src/librustc_trait_selection/traits/query/normalize.rs

   1 //! Code for the 'normalization' query. This consists of a wrapper
   2 //! which folds deeply, invoking the underlying
   3 //! `normalize_projection_ty` query when it encounters projections.
   4
   5 use crate::infer::at::At;
   6 use crate::infer::canonical::OriginalQueryValues;
   7 use crate::infer::{InferCtxt, InferOk};
   8 use crate::traits::error_reporting::InferCtxtExt;
   9 use crate::traits::{Obligation, ObligationCause, PredicateObligation, Reveal};
  10 use rustc_data_structures::mini_map::MiniMap;
  11 use rustc_data_structures::stack::ensure_sufficient_stack;
  12 use rustc_infer::traits::Normalized;
  13 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
  14 use rustc_middle::ty::subst::Subst;
  15 use rustc_middle::ty::{self, Ty, TyCtxt};
  16
  17 use super::NoSolution;
  18
  19 pub use rustc_middle::traits::query::NormalizationResult;
  20
  21 pub trait AtExt<'tcx> {
  22     fn normalize<T>(&self, value: &T) -> Result<Normalized<'tcx, T>, NoSolution>
  23     where
  24         T: TypeFoldable<'tcx>;
  25 }
  26
  27 impl<'cx, 'tcx> AtExt<'tcx> for At<'cx, 'tcx> {
  28     /// Normalize `value` in the context of the inference context,
  29     /// yielding a resulting type, or an error if `value` cannot be
  30     /// normalized. If you don't care about regions, you should prefer
  31     /// `normalize_erasing_regions`, which is more efficient.
  32     ///
  33     /// If the normalization succeeds and is unambiguous, returns back
  34     /// the normalized value along with various outlives relations (in
  35     /// the form of obligations that must be discharged).
  36     ///
  37     /// N.B., this will *eventually* be the main means of
  38     /// normalizing, but for now should be used only when we actually
  39     /// know that normalization will succeed, since error reporting
  40     /// and other details are still "under development".
  41     fn normalize<T>(&self, value: &T) -> Result<Normalized<'tcx, T>, NoSolution>
  42     where
  43         T: TypeFoldable<'tcx>,
  44     {
  45         debug!(
  46             "normalize::<{}>(value={:?}, param_env={:?})",
  47             ::std::any::type_name::<T>(),
  48             value,
  49             self.param_env,
  50         );
  51         if !value.has_projections() {
  52             return Ok(Normalized { value: value.clone(), obligations: vec![] });
  53         }
  54
  55         let mut normalizer = QueryNormalizer {
  56             infcx: self.infcx,
  57             cause: self.cause,
  58             param_env: self.param_env,
  59             obligations: vec![],
  60             error: false,
  61             cache: MiniMap::new(),
  62             anon_depth: 0,
  63         };
  64
  65         let result = value.fold_with(&mut normalizer);
  66         debug!(
  67             "normalize::<{}>: result={:?} with {} obligations",
  68             ::std::any::type_name::<T>(),
  69             result,
  70             normalizer.obligations.len(),
  71         );
  72         debug!(
  73             "normalize::<{}>: obligations={:?}",
  74             ::std::any::type_name::<T>(),
  75             normalizer.obligations,
  76         );
  77         if normalizer.error {
  78             Err(NoSolution)
  79         } else {
  80             Ok(Normalized { value: result, obligations: normalizer.obligations })
  81         }
  82     }
  83 }
  84
  85 struct QueryNormalizer<'cx, 'tcx> {
  86     infcx: &'cx InferCtxt<'cx, 'tcx>,
  87     cause: &'cx ObligationCause<'tcx>,
  88     param_env: ty::ParamEnv<'tcx>,
  89     obligations: Vec<PredicateObligation<'tcx>>,
  90     cache: MiniMap<Ty<'tcx>, Ty<'tcx>>,
  91     error: bool,
  92     anon_depth: usize,
  93 }
  94
  95 impl<'cx, 'tcx> TypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
  96     fn tcx<'c>(&'c self) -> TyCtxt<'tcx> {
  97         self.infcx.tcx
  98     }
  99
 100     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
 101         if !ty.has_projections() {
 102             return ty;
 103         }
 104
 105         if let Some(ty) = self.cache.get(&ty) {
 106             return ty;
 107         }
 108
 109         let ty = ty.super_fold_with(self);
 110         let res = (|| match ty.kind {
 111             ty::Opaque(def_id, substs) => {
 112                 // Only normalize `impl Trait` after type-checking, usually in codegen.
