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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 | |
1b1a35ee | 4 | use crate::errors::{CopyImplOnNonAdt, CopyImplOnTypeWithDtor, DropImplOnWrongItem}; |
dfeec247 XL |
5 | use rustc_errors::struct_span_err; |
6 | use rustc_hir as hir; | |
f9f354fc | 7 | use rustc_hir::def_id::{DefId, LocalDefId}; |
3dfed10e | 8 | use rustc_hir::lang_items::LangItem; |
dfeec247 | 9 | use rustc_hir::ItemKind; |
74b04a01 XL |
10 | use rustc_infer::infer; |
11 | use rustc_infer::infer::outlives::env::OutlivesEnvironment; | |
ba9703b0 | 12 | use rustc_infer::infer::{RegionckMode, TyCtxtInferExt}; |
ba9703b0 XL |
13 | use rustc_middle::ty::adjustment::CoerceUnsizedInfo; |
14 | use rustc_middle::ty::TypeFoldable; | |
15 | use rustc_middle::ty::{self, Ty, TyCtxt}; | |
16 | use rustc_trait_selection::traits::error_reporting::InferCtxtExt; | |
17 | use rustc_trait_selection::traits::misc::{can_type_implement_copy, CopyImplementationError}; | |
18 | use rustc_trait_selection::traits::predicate_for_trait_def; | |
19 | use rustc_trait_selection::traits::{self, ObligationCause, TraitEngine, TraitEngineExt}; | |
60c5eb7d | 20 | |
416331ca | 21 | pub fn check_trait(tcx: TyCtxt<'_>, trait_def_id: DefId) { |
74b04a01 | 22 | let lang_items = tcx.lang_items(); |
8bb4bdeb | 23 | Checker { tcx, trait_def_id } |
74b04a01 XL |
24 | .check(lang_items.drop_trait(), visit_implementation_of_drop) |
25 | .check(lang_items.copy_trait(), visit_implementation_of_copy) | |
26 | .check(lang_items.coerce_unsized_trait(), visit_implementation_of_coerce_unsized) | |
27 | .check(lang_items.dispatch_from_dyn_trait(), visit_implementation_of_dispatch_from_dyn); | |
32a655c1 SL |
28 | } |
29 | ||
dc9dc135 XL |
30 | struct Checker<'tcx> { |
31 | tcx: TyCtxt<'tcx>, | |
32 | trait_def_id: DefId, | |
8bb4bdeb XL |
33 | } |
34 | ||
dc9dc135 | 35 | impl<'tcx> Checker<'tcx> { |
8bb4bdeb | 36 | fn check<F>(&self, trait_def_id: Option<DefId>, mut f: F) -> &Self |
dc9dc135 | 37 | where |
f9f354fc | 38 | F: FnMut(TyCtxt<'tcx>, LocalDefId), |
8bb4bdeb XL |
39 | { |
40 | if Some(self.trait_def_id) == trait_def_id { | |
6a06907d | 41 | for &impl_def_id in self.tcx.hir().trait_impls(self.trait_def_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. |
1b1a35ee | 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 | 56 | let sp = match tcx.hir().expect_item(impl_hir_id).kind { |
5869c6ff | 57 | ItemKind::Impl(ref impl_) => impl_.self_ty.span, |
dfeec247 XL |
58 | _ => bug!("expected Drop impl item"), |
59 | }; | |
60 | ||
1b1a35ee | 61 | tcx.sess.emit_err(DropImplOnWrongItem { span: sp }); |
32a655c1 SL |
62 | } |
63 | ||
f9f354fc | 64 | fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) { |
32a655c1 SL |
65 | debug!("visit_implementation_of_copy: impl_did={:?}", impl_did); |
66 | ||
3dfed10e | 67 | let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did); |
32a655c1 | 68 | |
7cac9316 | 69 | let self_type = tcx.type_of(impl_did); |
dfeec247 | 70 | debug!("visit_implementation_of_copy: self_type={:?} (bound)", self_type); |
32a655c1 | 71 | |
dc9dc135 | 72 | let span = tcx.hir().span(impl_hir_id); |
7cac9316 | 73 | let param_env = tcx.param_env(impl_did); |
