src/librustc_typeck/check/method/mod.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Method lookup: the secret sauce of Rust. See `README.md`.
  12
  13 use check::FnCtxt;
  14 use hir::def::Def;
  15 use hir::def_id::DefId;
  16 use rustc::ty::subst::Substs;
  17 use rustc::traits;
  18 use rustc::ty::{self, ToPredicate, ToPolyTraitRef, TraitRef, TypeFoldable};
  19 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow};
  20 use rustc::ty::subst::Subst;
  21 use rustc::infer::{self, InferOk};
  22
  23 use syntax::ast;
  24 use syntax_pos::Span;
  25
  26 use rustc::hir;
  27
  28 pub use self::MethodError::*;
  29 pub use self::CandidateSource::*;
  30
  31 pub use self::suggest::AllTraitsVec;
  32
  33 mod confirm;
  34 pub mod probe;
  35 mod suggest;
  36
  37 use self::probe::IsSuggestion;
  38
  39 pub enum MethodError<'tcx> {
  40     // Did not find an applicable method, but we did find various near-misses that may work.
  41     NoMatch(NoMatchData<'tcx>),
  42
  43     // Multiple methods might apply.
  44     Ambiguity(Vec<CandidateSource>),
  45
  46     // Using a `Fn`/`FnMut`/etc method on a raw closure type before we have inferred its kind.
  47     ClosureAmbiguity(// DefId of fn trait
  48                      DefId),
  49
  50     // Found an applicable method, but it is not visible.
  51     PrivateMatch(Def),
  52 }
  53
  54 // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which
  55 // could lead to matches if satisfied, and a list of not-in-scope traits which may work.
  56 pub struct NoMatchData<'tcx> {
  57     pub static_candidates: Vec<CandidateSource>,
  58     pub unsatisfied_predicates: Vec<TraitRef<'tcx>>,
  59     pub out_of_scope_traits: Vec<DefId>,
  60     pub mode: probe::Mode,
  61 }
  62
  63 impl<'tcx> NoMatchData<'tcx> {
  64     pub fn new(static_candidates: Vec<CandidateSource>,
  65                unsatisfied_predicates: Vec<TraitRef<'tcx>>,
  66                out_of_scope_traits: Vec<DefId>,
  67                mode: probe::Mode)
  68                -> Self {
  69         NoMatchData {
  70             static_candidates: static_candidates,
  71             unsatisfied_predicates: unsatisfied_predicates,
  72             out_of_scope_traits: out_of_scope_traits,
  73             mode: mode,
  74         }
  75     }
  76 }
  77
  78 // A pared down enum describing just the places from which a method
  79 // candidate can arise. Used for error reporting only.
  80 #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
  81 pub enum CandidateSource {
  82     ImplSource(DefId),
  83     TraitSource(// trait id
  84                 DefId),
  85 }
  86
  87 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  88     /// Determines whether the type `self_ty` supports a method name `method_name` or not.
  89     pub fn method_exists(&self,
  90                          span: Span,
  91                          method_name: ast::Name,
  92                          self_ty: ty::Ty<'tcx>,
  93                          call_expr_id: ast::NodeId,
  94                          allow_private: bool)
  95                          -> bool {
  96         let mode = probe::Mode::MethodCall;
  97         match self.probe_for_name(span, mode, method_name, IsSuggestion(false),
  98                                   self_ty, call_expr_id) {
  99             Ok(..) => true,
 100             Err(NoMatch(..)) => false,
 101             Err(Ambiguity(..)) => true,
 102             Err(ClosureAmbiguity(..)) => true,
 103             Err(PrivateMatch(..)) => allow_private,
 104         }
 105     }
 106
 107     /// Performs method lookup. If lookup is successful, it will return the callee
 108     /// and store an appropriate adjustment for the self-expr. In some cases it may
 109     /// report an error (e.g., invoking the `drop` method).
