src/librustc_typeck/check/closure.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 //! Code for type-checking closure expressions.
  12
  13 use super::{check_fn, Expectation, FnCtxt};
  14
  15 use astconv::AstConv;
  16 use rustc::infer::type_variable::TypeVariableOrigin;
  17 use rustc::ty::{self, ToPolyTraitRef, Ty};
  18 use std::cmp;
  19 use std::iter;
  20 use syntax::abi::Abi;
  21 use rustc::hir;
  22
  23 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  24     pub fn check_expr_closure(&self,
  25                               expr: &hir::Expr,
  26                               _capture: hir::CaptureClause,
  27                               decl: &'gcx hir::FnDecl,
  28                               body_id: hir::BodyId,
  29                               expected: Expectation<'tcx>)
  30                               -> Ty<'tcx> {
  31         debug!("check_expr_closure(expr={:?},expected={:?})",
  32                expr,
  33                expected);
  34
  35         // It's always helpful for inference if we know the kind of
  36         // closure sooner rather than later, so first examine the expected
  37         // type, and see if can glean a closure kind from there.
  38         let (expected_sig, expected_kind) = match expected.to_option(self) {
  39             Some(ty) => self.deduce_expectations_from_expected_type(ty),
  40             None => (None, None),
  41         };
  42         let body = self.tcx.hir.body(body_id);
  43         self.check_closure(expr, expected_kind, decl, body, expected_sig)
  44     }
  45
  46     fn check_closure(&self,
  47                      expr: &hir::Expr,
  48                      opt_kind: Option<ty::ClosureKind>,
  49                      decl: &'gcx hir::FnDecl,
  50                      body: &'gcx hir::Body,
  51                      expected_sig: Option<ty::FnSig<'tcx>>)
  52                      -> Ty<'tcx> {
  53         debug!("check_closure opt_kind={:?} expected_sig={:?}",
  54                opt_kind,
  55                expected_sig);
  56
  57         let expr_def_id = self.tcx.hir.local_def_id(expr.id);
  58         let sig = AstConv::ty_of_closure(self,
  59                                          hir::Unsafety::Normal,
  60                                          decl,
  61                                          Abi::RustCall,
  62                                          expected_sig);
  63
  64         // Create type variables (for now) to represent the transformed
  65         // types of upvars. These will be unified during the upvar
  66         // inference phase (`upvar.rs`).
  67         let closure_type = self.tcx.mk_closure(expr_def_id,
  68             self.parameter_environment.free_substs.extend_to(self.tcx, expr_def_id,
  69                 |_, _| span_bug!(expr.span, "closure has region param"),
  70                 |_, _| self.infcx.next_ty_var(TypeVariableOrigin::TransformedUpvar(expr.span))
  71             )
  72         );
  73
  74         debug!("check_closure: expr.id={:?} closure_type={:?}", expr.id, closure_type);
  75
  76         let extent = self.tcx.region_maps.call_site_extent(expr.id, body.value.id);
  77         let fn_sig = self.tcx.liberate_late_bound_regions(extent, &sig);
  78         let fn_sig = self.inh.normalize_associated_types_in(body.value.span,
  79                                                             body.value.id, &fn_sig);
  80
  81         check_fn(self, fn_sig, decl, expr.id, body);
  82
  83         // Tuple up the arguments and insert the resulting function type into
  84         // the `closures` table.
  85         let sig = sig.map_bound(|sig| self.tcx.mk_fn_sig(
  86             iter::once(self.tcx.intern_tup(sig.inputs(), false)),
  87             sig.output(),
  88             sig.variadic,
  89             sig.unsafety,
  90             sig.abi
  91         ));
  92
  93         debug!("closure for {:?} --> sig={:?} opt_kind={:?}",
  94                expr_def_id,
  95                sig,
  96                opt_kind);
  97
  98         self.tables.borrow_mut().closure_tys.insert(expr.id, sig);
  99         match opt_kind {
 100             Some(kind) => {
 101                 self.tables.borrow_mut().closure_kinds.insert(expr.id, kind);
 102             }
 103             None => {}
 104         }
 105
 106         closure_type
 107     }
 108
 109     fn deduce_expectations_from_expected_type
 110         (&self,
 111          expected_ty: Ty<'tcx>)
 112          -> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
 113         debug!("deduce_expectations_from_expected_type(expected_ty={:?})",
 114                expected_ty);
 115
 116         match expected_ty.sty {
 117             ty::TyDynamic(ref object_type, ..) => {
 118                 let sig = object_type.projection_bounds()
 119                     .filter_map(|pb| {
 120                         let pb = pb.with_self_ty(self.tcx, self.tcx.types.err);
 121                         self.deduce_sig_from_projection(&pb)
 122                     })
 123                     .next();
 124                 let kind = object_type.principal()
 125                     .and_then(|p| self.tcx.lang_items.fn_trait_kind(p.def_id()));
 126                 (sig, kind)
 127             }
 128             ty::TyInfer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
 129             _ => (None, None),
 130         }
 131     }
 132
 133     fn deduce_expectations_from_obligations
 134         (&self,
 135          expected_vid: ty::TyVid)
 136          -> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
 137         let fulfillment_cx = self.fulfillment_cx.borrow();
 138         // Here `expected_ty` is known to be a type inference variable.
