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| 1 | +use super::{ConstEvalResult, ErrorHandled, GlobalId}; |
| 2 | + |
| 3 | +use crate::mir; |
| 4 | +use crate::hir::def_id::DefId; |
| 5 | +use crate::ty::{self, TyCtxt}; |
| 6 | +use crate::ty::subst::{InternalSubsts, SubstsRef}; |
| 7 | +use syntax_pos::Span; |
| 8 | + |
| 9 | + |
| 10 | +impl<'tcx> TyCtxt<'tcx> { |
| 11 | + |
| 12 | + /// Evaluates a constant without providing any substitutions. This is useful to evaluate consts |
| 13 | + /// that can't take any generic arguments like statics, const items or enum discriminants. If a |
| 14 | + /// generic parameter is used within the constant `ErrorHandled::ToGeneric` will be returned. |
| 15 | + pub fn const_eval_poly(self, def_id: DefId) -> ConstEvalResult<'tcx> { |
| 16 | + // In some situations def_id will have substitutions within scope, but they aren't allowed |
| 17 | + // to be used. So we can't use `Instance::mono`, instead we feed unresolved substitutions |
| 18 | + // into `const_eval` which will return `ErrorHandled::ToGeneric` if any og them are |
| 19 | + // encountered. |
| 20 | + let substs = InternalSubsts::identity_for_item(self, def_id); |
| 21 | + let instance = ty::Instance::new(def_id, substs); |
| 22 | + let cid = GlobalId { |
| 23 | + instance, |
| 24 | + promoted: None, |
| 25 | + }; |
| 26 | + let param_env = self.param_env(def_id); |
| 27 | + self.const_eval_validated(param_env.and(cid)) |
| 28 | + } |
| 29 | + |
| 30 | + /// Resolves and evaluates a constant. |
| 31 | + /// |
| 32 | + /// The constant can be located on a trait like `<A as B>::C`, in which case the given |
| 33 | + /// substitutions and environment are used to resolve the constant. Alternatively if the |
| 34 | + /// constant has generic parameters in scope the substitutions are used to evaluate the value of |
| 35 | + /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count |
| 36 | + /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still |
| 37 | + /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is |
| 38 | + /// returned. |
| 39 | + pub fn const_eval_resolve( |
| 40 | + self, |
| 41 | + param_env: ty::ParamEnv<'tcx>, |
| 42 | + def_id: DefId, |
| 43 | + substs: SubstsRef<'tcx>, |
| 44 | + span: Option<Span> |
| 45 | + ) -> ConstEvalResult<'tcx> { |
| 46 | + let instance = ty::Instance::resolve( |
| 47 | + self, |
| 48 | + param_env, |
| 49 | + def_id, |
| 50 | + substs, |
| 51 | + ); |
| 52 | + if let Some(instance) = instance { |
| 53 | + self.const_eval_instance(param_env, instance, span) |
| 54 | + } else { |
| 55 | + Err(ErrorHandled::TooGeneric) |
| 56 | + } |
| 57 | + } |
| 58 | + |
| 59 | + pub fn const_eval_instance( |
| 60 | + self, |
| 61 | + param_env: ty::ParamEnv<'tcx>, |
| 62 | + instance: ty::Instance<'tcx>, |
| 63 | + span: Option<Span> |
| 64 | + ) -> ConstEvalResult<'tcx> { |
| 65 | + let cid = GlobalId { |
| 66 | + instance, |
| 67 | + promoted: None, |
| 68 | + }; |
| 69 | + if let Some(span) = span { |
| 70 | + self.at(span).const_eval_validated(param_env.and(cid)) |
| 71 | + } else { |
| 72 | + self.const_eval_validated(param_env.and(cid)) |
| 73 | + } |
| 74 | + } |
| 75 | + |
| 76 | + /// Evaluate a promoted constant. |
| 77 | + pub fn const_eval_promoted( |
| 78 | + self, |
| 79 | + instance: ty::Instance<'tcx>, |
| 80 | + promoted: mir::Promoted |
| 81 | + ) -> ConstEvalResult<'tcx> { |
| 82 | + let cid = GlobalId { |
| 83 | + instance, |
| 84 | + promoted: Some(promoted), |
| 85 | + }; |
| 86 | + let param_env = ty::ParamEnv::reveal_all(); |
| 87 | + self.const_eval_validated(param_env.and(cid)) |
| 88 | + } |
| 89 | +} |
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