1 //! Check properties that are required by built-in traits and set
2 //! up data structures required by type-checking/codegen.
4 use rustc_errors::struct_span_err;
6 use rustc_hir::def_id::{DefId, LocalDefId};
7 use rustc_hir::lang_items::{
8 CoerceUnsizedTraitLangItem, DispatchFromDynTraitLangItem, UnsizeTraitLangItem,
10 use rustc_hir::ItemKind;
11 use rustc_infer::infer;
12 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
13 use rustc_infer::infer::{RegionckMode, TyCtxtInferExt};
14 use rustc_middle::ty::adjustment::CoerceUnsizedInfo;
15 use rustc_middle::ty::TypeFoldable;
16 use rustc_middle::ty::{self, Ty, TyCtxt};
17 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
18 use rustc_trait_selection::traits::misc::{can_type_implement_copy, CopyImplementationError};
19 use rustc_trait_selection::traits::predicate_for_trait_def;
20 use rustc_trait_selection::traits::{self, ObligationCause, TraitEngine, TraitEngineExt};
22 pub fn check_trait(tcx: TyCtxt<'_>, trait_def_id: DefId) {
23 let lang_items = tcx.lang_items();
24 Checker { tcx, trait_def_id }
25 .check(lang_items.drop_trait(), visit_implementation_of_drop)
26 .check(lang_items.copy_trait(), visit_implementation_of_copy)
27 .check(lang_items.coerce_unsized_trait(), visit_implementation_of_coerce_unsized)
28 .check(lang_items.dispatch_from_dyn_trait(), visit_implementation_of_dispatch_from_dyn);
31 struct Checker<'tcx> {
36 impl<'tcx> Checker<'tcx> {
37 fn check<F>(&self, trait_def_id: Option<DefId>, mut f: F) -> &Self
39 F: FnMut(TyCtxt<'tcx>, LocalDefId),
41 if Some(self.trait_def_id) == trait_def_id {
42 for &impl_id in self.tcx.hir().trait_impls(self.trait_def_id) {
43 let impl_def_id = self.tcx.hir().local_def_id(impl_id);
44 f(self.tcx, impl_def_id);
51 fn visit_implementation_of_drop(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
52 // Destructors only work on nominal types.
53 if let ty::Adt(..) | ty::Error(_) = tcx.type_of(impl_did).kind {
57 let impl_hir_id = tcx.hir().as_local_hir_id(impl_did);
58 let sp = match tcx.hir().expect_item(impl_hir_id).kind {
59 ItemKind::Impl { self_ty, .. } => self_ty.span,
60 _ => bug!("expected Drop impl item"),
67 "the `Drop` trait may only be implemented for structs, enums, and unions",
69 .span_label(sp, "must be a struct, enum, or union")
73 fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
74 debug!("visit_implementation_of_copy: impl_did={:?}", impl_did);
76 let impl_hir_id = tcx.hir().as_local_hir_id(impl_did);
78 let self_type = tcx.type_of(impl_did);
79 debug!("visit_implementation_of_copy: self_type={:?} (bound)", self_type);
81 let span = tcx.hir().span(impl_hir_id);
82 let param_env = tcx.param_env(impl_did);
83 assert!(!self_type.has_escaping_bound_vars());
85 debug!("visit_implementation_of_copy: self_type={:?} (free)", self_type);
87 match can_type_implement_copy(tcx, param_env, self_type) {
89 Err(CopyImplementationError::InfrigingFields(fields)) => {
90 let item = tcx.hir().expect_item(impl_hir_id);
91 let span = if let ItemKind::Impl { of_trait: Some(ref tr), .. } = item.kind {
97 let mut err = struct_span_err!(
101 "the trait `Copy` may not be implemented for this type"
103 for span in fields.iter().map(|f| tcx.def_span(f.did)) {
104 err.span_label(span, "this field does not implement `Copy`");
108 Err(CopyImplementationError::NotAnAdt) => {
109 let item = tcx.hir().expect_item(impl_hir_id);
111 if let ItemKind::Impl { self_ty, .. } = item.kind { self_ty.span } else { span };
117 "the trait `Copy` may not be implemented for this type"
119 .span_label(span, "type is not a structure or enumeration")
122 Err(CopyImplementationError::HasDestructor) => {
127 "the trait `Copy` may not be implemented for this type; the \
128 type has a destructor"