 110     ///
 111     /// # Arguments
 112     ///
 113     /// Given a method call like `foo.bar::<T1,...Tn>(...)`:
 114     ///
 115     /// * `fcx`:                   the surrounding `FnCtxt` (!)
 116     /// * `span`:                  the span for the method call
 117     /// * `method_name`:           the name of the method being called (`bar`)
 118     /// * `self_ty`:               the (unadjusted) type of the self expression (`foo`)
 119     /// * `supplied_method_types`: the explicit method type parameters, if any (`T1..Tn`)
 120     /// * `self_expr`:             the self expression (`foo`)
 121     pub fn lookup_method(&self,
 122                          span: Span,
 123                          method_name: ast::Name,
 124                          self_ty: ty::Ty<'tcx>,
 125                          supplied_method_types: Vec<ty::Ty<'tcx>>,
 126                          call_expr: &'gcx hir::Expr,
 127                          self_expr: &'gcx hir::Expr)
 128                          -> Result<ty::MethodCallee<'tcx>, MethodError<'tcx>> {
 129         debug!("lookup(method_name={}, self_ty={:?}, call_expr={:?}, self_expr={:?})",
 130                method_name,
 131                self_ty,
 132                call_expr,
 133                self_expr);
 134
 135         let mode = probe::Mode::MethodCall;
 136         let self_ty = self.resolve_type_vars_if_possible(&self_ty);
 137         let pick = self.probe_for_name(span, mode, method_name, IsSuggestion(false),
 138                                        self_ty, call_expr.id)?;
 139
 140         if let Some(import_id) = pick.import_id {
 141             let import_def_id = self.tcx.hir.local_def_id(import_id);
 142             debug!("used_trait_import: {:?}", import_def_id);
 143             self.tables.borrow_mut().used_trait_imports.insert(import_def_id);
 144         }
 145
 146         self.tcx.check_stability(pick.item.def_id, call_expr.id, span);
 147
 148         Ok(self.confirm_method(span,
 149                                self_expr,
 150                                call_expr,
 151                                self_ty,
 152                                pick,
 153                                supplied_method_types))
 154     }
 155
 156     pub fn lookup_method_in_trait(&self,
 157                                   span: Span,
 158                                   self_expr: Option<&hir::Expr>,
 159                                   m_name: ast::Name,
 160                                   trait_def_id: DefId,
 161                                   self_ty: ty::Ty<'tcx>,
 162                                   opt_input_types: Option<Vec<ty::Ty<'tcx>>>)
 163                                   -> Option<InferOk<'tcx, ty::MethodCallee<'tcx>>> {
 164         self.lookup_method_in_trait_adjusted(span,
 165                                              self_expr,
 166                                              m_name,
 167                                              trait_def_id,
 168                                              0,
 169                                              false,
 170                                              self_ty,
 171                                              opt_input_types)
 172     }
 173
 174     /// `lookup_in_trait_adjusted` is used for overloaded operators.
 175     /// It does a very narrow slice of what the normal probe/confirm path does.
 176     /// In particular, it doesn't really do any probing: it simply constructs
 177     /// an obligation for aparticular trait with the given self-type and checks
 178     /// whether that trait is implemented.
 179     ///
 180     /// FIXME(#18741) -- It seems likely that we can consolidate some of this
 181     /// code with the other method-lookup code. In particular, autoderef on
 182     /// index is basically identical to autoderef with normal probes, except
 183     /// that the test also looks for built-in indexing. Also, the second half of
 184     /// this method is basically the same as confirmation.
