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Make const bound handling more like types/regions.

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Currently there is `Ty` and `BoundTy`, and `Region` and `BoundRegion`,
and `Const` and... `BoundVar`. An annoying inconsistency.

This commit repurposes the existing `BoundConst`, which was barely used,
so it's the partner to `Const`. Unlike `BoundTy`/`BoundRegion` it lacks
a `kind` field but it's still nice to have because it makes the const
code more similar to the ty/region code everywhere.

The commit also removes `impl From<BoundVar> for BoundTy`, which has a
single use and doesn't seem worth it.

These changes fix the "FIXME: We really should have a separate
`BoundConst` for consts".
This commit is contained in:
Nicholas Nethercote 2025-07-30 14:21:00 +10:00
parent 94cc5bb962
commit 507dec4dc3
21 changed files with 82 additions and 69 deletions
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4
compiler/rustc_borrowck/src/type_check/relate_tys.rs
View File

@ -187,7 +187,7 @@ impl<'a, 'b, 'tcx> NllTypeRelating<'a, 'b, 'tcx> {
types: &mut |_bound_ty: ty::BoundTy| {
unreachable!("we only replace regions in nll_relate, not types")
},
consts: &mut |_bound_var: ty::BoundVar| {
consts: &mut |_bound_const: ty::BoundConst| {
unreachable!("we only replace regions in nll_relate, not consts")
},
};
@ -226,7 +226,7 @@ impl<'a, 'b, 'tcx> NllTypeRelating<'a, 'b, 'tcx> {
types: &mut |_bound_ty: ty::BoundTy| {
unreachable!("we only replace regions in nll_relate, not types")
},
consts: &mut |_bound_var: ty::BoundVar| {
consts: &mut |_bound_const: ty::BoundConst| {
unreachable!("we only replace regions in nll_relate, not consts")
},
};

2
compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
View File

@ -2498,7 +2498,7 @@ fn param_env_with_gat_bounds<'tcx>(
ty::Const::new_bound(
tcx,
ty::INNERMOST,
ty::BoundVar::from_usize(bound_vars.len() - 1),
ty::BoundConst { var: ty::BoundVar::from_usize(bound_vars.len() - 1) },
)
.into()
}

10
compiler/rustc_hir_analysis/src/collect/item_bounds.rs
View File

@ -189,7 +189,7 @@ fn remap_gat_vars_and_recurse_into_nested_projections<'tcx>(
}
ty::GenericArgKind::Const(ct) => {
if let ty::ConstKind::Bound(ty::INNERMOST, bv) = ct.kind() {
mapping.insert(bv, tcx.mk_param_from_def(param))
mapping.insert(bv.var, tcx.mk_param_from_def(param))
} else {
return None;
}
@ -307,16 +307,16 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for MapAndCompressBoundVars<'tcx> {
return ct;
}
if let ty::ConstKind::Bound(binder, old_var) = ct.kind()
if let ty::ConstKind::Bound(binder, old_bound) = ct.kind()
&& self.binder == binder
{
let mapped = if let Some(mapped) = self.mapping.get(&old_var) {
let mapped = if let Some(mapped) = self.mapping.get(&old_bound.var) {
mapped.expect_const()
} else {
let var = ty::BoundVar::from_usize(self.still_bound_vars.len());
self.still_bound_vars.push(ty::BoundVariableKind::Const);
let mapped = ty::Const::new_bound(self.tcx, ty::INNERMOST, var);
self.mapping.insert(old_var, mapped.into());
let mapped = ty::Const::new_bound(self.tcx, ty::INNERMOST, ty::BoundConst { var });
self.mapping.insert(old_bound.var, mapped.into());
mapped
};

2
compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
View File

@ -1077,7 +1077,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for GenericParamAndBoundVarCollector<'_, 't
ty::ConstKind::Param(param) => {
self.params.insert(param.index);
}
ty::ConstKind::Bound(db, ty::BoundVar { .. }) if db >= self.depth => {
ty::ConstKind::Bound(db, _) if db >= self.depth => {
let guar = self.cx.dcx().delayed_bug("unexpected escaping late-bound const var");
return ControlFlow::Break(guar);
}

