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.
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.
11 //! Code for type-checking closure expressions.
13 use super::{check_fn, Expectation, FnCtxt};
16 use rustc::infer::type_variable::TypeVariableOrigin;
17 use rustc::ty::{self, ToPolyTraitRef, Ty};
18 use rustc::ty::subst::Substs;
24 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
25 pub fn check_expr_closure(&self,
27 _capture: hir::CaptureClause,
28 decl: &'gcx hir::FnDecl,
30 expected: Expectation<'tcx>)
32 debug!("check_expr_closure(expr={:?},expected={:?})",
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),
43 let body = self.tcx.hir.body(body_id);
44 self.check_closure(expr, expected_kind, decl, body, expected_sig)
47 fn check_closure(&self,
49 opt_kind: Option<ty::ClosureKind>,
50 decl: &'gcx hir::FnDecl,
51 body: &'gcx hir::Body,
52 expected_sig: Option<ty::FnSig<'tcx>>)
54 debug!("check_closure opt_kind={:?} expected_sig={:?}",
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,
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);
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))
80 debug!("check_closure: expr.id={:?} closure_type={:?}", expr.id, closure_type);
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,
88 check_fn(self, self.param_env, fn_sig, decl, expr.id, body);
90 // Tuple up the arguments and insert the resulting function type into
91 // the `closures` table.
92 let sig = sig.map_bound(|sig| self.tcx.mk_fn_sig(
93 iter::once(self.tcx.intern_tup(sig.inputs(), false)),
100 debug!("closure for {:?} --> sig={:?} opt_kind={:?}",
106 let mut tables = self.tables.borrow_mut();
107 tables.closure_tys_mut().insert(expr.hir_id, sig);
110 tables.closure_kinds_mut().insert(expr.hir_id, (kind, None));
119 fn deduce_expectations_from_expected_type
121 expected_ty: Ty<'tcx>)
122 -> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
123 debug!("deduce_expectations_from_expected_type(expected_ty={:?})",
126 match expected_ty.sty {
127 ty::TyDynamic(ref object_type, ..) => {
128 let sig = object_type.projection_bounds()
130 let pb = pb.with_self_ty(self.tcx, self.tcx.types.err);
131 self.deduce_sig_from_projection(&pb)
134 let kind = object_type.principal()
135 .and_then(|p| self.tcx.lang_items.fn_trait_kind(p.def_id()));
138 ty::TyInfer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
139 ty::TyFnPtr(sig) => (Some(sig.skip_binder().clone()), Some(ty::ClosureKind::Fn)),
144 fn deduce_expectations_from_obligations
146 expected_vid: ty::TyVid)
147 -> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
148 let fulfillment_cx = self.fulfillment_cx.borrow();
149 // Here `expected_ty` is known to be a type inference variable.
151 let expected_sig = fulfillment_cx.pending_obligations()
153 .map(|obligation| &obligation.obligation)
154 .filter_map(|obligation| {
155 debug!("deduce_expectations_from_obligations: obligation.predicate={:?}",
156 obligation.predicate);
158 match obligation.predicate {
159 // Given a Projection predicate, we can potentially infer
160 // the complete signature.
161 ty::Predicate::Projection(ref proj_predicate) => {
162 let trait_ref = proj_predicate.to_poly_trait_ref(self.tcx);
163 self.self_type_matches_expected_vid(trait_ref, expected_vid)
164 .and_then(|_| self.deduce_sig_from_projection(proj_predicate))
171 // Even if we can't infer the full signature, we may be able to
172 // infer the kind. This can occur if there is a trait-reference
173 // like `F : Fn<A>`. Note that due to subtyping we could encounter
174 // many viable options, so pick the most restrictive.
175 let expected_kind = fulfillment_cx.pending_obligations()
177 .map(|obligation| &obligation.obligation)
178 .filter_map(|obligation| {
179 let opt_trait_ref = match obligation.predicate {
180 ty::Predicate::Projection(ref data) => Some(data.to_poly_trait_ref(self.tcx)),
181 ty::Predicate::Trait(ref data) => Some(data.to_poly_trait_ref()),
182 ty::Predicate::Equate(..) => None,
183 ty::Predicate::Subtype(..) => None,
184 ty::Predicate::RegionOutlives(..) => None,
185 ty::Predicate::TypeOutlives(..) => None,
186 ty::Predicate::WellFormed(..) => None,
187 ty::Predicate::ObjectSafe(..) => None,
189 // NB: This predicate is created by breaking down a
190 // `ClosureType: FnFoo()` predicate, where
191 // `ClosureType` represents some `TyClosure`. It can't
192 // possibly be referring to the current closure,
193 // because we haven't produced the `TyClosure` for
194 // this closure yet; this is exactly why the other
195 // code is looking for a self type of a unresolved
196 // inference variable.
197 ty::Predicate::ClosureKind(..) => None,
199 opt_trait_ref.and_then(|tr| self.self_type_matches_expected_vid(tr, expected_vid))
200 .and_then(|tr| self.tcx.lang_items.fn_trait_kind(tr.def_id()))
203 |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
205 (expected_sig, expected_kind)
208 /// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
209 /// everything we need to know about a closure.
210 fn deduce_sig_from_projection(&self,
211 projection: &ty::PolyProjectionPredicate<'tcx>)
212 -> Option<ty::FnSig<'tcx>> {
215 debug!("deduce_sig_from_projection({:?})", projection);
217 let trait_ref = projection.to_poly_trait_ref(tcx);
219 if tcx.lang_items.fn_trait_kind(trait_ref.def_id()).is_none() {
223 let arg_param_ty = trait_ref.substs().type_at(1);
224 let arg_param_ty = self.resolve_type_vars_if_possible(&arg_param_ty);
225 debug!("deduce_sig_from_projection: arg_param_ty {:?}",
228 let input_tys = match arg_param_ty.sty {
229 ty::TyTuple(tys, _) => tys.into_iter(),
235 let ret_param_ty = projection.0.ty;
236 let ret_param_ty = self.resolve_type_vars_if_possible(&ret_param_ty);
237 debug!("deduce_sig_from_projection: ret_param_ty {:?}", ret_param_ty);
239 let fn_sig = self.tcx.mk_fn_sig(
243 hir::Unsafety::Normal,
246 debug!("deduce_sig_from_projection: fn_sig {:?}", fn_sig);
251 fn self_type_matches_expected_vid(&self,
252 trait_ref: ty::PolyTraitRef<'tcx>,
253 expected_vid: ty::TyVid)
254 -> Option<ty::PolyTraitRef<'tcx>> {
255 let self_ty = self.shallow_resolve(trait_ref.self_ty());
256 debug!("self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?})",
260 ty::TyInfer(ty::TyVar(v)) if expected_vid == v => Some(trait_ref),