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;
12 use rustc::infer::{self, InferOk, TypeOrigin};
14 use rustc::traits::{self, ProjectionMode};
15 use rustc::ty::error::ExpectedFound;
16 use rustc::ty::subst::{self, Subst, Substs, VecPerParamSpace};
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<'a, 'tcx>(ccx: &CrateCtxt<'a, '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={:?})",
44 debug!("compare_impl_method: impl_trait_ref (liberated) = {:?}",
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::ExplicitSelfCategory::Static,
60 &ty::ExplicitSelfCategory::Static) => {}
61 (&ty::ExplicitSelfCategory::Static, _) => {
62 let mut err = struct_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);
67 err.span_label(impl_m_span, &format!("`{}` used in impl",
68 impl_m.explicit_self));
69 if let Some(span) = tcx.map.span_if_local(trait_m.def_id) {
70 err.span_label(span, &format!("trait declared without `{}`",
71 impl_m.explicit_self));
76 (_, &ty::ExplicitSelfCategory::Static) => {
77 let mut err = struct_span_err!(tcx.sess, impl_m_span, E0186,
78 "method `{}` has a `{}` declaration in the trait, \
81 trait_m.explicit_self);
82 err.span_label(impl_m_span, &format!("expected `{}` in impl",
83 trait_m.explicit_self));
84 if let Some(span) = tcx.map.span_if_local(trait_m.def_id) {
85 err.span_label(span, & format!("`{}` used in trait",
86 trait_m.explicit_self));
92 // Let the type checker catch other errors below
96 let num_impl_m_type_params = impl_m.generics.types.len(subst::FnSpace);
97 let num_trait_m_type_params = trait_m.generics.types.len(subst::FnSpace);
98 if num_impl_m_type_params != num_trait_m_type_params {
99 span_err!(tcx.sess, impl_m_span, E0049,
100 "method `{}` has {} type parameter{} \
101 but its trait declaration has {} type parameter{}",
103 num_impl_m_type_params,
104 if num_impl_m_type_params == 1 {""} else {"s"},
105 num_trait_m_type_params,
106 if num_trait_m_type_params == 1 {""} else {"s"});
110 if impl_m.fty.sig.0.inputs.len() != trait_m.fty.sig.0.inputs.len() {
111 span_err!(tcx.sess, impl_m_span, E0050,
112 "method `{}` has {} parameter{} \
113 but the declaration in trait `{}` has {}",
115 impl_m.fty.sig.0.inputs.len(),
116 if impl_m.fty.sig.0.inputs.len() == 1 {""} else {"s"},
117 tcx.item_path_str(trait_m.def_id),
118 trait_m.fty.sig.0.inputs.len());
122 // This code is best explained by example. Consider a trait:
124 // trait Trait<'t,T> {
125 // fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
130 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
131 // fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
134 // We wish to decide if those two method types are compatible.
136 // We start out with trait_to_impl_substs, that maps the trait
137 // type parameters to impl type parameters. This is taken from the
138 // impl trait reference:
140 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
142 // We create a mapping `dummy_substs` that maps from the impl type
143 // parameters to fresh types and regions. For type parameters,
144 // this is the identity transform, but we could as well use any
145 // skolemized types. For regions, we convert from bound to free
146 // regions (Note: but only early-bound regions, i.e., those
147 // declared on the impl or used in type parameter bounds).
149 // impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
151 // Now we can apply skol_substs to the type of the impl method
152 // to yield a new function type in terms of our fresh, skolemized
155 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
157 // We now want to extract and substitute the type of the *trait*
158 // method and compare it. To do so, we must create a compound
159 // substitution by combining trait_to_impl_substs and
160 // impl_to_skol_substs, and also adding a mapping for the method
161 // type parameters. We extend the mapping to also include
162 // the method parameters.
164 // trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
166 // Applying this to the trait method type yields:
168 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
170 // This type is also the same but the name of the bound region ('a
171 // vs 'b). However, the normal subtyping rules on fn types handle
172 // this kind of equivalency just fine.
174 // We now use these substitutions to ensure that all declared bounds are
175 // satisfied by the implementation's method.
177 // We do this by creating a parameter environment which contains a
178 // substitution corresponding to impl_to_skol_substs. We then build
179 // trait_to_skol_substs and use it to convert the predicates contained
180 // in the trait_m.generics to the skolemized form.
182 // Finally we register each of these predicates as an obligation in
183 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
185 // Create a parameter environment that represents the implementation's
187 let impl_m_node_id = tcx.map.as_local_node_id(impl_m.def_id).unwrap();
188 let impl_param_env = ty::ParameterEnvironment::for_item(tcx, impl_m_node_id);
190 // Create mapping from impl to skolemized.
191 let impl_to_skol_substs = &impl_param_env.free_substs;
193 // Create mapping from trait to skolemized.