a1dfa0c6 | 74 | assert!(!self_type.has_escaping_bound_vars()); |
32a655c1 | 75 | |
dfeec247 | 76 | debug!("visit_implementation_of_copy: self_type={:?} (free)", self_type); |
32a655c1 | 77 | |
dfeec247 | 78 | match can_type_implement_copy(tcx, param_env, self_type) { |
32a655c1 | 79 | Ok(()) => {} |
94b46f34 | 80 | Err(CopyImplementationError::InfrigingFields(fields)) => { |
dc9dc135 | 81 | let item = tcx.hir().expect_item(impl_hir_id); |
5869c6ff | 82 | let span = if let ItemKind::Impl(hir::Impl { of_trait: Some(ref tr), .. }) = item.kind { |
32a655c1 SL |
83 | tr.path.span |
84 | } else { | |
85 | span | |
86 | }; | |
87 | ||
dfeec247 XL |
88 | let mut err = struct_span_err!( |
89 | tcx.sess, | |
90 | span, | |
91 | E0204, | |
92 | "the trait `Copy` may not be implemented for this type" | |
93 | ); | |
94b46f34 | 94 | for span in fields.iter().map(|f| tcx.def_span(f.did)) { |
0bf4aa26 | 95 | err.span_label(span, "this field does not implement `Copy`"); |
94b46f34 XL |
96 | } |
97 | err.emit() | |
32a655c1 SL |
98 | } |
99 | Err(CopyImplementationError::NotAnAdt) => { | |
dc9dc135 | 100 | let item = tcx.hir().expect_item(impl_hir_id); |
dfeec247 | 101 | let span = |
5869c6ff | 102 | if let ItemKind::Impl(ref impl_) = item.kind { impl_.self_ty.span } else { span }; |
dfeec247 | 103 | |
1b1a35ee | 104 | tcx.sess.emit_err(CopyImplOnNonAdt { span }); |
32a655c1 SL |
105 | } |
106 | Err(CopyImplementationError::HasDestructor) => { | |
1b1a35ee | 107 | tcx.sess.emit_err(CopyImplOnTypeWithDtor { span }); |
32a655c1 SL |
108 | } |
109 | } | |
110 | } | |
111 | ||
f9f354fc | 112 | fn visit_implementation_of_coerce_unsized(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) { |
dfeec247 | 113 | debug!("visit_implementation_of_coerce_unsized: impl_did={:?}", impl_did); |
32a655c1 | 114 | |
cc61c64b XL |
115 | // Just compute this for the side-effects, in particular reporting |
116 | // errors; other parts of the code may demand it for the info of | |
117 | // course. | |
f9f354fc XL |
118 | let span = tcx.def_span(impl_did); |
119 | tcx.at(span).coerce_unsized_info(impl_did); | |
cc61c64b XL |
120 | } |
121 | ||
f9f354fc | 122 | fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDefId) { |
dfeec247 | 123 | debug!("visit_implementation_of_dispatch_from_dyn: impl_did={:?}", impl_did); |
a1dfa0c6 | 124 | |
3dfed10e | 125 | let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did); |
f9f354fc | 126 | let span = tcx.hir().span(impl_hir_id); |
a1dfa0c6 | 127 | |
3dfed10e | 128 | let dispatch_from_dyn_trait = tcx.require_lang_item(LangItem::DispatchFromDyn, Some(span)); |
a1dfa0c6 | 129 | |
f9f354fc XL |
130 | let source = tcx.type_of(impl_did); |
131 | assert!(!source.has_escaping_bound_vars()); | |
132 | let target = { | |
133 | let trait_ref = tcx.impl_trait_ref(impl_did).unwrap(); | |
134 | assert_eq!(trait_ref.def_id, dispatch_from_dyn_trait); | |
a1dfa0c6 | 135 | |
f9f354fc XL |
136 | trait_ref.substs.type_at(1) |
137 | }; | |
a1dfa0c6 | 138 | |
f9f354fc | 139 | debug!("visit_implementation_of_dispatch_from_dyn: {:?} -> {:?}", source, target); |
a1dfa0c6 | 140 | |
f9f354fc | 141 | let param_env = tcx.param_env(impl_did); |
