src/librustc_typeck/check/autoderef.rs

   1 use super::method::MethodCallee;
   2 use super::{FnCtxt, Needs, PlaceOp};
   3
   4 use rustc_ast::ast::Ident;
   5 use rustc_errors::struct_span_err;
   6 use rustc_hir as hir;
   7 use rustc_infer::infer::{InferCtxt, InferOk};
   8 use rustc_middle::ty::adjustment::{Adjust, Adjustment, OverloadedDeref};
   9 use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt, WithConstness};
  10 use rustc_middle::ty::{ToPredicate, TypeFoldable};
  11 use rustc_session::DiagnosticMessageId;
  12 use rustc_span::Span;
  13 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  14 use rustc_trait_selection::traits::{self, TraitEngine};
  15
  16 use std::iter;
  17
  18 #[derive(Copy, Clone, Debug)]
  19 enum AutoderefKind {
  20     Builtin,
  21     Overloaded,
  22 }
  23
  24 pub struct Autoderef<'a, 'tcx> {
  25     infcx: &'a InferCtxt<'a, 'tcx>,
  26     body_id: hir::HirId,
  27     param_env: ty::ParamEnv<'tcx>,
  28     steps: Vec<(Ty<'tcx>, AutoderefKind)>,
  29     cur_ty: Ty<'tcx>,
  30     obligations: Vec<traits::PredicateObligation<'tcx>>,
  31     at_start: bool,
  32     include_raw_pointers: bool,
  33     span: Span,
  34     silence_errors: bool,
  35     reached_recursion_limit: bool,
  36 }
  37
  38 impl<'a, 'tcx> Iterator for Autoderef<'a, 'tcx> {
  39     type Item = (Ty<'tcx>, usize);
  40
  41     fn next(&mut self) -> Option<Self::Item> {
  42         let tcx = self.infcx.tcx;
  43
  44         debug!("autoderef: steps={:?}, cur_ty={:?}", self.steps, self.cur_ty);
  45         if self.at_start {
  46             self.at_start = false;
  47             debug!("autoderef stage #0 is {:?}", self.cur_ty);
  48             return Some((self.cur_ty, 0));
  49         }
  50
  51         if self.steps.len() >= *tcx.sess.recursion_limit.get() {
  52             if !self.silence_errors {
  53                 report_autoderef_recursion_limit_error(tcx, self.span, self.cur_ty);
  54             }
  55             self.reached_recursion_limit = true;
  56             return None;
  57         }
  58
  59         if self.cur_ty.is_ty_var() {
  60             return None;
  61         }
  62
  63         // Otherwise, deref if type is derefable:
  64         let (kind, new_ty) = if let Some(mt) = self.cur_ty.builtin_deref(self.include_raw_pointers)
  65         {
  66             (AutoderefKind::Builtin, mt.ty)
  67         } else {
  68             let ty = self.overloaded_deref_ty(self.cur_ty)?;
  69             (AutoderefKind::Overloaded, ty)
  70         };
  71
  72         if new_ty.references_error() {
  73             return None;
  74         }
  75
  76         self.steps.push((self.cur_ty, kind));
  77         debug!(
  78             "autoderef stage #{:?} is {:?} from {:?}",
  79             self.steps.len(),
  80             new_ty,
  81             (self.cur_ty, kind)
  82         );
  83         self.cur_ty = new_ty;
  84
  85         Some((self.cur_ty, self.steps.len()))
  86     }
  87 }
  88
  89 impl<'a, 'tcx> Autoderef<'a, 'tcx> {
  90     pub fn new(
  91         infcx: &'a InferCtxt<'a, 'tcx>,
  92         param_env: ty::ParamEnv<'tcx>,
  93         body_id: hir::HirId,
  94         span: Span,
  95         base_ty: Ty<'tcx>,
  96     ) -> Autoderef<'a, 'tcx> {
  97         Autoderef {
  98             infcx,
  99             body_id,
 100             param_env,
 101             steps: vec![],
 102             cur_ty: infcx.resolve_vars_if_possible(&base_ty),
 103             obligations: vec![],
 104             at_start: true,
 105             include_raw_pointers: false,
 106             silence_errors: false,
 107             reached_recursion_limit: false,
 108             span,
 109         }
 110     }
 111
 112     fn overloaded_deref_ty(&mut self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
 113         debug!("overloaded_deref_ty({:?})", ty);
 114
 115         let tcx = self.infcx.tcx;
 116
 117         // <cur_ty as Deref>
 118         let trait_ref = TraitRef {
 119             def_id: tcx.lang_items().deref_trait()?,
 120             substs: tcx.mk_substs_trait(self.cur_ty, &[]),
 121         };
 122
 123         let cause = traits::ObligationCause::misc(self.span, self.body_id);
 124
 125         let obligation = traits::Obligation::new(
 126             cause.clone(),
 127             self.param_env,
 128             trait_ref.without_const().to_predicate(),
 129         );
 130         if !self.infcx.predicate_may_hold(&obligation) {
 131             debug!("overloaded_deref_ty: cannot match obligation");
 132             return None;
 133         }
 134
 135         let mut fulfillcx = traits::FulfillmentContext::new_in_snapshot();
 136         let normalized_ty = fulfillcx.normalize_projection_type(
 137             &self.infcx,
 138             self.param_env,
 139             ty::ProjectionTy::from_ref_and_name(tcx, trait_ref, Ident::from_str("Target")),
 140             cause,
 141         );
 142         if let Err(e) = fulfillcx.select_where_possible(&self.infcx) {
 143             // This shouldn't happen, except for evaluate/fulfill mismatches,
 144             // but that's not a reason for an ICE (`predicate_may_hold` is conservative
 145             // by design).
