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};
18 use syntax::codemap::Span;
19 use syntax::parse::token;
23 /// Checks that a method from an impl conforms to the signature of
24 /// the same method as declared in the trait.
28 /// - impl_m: type of the method we are checking
29 /// - impl_m_span: span to use for reporting errors
30 /// - impl_m_body_id: id of the method body
31 /// - trait_m: the method in the trait
32 /// - impl_trait_ref: the TraitRef corresponding to the trait implementation
34 pub fn compare_impl_method<'tcx>(tcx: &ty::ctxt<'tcx>,
35 impl_m: &ty::Method<'tcx>,
37 impl_m_body_id: ast::NodeId,
38 trait_m: &ty::Method<'tcx>,
39 impl_trait_ref: &ty::TraitRef<'tcx>) {
40 debug!("compare_impl_method(impl_trait_ref={:?})",
43 debug!("compare_impl_method: impl_trait_ref (liberated) = {:?}",
46 let mut infcx = infer::new_infer_ctxt(tcx, &tcx.tables, None, true);
47 let mut fulfillment_cx = infcx.fulfillment_cx.borrow_mut();
49 let trait_to_impl_substs = &impl_trait_ref.substs;
51 // Try to give more informative error messages about self typing
52 // mismatches. Note that any mismatch will also be detected
53 // below, where we construct a canonical function type that
54 // includes the self parameter as a normal parameter. It's just
55 // that the error messages you get out of this code are a bit more
56 // inscrutable, particularly for cases where one method has no
58 match (&trait_m.explicit_self, &impl_m.explicit_self) {
59 (&ty::StaticExplicitSelfCategory,
60 &ty::StaticExplicitSelfCategory) => {}
61 (&ty::StaticExplicitSelfCategory, _) => {
62 span_err!(tcx.sess, impl_m_span, E0185,
63 "method `{}` has a `{}` declaration in the impl, \
64 but not in the trait",
66 impl_m.explicit_self);
69 (_, &ty::StaticExplicitSelfCategory) => {
70 span_err!(tcx.sess, impl_m_span, E0186,
71 "method `{}` has a `{}` declaration in the trait, \
74 trait_m.explicit_self);
78 // Let the type checker catch other errors below
82 let num_impl_m_type_params = impl_m.generics.types.len(subst::FnSpace);
83 let num_trait_m_type_params = trait_m.generics.types.len(subst::FnSpace);
84 if num_impl_m_type_params != num_trait_m_type_params {
85 span_err!(tcx.sess, impl_m_span, E0049,
86 "method `{}` has {} type parameter{} \
87 but its trait declaration has {} type parameter{}",
88 token::get_name(trait_m.name),
89 num_impl_m_type_params,
90 if num_impl_m_type_params == 1 {""} else {"s"},
91 num_trait_m_type_params,
92 if num_trait_m_type_params == 1 {""} else {"s"});
96 if impl_m.fty.sig.0.inputs.len() != trait_m.fty.sig.0.inputs.len() {
97 span_err!(tcx.sess, impl_m_span, E0050,
98 "method `{}` has {} parameter{} \
99 but the declaration in trait `{}` has {}",
100 token::get_name(trait_m.name),
101 impl_m.fty.sig.0.inputs.len(),
102 if impl_m.fty.sig.0.inputs.len() == 1 {""} else {"s"},
103 tcx.item_path_str(trait_m.def_id),
104 trait_m.fty.sig.0.inputs.len());
108 // This code is best explained by example. Consider a trait:
110 // trait Trait<'t,T> {
111 // fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
116 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
117 // fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
120 // We wish to decide if those two method types are compatible.
122 // We start out with trait_to_impl_substs, that maps the trait
123 // type parameters to impl type parameters. This is taken from the
124 // impl trait reference:
126 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
128 // We create a mapping `dummy_substs` that maps from the impl type
129 // parameters to fresh types and regions. For type parameters,
130 // this is the identity transform, but we could as well use any
131 // skolemized types. For regions, we convert from bound to free
132 // regions (Note: but only early-bound regions, i.e., those
133 // declared on the impl or used in type parameter bounds).