 185     pub fn lookup_method_in_trait_adjusted(&self,
 186                                            span: Span,
 187                                            self_expr: Option<&hir::Expr>,
 188                                            m_name: ast::Name,
 189                                            trait_def_id: DefId,
 190                                            autoderefs: usize,
 191                                            unsize: bool,
 192                                            self_ty: ty::Ty<'tcx>,
 193                                            opt_input_types: Option<Vec<ty::Ty<'tcx>>>)
 194                                            -> Option<InferOk<'tcx, ty::MethodCallee<'tcx>>> {
 195         debug!("lookup_in_trait_adjusted(self_ty={:?}, self_expr={:?}, \
 196                 m_name={}, trait_def_id={:?})",
 197                self_ty,
 198                self_expr,
 199                m_name,
 200                trait_def_id);
 201
 202         // Construct a trait-reference `self_ty : Trait<input_tys>`
 203         let substs = Substs::for_item(self.tcx,
 204                                       trait_def_id,
 205                                       |def, _| self.region_var_for_def(span, def),
 206                                       |def, substs| {
 207             if def.index == 0 {
 208                 self_ty
 209             } else if let Some(ref input_types) = opt_input_types {
 210                 input_types[def.index as usize - 1]
 211             } else {
 212                 self.type_var_for_def(span, def, substs)
 213             }
 214         });
 215
 216         let trait_ref = ty::TraitRef::new(trait_def_id, substs);
 217
 218         // Construct an obligation
 219         let poly_trait_ref = trait_ref.to_poly_trait_ref();
 220         let obligation =
 221             traits::Obligation::misc(span, self.body_id, poly_trait_ref.to_predicate());
 222
 223         // Now we want to know if this can be matched
 224         let mut selcx = traits::SelectionContext::new(self);
 225         if !selcx.evaluate_obligation(&obligation) {
 226             debug!("--> Cannot match obligation");
 227             return None; // Cannot be matched, no such method resolution is possible.
 228         }
 229
 230         // Trait must have a method named `m_name` and it should not have
 231         // type parameters or early-bound regions.
 232         let tcx = self.tcx;
 233         let method_item = self.associated_item(trait_def_id, m_name).unwrap();
 234         let def_id = method_item.def_id;
 235         let generics = tcx.item_generics(def_id);
 236         assert_eq!(generics.types.len(), 0);
 237         assert_eq!(generics.regions.len(), 0);
 238
 239         debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
 240         let mut obligations = vec![];
 241
 242         // Instantiate late-bound regions and substitute the trait
 243         // parameters into the method type to get the actual method type.
 244         //
 245         // NB: Instantiate late-bound regions first so that
 246         // `instantiate_type_scheme` can normalize associated types that
 247         // may reference those regions.
 248         let original_method_ty = tcx.item_type(def_id);
 249         let fn_sig = original_method_ty.fn_sig();
 250         let fn_sig = self.replace_late_bound_regions_with_fresh_var(span,
 251                                                                     infer::FnCall,
 252                                                                     &fn_sig).0;
 253         let fn_sig = fn_sig.subst(self.tcx, substs);
 254         let fn_sig = match self.normalize_associated_types_in_as_infer_ok(span, &fn_sig) {
 255             InferOk { value, obligations: o } => {
 256                 obligations.extend(o);
 257                 value
 258             }
 259         };
 260         let transformed_self_ty = fn_sig.inputs()[0];
 261         let method_ty = tcx.mk_fn_def(def_id, substs, ty::Binder(fn_sig));
 262
 263         debug!("lookup_in_trait_adjusted: matched method method_ty={:?} obligation={:?}",
 264                method_ty,
 265                obligation);
 266
 267         // Register obligations for the parameters.  This will include the
 268         // `Self` parameter, which in turn has a bound of the main trait,
 269         // so this also effectively registers `obligation` as well.  (We
 270         // used to register `obligation` explicitly, but that resulted in
 271         // double error messages being reported.)
 272         //
 273         // Note that as the method comes from a trait, it should not have
 274         // any late-bound regions appearing in its bounds.