 139
 140         let expected_sig = fulfillment_cx.pending_obligations()
 141             .iter()
 142             .map(|obligation| &obligation.obligation)
 143             .filter_map(|obligation| {
 144                 debug!("deduce_expectations_from_obligations: obligation.predicate={:?}",
 145                        obligation.predicate);
 146
 147                 match obligation.predicate {
 148                     // Given a Projection predicate, we can potentially infer
 149                     // the complete signature.
 150                     ty::Predicate::Projection(ref proj_predicate) => {
 151                         let trait_ref = proj_predicate.to_poly_trait_ref();
 152                         self.self_type_matches_expected_vid(trait_ref, expected_vid)
 153                             .and_then(|_| self.deduce_sig_from_projection(proj_predicate))
 154                     }
 155                     _ => None,
 156                 }
 157             })
 158             .next();
 159
 160         // Even if we can't infer the full signature, we may be able to
 161         // infer the kind. This can occur if there is a trait-reference
 162         // like `F : Fn<A>`. Note that due to subtyping we could encounter
 163         // many viable options, so pick the most restrictive.
 164         let expected_kind = fulfillment_cx.pending_obligations()
 165             .iter()
 166             .map(|obligation| &obligation.obligation)
 167             .filter_map(|obligation| {
 168                 let opt_trait_ref = match obligation.predicate {
 169                     ty::Predicate::Projection(ref data) => Some(data.to_poly_trait_ref()),
 170                     ty::Predicate::Trait(ref data) => Some(data.to_poly_trait_ref()),
 171                     ty::Predicate::Equate(..) => None,
 172                     ty::Predicate::RegionOutlives(..) => None,
 173                     ty::Predicate::TypeOutlives(..) => None,
 174                     ty::Predicate::WellFormed(..) => None,
 175                     ty::Predicate::ObjectSafe(..) => None,
 176
 177                     // NB: This predicate is created by breaking down a
 178                     // `ClosureType: FnFoo()` predicate, where
 179                     // `ClosureType` represents some `TyClosure`. It can't
 180                     // possibly be referring to the current closure,
 181                     // because we haven't produced the `TyClosure` for
 182                     // this closure yet; this is exactly why the other
 183                     // code is looking for a self type of a unresolved
 184                     // inference variable.
 185                     ty::Predicate::ClosureKind(..) => None,
 186                 };
 187                 opt_trait_ref.and_then(|tr| self.self_type_matches_expected_vid(tr, expected_vid))
 188                     .and_then(|tr| self.tcx.lang_items.fn_trait_kind(tr.def_id()))
 189             })
 190             .fold(None,
 191                   |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
 192
 193         (expected_sig, expected_kind)
 194     }
 195
 196     /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
 197     /// everything we need to know about a closure.
 198     fn deduce_sig_from_projection(&self,
 199                                   projection: &ty::PolyProjectionPredicate<'tcx>)
 200                                   -> Option<ty::FnSig<'tcx>> {
 201         let tcx = self.tcx;
 202
 203         debug!("deduce_sig_from_projection({:?})", projection);
 204
 205         let trait_ref = projection.to_poly_trait_ref();
 206
 207         if tcx.lang_items.fn_trait_kind(trait_ref.def_id()).is_none() {
 208             return None;
 209         }
 210
 211         let arg_param_ty = trait_ref.substs().type_at(1);
 212         let arg_param_ty = self.resolve_type_vars_if_possible(&arg_param_ty);
 213         debug!("deduce_sig_from_projection: arg_param_ty {:?}",
 214                arg_param_ty);
 215
 216         let input_tys = match arg_param_ty.sty {
 217             ty::TyTuple(tys, _) => tys.into_iter(),
 218             _ => {
 219                 return None;
 220             }
 221         };
 222
 223         let ret_param_ty = projection.0.ty;
 224         let ret_param_ty = self.resolve_type_vars_if_possible(&ret_param_ty);
 225         debug!("deduce_sig_from_projection: ret_param_ty {:?}", ret_param_ty);
 226
 227         let fn_sig = self.tcx.mk_fn_sig(
 228             input_tys.cloned(),
 229             ret_param_ty,
 230             false,
 231             hir::Unsafety::Normal,
 232             Abi::Rust
 233         );
 234         debug!("deduce_sig_from_projection: fn_sig {:?}", fn_sig);
 235
 236         Some(fn_sig)
 237     }
 238
 239     fn self_type_matches_expected_vid(&self,
 240                                       trait_ref: ty::PolyTraitRef<'tcx>,
 241                                       expected_vid: ty::TyVid)
 242                                       -> Option<ty::PolyTraitRef<'tcx>> {
 243         let self_ty = self.shallow_resolve(trait_ref.self_ty());
 244         debug!("self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?})",
 245                trait_ref,
 246                self_ty);
 247         match self_ty.sty {
 248             ty::TyInfer(ty::TyVar(v)) if expected_vid == v => Some(trait_ref),
 249             _ => None,
 250         }
 251     }
 252 }