 146             debug!("overloaded_deref_ty: encountered errors {:?} while fulfilling", e);
 147             return None;
 148         }
 149         let obligations = fulfillcx.pending_obligations();
 150         debug!("overloaded_deref_ty({:?}) = ({:?}, {:?})", ty, normalized_ty, obligations);
 151         self.obligations.extend(obligations);
 152
 153         Some(self.infcx.resolve_vars_if_possible(&normalized_ty))
 154     }
 155
 156     /// Returns the final type, generating an error if it is an
 157     /// unresolved inference variable.
 158     pub fn unambiguous_final_ty(&self, fcx: &FnCtxt<'a, 'tcx>) -> Ty<'tcx> {
 159         fcx.structurally_resolved_type(self.span, self.cur_ty)
 160     }
 161
 162     /// Returns the final type we ended up with, which may well be an
 163     /// inference variable (we will resolve it first, if possible).
 164     pub fn maybe_ambiguous_final_ty(&self) -> Ty<'tcx> {
 165         self.infcx.resolve_vars_if_possible(&self.cur_ty)
 166     }
 167
 168     pub fn step_count(&self) -> usize {
 169         self.steps.len()
 170     }
 171
 172     /// Returns the adjustment steps.
 173     pub fn adjust_steps(&self, fcx: &FnCtxt<'a, 'tcx>, needs: Needs) -> Vec<Adjustment<'tcx>> {
 174         fcx.register_infer_ok_obligations(self.adjust_steps_as_infer_ok(fcx, needs))
 175     }
 176
 177     pub fn adjust_steps_as_infer_ok(
 178         &self,
 179         fcx: &FnCtxt<'a, 'tcx>,
 180         needs: Needs,
 181     ) -> InferOk<'tcx, Vec<Adjustment<'tcx>>> {
 182         let mut obligations = vec![];
 183         let targets = self.steps.iter().skip(1).map(|&(ty, _)| ty).chain(iter::once(self.cur_ty));
 184         let steps: Vec<_> = self
 185             .steps
 186             .iter()
 187             .map(|&(source, kind)| {
 188                 if let AutoderefKind::Overloaded = kind {
 189                     fcx.try_overloaded_deref(self.span, source, needs).and_then(
 190                         |InferOk { value: method, obligations: o }| {
 191                             obligations.extend(o);
 192                             if let ty::Ref(region, _, mutbl) = method.sig.output().kind {
 193                                 Some(OverloadedDeref { region, mutbl })
 194                             } else {
 195                                 None
 196                             }
 197                         },
 198                     )
 199                 } else {
 200                     None
 201                 }
 202             })
 203             .zip(targets)
 204             .map(|(autoderef, target)| Adjustment { kind: Adjust::Deref(autoderef), target })
 205             .collect();
 206
 207         InferOk { obligations, value: steps }
 208     }
 209
 210     /// also dereference through raw pointer types
 211     /// e.g., assuming ptr_to_Foo is the type `*const Foo`
 212     /// fcx.autoderef(span, ptr_to_Foo)  => [*const Foo]
 213     /// fcx.autoderef(span, ptr_to_Foo).include_raw_ptrs() => [*const Foo, Foo]
 214     pub fn include_raw_pointers(mut self) -> Self {
 215         self.include_raw_pointers = true;
 216         self
 217     }
 218
 219     pub fn silence_errors(mut self) -> Self {
 220         self.silence_errors = true;
 221         self
 222     }
 223
 224     pub fn reached_recursion_limit(&self) -> bool {
 225         self.reached_recursion_limit
 226     }
 227
 228     pub fn finalize(self, fcx: &FnCtxt<'a, 'tcx>) {
 229         fcx.register_predicates(self.into_obligations());
 230     }
 231
 232     pub fn into_obligations(self) -> Vec<traits::PredicateObligation<'tcx>> {
 233         self.obligations
 234     }
 235 }
 236
 237 pub fn report_autoderef_recursion_limit_error<'tcx>(tcx: TyCtxt<'tcx>, span: Span, ty: Ty<'tcx>) {
 238     // We've reached the recursion limit, error gracefully.
 239     let suggested_limit = *tcx.sess.recursion_limit.get() * 2;
 240     let msg = format!("reached the recursion limit while auto-dereferencing `{:?}`", ty);
 241     let error_id = (DiagnosticMessageId::ErrorId(55), Some(span), msg);
 242     let fresh = tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
 243     if fresh {
 244         struct_span_err!(
 245             tcx.sess,
 246             span,
 247             E0055,
 248             "reached the recursion limit while auto-dereferencing `{:?}`",
 249             ty
 250         )
 251         .span_label(span, "deref recursion limit reached")
 252         .help(&format!(
 253             "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate (`{}`)",
 254             suggested_limit, tcx.crate_name,
 255         ))
 256         .emit();
 257     }
 258 }
 259
 260 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 261     pub fn autoderef(&'a self, span: Span, base_ty: Ty<'tcx>) -> Autoderef<'a, 'tcx> {
 262         Autoderef::new(self, self.param_env, self.body_id, span, base_ty)
 263     }
 264
 265     pub fn try_overloaded_deref(
 266         &self,
 267         span: Span,
 268         base_ty: Ty<'tcx>,
 269         needs: Needs,
 270     ) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 271         self.try_overloaded_place_op(span, base_ty, &[], needs, PlaceOp::Deref)
 272     }
 273 }