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.
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 use middle::free_region::FreeRegionMap;
14 use middle::ty::{self};
15 use middle::subst::{self, Subst, Substs, VecPerParamSpace};
16 use util::ppaux::{self, Repr};
19 use syntax::codemap::Span;
20 use syntax::parse::token;
24 /// Checks that a method from an impl conforms to the signature of
25 /// the same method as declared in the trait.
29 /// - impl_m: type of the method we are checking
30 /// - impl_m_span: span to use for reporting errors
31 /// - impl_m_body_id: id of the method body
32 /// - trait_m: the method in the trait
33 /// - impl_trait_ref: the TraitRef corresponding to the trait implementation
35 pub fn compare_impl_method<'tcx>(tcx: &ty::ctxt<'tcx>,
36 impl_m: &ty::Method<'tcx>,
38 impl_m_body_id: ast::NodeId,
39 trait_m: &ty::Method<'tcx>,
40 impl_trait_ref: &ty::TraitRef<'tcx>) {
41 debug!("compare_impl_method(impl_trait_ref={})",
42 impl_trait_ref.repr(tcx));
44 debug!("compare_impl_method: impl_trait_ref (liberated) = {}",
45 impl_trait_ref.repr(tcx));
47 let infcx = infer::new_infer_ctxt(tcx);
48 let mut fulfillment_cx = traits::FulfillmentContext::new();
50 let trait_to_impl_substs = &impl_trait_ref.substs;
52 // Try to give more informative error messages about self typing
53 // mismatches. Note that any mismatch will also be detected
54 // below, where we construct a canonical function type that
55 // includes the self parameter as a normal parameter. It's just
56 // that the error messages you get out of this code are a bit more
57 // inscrutable, particularly for cases where one method has no
59 match (&trait_m.explicit_self, &impl_m.explicit_self) {
60 (&ty::StaticExplicitSelfCategory,
61 &ty::StaticExplicitSelfCategory) => {}
62 (&ty::StaticExplicitSelfCategory, _) => {
63 span_err!(tcx.sess, impl_m_span, E0185,
64 "method `{}` has a `{}` declaration in the impl, \
65 but not in the trait",
66 token::get_name(trait_m.name),
67 ppaux::explicit_self_category_to_str(
68 &impl_m.explicit_self));
71 (_, &ty::StaticExplicitSelfCategory) => {
72 span_err!(tcx.sess, impl_m_span, E0186,
73 "method `{}` has a `{}` declaration in the trait, \
75 token::get_name(trait_m.name),
76 ppaux::explicit_self_category_to_str(
77 &trait_m.explicit_self));
81 // Let the type checker catch other errors below
85 let num_impl_m_type_params = impl_m.generics.types.len(subst::FnSpace);
86 let num_trait_m_type_params = trait_m.generics.types.len(subst::FnSpace);
87 if num_impl_m_type_params != num_trait_m_type_params {
88 span_err!(tcx.sess, impl_m_span, E0049,
89 "method `{}` has {} type parameter{} \
90 but its trait declaration has {} type parameter{}",
91 token::get_name(trait_m.name),
92 num_impl_m_type_params,
93 if num_impl_m_type_params == 1 {""} else {"s"},
94 num_trait_m_type_params,
95 if num_trait_m_type_params == 1 {""} else {"s"});
99 if impl_m.fty.sig.0.inputs.len() != trait_m.fty.sig.0.inputs.len() {
100 span_err!(tcx.sess, impl_m_span, E0050,
101 "method `{}` has {} parameter{} \
102 but the declaration in trait `{}` has {}",
103 token::get_name(trait_m.name),
104 impl_m.fty.sig.0.inputs.len(),
105 if impl_m.fty.sig.0.inputs.len() == 1 {""} else {"s"},
106 ty::item_path_str(tcx, trait_m.def_id),
107 trait_m.fty.sig.0.inputs.len());
111 // This code is best explained by example. Consider a trait:
113 // trait Trait<'t,T> {
114 // fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
119 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
120 // fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
123 // We wish to decide if those two method types are compatible.
