diff --git a/compiler/rustc_infer/src/infer/relate/lattice.rs b/compiler/rustc_infer/src/infer/relate/lattice.rs index 1e4db70898686..9564baa6ab287 100644 --- a/compiler/rustc_infer/src/infer/relate/lattice.rs +++ b/compiler/rustc_infer/src/infer/relate/lattice.rs @@ -26,96 +26,6 @@ use tracing::{debug, instrument}; use super::StructurallyRelateAliases; use super::combine::{CombineFields, PredicateEmittingRelation}; use crate::infer::{DefineOpaqueTypes, InferCtxt, SubregionOrigin}; -use crate::traits::ObligationCause; - -/// Trait for returning data about a lattice, and for abstracting -/// over the "direction" of the lattice operation (LUB/GLB). -/// -/// GLB moves "down" the lattice (to smaller values); LUB moves -/// "up" the lattice (to bigger values). -trait LatticeDir<'f, 'tcx>: PredicateEmittingRelation> { - fn infcx(&self) -> &'f InferCtxt<'tcx>; - - fn cause(&self) -> &ObligationCause<'tcx>; - - fn define_opaque_types(&self) -> DefineOpaqueTypes; - - // Relates the type `v` to `a` and `b` such that `v` represents - // the LUB/GLB of `a` and `b` as appropriate. - // - // Subtle hack: ordering *may* be significant here. This method - // relates `v` to `a` first, which may help us to avoid unnecessary - // type variable obligations. See caller for details. - fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()>; -} - -/// Relates two types using a given lattice. -#[instrument(skip(this), level = "debug")] -fn super_lattice_tys<'a, 'tcx: 'a, L>( - this: &mut L, - a: Ty<'tcx>, - b: Ty<'tcx>, -) -> RelateResult<'tcx, Ty<'tcx>> -where - L: LatticeDir<'a, 'tcx>, -{ - if a == b { - return Ok(a); - } - - let infcx = this.infcx(); - - let a = infcx.shallow_resolve(a); - let b = infcx.shallow_resolve(b); - - match (a.kind(), b.kind()) { - // If one side is known to be a variable and one is not, - // create a variable (`v`) to represent the LUB. Make sure to - // relate `v` to the non-type-variable first (by passing it - // first to `relate_bound`). Otherwise, we would produce a - // subtype obligation that must then be processed. - // - // Example: if the LHS is a type variable, and RHS is - // `Box`, then we current compare `v` to the RHS first, - // which will instantiate `v` with `Box`. Then when `v` - // is compared to the LHS, we instantiate LHS with `Box`. - // But if we did in reverse order, we would create a `v <: - // LHS` (or vice versa) constraint and then instantiate - // `v`. This would require further processing to achieve same - // end-result; in particular, this screws up some of the logic - // in coercion, which expects LUB to figure out that the LHS - // is (e.g.) `Box`. A more obvious solution might be to - // iterate on the subtype obligations that are returned, but I - // think this suffices. -nmatsakis - (&ty::Infer(TyVar(..)), _) => { - let v = infcx.next_ty_var(this.cause().span); - this.relate_bound(v, b, a)?; - Ok(v) - } - (_, &ty::Infer(TyVar(..))) => { - let v = infcx.next_ty_var(this.cause().span); - this.relate_bound(v, a, b)?; - Ok(v) - } - - ( - &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }), - &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }), - ) if a_def_id == b_def_id => infcx.super_combine_tys(this, a, b), - - (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _) - | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. })) - if this.define_opaque_types() == DefineOpaqueTypes::Yes - && def_id.is_local() - && !this.infcx().next_trait_solver() => - { - this.register_goals(infcx.handle_opaque_type(a, b, this.span(), this.param_env())?); - Ok(a) - } - - _ => infcx.super_combine_tys(this, a, b), - } -} #[derive(Clone, Copy)] pub(crate) enum LatticeOpKind { @@ -173,9 +83,70 @@ impl<'tcx> TypeRelation> for LatticeOp<'_, '_, 'tcx> { } } + /// Relates two types using a given lattice. #[instrument(skip(self), level = "trace")] fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { - super_lattice_tys(self, a, b) + if a == b { + return Ok(a); + } + + let infcx = self.fields.infcx; + + let a = infcx.shallow_resolve(a); + let b = infcx.shallow_resolve(b); + + match (a.kind(), b.kind()) { + // If one side is known to be a variable and one is not, + // create a variable (`v`) to represent the LUB. Make sure to + // relate `v` to the non-type-variable first (by passing it + // first to `relate_bound`). Otherwise, we would produce a + // subtype obligation that must then be processed. + // + // Example: if the LHS is a type variable, and RHS is + // `Box`, then we current compare `v` to the RHS first, + // which will instantiate `v` with `Box`. Then when `v` + // is compared to the LHS, we instantiate LHS with `Box`. + // But if we did in reverse order, we would create a `v <: + // LHS` (or vice versa) constraint and then instantiate + // `v`. This would require further processing to achieve same + // end-result; in particular, this screws up some of the logic + // in coercion, which expects LUB to figure out that the LHS + // is (e.g.) `Box`. A more obvious solution might be to + // iterate on the subtype obligations that are returned, but I + // think this suffices. -nmatsakis + (&ty::Infer(TyVar(..)), _) => { + let v = infcx.next_ty_var(self.fields.trace.cause.span); + self.relate_bound(v, b, a)?; + Ok(v) + } + (_, &ty::Infer(TyVar(..))) => { + let v = infcx.next_ty_var(self.fields.trace.cause.span); + self.relate_bound(v, a, b)?; + Ok(v) + } + + ( + &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }), + &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }), + ) if a_def_id == b_def_id => infcx.super_combine_tys(self, a, b), + + (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _) + | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. })) + if self.fields.define_opaque_types == DefineOpaqueTypes::Yes + && def_id.is_local() + && !infcx.next_trait_solver() => + { + self.register_goals(infcx.handle_opaque_type( + a, + b, + self.span(), + self.param_env(), + )?); + Ok(a) + } + + _ => infcx.super_combine_tys(self, a, b), + } } #[instrument(skip(self), level = "trace")] @@ -231,15 +202,13 @@ impl<'tcx> TypeRelation> for LatticeOp<'_, '_, 'tcx> { } } -impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for LatticeOp<'combine, 'infcx, 'tcx> { - fn infcx(&self) -> &'infcx InferCtxt<'tcx> { - self.fields.infcx - } - - fn cause(&self) -> &ObligationCause<'tcx> { - &self.fields.trace.cause - } - +impl<'combine, 'infcx, 'tcx> LatticeOp<'combine, 'infcx, 'tcx> { + // Relates the type `v` to `a` and `b` such that `v` represents + // the LUB/GLB of `a` and `b` as appropriate. + // + // Subtle hack: ordering *may* be significant here. This method + // relates `v` to `a` first, which may help us to avoid unnecessary + // type variable obligations. See caller for details. fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> { let mut sub = self.fields.sub(); match self.kind { @@ -254,10 +223,6 @@ impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for LatticeOp<'combine, 'i } Ok(()) } - - fn define_opaque_types(&self) -> DefineOpaqueTypes { - self.fields.define_opaque_types - } } impl<'tcx> PredicateEmittingRelation> for LatticeOp<'_, '_, 'tcx> {