src/librustc_typeck/check/autoderef.rs

   1 use super::method::MethodCallee;
   2 use super::{FnCtxt, Needs, PlaceOp};
   3
   4 use rustc::infer::{InferCtxt, InferOk};
   5 use rustc::session::DiagnosticMessageId;
   6 use rustc::traits::{self, TraitEngine};
   7 use rustc::ty::adjustment::{Adjust, Adjustment, OverloadedDeref};
   8 use rustc::ty::{self, TraitRef, Ty, TyCtxt};
   9 use rustc::ty::{ToPredicate, TypeFoldable};
  10 use rustc_hir as hir;
  11
  12 use rustc_span::Span;
  13 use syntax::ast::Ident;
  14
  15 use rustc_error_codes::*;
  16
  17 use std::iter;
  18
  19 #[derive(Copy, Clone, Debug)]
  20 enum AutoderefKind {
  21     Builtin,
  22     Overloaded,
  23 }
  24
  25 pub struct Autoderef<'a, 'tcx> {
  26     infcx: &'a InferCtxt<'a, 'tcx>,
  27     body_id: hir::HirId,
  28     param_env: ty::ParamEnv<'tcx>,
  29     steps: Vec<(Ty<'tcx>, AutoderefKind)>,
  30     cur_ty: Ty<'tcx>,
  31     obligations: Vec<traits::PredicateObligation<'tcx>>,
  32     at_start: bool,
  33     include_raw_pointers: bool,
  34     span: Span,
  35     silence_errors: bool,
  36     reached_recursion_limit: bool,
  37 }
  38
  39 impl<'a, 'tcx> Iterator for Autoderef<'a, 'tcx> {
  40     type Item = (Ty<'tcx>, usize);
  41
  42     fn next(&mut self) -> Option<Self::Item> {
  43         let tcx = self.infcx.tcx;
  44
  45         debug!("autoderef: steps={:?}, cur_ty={:?}", self.steps, self.cur_ty);
  46         if self.at_start {
  47             self.at_start = false;
  48             debug!("autoderef stage #0 is {:?}", self.cur_ty);
  49             return Some((self.cur_ty, 0));
  50         }
  51
  52         if self.steps.len() >= *tcx.sess.recursion_limit.get() {
  53             if !self.silence_errors {
  54                 report_autoderef_recursion_limit_error(tcx, self.span, self.cur_ty);
  55             }
  56             self.reached_recursion_limit = true;
  57             return None;
  58         }
  59
  60         if self.cur_ty.is_ty_var() {
  61             return None;
  62         }
  63
  64         // Otherwise, deref if type is derefable:
  65         let (kind, new_ty) = if let Some(mt) = self.cur_ty.builtin_deref(self.include_raw_pointers)
  66         {
  67             (AutoderefKind::Builtin, mt.ty)
  68         } else {
  69             let ty = self.overloaded_deref_ty(self.cur_ty)?;
  70             (AutoderefKind::Overloaded, ty)
  71         };
  72
  73         if new_ty.references_error() {
  74             return None;
  75         }
  76
  77         self.steps.push((self.cur_ty, kind));
  78         debug!(
  79             "autoderef stage #{:?} is {:?} from {:?}",
  80             self.steps.len(),
  81             new_ty,
  82             (self.cur_ty, kind)
  83         );
  84         self.cur_ty = new_ty;
  85
  86         Some((self.cur_ty, self.steps.len()))
  87     }
  88 }
  89
  90 impl<'a, 'tcx> Autoderef<'a, 'tcx> {
  91     pub fn new(
  92         infcx: &'a InferCtxt<'a, 'tcx>,
  93         param_env: ty::ParamEnv<'tcx>,
  94         body_id: hir::HirId,
  95         span: Span,
  96         base_ty: Ty<'tcx>,
  97     ) -> Autoderef<'a, 'tcx> {
  98         Autoderef {
  99             infcx,
 100             body_id,
 101             param_env,
 102             steps: vec![],
 103             cur_ty: infcx.resolve_vars_if_possible(&base_ty),
 104             obligations: vec![],
 105             at_start: true,
 106             include_raw_pointers: false,
 107             silence_errors: false,
 108             reached_recursion_limit: false,
 109             span,
 110         }
 111     }
 112
 113     fn overloaded_deref_ty(&mut self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
 114         debug!("overloaded_deref_ty({:?})", ty);
 115
 116         let tcx = self.infcx.tcx;
 117
 118         // <cur_ty as Deref>
 119         let trait_ref = TraitRef {
 120             def_id: tcx.lang_items().deref_trait()?,
 121             substs: tcx.mk_substs_trait(self.cur_ty, &[]),
 122         };
 123
 124         let cause = traits::ObligationCause::misc(self.span, self.body_id);
 125
 126         let obligation =
 127             traits::Obligation::new(cause.clone(), self.param_env, trait_ref.to_predicate());
 128         if !self.infcx.predicate_may_hold(&obligation) {
 129             debug!("overloaded_deref_ty: cannot match obligation");
 130             return None;
 131         }
 132
 133         let mut fulfillcx = traits::FulfillmentContext::new_in_snapshot();
 134         let normalized_ty = fulfillcx.normalize_projection_type(
 135             &self.infcx,
 136             self.param_env,
 137             ty::ProjectionTy::from_ref_and_name(tcx, trait_ref, Ident::from_str("Target")),
 138             cause,
 139         );
 140         if let Err(e) = fulfillcx.select_where_possible(&self.infcx) {
 141             // This shouldn't happen, except for evaluate/fulfill mismatches,
 142             // but that's not a reason for an ICE (`predicate_may_hold` is conservative
 143             // by design).
