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)]
23 /// Whether we do the orphan check relative to this crate or
24 /// to some remote crate.
30 #[derive(Debug, Copy, Clone)]
33 Downstream { used_to_be_broken: bool }
36 pub struct OverlapResult<'tcx> {
37 pub impl_header: ty::ImplHeader<'tcx>,
38 pub intercrate_ambiguity_causes: Vec<IntercrateAmbiguityCause>,
41 /// If there are types that satisfy both impls, returns a suitably-freshened
42 /// `ImplHeader` with those types substituted
43 pub fn overlapping_impls<'cx, 'gcx, 'tcx>(infcx: &InferCtxt<'cx, 'gcx, 'tcx>,
46 -> Option<OverlapResult<'tcx>>
48 debug!("impl_can_satisfy(\
54 let selcx = &mut SelectionContext::intercrate(infcx);
55 overlap(selcx, impl1_def_id, impl2_def_id)
58 fn with_fresh_ty_vars<'cx, 'gcx, 'tcx>(selcx: &mut SelectionContext<'cx, 'gcx, 'tcx>,
59 param_env: ty::ParamEnv<'tcx>,
61 -> ty::ImplHeader<'tcx>
63 let tcx = selcx.tcx();
64 let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
66 let header = ty::ImplHeader {
68 self_ty: tcx.type_of(impl_def_id),
69 trait_ref: tcx.impl_trait_ref(impl_def_id),
70 predicates: tcx.predicates_of(impl_def_id).predicates
71 }.subst(tcx, impl_substs);
73 let Normalized { value: mut header, obligations } =
74 traits::normalize(selcx, param_env, ObligationCause::dummy(), &header);
76 header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
80 /// Can both impl `a` and impl `b` be satisfied by a common type (including
81 /// `where` clauses)? If so, returns an `ImplHeader` that unifies the two impls.
82 fn overlap<'cx, 'gcx, 'tcx>(selcx: &mut SelectionContext<'cx, 'gcx, 'tcx>,
85 -> Option<OverlapResult<'tcx>>
87 debug!("overlap(a_def_id={:?}, b_def_id={:?})",
91 // For the purposes of this check, we don't bring any skolemized
92 // types into scope; instead, we replace the generic types with
93 // fresh type variables, and hence we do our evaluations in an
95 let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
97 let a_impl_header = with_fresh_ty_vars(selcx, param_env, a_def_id);
98 let b_impl_header = with_fresh_ty_vars(selcx, param_env, b_def_id);
100 debug!("overlap: a_impl_header={:?}", a_impl_header);
101 debug!("overlap: b_impl_header={:?}", b_impl_header);
103 // Do `a` and `b` unify? If not, no overlap.
104 let obligations = match selcx.infcx().at(&ObligationCause::dummy(), param_env)
105 .eq_impl_headers(&a_impl_header, &b_impl_header) {
106 Ok(InferOk { obligations, value: () }) => {
109 Err(_) => return None
112 debug!("overlap: unification check succeeded");
114 // Are any of the obligations unsatisfiable? If so, no overlap.
115 let infcx = selcx.infcx();
116 let opt_failing_obligation =
117 a_impl_header.predicates
119 .chain(&b_impl_header.predicates)
120 .map(|p| infcx.resolve_type_vars_if_possible(p))
121 .map(|p| Obligation { cause: ObligationCause::dummy(),
126 .find(|o| !selcx.evaluate_obligation(o));
128 if let Some(failing_obligation) = opt_failing_obligation {
129 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
134 impl_header: selcx.infcx().resolve_type_vars_if_possible(&a_impl_header),
135 intercrate_ambiguity_causes: selcx.intercrate_ambiguity_causes().to_vec(),
139 pub fn trait_ref_is_knowable<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
140 trait_ref: ty::TraitRef<'tcx>)
143 debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
144 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Remote).is_ok() {
145 // A downstream or cousin crate is allowed to implement some
146 // substitution of this trait-ref.
148 // A trait can be implementable for a trait ref by both the current
149 // crate and crates downstream of it. Older versions of rustc
150 // were not aware of this, causing incoherence (issue #43355).
151 let used_to_be_broken =
152 orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok();
153 if used_to_be_broken {
154 debug!("trait_ref_is_knowable({:?}) - USED TO BE BROKEN", trait_ref);
156 return Some(Conflict::Downstream { used_to_be_broken });
159 if trait_ref_is_local_or_fundamental(tcx, trait_ref) {
160 // This is a local or fundamental trait, so future-compatibility
161 // is no concern. We know that downstream/cousin crates are not
162 // allowed to implement a substitution of this trait ref, which
163 // means impls could only come from dependencies of this crate,
164 // which we already know about.
168 // This is a remote non-fundamental trait, so if another crate
169 // can be the "final owner" of a substitution of this trait-ref,
170 // they are allowed to implement it future-compatibly.
