| // we don't have to assume that this is unsizing coercion (it will always lead to an error) |
| // |
| // However, we don't want to bail early all the time, since the unholdable obligations |
| // may be interesting for diagnostics (such as trying to coerce `&T` to `&dyn Id<This = U>`), |
| // so we only bail if there (likely) is another way to convert the types. |
| if !self.infcx.predicate_may_hold(&root_obligation) { |
| if let Some(dyn_metadata_adt_def_id) = self.tcx.lang_items().get(LangItem::DynMetadata) |
| && let Some(metadata_type_def_id) = self.tcx.lang_items().get(LangItem::Metadata) |
| { |
| self.probe(|_ |
| let ocx = ObligationCtxt::new(&self.infcx); |
|
| // returns `true` if `::Metadata` is `DynMetadata<_>` |
| let has_dyn_trait_metadata = |ty |
| let metadata_ty: Result<_, _> = ocx.structurally_normalize_ty( |
| &ObligationCause::dummy(), |
| self.fcx.param_env, |
| Ty::new_alias( |
| self.tcx, |
| ty::AliasTyKind::Projection, |
| AliasTy::new(self.tcx, metadata_type_def_id, [ty]), |
| ), |
| ); |
|
| metadata_ty.is_ok_and(|metadata_ty |
| metadata_ty |
| .ty_adt_def() |
| .is_some_and(|d |
| }) |
| }; |
|
| // If both types are raw pointers to a (wrapper over a) trait object, |
| // this might be a cast like `*const W -> *const dyn Trait`. |
| // So it's better to bail and try that. (even if the cast is not possible, for |
| // example due to vtables not matching, cast diagnostic will likely still be better) |
| // |
| // N.B. use `target`, not `coerce_target` (the latter is a var) |
| if let &ty::RawPtr(source_pointee, _) = coerce_source.kind() |
| && let &ty::RawPtr(target_pointee, _) = target.kind() |
| && has_dyn_trait_metadata(source_pointee) |
| && has_dyn_trait_metadata(target_pointee) |
| { |
| return Err(TypeError::Mismatch); |
| } |
|
| Ok(()) |
| })?; |
| } |
| } |