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::AutorefArgs;
  13 use super::check_argument_types;
  14 use super::check_expr;
  15 use super::check_method_argument_types;
  16 use super::demand;
  17 use super::DeferredCallResolution;
  18 use super::err_args;
  19 use super::Expectation;
  20 use super::expected_types_for_fn_args;
  21 use super::FnCtxt;
  22 use super::LvaluePreference;
  23 use super::method;
  24 use super::structurally_resolved_type;
  25 use super::TupleArgumentsFlag;
  26 use super::UnresolvedTypeAction;
  27 use super::write_call;
  28
  29 use CrateCtxt;
  30 use middle::infer;
  31 use middle::ty::{self, Ty, ClosureTyper};
  32 use syntax::ast;
  33 use syntax::codemap::Span;
  34 use syntax::parse::token;
  35 use syntax::ptr::P;
  36 use util::ppaux::Repr;
  37
  38 /// Check that it is legal to call methods of the trait corresponding
  39 /// to `trait_id` (this only cares about the trait, not the specific
  40 /// method that is called)
  41 pub fn check_legal_trait_for_method_call(ccx: &CrateCtxt, span: Span, trait_id: ast::DefId) {
  42     let tcx = ccx.tcx;
  43     let did = Some(trait_id);
  44     let li = &tcx.lang_items;
  45
  46     if did == li.drop_trait() {
  47         span_err!(tcx.sess, span, E0040, "explicit use of destructor method");
  48     } else if !tcx.sess.features.borrow().unboxed_closures {
  49         // the #[feature(unboxed_closures)] feature isn't
  50         // activated so we need to enforce the closure
  51         // restrictions.
  52
  53         let method = if did == li.fn_trait() {
  54             "call"
  55         } else if did == li.fn_mut_trait() {
  56             "call_mut"
  57         } else if did == li.fn_once_trait() {
  58             "call_once"
  59         } else {
  60             return // not a closure method, everything is OK.
  61         };
  62
  63         span_err!(tcx.sess, span, E0174,
  64                   "explicit use of unboxed closure method `{}` is experimental",
  65                   method);
  66         span_help!(tcx.sess, span,
  67                    "add `#![feature(unboxed_closures)]` to the crate attributes to enable");
  68     }
  69 }
  70
  71 pub fn check_call<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
  72                             call_expr: &'tcx ast::Expr,
  73                             callee_expr: &'tcx ast::Expr,
  74                             arg_exprs: &'tcx [P<ast::Expr>],
  75                             expected: Expectation<'tcx>)
  76 {
  77     check_expr(fcx, callee_expr);
  78     let original_callee_ty = fcx.expr_ty(callee_expr);
  79     let (callee_ty, _, result) =
  80         autoderef(fcx,
  81                   callee_expr.span,
  82                   original_callee_ty,
  83                   Some(callee_expr),
  84                   UnresolvedTypeAction::Error,
  85                   LvaluePreference::NoPreference,
  86                   |adj_ty, idx| {
  87                       let autoderefref = ty::AutoDerefRef { autoderefs: idx, autoref: None };
  88                       try_overloaded_call_step(fcx, call_expr, callee_expr,
  89                                                adj_ty, autoderefref)
  90                   });
  91
  92     match result {
  93         None => {
  94             // this will report an error since original_callee_ty is not a fn
  95             confirm_builtin_call(fcx, call_expr, original_callee_ty, arg_exprs, expected);
  96         }
  97
  98         Some(CallStep::Builtin) => {
  99             confirm_builtin_call(fcx, call_expr, callee_ty, arg_exprs, expected);
 100         }
 101
 102         Some(CallStep::DeferredClosure(fn_sig)) => {
 103             confirm_deferred_closure_call(fcx, call_expr, arg_exprs, expected, fn_sig);
 104         }
 105
 106         Some(CallStep::Overloaded(method_callee)) => {
 107             confirm_overloaded_call(fcx, call_expr, callee_expr,
 108                                     arg_exprs, expected, method_callee);
 109         }
 110     }
 111 }
 112
 113 enum CallStep<'tcx> {
 114     Builtin,
 115     DeferredClosure(ty::FnSig<'tcx>),
 116     Overloaded(ty::MethodCallee<'tcx>)
 117 }
 118
 119 fn try_overloaded_call_step<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 120                                       call_expr: &'tcx ast::Expr,
 121                                       callee_expr: &'tcx ast::Expr,
 122                                       adjusted_ty: Ty<'tcx>,
 123                                       autoderefref: ty::AutoDerefRef<'tcx>)
 124                                       -> Option<CallStep<'tcx>>
 125 {
 126     debug!("try_overloaded_call_step(call_expr={}, adjusted_ty={}, autoderefref={})",
 127            call_expr.repr(fcx.tcx()),
 128            adjusted_ty.repr(fcx.tcx()),
 129            autoderefref.repr(fcx.tcx()));
 130
 131     // If the callee is a bare function or a closure, then we're all set.
