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, Debug)]
29 #[derive(Debug, Copy, Clone)]
35 pub struct OverlapResult<'tcx> {
36 pub impl_header: ty::ImplHeader<'tcx>,
37 pub intercrate_ambiguity_causes: Vec<IntercrateAmbiguityCause>,
40 /// If there are types that satisfy both impls, returns a suitably-freshened
41 /// `ImplHeader` with those types substituted
42 pub fn overlapping_impls<'cx, 'gcx, 'tcx>(infcx: &InferCtxt<'cx, 'gcx, 'tcx>,
45 -> Option<OverlapResult<'tcx>>
47 debug!("impl_can_satisfy(\
53 let selcx = &mut SelectionContext::intercrate(infcx);
54 overlap(selcx, impl1_def_id, impl2_def_id)
57 fn with_fresh_ty_vars<'cx, 'gcx, 'tcx>(selcx: &mut SelectionContext<'cx, 'gcx, 'tcx>,
58 param_env: ty::ParamEnv<'tcx>,
60 -> ty::ImplHeader<'tcx>
62 let tcx = selcx.tcx();
63 let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
65 let header = ty::ImplHeader {
67 self_ty: tcx.type_of(impl_def_id),
68 trait_ref: tcx.impl_trait_ref(impl_def_id),
69 predicates: tcx.predicates_of(impl_def_id).predicates
70 }.subst(tcx, impl_substs);
72 let Normalized { value: mut header, obligations } =
73 traits::normalize(selcx, param_env, ObligationCause::dummy(), &header);
75 header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
79 /// Can both impl `a` and impl `b` be satisfied by a common type (including
80 /// `where` clauses)? If so, returns an `ImplHeader` that unifies the two impls.
81 fn overlap<'cx, 'gcx, 'tcx>(selcx: &mut SelectionContext<'cx, 'gcx, 'tcx>,
84 -> Option<OverlapResult<'tcx>>
86 debug!("overlap(a_def_id={:?}, b_def_id={:?})",
90 // For the purposes of this check, we don't bring any skolemized
91 // types into scope; instead, we replace the generic types with
92 // fresh type variables, and hence we do our evaluations in an
94 let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
96 let a_impl_header = with_fresh_ty_vars(selcx, param_env, a_def_id);
97 let b_impl_header = with_fresh_ty_vars(selcx, param_env, b_def_id);
99 debug!("overlap: a_impl_header={:?}", a_impl_header);
100 debug!("overlap: b_impl_header={:?}", b_impl_header);
102 // Do `a` and `b` unify? If not, no overlap.
103 let obligations = match selcx.infcx().at(&ObligationCause::dummy(), param_env)
104 .eq_impl_headers(&a_impl_header, &b_impl_header) {
105 Ok(InferOk { obligations, value: () }) => {
108 Err(_) => return None
111 debug!("overlap: unification check succeeded");
113 // Are any of the obligations unsatisfiable? If so, no overlap.
114 let infcx = selcx.infcx();
115 let opt_failing_obligation =
116 a_impl_header.predicates
118 .chain(&b_impl_header.predicates)
119 .map(|p| infcx.resolve_type_vars_if_possible(p))
120 .map(|p| Obligation { cause: ObligationCause::dummy(),
125 .find(|o| !selcx.evaluate_obligation(o));
127 if let Some(failing_obligation) = opt_failing_obligation {
128 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
133 impl_header: selcx.infcx().resolve_type_vars_if_possible(&a_impl_header),
134 intercrate_ambiguity_causes: selcx.intercrate_ambiguity_causes().to_vec(),
138 pub fn trait_ref_is_knowable<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
139 trait_ref: ty::TraitRef<'tcx>,
143 debug!("trait_ref_is_knowable(trait_ref={:?}, broken={:?})", trait_ref, broken);
144 let mode = if broken {
145 InferIsLocal::BrokenYes
149 if orphan_check_trait_ref(tcx, trait_ref, mode).is_ok() {
150 // A downstream or cousin crate is allowed to implement some
151 // substitution of this trait-ref.
152 debug!("trait_ref_is_knowable: downstream crate might implement");
153 return Some(Conflict::Downstream);
156 if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
157 // This is a local or fundamental trait, so future-compatibility
158 // is no concern. We know that downstream/cousin crates are not
159 // allowed to implement a substitution of this trait ref, which
160 // means impls could only come from dependencies of this crate,
161 // which we already know about.
164 // This is a remote non-fundamental trait, so if another crate
165 // can be the "final owner" of a substitution of this trait-ref,
166 // they are allowed to implement it future-compatibly.
168 // However, if we are a final owner, then nobody else can be,
169 // and if we are an intermediate owner, then we don't care
170 // about future-compatibility, which means that we're OK if
172 if orphan_check_trait_ref(tcx, trait_ref, InferIsLocal::No).is_ok() {
173 debug!("trait_ref_is_knowable: orphan check passed");
176 debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
177 return Some(Conflict::Upstream);
181 pub fn trait_ref_is_local_or_fundamental<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
182 trait_ref: ty::TraitRef<'tcx>)
184 trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, "fundamental")
187 pub enum OrphanCheckErr<'tcx> {
189 UncoveredTy(Ty<'tcx>),
192 /// Checks the coherence orphan rules. `impl_def_id` should be the
193 /// def-id of a trait impl. To pass, either the trait must be local, or else
194 /// two conditions must be satisfied:
196 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
197 /// 2. Some local type must appear in `Self`.