a1dfa0c6 | 142 | |
f9f354fc | 143 | let create_err = |msg: &str| struct_span_err!(tcx.sess, span, E0378, "{}", msg); |
a1dfa0c6 | 144 | |
f9f354fc XL |
145 | tcx.infer_ctxt().enter(|infcx| { |
146 | let cause = ObligationCause::misc(span, impl_hir_id); | |
a1dfa0c6 | 147 | |
f9f354fc | 148 | use ty::TyKind::*; |
1b1a35ee | 149 | match (source.kind(), target.kind()) { |
f9f354fc XL |
150 | (&Ref(r_a, _, mutbl_a), Ref(r_b, _, mutbl_b)) |
151 | if infcx.at(&cause, param_env).eq(r_a, r_b).is_ok() && mutbl_a == *mutbl_b => {} | |
152 | (&RawPtr(tm_a), &RawPtr(tm_b)) if tm_a.mutbl == tm_b.mutbl => (), | |
153 | (&Adt(def_a, substs_a), &Adt(def_b, substs_b)) | |
154 | if def_a.is_struct() && def_b.is_struct() => | |
155 | { | |
156 | if def_a != def_b { | |
157 | let source_path = tcx.def_path_str(def_a.did); | |
158 | let target_path = tcx.def_path_str(def_b.did); | |
159 | ||
160 | create_err(&format!( | |
161 | "the trait `DispatchFromDyn` may only be implemented \ | |
a1dfa0c6 XL |
162 | for a coercion between structures with the same \ |
163 | definition; expected `{}`, found `{}`", | |
f9f354fc XL |
164 | source_path, target_path, |
165 | )) | |
166 | .emit(); | |
a1dfa0c6 | 167 | |
f9f354fc XL |
168 | return; |
169 | } | |
a1dfa0c6 | 170 | |
f9f354fc XL |
171 | if def_a.repr.c() || def_a.repr.packed() { |
172 | create_err( | |
173 | "structs implementing `DispatchFromDyn` may not have \ | |
dfeec247 | 174 | `#[repr(packed)]` or `#[repr(C)]`", |
f9f354fc XL |
175 | ) |
176 | .emit(); | |
177 | } | |
a1dfa0c6 | 178 | |
f9f354fc | 179 | let fields = &def_a.non_enum_variant().fields; |
a1dfa0c6 | 180 | |
f9f354fc XL |
181 | let coerced_fields = fields |
182 | .iter() | |
183 | .filter_map(|field| { | |
184 | let ty_a = field.ty(tcx, substs_a); | |
185 | let ty_b = field.ty(tcx, substs_b); | |
dfeec247 | 186 | |
f9f354fc XL |
187 | if let Ok(layout) = tcx.layout_of(param_env.and(ty_a)) { |
188 | if layout.is_zst() && layout.align.abi.bytes() == 1 { | |
189 | // ignore ZST fields with alignment of 1 byte | |
190 | return None; | |
48663c56 | 191 | } |
f9f354fc | 192 | } |
48663c56 | 193 | |
f9f354fc XL |
194 | if let Ok(ok) = infcx.at(&cause, param_env).eq(ty_a, ty_b) { |
195 | if ok.obligations.is_empty() { | |
196 | create_err( | |
197 | "the trait `DispatchFromDyn` may only be implemented \ | |
a1dfa0c6 | 198 | for structs containing the field being coerced, \ |
dfeec247 | 199 | ZST fields with 1 byte alignment, and nothing else", |
f9f354fc XL |
200 | ) |
201 | .note(&format!( | |
202 | "extra field `{}` of type `{}` is not allowed", | |
203 | field.ident, ty_a, | |
204 | )) | |
205 | .emit(); | |
206 | ||
207 | return None; | |
a1dfa0c6 | 208 | } |
f9f354fc | 209 | } |
a1dfa0c6 | 210 | |
f9f354fc XL |
211 | Some(field) |
212 | }) | |
213 | .collect::<Vec<_>>(); | |
a1dfa0c6 | 214 | |
f9f354fc XL |
215 | if coerced_fields.is_empty() { |
216 | create_err( | |
217 | "the trait `DispatchFromDyn` may only be implemented \ | |
a1dfa0c6 | 218 | for a coercion between structures with a single field \ |
dfeec247 | 219 | being coerced, none found", |
f9f354fc XL |
220 | ) |
221 | .emit(); | |
222 | } else if coerced_fields.len() > 1 { | |