130 .span_label(span, "Copy not allowed on types with destructors")
136 fn visit_implementation_of_coerce_unsized(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) {
137 debug!("visit_implementation_of_coerce_unsized: impl_did={:?}", impl_did);
139 // Just compute this for the side-effects, in particular reporting
140 // errors; other parts of the code may demand it for the info of
142 let span = tcx.def_span(impl_did);
143 tcx.at(span).coerce_unsized_info(impl_did);
146 fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
147 debug!("visit_implementation_of_dispatch_from_dyn: impl_did={:?}", impl_did);
149 let impl_hir_id = tcx.hir().as_local_hir_id(impl_did);
150 let span = tcx.hir().span(impl_hir_id);
152 let dispatch_from_dyn_trait = tcx.require_lang_item(DispatchFromDynTraitLangItem, Some(span));
154 let source = tcx.type_of(impl_did);
155 assert!(!source.has_escaping_bound_vars());
157 let trait_ref = tcx.impl_trait_ref(impl_did).unwrap();
158 assert_eq!(trait_ref.def_id, dispatch_from_dyn_trait);
160 trait_ref.substs.type_at(1)
163 debug!("visit_implementation_of_dispatch_from_dyn: {:?} -> {:?}", source, target);
165 let param_env = tcx.param_env(impl_did);
167 let create_err = |msg: &str| struct_span_err!(tcx.sess, span, E0378, "{}", msg);
169 tcx.infer_ctxt().enter(|infcx| {
170 let cause = ObligationCause::misc(span, impl_hir_id);
173 match (&source.kind, &target.kind) {
174 (&Ref(r_a, _, mutbl_a), Ref(r_b, _, mutbl_b))
175 if infcx.at(&cause, param_env).eq(r_a, r_b).is_ok() && mutbl_a == *mutbl_b => {}
176 (&RawPtr(tm_a), &RawPtr(tm_b)) if tm_a.mutbl == tm_b.mutbl => (),
177 (&Adt(def_a, substs_a), &Adt(def_b, substs_b))
178 if def_a.is_struct() && def_b.is_struct() =>
181 let source_path = tcx.def_path_str(def_a.did);
182 let target_path = tcx.def_path_str(def_b.did);
185 "the trait `DispatchFromDyn` may only be implemented \
186 for a coercion between structures with the same \
187 definition; expected `{}`, found `{}`",
188 source_path, target_path,
195 if def_a.repr.c() || def_a.repr.packed() {
197 "structs implementing `DispatchFromDyn` may not have \
198 `#[repr(packed)]` or `#[repr(C)]`",
203 let fields = &def_a.non_enum_variant().fields;
205 let coerced_fields = fields
207 .filter_map(|field| {
208 let ty_a = field.ty(tcx, substs_a);
209 let ty_b = field.ty(tcx, substs_b);
211 if let Ok(layout) = tcx.layout_of(param_env.and(ty_a)) {
212 if layout.is_zst() && layout.align.abi.bytes() == 1 {
213 // ignore ZST fields with alignment of 1 byte
218 if let Ok(ok) = infcx.at(&cause, param_env).eq(ty_a, ty_b) {
219 if ok.obligations.is_empty() {
221 "the trait `DispatchFromDyn` may only be implemented \
222 for structs containing the field being coerced, \
223 ZST fields with 1 byte alignment, and nothing else",
226 "extra field `{}` of type `{}` is not allowed",
237 .collect::<Vec<_>>();
239 if coerced_fields.is_empty() {
241 "the trait `DispatchFromDyn` may only be implemented \
242 for a coercion between structures with a single field \
243 being coerced, none found",
246 } else if coerced_fields.len() > 1 {
248 "implementing the `DispatchFromDyn` trait requires multiple coercions",
251 "the trait `DispatchFromDyn` may only be implemented \
252 for a coercion between structures with a single field \
256 "currently, {} fields need coercions: {}",
257 coerced_fields.len(),
262 "`{}` (`{}` to `{}`)",
264 field.ty(tcx, substs_a),
265 field.ty(tcx, substs_b),
273 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
275 for field in coerced_fields {
276 let predicate = predicate_for_trait_def(
280 dispatch_from_dyn_trait,
282 field.ty(tcx, substs_a),
283 &[field.ty(tcx, substs_b).into()],
286 fulfill_cx.register_predicate_obligation(&infcx, predicate);
289 // Check that all transitive obligations are satisfied.
