src/librustc_typeck/check/callee.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 use super::autoderef;
  12 use super::check_argument_types;
  13 use super::check_expr;
  14 use super::check_method_argument_types;
  15 use super::demand;
  16 use super::DeferredCallResolution;
  17 use super::err_args;
  18 use super::Expectation;
  19 use super::expected_types_for_fn_args;
  20 use super::FnCtxt;
  21 use super::LvaluePreference;
  22 use super::method;
  23 use super::structurally_resolved_type;
  24 use super::TupleArgumentsFlag;
  25 use super::UnresolvedTypeAction;
  26 use super::write_call;
  27
  28 use CrateCtxt;
  29 use middle::infer;
  30 use middle::ty::{self, Ty};
  31 use syntax::ast;
  32 use syntax::codemap::Span;
  33 use syntax::parse::token;
  34 use syntax::ptr::P;
  35
  36 /// Check that it is legal to call methods of the trait corresponding
  37 /// to `trait_id` (this only cares about the trait, not the specific
  38 /// method that is called)
  39 pub fn check_legal_trait_for_method_call(ccx: &CrateCtxt, span: Span, trait_id: ast::DefId) {
  40     let tcx = ccx.tcx;
  41     let did = Some(trait_id);
  42     let li = &tcx.lang_items;
  43
  44     if did == li.drop_trait() {
  45         span_err!(tcx.sess, span, E0040, "explicit use of destructor method");
  46     } else if !tcx.sess.features.borrow().unboxed_closures {
  47         // the #[feature(unboxed_closures)] feature isn't
  48         // activated so we need to enforce the closure
  49         // restrictions.
  50
  51         let method = if did == li.fn_trait() {
  52             "call"
  53         } else if did == li.fn_mut_trait() {
  54             "call_mut"
  55         } else if did == li.fn_once_trait() {
  56             "call_once"
  57         } else {
  58             return // not a closure method, everything is OK.
  59         };
  60
  61         span_err!(tcx.sess, span, E0174,
  62                   "explicit use of unboxed closure method `{}` is experimental",
  63                   method);
  64         fileline_help!(tcx.sess, span,
  65                    "add `#![feature(unboxed_closures)]` to the crate attributes to enable");
  66     }
  67 }
  68
  69 pub fn check_call<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
  70                             call_expr: &'tcx ast::Expr,
  71                             callee_expr: &'tcx ast::Expr,
  72                             arg_exprs: &'tcx [P<ast::Expr>],
  73                             expected: Expectation<'tcx>)
  74 {
  75     check_expr(fcx, callee_expr);
  76     let original_callee_ty = fcx.expr_ty(callee_expr);
  77     let (callee_ty, _, result) =
  78         autoderef(fcx,
  79                   callee_expr.span,
  80                   original_callee_ty,
  81                   Some(callee_expr),
  82                   UnresolvedTypeAction::Error,
  83                   LvaluePreference::NoPreference,
  84                   |adj_ty, idx| {
  85                       try_overloaded_call_step(fcx, call_expr, callee_expr, adj_ty, idx)
  86                   });
  87
  88     match result {
  89         None => {
  90             // this will report an error since original_callee_ty is not a fn
  91             confirm_builtin_call(fcx, call_expr, original_callee_ty, arg_exprs, expected);
  92         }
  93
  94         Some(CallStep::Builtin) => {
  95             confirm_builtin_call(fcx, call_expr, callee_ty, arg_exprs, expected);
  96         }
  97
  98         Some(CallStep::DeferredClosure(fn_sig)) => {
  99             confirm_deferred_closure_call(fcx, call_expr, arg_exprs, expected, fn_sig);
 100         }
 101
 102         Some(CallStep::Overloaded(method_callee)) => {
 103             confirm_overloaded_call(fcx, call_expr, callee_expr,
 104                                     arg_exprs, expected, method_callee);
 105         }
 106     }
 107 }
 108
 109 enum CallStep<'tcx> {
 110     Builtin,
 111     DeferredClosure(ty::FnSig<'tcx>),
 112     Overloaded(ty::MethodCallee<'tcx>)
 113 }
 114
 115 fn try_overloaded_call_step<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 116                                       call_expr: &'tcx ast::Expr,
 117                                       callee_expr: &'tcx ast::Expr,
 118                                       adjusted_ty: Ty<'tcx>,
 119                                       autoderefs: usize)
 120                                       -> Option<CallStep<'tcx>>
 121 {
 122     debug!("try_overloaded_call_step(call_expr={:?}, adjusted_ty={:?}, autoderefs={})",
 123            call_expr,
 124            adjusted_ty,
 125            autoderefs);
 126
 127     // If the callee is a bare function or a closure, then we're all set.