8
compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
View File

@ -2107,9 +2107,11 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
let name = tcx.item_name(param_def_id);
ty::Const::new_param(tcx, ty::ParamConst::new(index, name))
}
Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => {
ty::Const::new_bound(tcx, debruijn, ty::BoundVar::from_u32(index))
}
Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => ty::Const::new_bound(
tcx,
debruijn,
ty::BoundConst { var: ty::BoundVar::from_u32(index) },
),
Some(rbv::ResolvedArg::Error(guar)) => ty::Const::new_error(tcx, guar),
arg => bug!("unexpected bound var resolution for {:?}: {arg:?}", path_hir_id),
}

6
compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
View File

@ -752,7 +752,8 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
) -> Ty<'tcx> {
debug_assert!(!self.infcx.is_some_and(|infcx| ty_var != infcx.shallow_resolve(ty_var)));
let var = self.canonical_var(var_kind, ty_var.into());
Ty::new_bound(self.tcx, self.binder_index, var.into())
let bt = ty::BoundTy { var, kind: ty::BoundTyKind::Anon };
Ty::new_bound(self.tcx, self.binder_index, bt)
}
/// Given a type variable `const_var` of the given kind, first check
@ -768,6 +769,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
!self.infcx.is_some_and(|infcx| ct_var != infcx.shallow_resolve_const(ct_var))
);
let var = self.canonical_var(var_kind, ct_var.into());
ty::Const::new_bound(self.tcx, self.binder_index, var)
let bc = ty::BoundConst { var };
ty::Const::new_bound(self.tcx, self.binder_index, bc)
}
}

4
compiler/rustc_infer/src/infer/canonical/instantiate.rs
View File

@ -133,7 +133,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for CanonicalInstantiator<'tcx> {
fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
match ct.kind() {
ty::ConstKind::Bound(debruijn, bound_const) if debruijn == self.current_index => {
self.var_values[bound_const.as_usize()].expect_const()
self.var_values[bound_const.var.as_usize()].expect_const()
}
_ => ct.super_fold_with(self),
}
@ -217,7 +217,7 @@ fn highest_var_in_clauses<'tcx>(c: ty::Clauses<'tcx>) -> usize {
if let ty::ConstKind::Bound(debruijn, bound_const) = ct.kind()
&& debruijn == self.current_index
{
self.max_var = self.max_var.max(bound_const.as_usize());
self.max_var = self.max_var.max(bound_const.var.as_usize());
} else if ct.has_vars_bound_at_or_above(self.current_index) {
ct.super_visit_with(self);
}

6
compiler/rustc_infer/src/infer/canonical/query_response.rs
View File

@ -433,12 +433,12 @@ impl<'tcx> InferCtxt<'tcx> {
}
GenericArgKind::Lifetime(result_value) => {
// e.g., here `result_value` might be `'?1` in the example above...
if let ty::ReBound(debruijn, br) = result_value.kind() {
if let ty::ReBound(debruijn, b) = result_value.kind() {
// ... in which case we would set `canonical_vars[0]` to `Some('static)`.
// We only allow a `ty::INNERMOST` index in generic parameters.
assert_eq!(debruijn, ty::INNERMOST);
opt_values[br.var] = Some(*original_value);
opt_values[b.var] = Some(*original_value);
}
}
GenericArgKind::Const(result_value) => {
@ -447,7 +447,7 @@ impl<'tcx> InferCtxt<'tcx> {
// We only allow a `ty::INNERMOST` index in generic parameters.
assert_eq!(debruijn, ty::INNERMOST);
opt_values[b] = Some(*original_value);
opt_values[b.var] = Some(*original_value);
}
}
}

4
compiler/rustc_infer/src/infer/mod.rs
View File

@ -1208,8 +1208,8 @@ impl<'tcx> InferCtxt<'tcx> {
fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx> {
self.args[bt.var.index()].expect_ty()
}
fn replace_const(&mut self, bv: ty::BoundVar) -> ty::Const<'tcx> {
self.args[bv.index()].expect_const()
fn replace_const(&mut self, bc: ty::BoundConst) -> ty::Const<'tcx> {
self.args[bc.var.index()].expect_const()
}
}
let delegate = ToFreshVars { args };

