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Commit | Line | Data |
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32a655c1 | 1 | //! Check properties that are required by built-in traits and set |
94b46f34 | 2 | //! up data structures required by type-checking/codegen. |
32a655c1 | 3 | |
dfeec247 XL |
4 | use rustc_errors::struct_span_err; |
5 | use rustc_hir as hir; | |
f9f354fc | 6 | use rustc_hir::def_id::{DefId, LocalDefId}; |
3dfed10e | 7 | use rustc_hir::lang_items::LangItem; |
dfeec247 | 8 | use rustc_hir::ItemKind; |
74b04a01 XL |
9 | use rustc_infer::infer; |
10 | use rustc_infer::infer::outlives::env::OutlivesEnvironment; | |
ba9703b0 | 11 | use rustc_infer::infer::{RegionckMode, TyCtxtInferExt}; |
ba9703b0 XL |
12 | use rustc_middle::ty::adjustment::CoerceUnsizedInfo; |
13 | use rustc_middle::ty::TypeFoldable; | |
14 | use rustc_middle::ty::{self, Ty, TyCtxt}; | |
15 | use rustc_trait_selection::traits::error_reporting::InferCtxtExt; | |
16 | use rustc_trait_selection::traits::misc::{can_type_implement_copy, CopyImplementationError}; | |
17 | use rustc_trait_selection::traits::predicate_for_trait_def; | |
18 | use rustc_trait_selection::traits::{self, ObligationCause, TraitEngine, TraitEngineExt}; | |
60c5eb7d | 19 | |
416331ca | 20 | pub fn check_trait(tcx: TyCtxt<'_>, trait_def_id: DefId) { |
74b04a01 | 21 | let lang_items = tcx.lang_items(); |
8bb4bdeb | 22 | Checker { tcx, trait_def_id } |
74b04a01 XL |
23 | .check(lang_items.drop_trait(), visit_implementation_of_drop) |
24 | .check(lang_items.copy_trait(), visit_implementation_of_copy) | |
25 | .check(lang_items.coerce_unsized_trait(), visit_implementation_of_coerce_unsized) | |
26 | .check(lang_items.dispatch_from_dyn_trait(), visit_implementation_of_dispatch_from_dyn); | |
32a655c1 SL |
27 | } |
28 | ||
dc9dc135 XL |
29 | struct Checker<'tcx> { |
30 | tcx: TyCtxt<'tcx>, | |
31 | trait_def_id: DefId, | |
8bb4bdeb XL |
32 | } |
33 | ||
dc9dc135 | 34 | impl<'tcx> Checker<'tcx> { |
8bb4bdeb | 35 | fn check<F>(&self, trait_def_id: Option<DefId>, mut f: F) -> &Self |
dc9dc135 | 36 | where |
f9f354fc | 37 | F: FnMut(TyCtxt<'tcx>, LocalDefId), |
8bb4bdeb XL |
38 | { |
39 | if Some(self.trait_def_id) == trait_def_id { | |
0731742a | 40 | for &impl_id in self.tcx.hir().trait_impls(self.trait_def_id) { |
416331ca | 41 | let impl_def_id = self.tcx.hir().local_def_id(impl_id); |
b7449926 | 42 | f(self.tcx, impl_def_id); |
8bb4bdeb | 43 | } |
32a655c1 | 44 | } |
8bb4bdeb | 45 | self |
32a655c1 SL |
46 | } |
47 | } | |
48 | ||
f9f354fc | 49 | fn visit_implementation_of_drop(tcx: TyCtxt<'_>, impl_did: LocalDefId) { |
dfeec247 | 50 | // Destructors only work on nominal types. |
f035d41b | 51 | if let ty::Adt(..) | ty::Error(_) = tcx.type_of(impl_did).kind { |
dfeec247 | 52 | return; |
32a655c1 | 53 | } |
dfeec247 | 54 | |
3dfed10e | 55 | let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did); |
dfeec247 XL |
56 | let sp = match tcx.hir().expect_item(impl_hir_id).kind { |
57 | ItemKind::Impl { self_ty, .. } => self_ty.span, | |
58 | _ => bug!("expected Drop impl item"), | |
59 | }; | |
60 | ||
61 | struct_span_err!( | |
62 | tcx.sess, | |
63 | sp, | |
64 | E0120, | |
65 | "the `Drop` trait may only be implemented for structs, enums, and unions", | |
66 | ) | |
67 | .span_label(sp, "must be a struct, enum, or union") | |
