty_vars(selcx, param_env, b_def_id);
89 debug!("overlap: a_impl_header={:?}", a_impl_header);
90 debug!("overlap: b_impl_header={:?}", b_impl_header);
92 // Do `a` and `b` unify? If not, no overlap.
93 let obligations = match selcx.infcx().at(&ObligationCause::dummy(), param_env)
94 .eq_impl_headers(&a_impl_header, &b_impl_header) {
95 Ok(InferOk { obligations, value: () }) => {
101 debug!("overlap: unification check succeeded");
103 // Are any of the obligations unsatisfiable? If so, no overlap.
104 let infcx = selcx.infcx();
105 let opt_failing_obligation =
106 a_impl_header.predicates
108 .chain(&b_impl_header.predicates)
109 .map(|p| infcx.resolve_type_vars_if_possible(p))
110 .map(|p| Obligation { cause: ObligationCause::dummy(),
115 .find(|o| !selcx.evaluate_obligation(o));
117 if let Some(failing_obligation) = opt_failing_obligation {
118 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
123 impl_header: selcx.infcx().resolve_type_vars_if_possible(&a_impl_header),
124 intercrate_ambiguity_causes: selcx.intercrate_ambiguity_causes().to_vec(),
128 pub fn trait_ref_is_knowable<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
129 trait_ref: ty::TraitRef<'tcx>) -> bool
131 debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
133 // if the orphan rules pass, that means that no ancestor crate can
134 // impl this, so it's up to us.
135 if orphan_check_trait_ref(tcx, trait_ref, InferIsLocal(false)).is_ok() {
136 debug!("trait_ref_is_knowable: orphan check passed");
140 // if the trait is not marked fundamental, then it's always possible that
141 // an ancestor crate will impl this in the future, if they haven't
143 if !trait_ref_is_local_or_fundamental(tcx, trait_ref) {
144 debug!("trait_ref_is_knowable: trait is neither local nor fundamental");
148 // find out when some downstream (or cousin) crate could impl this
149 // trait-ref, presuming that all the parameters were instantiated
150 // with downstream types. If not, then it could only be
151 // implemented by an upstream crate, which means that the impl
152 // must be visible to us, and -- since the trait is fundamental
154 orphan_check_trait_ref(tcx, trait_ref, InferIsLocal(true)).is_err()
157 pub fn trait_ref_is_local_or_fundamental<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
158 trait_ref: ty::TraitRef<'tcx>)
160 trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, "fundamental")
163 pub enum OrphanCheckErr<'tcx> {
165 UncoveredTy(Ty<'tcx>),
168 /// Checks the coherence orphan rules. `impl_def_id` should be the
169 /// def-id of a trait impl. To pass, either the trait must be local, or else
170 /// two conditions must be satisfied:
172 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
173 /// 2. Some local type must appear in `Self`.
174 pub fn orphan_check<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
176 -> Result<(), OrphanCheckErr<'tcx>>
178 debug!("orphan_check({:?})", impl_def_id);
180 // We only except this routine to be invoked on implementations
181 // of a trait, not inherent implementations.
182 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
183 debug!("orphan_check: trait_ref={:?}", trait_ref);
185 // If the *trait* is local to the crate, ok.
186 if trait_ref.def_id.is_local() {
187 debug!("trait {:?} is local to current crate",
192 orphan_check_trait_ref(tcx, trait_ref, InferIsLocal(false))
195 fn orphan_check_trait_ref<'tcx>(tcx: TyCtxt,
196 trait_ref: ty::TraitRef<'tcx>,
197 infer_is_local: InferIsLocal)
198 -> Result<(), OrphanCheckErr<'tcx>>
200 debug!("orphan_check_trait_ref(trait_ref={:?}, infer_is_local={})",
201 trait_ref, infer_is_local.0);
203 // First, create an ordered iterator over all the type parameters to the trait, with the self
204 // type appearing first.
205 // Find the first input type that either references a type parameter OR
207 for input_ty in trait_ref.input_types() {
208 if ty_is_local(tcx, input_ty, infer_is_local) {
209 debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty);
211 // First local input type. Check that there are no
212 // uncovered type parameters.
213 let uncovered_tys = uncovered_tys(tcx, input_ty, infer_is_local);
214 for uncovered_ty in uncovered_tys {
215 if let Some(param) = uncovered_ty.walk().find(|t| is_type_parameter(t)) {
216 debug!("orphan_check_trait_ref: uncovered type `{:?}`", param);
217 return Err(OrphanCheckErr::UncoveredTy(param));
221 // OK, found local type, all prior types upheld invariant.
225 // Otherwise, enforce invariant that there are no type
226 // parameters reachable.
227 if !infer_is_local.0 {
228 if let Some(param) = input_ty.walk().find(|t| is_type_parameter(t)) {
229 debug!("orphan_check_trait_ref: uncovered type `{:?}`", param);
230 return Err(OrphanCheckErr::UncoveredTy(param));
235 // If we exit above loop, never found a local type.
236 debug!("orphan_check_trait_ref: no local type");
237 return Err(OrphanCheckErr::NoLocalInputType);
240 fn uncovered_tys<'tcx>(tcx: TyCtxt, ty: Ty<'tcx>, infer_is_local: InferIsLocal)
242 if ty_is_local_constructor(ty, infer_is_local) {
244 } else if fundamental_ty(tcx, ty) {
246 .flat_map(|t| uncovered_tys(tcx, t, infer_is_local))
253 fn is_type_parameter(ty: Ty) -> bool {
255 ty::TyProjection(..) | ty::TyParam(..) => true,
260 fn ty_is_local(tcx: TyCtxt, ty: Ty, infer_is_local: InferIsLocal) -> bool {
261 ty_is_local_constructor(ty, infer_is_local) ||
262 fundamental_ty(tcx, ty) && ty.walk_shallow().any(|t| ty_is_local(tcx, t, infer_is_local))
265 fn fundamental_ty(tcx: TyCtxt, ty: Ty) -> bool {
267 ty::TyRef(..) => true,
268 ty::TyAdt(def, _) => def.is_fundamental(),
269 ty::TyDynamic(ref data, ..) => {
270 data.principal().map_or(false, |p| tcx.has_attr(p.def_id(), "fundamental"))
276 fn ty_is_local_constructor(ty: Ty, infer_is_local: InferIsLocal)-> bool {
277 debug!("ty_is_local_constructor({:?})", ty);
295 ty::TyProjection(..) => {
303 ty::TyAdt(def, _) => {
307 ty::TyForeign(did) => {
311 ty::TyDynamic(ref tt, ..) => {
312 tt.principal().map_or(false, |p| p.def_id().is_local())
319 ty::TyClosure(..) | ty::TyGenerator(..) | ty::TyAnon(..) => {
320 bug!("ty_is_local invoked on unexpected type: {:?}", ty)