172 // However, if we are a final owner, then nobody else can be,
173 // and if we are an intermediate owner, then we don't care
174 // about future-compatibility, which means that we're OK if
176 if orphan_check_trait_ref(tcx, trait_ref, InCrate::Local).is_ok() {
177 debug!("trait_ref_is_knowable: orphan check passed");
180 debug!("trait_ref_is_knowable: nonlocal, nonfundamental, unowned");
181 return Some(Conflict::Upstream);
185 pub fn trait_ref_is_local_or_fundamental<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
186 trait_ref: ty::TraitRef<'tcx>)
188 trait_ref.def_id.krate == LOCAL_CRATE || tcx.has_attr(trait_ref.def_id, "fundamental")
191 pub enum OrphanCheckErr<'tcx> {
193 UncoveredTy(Ty<'tcx>),
196 /// Checks the coherence orphan rules. `impl_def_id` should be the
197 /// def-id of a trait impl. To pass, either the trait must be local, or else
198 /// two conditions must be satisfied:
200 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
201 /// 2. Some local type must appear in `Self`.
202 pub fn orphan_check<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
204 -> Result<(), OrphanCheckErr<'tcx>>
206 debug!("orphan_check({:?})", impl_def_id);
208 // We only except this routine to be invoked on implementations
209 // of a trait, not inherent implementations.
210 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
211 debug!("orphan_check: trait_ref={:?}", trait_ref);
213 // If the *trait* is local to the crate, ok.
214 if trait_ref.def_id.is_local() {
215 debug!("trait {:?} is local to current crate",
220 orphan_check_trait_ref(tcx, trait_ref, InCrate::Local)
223 fn orphan_check_trait_ref<'tcx>(tcx: TyCtxt,
224 trait_ref: ty::TraitRef<'tcx>,
226 -> Result<(), OrphanCheckErr<'tcx>>
228 debug!("orphan_check_trait_ref(trait_ref={:?}, in_crate={:?})",
229 trait_ref, in_crate);
231 // First, create an ordered iterator over all the type parameters to the trait, with the self
232 // type appearing first.
233 // Find the first input type that either references a type parameter OR
235 for input_ty in trait_ref.input_types() {
236 if ty_is_local(tcx, input_ty, in_crate) {
237 debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty);
239 // First local input type. Check that there are no
240 // uncovered type parameters.
241 let uncovered_tys = uncovered_tys(tcx, input_ty, in_crate);
242 for uncovered_ty in uncovered_tys {
243 if let Some(param) = uncovered_ty.walk()
244 .find(|t| is_possibly_remote_type(t, in_crate))
246 debug!("orphan_check_trait_ref: uncovered type `{:?}`", param);
247 return Err(OrphanCheckErr::UncoveredTy(param));
251 // OK, found local type, all prior types upheld invariant.
255 // Otherwise, enforce invariant that there are no type
256 // parameters reachable.
257 if let Some(param) = input_ty.walk()
258 .find(|t| is_possibly_remote_type(t, in_crate))
260 debug!("orphan_check_trait_ref: uncovered type `{:?}`", param);
261 return Err(OrphanCheckErr::UncoveredTy(param));
265 // If we exit above loop, never found a local type.
266 debug!("orphan_check_trait_ref: no local type");
267 return Err(OrphanCheckErr::NoLocalInputType);
270 fn uncovered_tys<'tcx>(tcx: TyCtxt, ty: Ty<'tcx>, in_crate: InCrate)
272 if ty_is_local_constructor(ty, in_crate) {
274 } else if fundamental_ty(tcx, ty) {
276 .flat_map(|t| uncovered_tys(tcx, t, in_crate))
283 fn is_possibly_remote_type(ty: Ty, _in_crate: InCrate) -> bool {
285 ty::TyProjection(..) | ty::TyParam(..) => true,
290 fn ty_is_local(tcx: TyCtxt, ty: Ty, in_crate: InCrate) -> bool {
291 ty_is_local_constructor(ty, in_crate) ||
292 fundamental_ty(tcx, ty) && ty.walk_shallow().any(|t| ty_is_local(tcx, t, in_crate))
295 fn fundamental_ty(tcx: TyCtxt, ty: Ty) -> bool {
297 ty::TyRef(..) => true,
298 ty::TyAdt(def, _) => def.is_fundamental(),
299 ty::TyDynamic(ref data, ..) => {
300 data.principal().map_or(false, |p| tcx.has_attr(p.def_id(), "fundamental"))
306 fn def_id_is_local(def_id: DefId, in_crate: InCrate) -> bool {
308 // The type is local to *this* crate - it will not be
309 // local in any other crate.
310 InCrate::Remote => false,
311 InCrate::Local => def_id.is_local()
315 fn ty_is_local_constructor(ty: Ty, in_crate: InCrate) -> bool {
316 debug!("ty_is_local_constructor({:?})", ty);
334 ty::TyProjection(..) => {
338 ty::TyInfer(..) => match in_crate {
339 InCrate::Local => false,
340 // The inference variable might be unified with a local
341 // type in that remote crate.
342 InCrate::Remote => true,
345 ty::TyAdt(def, _) => def_id_is_local(def.did, in_crate),
346 ty::TyForeign(did) => def_id_is_local(did, in_crate),
348 ty::TyDynamic(ref tt, ..) => {
349 tt.principal().map_or(false, |p| {
350 def_id_is_local(p.def_id(), in_crate)
358 ty::TyClosure(..) | ty::TyGenerator(..) | ty::TyAnon(..) => {
359 bug!("ty_is_local invoked on unexpected type: {:?}", ty)