290 if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) {
291 infcx.report_fulfillment_errors(&errors, None, false);
294 // Finally, resolve all regions.
295 let outlives_env = OutlivesEnvironment::new(param_env);
296 infcx.resolve_regions_and_report_errors(
297 impl_did.to_def_id(),
299 RegionckMode::default(),
305 "the trait `DispatchFromDyn` may only be implemented \
306 for a coercion between structures",
314 pub fn coerce_unsized_info(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUnsizedInfo {
315 debug!("compute_coerce_unsized_info(impl_did={:?})", impl_did);
317 // this provider should only get invoked for local def-ids
318 let impl_hir_id = tcx.hir().as_local_hir_id(impl_did.expect_local());
319 let span = tcx.hir().span(impl_hir_id);
321 let coerce_unsized_trait = tcx.require_lang_item(CoerceUnsizedTraitLangItem, Some(span));
323 let unsize_trait = tcx.lang_items().require(UnsizeTraitLangItem).unwrap_or_else(|err| {
324 tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err));
327 let source = tcx.type_of(impl_did);
328 let trait_ref = tcx.impl_trait_ref(impl_did).unwrap();
329 assert_eq!(trait_ref.def_id, coerce_unsized_trait);
330 let target = trait_ref.substs.type_at(1);
331 debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (bound)", source, target);
333 let param_env = tcx.param_env(impl_did);
334 assert!(!source.has_escaping_bound_vars());
336 let err_info = CoerceUnsizedInfo { custom_kind: None };
338 debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (free)", source, target);
340 tcx.infer_ctxt().enter(|infcx| {
341 let cause = ObligationCause::misc(span, impl_hir_id);
342 let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>,
343 mt_b: ty::TypeAndMut<'tcx>,
344 mk_ptr: &dyn Fn(Ty<'tcx>) -> Ty<'tcx>| {
345 if (mt_a.mutbl, mt_b.mutbl) == (hir::Mutability::Not, hir::Mutability::Mut) {
347 .report_mismatched_types(
351 ty::error::TypeError::Mutability,
355 (mt_a.ty, mt_b.ty, unsize_trait, None)
357 let (source, target, trait_def_id, kind) = match (&source.kind, &target.kind) {
358 (&ty::Ref(r_a, ty_a, mutbl_a), &ty::Ref(r_b, ty_b, mutbl_b)) => {
359 infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a);
360 let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a };
361 let mt_b = ty::TypeAndMut { ty: ty_b, mutbl: mutbl_b };
362 check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty))
365 (&ty::Ref(_, ty_a, mutbl_a), &ty::RawPtr(mt_b)) => {
366 let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a };
367 check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
370 (&ty::RawPtr(mt_a), &ty::RawPtr(mt_b)) => {
371 check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
374 (&ty::Adt(def_a, substs_a), &ty::Adt(def_b, substs_b))
375 if def_a.is_struct() && def_b.is_struct() =>
378 let source_path = tcx.def_path_str(def_a.did);
379 let target_path = tcx.def_path_str(def_b.did);
384 "the trait `CoerceUnsized` may only be implemented \
385 for a coercion between structures with the same \
386 definition; expected `{}`, found `{}`",
394 // Here we are considering a case of converting
395 // `S<P0...Pn>` to S<Q0...Qn>`. As an example, let's imagine a struct `Foo<T, U>`,
396 // which acts like a pointer to `U`, but carries along some extra data of type `T`:
398 // struct Foo<T, U> {
403 // We might have an impl that allows (e.g.) `Foo<T, [i32; 3]>` to be unsized
404 // to `Foo<T, [i32]>`. That impl would look like:
406 // impl<T, U: Unsize<V>, V> CoerceUnsized<Foo<T, V>> for Foo<T, U> {}
408 // Here `U = [i32; 3]` and `V = [i32]`. At runtime,
409 // when this coercion occurs, we would be changing the