68 | .emit(); | |
32a655c1 SL |
69 | } |
70 | ||
f9f354fc | 71 | fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) { |
32a655c1 SL |
72 | debug!("visit_implementation_of_copy: impl_did={:?}", impl_did); |
73 | ||
3dfed10e | 74 | let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did); |
32a655c1 | 75 | |
7cac9316 | 76 | let self_type = tcx.type_of(impl_did); |
dfeec247 | 77 | debug!("visit_implementation_of_copy: self_type={:?} (bound)", self_type); |
32a655c1 | 78 | |
dc9dc135 | 79 | let span = tcx.hir().span(impl_hir_id); |
7cac9316 | 80 | let param_env = tcx.param_env(impl_did); |
a1dfa0c6 | 81 | assert!(!self_type.has_escaping_bound_vars()); |
32a655c1 | 82 | |
dfeec247 | 83 | debug!("visit_implementation_of_copy: self_type={:?} (free)", self_type); |
32a655c1 | 84 | |
dfeec247 | 85 | match can_type_implement_copy(tcx, param_env, self_type) { |
32a655c1 | 86 | Ok(()) => {} |
94b46f34 | 87 | Err(CopyImplementationError::InfrigingFields(fields)) => { |
dc9dc135 | 88 | let item = tcx.hir().expect_item(impl_hir_id); |
dfeec247 | 89 | let span = if let ItemKind::Impl { of_trait: Some(ref tr), .. } = item.kind { |
32a655c1 SL |
90 | tr.path.span |
91 | } else { | |
92 | span | |
93 | }; | |
94 | ||
dfeec247 XL |
95 | let mut err = struct_span_err!( |
96 | tcx.sess, | |
97 | span, | |
98 | E0204, | |
99 | "the trait `Copy` may not be implemented for this type" | |
100 | ); | |
94b46f34 | 101 | for span in fields.iter().map(|f| tcx.def_span(f.did)) { |
0bf4aa26 | 102 | err.span_label(span, "this field does not implement `Copy`"); |
94b46f34 XL |
103 | } |
104 | err.emit() | |
32a655c1 SL |
105 | } |
106 | Err(CopyImplementationError::NotAnAdt) => { | |
dc9dc135 | 107 | let item = tcx.hir().expect_item(impl_hir_id); |
dfeec247 XL |
108 | let span = |
109 | if let ItemKind::Impl { self_ty, .. } = item.kind { self_ty.span } else { span }; | |
110 | ||
111 | struct_span_err!( | |
112 | tcx.sess, | |
113 | span, | |
114 | E0206, | |
115 | "the trait `Copy` may not be implemented for this type" | |
116 | ) | |
117 | .span_label(span, "type is not a structure or enumeration") | |
118 | .emit(); | |
32a655c1 SL |
119 | } |
120 | Err(CopyImplementationError::HasDestructor) => { | |
dfeec247 XL |
121 | struct_span_err!( |
122 | tcx.sess, | |
123 | span, | |
124 | E0184, | |
125 | "the trait `Copy` may not be implemented for this type; the \ | |
126 | type has a destructor" | |
127 | ) | |
128 | .span_label(span, "Copy not allowed on types with destructors") | |
129 | .emit(); | |
32a655c1 SL |
130 | } |
131 | } | |
132 | } | |
133 | ||
f9f354fc | 134 | fn visit_implementation_of_coerce_unsized(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) { |
dfeec247 | 135 | debug!("visit_implementation_of_coerce_unsized: impl_did={:?}", impl_did); |
32a655c1 | 136 | |
cc61c64b XL |
137 | // Just compute this for the side-effects, in particular reporting |
138 | // errors; other parts of the code may demand it for the info of | |
139 | // course. | |
f9f354fc XL |
140 | let span = tcx.def_span(impl_did); |
141 | tcx.at(span).coerce_unsized_info(impl_did); | |
cc61c64b XL |
142 | } |
143 | ||
f9f354fc | 144 | fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDefId) { |
dfeec247 | 145 | debug!("visit_implementation_of_dispatch_from_dyn: impl_did={:?}", impl_did); |
