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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.
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 //! See `README.md` for high-level documentation
12
13 use super::Normalized;
14 use super::SelectionContext;
15 use super::ObligationCause;
16 use super::PredicateObligation;
17 use super::project;
18 use super::util;
19
20 use middle::cstore::LOCAL_CRATE;
21 use middle::def_id::DefId;
22 use middle::subst::{Subst, Substs, TypeSpace};
23 use middle::ty::{self, Ty};
24 use middle::infer::{self, InferCtxt, TypeOrigin};
25 use syntax::codemap::{DUMMY_SP, Span};
26
27 #[derive(Copy, Clone)]
28 struct InferIsLocal(bool);
29
30 /// If there are types that satisfy both impls, returns a `TraitRef`
31 /// with those types substituted (by updating the given `infcx`)
32 pub fn overlapping_impls<'cx, 'tcx>(infcx: &InferCtxt<'cx, 'tcx>,
33 impl1_def_id: DefId,
34 impl2_def_id: DefId)
35 -> Option<ty::TraitRef<'tcx>>
36 {
37 debug!("impl_can_satisfy(\
38 impl1_def_id={:?}, \
39 impl2_def_id={:?})",
40 impl1_def_id,
41 impl2_def_id);
42
43 let selcx = &mut SelectionContext::intercrate(infcx);
44 overlap(selcx, impl1_def_id, impl2_def_id)
45 }
46
47 /// Can both impl `a` and impl `b` be satisfied by a common type (including
48 /// `where` clauses)? If so, returns a `TraitRef` that unifies the two impls.
49 fn overlap<'cx, 'tcx>(selcx: &mut SelectionContext<'cx, 'tcx>,
50 a_def_id: DefId,
51 b_def_id: DefId)
52 -> Option<ty::TraitRef<'tcx>>
53 {
54 debug!("overlap(a_def_id={:?}, b_def_id={:?})",
55 a_def_id,
56 b_def_id);
57
58 let (a_trait_ref, a_obligations) = impl_trait_ref_and_oblig(selcx,
59 a_def_id,
60 util::fresh_type_vars_for_impl);
61
62 let (b_trait_ref, b_obligations) = impl_trait_ref_and_oblig(selcx,
63 b_def_id,
64 util::fresh_type_vars_for_impl);
65
66 debug!("overlap: a_trait_ref={:?} a_obligations={:?}", a_trait_ref, a_obligations);
67
68 debug!("overlap: b_trait_ref={:?} b_obligations={:?}", b_trait_ref, b_obligations);
69
70 // Do `a` and `b` unify? If not, no overlap.
71 if let Err(_) = infer::mk_eq_trait_refs(selcx.infcx(),
72 true,
73 TypeOrigin::Misc(DUMMY_SP),
74 a_trait_ref,
75 b_trait_ref) {
76 return None;
77 }
78
79 debug!("overlap: unification check succeeded");
80
81 // Are any of the obligations unsatisfiable? If so, no overlap.
82 let infcx = selcx.infcx();
83 let opt_failing_obligation =
84 a_obligations.iter()
85 .chain(&b_obligations)
86 .map(|o| infcx.resolve_type_vars_if_possible(o))
87 .find(|o| !selcx.evaluate_obligation(o));
88
89 if let Some(failing_obligation) = opt_failing_obligation {
90 debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
91 return None
92 }
93
94 Some(selcx.infcx().resolve_type_vars_if_possible(&a_trait_ref))
95 }
96
97 pub fn trait_ref_is_knowable<'tcx>(tcx: &ty::ctxt<'tcx>, trait_ref: &ty::TraitRef<'tcx>) -> bool
98 {
99 debug!("trait_ref_is_knowable(trait_ref={:?})", trait_ref);
100
101 // if the orphan rules pass, that means that no ancestor crate can
102 // impl this, so it's up to us.
103 if orphan_check_trait_ref(tcx, trait_ref, InferIsLocal(false)).is_ok() {
104 debug!("trait_ref_is_knowable: orphan check passed");
105 return true;
106 }
107
108 // if the trait is not marked fundamental, then it's always possible that
109 // an ancestor crate will impl this in the future, if they haven't
110 // already
111 if
112 trait_ref.def_id.krate != LOCAL_CRATE &&
113 !tcx.has_attr(trait_ref.def_id, "fundamental")
114 {
115 debug!("trait_ref_is_knowable: trait is neither local nor fundamental");
116 return false;
117 }
118
119 // find out when some downstream (or cousin) crate could impl this
120 // trait-ref, presuming that all the parameters were instantiated
121 // with downstream types. If not, then it could only be
122 // implemented by an upstream crate, which means that the impl
123 // must be visible to us, and -- since the trait is fundamental
124 // -- we can test.
