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, Reveal};
15 use rustc::ty::error::{ExpectedFound, TypeError};
16 use rustc::ty::subst::{Subst, Substs};
17 use rustc::hir::{ImplItemKind, TraitItem_, Ty_};
25 /// Checks that a method from an impl conforms to the signature of
26 /// the same method as declared in the trait.
30 /// - impl_m: type of the method we are checking
31 /// - impl_m_span: span to use for reporting errors
32 /// - impl_m_body_id: id of the method body
33 /// - trait_m: the method in the trait
34 /// - impl_trait_ref: the TraitRef corresponding to the trait implementation
36 pub fn compare_impl_method<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
37 impl_m: &ty::Method<'tcx>,
39 impl_m_body_id: ast::NodeId,
40 trait_m: &ty::Method<'tcx>,
41 impl_trait_ref: &ty::TraitRef<'tcx>) {
42 debug!("compare_impl_method(impl_trait_ref={:?})",
45 debug!("compare_impl_method: impl_trait_ref (liberated) = {:?}",
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::ExplicitSelfCategory::Static,
61 &ty::ExplicitSelfCategory::Static) => {}
62 (&ty::ExplicitSelfCategory::Static, _) => {
63 let mut err = struct_span_err!(tcx.sess, impl_m_span, E0185,
64 "method `{}` has a `{}` declaration in the impl, \
65 but not in the trait",
67 impl_m.explicit_self);
68 err.span_label(impl_m_span, &format!("`{}` used in impl",
69 impl_m.explicit_self));
70 if let Some(span) = tcx.map.span_if_local(trait_m.def_id) {
71 err.span_label(span, &format!("trait declared without `{}`",
72 impl_m.explicit_self));
77 (_, &ty::ExplicitSelfCategory::Static) => {
78 let mut err = struct_span_err!(tcx.sess, impl_m_span, E0186,
79 "method `{}` has a `{}` declaration in the trait, \
82 trait_m.explicit_self);
83 err.span_label(impl_m_span, &format!("expected `{}` in impl",
84 trait_m.explicit_self));
85 if let Some(span) = tcx.map.span_if_local(trait_m.def_id) {
86 err.span_label(span, & format!("`{}` used in trait",
87 trait_m.explicit_self));
93 // Let the type checker catch other errors below
97 let num_impl_m_type_params = impl_m.generics.types.len();
98 let num_trait_m_type_params = trait_m.generics.types.len();
99 if num_impl_m_type_params != num_trait_m_type_params {
100 span_err!(tcx.sess, impl_m_span, E0049,
101 "method `{}` has {} type parameter{} \
102 but its trait declaration has {} type parameter{}",
104 num_impl_m_type_params,
105 if num_impl_m_type_params == 1 {""} else {"s"},
106 num_trait_m_type_params,
107 if num_trait_m_type_params == 1 {""} else {"s"});
111 if impl_m.fty.sig.0.inputs.len() != trait_m.fty.sig.0.inputs.len() {
112 span_err!(tcx.sess, impl_m_span, E0050,
113 "method `{}` has {} parameter{} \
114 but the declaration in trait `{}` has {}",
116 impl_m.fty.sig.0.inputs.len(),
117 if impl_m.fty.sig.0.inputs.len() == 1 {""} else {"s"},
118 tcx.item_path_str(trait_m.def_id),
119 trait_m.fty.sig.0.inputs.len());
123 // This code is best explained by example. Consider a trait:
125 // trait Trait<'t,T> {
126 // fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
131 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
132 // fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
135 // We wish to decide if those two method types are compatible.
137 // We start out with trait_to_impl_substs, that maps the trait
138 // type parameters to impl type parameters. This is taken from the
139 // impl trait reference:
141 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
143 // We create a mapping `dummy_substs` that maps from the impl type
144 // parameters to fresh types and regions. For type parameters,
145 // this is the identity transform, but we could as well use any
146 // skolemized types. For regions, we convert from bound to free
147 // regions (Note: but only early-bound regions, i.e., those
148 // declared on the impl or used in type parameter bounds).
150 // impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
152 // Now we can apply skol_substs to the type of the impl method
153 // to yield a new function type in terms of our fresh, skolemized
156 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
158 // We now want to extract and substitute the type of the *trait*
159 // method and compare it. To do so, we must create a compound
160 // substitution by combining trait_to_impl_substs and
161 // impl_to_skol_substs, and also adding a mapping for the method
162 // type parameters. We extend the mapping to also include
163 // the method parameters.
165 // trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
167 // Applying this to the trait method type yields:
169 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
171 // This type is also the same but the name of the bound region ('a
172 // vs 'b). However, the normal subtyping rules on fn types handle
173 // this kind of equivalency just fine.
175 // We now use these substitutions to ensure that all declared bounds are
176 // satisfied by the implementation's method.