a1dfa0c6 | 146 | |
3dfed10e | 147 | let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did); |
f9f354fc | 148 | let span = tcx.hir().span(impl_hir_id); |
a1dfa0c6 | 149 | |
3dfed10e | 150 | let dispatch_from_dyn_trait = tcx.require_lang_item(LangItem::DispatchFromDyn, Some(span)); |
a1dfa0c6 | 151 | |
f9f354fc XL |
152 | let source = tcx.type_of(impl_did); |
153 | assert!(!source.has_escaping_bound_vars()); | |
154 | let target = { | |
155 | let trait_ref = tcx.impl_trait_ref(impl_did).unwrap(); | |
156 | assert_eq!(trait_ref.def_id, dispatch_from_dyn_trait); | |
a1dfa0c6 | 157 | |
f9f354fc XL |
158 | trait_ref.substs.type_at(1) |
159 | }; | |
a1dfa0c6 | 160 | |
f9f354fc | 161 | debug!("visit_implementation_of_dispatch_from_dyn: {:?} -> {:?}", source, target); |
a1dfa0c6 | 162 | |
f9f354fc | 163 | let param_env = tcx.param_env(impl_did); |
a1dfa0c6 | 164 | |
f9f354fc | 165 | let create_err = |msg: &str| struct_span_err!(tcx.sess, span, E0378, "{}", msg); |
a1dfa0c6 | 166 | |
f9f354fc XL |
167 | tcx.infer_ctxt().enter(|infcx| { |
168 | let cause = ObligationCause::misc(span, impl_hir_id); | |
a1dfa0c6 | 169 | |
f9f354fc XL |
170 | use ty::TyKind::*; |
171 | match (&source.kind, &target.kind) { | |
172 | (&Ref(r_a, _, mutbl_a), Ref(r_b, _, mutbl_b)) | |
173 | if infcx.at(&cause, param_env).eq(r_a, r_b).is_ok() && mutbl_a == *mutbl_b => {} | |
174 | (&RawPtr(tm_a), &RawPtr(tm_b)) if tm_a.mutbl == tm_b.mutbl => (), | |
175 | (&Adt(def_a, substs_a), &Adt(def_b, substs_b)) | |
176 | if def_a.is_struct() && def_b.is_struct() => | |
177 | { | |
178 | if def_a != def_b { | |
179 | let source_path = tcx.def_path_str(def_a.did); | |
180 | let target_path = tcx.def_path_str(def_b.did); | |
181 | ||
182 | create_err(&format!( | |
183 | "the trait `DispatchFromDyn` may only be implemented \ | |
a1dfa0c6 XL |
184 | for a coercion between structures with the same \ |
185 | definition; expected `{}`, found `{}`", | |
f9f354fc XL |
186 | source_path, target_path, |
187 | )) | |
188 | .emit(); | |
a1dfa0c6 | 189 | |
f9f354fc XL |
190 | return; |
191 | } | |
a1dfa0c6 | 192 | |
f9f354fc XL |
193 | if def_a.repr.c() || def_a.repr.packed() { |
194 | create_err( | |
195 | "structs implementing `DispatchFromDyn` may not have \ | |
dfeec247 | 196 | `#[repr(packed)]` or `#[repr(C)]`", |
f9f354fc XL |
197 | ) |
198 | .emit(); | |
199 | } | |
a1dfa0c6 | 200 | |
f9f354fc | 201 | let fields = &def_a.non_enum_variant().fields; |
a1dfa0c6 | 202 | |
f9f354fc XL |
203 | let coerced_fields = fields |
204 | .iter() | |
205 | .filter_map(|field| { | |
206 | let ty_a = field.ty(tcx, substs_a); | |
207 | let ty_b = field.ty(tcx, substs_b); | |
dfeec247 | 208 | |
f9f354fc XL |
209 | if let Ok(layout) = tcx.layout_of(param_env.and(ty_a)) { |
210 | if layout.is_zst() && layout.align.abi.bytes() == 1 { | |
211 | // ignore ZST fields with alignment of 1 byte | |
212 | return None; | |
48663c56 | 213 | } |
f9f354fc | 214 | } |
48663c56 | 215 | |
f9f354fc XL |
216 | if let Ok(ok) = infcx.at(&cause, param_env).eq(ty_a, ty_b) { |
217 | if ok.obligations.is_empty() { | |
218 | create_err( | |
219 | "the trait `DispatchFromDyn` may only be implemented \ | |
a1dfa0c6 | 220 | for structs containing the field being coerced, \ |
dfeec247 | 221 | ZST fields with 1 byte alignment, and nothing else", |
f9f354fc XL |
222 | ) |
