src/librustc_mir/interpret/util.rs

   1 use rustc_middle::mir::interpret::InterpResult;
   2 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeVisitor};
   3 use std::convert::TryInto;
   4
   5 /// Returns `true` if a used generic parameter requires substitution.
   6 crate fn ensure_monomorphic_enough<'tcx, T>(tcx: TyCtxt<'tcx>, ty: T) -> InterpResult<'tcx>
   7 where
   8     T: TypeFoldable<'tcx>,
   9 {
  10     debug!("ensure_monomorphic_enough: ty={:?}", ty);
  11     if !ty.needs_subst() {
  12         return Ok(());
  13     }
  14
  15     struct UsedParamsNeedSubstVisitor<'tcx> {
  16         tcx: TyCtxt<'tcx>,
  17     };
  18
  19     impl<'tcx> TypeVisitor<'tcx> for UsedParamsNeedSubstVisitor<'tcx> {
  20         fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
  21             if !c.needs_subst() {
  22                 return false;
  23             }
  24
  25             match c.val {
  26                 ty::ConstKind::Param(..) => true,
  27                 _ => c.super_visit_with(self),
  28             }
  29         }
  30
  31         fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
  32             if !ty.needs_subst() {
  33                 return false;
  34             }
  35
  36             match ty.kind {
  37                 ty::Param(_) => true,
  38                 ty::Closure(def_id, substs)
  39                 | ty::Generator(def_id, substs, ..)
  40                 | ty::FnDef(def_id, substs) => {
  41                     let unused_params = self.tcx.unused_generic_params(def_id);
  42                     for (index, subst) in substs.into_iter().enumerate() {
  43                         let index = index
  44                             .try_into()
  45                             .expect("more generic parameters than can fit into a `u32`");
  46                         let is_used =
  47                             unused_params.contains(index).map(|unused| !unused).unwrap_or(true);
  48                         // Only recurse when generic parameters in fns, closures and generators
  49                         // are used and require substitution.
  50                         match (is_used, subst.needs_subst()) {
  51                             // Just in case there are closures or generators within this subst,
  52                             // recurse.
  53                             (true, true) if subst.super_visit_with(self) => {
  54                                 // Only return when we find a parameter so the remaining substs
  55                                 // are not skipped.
  56                                 return true;
  57                             }
  58                             // Confirm that polymorphization replaced the parameter with
  59                             // `ty::Param`/`ty::ConstKind::Param`.
  60                             (false, true) if cfg!(debug_assertions) => match subst.unpack() {
  61                                 ty::subst::GenericArgKind::Type(ty) => {
  62                                     assert!(matches!(ty.kind, ty::Param(_)))
  63                                 }
  64                                 ty::subst::GenericArgKind::Const(ct) => {
  65                                     assert!(matches!(ct.val, ty::ConstKind::Param(_)))
  66                                 }
  67                                 ty::subst::GenericArgKind::Lifetime(..) => (),
  68                             },
  69                             _ => {}
  70                         }
  71                     }
  72                     false
  73                 }
  74                 _ => ty.super_visit_with(self),
  75             }
  76         }
  77     }
  78
  79     let mut vis = UsedParamsNeedSubstVisitor { tcx };
  80     if ty.visit_with(&mut vis) {
  81         throw_inval!(TooGeneric);
  82     } else {
  83         Ok(())
  84     }
  85 }