178 // We do this by creating a parameter environment which contains a
179 // substitution corresponding to impl_to_skol_substs. We then build
180 // trait_to_skol_substs and use it to convert the predicates contained
181 // in the trait_m.generics to the skolemized form.
183 // Finally we register each of these predicates as an obligation in
184 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
186 // Create a parameter environment that represents the implementation's
188 let impl_m_node_id = tcx.map.as_local_node_id(impl_m.def_id).unwrap();
189 let impl_param_env = ty::ParameterEnvironment::for_item(tcx, impl_m_node_id);
191 // Create mapping from impl to skolemized.
192 let impl_to_skol_substs = &impl_param_env.free_substs;
194 // Create mapping from trait to skolemized.
195 let trait_to_skol_substs =
196 impl_to_skol_substs.rebase_onto(tcx, impl_m.container_id(),
197 trait_to_impl_substs.subst(tcx, impl_to_skol_substs));
198 debug!("compare_impl_method: trait_to_skol_substs={:?}",
199 trait_to_skol_substs);
201 // Check region bounds. FIXME(@jroesch) refactor this away when removing
203 if !check_region_bounds_on_impl_method(ccx,
208 trait_to_skol_substs,
209 impl_to_skol_substs) {
213 tcx.infer_ctxt(None, None, Reveal::NotSpecializable).enter(|mut infcx| {
214 let mut fulfillment_cx = traits::FulfillmentContext::new();
216 // Create obligations for each predicate declared by the impl
217 // definition in the context of the trait's parameter
218 // environment. We can't just use `impl_env.caller_bounds`,
219 // however, because we want to replace all late-bound regions with
221 let impl_predicates = tcx.lookup_predicates(impl_m.predicates.parent.unwrap());
222 let mut hybrid_preds = impl_predicates.instantiate(tcx, impl_to_skol_substs);
224 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
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 method-level 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 hybrid_preds.predicates.extend(
234 trait_m.predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
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.predicates);
241 let trait_param_env = traits::normalize_param_env_or_error(tcx,
243 normalize_cause.clone());
244 // FIXME(@jroesch) this seems ugly, but is a temporary change
245 infcx.parameter_environment = trait_param_env;
247 debug!("compare_impl_method: caller_bounds={:?}",
248 infcx.parameter_environment.caller_bounds);
250 let mut selcx = traits::SelectionContext::new(&infcx);
252 let impl_m_own_bounds = impl_m.predicates.instantiate_own(tcx, impl_to_skol_substs);
253 let (impl_m_own_bounds, _) =
254 infcx.replace_late_bound_regions_with_fresh_var(
256 infer::HigherRankedType,
257 &ty::Binder(impl_m_own_bounds.predicates));
258 for predicate in impl_m_own_bounds {
259 let traits::Normalized { value: predicate, .. } =
260 traits::normalize(&mut selcx, normalize_cause.clone(), &predicate);
262 let cause = traits::ObligationCause {
264 body_id: impl_m_body_id,
265 code: traits::ObligationCauseCode::CompareImplMethodObligation
268 fulfillment_cx.register_predicate_obligation(
270 traits::Obligation::new(cause, predicate));
273 // We now need to check that the signature of the impl method is
274 // compatible with that of the trait method. We do this by
275 // checking that `impl_fty <: trait_fty`.
277 // FIXME. Unfortunately, this doesn't quite work right now because
278 // associated type normalization is not integrated into subtype
279 // checks. For the comparison to be valid, we need to
280 // normalize the associated types in the impl/trait methods
281 // first. However, because function types bind regions, just
282 // calling `normalize_associated_types_in` would have no effect on
283 // any associated types appearing in the fn arguments or return
286 // Compute skolemized form of impl and trait method tys.