 128     match structurally_resolved_type(fcx, callee_expr.span, adjusted_ty).sty {
 129         ty::TyBareFn(..) => {
 130             fcx.write_autoderef_adjustment(callee_expr.id, autoderefs);
 131             return Some(CallStep::Builtin);
 132         }
 133
 134         ty::TyClosure(def_id, ref substs) => {
 135             assert_eq!(def_id.krate, ast::LOCAL_CRATE);
 136
 137             // Check whether this is a call to a closure where we
 138             // haven't yet decided on whether the closure is fn vs
 139             // fnmut vs fnonce. If so, we have to defer further processing.
 140             if fcx.infcx().closure_kind(def_id).is_none() {
 141                 let closure_ty =
 142                     fcx.infcx().closure_type(def_id, substs);
 143                 let fn_sig =
 144                     fcx.infcx().replace_late_bound_regions_with_fresh_var(call_expr.span,
 145                                                                           infer::FnCall,
 146                                                                           &closure_ty.sig).0;
 147                 fcx.record_deferred_call_resolution(def_id, Box::new(CallResolution {
 148                     call_expr: call_expr,
 149                     callee_expr: callee_expr,
 150                     adjusted_ty: adjusted_ty,
 151                     autoderefs: autoderefs,
 152                     fn_sig: fn_sig.clone(),
 153                     closure_def_id: def_id
 154                 }));
 155                 return Some(CallStep::DeferredClosure(fn_sig));
 156             }
 157         }
 158
 159         // Hack: we know that there are traits implementing Fn for &F
 160         // where F:Fn and so forth. In the particular case of types
 161         // like `x: &mut FnMut()`, if there is a call `x()`, we would
 162         // normally translate to `FnMut::call_mut(&mut x, ())`, but
 163         // that winds up requiring `mut x: &mut FnMut()`. A little
 164         // over the top. The simplest fix by far is to just ignore
 165         // this case and deref again, so we wind up with
 166         // `FnMut::call_mut(&mut *x, ())`.
 167         ty::TyRef(..) if autoderefs == 0 => {
 168             return None;
 169         }
 170
 171         _ => {}
 172     }
 173
 174     try_overloaded_call_traits(fcx, call_expr, callee_expr, adjusted_ty, autoderefs)
 175         .map(|method_callee| CallStep::Overloaded(method_callee))
 176 }
 177
 178 fn try_overloaded_call_traits<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 179                                        call_expr: &ast::Expr,
 180                                        callee_expr: &ast::Expr,
 181                                        adjusted_ty: Ty<'tcx>,
 182                                        autoderefs: usize)
 183                                        -> Option<ty::MethodCallee<'tcx>>
 184 {
 185     // Try the options that are least restrictive on the caller first.