125 // We start out with trait_to_impl_substs, that maps the trait
126 // type parameters to impl type parameters. This is taken from the
127 // impl trait reference:
129 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
131 // We create a mapping `dummy_substs` that maps from the impl type
132 // parameters to fresh types and regions. For type parameters,
133 // this is the identity transform, but we could as well use any
134 // skolemized types. For regions, we convert from bound to free
135 // regions (Note: but only early-bound regions, i.e., those
136 // declared on the impl or used in type parameter bounds).
138 // impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
140 // Now we can apply skol_substs to the type of the impl method
141 // to yield a new function type in terms of our fresh, skolemized
144 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
146 // We now want to extract and substitute the type of the *trait*
147 // method and compare it. To do so, we must create a compound
148 // substitution by combining trait_to_impl_substs and
149 // impl_to_skol_substs, and also adding a mapping for the method
150 // type parameters. We extend the mapping to also include
151 // the method parameters.
153 // trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
155 // Applying this to the trait method type yields:
157 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
159 // This type is also the same but the name of the bound region ('a
160 // vs 'b). However, the normal subtyping rules on fn types handle
161 // this kind of equivalency just fine.
163 // We now use these substitutions to ensure that all declared bounds are
164 // satisfied by the implementation's method.
166 // We do this by creating a parameter environment which contains a
167 // substitution corresponding to impl_to_skol_substs. We then build
168 // trait_to_skol_substs and use it to convert the predicates contained
169 // in the trait_m.generics to the skolemized form.
171 // Finally we register each of these predicates as an obligation in
172 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
174 // Create a parameter environment that represents the implementation's
177 ty::ParameterEnvironment::for_item(tcx, impl_m.def_id.node);
179 // Create mapping from impl to skolemized.
180 let impl_to_skol_substs = &impl_param_env.free_substs;
182 // Create mapping from trait to skolemized.
183 let trait_to_skol_substs =
185 .subst(tcx, impl_to_skol_substs)
186 .with_method(impl_to_skol_substs.types.get_slice(subst::FnSpace).to_vec(),
187 impl_to_skol_substs.regions().get_slice(subst::FnSpace).to_vec());
188 debug!("compare_impl_method: trait_to_skol_substs={}",
189 trait_to_skol_substs.repr(tcx));
191 // Check region bounds. FIXME(@jroesch) refactor this away when removing
193 if !check_region_bounds_on_impl_method(tcx,
198 &trait_to_skol_substs,
199 impl_to_skol_substs) {
203 // Create obligations for each predicate declared by the impl
204 // definition in the context of the trait's parameter
205 // environment. We can't just use `impl_env.caller_bounds`,
206 // however, because we want to replace all late-bound regions with
209 impl_m.predicates.instantiate(tcx, impl_to_skol_substs);
211 let (impl_bounds, _) =
212 infcx.replace_late_bound_regions_with_fresh_var(
214 infer::HigherRankedType,
215 &ty::Binder(impl_bounds));
216 debug!("compare_impl_method: impl_bounds={}",
217 impl_bounds.repr(tcx));
219 // Normalize the associated types in the trait_bounds.
220 let trait_bounds = trait_m.predicates.instantiate(tcx, &trait_to_skol_substs);
222 // Obtain the predicate split predicate sets for each.
223 let trait_pred = trait_bounds.predicates.split();
224 let impl_pred = impl_bounds.predicates.split();
226 // This is the only tricky bit of the new way we check implementation methods
227 // We need to build a set of predicates where only the FnSpace bounds
228 // are from the trait and we assume all other bounds from the implementation
229 // to be previously satisfied.
231 // We then register the obligations from the impl_m and check to see
232 // if all constraints hold.
233 let hybrid_preds = VecPerParamSpace::new(
239 // Construct trait parameter environment and then shift it into the skolemized viewpoint.
240 // The key step here is to update the caller_bounds's predicates to be
241 // the new hybrid bounds we computed.
