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use rustc_middle::mir::interpret::InterpResult;
use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor};
use std::convert::TryInto;
use std::ops::ControlFlow;
/// Checks whether a type contains generic parameters which require substitution.
///
/// In case it does, returns a `TooGeneric` const eval error. Note that due to polymorphization
/// types may be "concrete enough" even though they still contain generic parameters in
/// case these parameters are unused.
pub(crate) fn ensure_monomorphic_enough<'tcx, T>(tcx: TyCtxt<'tcx>, ty: T) -> InterpResult<'tcx>
where
T: TypeVisitable<'tcx>,
{
debug!("ensure_monomorphic_enough: ty={:?}", ty);
if !ty.needs_subst() {
return Ok(());
}
struct FoundParam;
struct UsedParamsNeedSubstVisitor<'tcx> {
tcx: TyCtxt<'tcx>,
}
impl<'tcx> TypeVisitor<'tcx> for UsedParamsNeedSubstVisitor<'tcx> {
type BreakTy = FoundParam;
fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
if !ty.needs_subst() {
return ControlFlow::CONTINUE;
}
match *ty.kind() {
ty::Param(_) => ControlFlow::Break(FoundParam),
ty::Closure(def_id, substs)
| ty::Generator(def_id, substs, ..)
| ty::FnDef(def_id, substs) => {
let instance = ty::InstanceDef::Item(ty::WithOptConstParam::unknown(def_id));
let unused_params = self.tcx.unused_generic_params(instance);
for (index, subst) in substs.into_iter().enumerate() {
let index = index
.try_into()
.expect("more generic parameters than can fit into a `u32`");
let is_used = unused_params.contains(index).map_or(true, |unused| !unused);
// Only recurse when generic parameters in fns, closures and generators
// are used and require substitution.
// Just in case there are closures or generators within this subst,
// recurse.
if is_used && subst.needs_subst() {
return subst.visit_with(self);
}
}
ControlFlow::CONTINUE
}
_ => ty.super_visit_with(self),
}
}
fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
match c.kind() {
ty::ConstKind::Param(..) => ControlFlow::Break(FoundParam),
_ => c.super_visit_with(self),
}
}
}
let mut vis = UsedParamsNeedSubstVisitor { tcx };
if matches!(ty.visit_with(&mut vis), ControlFlow::Break(FoundParam)) {
throw_inval!(TooGeneric);
} else {
Ok(())
}
}
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