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;
  16 use middle::subst;
  17 use middle::ty::{self, ToPolyTraitRef, Ty};
  18 use std::cmp;
  19 use syntax::abi;
  20 use rustc_front::hir;
  21
  22 pub fn check_expr_closure<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
  23                                    expr: &hir::Expr,
  24                                    _capture: hir::CaptureClause,
  25                                    decl: &'tcx hir::FnDecl,
  26                                    body: &'tcx hir::Block,
  27                                    expected: Expectation<'tcx>) {
  28     debug!("check_expr_closure(expr={:?},expected={:?})",
  29            expr,
  30            expected);
  31
  32     // It's always helpful for inference if we know the kind of
  33     // closure sooner rather than later, so first examine the expected
  34     // type, and see if can glean a closure kind from there.
  35     let (expected_sig,expected_kind) = match expected.to_option(fcx) {
  36         Some(ty) => deduce_expectations_from_expected_type(fcx, ty),
  37         None => (None, None)
  38     };
  39     check_closure(fcx, expr, expected_kind, decl, body, expected_sig)
  40 }
  41
  42 fn check_closure<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
  43                           expr: &hir::Expr,
  44                           opt_kind: Option<ty::ClosureKind>,
  45                           decl: &'tcx hir::FnDecl,
  46                           body: &'tcx hir::Block,
  47                           expected_sig: Option<ty::FnSig<'tcx>>) {
  48     let expr_def_id = fcx.tcx().map.local_def_id(expr.id);
  49
  50     debug!("check_closure opt_kind={:?} expected_sig={:?}",
  51            opt_kind,
  52            expected_sig);
  53
  54     let mut fn_ty = astconv::ty_of_closure(fcx,
  55                                            hir::Unsafety::Normal,
  56                                            decl,
  57                                            abi::RustCall,
  58                                            expected_sig);
  59
  60     // Create type variables (for now) to represent the transformed
  61     // types of upvars. These will be unified during the upvar
  62     // inference phase (`upvar.rs`).
  63     let num_upvars = fcx.tcx().with_freevars(expr.id, |fv| fv.len());
  64     let upvar_tys = fcx.infcx().next_ty_vars(num_upvars);
  65
  66     debug!("check_closure: expr.id={:?} upvar_tys={:?}",
  67            expr.id, upvar_tys);
  68
  69     let closure_type =
  70         fcx.ccx.tcx.mk_closure(
  71             expr_def_id,
  72             fcx.ccx.tcx.mk_substs(fcx.inh.infcx.parameter_environment.free_substs.clone()),
  73             upvar_tys);
  74
  75     fcx.write_ty(expr.id, closure_type);
  76
  77     let fn_sig = fcx.tcx().liberate_late_bound_regions(
  78         fcx.tcx().region_maps.item_extent(body.id), &fn_ty.sig);
  79
  80     check_fn(fcx.ccx,
  81              hir::Unsafety::Normal,
  82              expr.id,
  83              &fn_sig,
  84              decl,
  85              expr.id,
  86              &*body,
  87              fcx.inh);
  88
  89     // Tuple up the arguments and insert the resulting function type into
  90     // the `closures` table.
  91     fn_ty.sig.0.inputs = vec![fcx.tcx().mk_tup(fn_ty.sig.0.inputs)];
  92
  93     debug!("closure for {:?} --> sig={:?} opt_kind={:?}",
  94            expr_def_id,
  95            fn_ty.sig,
  96            opt_kind);
  97
  98     fcx.inh.tables.borrow_mut().closure_tys.insert(expr_def_id, fn_ty);
  99     match opt_kind {
 100         Some(kind) => { fcx.inh.tables.borrow_mut().closure_kinds.insert(expr_def_id, kind); }
 101         None => { }
 102     }
 103 }
 104
 105 fn deduce_expectations_from_expected_type<'a,'tcx>(
 106     fcx: &FnCtxt<'a,'tcx>,
 107     expected_ty: Ty<'tcx>)
 108     -> (Option<ty::FnSig<'tcx>>,Option<ty::ClosureKind>)
 109 {
 110     debug!("deduce_expectations_from_expected_type(expected_ty={:?})",
 111            expected_ty);
 112
 113     match expected_ty.sty {
 114         ty::TyTrait(ref object_type) => {
 115             let proj_bounds = object_type.projection_bounds_with_self_ty(fcx.tcx(),
 116                                                                          fcx.tcx().types.err);
 117             let sig = proj_bounds.iter()
 118                                  .filter_map(|pb| deduce_sig_from_projection(fcx, pb))
 119                                  .next();
 120             let kind = fcx.tcx().lang_items.fn_trait_kind(object_type.principal_def_id());
 121             (sig, kind)
 122         }
 123         ty::TyInfer(ty::TyVar(vid)) => {
 124             deduce_expectations_from_obligations(fcx, vid)
 125         }
 126         _ => {
 127             (None, None)
 128         }
 129     }
 130 }
 131
 132 fn deduce_expectations_from_obligations<'a,'tcx>(
 133     fcx: &FnCtxt<'a,'tcx>,
 134     expected_vid: ty::TyVid)
 135     -> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>)
 136 {
 137     let fulfillment_cx = fcx.inh.infcx.fulfillment_cx.borrow();
 138     // Here `expected_ty` is known to be a type inference variable.