410 // field `ptr` from a thin pointer of type `*mut [i32;
411 // 3]` to a fat pointer of type `*mut [i32]` (with
412 // extra data `3`). **The purpose of this check is to
413 // make sure that we know how to do this conversion.**
415 // To check if this impl is legal, we would walk down
416 // the fields of `Foo` and consider their types with
417 // both substitutes. We are looking to find that
418 // exactly one (non-phantom) field has changed its
419 // type, which we will expect to be the pointer that
420 // is becoming fat (we could probably generalize this
421 // to multiple thin pointers of the same type becoming
422 // fat, but we don't). In this case:
424 // - `extra` has type `T` before and type `T` after
425 // - `ptr` has type `*mut U` before and type `*mut V` after
427 // Since just one field changed, we would then check
428 // that `*mut U: CoerceUnsized<*mut V>` is implemented
429 // (in other words, that we know how to do this
430 // conversion). This will work out because `U:
431 // Unsize<V>`, and we have a builtin rule that `*mut
432 // U` can be coerced to `*mut V` if `U: Unsize<V>`.
433 let fields = &def_a.non_enum_variant().fields;
434 let diff_fields = fields
437 .filter_map(|(i, f)| {
438 let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b));
440 if tcx.type_of(f.did).is_phantom_data() {
441 // Ignore PhantomData fields
445 // Ignore fields that aren't changed; it may
446 // be that we could get away with subtyping or
447 // something more accepting, but we use
448 // equality because we want to be able to
449 // perform this check without computing
450 // variance where possible. (This is because
451 // we may have to evaluate constraint
452 // expressions in the course of execution.)
454 if let Ok(ok) = infcx.at(&cause, param_env).eq(a, b) {
455 if ok.obligations.is_empty() {
460 // Collect up all fields that were significantly changed
461 // i.e., those that contain T in coerce_unsized T -> U
464 .collect::<Vec<_>>();
466 if diff_fields.is_empty() {
471 "the trait `CoerceUnsized` may only be implemented \
472 for a coercion between structures with one field \
473 being coerced, none found"
477 } else if diff_fields.len() > 1 {
478 let item = tcx.hir().expect_item(impl_hir_id);
479 let span = if let ItemKind::Impl { of_trait: Some(ref t), .. } = item.kind {
482 tcx.hir().span(impl_hir_id)
489 "implementing the trait \
490 `CoerceUnsized` requires multiple \
494 "`CoerceUnsized` may only be implemented for \
495 a coercion between structures with one field being coerced",
498 "currently, {} fields need coercions: {}",
503 format!("`{}` (`{}` to `{}`)", fields[i].ident, a, b)
508 .span_label(span, "requires multiple coercions")
513 let (i, a, b) = diff_fields[0];
514 let kind = ty::adjustment::CustomCoerceUnsized::Struct(i);
515 (a, b, coerce_unsized_trait, Some(kind))
523 "the trait `CoerceUnsized` may only be implemented \
524 for a coercion between structures"
531 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
533 // Register an obligation for `A: Trait<B>`.
534 let cause = traits::ObligationCause::misc(span, impl_hir_id);
535 let predicate = predicate_for_trait_def(
544 fulfill_cx.register_predicate_obligation(&infcx, predicate);
546 // Check that all transitive obligations are satisfied.
547 if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) {
548 infcx.report_fulfillment_errors(&errors, None, false);
551 // Finally, resolve all regions.
552 let outlives_env = OutlivesEnvironment::new(param_env);
553 infcx.resolve_regions_and_report_errors(impl_did, &outlives_env, RegionckMode::default());
555 CoerceUnsizedInfo { custom_kind: kind }