src/librustc_typeck/check/autoderef.rs

   1 use super::{FnCtxt, PlaceOp, Needs};
   2 use super::method::MethodCallee;
   3
   4 use rustc::hir;
   5 use rustc::infer::{InferCtxt, InferOk};
   6 use rustc::session::DiagnosticMessageId;
   7 use rustc::traits::{self, TraitEngine};
   8 use rustc::ty::{self, Ty, TyCtxt, TraitRef};
   9 use rustc::ty::{ToPredicate, TypeFoldable};
  10 use rustc::ty::adjustment::{Adjustment, Adjust, OverloadedDeref};
  11
  12 use syntax_pos::Span;
  13 use syntax::ast::Ident;
  14
  15 use std::iter;
  16
  17 #[derive(Copy, Clone, Debug)]
  18 enum AutoderefKind {
  19     Builtin,
  20     Overloaded,
  21 }
  22
  23 pub struct Autoderef<'a, 'gcx: 'tcx, 'tcx: 'a> {
  24     infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
  25     body_id: hir::HirId,
  26     param_env: ty::ParamEnv<'tcx>,
  27     steps: Vec<(Ty<'tcx>, AutoderefKind)>,
  28     cur_ty: Ty<'tcx>,
  29     obligations: Vec<traits::PredicateObligation<'tcx>>,
  30     at_start: bool,
  31     include_raw_pointers: bool,
  32     span: Span,
  33     silence_errors: bool,
  34     reached_recursion_limit: bool
  35 }
  36
  37 impl<'a, 'gcx, 'tcx> Iterator for Autoderef<'a, 'gcx, 'tcx> {
  38     type Item = (Ty<'tcx>, usize);
  39
  40     fn next(&mut self) -> Option<Self::Item> {
  41         let tcx = self.infcx.tcx;
  42
  43         debug!("autoderef: steps={:?}, cur_ty={:?}",
  44                self.steps,
  45                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) =
  66             if let Some(mt) = self.cur_ty.builtin_deref(self.include_raw_pointers) {
  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!("autoderef stage #{:?} is {:?} from {:?}",
  79                self.steps.len(),
  80                new_ty,
  81                (self.cur_ty, kind));
  82         self.cur_ty = new_ty;
  83
  84         Some((self.cur_ty, self.steps.len()))
  85     }
  86 }
  87
  88 impl<'a, 'gcx, 'tcx> Autoderef<'a, 'gcx, 'tcx> {
  89     pub fn new(infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
  90                param_env: ty::ParamEnv<'tcx>,
  91                body_id: hir::HirId,
  92                span: Span,
  93                base_ty: Ty<'tcx>)
  94                -> Autoderef<'a, 'gcx, 'tcx>
  95     {
  96         Autoderef {
  97             infcx,
  98             body_id,
  99             param_env,
 100             steps: vec![],
 101             cur_ty: infcx.resolve_vars_if_possible(&base_ty),
 102             obligations: vec![],
 103             at_start: true,
 104             include_raw_pointers: false,
 105             silence_errors: false,
 106             reached_recursion_limit: false,
 107             span,
 108         }
 109     }
 110
 111     fn overloaded_deref_ty(&mut self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
 112         debug!("overloaded_deref_ty({:?})", ty);
 113
 114         let tcx = self.infcx.tcx;
 115
 116         // <cur_ty as Deref>
 117         let trait_ref = TraitRef {
 118             def_id: tcx.lang_items().deref_trait()?,
 119             substs: tcx.mk_substs_trait(self.cur_ty, &[]),
 120         };
 121
 122         let cause = traits::ObligationCause::misc(self.span, self.body_id);
 123
 124         let obligation = traits::Obligation::new(cause.clone(),
 125                                                  self.param_env,
 126                                                  trait_ref.to_predicate());
 127         if !self.infcx.predicate_may_hold(&obligation) {
 128             debug!("overloaded_deref_ty: cannot match obligation");
 129             return None;
 130         }
 131
 132         let mut fulfillcx = traits::FulfillmentContext::new_in_snapshot();
 133         let normalized_ty = fulfillcx.normalize_projection_type(
 134             &self.infcx,
 135             self.param_env,
 136             ty::ProjectionTy::from_ref_and_name(
 137                 tcx,
 138                 trait_ref,
 139                 Ident::from_str("Target"),
 140             ),
 141             cause);
 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",
 147                    e);
 148             return None;
 149         }
 150         let obligations = fulfillcx.pending_obligations();
 151         debug!("overloaded_deref_ty({:?}) = ({:?}, {:?})",
 152                ty, normalized_ty, obligations);
 153         self.obligations.extend(obligations);
 154
 155         Some(self.infcx.resolve_vars_if_possible(&normalized_ty))
 156     }
 157
 158     /// Returns the final type, generating an error if it is an
 159     /// unresolved inference variable.