 139
 140     let expected_sig =
 141         fulfillment_cx
 142         .pending_obligations()
 143         .iter()
 144         .filter_map(|obligation| {
 145             debug!("deduce_expectations_from_obligations: obligation.predicate={:?}",
 146                    obligation.predicate);
 147
 148             match obligation.predicate {
 149                 // Given a Projection predicate, we can potentially infer
 150                 // the complete signature.
 151                 ty::Predicate::Projection(ref proj_predicate) => {
 152                     let trait_ref = proj_predicate.to_poly_trait_ref();
 153                     self_type_matches_expected_vid(fcx, trait_ref, expected_vid)
 154                         .and_then(|_| deduce_sig_from_projection(fcx, proj_predicate))
 155                 }
 156                 _ => {
 157                     None
 158                 }
 159             }
 160         })
 161         .next();
 162
 163     // Even if we can't infer the full signature, we may be able to
 164     // infer the kind. This can occur if there is a trait-reference
 165     // like `F : Fn<A>`. Note that due to subtyping we could encounter
 166     // many viable options, so pick the most restrictive.
 167     let expected_kind =
 168         fulfillment_cx
 169         .pending_obligations()
 170         .iter()
 171         .filter_map(|obligation| {
 172             let opt_trait_ref = match obligation.predicate {
 173                 ty::Predicate::Projection(ref data) => Some(data.to_poly_trait_ref()),
 174                 ty::Predicate::Trait(ref data) => Some(data.to_poly_trait_ref()),
 175                 ty::Predicate::Equate(..) => None,
 176                 ty::Predicate::RegionOutlives(..) => None,
 177                 ty::Predicate::TypeOutlives(..) => None,
 178                 ty::Predicate::WellFormed(..) => None,
 179                 ty::Predicate::ObjectSafe(..) => None,
 180             };
 181             opt_trait_ref
 182                 .and_then(|trait_ref| self_type_matches_expected_vid(fcx, trait_ref, expected_vid))
 183                 .and_then(|trait_ref| fcx.tcx().lang_items.fn_trait_kind(trait_ref.def_id()))
 184         })
 185         .fold(None, pick_most_restrictive_closure_kind);
 186
 187     (expected_sig, expected_kind)
 188 }
 189
 190 fn pick_most_restrictive_closure_kind(best: Option<ty::ClosureKind>,
 191                                       cur: ty::ClosureKind)
 192                                       -> Option<ty::ClosureKind>
 193 {
 194     match best {
 195         None => Some(cur),
 196         Some(best) => Some(cmp::min(best, cur))
 197     }
 198 }
 199
 200 /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
 201 /// everything we need to know about a closure.
 202 fn deduce_sig_from_projection<'a,'tcx>(
 203     fcx: &FnCtxt<'a,'tcx>,
 204     projection: &ty::PolyProjectionPredicate<'tcx>)
 205     -> Option<ty::FnSig<'tcx>>
 206 {
 207     let tcx = fcx.tcx();
 208
 209     debug!("deduce_sig_from_projection({:?})",
 210            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().types.get(subst::TypeSpace, 0);
 219     let arg_param_ty = fcx.infcx().resolve_type_vars_if_possible(&arg_param_ty);
 220     debug!("deduce_sig_from_projection: arg_param_ty {:?}", arg_param_ty);
 221
 222     let input_tys = match arg_param_ty.sty {
 223         ty::TyTuple(ref tys) => { (*tys).clone() }
 224         _ => { return None; }
 225     };
 226     debug!("deduce_sig_from_projection: input_tys {:?}", input_tys);
 227
 228     let ret_param_ty = projection.0.ty;
 229     let ret_param_ty = fcx.infcx().resolve_type_vars_if_possible(&ret_param_ty);
 230     debug!("deduce_sig_from_projection: ret_param_ty {:?}", ret_param_ty);
 231
 232     let fn_sig = ty::FnSig {
 233         inputs: input_tys,
 234         output: ty::FnConverging(ret_param_ty),
 235         variadic: false
 236     };
 237     debug!("deduce_sig_from_projection: fn_sig {:?}", fn_sig);
 238
 239     Some(fn_sig)
 240 }
 241
 242 fn self_type_matches_expected_vid<'a,'tcx>(
 243     fcx: &FnCtxt<'a,'tcx>,
 244     trait_ref: ty::PolyTraitRef<'tcx>,
 245     expected_vid: ty::TyVid)
 246     -> Option<ty::PolyTraitRef<'tcx>>
 247 {
 248     let self_ty = fcx.infcx().shallow_resolve(trait_ref.self_ty());
 249     debug!("self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?})",
 250            trait_ref,
 251            self_ty);
 252     match self_ty.sty {
 253         ty::TyInfer(ty::TyVar(v)) if expected_vid == v => Some(trait_ref),
 254         _ => None,
 255     }
 256 }