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 rustc::ty::subst::Substs;
  19 use std::cmp;
  20 use std::iter;
  21 use syntax::abi::Abi;
  22 use rustc::hir;
  23
  24 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  25     pub fn check_expr_closure(&self,
  26                               expr: &hir::Expr,
  27                               _capture: hir::CaptureClause,
  28                               decl: &'gcx hir::FnDecl,
  29                               body_id: hir::BodyId,
  30                               expected: Expectation<'tcx>)
  31                               -> Ty<'tcx> {
  32         debug!("check_expr_closure(expr={:?},expected={:?})",
  33                expr,
  34                expected);
  35
  36         // It's always helpful for inference if we know the kind of
  37         // closure sooner rather than later, so first examine the expected
  38         // type, and see if can glean a closure kind from there.
  39         let (expected_sig, expected_kind) = match expected.to_option(self) {
  40             Some(ty) => self.deduce_expectations_from_expected_type(ty),
  41             None => (None, None),
  42         };
  43         let body = self.tcx.hir.body(body_id);
  44         self.check_closure(expr, expected_kind, decl, body, expected_sig)
  45     }
  46
  47     fn check_closure(&self,
  48                      expr: &hir::Expr,
  49                      opt_kind: Option<ty::ClosureKind>,
  50                      decl: &'gcx hir::FnDecl,
  51                      body: &'gcx hir::Body,
  52                      expected_sig: Option<ty::FnSig<'tcx>>)
  53                      -> Ty<'tcx> {
  54         debug!("check_closure opt_kind={:?} expected_sig={:?}",
  55                opt_kind,
  56                expected_sig);
  57
  58         let expr_def_id = self.tcx.hir.local_def_id(expr.id);
  59         let sig = AstConv::ty_of_closure(self,
  60                                          hir::Unsafety::Normal,
  61                                          decl,
  62                                          Abi::RustCall,
  63                                          expected_sig);
  64         // `deduce_expectations_from_expected_type` introduces late-bound
  65         // lifetimes defined elsewhere, which we need to anonymize away.
  66         let sig = self.tcx.anonymize_late_bound_regions(&sig);
  67
  68         // Create type variables (for now) to represent the transformed
  69         // types of upvars. These will be unified during the upvar
  70         // inference phase (`upvar.rs`).
  71         let base_substs = Substs::identity_for_item(self.tcx,
  72             self.tcx.closure_base_def_id(expr_def_id));
  73         let closure_type = self.tcx.mk_closure(expr_def_id,
  74             base_substs.extend_to(self.tcx, expr_def_id,
  75                 |_, _| span_bug!(expr.span, "closure has region param"),
  76                 |_, _| self.infcx.next_ty_var(TypeVariableOrigin::TransformedUpvar(expr.span))
  77             )
  78         );
  79
  80         debug!("check_closure: expr.id={:?} closure_type={:?}", expr.id, closure_type);
  81
  82         let fn_sig = self.liberate_late_bound_regions(expr_def_id, &sig);
  83         let fn_sig = self.inh.normalize_associated_types_in(body.value.span,
  84                                                             body.value.id, &fn_sig);
  85
  86         check_fn(self, fn_sig, decl, expr.id, body);
  87
  88         // Tuple up the arguments and insert the resulting function type into
  89         // the `closures` table.
  90         let sig = sig.map_bound(|sig| self.tcx.mk_fn_sig(
  91             iter::once(self.tcx.intern_tup(sig.inputs(), false)),
  92             sig.output(),
  93             sig.variadic,
  94             sig.unsafety,
  95             sig.abi
  96         ));
  97
  98         debug!("closure for {:?} --> sig={:?} opt_kind={:?}",
  99                expr_def_id,
 100                sig,
 101                opt_kind);
 102
 103         self.tables.borrow_mut().closure_tys.insert(expr.id, sig);
 104         match opt_kind {
 105             Some(kind) => {
 106                 self.tables.borrow_mut().closure_kinds.insert(expr.id, (kind, None));
 107             }
 108             None => {}
 109         }
 110
 111         closure_type
 112     }
 113
 114     fn deduce_expectations_from_expected_type
 115         (&self,
 116          expected_ty: Ty<'tcx>)
 117          -> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
 118         debug!("deduce_expectations_from_expected_type(expected_ty={:?})",
 119                expected_ty);
 120
 121         match expected_ty.sty {
 122             ty::TyDynamic(ref object_type, ..) => {
 123                 let sig = object_type.projection_bounds()
 124                     .filter_map(|pb| {
 125                         let pb = pb.with_self_ty(self.tcx, self.tcx.types.err);
 126                         self.deduce_sig_from_projection(&pb)
 127                     })
 128                     .next();
 129                 let kind = object_type.principal()
 130                     .and_then(|p| self.tcx.lang_items.fn_trait_kind(p.def_id()));
 131                 (sig, kind)
 132             }
 133             ty::TyInfer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
 134             ty::TyFnPtr(sig) => (Some(sig.skip_binder().clone()), Some(ty::ClosureKind::Fn)),
 135             _ => (None, None),
 136         }
 137     }
 138
 139     fn deduce_expectations_from_obligations
 140         (&self,
 141          expected_vid: ty::TyVid)
 142          -> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
 143         let fulfillment_cx = self.fulfillment_cx.borrow();
 144         // Here `expected_ty` is known to be a type inference variable.