 113                 match self.param_env.reveal() {
 114                     Reveal::UserFacing => ty,
 115
 116                     Reveal::All => {
 117                         let recursion_limit = self.tcx().sess.recursion_limit();
 118                         if !recursion_limit.value_within_limit(self.anon_depth) {
 119                             let obligation = Obligation::with_depth(
 120                                 self.cause.clone(),
 121                                 recursion_limit.0,
 122                                 self.param_env,
 123                                 ty,
 124                             );
 125                             self.infcx.report_overflow_error(&obligation, true);
 126                         }
 127
 128                         let generic_ty = self.tcx().type_of(def_id);
 129                         let concrete_ty = generic_ty.subst(self.tcx(), substs);
 130                         self.anon_depth += 1;
 131                         if concrete_ty == ty {
 132                             bug!(
 133                                 "infinite recursion generic_ty: {:#?}, substs: {:#?}, \
 134                                  concrete_ty: {:#?}, ty: {:#?}",
 135                                 generic_ty,
 136                                 substs,
 137                                 concrete_ty,
 138                                 ty
 139                             );
 140                         }
 141                         let folded_ty = ensure_sufficient_stack(|| self.fold_ty(concrete_ty));
 142                         self.anon_depth -= 1;
 143                         folded_ty
 144                     }
 145                 }
 146             }
 147
 148             ty::Projection(ref data) if !data.has_escaping_bound_vars() => {
 149                 // This is kind of hacky -- we need to be able to
 150                 // handle normalization within binders because
 151                 // otherwise we wind up a need to normalize when doing
 152                 // trait matching (since you can have a trait
 153                 // obligation like `for<'a> T::B: Fn(&'a i32)`), but
 154                 // we can't normalize with bound regions in scope. So
 155                 // far now we just ignore binders but only normalize
 156                 // if all bound regions are gone (and then we still
 157                 // have to renormalize whenever we instantiate a
 158                 // binder). It would be better to normalize in a
 159                 // binding-aware fashion.
 160
 161                 let tcx = self.infcx.tcx;
 162
 163                 let mut orig_values = OriginalQueryValues::default();
 164                 // HACK(matthewjasper) `'static` is special-cased in selection,
 165                 // so we cannot canonicalize it.
 166                 let c_data = self
 167                     .infcx
 168                     .canonicalize_hr_query_hack(&self.param_env.and(*data), &mut orig_values);
 169                 debug!("QueryNormalizer: c_data = {:#?}", c_data);
 170                 debug!("QueryNormalizer: orig_values = {:#?}", orig_values);
 171                 match tcx.normalize_projection_ty(c_data) {
 172                     Ok(result) => {
 173                         // We don't expect ambiguity.
 174                         if result.is_ambiguous() {
 175                             self.error = true;
 176                             return ty;
 177                         }
 178
 179                         match self.infcx.instantiate_query_response_and_region_obligations(
 180                             self.cause,
 181                             self.param_env,
 182                             &orig_values,
 183                             &result,
 184                         ) {
 185                             Ok(InferOk { value: result, obligations }) => {
 186                                 debug!("QueryNormalizer: result = {:#?}", result);
 187                                 debug!("QueryNormalizer: obligations = {:#?}", obligations);
 188                                 self.obligations.extend(obligations);
 189                                 result.normalized_ty
 190                             }
 191
 192                             Err(_) => {
 193                                 self.error = true;
 194                                 ty
 195                             }
 196                         }
 197                     }
 198
 199                     Err(NoSolution) => {
 200                         self.error = true;
 201                         ty
 202                     }
 203                 }
 204             }
 205
 206             _ => ty,
 207         })();
 208         self.cache.insert(ty, res);
 209         res
 210     }
 211
 212     fn fold_const(&mut self, constant: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
 213         let constant = constant.super_fold_with(self);
 214         constant.eval(self.infcx.tcx, self.param_env)
 215     }
 216 }