242 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_body_id);
243 let trait_param_env = impl_param_env.with_caller_bounds(hybrid_preds.into_vec());
244 let trait_param_env = traits::normalize_param_env_or_error(trait_param_env,
245 normalize_cause.clone());
247 debug!("compare_impl_method: trait_bounds={}",
248 trait_param_env.caller_bounds.repr(tcx));
250 let mut selcx = traits::SelectionContext::new(&infcx, &trait_param_env);
252 for predicate in impl_pred.fns {
253 let traits::Normalized { value: predicate, .. } =
254 traits::normalize(&mut selcx, normalize_cause.clone(), &predicate);
256 let cause = traits::ObligationCause {
258 body_id: impl_m_body_id,
259 code: traits::ObligationCauseCode::CompareImplMethodObligation
262 fulfillment_cx.register_predicate_obligation(
264 traits::Obligation::new(cause, predicate));
267 // We now need to check that the signature of the impl method is
268 // compatible with that of the trait method. We do this by
269 // checking that `impl_fty <: trait_fty`.
271 // FIXME. Unfortunately, this doesn't quite work right now because
272 // associated type normalization is not integrated into subtype
273 // checks. For the comparison to be valid, we need to
274 // normalize the associated types in the impl/trait methods
275 // first. However, because function types bind regions, just
276 // calling `normalize_associated_types_in` would have no effect on
277 // any associated types appearing in the fn arguments or return
280 // Compute skolemized form of impl and trait method tys.
281 let impl_fty = ty::mk_bare_fn(tcx, None, tcx.mk_bare_fn(impl_m.fty.clone()));
282 let impl_fty = impl_fty.subst(tcx, impl_to_skol_substs);
283 let trait_fty = ty::mk_bare_fn(tcx, None, tcx.mk_bare_fn(trait_m.fty.clone()));
284 let trait_fty = trait_fty.subst(tcx, &trait_to_skol_substs);
286 let err = infcx.commit_if_ok(|snapshot| {
287 let origin = infer::MethodCompatCheck(impl_m_span);
290 infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
291 infer::HigherRankedType,
294 impl_sig.subst(tcx, impl_to_skol_substs);
296 assoc::normalize_associated_types_in(&infcx,
305 tcx.mk_bare_fn(ty::BareFnTy { unsafety: impl_m.fty.unsafety,
307 sig: ty::Binder(impl_sig) }));
308 debug!("compare_impl_method: impl_fty={}",
311 let (trait_sig, skol_map) =
312 infcx.skolemize_late_bound_regions(&trait_m.fty.sig, snapshot);
314 trait_sig.subst(tcx, &trait_to_skol_substs);
316 assoc::normalize_associated_types_in(&infcx,
325 tcx.mk_bare_fn(ty::BareFnTy { unsafety: trait_m.fty.unsafety,
326 abi: trait_m.fty.abi,
327 sig: ty::Binder(trait_sig) }));
329 debug!("compare_impl_method: trait_fty={}",
330 trait_fty.repr(tcx));
332 try!(infer::mk_subty(&infcx, false, origin, impl_fty, trait_fty));
334 infcx.leak_check(&skol_map, snapshot)
340 debug!("checking trait method for compatibility: impl ty {}, trait ty {}",
342 trait_fty.repr(tcx));
343 span_err!(tcx.sess, impl_m_span, E0053,
344 "method `{}` has an incompatible type for trait: {}",
345 token::get_name(trait_m.name),
346 ty::type_err_to_str(tcx, &terr));
351 // Check that all obligations are satisfied by the implementation's
353 match fulfillment_cx.select_all_or_error(&infcx, &trait_param_env) {
354 Err(ref errors) => { traits::report_fulfillment_errors(&infcx, errors) }
358 // Finally, resolve all regions. This catches wily misuses of
359 // lifetime parameters. We have to build up a plausible lifetime
360 // environment based on what we find in the trait. We could also
361 // include the obligations derived from the method argument types,
362 // but I don't think it's necessary -- after all, those are still
363 // in effect when type-checking the body, and all the
364 // where-clauses in the header etc should be implied by the trait
365 // anyway, so it shouldn't be needed there either. Anyway, we can
366 // always add more relations later (it's backwards compat).