 132     match structurally_resolved_type(fcx, callee_expr.span, adjusted_ty).sty {
 133         ty::ty_bare_fn(..) => {
 134             fcx.write_adjustment(callee_expr.id,
 135                                  callee_expr.span,
 136                                  ty::AdjustDerefRef(autoderefref));
 137             return Some(CallStep::Builtin);
 138         }
 139
 140         ty::ty_closure(def_id, _, substs) => {
 141             assert_eq!(def_id.krate, ast::LOCAL_CRATE);
 142
 143             // Check whether this is a call to a closure where we
 144             // haven't yet decided on whether the closure is fn vs
 145             // fnmut vs fnonce. If so, we have to defer further processing.
 146             if fcx.closure_kind(def_id).is_none() {
 147                 let closure_ty =
 148                     fcx.closure_type(def_id, substs);
 149                 let fn_sig =
 150                     fcx.infcx().replace_late_bound_regions_with_fresh_var(call_expr.span,
 151                                                                           infer::FnCall,
 152                                                                           &closure_ty.sig).0;
 153                 fcx.record_deferred_call_resolution(
 154                     def_id,
 155                     box CallResolution {call_expr: call_expr,
 156                                         callee_expr: callee_expr,
 157                                         adjusted_ty: adjusted_ty,
 158                                         autoderefref: autoderefref,
 159                                         fn_sig: fn_sig.clone(),
 160                                         closure_def_id: def_id});
 161                 return Some(CallStep::DeferredClosure(fn_sig));
 162             }
 163         }
 164
 165         _ => {}
 166     }
 167
 168     try_overloaded_call_traits(fcx, call_expr, callee_expr, adjusted_ty, autoderefref)
 169         .map(|method_callee| CallStep::Overloaded(method_callee))
 170 }
 171
 172 fn try_overloaded_call_traits<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 173                                        call_expr: &ast::Expr,
 174                                        callee_expr: &ast::Expr,
 175                                        adjusted_ty: Ty<'tcx>,
 176                                        autoderefref: ty::AutoDerefRef<'tcx>)
 177                                        -> Option<ty::MethodCallee<'tcx>>
 178 {
 179     // Try the options that are least restrictive on the caller first.
 180     for &(opt_trait_def_id, method_name) in [
 181         (fcx.tcx().lang_items.fn_trait(), token::intern("call")),
 182         (fcx.tcx().lang_items.fn_mut_trait(), token::intern("call_mut")),
 183         (fcx.tcx().lang_items.fn_once_trait(), token::intern("call_once")),
 184     ].iter() {
 185         let trait_def_id = match opt_trait_def_id {
 186             Some(def_id) => def_id,
 187             None => continue,
 188         };
 189
 190         match method::lookup_in_trait_adjusted(fcx,
 191                                                call_expr.span,
 192                                                Some(&*callee_expr),
 193                                                method_name,
 194                                                trait_def_id,
 195                                                autoderefref.clone(),
 196                                                adjusted_ty,
 197                                                None) {
 198             None => continue,
 199             Some(method_callee) => {
 200                 return Some(method_callee);
 201             }
 202         }
 203     }
 204
 205     None
 206 }
 207
 208 fn confirm_builtin_call<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
 209                                  call_expr: &ast::Expr,
 210                                  callee_ty: Ty<'tcx>,
 211                                  arg_exprs: &'tcx [P<ast::Expr>],
 212                                  expected: Expectation<'tcx>)
 213 {
 214     let error_fn_sig;
 215
 216     let fn_sig = match callee_ty.sty {
 217         ty::ty_bare_fn(_, &ty::BareFnTy {ref sig, ..}) => {
 218             sig
 219         }
 220         _ => {
 221             fcx.type_error_message(call_expr.span, |actual| {
 222                 format!("expected function, found `{}`", actual)
 223             }, callee_ty, None);
 224
 225             // This is the "default" function signature, used in case of error.