198 pub fn orphan_check<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
200 -> Result<(), OrphanCheckErr<'tcx>>
202 debug!("orphan_check({:?})", impl_def_id);
204 // We only except this routine to be invoked on implementations
205 // of a trait, not inherent implementations.
206 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
207 debug!("orphan_check: trait_ref={:?}", trait_ref);
209 // If the *trait* is local to the crate, ok.
210 if trait_ref.def_id.is_local() {
211 debug!("trait {:?} is local to current crate",
216 orphan_check_trait_ref(tcx, trait_ref, InferIsLocal::No)
219 fn orphan_check_trait_ref<'tcx>(tcx: TyCtxt,
220 trait_ref: ty::TraitRef<'tcx>,
221 infer_is_local: InferIsLocal)
222 -> Result<(), OrphanCheckErr<'tcx>>
224 debug!("orphan_check_trait_ref(trait_ref={:?}, infer_is_local={:?})",
225 trait_ref, infer_is_local);
227 // First, create an ordered iterator over all the type parameters to the trait, with the self
228 // type appearing first.
229 // Find the first input type that either references a type parameter OR
231 for input_ty in trait_ref.input_types() {
232 if ty_is_local(tcx, input_ty, infer_is_local) {
233 debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty);
235 // First local input type. Check that there are no
236 // uncovered type parameters.
237 let uncovered_tys = uncovered_tys(tcx, input_ty, infer_is_local);
238 for uncovered_ty in uncovered_tys {
239 if let Some(param) = uncovered_ty.walk()
240 .find(|t| is_possibly_remote_type(t, infer_is_local))
242 debug!("orphan_check_trait_ref: uncovered type `{:?}`", param);
243 return Err(OrphanCheckErr::UncoveredTy(param));
247 // OK, found local type, all prior types upheld invariant.
251 // Otherwise, enforce invariant that there are no type
252 // parameters reachable.
253 if let Some(param) = input_ty.walk()
254 .find(|t| is_possibly_remote_type(t, infer_is_local))
256 debug!("orphan_check_trait_ref: uncovered type `{:?}`", param);
257 return Err(OrphanCheckErr::UncoveredTy(param));
261 // If we exit above loop, never found a local type.
262 debug!("orphan_check_trait_ref: no local type");
263 return Err(OrphanCheckErr::NoLocalInputType);
266 fn uncovered_tys<'tcx>(tcx: TyCtxt, ty: Ty<'tcx>, infer_is_local: InferIsLocal)
268 if ty_is_local_constructor(ty, infer_is_local) {
270 } else if fundamental_ty(tcx, ty) {
272 .flat_map(|t| uncovered_tys(tcx, t, infer_is_local))
279 fn is_possibly_remote_type(ty: Ty, _infer_is_local: InferIsLocal) -> bool {
281 ty::TyProjection(..) | ty::TyParam(..) => true,
286 fn ty_is_local(tcx: TyCtxt, ty: Ty, infer_is_local: InferIsLocal) -> bool {
287 ty_is_local_constructor(ty, infer_is_local) ||
288 fundamental_ty(tcx, ty) && ty.walk_shallow().any(|t| ty_is_local(tcx, t, infer_is_local))
291 fn fundamental_ty(tcx: TyCtxt, ty: Ty) -> bool {
293 ty::TyRef(..) => true,
294 ty::TyAdt(def, _) => def.is_fundamental(),
295 ty::TyDynamic(ref data, ..) => {
296 data.principal().map_or(false, |p| tcx.has_attr(p.def_id(), "fundamental"))
302 fn def_id_is_local(def_id: DefId, infer_is_local: InferIsLocal) -> bool {
303 match infer_is_local {
304 InferIsLocal::Yes => false,
306 InferIsLocal::BrokenYes => def_id.is_local()
310 fn ty_is_local_constructor(ty: Ty, infer_is_local: InferIsLocal) -> bool {
311 debug!("ty_is_local_constructor({:?})", ty);
329 ty::TyProjection(..) => {
333 ty::TyInfer(..) => match infer_is_local {
334 InferIsLocal::No => false,
336 InferIsLocal::BrokenYes => true
339 ty::TyAdt(def, _) => def_id_is_local(def.did, infer_is_local),
340 ty::TyForeign(did) => def_id_is_local(did, infer_is_local),
342 ty::TyDynamic(ref tt, ..) => {
343 tt.principal().map_or(false, |p| {
344 def_id_is_local(p.def_id(), infer_is_local)
352 ty::TyClosure(..) | ty::TyGenerator(..) | ty::TyAnon(..) => {
353 bug!("ty_is_local invoked on unexpected type: {:?}", ty)