367 let mut free_regions = FreeRegionMap::new();
368 free_regions.relate_free_regions_from_predicates(tcx, &trait_param_env.caller_bounds);
370 infcx.resolve_regions_and_report_errors(&free_regions, impl_m_body_id);
372 fn check_region_bounds_on_impl_method<'tcx>(tcx: &ty::ctxt<'tcx>,
374 impl_m: &ty::Method<'tcx>,
375 trait_generics: &ty::Generics<'tcx>,
376 impl_generics: &ty::Generics<'tcx>,
377 trait_to_skol_substs: &Substs<'tcx>,
378 impl_to_skol_substs: &Substs<'tcx>)
382 let trait_params = trait_generics.regions.get_slice(subst::FnSpace);
383 let impl_params = impl_generics.regions.get_slice(subst::FnSpace);
385 debug!("check_region_bounds_on_impl_method: \
388 trait_to_skol_substs={} \
389 impl_to_skol_substs={}",
390 trait_generics.repr(tcx),
391 impl_generics.repr(tcx),
392 trait_to_skol_substs.repr(tcx),
393 impl_to_skol_substs.repr(tcx));
395 // Must have same number of early-bound lifetime parameters.
396 // Unfortunately, if the user screws up the bounds, then this
397 // will change classification between early and late. E.g.,
398 // if in trait we have `<'a,'b:'a>`, and in impl we just have
399 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
400 // in trait but 0 in the impl. But if we report "expected 2
401 // but found 0" it's confusing, because it looks like there
402 // are zero. Since I don't quite know how to phrase things at
403 // the moment, give a kind of vague error message.
404 if trait_params.len() != impl_params.len() {
405 span_err!(tcx.sess, span, E0195,
406 "lifetime parameters or bounds on method `{}` do \
407 not match the trait declaration",
408 token::get_name(impl_m.name));
416 pub fn compare_const_impl<'tcx>(tcx: &ty::ctxt<'tcx>,
417 impl_c: &ty::AssociatedConst<'tcx>,
419 trait_c: &ty::AssociatedConst<'tcx>,
420 impl_trait_ref: &ty::TraitRef<'tcx>) {
421 debug!("compare_const_impl(impl_trait_ref={})",
422 impl_trait_ref.repr(tcx));
424 let infcx = infer::new_infer_ctxt(tcx);
425 let mut fulfillment_cx = traits::FulfillmentContext::new();
427 // The below is for the most part highly similar to the procedure
428 // for methods above. It is simpler in many respects, especially
429 // because we shouldn't really have to deal with lifetimes or
430 // predicates. In fact some of this should probably be put into
431 // shared functions because of DRY violations...
432 let trait_to_impl_substs = &impl_trait_ref.substs;
434 // Create a parameter environment that represents the implementation's
437 ty::ParameterEnvironment::for_item(tcx, impl_c.def_id.node);
439 // Create mapping from impl to skolemized.
440 let impl_to_skol_substs = &impl_param_env.free_substs;
442 // Create mapping from trait to skolemized.
443 let trait_to_skol_substs =
445 .subst(tcx, impl_to_skol_substs)
446 .with_method(impl_to_skol_substs.types.get_slice(subst::FnSpace).to_vec(),
447 impl_to_skol_substs.regions().get_slice(subst::FnSpace).to_vec());
448 debug!("compare_const_impl: trait_to_skol_substs={}",
449 trait_to_skol_substs.repr(tcx));
451 // Compute skolemized form of impl and trait const tys.
452 let impl_ty = impl_c.ty.subst(tcx, impl_to_skol_substs);
453 let trait_ty = trait_c.ty.subst(tcx, &trait_to_skol_substs);
455 let err = infcx.commit_if_ok(|_| {
456 let origin = infer::Misc(impl_c_span);
458 // There is no "body" here, so just pass dummy id.
460 assoc::normalize_associated_types_in(&infcx,
466 debug!("compare_const_impl: impl_ty={}",
470 assoc::normalize_associated_types_in(&infcx,
476 debug!("compare_const_impl: trait_ty={}",
479 infer::mk_subty(&infcx, false, origin, impl_ty, trait_ty)
485 debug!("checking associated const for compatibility: impl ty {}, trait ty {}",
488 span_err!(tcx.sess, impl_c_span, E0326,
489 "implemented const `{}` has an incompatible type for \
491 token::get_name(trait_c.name),
492 ty::type_err_to_str(tcx, &terr));