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Rollup merge of rust-lang#73066 - ecstatic-morse:query-structural-eq2…
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…, r=pnkfelix

Querify whether a type has structural equality (Take 2)

Alternative to rust-lang#72177.

Unlike in rust-lang#72177, this helper method works for all types, falling back to a query for `TyKind::Adt`s that determines whether the `{Partial,}StructuralEq` traits are implemented.

This is my preferred interface for this method. I think this is better than just documenting that the helper only works for ADTs. If others disagree, we can just merge rust-lang#72177 with the fixes applied. This has already taken far too long.
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Dylan-DPC authored Jun 12, 2020
2 parents f27f659 + 2801761 commit aeb8dd7
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11 changes: 11 additions & 0 deletions src/librustc_middle/query/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -789,6 +789,17 @@ rustc_queries! {
desc { "computing whether `{}` needs drop", env.value }
}

/// Query backing `TyS::is_structural_eq_shallow`.
///
/// This is only correct for ADTs. Call `is_structural_eq_shallow` to handle all types
/// correctly.
query has_structural_eq_impls(ty: Ty<'tcx>) -> bool {
desc {
"computing whether `{:?}` implements `PartialStructuralEq` and `StructuralEq`",
ty
}
}

/// A list of types where the ADT requires drop if and only if any of
/// those types require drop. If the ADT is known to always need drop
/// then `Err(AlwaysRequiresDrop)` is returned.
Expand Down
51 changes: 51 additions & 0 deletions src/librustc_middle/ty/util.rs
Original file line number Diff line number Diff line change
Expand Up @@ -778,6 +778,57 @@ impl<'tcx> ty::TyS<'tcx> {
}
}

/// Returns `true` if equality for this type is both reflexive and structural.
///
/// Reflexive equality for a type is indicated by an `Eq` impl for that type.
///
/// Primitive types (`u32`, `str`) have structural equality by definition. For composite data
/// types, equality for the type as a whole is structural when it is the same as equality
/// between all components (fields, array elements, etc.) of that type. For ADTs, structural
/// equality is indicated by an implementation of `PartialStructuralEq` and `StructuralEq` for
/// that type.
///
/// This function is "shallow" because it may return `true` for a composite type whose fields
/// are not `StructuralEq`. For example, `[T; 4]` has structural equality regardless of `T`
/// because equality for arrays is determined by the equality of each array element. If you
/// want to know whether a given call to `PartialEq::eq` will proceed structurally all the way
/// down, you will need to use a type visitor.
#[inline]
pub fn is_structural_eq_shallow(&'tcx self, tcx: TyCtxt<'tcx>) -> bool {
match self.kind {
// Look for an impl of both `PartialStructuralEq` and `StructuralEq`.
Adt(..) => tcx.has_structural_eq_impls(self),

// Primitive types that satisfy `Eq`.
Bool | Char | Int(_) | Uint(_) | Str | Never => true,

// Composite types that satisfy `Eq` when all of their fields do.
//
// Because this function is "shallow", we return `true` for these composites regardless
// of the type(s) contained within.
Ref(..) | Array(..) | Slice(_) | Tuple(..) => true,

// Raw pointers use bitwise comparison.
RawPtr(_) | FnPtr(_) => true,

// Floating point numbers are not `Eq`.
Float(_) => false,

// Conservatively return `false` for all others...

// Anonymous function types
FnDef(..) | Closure(..) | Dynamic(..) | Generator(..) => false,

// Generic or inferred types
//
// FIXME(ecstaticmorse): Maybe we should `bug` here? This should probably only be
// called for known, fully-monomorphized types.
Projection(_) | Opaque(..) | Param(_) | Bound(..) | Placeholder(_) | Infer(_) => false,

Foreign(_) | GeneratorWitness(..) | Error => false,
}
}

pub fn same_type(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
match (&a.kind, &b.kind) {
(&Adt(did_a, substs_a), &Adt(did_b, substs_b)) => {
Expand Down
6 changes: 1 addition & 5 deletions src/librustc_mir/transform/check_consts/qualifs.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,6 @@
//!
//! See the `Qualif` trait for more info.
use rustc_infer::infer::TyCtxtInferExt;
use rustc_middle::mir::*;
use rustc_middle::ty::{self, subst::SubstsRef, AdtDef, Ty};
use rustc_span::DUMMY_SP;
Expand Down Expand Up @@ -137,10 +136,7 @@ impl Qualif for CustomEq {
substs: SubstsRef<'tcx>,
) -> bool {
let ty = cx.tcx.mk_ty(ty::Adt(adt, substs));
let id = cx.tcx.hir().local_def_id_to_hir_id(cx.def_id.as_local().unwrap());
cx.tcx
.infer_ctxt()
.enter(|infcx| !traits::type_marked_structural(id, cx.body.span, &infcx, ty))
!ty.is_structural_eq_shallow(cx.tcx)
}
}