135 // impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
137 // Now we can apply skol_substs to the type of the impl method
138 // to yield a new function type in terms of our fresh, skolemized
141 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
143 // We now want to extract and substitute the type of the *trait*
144 // method and compare it. To do so, we must create a compound
145 // substitution by combining trait_to_impl_substs and
146 // impl_to_skol_substs, and also adding a mapping for the method
147 // type parameters. We extend the mapping to also include
148 // the method parameters.
150 // trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
152 // Applying this to the trait method type yields:
154 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
156 // This type is also the same but the name of the bound region ('a
157 // vs 'b). However, the normal subtyping rules on fn types handle
158 // this kind of equivalency just fine.
160 // We now use these substitutions to ensure that all declared bounds are
161 // satisfied by the implementation's method.
163 // We do this by creating a parameter environment which contains a
164 // substitution corresponding to impl_to_skol_substs. We then build
165 // trait_to_skol_substs and use it to convert the predicates contained
166 // in the trait_m.generics to the skolemized form.
168 // Finally we register each of these predicates as an obligation in
169 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
171 // Create a parameter environment that represents the implementation's
174 ty::ParameterEnvironment::for_item(tcx, impl_m.def_id.node);
176 // Create mapping from impl to skolemized.
177 let impl_to_skol_substs = &impl_param_env.free_substs;
179 // Create mapping from trait to skolemized.
180 let trait_to_skol_substs =
182 .subst(tcx, impl_to_skol_substs)
183 .with_method(impl_to_skol_substs.types.get_slice(subst::FnSpace).to_vec(),
184 impl_to_skol_substs.regions().get_slice(subst::FnSpace).to_vec());
185 debug!("compare_impl_method: trait_to_skol_substs={:?}",
186 trait_to_skol_substs);
188 // Check region bounds. FIXME(@jroesch) refactor this away when removing
190 if !check_region_bounds_on_impl_method(tcx,
195 &trait_to_skol_substs,
196 impl_to_skol_substs) {
200 // Create obligations for each predicate declared by the impl
201 // definition in the context of the trait's parameter
202 // environment. We can't just use `impl_env.caller_bounds`,
203 // however, because we want to replace all late-bound regions with
206 impl_m.predicates.instantiate(tcx, impl_to_skol_substs);
208 let (impl_bounds, _) =
209 infcx.replace_late_bound_regions_with_fresh_var(
211 infer::HigherRankedType,
212 &ty::Binder(impl_bounds));
213 debug!("compare_impl_method: impl_bounds={:?}",
216 // Normalize the associated types in the trait_bounds.
217 let trait_bounds = trait_m.predicates.instantiate(tcx, &trait_to_skol_substs);
219 // Obtain the predicate split predicate sets for each.
220 let trait_pred = trait_bounds.predicates.split();
221 let impl_pred = impl_bounds.predicates.split();
223 // This is the only tricky bit of the new way we check implementation methods
224 // We need to build a set of predicates where only the FnSpace bounds
225 // are from the trait and we assume all other bounds from the implementation
226 // to be previously satisfied.
228 // We then register the obligations from the impl_m and check to see
229 // if all constraints hold.
230 let hybrid_preds = VecPerParamSpace::new(
236 // Construct trait parameter environment and then shift it into the skolemized viewpoint.
237 // The key step here is to update the caller_bounds's predicates to be
238 // the new hybrid bounds we computed.