 145
 146         let expected_sig = fulfillment_cx.pending_obligations()
 147             .iter()
 148             .map(|obligation| &obligation.obligation)
 149             .filter_map(|obligation| {
 150                 debug!("deduce_expectations_from_obligations: obligation.predicate={:?}",
 151                        obligation.predicate);
 152
 153                 match obligation.predicate {
 154                     // Given a Projection predicate, we can potentially infer
 155                     // the complete signature.
 156                     ty::Predicate::Projection(ref proj_predicate) => {
 157                         let trait_ref = proj_predicate.to_poly_trait_ref();
 158                         self.self_type_matches_expected_vid(trait_ref, expected_vid)
 159                             .and_then(|_| self.deduce_sig_from_projection(proj_predicate))
 160                     }
 161                     _ => None,
 162                 }
 163             })
 164             .next();
 165
 166         // Even if we can't infer the full signature, we may be able to
 167         // infer the kind. This can occur if there is a trait-reference
 168         // like `F : Fn<A>`. Note that due to subtyping we could encounter
 169         // many viable options, so pick the most restrictive.
 170         let expected_kind = fulfillment_cx.pending_obligations()
 171             .iter()
 172             .map(|obligation| &obligation.obligation)
 173             .filter_map(|obligation| {
 174                 let opt_trait_ref = match obligation.predicate {
 175                     ty::Predicate::Projection(ref data) => Some(data.to_poly_trait_ref()),
 176                     ty::Predicate::Trait(ref data) => Some(data.to_poly_trait_ref()),
 177                     ty::Predicate::Equate(..) => None,
 178                     ty::Predicate::Subtype(..) => None,
 179                     ty::Predicate::RegionOutlives(..) => None,
 180                     ty::Predicate::TypeOutlives(..) => None,
 181                     ty::Predicate::WellFormed(..) => None,
 182                     ty::Predicate::ObjectSafe(..) => None,
 183
 184                     // NB: This predicate is created by breaking down a
 185                     // `ClosureType: FnFoo()` predicate, where
 186                     // `ClosureType` represents some `TyClosure`. It can't
 187                     // possibly be referring to the current closure,
 188                     // because we haven't produced the `TyClosure` for
 189                     // this closure yet; this is exactly why the other
 190                     // code is looking for a self type of a unresolved
 191                     // inference variable.
 192                     ty::Predicate::ClosureKind(..) => None,
 193                 };
 194                 opt_trait_ref.and_then(|tr| self.self_type_matches_expected_vid(tr, expected_vid))
 195                     .and_then(|tr| self.tcx.lang_items.fn_trait_kind(tr.def_id()))
 196             })
 197             .fold(None,
 198                   |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
 199
 200         (expected_sig, expected_kind)
 201     }
 202
 203     /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
 204     /// everything we need to know about a closure.
 205     fn deduce_sig_from_projection(&self,
 206                                   projection: &ty::PolyProjectionPredicate<'tcx>)
 207                                   -> Option<ty::FnSig<'tcx>> {
 208         let tcx = self.tcx;
 209
 210         debug!("deduce_sig_from_projection({:?})", projection);
 211
 212         let trait_ref = projection.to_poly_trait_ref();
 213
 214         if tcx.lang_items.fn_trait_kind(trait_ref.def_id()).is_none() {
 215             return None;
 216         }
 217
 218         let arg_param_ty = trait_ref.substs().type_at(1);
 219         let arg_param_ty = self.resolve_type_vars_if_possible(&arg_param_ty);
 220         debug!("deduce_sig_from_projection: arg_param_ty {:?}",
 221                arg_param_ty);
 222
 223         let input_tys = match arg_param_ty.sty {
 224             ty::TyTuple(tys, _) => tys.into_iter(),
 225             _ => {
 226                 return None;
 227             }
 228         };
 229
 230         let ret_param_ty = projection.0.ty;
 231         let ret_param_ty = self.resolve_type_vars_if_possible(&ret_param_ty);
 232         debug!("deduce_sig_from_projection: ret_param_ty {:?}", ret_param_ty);
 233
 234         let fn_sig = self.tcx.mk_fn_sig(
 235             input_tys.cloned(),
 236             ret_param_ty,
 237             false,
 238             hir::Unsafety::Normal,
 239             Abi::Rust
 240         );
 241         debug!("deduce_sig_from_projection: fn_sig {:?}", fn_sig);
 242
 243         Some(fn_sig)
 244     }
 245
 246     fn self_type_matches_expected_vid(&self,
 247                                       trait_ref: ty::PolyTraitRef<'tcx>,
 248                                       expected_vid: ty::TyVid)
 249                                       -> Option<ty::PolyTraitRef<'tcx>> {
 250         let self_ty = self.shallow_resolve(trait_ref.self_ty());
 251         debug!("self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?})",
 252                trait_ref,
 253                self_ty);
 254         match self_ty.sty {
 255             ty::TyInfer(ty::TyVar(v)) if expected_vid == v => Some(trait_ref),
 256             _ => None,
 257         }
 258     }
 259 }