223 | .note(&format!( | |
224 | "extra field `{}` of type `{}` is not allowed", | |
225 | field.ident, ty_a, | |
226 | )) | |
227 | .emit(); | |
228 | ||
229 | return None; | |
a1dfa0c6 | 230 | } |
f9f354fc | 231 | } |
a1dfa0c6 | 232 | |
f9f354fc XL |
233 | Some(field) |
234 | }) | |
235 | .collect::<Vec<_>>(); | |
a1dfa0c6 | 236 | |
f9f354fc XL |
237 | if coerced_fields.is_empty() { |
238 | create_err( | |
239 | "the trait `DispatchFromDyn` may only be implemented \ | |
a1dfa0c6 | 240 | for a coercion between structures with a single field \ |
dfeec247 | 241 | being coerced, none found", |
f9f354fc XL |
242 | ) |
243 | .emit(); | |
244 | } else if coerced_fields.len() > 1 { | |
245 | create_err( | |
246 | "implementing the `DispatchFromDyn` trait requires multiple coercions", | |
247 | ) | |
248 | .note( | |
249 | "the trait `DispatchFromDyn` may only be implemented \ | |
a1dfa0c6 | 250 | for a coercion between structures with a single field \ |
dfeec247 | 251 | being coerced", |
f9f354fc XL |
252 | ) |
253 | .note(&format!( | |
254 | "currently, {} fields need coercions: {}", | |
255 | coerced_fields.len(), | |
256 | coerced_fields | |
257 | .iter() | |
258 | .map(|field| { | |
259 | format!( | |
260 | "`{}` (`{}` to `{}`)", | |
261 | field.ident, | |
262 | field.ty(tcx, substs_a), | |
263 | field.ty(tcx, substs_b), | |
264 | ) | |
265 | }) | |
266 | .collect::<Vec<_>>() | |
267 | .join(", ") | |
268 | )) | |
269 | .emit(); | |
270 | } else { | |
271 | let mut fulfill_cx = TraitEngine::new(infcx.tcx); | |
272 | ||
273 | for field in coerced_fields { | |
274 | let predicate = predicate_for_trait_def( | |
275 | tcx, | |
276 | param_env, | |
277 | cause.clone(), | |
278 | dispatch_from_dyn_trait, | |
279 | 0, | |
280 | field.ty(tcx, substs_a), | |
281 | &[field.ty(tcx, substs_b).into()], | |
282 | ); | |
a1dfa0c6 | 283 | |
f9f354fc XL |
284 | fulfill_cx.register_predicate_obligation(&infcx, predicate); |
285 | } | |
a1dfa0c6 | 286 | |
f9f354fc XL |
287 | // Check that all transitive obligations are satisfied. |
288 | if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) { | |
289 | infcx.report_fulfillment_errors(&errors, None, false); | |
a1dfa0c6 | 290 | } |
f9f354fc XL |
291 | |
292 | // Finally, resolve all regions. | |
293 | let outlives_env = OutlivesEnvironment::new(param_env); | |
294 | infcx.resolve_regions_and_report_errors( | |
295 | impl_did.to_def_id(), | |
296 | &outlives_env, | |
297 | RegionckMode::default(), | |
298 | ); | |
a1dfa0c6 | 299 | } |
f9f354fc XL |
300 | } |
301 | _ => { | |
302 | create_err( | |
303 | "the trait `DispatchFromDyn` may only be implemented \ | |
dfeec247 | 304 | for a coercion between structures", |
f9f354fc XL |
305 | ) |
306 | .emit(); | |
a1dfa0c6 | 307 | } |
f9f354fc XL |
308 | } |
309 | }) | |
a1dfa0c6 XL |
310 | } |
311 | ||
ba9703b0 | 312 | pub fn coerce_unsized_info(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUnsizedInfo { |
cc61c64b | 313 | debug!("compute_coerce_unsized_info(impl_did={:?})", impl_did); |
f9f354fc XL |
314 | |
315 | // this provider should only get invoked for local def-ids | |
3dfed10e | 316 | let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did.expect_local()); |
f9f354fc XL |
317 | let span = tcx.hir().span(impl_hir_id); |
318 | ||
3dfed10e | 319 | let coerce_unsized_trait = tcx.require_lang_item(LangItem::CoerceUnsized, Some(span)); |