223 | create_err( | |
224 | "implementing the `DispatchFromDyn` trait requires multiple coercions", | |
225 | ) | |
226 | .note( | |
227 | "the trait `DispatchFromDyn` may only be implemented \ | |
a1dfa0c6 | 228 | for a coercion between structures with a single field \ |
dfeec247 | 229 | being coerced", |
f9f354fc XL |
230 | ) |
231 | .note(&format!( | |
232 | "currently, {} fields need coercions: {}", | |
233 | coerced_fields.len(), | |
234 | coerced_fields | |
235 | .iter() | |
236 | .map(|field| { | |
237 | format!( | |
238 | "`{}` (`{}` to `{}`)", | |
239 | field.ident, | |
240 | field.ty(tcx, substs_a), | |
241 | field.ty(tcx, substs_b), | |
242 | ) | |
243 | }) | |
244 | .collect::<Vec<_>>() | |
245 | .join(", ") | |
246 | )) | |
247 | .emit(); | |
248 | } else { | |
6a06907d | 249 | let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx); |
f9f354fc XL |
250 | |
251 | for field in coerced_fields { | |
252 | let predicate = predicate_for_trait_def( | |
253 | tcx, | |
254 | param_env, | |
255 | cause.clone(), | |
256 | dispatch_from_dyn_trait, | |
257 | 0, | |
258 | field.ty(tcx, substs_a), | |
259 | &[field.ty(tcx, substs_b).into()], | |
260 | ); | |
a1dfa0c6 | 261 | |
f9f354fc XL |
262 | fulfill_cx.register_predicate_obligation(&infcx, predicate); |
263 | } | |
a1dfa0c6 | 264 | |
f9f354fc XL |
265 | // Check that all transitive obligations are satisfied. |
266 | if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) { | |
267 | infcx.report_fulfillment_errors(&errors, None, false); | |
a1dfa0c6 | 268 | } |
f9f354fc XL |
269 | |
270 | // Finally, resolve all regions. | |
271 | let outlives_env = OutlivesEnvironment::new(param_env); | |
272 | infcx.resolve_regions_and_report_errors( | |
273 | impl_did.to_def_id(), | |
274 | &outlives_env, | |
275 | RegionckMode::default(), | |
276 | ); | |
a1dfa0c6 | 277 | } |
f9f354fc XL |
278 | } |
279 | _ => { | |
280 | create_err( | |
281 | "the trait `DispatchFromDyn` may only be implemented \ | |
dfeec247 | 282 | for a coercion between structures", |
f9f354fc XL |
283 | ) |
284 | .emit(); | |
a1dfa0c6 | 285 | } |
f9f354fc XL |
286 | } |
287 | }) | |
a1dfa0c6 XL |
288 | } |
289 | ||
ba9703b0 | 290 | pub fn coerce_unsized_info(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUnsizedInfo { |
cc61c64b | 291 | debug!("compute_coerce_unsized_info(impl_did={:?})", impl_did); |
f9f354fc XL |
292 | |
293 | // this provider should only get invoked for local def-ids | |
3dfed10e | 294 | let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did.expect_local()); |
f9f354fc XL |
295 | let span = tcx.hir().span(impl_hir_id); |
296 | ||
3dfed10e | 297 | let coerce_unsized_trait = tcx.require_lang_item(LangItem::CoerceUnsized, Some(span)); |
cc61c64b | 298 | |
3dfed10e | 299 | let unsize_trait = tcx.lang_items().require(LangItem::Unsize).unwrap_or_else(|err| { |
e74abb32 | 300 | tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err)); |
0bf4aa26 | 301 | }); |
32a655c1 | 302 | |
e74abb32 XL |
303 | let source = tcx.type_of(impl_did); |
304 | let trait_ref = tcx.impl_trait_ref(impl_did).unwrap(); | |
cc61c64b | 305 | assert_eq!(trait_ref.def_id, coerce_unsized_trait); |