125 orphan_check_trait_ref(tcx, trait_ref, InferIsLocal(true)).is_err()
126 }
127
128 type SubstsFn = for<'a,'tcx> fn(infcx: &InferCtxt<'a, 'tcx>,
129 span: Span,
130 impl_def_id: DefId)
131 -> Substs<'tcx>;
132
133 /// Instantiate fresh variables for all bound parameters of the impl
134 /// and return the impl trait ref with those variables substituted.
135 fn impl_trait_ref_and_oblig<'a,'tcx>(selcx: &mut SelectionContext<'a,'tcx>,
136 impl_def_id: DefId,
137 substs_fn: SubstsFn)
138 -> (ty::TraitRef<'tcx>,
139 Vec<PredicateObligation<'tcx>>)
140 {
141 let impl_substs =
142 &substs_fn(selcx.infcx(), DUMMY_SP, impl_def_id);
143 let impl_trait_ref =
144 selcx.tcx().impl_trait_ref(impl_def_id).unwrap();
145 let impl_trait_ref =
146 impl_trait_ref.subst(selcx.tcx(), impl_substs);
147 let Normalized { value: impl_trait_ref, obligations: normalization_obligations1 } =
148 project::normalize(selcx, ObligationCause::dummy(), &impl_trait_ref);
149
150 let predicates = selcx.tcx().lookup_predicates(impl_def_id);
151 let predicates = predicates.instantiate(selcx.tcx(), impl_substs);
152 let Normalized { value: predicates, obligations: normalization_obligations2 } =
153 project::normalize(selcx, ObligationCause::dummy(), &predicates);
154 let impl_obligations =
155 util::predicates_for_generics(ObligationCause::dummy(), 0, &predicates);
156
157 let impl_obligations: Vec<_> =
158 impl_obligations.into_iter()
159 .chain(normalization_obligations1)
160 .chain(normalization_obligations2)
161 .collect();
162
163 (impl_trait_ref, impl_obligations)
164 }
165
166 pub enum OrphanCheckErr<'tcx> {
167 NoLocalInputType,
168 UncoveredTy(Ty<'tcx>),
169 }
170
171 /// Checks the coherence orphan rules. `impl_def_id` should be the
172 /// def-id of a trait impl. To pass, either the trait must be local, or else
173 /// two conditions must be satisfied:
174 ///
175 /// 1. All type parameters in `Self` must be "covered" by some local type constructor.
176 /// 2. Some local type must appear in `Self`.
177 pub fn orphan_check<'tcx>(tcx: &ty::ctxt<'tcx>,
178 impl_def_id: DefId)
179 -> Result<(), OrphanCheckErr<'tcx>>
180 {
181 debug!("orphan_check({:?})", impl_def_id);
182
183 // We only except this routine to be invoked on implementations
184 // of a trait, not inherent implementations.
185 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
186 debug!("orphan_check: trait_ref={:?}", trait_ref);
187
188 // If the *trait* is local to the crate, ok.
189 if trait_ref.def_id.is_local() {
190 debug!("trait {:?} is local to current crate",
191 trait_ref.def_id);
192 return Ok(());
193 }
194
195 orphan_check_trait_ref(tcx, &trait_ref, InferIsLocal(false))
196 }
197
198 fn orphan_check_trait_ref<'tcx>(tcx: &ty::ctxt<'tcx>,
199 trait_ref: &ty::TraitRef<'tcx>,
200 infer_is_local: InferIsLocal)
201 -> Result<(), OrphanCheckErr<'tcx>>
202 {
203 debug!("orphan_check_trait_ref(trait_ref={:?}, infer_is_local={})",
204 trait_ref, infer_is_local.0);
205
206 // First, create an ordered iterator over all the type parameters to the trait, with the self
207 // type appearing first.
208 let input_tys = Some(trait_ref.self_ty());
209 let input_tys = input_tys.iter().chain(trait_ref.substs.types.get_slice(TypeSpace));
210
211 // Find the first input type that either references a type parameter OR
212 // some local type.
213 for input_ty in input_tys {
214 if ty_is_local(tcx, input_ty, infer_is_local) {
215 debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty);
216
217 // First local input type. Check that there are no
218 // uncovered type parameters.