cc61c64b | 320 | |
3dfed10e | 321 | let unsize_trait = tcx.lang_items().require(LangItem::Unsize).unwrap_or_else(|err| { |
e74abb32 | 322 | tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err)); |
0bf4aa26 | 323 | }); |
32a655c1 | 324 | |
e74abb32 XL |
325 | let source = tcx.type_of(impl_did); |
326 | let trait_ref = tcx.impl_trait_ref(impl_did).unwrap(); | |
cc61c64b | 327 | assert_eq!(trait_ref.def_id, coerce_unsized_trait); |
32a655c1 | 328 | let target = trait_ref.substs.type_at(1); |
dfeec247 | 329 | debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (bound)", source, target); |
32a655c1 | 330 | |
e74abb32 | 331 | let param_env = tcx.param_env(impl_did); |
a1dfa0c6 | 332 | assert!(!source.has_escaping_bound_vars()); |
32a655c1 | 333 | |
cc61c64b XL |
334 | let err_info = CoerceUnsizedInfo { custom_kind: None }; |
335 | ||
dfeec247 | 336 | debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (free)", source, target); |
32a655c1 | 337 | |
e74abb32 | 338 | tcx.infer_ctxt().enter(|infcx| { |
9fa01778 | 339 | let cause = ObligationCause::misc(span, impl_hir_id); |
dc9dc135 XL |
340 | let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>, |
341 | mt_b: ty::TypeAndMut<'tcx>, | |
342 | mk_ptr: &dyn Fn(Ty<'tcx>) -> Ty<'tcx>| { | |
dfeec247 XL |
343 | if (mt_a.mutbl, mt_b.mutbl) == (hir::Mutability::Not, hir::Mutability::Mut) { |
344 | infcx | |
345 | .report_mismatched_types( | |
346 | &cause, | |
347 | mk_ptr(mt_b.ty), | |
348 | target, | |
349 | ty::error::TypeError::Mutability, | |
350 | ) | |
32a655c1 SL |
351 | .emit(); |
352 | } | |
353 | (mt_a.ty, mt_b.ty, unsize_trait, None) | |
354 | }; | |
e74abb32 | 355 | let (source, target, trait_def_id, kind) = match (&source.kind, &target.kind) { |
b7449926 | 356 | (&ty::Ref(r_a, ty_a, mutbl_a), &ty::Ref(r_b, ty_b, mutbl_b)) => { |
32a655c1 | 357 | infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a); |
94b46f34 XL |
358 | let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a }; |
359 | let mt_b = ty::TypeAndMut { ty: ty_b, mutbl: mutbl_b }; | |
e74abb32 | 360 | check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty)) |
32a655c1 SL |
361 | } |
362 | ||
b7449926 | 363 | (&ty::Ref(_, ty_a, mutbl_a), &ty::RawPtr(mt_b)) => { |
94b46f34 | 364 | let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a }; |
e74abb32 | 365 | check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty)) |
94b46f34 XL |
366 | } |
367 | ||
b7449926 | 368 | (&ty::RawPtr(mt_a), &ty::RawPtr(mt_b)) => { |
e74abb32 | 369 | check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty)) |
32a655c1 SL |
370 | } |
371 | ||
dfeec247 XL |
372 | (&ty::Adt(def_a, substs_a), &ty::Adt(def_b, substs_b)) |
373 | if def_a.is_struct() && def_b.is_struct() => | |
374 | { | |
32a655c1 | 375 | if def_a != def_b { |
e74abb32 XL |
376 | let source_path = tcx.def_path_str(def_a.did); |
377 | let target_path = tcx.def_path_str(def_b.did); | |
dfeec247 XL |
378 | struct_span_err!( |
379 | tcx.sess, | |
380 | span, | |
381 | E0377, | |
382 | "the trait `CoerceUnsized` may only be implemented \ | |
32a655c1 | 383 | for a coercion between structures with the same \ |
a1dfa0c6 | 384 | definition; expected `{}`, found `{}`", |
dfeec247 XL |
385 | source_path, |
386 | target_path | |
387 | ) | |
388 | .emit(); | |
