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Remove LatticeDir trait.
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It's no longer necessary now that the `glb` and `lub` modules have been
merged.
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@nnethercote
nnethercote committed Oct 3, 2024
1 parent 0aab101 commit ee227de
Showing 1 changed file with 69 additions and 104 deletions.
173 changes: 69 additions & 104 deletions compiler/rustc_infer/src/infer/relate/lattice.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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<InferCtxt<'tcx>> {
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<i32>`, then we current compare `v` to the RHS first,
// which will instantiate `v` with `Box<i32>`. Then when `v`
// is compared to the LHS, we instantiate LHS with `Box<i32>`.
// 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<i32>`. 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 {
Expand Down Expand Up @@ -173,9 +83,70 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> 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<i32>`, then we current compare `v` to the RHS first,
// which will instantiate `v` with `Box<i32>`. Then when `v`
// is compared to the LHS, we instantiate LHS with `Box<i32>`.
// 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<i32>`. 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")]
Expand Down Expand Up @@ -231,15 +202,13 @@ impl<'tcx> TypeRelation<TyCtxt<'tcx>> 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 {
Expand All @@ -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<InferCtxt<'tcx>> for LatticeOp<'_, '_, 'tcx> {
Expand Down

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