 226             // In that case, we check each argument against "error" in order to
 227             // set up all the node type bindings.
 228             error_fn_sig = ty::Binder(ty::FnSig {
 229                 inputs: err_args(fcx.tcx(), arg_exprs.len()),
 230                 output: ty::FnConverging(fcx.tcx().types.err),
 231                 variadic: false
 232             });
 233
 234             &error_fn_sig
 235         }
 236     };
 237
 238     // Replace any late-bound regions that appear in the function
 239     // signature with region variables. We also have to
 240     // renormalize the associated types at this point, since they
 241     // previously appeared within a `Binder<>` and hence would not
 242     // have been normalized before.
 243     let fn_sig =
 244         fcx.infcx().replace_late_bound_regions_with_fresh_var(call_expr.span,
 245                                                               infer::FnCall,
 246                                                               fn_sig).0;
 247     let fn_sig =
 248         fcx.normalize_associated_types_in(call_expr.span, &fn_sig);
 249
 250     // Call the generic checker.
 251     let expected_arg_tys = expected_types_for_fn_args(fcx,
 252                                                       call_expr.span,
 253                                                       expected,
 254                                                       fn_sig.output,
 255                                                       &fn_sig.inputs);
 256     check_argument_types(fcx,
 257                          call_expr.span,
 258                          &fn_sig.inputs,
 259                          &expected_arg_tys[],
 260                          arg_exprs,
 261                          AutorefArgs::No,
 262                          fn_sig.variadic,
 263                          TupleArgumentsFlag::DontTupleArguments);
 264
 265     write_call(fcx, call_expr, fn_sig.output);
 266 }
 267
 268 fn confirm_deferred_closure_call<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
 269                                           call_expr: &ast::Expr,
 270                                           arg_exprs: &'tcx [P<ast::Expr>],
 271                                           expected: Expectation<'tcx>,
 272                                           fn_sig: ty::FnSig<'tcx>)
 273 {
 274     // `fn_sig` is the *signature* of the cosure being called. We
 275     // don't know the full details yet (`Fn` vs `FnMut` etc), but we
 276     // do know the types expected for each argument and the return
 277     // type.
