compiler/rustc_middle/src/ty/consts/kind.rs

   1 use super::Const;
   2 use crate::mir;
   3 use crate::mir::interpret::{AllocId, ConstValue, Scalar};
   4 use crate::ty::abstract_const::CastKind;
   5 use crate::ty::subst::{InternalSubsts, SubstsRef};
   6 use crate::ty::ParamEnv;
   7 use crate::ty::{self, List, Ty, TyCtxt, TypeVisitableExt};
   8 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
   9 use rustc_errors::ErrorGuaranteed;
  10 use rustc_hir::def_id::DefId;
  11 use rustc_macros::HashStable;
  12 use rustc_target::abi::Size;
  13
  14 use super::ScalarInt;
  15
  16 /// An unevaluated (potentially generic) constant used in the type-system.
  17 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable, Lift)]
  18 #[derive(Hash, HashStable, TypeFoldable, TypeVisitable)]
  19 pub struct UnevaluatedConst<'tcx> {
  20     pub def: ty::WithOptConstParam<DefId>,
  21     pub substs: SubstsRef<'tcx>,
  22 }
  23
  24 impl rustc_errors::IntoDiagnosticArg for UnevaluatedConst<'_> {
  25     fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
  26         format!("{:?}", self).into_diagnostic_arg()
  27     }
  28 }
  29
  30 impl<'tcx> UnevaluatedConst<'tcx> {
  31     #[inline]
  32     pub fn expand(self) -> mir::UnevaluatedConst<'tcx> {
  33         mir::UnevaluatedConst { def: self.def, substs: self.substs, promoted: None }
  34     }
  35 }
  36
  37 impl<'tcx> UnevaluatedConst<'tcx> {
  38     #[inline]
  39     pub fn new(
  40         def: ty::WithOptConstParam<DefId>,
  41         substs: SubstsRef<'tcx>,
  42     ) -> UnevaluatedConst<'tcx> {
  43         UnevaluatedConst { def, substs }
  44     }
  45 }
  46
  47 /// Represents a constant in Rust.
  48 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)]
  49 #[derive(Hash, HashStable, TypeFoldable, TypeVisitable)]
  50 #[derive(derive_more::From)]
  51 pub enum ConstKind<'tcx> {
  52     /// A const generic parameter.
  53     Param(ty::ParamConst),
  54
  55     /// Infer the value of the const.
  56     Infer(InferConst<'tcx>),
  57
  58     /// Bound const variable, used only when preparing a trait query.
  59     Bound(ty::DebruijnIndex, ty::BoundVar),
  60
  61     /// A placeholder const - universally quantified higher-ranked const.
  62     Placeholder(ty::PlaceholderConst<'tcx>),
  63
  64     /// Used in the HIR by using `Unevaluated` everywhere and later normalizing to one of the other
  65     /// variants when the code is monomorphic enough for that.
  66     Unevaluated(UnevaluatedConst<'tcx>),
  67
  68     /// Used to hold computed value.
  69     Value(ty::ValTree<'tcx>),
  70
  71     /// A placeholder for a const which could not be computed; this is
  72     /// propagated to avoid useless error messages.
  73     #[from(ignore)]
  74     Error(ErrorGuaranteed),
  75
  76     /// Expr which contains an expression which has partially evaluated items.