 186     for &(opt_trait_def_id, method_name) in &[
 187         (fcx.tcx().lang_items.fn_trait(), token::intern("call")),
 188         (fcx.tcx().lang_items.fn_mut_trait(), token::intern("call_mut")),
 189         (fcx.tcx().lang_items.fn_once_trait(), token::intern("call_once")),
 190     ] {
 191         let trait_def_id = match opt_trait_def_id {
 192             Some(def_id) => def_id,
 193             None => continue,
 194         };
 195
 196         match method::lookup_in_trait_adjusted(fcx,
 197                                                call_expr.span,
 198                                                Some(&*callee_expr),
 199                                                method_name,
 200                                                trait_def_id,
 201                                                autoderefs,
 202                                                false,
 203                                                adjusted_ty,
 204                                                None) {
 205             None => continue,
 206             Some(method_callee) => {
 207                 return Some(method_callee);
 208             }
 209         }
 210     }
 211
 212     None
 213 }
 214
 215 fn confirm_builtin_call<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
 216                                  call_expr: &ast::Expr,
 217                                  callee_ty: Ty<'tcx>,
 218                                  arg_exprs: &'tcx [P<ast::Expr>],
 219                                  expected: Expectation<'tcx>)
 220 {
 221     let error_fn_sig;
 222
 223     let fn_sig = match callee_ty.sty {
 224         ty::TyBareFn(_, &ty::BareFnTy {ref sig, ..}) => {
 225             sig
 226         }
 227         _ => {
 228             fcx.type_error_message(call_expr.span, |actual| {
 229                 format!("expected function, found `{}`", actual)
 230             }, callee_ty, None);
 231
 232             // This is the "default" function signature, used in case of error.
 233             // In that case, we check each argument against "error" in order to
 234             // set up all the node type bindings.
 235             error_fn_sig = ty::Binder(ty::FnSig {
 236                 inputs: err_args(fcx.tcx(), arg_exprs.len()),
 237                 output: ty::FnConverging(fcx.tcx().types.err),
 238                 variadic: false
 239             });
 240
 241             &error_fn_sig
 242         }
 243     };
 244
 245     // Replace any late-bound regions that appear in the function
 246     // signature with region variables. We also have to
 247     // renormalize the associated types at this point, since they
 248     // previously appeared within a `Binder<>` and hence would not
 249     // have been normalized before.
 250     let fn_sig =
 251         fcx.infcx().replace_late_bound_regions_with_fresh_var(call_expr.span,
 252                                                               infer::FnCall,
 253                                                               fn_sig).0;
 254     let fn_sig =
 255         fcx.normalize_associated_types_in(call_expr.span, &fn_sig);
 256
 257     // Call the generic checker.
 258     let expected_arg_tys = expected_types_for_fn_args(fcx,
 259                                                       call_expr.span,
 260                                                       expected,
 261                                                       fn_sig.output,
 262                                                       &fn_sig.inputs);
 263     check_argument_types(fcx,
 264                          call_expr.span,
 265                          &fn_sig.inputs,
 266                          &expected_arg_tys[..],
 267                          arg_exprs,
 268                          fn_sig.variadic,
 269                          TupleArgumentsFlag::DontTupleArguments);
 270
 271     write_call(fcx, call_expr, fn_sig.output);
 272 }
 273
 274 fn confirm_deferred_closure_call<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
 275                                           call_expr: &ast::Expr,
 276                                           arg_exprs: &'tcx [P<ast::Expr>],
 277                                           expected: Expectation<'tcx>,
 278                                           fn_sig: ty::FnSig<'tcx>)
 279 {
 280     // `fn_sig` is the *signature* of the cosure being called. We
 281     // don't know the full details yet (`Fn` vs `FnMut` etc), but we
 282     // do know the types expected for each argument and the return
 283     // type.