4
compiler/rustc_infer/src/infer/relate/higher_ranked.rs
View File

@ -45,10 +45,10 @@ impl<'tcx> InferCtxt<'tcx> {
ty::PlaceholderType { universe: next_universe, bound: bound_ty },
)
},
consts: &mut |bound_var: ty::BoundVar| {
consts: &mut |bound_const: ty::BoundConst| {
ty::Const::new_placeholder(
self.tcx,
ty::PlaceholderConst { universe: next_universe, bound: bound_var },
ty::PlaceholderConst { universe: next_universe, bound: bound_const },
)
},
};

14
compiler/rustc_middle/src/ty/consts.rs
View File

@ -93,9 +93,9 @@ impl<'tcx> Const<'tcx> {
pub fn new_bound(
tcx: TyCtxt<'tcx>,
debruijn: ty::DebruijnIndex,
var: ty::BoundVar,
bound_const: ty::BoundConst,
) -> Const<'tcx> {
Const::new(tcx, ty::ConstKind::Bound(debruijn, var))
Const::new(tcx, ty::ConstKind::Bound(debruijn, bound_const))
}
#[inline]
@ -168,12 +168,16 @@ impl<'tcx> rustc_type_ir::inherent::Const<TyCtxt<'tcx>> for Const<'tcx> {
Const::new_var(tcx, vid)
}
fn new_bound(interner: TyCtxt<'tcx>, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self {
Const::new_bound(interner, debruijn, var)
fn new_bound(
interner: TyCtxt<'tcx>,
debruijn: ty::DebruijnIndex,
bound_const: ty::BoundConst,
) -> Self {
Const::new_bound(interner, debruijn, bound_const)
}
fn new_anon_bound(tcx: TyCtxt<'tcx>, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self {
Const::new_bound(tcx, debruijn, var)
Const::new_bound(tcx, debruijn, ty::BoundConst { var })
}
fn new_placeholder(tcx: TyCtxt<'tcx>, placeholder: ty::PlaceholderConst) -> Self {

2
compiler/rustc_middle/src/ty/context.rs
View File

@ -152,7 +152,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
type PlaceholderConst = ty::PlaceholderConst;
type ParamConst = ty::ParamConst;
type BoundConst = ty::BoundVar;
type BoundConst = ty::BoundConst;
type ValueConst = ty::Value<'tcx>;
type ExprConst = ty::Expr<'tcx>;
type ValTree = ty::ValTree<'tcx>;