  77     Expr(Expr<'tcx>),
  78 }
  79
  80 impl<'tcx> From<ty::ConstVid<'tcx>> for ConstKind<'tcx> {
  81     fn from(const_vid: ty::ConstVid<'tcx>) -> Self {
  82         InferConst::Var(const_vid).into()
  83     }
  84 }
  85
  86 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash)]
  87 #[derive(HashStable, TyEncodable, TyDecodable, TypeVisitable, TypeFoldable)]
  88 pub enum Expr<'tcx> {
  89     Binop(mir::BinOp, Const<'tcx>, Const<'tcx>),
  90     UnOp(mir::UnOp, Const<'tcx>),
  91     FunctionCall(Const<'tcx>, &'tcx List<Const<'tcx>>),
  92     Cast(CastKind, Const<'tcx>, Ty<'tcx>),
  93 }
  94
  95 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
  96 static_assert_size!(Expr<'_>, 24);
  97
  98 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
  99 static_assert_size!(ConstKind<'_>, 32);
 100
 101 impl<'tcx> ConstKind<'tcx> {
 102     #[inline]
 103     pub fn try_to_value(self) -> Option<ty::ValTree<'tcx>> {
 104         if let ConstKind::Value(val) = self { Some(val) } else { None }
 105     }
 106
 107     #[inline]
 108     pub fn try_to_scalar(self) -> Option<Scalar<AllocId>> {
 109         self.try_to_value()?.try_to_scalar()
 110     }
 111
 112     #[inline]
 113     pub fn try_to_scalar_int(self) -> Option<ScalarInt> {
 114         self.try_to_value()?.try_to_scalar_int()
 115     }
 116
 117     #[inline]
 118     pub fn try_to_bits(self, size: Size) -> Option<u128> {
 119         self.try_to_scalar_int()?.to_bits(size).ok()
 120     }
 121
 122     #[inline]
 123     pub fn try_to_bool(self) -> Option<bool> {
 124         self.try_to_scalar_int()?.try_into().ok()
 125     }
 126
 127     #[inline]
 128     pub fn try_to_target_usize(self, tcx: TyCtxt<'tcx>) -> Option<u64> {
 129         self.try_to_value()?.try_to_target_usize(tcx)
 130     }
 131 }
 132
 133 /// An inference variable for a const, for use in const generics.
 134 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable, Hash)]
 135 pub enum InferConst<'tcx> {
 136     /// Infer the value of the const.
 137     Var(ty::ConstVid<'tcx>),
 138     /// A fresh const variable. See `infer::freshen` for more details.
 139     Fresh(u32),
 140 }
 141
 142 impl<CTX> HashStable<CTX> for InferConst<'_> {
 143     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
 144         match self {
 145             InferConst::Var(_) => panic!("const variables should not be hashed: {self:?}"),
 146             InferConst::Fresh(i) => i.hash_stable(hcx, hasher),
 147         }
 148     }
 149 }
 150
 151 enum EvalMode {
 152     Typeck,
 153     Mir,
 154 }
 155
 156 enum EvalResult<'tcx> {
 157     ValTree(ty::ValTree<'tcx>),
 158     ConstVal(ConstValue<'tcx>),
 159 }
 160
 161 impl<'tcx> ConstKind<'tcx> {
 162     #[inline]
 163     /// Tries to evaluate the constant if it is `Unevaluated`. If that doesn't succeed, return the
 164     /// unevaluated constant.
 165     pub fn eval(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Self {
 166         self.try_eval_for_typeck(tcx, param_env).and_then(Result::ok).map_or(self, ConstKind::Value)
 167     }
 168
 169     #[inline]
 170     /// Tries to evaluate the constant if it is `Unevaluated`. If that isn't possible or necessary
 171     /// return `None`.
 172     // FIXME(@lcnr): Completely rework the evaluation/normalization system for `ty::Const` once valtrees are merged.
 173     pub fn try_eval_for_mir(
 174         self,
 175         tcx: TyCtxt<'tcx>,
 176         param_env: ParamEnv<'tcx>,
 177     ) -> Option<Result<ConstValue<'tcx>, ErrorGuaranteed>> {
 178         match self.try_eval_inner(tcx, param_env, EvalMode::Mir) {
 179             Some(Ok(EvalResult::ValTree(_))) => unreachable!(),
 180             Some(Ok(EvalResult::ConstVal(v))) => Some(Ok(v)),
 181             Some(Err(e)) => Some(Err(e)),
 182             None => None,
 183         }
 184     }
 185
 186     #[inline]
 187     /// Tries to evaluate the constant if it is `Unevaluated`. If that isn't possible or necessary
 188     /// return `None`.
 189     // FIXME(@lcnr): Completely rework the evaluation/normalization system for `ty::Const` once valtrees are merged.