194 let trait_to_skol_substs =
196 .subst(tcx, impl_to_skol_substs).clone()
197 .with_method(impl_to_skol_substs.types.get_slice(subst::FnSpace).to_vec(),
198 impl_to_skol_substs.regions.get_slice(subst::FnSpace).to_vec());
199 debug!("compare_impl_method: trait_to_skol_substs={:?}",
200 trait_to_skol_substs);
202 // Check region bounds. FIXME(@jroesch) refactor this away when removing
204 if !check_region_bounds_on_impl_method(ccx,
209 &trait_to_skol_substs,
210 impl_to_skol_substs) {
214 tcx.infer_ctxt(None, None, ProjectionMode::AnyFinal).enter(|mut infcx| {
215 let mut fulfillment_cx = traits::FulfillmentContext::new();
217 // Normalize the associated types in the trait_bounds.
218 let trait_bounds = trait_m.predicates.instantiate(tcx, &trait_to_skol_substs);
220 // Create obligations for each predicate declared by the impl
221 // definition in the context of the trait's parameter
222 // environment. We can't just use `impl_env.caller_bounds`,
223 // however, because we want to replace all late-bound regions with
226 impl_m.predicates.instantiate(tcx, impl_to_skol_substs);
228 debug!("compare_impl_method: impl_bounds={:?}", impl_bounds);
230 // Obtain the predicate split predicate sets for each.
231 let trait_pred = trait_bounds.predicates.split();
232 let impl_pred = impl_bounds.predicates.split();
234 // This is the only tricky bit of the new way we check implementation methods
235 // We need to build a set of predicates where only the FnSpace bounds
236 // are from the trait and we assume all other bounds from the implementation
237 // to be previously satisfied.
239 // We then register the obligations from the impl_m and check to see
240 // if all constraints hold.
241 let hybrid_preds = VecPerParamSpace::new(
247 // Construct trait parameter environment and then shift it into the skolemized viewpoint.
248 // The key step here is to update the caller_bounds's predicates to be
249 // the new hybrid bounds we computed.
250 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_body_id);
251 let trait_param_env = impl_param_env.with_caller_bounds(hybrid_preds.into_vec());
252 let trait_param_env = traits::normalize_param_env_or_error(tcx,
254 normalize_cause.clone());
255 // FIXME(@jroesch) this seems ugly, but is a temporary change
256 infcx.parameter_environment = trait_param_env;
258 debug!("compare_impl_method: trait_bounds={:?}",
259 infcx.parameter_environment.caller_bounds);
261 let mut selcx = traits::SelectionContext::new(&infcx);
263 let (impl_pred_fns, _) =
264 infcx.replace_late_bound_regions_with_fresh_var(
266 infer::HigherRankedType,
267 &ty::Binder(impl_pred.fns));
268 for predicate in impl_pred_fns {
269 let traits::Normalized { value: predicate, .. } =
270 traits::normalize(&mut selcx, normalize_cause.clone(), &predicate);
272 let cause = traits::ObligationCause {
274 body_id: impl_m_body_id,
275 code: traits::ObligationCauseCode::CompareImplMethodObligation
278 fulfillment_cx.register_predicate_obligation(
280 traits::Obligation::new(cause, predicate));
283 // We now need to check that the signature of the impl method is
284 // compatible with that of the trait method. We do this by
285 // checking that `impl_fty <: trait_fty`.
287 // FIXME. Unfortunately, this doesn't quite work right now because
288 // associated type normalization is not integrated into subtype
289 // checks. For the comparison to be valid, we need to
290 // normalize the associated types in the impl/trait methods
291 // first. However, because function types bind regions, just
292 // calling `normalize_associated_types_in` would have no effect on
293 // any associated types appearing in the fn arguments or return
296 // Compute skolemized form of impl and trait method tys.
298 let origin = TypeOrigin::MethodCompatCheck(impl_m_span);
301 infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
302 infer::HigherRankedType,
305 impl_sig.subst(tcx, impl_to_skol_substs);
307 assoc::normalize_associated_types_in(&infcx,
312 let impl_fty = tcx.mk_fn_ptr(tcx.mk_bare_fn(ty::BareFnTy {
313 unsafety: impl_m.fty.unsafety,
315 sig: ty::Binder(impl_sig)
317 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
319 let trait_sig = tcx.liberate_late_bound_regions(
320 infcx.parameter_environment.free_id_outlive,
323 trait_sig.subst(tcx, &trait_to_skol_substs);
325 assoc::normalize_associated_types_in(&infcx,
330 let trait_fty = tcx.mk_fn_ptr(tcx.mk_bare_fn(ty::BareFnTy {
331 unsafety: trait_m.fty.unsafety,
332 abi: trait_m.fty.abi,
333 sig: ty::Binder(trait_sig)
336 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
338 if let Err(terr) = infcx.sub_types(false, origin, impl_fty, trait_fty) {
339 debug!("sub_types failed: impl ty {:?}, trait ty {:?}",
343 let mut diag = struct_span_err!(
344 tcx.sess, origin.span(), E0053,
345 "method `{}` has an incompatible type for trait", trait_m.name
349 Some(infer::ValuePairs::Types(ExpectedFound {
358 // Check that all obligations are satisfied by the implementation's
360 if let Err(ref errors) = fulfillment_cx.select_all_or_error(&infcx) {
361 infcx.report_fulfillment_errors(errors);
365 // Finally, resolve all regions. This catches wily misuses of
366 // lifetime parameters. We have to build up a plausible lifetime
367 // environment based on what we find in the trait. We could also
368 // include the obligations derived from the method argument types,
369 // but I don't think it's necessary -- after all, those are still
370 // in effect when type-checking the body, and all the
371 // where-clauses in the header etc should be implied by the trait
372 // anyway, so it shouldn't be needed there either. Anyway, we can
373 // always add more relations later (it's backwards compat).