32a655c1 | 306 | let target = trait_ref.substs.type_at(1); |
dfeec247 | 307 | debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (bound)", source, target); |
32a655c1 | 308 | |
e74abb32 | 309 | let param_env = tcx.param_env(impl_did); |
a1dfa0c6 | 310 | assert!(!source.has_escaping_bound_vars()); |
32a655c1 | 311 | |
cc61c64b XL |
312 | let err_info = CoerceUnsizedInfo { custom_kind: None }; |
313 | ||
dfeec247 | 314 | debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (free)", source, target); |
32a655c1 | 315 | |
e74abb32 | 316 | tcx.infer_ctxt().enter(|infcx| { |
9fa01778 | 317 | let cause = ObligationCause::misc(span, impl_hir_id); |
dc9dc135 XL |
318 | let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>, |
319 | mt_b: ty::TypeAndMut<'tcx>, | |
320 | mk_ptr: &dyn Fn(Ty<'tcx>) -> Ty<'tcx>| { | |
dfeec247 XL |
321 | if (mt_a.mutbl, mt_b.mutbl) == (hir::Mutability::Not, hir::Mutability::Mut) { |
322 | infcx | |
323 | .report_mismatched_types( | |
324 | &cause, | |
325 | mk_ptr(mt_b.ty), | |
326 | target, | |
327 | ty::error::TypeError::Mutability, | |
328 | ) | |
32a655c1 SL |
329 | .emit(); |
330 | } | |
331 | (mt_a.ty, mt_b.ty, unsize_trait, None) | |
332 | }; | |
1b1a35ee | 333 | let (source, target, trait_def_id, kind) = match (source.kind(), target.kind()) { |
b7449926 | 334 | (&ty::Ref(r_a, ty_a, mutbl_a), &ty::Ref(r_b, ty_b, mutbl_b)) => { |
32a655c1 | 335 | infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a); |
94b46f34 XL |
336 | let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a }; |
337 | let mt_b = ty::TypeAndMut { ty: ty_b, mutbl: mutbl_b }; | |
e74abb32 | 338 | check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty)) |
32a655c1 SL |
339 | } |
340 | ||
b7449926 | 341 | (&ty::Ref(_, ty_a, mutbl_a), &ty::RawPtr(mt_b)) => { |
94b46f34 | 342 | let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a }; |
e74abb32 | 343 | check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty)) |
94b46f34 XL |
344 | } |
345 | ||
b7449926 | 346 | (&ty::RawPtr(mt_a), &ty::RawPtr(mt_b)) => { |
e74abb32 | 347 | check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty)) |
32a655c1 SL |
348 | } |
349 | ||
dfeec247 XL |
350 | (&ty::Adt(def_a, substs_a), &ty::Adt(def_b, substs_b)) |
351 | if def_a.is_struct() && def_b.is_struct() => | |
352 | { | |
32a655c1 | 353 | if def_a != def_b { |
e74abb32 XL |
354 | let source_path = tcx.def_path_str(def_a.did); |
355 | let target_path = tcx.def_path_str(def_b.did); | |
dfeec247 XL |
356 | struct_span_err!( |
357 | tcx.sess, | |
358 | span, | |
359 | E0377, | |
360 | "the trait `CoerceUnsized` may only be implemented \ | |
32a655c1 | 361 | for a coercion between structures with the same \ |
a1dfa0c6 | 362 | definition; expected `{}`, found `{}`", |
dfeec247 XL |
363 | source_path, |
364 | target_path | |
365 | ) | |
366 | .emit(); | |
cc61c64b | 367 | return err_info; |
32a655c1 SL |
368 | } |
369 | ||
cc61c64b XL |
370 | // Here we are considering a case of converting |
371 | // `S<P0...Pn>` to S<Q0...Qn>`. As an example, let's imagine a struct `Foo<T, U>`, | |
372 | // which acts like a pointer to `U`, but carries along some extra data of type `T`: | |
373 | // | |