 284
 285     let expected_arg_tys =
 286         expected_types_for_fn_args(fcx,
 287                                    call_expr.span,
 288                                    expected,
 289                                    fn_sig.output.clone(),
 290                                    &*fn_sig.inputs);
 291
 292     check_argument_types(fcx,
 293                          call_expr.span,
 294                          &*fn_sig.inputs,
 295                          &*expected_arg_tys,
 296                          arg_exprs,
 297                          fn_sig.variadic,
 298                          TupleArgumentsFlag::TupleArguments);
 299
 300     write_call(fcx, call_expr, fn_sig.output);
 301 }
 302
 303 fn confirm_overloaded_call<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 304                                     call_expr: &ast::Expr,
 305                                     callee_expr: &'tcx ast::Expr,
 306                                     arg_exprs: &'tcx [P<ast::Expr>],
 307                                     expected: Expectation<'tcx>,
 308                                     method_callee: ty::MethodCallee<'tcx>)
 309 {
 310     let output_type =
 311         check_method_argument_types(fcx,
 312                                     call_expr.span,
 313                                     method_callee.ty,
 314                                     callee_expr,
 315                                     arg_exprs,
 316                                     TupleArgumentsFlag::TupleArguments,
 317                                     expected);
 318     write_call(fcx, call_expr, output_type);
 319
 320     write_overloaded_call_method_map(fcx, call_expr, method_callee);
 321 }
 322
 323 fn write_overloaded_call_method_map<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 324                                              call_expr: &ast::Expr,
 325                                              method_callee: ty::MethodCallee<'tcx>) {
 326     let method_call = ty::MethodCall::expr(call_expr.id);
 327     fcx.inh.tables.borrow_mut().method_map.insert(method_call, method_callee);
 328 }
 329
 330 #[derive(Debug)]
 331 struct CallResolution<'tcx> {
 332     call_expr: &'tcx ast::Expr,
 333     callee_expr: &'tcx ast::Expr,
 334     adjusted_ty: Ty<'tcx>,
 335     autoderefs: usize,
 336     fn_sig: ty::FnSig<'tcx>,
 337     closure_def_id: ast::DefId,
 338 }
 339
 340 impl<'tcx> DeferredCallResolution<'tcx> for CallResolution<'tcx> {
 341     fn resolve<'a>(&mut self, fcx: &FnCtxt<'a,'tcx>) {
 342         debug!("DeferredCallResolution::resolve() {:?}",
 343                self);
 344
 345         // we should not be invoked until the closure kind has been
 346         // determined by upvar inference
 347         assert!(fcx.infcx().closure_kind(self.closure_def_id).is_some());
 348
 349         // We may now know enough to figure out fn vs fnmut etc.
 350         match try_overloaded_call_traits(fcx, self.call_expr, self.callee_expr,
 351                                          self.adjusted_ty, self.autoderefs) {
 352             Some(method_callee) => {
 353                 // One problem is that when we get here, we are going
 354                 // to have a newly instantiated function signature
 355                 // from the call trait. This has to be reconciled with
 356                 // the older function signature we had before. In
 357                 // principle we *should* be able to fn_sigs(), but we
 358                 // can't because of the annoying need for a TypeTrace.
 359                 // (This always bites me, should find a way to
 360                 // refactor it.)
 361                 let method_sig = fcx.tcx().no_late_bound_regions(method_callee.ty.fn_sig())
 362                                           .unwrap();
 363
 364                 debug!("attempt_resolution: method_callee={:?}",
 365                        method_callee);
 366
 367                 for (&method_arg_ty, &self_arg_ty) in
 368                     method_sig.inputs[1..].iter().zip(&self.fn_sig.inputs)
 369                 {
 370                     demand::eqtype(fcx, self.call_expr.span, self_arg_ty, method_arg_ty);
 371                 }
 372
 373                 let nilty = fcx.tcx().mk_nil();
 374                 demand::eqtype(fcx,
 375                                self.call_expr.span,
 376                                method_sig.output.unwrap_or(nilty),
 377                                self.fn_sig.output.unwrap_or(nilty));
 378
 379                 write_overloaded_call_method_map(fcx, self.call_expr, method_callee);
 380             }
 381             None => {
 382                 fcx.tcx().sess.span_bug(
 383                     self.call_expr.span,
 384                     "failed to find an overloaded call trait for closure call");
 385             }
 386         }
 387     }
 388 }