24
compiler/rustc_middle/src/ty/fold.rs
View File

@ -3,7 +3,7 @@ use rustc_hir::def_id::DefId;
use rustc_type_ir::data_structures::DelayedMap;
use crate::ty::{
self, Binder, BoundTy, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
self, Binder, BoundConst, BoundTy, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
TypeVisitableExt,
};
@ -60,7 +60,7 @@ where
pub trait BoundVarReplacerDelegate<'tcx> {
fn replace_region(&mut self, br: ty::BoundRegion) -> ty::Region<'tcx>;
fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx>;
fn replace_const(&mut self, bv: ty::BoundVar) -> ty::Const<'tcx>;
fn replace_const(&mut self, bc: ty::BoundConst) -> ty::Const<'tcx>;
}
/// A simple delegate taking 3 mutable functions. The used functions must
@ -69,7 +69,7 @@ pub trait BoundVarReplacerDelegate<'tcx> {
pub struct FnMutDelegate<'a, 'tcx> {
pub regions: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
pub types: &'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a),
pub consts: &'a mut (dyn FnMut(ty::BoundVar) -> ty::Const<'tcx> + 'a),
pub consts: &'a mut (dyn FnMut(ty::BoundConst) -> ty::Const<'tcx> + 'a),
}
impl<'a, 'tcx> BoundVarReplacerDelegate<'tcx> for FnMutDelegate<'a, 'tcx> {
@ -79,8 +79,8 @@ impl<'a, 'tcx> BoundVarReplacerDelegate<'tcx> for FnMutDelegate<'a, 'tcx> {
fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx> {
(self.types)(bt)
}
fn replace_const(&mut self, bv: ty::BoundVar) -> ty::Const<'tcx> {
(self.consts)(bv)
fn replace_const(&mut self, bc: ty::BoundConst) -> ty::Const<'tcx> {
(self.consts)(bc)
}
}
@ -300,7 +300,13 @@ impl<'tcx> TyCtxt<'tcx> {
ty::BoundTy { var: shift_bv(t.var), kind: t.kind },
)
},
consts: &mut |c| ty::Const::new_bound(self, ty::INNERMOST, shift_bv(c)),
consts: &mut |c| {
ty::Const::new_bound(
self,
ty::INNERMOST,
ty::BoundConst { var: shift_bv(c.var) },
)
},
},
)
}
@ -343,12 +349,12 @@ impl<'tcx> TyCtxt<'tcx> {
.expect_ty();
Ty::new_bound(self.tcx, ty::INNERMOST, BoundTy { var, kind })
}
fn replace_const(&mut self, bv: ty::BoundVar) -> ty::Const<'tcx> {
let entry = self.map.entry(bv);
fn replace_const(&mut self, bc: ty::BoundConst) -> ty::Const<'tcx> {
let entry = self.map.entry(bc.var);
let index = entry.index();
let var = ty::BoundVar::from_usize(index);
let () = entry.or_insert_with(|| ty::BoundVariableKind::Const).expect_const();
ty::Const::new_bound(self.tcx, ty::INNERMOST, var)
ty::Const::new_bound(self.tcx, ty::INNERMOST, BoundConst { var })
}
}

23
compiler/rustc_middle/src/ty/mod.rs
View File

@ -968,34 +968,43 @@ impl<'tcx> rustc_type_ir::inherent::PlaceholderLike<TyCtxt<'tcx>> for Placeholde
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
#[derive(TyEncodable, TyDecodable)]
pub struct BoundConst<'tcx> {
pub struct BoundConst {
pub var: BoundVar,
pub ty: Ty<'tcx>,
}
pub type PlaceholderConst = Placeholder<BoundVar>;
impl<'tcx> rustc_type_ir::inherent::BoundVarLike<TyCtxt<'tcx>> for BoundConst {
fn var(self) -> BoundVar {
self.var
}
fn assert_eq(self, _var: ty::BoundVariableKind) {
unreachable!()
}
}
pub type PlaceholderConst = Placeholder<BoundConst>;
impl<'tcx> rustc_type_ir::inherent::PlaceholderLike<TyCtxt<'tcx>> for PlaceholderConst {
type Bound = BoundVar;
type Bound = BoundConst;
fn universe(self) -> UniverseIndex {
self.universe
}
fn var(self) -> BoundVar {
self.bound
self.bound.var
}
fn with_updated_universe(self, ui: UniverseIndex) -> Self {
Placeholder { universe: ui, ..self }
}
fn new(ui: UniverseIndex, bound: BoundVar) -> Self {
fn new(ui: UniverseIndex, bound: BoundConst) -> Self {
Placeholder { universe: ui, bound }
}
fn new_anon(ui: UniverseIndex, var: BoundVar) -> Self {
Placeholder { universe: ui, bound: var }
Placeholder { universe: ui, bound: BoundConst { var } }
}
}

6
compiler/rustc_middle/src/ty/sty.rs
View File

@ -403,12 +403,6 @@ pub enum BoundTyKind {
Param(DefId),
}
impl From<BoundVar> for BoundTy {
fn from(var: BoundVar) -> Self {
BoundTy { var, kind: BoundTyKind::Anon }
}
}
/// Constructors for `Ty`
impl<'tcx> Ty<'tcx> {
/// Avoid using this in favour of more specific `new_*` methods, where possible.