 278
 279     let expected_arg_tys =
 280         expected_types_for_fn_args(fcx,
 281                                    call_expr.span,
 282                                    expected,
 283                                    fn_sig.output.clone(),
 284                                    &*fn_sig.inputs);
 285
 286     check_argument_types(fcx,
 287                          call_expr.span,
 288                          &*fn_sig.inputs,
 289                          &*expected_arg_tys,
 290                          arg_exprs,
 291                          AutorefArgs::No,
 292                          fn_sig.variadic,
 293                          TupleArgumentsFlag::TupleArguments);
 294
 295     write_call(fcx, call_expr, fn_sig.output);
 296 }
 297
 298 fn confirm_overloaded_call<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 299                                     call_expr: &ast::Expr,
 300                                     callee_expr: &'tcx ast::Expr,
 301                                     arg_exprs: &'tcx [P<ast::Expr>],
 302                                     expected: Expectation<'tcx>,
 303                                     method_callee: ty::MethodCallee<'tcx>)
 304 {
 305     let output_type =
 306         check_method_argument_types(fcx,
 307                                     call_expr.span,
 308                                     method_callee.ty,
 309                                     callee_expr,
 310                                     arg_exprs,
 311                                     AutorefArgs::No,
 312                                     TupleArgumentsFlag::TupleArguments,
 313                                     expected);
 314     write_call(fcx, call_expr, output_type);
 315
 316     write_overloaded_call_method_map(fcx, call_expr, method_callee);
 317 }
 318
 319 fn write_overloaded_call_method_map<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 320                                              call_expr: &ast::Expr,
 321                                              method_callee: ty::MethodCallee<'tcx>) {
 322     let method_call = ty::MethodCall::expr(call_expr.id);
 323     fcx.inh.method_map.borrow_mut().insert(method_call, method_callee);
 324 }
 325
 326 struct CallResolution<'tcx> {
 327     call_expr: &'tcx ast::Expr,
 328     callee_expr: &'tcx ast::Expr,
 329     adjusted_ty: Ty<'tcx>,
 330     autoderefref: ty::AutoDerefRef<'tcx>,
 331     fn_sig: ty::FnSig<'tcx>,
 332     closure_def_id: ast::DefId,
 333 }
 334
 335 impl<'tcx> Repr<'tcx> for CallResolution<'tcx> {
 336     fn repr(&self, tcx: &ty::ctxt<'tcx>) -> String {
 337         format!("CallResolution(call_expr={}, callee_expr={}, adjusted_ty={}, \
 338                 autoderefref={}, fn_sig={}, closure_def_id={})",
 339                 self.call_expr.repr(tcx),
 340                 self.callee_expr.repr(tcx),
 341                 self.adjusted_ty.repr(tcx),
 342                 self.autoderefref.repr(tcx),
 343                 self.fn_sig.repr(tcx),
 344                 self.closure_def_id.repr(tcx))
 345     }
 346 }
 347
 348 impl<'tcx> DeferredCallResolution<'tcx> for CallResolution<'tcx> {
 349     fn resolve<'a>(&mut self, fcx: &FnCtxt<'a,'tcx>) {
 350         debug!("DeferredCallResolution::resolve() {}",
 351                self.repr(fcx.tcx()));
 352
 353         // we should not be invoked until the closure kind has been
 354         // determined by upvar inference
 355         assert!(fcx.closure_kind(self.closure_def_id).is_some());
 356
 357         // We may now know enough to figure out fn vs fnmut etc.
 358         match try_overloaded_call_traits(fcx, self.call_expr, self.callee_expr,
 359                                          self.adjusted_ty, self.autoderefref.clone()) {
 360             Some(method_callee) => {
 361                 // One problem is that when we get here, we are going
 362                 // to have a newly instantiated function signature
 363                 // from the call trait. This has to be reconciled with
 364                 // the older function signature we had before. In
 365                 // principle we *should* be able to fn_sigs(), but we
 366                 // can't because of the annoying need for a TypeTrace.
 367                 // (This always bites me, should find a way to
 368                 // refactor it.)
 369                 let method_sig =
 370                     ty::assert_no_late_bound_regions(fcx.tcx(),
 371                                                      ty::ty_fn_sig(method_callee.ty));
 372
 373                 debug!("attempt_resolution: method_callee={}",
 374                        method_callee.repr(fcx.tcx()));
 375
 376                 for (&method_arg_ty, &self_arg_ty) in
 377                     method_sig.inputs[1..].iter().zip(self.fn_sig.inputs.iter())
 378                 {
 379                     demand::eqtype(fcx, self.call_expr.span, self_arg_ty, method_arg_ty);
 380                 }
 381
 382                 demand::eqtype(fcx,
 383                                self.call_expr.span,
 384                                method_sig.output.unwrap(),
 385                                self.fn_sig.output.unwrap());
 386
 387                 write_overloaded_call_method_map(fcx, self.call_expr, method_callee);
 388             }
 389             None => {
 390                 fcx.tcx().sess.span_bug(
 391                     self.call_expr.span,
 392                     "failed to find an overloaded call trait for closure call");
 393             }
 394         }
 395     }
 396 }