 190     pub fn try_eval_for_typeck(
 191         self,
 192         tcx: TyCtxt<'tcx>,
 193         param_env: ParamEnv<'tcx>,
 194     ) -> Option<Result<ty::ValTree<'tcx>, ErrorGuaranteed>> {
 195         match self.try_eval_inner(tcx, param_env, EvalMode::Typeck) {
 196             Some(Ok(EvalResult::ValTree(v))) => Some(Ok(v)),
 197             Some(Ok(EvalResult::ConstVal(_))) => unreachable!(),
 198             Some(Err(e)) => Some(Err(e)),
 199             None => None,
 200         }
 201     }
 202
 203     #[inline]
 204     fn try_eval_inner(
 205         self,
 206         tcx: TyCtxt<'tcx>,
 207         param_env: ParamEnv<'tcx>,
 208         eval_mode: EvalMode,
 209     ) -> Option<Result<EvalResult<'tcx>, ErrorGuaranteed>> {
 210         assert!(!self.has_escaping_bound_vars(), "escaping vars in {self:?}");
 211         if let ConstKind::Unevaluated(unevaluated) = self {
 212             use crate::mir::interpret::ErrorHandled;
 213
 214             // HACK(eddyb) this erases lifetimes even though `const_eval_resolve`
 215             // also does later, but we want to do it before checking for
 216             // inference variables.
 217             // Note that we erase regions *before* calling `with_reveal_all_normalized`,
 218             // so that we don't try to invoke this query with
 219             // any region variables.
 220
 221             // HACK(eddyb) when the query key would contain inference variables,
 222             // attempt using identity substs and `ParamEnv` instead, that will succeed
 223             // when the expression doesn't depend on any parameters.
 224             // FIXME(eddyb, skinny121) pass `InferCtxt` into here when it's available, so that
 225             // we can call `infcx.const_eval_resolve` which handles inference variables.
 226             let param_env_and = if (param_env, unevaluated).has_non_region_infer() {
 227                 tcx.param_env(unevaluated.def.did).and(ty::UnevaluatedConst {
 228                     def: unevaluated.def,
 229                     substs: InternalSubsts::identity_for_item(tcx, unevaluated.def.did),
 230                 })
 231             } else {
 232                 tcx.erase_regions(param_env)
 233                     .with_reveal_all_normalized(tcx)
 234                     .and(tcx.erase_regions(unevaluated))
 235             };
 236
 237             // FIXME(eddyb) maybe the `const_eval_*` methods should take
 238             // `ty::ParamEnvAnd` instead of having them separate.
 239             let (param_env, unevaluated) = param_env_and.into_parts();
 240             // try to resolve e.g. associated constants to their definition on an impl, and then
 241             // evaluate the const.
 242             match eval_mode {
 243                 EvalMode::Typeck => {
 244                     match tcx.const_eval_resolve_for_typeck(param_env, unevaluated, None) {
 245                         // NOTE(eddyb) `val` contains no lifetimes/types/consts,
 246                         // and we use the original type, so nothing from `substs`
 247                         // (which may be identity substs, see above),
 248                         // can leak through `val` into the const we return.
 249                         Ok(val) => Some(Ok(EvalResult::ValTree(val?))),
 250                         Err(ErrorHandled::TooGeneric) => None,
 251                         Err(ErrorHandled::Reported(e)) => Some(Err(e)),
 252                     }
 253                 }
 254                 EvalMode::Mir => {
 255                     match tcx.const_eval_resolve(param_env, unevaluated.expand(), None) {
 256                         // NOTE(eddyb) `val` contains no lifetimes/types/consts,
 257                         // and we use the original type, so nothing from `substs`
 258                         // (which may be identity substs, see above),
 259                         // can leak through `val` into the const we return.
 260                         Ok(val) => Some(Ok(EvalResult::ConstVal(val))),
 261                         Err(ErrorHandled::TooGeneric) => None,
 262                         Err(ErrorHandled::Reported(e)) => Some(Err(e)),
 263                     }
 264                 }
 265             }
 266         } else {
 267             None
 268         }
 269     }
 270 }