 275         let bounds = self.tcx.item_predicates(def_id).instantiate(self.tcx, substs);
 276         let bounds = match self.normalize_associated_types_in_as_infer_ok(span, &bounds) {
 277             InferOk { value, obligations: o } => {
 278                 obligations.extend(o);
 279                 value
 280             }
 281         };
 282         assert!(!bounds.has_escaping_regions());
 283
 284         let cause = traits::ObligationCause::misc(span, self.body_id);
 285         obligations.extend(traits::predicates_for_generics(cause.clone(), &bounds));
 286
 287         // Also add an obligation for the method type being well-formed.
 288         obligations.push(traits::Obligation::new(cause, ty::Predicate::WellFormed(method_ty)));
 289
 290         // Insert any adjustments needed (always an autoref of some mutability).
 291         if let Some(self_expr) = self_expr {
 292             debug!("lookup_in_trait_adjusted: inserting adjustment if needed \
 293                     (self-id={}, autoderefs={}, unsize={}, fty={:?})",
 294                     self_expr.id, autoderefs, unsize, original_method_ty);
 295
 296             let original_sig = original_method_ty.fn_sig();
 297             let autoref = match (&original_sig.input(0).skip_binder().sty,
 298                                  &transformed_self_ty.sty) {
 299                 (&ty::TyRef(..), &ty::TyRef(region, ty::TypeAndMut { mutbl, ty: _ })) => {
 300                     // Trait method is fn(&self) or fn(&mut self), need an
 301                     // autoref. Pull the region etc out of the type of first argument.
 302                     Some(AutoBorrow::Ref(region, mutbl))
 303                 }
 304                 _ => {
 305                     // Trait method is fn(self), no transformation needed.
 306                     assert!(!unsize);
 307                     None
 308                 }
 309             };
 310
 311             self.apply_adjustment(self_expr.id, Adjustment {
 312                 kind: Adjust::DerefRef {
 313                     autoderefs: autoderefs,
 314                     autoref: autoref,
 315                     unsize: unsize
 316                 },
 317                 target: transformed_self_ty
 318             });
 319         }
 320
 321         let callee = ty::MethodCallee {
 322             def_id: def_id,
 323             ty: method_ty,
 324             substs: trait_ref.substs,
 325         };
 326
 327         debug!("callee = {:?}", callee);
 328
 329         Some(InferOk {
 330             obligations,
 331             value: callee
 332         })
 333     }
 334
 335     pub fn resolve_ufcs(&self,
 336                         span: Span,
 337                         method_name: ast::Name,
 338                         self_ty: ty::Ty<'tcx>,
 339                         expr_id: ast::NodeId)
 340                         -> Result<Def, MethodError<'tcx>> {
 341         let mode = probe::Mode::Path;
 342         let pick = self.probe_for_name(span, mode, method_name, IsSuggestion(false),
 343                                        self_ty, expr_id)?;
 344
 345         if let Some(import_id) = pick.import_id {
 346             let import_def_id = self.tcx.hir.local_def_id(import_id);
 347             debug!("used_trait_import: {:?}", import_def_id);
 348             self.tables.borrow_mut().used_trait_imports.insert(import_def_id);
 349         }
 350
 351         let def = pick.item.def();
 352
 353         self.tcx.check_stability(def.def_id(), expr_id, span);
 354
 355         if let probe::InherentImplPick = pick.kind {
 356             if !self.tcx.vis_is_accessible_from(pick.item.vis, self.body_id) {
 357                 let msg = format!("{} `{}` is private", def.kind_name(), method_name);
 358                 self.tcx.sess.span_err(span, &msg);
 359             }
 360         }
 361         Ok(def)
 362     }
 363
 364     /// Find item with name `item_name` defined in impl/trait `def_id`
 365     /// and return it, or `None`, if no such item was defined there.
 366     pub fn associated_item(&self, def_id: DefId, item_name: ast::Name)
 367                            -> Option<ty::AssociatedItem> {
 368         self.tcx.associated_items(def_id).find(|item| item.name == item_name)
 369     }
 370 }