cc61c64b | 389 | return err_info; |
32a655c1 SL |
390 | } |
391 | ||
cc61c64b XL |
392 | // Here we are considering a case of converting |
393 | // `S<P0...Pn>` to S<Q0...Qn>`. As an example, let's imagine a struct `Foo<T, U>`, | |
394 | // which acts like a pointer to `U`, but carries along some extra data of type `T`: | |
395 | // | |
396 | // struct Foo<T, U> { | |
397 | // extra: T, | |
398 | // ptr: *mut U, | |
399 | // } | |
400 | // | |
401 | // We might have an impl that allows (e.g.) `Foo<T, [i32; 3]>` to be unsized | |
402 | // to `Foo<T, [i32]>`. That impl would look like: | |
403 | // | |
404 | // impl<T, U: Unsize<V>, V> CoerceUnsized<Foo<T, V>> for Foo<T, U> {} | |
405 | // | |
406 | // Here `U = [i32; 3]` and `V = [i32]`. At runtime, | |
407 | // when this coercion occurs, we would be changing the | |
408 | // field `ptr` from a thin pointer of type `*mut [i32; | |
409 | // 3]` to a fat pointer of type `*mut [i32]` (with | |
410 | // extra data `3`). **The purpose of this check is to | |
411 | // make sure that we know how to do this conversion.** | |
412 | // | |
413 | // To check if this impl is legal, we would walk down | |
414 | // the fields of `Foo` and consider their types with | |
415 | // both substitutes. We are looking to find that | |
416 | // exactly one (non-phantom) field has changed its | |
417 | // type, which we will expect to be the pointer that | |
418 | // is becoming fat (we could probably generalize this | |
0bf4aa26 | 419 | // to multiple thin pointers of the same type becoming |
cc61c64b XL |
420 | // fat, but we don't). In this case: |
421 | // | |
422 | // - `extra` has type `T` before and type `T` after | |
423 | // - `ptr` has type `*mut U` before and type `*mut V` after | |
424 | // | |
425 | // Since just one field changed, we would then check | |
426 | // that `*mut U: CoerceUnsized<*mut V>` is implemented | |
427 | // (in other words, that we know how to do this | |
428 | // conversion). This will work out because `U: | |
429 | // Unsize<V>`, and we have a builtin rule that `*mut | |
430 | // U` can be coerced to `*mut V` if `U: Unsize<V>`. | |
2c00a5a8 | 431 | let fields = &def_a.non_enum_variant().fields; |
dfeec247 XL |
432 | let diff_fields = fields |
433 | .iter() | |
32a655c1 SL |
434 | .enumerate() |
435 | .filter_map(|(i, f)| { | |
e74abb32 | 436 | let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b)); |
32a655c1 | 437 | |
e74abb32 | 438 | if tcx.type_of(f.did).is_phantom_data() { |
32a655c1 SL |
439 | // Ignore PhantomData fields |
440 | return None; | |
441 | } | |
442 | ||
cc61c64b XL |
443 | // Ignore fields that aren't changed; it may |
444 | // be that we could get away with subtyping or | |
445 | // something more accepting, but we use | |
446 | // equality because we want to be able to | |
447 | // perform this check without computing | |
448 | // variance where possible. (This is because | |
449 | // we may have to evaluate constraint | |
450 | // expressions in the course of execution.) | |
0731742a | 451 | // See e.g., #41936. |
7cac9316 | 452 | if let Ok(ok) = infcx.at(&cause, param_env).eq(a, b) { |
32a655c1 SL |
453 | if ok.obligations.is_empty() { |
454 | return None; | |
455 | } | |
456 | } | |
457 | ||
458 | // Collect up all fields that were significantly changed | |
0731742a | 459 | // i.e., those that contain T in coerce_unsized T -> U |
