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Diffstat (limited to '')
-rw-r--r-- | compiler/rustc_ty_utils/src/structural_match.rs | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/compiler/rustc_ty_utils/src/structural_match.rs b/compiler/rustc_ty_utils/src/structural_match.rs new file mode 100644 index 000000000..a55bb7e7e --- /dev/null +++ b/compiler/rustc_ty_utils/src/structural_match.rs @@ -0,0 +1,44 @@ +use rustc_hir::lang_items::LangItem; +use rustc_middle::ty::query::Providers; +use rustc_middle::ty::{self, Ty, TyCtxt}; + +use rustc_infer::infer::TyCtxtInferExt; +use rustc_trait_selection::traits::{ObligationCause, ObligationCtxt}; + +/// This method returns true if and only if `adt_ty` itself has been marked as +/// eligible for structural-match: namely, if it implements both +/// `StructuralPartialEq` and `StructuralEq` (which are respectively injected by +/// `#[derive(PartialEq)]` and `#[derive(Eq)]`). +/// +/// Note that this does *not* recursively check if the substructure of `adt_ty` +/// implements the traits. +fn has_structural_eq_impls<'tcx>(tcx: TyCtxt<'tcx>, adt_ty: Ty<'tcx>) -> bool { + let ref infcx = tcx.infer_ctxt().build(); + let cause = ObligationCause::dummy(); + + let ocx = ObligationCtxt::new(infcx); + // require `#[derive(PartialEq)]` + let structural_peq_def_id = + infcx.tcx.require_lang_item(LangItem::StructuralPeq, Some(cause.span)); + ocx.register_bound(cause.clone(), ty::ParamEnv::empty(), adt_ty, structural_peq_def_id); + // for now, require `#[derive(Eq)]`. (Doing so is a hack to work around + // the type `for<'a> fn(&'a ())` failing to implement `Eq` itself.) + let structural_teq_def_id = + infcx.tcx.require_lang_item(LangItem::StructuralTeq, Some(cause.span)); + ocx.register_bound(cause, ty::ParamEnv::empty(), adt_ty, structural_teq_def_id); + + // We deliberately skip *reporting* fulfillment errors (via + // `report_fulfillment_errors`), for two reasons: + // + // 1. The error messages would mention `std::marker::StructuralPartialEq` + // (a trait which is solely meant as an implementation detail + // for now), and + // + // 2. We are sometimes doing future-incompatibility lints for + // now, so we do not want unconditional errors here. + ocx.select_all_or_error().is_empty() +} + +pub fn provide(providers: &mut Providers) { + providers.has_structural_eq_impls = has_structural_eq_impls; +} |