1 use rustc_middle::mir::interpret::InterpResult;
2 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor};
3 use std::convert::TryInto;
4 use std::ops::ControlFlow;
6 /// Checks whether a type contains generic parameters which require substitution.
8 /// In case it does, returns a `TooGeneric` const eval error. Note that due to polymorphization
9 /// types may be "concrete enough" even though they still contain generic parameters in
10 /// case these parameters are unused.
11 pub(crate) fn ensure_monomorphic_enough<'tcx, T>(tcx: TyCtxt<'tcx>, ty: T) -> InterpResult<'tcx>
13 T: TypeVisitable<'tcx>,
15 debug!("ensure_monomorphic_enough: ty={:?}", ty);
16 if !ty.needs_subst() {
21 struct UsedParamsNeedSubstVisitor<'tcx> {
25 impl<'tcx> TypeVisitor<'tcx> for UsedParamsNeedSubstVisitor<'tcx> {
26 type BreakTy = FoundParam;
28 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
29 if !ty.needs_subst() {
30 return ControlFlow::CONTINUE;
34 ty::Param(_) => ControlFlow::Break(FoundParam),
35 ty::Closure(def_id, substs)
36 | ty::Generator(def_id, substs, ..)
37 | ty::FnDef(def_id, substs) => {
38 let instance = ty::InstanceDef::Item(ty::WithOptConstParam::unknown(def_id));
39 let unused_params = self.tcx.unused_generic_params(instance);
40 for (index, subst) in substs.into_iter().enumerate() {
43 .expect("more generic parameters than can fit into a `u32`");
44 let is_used = unused_params.contains(index).map_or(true, |unused| !unused);
45 // Only recurse when generic parameters in fns, closures and generators
46 // are used and require substitution.
47 // Just in case there are closures or generators within this subst,
49 if is_used && subst.needs_subst() {
50 return subst.visit_with(self);
55 _ => ty.super_visit_with(self),
59 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
61 ty::ConstKind::Param(..) => ControlFlow::Break(FoundParam),
62 _ => c.super_visit_with(self),
67 let mut vis = UsedParamsNeedSubstVisitor { tcx };
68 if matches!(ty.visit_with(&mut vis), ControlFlow::Break(FoundParam)) {
69 throw_inval!(TooGeneric);