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