 160     pub fn unambiguous_final_ty(&self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx> {
 161         fcx.structurally_resolved_type(self.span, self.cur_ty)
 162     }
 163
 164     /// Returns the final type we ended up with, which may well be an
 165     /// inference variable (we will resolve it first, if possible).
 166     pub fn maybe_ambiguous_final_ty(&self) -> Ty<'tcx> {
 167         self.infcx.resolve_vars_if_possible(&self.cur_ty)
 168     }
 169
 170     pub fn step_count(&self) -> usize {
 171         self.steps.len()
 172     }
 173
 174     /// Returns the adjustment steps.
 175     pub fn adjust_steps(&self, fcx: &FnCtxt<'a, 'gcx, 'tcx>, needs: Needs)
 176                         -> Vec<Adjustment<'tcx>> {
 177         fcx.register_infer_ok_obligations(self.adjust_steps_as_infer_ok(fcx, needs))
 178     }
 179
 180     pub fn adjust_steps_as_infer_ok(&self, fcx: &FnCtxt<'a, 'gcx, 'tcx>, needs: Needs)
 181                                     -> InferOk<'tcx, Vec<Adjustment<'tcx>>> {
 182         let mut obligations = vec![];
 183         let targets = self.steps.iter().skip(1).map(|&(ty, _)| ty)
 184             .chain(iter::once(self.cur_ty));
 185         let steps: Vec<_> = self.steps.iter().map(|&(source, kind)| {
 186             if let AutoderefKind::Overloaded = kind {
 187                 fcx.try_overloaded_deref(self.span, source, needs)
 188                     .and_then(|InferOk { value: method, obligations: o }| {
 189                         obligations.extend(o);
 190                         if let ty::Ref(region, _, mutbl) = method.sig.output().sty {
 191                             Some(OverloadedDeref {
 192                                 region,
 193                                 mutbl,
 194                             })
 195                         } else {
 196                             None
 197                         }
 198                     })
 199             } else {
 200                 None
 201             }
 202         }).zip(targets).map(|(autoderef, target)| {
 203             Adjustment {
 204                 kind: Adjust::Deref(autoderef),
 205                 target
 206             }
 207         }).collect();
 208
 209         InferOk {
 210             obligations,
 211             value: steps
 212         }
 213     }
 214
 215     /// also dereference through raw pointer types
 216     /// e.g., assuming ptr_to_Foo is the type `*const Foo`
 217     /// fcx.autoderef(span, ptr_to_Foo)  => [*const Foo]
 218     /// fcx.autoderef(span, ptr_to_Foo).include_raw_ptrs() => [*const Foo, Foo]
 219     pub fn include_raw_pointers(mut self) -> Self {
 220         self.include_raw_pointers = true;
 221         self
 222     }
 223
 224     pub fn silence_errors(mut self) -> Self {
 225         self.silence_errors = true;
 226         self
 227     }
 228
 229     pub fn reached_recursion_limit(&self) -> bool {
 230         self.reached_recursion_limit
 231     }
 232
 233     pub fn finalize(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) {
 234         fcx.register_predicates(self.into_obligations());
 235     }
 236
 237     pub fn into_obligations(self) -> Vec<traits::PredicateObligation<'tcx>> {
 238         self.obligations
 239     }
 240 }
 241
 242 pub fn report_autoderef_recursion_limit_error<'a, 'gcx, 'tcx>(
 243     tcx: TyCtxt<'a, 'gcx, 'tcx>, span: Span, ty: Ty<'tcx>)
 244 {
 245     // We've reached the recursion limit, error gracefully.
 246     let suggested_limit = *tcx.sess.recursion_limit.get() * 2;
 247     let msg = format!("reached the recursion limit while auto-dereferencing `{:?}`",
 248                       ty);
 249     let error_id = (DiagnosticMessageId::ErrorId(55), Some(span), msg);
 250     let fresh = tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
 251     if fresh {
 252         struct_span_err!(tcx.sess,
 253                          span,
 254                          E0055,
 255                          "reached the recursion limit while auto-dereferencing `{:?}`",
 256                          ty)
 257             .span_label(span, "deref recursion limit reached")
 258             .help(&format!(
 259                 "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
 260                 suggested_limit))
 261             .emit();
 262     }
 263 }
 264
 265 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 266     pub fn autoderef(&'a self, span: Span, base_ty: Ty<'tcx>) -> Autoderef<'a, 'gcx, 'tcx> {
 267         Autoderef::new(self, self.param_env, self.body_id, span, base_ty)
 268     }
 269
 270     pub fn try_overloaded_deref(&self,
 271                                 span: Span,
 272                                 base_ty: Ty<'tcx>,
 273                                 needs: Needs)
 274                                 -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
 275         self.try_overloaded_place_op(span, base_ty, &[], needs, PlaceOp::Deref)
 276     }
 277 }