288 let origin = TypeOrigin::MethodCompatCheck(impl_m_span);
291 infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
292 infer::HigherRankedType,
295 impl_sig.subst(tcx, impl_to_skol_substs);
297 assoc::normalize_associated_types_in(&infcx,
302 let impl_args = impl_sig.inputs.clone();
303 let impl_fty = tcx.mk_fn_ptr(tcx.mk_bare_fn(ty::BareFnTy {
304 unsafety: impl_m.fty.unsafety,
306 sig: ty::Binder(impl_sig)
308 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
310 let trait_sig = tcx.liberate_late_bound_regions(
311 infcx.parameter_environment.free_id_outlive,
314 trait_sig.subst(tcx, trait_to_skol_substs);
316 assoc::normalize_associated_types_in(&infcx,
321 let trait_args = trait_sig.inputs.clone();
322 let trait_fty = tcx.mk_fn_ptr(tcx.mk_bare_fn(ty::BareFnTy {
323 unsafety: trait_m.fty.unsafety,
324 abi: trait_m.fty.abi,
325 sig: ty::Binder(trait_sig)
328 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
330 if let Err(terr) = infcx.sub_types(false, origin, impl_fty, trait_fty) {
331 debug!("sub_types failed: impl ty {:?}, trait ty {:?}",
335 let impl_m_iter = match tcx.map.expect_impl_item(impl_m_node_id).node {
336 ImplItemKind::Method(ref impl_m_sig, _) => impl_m_sig.decl.inputs.iter(),
337 _ => bug!("{:?} is not a method", impl_m)
340 let (impl_err_span, trait_err_span) = match terr {
341 TypeError::Mutability => {
342 if let Some(trait_m_node_id) = tcx.map.as_local_node_id(trait_m.def_id) {
343 let trait_m_iter = match tcx.map.expect_trait_item(trait_m_node_id).node {
344 TraitItem_::MethodTraitItem(ref trait_m_sig, _) =>
345 trait_m_sig.decl.inputs.iter(),
346 _ => bug!("{:?} is not a MethodTraitItem", trait_m)
349 impl_m_iter.zip(trait_m_iter).find(|&(ref impl_arg, ref trait_arg)| {
350 match (&impl_arg.ty.node, &trait_arg.ty.node) {
351 (&Ty_::TyRptr(_, ref impl_mt), &Ty_::TyRptr(_, ref trait_mt)) |
352 (&Ty_::TyPtr(ref impl_mt), &Ty_::TyPtr(ref trait_mt)) =>
353 impl_mt.mutbl != trait_mt.mutbl,
356 }).map(|(ref impl_arg, ref trait_arg)| {
357 match (impl_arg.to_self(), trait_arg.to_self()) {
358 (Some(impl_self), Some(trait_self)) =>
359 (impl_self.span, Some(trait_self.span)),
360 (None, None) => (impl_arg.ty.span, Some(trait_arg.ty.span)),
361 _ => bug!("impl and trait fns have different first args, \
362 impl: {:?}, trait: {:?}", impl_arg, trait_arg)
364 }).unwrap_or((origin.span(), tcx.map.span_if_local(trait_m.def_id)))
366 (origin.span(), tcx.map.span_if_local(trait_m.def_id))
369 TypeError::Sorts(ExpectedFound { expected, found }) => {
370 if let Some(trait_m_node_id) = tcx.map.as_local_node_id(trait_m.def_id) {
371 let trait_m_iter = match tcx.map.expect_trait_item(trait_m_node_id).node {
372 TraitItem_::MethodTraitItem(ref trait_m_sig, _) =>
373 trait_m_sig.decl.inputs.iter(),
374 _ => bug!("{:?} is not a MethodTraitItem", trait_m)
376 let impl_iter = impl_args.iter();
377 let trait_iter = trait_args.iter();
378 let arg_idx = impl_iter.zip(trait_iter)
379 .position(|(impl_arg_ty, trait_arg_ty)| {
380 *impl_arg_ty == found && *trait_arg_ty == expected
382 impl_m_iter.zip(trait_m_iter)
384 .map(|(impl_arg, trait_arg)|
385 (impl_arg.ty.span, Some(trait_arg.ty.span)))
387 (origin.span(), tcx.map.span_if_local(trait_m.def_id)))
389 (origin.span(), tcx.map.span_if_local(trait_m.def_id))
392 _ => (origin.span(), tcx.map.span_if_local(trait_m.def_id))
395 let origin = TypeOrigin::MethodCompatCheck(impl_err_span);
397 let mut diag = struct_span_err!(
398 tcx.sess, origin.span(), E0053,
399 "method `{}` has an incompatible type for trait", trait_m.name
405 trait_err_span.map(|sp| (sp, format!("type in trait"))),
406 Some(infer::ValuePairs::Types(ExpectedFound {
416 // Check that all obligations are satisfied by the implementation's
418 if let Err(ref errors) = fulfillment_cx.select_all_or_error(&infcx) {
419 infcx.report_fulfillment_errors(errors);
423 // Finally, resolve all regions. This catches wily misuses of
424 // lifetime parameters. We have to build up a plausible lifetime
425 // environment based on what we find in the trait. We could also
426 // include the obligations derived from the method argument types,
427 // but I don't think it's necessary -- after all, those are still
428 // in effect when type-checking the body, and all the
429 // where-clauses in the header etc should be implied by the trait
430 // anyway, so it shouldn't be needed there either. Anyway, we can
431 // always add more relations later (it's backwards compat).