219 let uncovered_tys = uncovered_tys(tcx, input_ty, infer_is_local);
220 for uncovered_ty in uncovered_tys {
221 if let Some(param) = uncovered_ty.walk().find(|t| is_type_parameter(t)) {
222 debug!("orphan_check_trait_ref: uncovered type `{:?}`", param);
223 return Err(OrphanCheckErr::UncoveredTy(param));
224 }
225 }
226
227 // OK, found local type, all prior types upheld invariant.
228 return Ok(());
229 }
230
231 // Otherwise, enforce invariant that there are no type
232 // parameters reachable.
233 if !infer_is_local.0 {
234 if let Some(param) = input_ty.walk().find(|t| is_type_parameter(t)) {
235 debug!("orphan_check_trait_ref: uncovered type `{:?}`", param);
236 return Err(OrphanCheckErr::UncoveredTy(param));
237 }
238 }
239 }
240
241 // If we exit above loop, never found a local type.
242 debug!("orphan_check_trait_ref: no local type");
243 return Err(OrphanCheckErr::NoLocalInputType);
244 }
245
246 fn uncovered_tys<'tcx>(tcx: &ty::ctxt<'tcx>,
247 ty: Ty<'tcx>,
248 infer_is_local: InferIsLocal)
249 -> Vec<Ty<'tcx>>
250 {
251 if ty_is_local_constructor(tcx, ty, infer_is_local) {
252 vec![]
253 } else if fundamental_ty(tcx, ty) {
254 ty.walk_shallow()
255 .flat_map(|t| uncovered_tys(tcx, t, infer_is_local))
256 .collect()
257 } else {
258 vec![ty]
259 }
260 }
261
262 fn is_type_parameter<'tcx>(ty: Ty<'tcx>) -> bool {
263 match ty.sty {
264 // FIXME(#20590) straighten story about projection types
265 ty::TyProjection(..) | ty::TyParam(..) => true,
266 _ => false,
267 }
268 }
269
270 fn ty_is_local<'tcx>(tcx: &ty::ctxt<'tcx>, ty: Ty<'tcx>, infer_is_local: InferIsLocal) -> bool
271 {
272 ty_is_local_constructor(tcx, ty, infer_is_local) ||
273 fundamental_ty(tcx, ty) && ty.walk_shallow().any(|t| ty_is_local(tcx, t, infer_is_local))
274 }
275
276 fn fundamental_ty<'tcx>(tcx: &ty::ctxt<'tcx>, ty: Ty<'tcx>) -> bool
277 {
278 match ty.sty {
279 ty::TyBox(..) | ty::TyRef(..) =>
280 true,
281 ty::TyEnum(def, _) | ty::TyStruct(def, _) =>
282 def.is_fundamental(),
283 ty::TyTrait(ref data) =>
284 tcx.has_attr(data.principal_def_id(), "fundamental"),
285 _ =>
286 false
287 }
288 }
289
290 fn ty_is_local_constructor<'tcx>(tcx: &ty::ctxt<'tcx>,
291 ty: Ty<'tcx>,
292 infer_is_local: InferIsLocal)
293 -> bool
294 {
295 debug!("ty_is_local_constructor({:?})", ty);
296
297 match ty.sty {
298 ty::TyBool |
299 ty::TyChar |
300 ty::TyInt(..) |
301 ty::TyUint(..) |
302 ty::TyFloat(..) |
303 ty::TyStr |
304 ty::TyBareFn(..) |
305 ty::TyArray(..) |
306 ty::TySlice(..) |
307 ty::TyRawPtr(..) |
308 ty::TyRef(..) |
309 ty::TyTuple(..) |
310 ty::TyParam(..) |
311 ty::TyProjection(..) => {
312 false
313 }
314
315 ty::TyInfer(..) => {
316 infer_is_local.0
317 }
318
319 ty::TyEnum(def, _) |
320 ty::TyStruct(def, _) => {
321 def.did.is_local()
322 }
323
324 ty::TyBox(_) => { // Box<T>
325 let krate = tcx.lang_items.owned_box().map(|d| d.krate);
326 krate == Some(LOCAL_CRATE)
327 }
328
329 ty::TyTrait(ref tt) => {
330 tt.principal_def_id().is_local()
331 }
332
333 ty::TyError => {
334 true
335 }
336
337 ty::TyClosure(..) => {
338 tcx.sess.bug(
339 &format!("ty_is_local invoked on unexpected type: {:?}",
340 ty))
341 }
342 }
343 }