6
compiler/rustc_middle/src/ty/typeck_results.rs
View File

@ -789,10 +789,10 @@ impl<'tcx> IsIdentity for CanonicalUserType<'tcx> {
},
GenericArgKind::Lifetime(r) => match r.kind() {
ty::ReBound(debruijn, br) => {
ty::ReBound(debruijn, b) => {
// We only allow a `ty::INNERMOST` index in generic parameters.
assert_eq!(debruijn, ty::INNERMOST);
cvar == br.var
cvar == b.var
}
_ => false,
},
@ -801,7 +801,7 @@ impl<'tcx> IsIdentity for CanonicalUserType<'tcx> {
ty::ConstKind::Bound(debruijn, b) => {
// We only allow a `ty::INNERMOST` index in generic parameters.
assert_eq!(debruijn, ty::INNERMOST);
cvar == b
cvar == b.var
}
_ => false,
},

5
compiler/rustc_trait_selection/src/traits/coherence.rs
View File

@ -535,7 +535,10 @@ fn plug_infer_with_placeholders<'tcx>(
ct,
ty::Const::new_placeholder(
self.infcx.tcx,
ty::Placeholder { universe: self.universe, bound: self.next_var() },
ty::Placeholder {
universe: self.universe,
bound: ty::BoundConst { var: self.next_var() },
},
),
)
else {

5
compiler/rustc_trait_selection/src/traits/mod.rs
View File

@ -706,7 +706,10 @@ fn replace_param_and_infer_args_with_placeholder<'tcx>(
self.idx += 1;
ty::Const::new_placeholder(
self.tcx,
ty::PlaceholderConst { universe: ty::UniverseIndex::ROOT, bound: idx },
ty::PlaceholderConst {
universe: ty::UniverseIndex::ROOT,
bound: ty::BoundConst { var: idx },
},
)
} else {
c.super_fold_with(self)

4
compiler/rustc_trait_selection/src/traits/util.rs
View File

@ -222,7 +222,7 @@ pub struct PlaceholderReplacer<'a, 'tcx> {
infcx: &'a InferCtxt<'tcx>,
mapped_regions: FxIndexMap<ty::PlaceholderRegion, ty::BoundRegion>,
mapped_types: FxIndexMap<ty::PlaceholderType, ty::BoundTy>,
mapped_consts: FxIndexMap<ty::PlaceholderConst, ty::BoundVar>,
mapped_consts: FxIndexMap<ty::PlaceholderConst, ty::BoundConst>,
universe_indices: &'a [Option<ty::UniverseIndex>],
current_index: ty::DebruijnIndex,
}
@ -232,7 +232,7 @@ impl<'a, 'tcx> PlaceholderReplacer<'a, 'tcx> {
infcx: &'a InferCtxt<'tcx>,
mapped_regions: FxIndexMap<ty::PlaceholderRegion, ty::BoundRegion>,
mapped_types: FxIndexMap<ty::PlaceholderType, ty::BoundTy>,
mapped_consts: FxIndexMap<ty::PlaceholderConst, ty::BoundVar>,
mapped_consts: FxIndexMap<ty::PlaceholderConst, ty::BoundConst>,
universe_indices: &'a [Option<ty::UniverseIndex>],
value: T,
) -> T {

2
compiler/rustc_type_ir/src/inherent.rs
View File

@ -251,7 +251,7 @@ pub trait Const<I: Interner<Const = Self>>:
fn new_var(interner: I, var: ty::ConstVid) -> Self;
fn new_bound(interner: I, debruijn: ty::DebruijnIndex, var: I::BoundConst) -> Self;
fn new_bound(interner: I, debruijn: ty::DebruijnIndex, bound_const: I::BoundConst) -> Self;
fn new_anon_bound(interner: I, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self;

10
compiler/rustc_type_ir/src/lib.rs
View File

@ -387,16 +387,6 @@ rustc_index::newtype_index! {
pub struct BoundVar {}
}
impl<I: Interner> inherent::BoundVarLike<I> for BoundVar {
fn var(self) -> BoundVar {
self
}
fn assert_eq(self, _var: I::BoundVarKind) {
unreachable!("FIXME: We really should have a separate `BoundConst` for consts")
}
}
/// Represents the various closure traits in the language. This
/// will determine the type of the environment (`self`, in the
/// desugaring) argument that the closure expects.