374 let mut free_regions = FreeRegionMap::new();
375 free_regions.relate_free_regions_from_predicates(
376 &infcx.parameter_environment.caller_bounds);
378 infcx.resolve_regions_and_report_errors(&free_regions, impl_m_body_id);
381 fn check_region_bounds_on_impl_method<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
383 impl_m: &ty::Method<'tcx>,
384 trait_generics: &ty::Generics<'tcx>,
385 impl_generics: &ty::Generics<'tcx>,
386 trait_to_skol_substs: &Substs<'tcx>,
387 impl_to_skol_substs: &Substs<'tcx>)
391 let trait_params = trait_generics.regions.get_slice(subst::FnSpace);
392 let impl_params = impl_generics.regions.get_slice(subst::FnSpace);
394 debug!("check_region_bounds_on_impl_method: \
395 trait_generics={:?} \
397 trait_to_skol_substs={:?} \
398 impl_to_skol_substs={:?}",
401 trait_to_skol_substs,
402 impl_to_skol_substs);
404 // Must have same number of early-bound lifetime parameters.
405 // Unfortunately, if the user screws up the bounds, then this
406 // will change classification between early and late. E.g.,
407 // if in trait we have `<'a,'b:'a>`, and in impl we just have
408 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
409 // in trait but 0 in the impl. But if we report "expected 2
410 // but found 0" it's confusing, because it looks like there
411 // are zero. Since I don't quite know how to phrase things at
412 // the moment, give a kind of vague error message.
413 if trait_params.len() != impl_params.len() {
414 struct_span_err!(ccx.tcx.sess, span, E0195,
415 "lifetime parameters or bounds on method `{}` do \
416 not match the trait declaration",impl_m.name)
417 .span_label(span, &format!("lifetimes do not match trait"))
426 pub fn compare_const_impl<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
427 impl_c: &ty::AssociatedConst<'tcx>,
429 trait_c: &ty::AssociatedConst<'tcx>,
430 impl_trait_ref: &ty::TraitRef<'tcx>) {
431 debug!("compare_const_impl(impl_trait_ref={:?})",
435 tcx.infer_ctxt(None, None, ProjectionMode::AnyFinal).enter(|infcx| {
436 let mut fulfillment_cx = traits::FulfillmentContext::new();
438 // The below is for the most part highly similar to the procedure
439 // for methods above. It is simpler in many respects, especially
440 // because we shouldn't really have to deal with lifetimes or
441 // predicates. In fact some of this should probably be put into
442 // shared functions because of DRY violations...
443 let trait_to_impl_substs = &impl_trait_ref.substs;
445 // Create a parameter environment that represents the implementation's
447 let impl_c_node_id = tcx.map.as_local_node_id(impl_c.def_id).unwrap();
448 let impl_param_env = ty::ParameterEnvironment::for_item(tcx, impl_c_node_id);
450 // Create mapping from impl to skolemized.
451 let impl_to_skol_substs = &impl_param_env.free_substs;
453 // Create mapping from trait to skolemized.
454 let trait_to_skol_substs =
456 .subst(tcx, impl_to_skol_substs).clone()
457 .with_method(impl_to_skol_substs.types.get_slice(subst::FnSpace).to_vec(),
458 impl_to_skol_substs.regions.get_slice(subst::FnSpace).to_vec());
459 debug!("compare_const_impl: trait_to_skol_substs={:?}",
460 trait_to_skol_substs);
462 // Compute skolemized form of impl and trait const tys.
463 let impl_ty = impl_c.ty.subst(tcx, impl_to_skol_substs);
464 let trait_ty = trait_c.ty.subst(tcx, &trait_to_skol_substs);
465 let origin = TypeOrigin::Misc(impl_c_span);
467 let err = infcx.commit_if_ok(|_| {
468 // There is no "body" here, so just pass dummy id.
470 assoc::normalize_associated_types_in(&infcx,
476 debug!("compare_const_impl: impl_ty={:?}",
480 assoc::normalize_associated_types_in(&infcx,
486 debug!("compare_const_impl: trait_ty={:?}",
489 infcx.sub_types(false, origin, impl_ty, trait_ty)
490 .map(|InferOk { obligations, .. }| {
491 // FIXME(#32730) propagate obligations
492 assert!(obligations.is_empty())
496 if let Err(terr) = err {
497 debug!("checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
500 let mut diag = struct_span_err!(
501 tcx.sess, origin.span(), E0326,
502 "implemented const `{}` has an incompatible type for trait",
507 Some(infer::ValuePairs::Types(ExpectedFound {