239 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_body_id);
240 let trait_param_env = impl_param_env.with_caller_bounds(hybrid_preds.into_vec());
241 let trait_param_env = traits::normalize_param_env_or_error(trait_param_env,
242 normalize_cause.clone());
243 // FIXME(@jroesch) this seems ugly, but is a temporary change
244 infcx.parameter_environment = trait_param_env;
246 debug!("compare_impl_method: trait_bounds={:?}",
247 infcx.parameter_environment.caller_bounds);
249 let mut selcx = traits::SelectionContext::new(&infcx);
251 for predicate in impl_pred.fns {
252 let traits::Normalized { value: predicate, .. } =
253 traits::normalize(&mut selcx, normalize_cause.clone(), &predicate);
255 let cause = traits::ObligationCause {
257 body_id: impl_m_body_id,
258 code: traits::ObligationCauseCode::CompareImplMethodObligation
261 fulfillment_cx.register_predicate_obligation(
263 traits::Obligation::new(cause, predicate));
266 // We now need to check that the signature of the impl method is
267 // compatible with that of the trait method. We do this by
268 // checking that `impl_fty <: trait_fty`.
270 // FIXME. Unfortunately, this doesn't quite work right now because
271 // associated type normalization is not integrated into subtype
272 // checks. For the comparison to be valid, we need to
273 // normalize the associated types in the impl/trait methods
274 // first. However, because function types bind regions, just
275 // calling `normalize_associated_types_in` would have no effect on
276 // any associated types appearing in the fn arguments or return
279 // Compute skolemized form of impl and trait method tys.
280 let impl_fty = tcx.mk_fn(None, tcx.mk_bare_fn(impl_m.fty.clone()));
281 let impl_fty = impl_fty.subst(tcx, impl_to_skol_substs);
282 let trait_fty = tcx.mk_fn(None, tcx.mk_bare_fn(trait_m.fty.clone()));
283 let trait_fty = trait_fty.subst(tcx, &trait_to_skol_substs);
285 let err = infcx.commit_if_ok(|snapshot| {
286 let origin = infer::MethodCompatCheck(impl_m_span);
289 infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
290 infer::HigherRankedType,
293 impl_sig.subst(tcx, impl_to_skol_substs);
295 assoc::normalize_associated_types_in(&infcx,
300 let impl_fty = tcx.mk_fn(None, tcx.mk_bare_fn(ty::BareFnTy {
301 unsafety: impl_m.fty.unsafety,
303 sig: ty::Binder(impl_sig)
305 debug!("compare_impl_method: impl_fty={:?}",
308 let (trait_sig, skol_map) =
309 infcx.skolemize_late_bound_regions(&trait_m.fty.sig, snapshot);
311 trait_sig.subst(tcx, &trait_to_skol_substs);
313 assoc::normalize_associated_types_in(&infcx,
318 let trait_fty = tcx.mk_fn(None, tcx.mk_bare_fn(ty::BareFnTy {
319 unsafety: trait_m.fty.unsafety,
320 abi: trait_m.fty.abi,
321 sig: ty::Binder(trait_sig)
324 debug!("compare_impl_method: trait_fty={:?}",
327 try!(infer::mk_subty(&infcx, false, origin, impl_fty, trait_fty));
329 infcx.leak_check(&skol_map, snapshot)
335 debug!("checking trait method for compatibility: impl ty {:?}, trait ty {:?}",
338 span_err!(tcx.sess, impl_m_span, E0053,
339 "method `{}` has an incompatible type for trait: {}",
340 token::get_name(trait_m.name),
346 // Check that all obligations are satisfied by the implementation's
348 match fulfillment_cx.select_all_or_error(&infcx) {
349 Err(ref errors) => { traits::report_fulfillment_errors(&infcx, errors) }
353 // Finally, resolve all regions. This catches wily misuses of
354 // lifetime parameters. We have to build up a plausible lifetime
355 // environment based on what we find in the trait. We could also
356 // include the obligations derived from the method argument types,
357 // but I don't think it's necessary -- after all, those are still
358 // in effect when type-checking the body, and all the
359 // where-clauses in the header etc should be implied by the trait
360 // anyway, so it shouldn't be needed there either. Anyway, we can
361 // always add more relations later (it's backwards compat).