Expand Down
2 changes: 1 addition & 1 deletion src/librustc_mir_build/hair/pattern/const_to_pat.rs
Original file line number Diff line number Diff line change
Expand Up @@ -80,7 +80,7 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
}

fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
traits::type_marked_structural(self.id, self.span, &self.infcx, ty)
ty.is_structural_eq_shallow(self.infcx.tcx)
}

fn to_pat(
Expand Down
2 changes: 1 addition & 1 deletion src/librustc_trait_selection/traits/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,6 @@ pub use self::specialize::specialization_graph::FutureCompatOverlapError;
pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
pub use self::specialize::{specialization_graph, translate_substs, OverlapError};
pub use self::structural_match::search_for_structural_match_violation;
pub use self::structural_match::type_marked_structural;
pub use self::structural_match::NonStructuralMatchTy;
pub use self::util::{elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs};
pub use self::util::{expand_trait_aliases, TraitAliasExpander};
Expand Down Expand Up @@ -553,6 +552,7 @@ fn type_implements_trait<'tcx>(

pub fn provide(providers: &mut ty::query::Providers<'_>) {
object_safety::provide(providers);
structural_match::provide(providers);
*providers = ty::query::Providers {
specialization_graph_of: specialize::specialization_graph_provider,
specializes: specialize::specializes,
Expand Down
34 changes: 21 additions & 13 deletions src/librustc_trait_selection/traits/structural_match.rs
Original file line number Diff line number Diff line change
@@ -1,10 +1,11 @@
use crate::infer::{InferCtxt, TyCtxtInferExt};
use crate::traits::ObligationCause;
use crate::traits::{self, ConstPatternStructural, TraitEngine};
use crate::traits::{self, TraitEngine};

use rustc_data_structures::fx::FxHashSet;
use rustc_hir as hir;
use rustc_hir::lang_items::{StructuralPeqTraitLangItem, StructuralTeqTraitLangItem};
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt, TypeFoldable, TypeVisitor};
use rustc_span::Span;

Expand Down Expand Up @@ -45,14 +46,14 @@ pub enum NonStructuralMatchTy<'tcx> {
/// that arose when the requirement was not enforced completely, see
/// Rust RFC 1445, rust-lang/rust#61188, and rust-lang/rust#62307.
pub fn search_for_structural_match_violation<'tcx>(
id: hir::HirId,
_id: hir::HirId,
span: Span,
tcx: TyCtxt<'tcx>,
ty: Ty<'tcx>,
) -> Option<NonStructuralMatchTy<'tcx>> {
// FIXME: we should instead pass in an `infcx` from the outside.
tcx.infer_ctxt().enter(|infcx| {
let mut search = Search { id, span, infcx, found: None, seen: FxHashSet::default() };
let mut search = Search { infcx, span, found: None, seen: FxHashSet::default() };
ty.visit_with(&mut search);
search.found
})
Expand All @@ -65,27 +66,26 @@ pub fn search_for_structural_match_violation<'tcx>(
///
/// Note that this does *not* recursively check if the substructure of `adt_ty`
/// implements the traits.
pub fn type_marked_structural(
id: hir::HirId,
span: Span,
fn type_marked_structural(
infcx: &InferCtxt<'_, 'tcx>,
adt_ty: Ty<'tcx>,
cause: ObligationCause<'tcx>,
) -> bool {
let mut fulfillment_cx = traits::FulfillmentContext::new();
let cause = ObligationCause::new(span, id, ConstPatternStructural);
// require `#[derive(PartialEq)]`
let structural_peq_def_id = infcx.tcx.require_lang_item(StructuralPeqTraitLangItem, Some(span));
let structural_peq_def_id =
infcx.tcx.require_lang_item(StructuralPeqTraitLangItem, Some(cause.span));
fulfillment_cx.register_bound(
infcx,
ty::ParamEnv::empty(),
adt_ty,
structural_peq_def_id,
cause,
cause.clone(),
);
// 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 cause = ObligationCause::new(span, id, ConstPatternStructural);
let structural_teq_def_id = infcx.tcx.require_lang_item(StructuralTeqTraitLangItem, Some(span));
let structural_teq_def_id =
infcx.tcx.require_lang_item(StructuralTeqTraitLangItem, Some(cause.span));
fulfillment_cx.register_bound(
infcx,
ty::ParamEnv::empty(),
Expand All @@ -110,7 +110,6 @@ pub fn type_marked_structural(
/// find instances of ADTs (specifically structs or enums) that do not implement
/// the structural-match traits (`StructuralPartialEq` and `StructuralEq`).
struct Search<'a, 'tcx> {
id: hir::HirId,
span: Span,

infcx: InferCtxt<'a, 'tcx>,
Expand All @@ -129,7 +128,7 @@ impl Search<'a, 'tcx> {
}

fn type_marked_structural(&self, adt_ty: Ty<'tcx>) -> bool {
type_marked_structural(self.id, self.span, &self.infcx, adt_ty)
adt_ty.is_structural_eq_shallow(self.tcx())
}
}

Expand Down Expand Up @@ -266,3 +265,12 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
false
}
}

pub fn provide(providers: &mut Providers<'_>) {
providers.has_structural_eq_impls = |tcx, ty| {
tcx.infer_ctxt().enter(|infcx| {
let cause = ObligationCause::dummy();
type_marked_structural(&infcx, ty, cause)
})
};
}

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