432 let mut free_regions = FreeRegionMap::new();
433 free_regions.relate_free_regions_from_predicates(
434 &infcx.parameter_environment.caller_bounds);
436 infcx.resolve_regions_and_report_errors(&free_regions, impl_m_body_id);
439 fn check_region_bounds_on_impl_method<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
441 impl_m: &ty::Method<'tcx>,
442 trait_generics: &ty::Generics<'tcx>,
443 impl_generics: &ty::Generics<'tcx>,
444 trait_to_skol_substs: &Substs<'tcx>,
445 impl_to_skol_substs: &Substs<'tcx>)
449 let trait_params = &trait_generics.regions[..];
450 let impl_params = &impl_generics.regions[..];
452 debug!("check_region_bounds_on_impl_method: \
453 trait_generics={:?} \
455 trait_to_skol_substs={:?} \
456 impl_to_skol_substs={:?}",
459 trait_to_skol_substs,
460 impl_to_skol_substs);
462 // Must have same number of early-bound lifetime parameters.
463 // Unfortunately, if the user screws up the bounds, then this
464 // will change classification between early and late. E.g.,
465 // if in trait we have `<'a,'b:'a>`, and in impl we just have
466 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
467 // in trait but 0 in the impl. But if we report "expected 2
468 // but found 0" it's confusing, because it looks like there
469 // are zero. Since I don't quite know how to phrase things at
470 // the moment, give a kind of vague error message.
471 if trait_params.len() != impl_params.len() {
472 struct_span_err!(ccx.tcx.sess, span, E0195,
473 "lifetime parameters or bounds on method `{}` do \
474 not match the trait declaration",impl_m.name)
475 .span_label(span, &format!("lifetimes do not match trait"))
484 pub fn compare_const_impl<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
485 impl_c: &ty::AssociatedConst<'tcx>,
487 trait_c: &ty::AssociatedConst<'tcx>,
488 impl_trait_ref: &ty::TraitRef<'tcx>) {
489 debug!("compare_const_impl(impl_trait_ref={:?})",
493 tcx.infer_ctxt(None, None, Reveal::NotSpecializable).enter(|infcx| {
494 let mut fulfillment_cx = traits::FulfillmentContext::new();
496 // The below is for the most part highly similar to the procedure
497 // for methods above. It is simpler in many respects, especially
498 // because we shouldn't really have to deal with lifetimes or
499 // predicates. In fact some of this should probably be put into
500 // shared functions because of DRY violations...
501 let trait_to_impl_substs = &impl_trait_ref.substs;
503 // Create a parameter environment that represents the implementation's
505 let impl_c_node_id = tcx.map.as_local_node_id(impl_c.def_id).unwrap();
506 let impl_param_env = ty::ParameterEnvironment::for_item(tcx, impl_c_node_id);
508 // Create mapping from impl to skolemized.
509 let impl_to_skol_substs = &impl_param_env.free_substs;
511 // Create mapping from trait to skolemized.
512 let trait_to_skol_substs =
513 impl_to_skol_substs.rebase_onto(tcx, impl_c.container.id(),
514 trait_to_impl_substs.subst(tcx, impl_to_skol_substs));
515 debug!("compare_const_impl: trait_to_skol_substs={:?}",
516 trait_to_skol_substs);
518 // Compute skolemized form of impl and trait const tys.
519 let impl_ty = impl_c.ty.subst(tcx, impl_to_skol_substs);
520 let trait_ty = trait_c.ty.subst(tcx, trait_to_skol_substs);
521 let mut origin = TypeOrigin::Misc(impl_c_span);
523 let err = infcx.commit_if_ok(|_| {
524 // There is no "body" here, so just pass dummy id.
526 assoc::normalize_associated_types_in(&infcx,
532 debug!("compare_const_impl: impl_ty={:?}",
536 assoc::normalize_associated_types_in(&infcx,
542 debug!("compare_const_impl: trait_ty={:?}",
545 infcx.sub_types(false, origin, impl_ty, trait_ty)
546 .map(|InferOk { obligations, .. }| {
547 // FIXME(#32730) propagate obligations
548 assert!(obligations.is_empty())
552 if let Err(terr) = err {
553 debug!("checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
557 // Locate the Span containing just the type of the offending impl
558 match tcx.map.expect_impl_item(impl_c_node_id).node {
559 ImplItemKind::Const(ref ty, _) => origin = TypeOrigin::Misc(ty.span),
560 _ => bug!("{:?} is not a impl const", impl_c)
563 let mut diag = struct_span_err!(
564 tcx.sess, origin.span(), E0326,
565 "implemented const `{}` has an incompatible type for trait",
569 // Add a label to the Span containing just the type of the item
570 let trait_c_node_id = tcx.map.as_local_node_id(trait_c.def_id).unwrap();
571 let trait_c_span = match tcx.map.expect_trait_item(trait_c_node_id).node {
572 TraitItem_::ConstTraitItem(ref ty, _) => ty.span,
573 _ => bug!("{:?} is not a trait const", trait_c)
579 Some((trait_c_span, format!("type in trait"))),
580 Some(infer::ValuePairs::Types(ExpectedFound {