362 let mut free_regions = FreeRegionMap::new();
363 free_regions.relate_free_regions_from_predicates(tcx,
364 &infcx.parameter_environment.caller_bounds);
366 infcx.resolve_regions_and_report_errors(&free_regions, impl_m_body_id);
368 fn check_region_bounds_on_impl_method<'tcx>(tcx: &ty::ctxt<'tcx>,
370 impl_m: &ty::Method<'tcx>,
371 trait_generics: &ty::Generics<'tcx>,
372 impl_generics: &ty::Generics<'tcx>,
373 trait_to_skol_substs: &Substs<'tcx>,
374 impl_to_skol_substs: &Substs<'tcx>)
378 let trait_params = trait_generics.regions.get_slice(subst::FnSpace);
379 let impl_params = impl_generics.regions.get_slice(subst::FnSpace);
381 debug!("check_region_bounds_on_impl_method: \
382 trait_generics={:?} \
384 trait_to_skol_substs={:?} \
385 impl_to_skol_substs={:?}",
388 trait_to_skol_substs,
389 impl_to_skol_substs);
391 // Must have same number of early-bound lifetime parameters.
392 // Unfortunately, if the user screws up the bounds, then this
393 // will change classification between early and late. E.g.,
394 // if in trait we have `<'a,'b:'a>`, and in impl we just have
395 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
396 // in trait but 0 in the impl. But if we report "expected 2
397 // but found 0" it's confusing, because it looks like there
398 // are zero. Since I don't quite know how to phrase things at
399 // the moment, give a kind of vague error message.
400 if trait_params.len() != impl_params.len() {
401 span_err!(tcx.sess, span, E0195,
402 "lifetime parameters or bounds on method `{}` do \
403 not match the trait declaration",
404 token::get_name(impl_m.name));
412 pub fn compare_const_impl<'tcx>(tcx: &ty::ctxt<'tcx>,
413 impl_c: &ty::AssociatedConst<'tcx>,
415 trait_c: &ty::AssociatedConst<'tcx>,
416 impl_trait_ref: &ty::TraitRef<'tcx>) {
417 debug!("compare_const_impl(impl_trait_ref={:?})",
420 let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, None, true);
421 let mut fulfillment_cx = infcx.fulfillment_cx.borrow_mut();
423 // The below is for the most part highly similar to the procedure
424 // for methods above. It is simpler in many respects, especially
425 // because we shouldn't really have to deal with lifetimes or
426 // predicates. In fact some of this should probably be put into
427 // shared functions because of DRY violations...
428 let trait_to_impl_substs = &impl_trait_ref.substs;
430 // Create a parameter environment that represents the implementation's
433 ty::ParameterEnvironment::for_item(tcx, impl_c.def_id.node);
435 // Create mapping from impl to skolemized.
436 let impl_to_skol_substs = &impl_param_env.free_substs;
438 // Create mapping from trait to skolemized.
439 let trait_to_skol_substs =
441 .subst(tcx, impl_to_skol_substs)
442 .with_method(impl_to_skol_substs.types.get_slice(subst::FnSpace).to_vec(),
443 impl_to_skol_substs.regions().get_slice(subst::FnSpace).to_vec());
444 debug!("compare_const_impl: trait_to_skol_substs={:?}",
445 trait_to_skol_substs);
447 // Compute skolemized form of impl and trait const tys.
448 let impl_ty = impl_c.ty.subst(tcx, impl_to_skol_substs);
449 let trait_ty = trait_c.ty.subst(tcx, &trait_to_skol_substs);
451 let err = infcx.commit_if_ok(|_| {
452 let origin = infer::Misc(impl_c_span);
454 // There is no "body" here, so just pass dummy id.
456 assoc::normalize_associated_types_in(&infcx,
462 debug!("compare_const_impl: impl_ty={:?}",
466 assoc::normalize_associated_types_in(&infcx,
472 debug!("compare_const_impl: trait_ty={:?}",
475 infer::mk_subty(&infcx, false, origin, impl_ty, trait_ty)
481 debug!("checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
484 span_err!(tcx.sess, impl_c_span, E0326,
485 "implemented const `{}` has an incompatible type for \
487 token::get_name(trait_c.name),