374 | // struct Foo<T, U> { | |
375 | // extra: T, | |
376 | // ptr: *mut U, | |
377 | // } | |
378 | // | |
379 | // We might have an impl that allows (e.g.) `Foo<T, [i32; 3]>` to be unsized | |
380 | // to `Foo<T, [i32]>`. That impl would look like: | |
381 | // | |
382 | // impl<T, U: Unsize<V>, V> CoerceUnsized<Foo<T, V>> for Foo<T, U> {} | |
383 | // | |
384 | // Here `U = [i32; 3]` and `V = [i32]`. At runtime, | |
385 | // when this coercion occurs, we would be changing the | |
386 | // field `ptr` from a thin pointer of type `*mut [i32; | |
387 | // 3]` to a fat pointer of type `*mut [i32]` (with | |
388 | // extra data `3`). **The purpose of this check is to | |
389 | // make sure that we know how to do this conversion.** | |
390 | // | |
391 | // To check if this impl is legal, we would walk down | |
392 | // the fields of `Foo` and consider their types with | |
393 | // both substitutes. We are looking to find that | |
394 | // exactly one (non-phantom) field has changed its | |
395 | // type, which we will expect to be the pointer that | |
396 | // is becoming fat (we could probably generalize this | |
0bf4aa26 | 397 | // to multiple thin pointers of the same type becoming |
cc61c64b XL |
398 | // fat, but we don't). In this case: |
399 | // | |
400 | // - `extra` has type `T` before and type `T` after | |
401 | // - `ptr` has type `*mut U` before and type `*mut V` after | |
402 | // | |
403 | // Since just one field changed, we would then check | |
404 | // that `*mut U: CoerceUnsized<*mut V>` is implemented | |
405 | // (in other words, that we know how to do this | |
406 | // conversion). This will work out because `U: | |
407 | // Unsize<V>`, and we have a builtin rule that `*mut | |
408 | // U` can be coerced to `*mut V` if `U: Unsize<V>`. | |
2c00a5a8 | 409 | let fields = &def_a.non_enum_variant().fields; |
dfeec247 XL |
410 | let diff_fields = fields |
411 | .iter() | |
32a655c1 SL |
412 | .enumerate() |
413 | .filter_map(|(i, f)| { | |
e74abb32 | 414 | let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b)); |
32a655c1 | 415 | |
e74abb32 | 416 | if tcx.type_of(f.did).is_phantom_data() { |
32a655c1 SL |
417 | // Ignore PhantomData fields |
418 | return None; | |
419 | } | |
420 | ||
cc61c64b XL |
421 | // Ignore fields that aren't changed; it may |
422 | // be that we could get away with subtyping or | |
423 | // something more accepting, but we use | |
424 | // equality because we want to be able to | |
425 | // perform this check without computing | |
426 | // variance where possible. (This is because | |
427 | // we may have to evaluate constraint | |
428 | // expressions in the course of execution.) | |
0731742a | 429 | // See e.g., #41936. |
7cac9316 | 430 | if let Ok(ok) = infcx.at(&cause, param_env).eq(a, b) { |
32a655c1 SL |
431 | if ok.obligations.is_empty() { |
432 | return None; | |
433 | } | |
434 | } | |
435 | ||
436 | // Collect up all fields that were significantly changed | |
0731742a | 437 | // i.e., those that contain T in coerce_unsized T -> U |
32a655c1 SL |
438 | Some((i, a, b)) |
439 | }) | |
440 | .collect::<Vec<_>>(); | |
441 | ||
442 | if diff_fields.is_empty() { | |
dfeec247 XL |
443 | struct_span_err!( |