 144             debug!("overloaded_deref_ty: encountered errors {:?} while fulfilling", e);
 145             return None;
 146         }
 147         let obligations = fulfillcx.pending_obligations();
 148         debug!("overloaded_deref_ty({:?}) = ({:?}, {:?})", ty, normalized_ty, obligations);
 149         self.obligations.extend(obligations);
 150
 151         Some(self.infcx.resolve_vars_if_possible(&normalized_ty))
 152     }
 153
 154     /// Returns the final type, generating an error if it is an
 155     /// unresolved inference variable.
 156     pub fn unambiguous_final_ty(&self, fcx: &FnCtxt<'a, 'tcx>) -> Ty<'tcx> {
 157         fcx.structurally_resolved_type(self.span, self.cur_ty)
 158     }
 159
 160     /// Returns the final type we ended up with, which may well be an
 161     /// inference variable (we will resolve it first, if possible).
 162     pub fn maybe_ambiguous_final_ty(&self) -> Ty<'tcx> {
 163         self.infcx.resolve_vars_if_possible(&self.cur_ty)
 164     }
 165
 166     pub fn step_count(&self) -> usize {
 167         self.steps.len()
 168     }
 169
 170     /// Returns the adjustment steps.
 171     pub fn adjust_steps(&self, fcx: &FnCtxt<'a, 'tcx>, needs: Needs) -> Vec<Adjustment<'tcx>> {
 172         fcx.register_infer_ok_obligations(self.adjust_steps_as_infer_ok(fcx, needs))
 173     }
 174
 175     pub fn adjust_steps_as_infer_ok(
 176         &self,
 177         fcx: &FnCtxt<'a, 'tcx>,
 178         needs: Needs,
 179     ) -> InferOk<'tcx, Vec<Adjustment<'tcx>>> {
 180         let mut obligations = vec![];
 181         let targets = self.steps.iter().skip(1).map(|&(ty, _)| ty).chain(iter::once(self.cur_ty));
 182         let steps: Vec<_> = self
 183             .steps
 184             .iter()
 185             .map(|&(source, kind)| {
 186                 if let AutoderefKind::Overloaded = kind {
 187                     fcx.try_overloaded_deref(self.span, source, needs).and_then(
 188                         |InferOk { value: method, obligations: o }| {
 189                             obligations.extend(o);
 190                             if let ty::Ref(region, _, mutbl) = method.sig.output().kind {
 191                                 Some(OverloadedDeref { region, mutbl })
 192                             } else {
 193                                 None
 194                             }
 195                         },
 196                     )
 197                 } else {
 198                     None
 199                 }
 200             })
 201             .zip(targets)
 202             .map(|(autoderef, target)| Adjustment { kind: Adjust::Deref(autoderef), target })
 203             .collect();
 204
 205         InferOk { obligations, value: steps }
 206     }
 207
 208     /// also dereference through raw pointer types
 209     /// e.g., assuming ptr_to_Foo is the type `*const Foo`
 210     /// fcx.autoderef(span, ptr_to_Foo)  => [*const Foo]
 211     /// fcx.autoderef(span, ptr_to_Foo).include_raw_ptrs() => [*const Foo, Foo]
 212     pub fn include_raw_pointers(mut self) -> Self {
 213         self.include_raw_pointers = true;
 214         self
 215     }
 216
 217     pub fn silence_errors(mut self) -> Self {
 218         self.silence_errors = true;
 219         self
 220     }
 221
 222     pub fn reached_recursion_limit(&self) -> bool {
 223         self.reached_recursion_limit
 224     }
 225
 226     pub fn finalize(self, fcx: &FnCtxt<'a, 'tcx>) {
 227         fcx.register_predicates(self.into_obligations());
 228     }
 229
 230     pub fn into_obligations(self) -> Vec<traits::PredicateObligation<'tcx>> {
 231         self.obligations
 232     }
 233 }
 234
 235 pub fn report_autoderef_recursion_limit_error<'tcx>(tcx: TyCtxt<'tcx>, span: Span, ty: Ty<'tcx>) {
 236     // We've reached the recursion limit, error gracefully.
 237     let suggested_limit = *tcx.sess.recursion_limit.get() * 2;
 238     let msg = format!("reached the recursion limit while auto-dereferencing `{:?}`", ty);
 239     let error_id = (DiagnosticMessageId::ErrorId(55), Some(span), msg);
 240     let fresh = tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
 241     if fresh {
 242         struct_span_err!(
 243             tcx.sess,
 244             span,
 245             E0055,
 246             "reached the recursion limit while auto-dereferencing `{:?}`",
 247             ty
 248         )
 249         .span_label(span, "deref recursion limit reached")
 250         .help(&format!(
 251             "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
 252             suggested_limit
 253         ))
 254         .emit();
 255     }
 256 }
 257
 258 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 259     pub fn autoderef(&'a self, span: Span, base_ty: Ty<'tcx>) -> Autoderef<'a, 'tcx> {
 260         Autoderef::new(self, self.param_env, self.body_id, span, base_ty)
 261     }
 262
 263     pub fn try_overloaded_deref(
 264         &self,
 265         span: Span,
 266         base_ty: Ty<'tcx>,
 267         needs: Needs,
 268     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 269         self.try_overloaded_place_op(span, base_ty, &[], needs, PlaceOp::Deref)
 270     }
 271 }