32a655c1 SL |
460 | Some((i, a, b)) |
461 | }) | |
462 | .collect::<Vec<_>>(); | |
463 | ||
464 | if diff_fields.is_empty() { | |
dfeec247 XL |
465 | struct_span_err!( |
466 | tcx.sess, | |
467 | span, | |
468 | E0374, | |
469 | "the trait `CoerceUnsized` may only be implemented \ | |
32a655c1 | 470 | for a coercion between structures with one field \ |
dfeec247 XL |
471 | being coerced, none found" |
472 | ) | |
473 | .emit(); | |
cc61c64b | 474 | return err_info; |
32a655c1 | 475 | } else if diff_fields.len() > 1 { |
e74abb32 | 476 | let item = tcx.hir().expect_item(impl_hir_id); |
dfeec247 | 477 | let span = if let ItemKind::Impl { of_trait: Some(ref t), .. } = item.kind { |
32a655c1 SL |
478 | t.path.span |
479 | } else { | |
e74abb32 | 480 | tcx.hir().span(impl_hir_id) |
32a655c1 SL |
481 | }; |
482 | ||
dfeec247 XL |
483 | struct_span_err!( |
484 | tcx.sess, | |
485 | span, | |
486 | E0375, | |
487 | "implementing the trait \ | |
32a655c1 | 488 | `CoerceUnsized` requires multiple \ |
dfeec247 XL |
489 | coercions" |
490 | ) | |
491 | .note( | |
492 | "`CoerceUnsized` may only be implemented for \ | |
493 | a coercion between structures with one field being coerced", | |
494 | ) | |
495 | .note(&format!( | |
496 | "currently, {} fields need coercions: {}", | |
497 | diff_fields.len(), | |
498 | diff_fields | |
499 | .iter() | |
500 | .map(|&(i, a, b)| { | |
501 | format!("`{}` (`{}` to `{}`)", fields[i].ident, a, b) | |
502 | }) | |
503 | .collect::<Vec<_>>() | |
504 | .join(", ") | |
505 | )) | |
506 | .span_label(span, "requires multiple coercions") | |
507 | .emit(); | |
cc61c64b | 508 | return err_info; |
32a655c1 SL |
509 | } |
510 | ||
511 | let (i, a, b) = diff_fields[0]; | |
512 | let kind = ty::adjustment::CustomCoerceUnsized::Struct(i); | |
513 | (a, b, coerce_unsized_trait, Some(kind)) | |
514 | } | |
515 | ||
516 | _ => { | |
dfeec247 XL |
517 | struct_span_err!( |
518 | tcx.sess, | |
519 | span, | |
520 | E0376, | |
521 | "the trait `CoerceUnsized` may only be implemented \ | |
522 | for a coercion between structures" | |
523 | ) | |
524 | .emit(); | |
cc61c64b | 525 | return err_info; |
32a655c1 SL |
526 | } |
527 | }; | |
528 | ||
0531ce1d | 529 | let mut fulfill_cx = TraitEngine::new(infcx.tcx); |
32a655c1 SL |
530 | |
531 | // Register an obligation for `A: Trait<B>`. | |
9fa01778 | 532 | let cause = traits::ObligationCause::misc(span, impl_hir_id); |
dfeec247 XL |
533 | let predicate = predicate_for_trait_def( |
534 | tcx, | |
535 | param_env, | |
536 | cause, | |
537 | trait_def_id, | |
538 | 0, | |
539 | source, | |
540 | &[target.into()], | |
541 | ); | |
32a655c1 SL |
542 | fulfill_cx.register_predicate_obligation(&infcx, predicate); |
543 | ||
544 | // Check that all transitive obligations are satisfied. | |
545 | if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) { | |
0531ce1d | 546 | infcx.report_fulfillment_errors(&errors, None, false); |
32a655c1 SL |
547 | } |
548 | ||
549 | // Finally, resolve all regions. | |
ff7c6d11 | 550 | let outlives_env = OutlivesEnvironment::new(param_env); |
f9f354fc | 551 | infcx.resolve_regions_and_report_errors(impl_did, &outlives_env, RegionckMode::default()); |
32a655c1 | 552 | |
dfeec247 | 553 | CoerceUnsizedInfo { custom_kind: kind } |
cc61c64b | 554 | }) |
32a655c1 | 555 | } |