444 | tcx.sess, | |
445 | span, | |
446 | E0374, | |
447 | "the trait `CoerceUnsized` may only be implemented \ | |
32a655c1 | 448 | for a coercion between structures with one field \ |
dfeec247 XL |
449 | being coerced, none found" |
450 | ) | |
451 | .emit(); | |
cc61c64b | 452 | return err_info; |
32a655c1 | 453 | } else if diff_fields.len() > 1 { |
e74abb32 | 454 | let item = tcx.hir().expect_item(impl_hir_id); |
5869c6ff XL |
455 | let span = if let ItemKind::Impl(hir::Impl { of_trait: Some(ref t), .. }) = |
456 | item.kind | |
457 | { | |
32a655c1 SL |
458 | t.path.span |
459 | } else { | |
e74abb32 | 460 | tcx.hir().span(impl_hir_id) |
32a655c1 SL |
461 | }; |
462 | ||
dfeec247 XL |
463 | struct_span_err!( |
464 | tcx.sess, | |
465 | span, | |
466 | E0375, | |
467 | "implementing the trait \ | |
32a655c1 | 468 | `CoerceUnsized` requires multiple \ |
dfeec247 XL |
469 | coercions" |
470 | ) | |
471 | .note( | |
472 | "`CoerceUnsized` may only be implemented for \ | |
473 | a coercion between structures with one field being coerced", | |
474 | ) | |
475 | .note(&format!( | |
476 | "currently, {} fields need coercions: {}", | |
477 | diff_fields.len(), | |
478 | diff_fields | |
479 | .iter() | |
480 | .map(|&(i, a, b)| { | |
481 | format!("`{}` (`{}` to `{}`)", fields[i].ident, a, b) | |
482 | }) | |
483 | .collect::<Vec<_>>() | |
484 | .join(", ") | |
485 | )) | |
486 | .span_label(span, "requires multiple coercions") | |
487 | .emit(); | |
cc61c64b | 488 | return err_info; |
32a655c1 SL |
489 | } |
490 | ||
491 | let (i, a, b) = diff_fields[0]; | |
492 | let kind = ty::adjustment::CustomCoerceUnsized::Struct(i); | |
493 | (a, b, coerce_unsized_trait, Some(kind)) | |
494 | } | |
495 | ||
496 | _ => { | |
dfeec247 XL |
497 | struct_span_err!( |
498 | tcx.sess, | |
499 | span, | |
500 | E0376, | |
501 | "the trait `CoerceUnsized` may only be implemented \ | |
502 | for a coercion between structures" | |
503 | ) | |
504 | .emit(); | |
cc61c64b | 505 | return err_info; |
32a655c1 SL |
506 | } |
507 | }; | |
508 | ||
6a06907d | 509 | let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx); |
32a655c1 SL |
510 | |
511 | // Register an obligation for `A: Trait<B>`. | |
9fa01778 | 512 | let cause = traits::ObligationCause::misc(span, impl_hir_id); |
dfeec247 XL |
513 | let predicate = predicate_for_trait_def( |
514 | tcx, | |
515 | param_env, | |
516 | cause, | |
517 | trait_def_id, | |
518 | 0, | |
519 | source, | |
520 | &[target.into()], | |
521 | ); | |
32a655c1 SL |
522 | fulfill_cx.register_predicate_obligation(&infcx, predicate); |
523 | ||
524 | // Check that all transitive obligations are satisfied. | |
525 | if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) { | |
0531ce1d | 526 | infcx.report_fulfillment_errors(&errors, None, false); |
32a655c1 SL |
527 | } |
528 | ||
529 | // Finally, resolve all regions. | |
ff7c6d11 | 530 | let outlives_env = OutlivesEnvironment::new(param_env); |
f9f354fc | 531 | infcx.resolve_regions_and_report_errors(impl_did, &outlives_env, RegionckMode::default()); |
32a655c1 | 532 | |
dfeec247 | 533 | CoerceUnsizedInfo { custom_kind: kind } |
cc61c64b | 534 | }) |
32a655c1 | 535 | } |