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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
Download Patch File Download Diff File Expand all files Collapse all files

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),
}