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Auto merge of #116167 - RalfJung:structural-eq, r=lcnr

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remove StructuralEq trait

The documentation given for the trait is outdated: *all* function pointers implement `PartialEq` and `Eq` these days. So the `StructuralEq` trait doesn't really seem to have any reason to exist any more.

One side-effect of this PR is that we allow matching on some consts that do not implement `Eq`. However, we already allowed matching on floats and consts containing floats, so this is not new, it is just allowed in more cases now. IMO it makes no sense at all to allow float matching but also sometimes require an `Eq` instance. If we want to require `Eq` we should adjust https://github.com/rust-lang/rust/pull/115893 to check for `Eq`, and rule out float matching for good.

Fixes https://github.com/rust-lang/rust/issues/115881
This commit is contained in:
bors 2024-01-26 00:17:00 +00:00
commit dd2559e08e
76 changed files with 273 additions and 536 deletions
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16
compiler/rustc_ty_utils/src/structural_match.rs
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@ -6,13 +6,12 @@ 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)]`).
/// eligible for structural-match: namely, if it implements
/// `StructuralPartialEq` (which is injected by `#[derive(PartialEq)]`).
///
/// 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 {
/// implements the trait.
fn has_structural_eq_impl<'tcx>(tcx: TyCtxt<'tcx>, adt_ty: Ty<'tcx>) -> bool {
let infcx = &tcx.infer_ctxt().build();
let cause = ObligationCause::dummy();
@ -21,11 +20,6 @@ fn has_structural_eq_impls<'tcx>(tcx: TyCtxt<'tcx>, adt_ty: Ty<'tcx>) -> bool {
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:
@ -40,5 +34,5 @@ fn has_structural_eq_impls<'tcx>(tcx: TyCtxt<'tcx>, adt_ty: Ty<'tcx>) -> bool {
}
pub(crate) fn provide(providers: &mut Providers) {
providers.has_structural_eq_impls = has_structural_eq_impls;
providers.has_structural_eq_impl = has_structural_eq_impl;
}