New upstream version 1.15.0+dfsg1

[rustc.git] / src / librustc_typeck / check / callee.rs

// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use super::{DeferredCallResolution, Expectation, FnCtxt, TupleArgumentsFlag};

use CrateCtxt;
use hir::def::Def;
use hir::def_id::{DefId, LOCAL_CRATE};
use hir::print;
use rustc::{infer, traits};
use rustc::ty::{self, LvaluePreference, Ty};
use syntax::symbol::Symbol;
use syntax_pos::Span;

use rustc::hir;

/// Check that it is legal to call methods of the trait corresponding
/// to `trait_id` (this only cares about the trait, not the specific
/// method that is called)
pub fn check_legal_trait_for_method_call(ccx: &CrateCtxt, span: Span, trait_id: DefId) {
    if ccx.tcx.lang_items.drop_trait() == Some(trait_id) {
        struct_span_err!(ccx.tcx.sess,
                         span,
                         E0040,
                         "explicit use of destructor method")
            .span_label(span, &format!("explicit destructor calls not allowed"))
            .emit();
    }
}

enum CallStep<'tcx> {
    Builtin,
    DeferredClosure(ty::FnSig<'tcx>),
    Overloaded(ty::MethodCallee<'tcx>),
}

impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
    pub fn check_call(&self,
                      call_expr: &'gcx hir::Expr,
                      callee_expr: &'gcx hir::Expr,
                      arg_exprs: &'gcx [hir::Expr],
                      expected: Expectation<'tcx>)
                      -> Ty<'tcx> {
        let original_callee_ty = self.check_expr(callee_expr);
        let expr_ty = self.structurally_resolved_type(call_expr.span, original_callee_ty);

        let mut autoderef = self.autoderef(callee_expr.span, expr_ty);
        let result = autoderef.by_ref()
            .flat_map(|(adj_ty, idx)| {
                self.try_overloaded_call_step(call_expr, callee_expr, adj_ty, idx)
            })
            .next();
        let callee_ty = autoderef.unambiguous_final_ty();
        autoderef.finalize(LvaluePreference::NoPreference, Some(callee_expr));

        let output = match result {
            None => {
                // this will report an error since original_callee_ty is not a fn
                self.confirm_builtin_call(call_expr, original_callee_ty, arg_exprs, expected)
            }

            Some(CallStep::Builtin) => {
                self.confirm_builtin_call(call_expr, callee_ty, arg_exprs, expected)
            }

            Some(CallStep::DeferredClosure(fn_sig)) => {
                self.confirm_deferred_closure_call(call_expr, arg_exprs, expected, fn_sig)
            }

            Some(CallStep::Overloaded(method_callee)) => {
                self.confirm_overloaded_call(call_expr,
                                             callee_expr,
                                             arg_exprs,
                                             expected,
                                             method_callee)
            }
        };

        // we must check that return type of called functions is WF:
        self.register_wf_obligation(output, call_expr.span, traits::MiscObligation);

        output
    }

    fn try_overloaded_call_step(&self,
                                call_expr: &'gcx hir::Expr,
                                callee_expr: &'gcx hir::Expr,
                                adjusted_ty: Ty<'tcx>,
                                autoderefs: usize)
                                -> Option<CallStep<'tcx>> {
        debug!("try_overloaded_call_step(call_expr={:?}, adjusted_ty={:?}, autoderefs={})",
               call_expr,
               adjusted_ty,
               autoderefs);

        // If the callee is a bare function or a closure, then we're all set.
        match self.structurally_resolved_type(callee_expr.span, adjusted_ty).sty {
            ty::TyFnDef(..) | ty::TyFnPtr(_) => {
                self.write_autoderef_adjustment(callee_expr.id, autoderefs, adjusted_ty);
                return Some(CallStep::Builtin);
            }

            ty::TyClosure(def_id, substs) => {
                assert_eq!(def_id.krate, LOCAL_CRATE);

                // Check whether this is a call to a closure where we
                // haven't yet decided on whether the closure is fn vs
                // fnmut vs fnonce. If so, we have to defer further processing.
                if self.closure_kind(def_id).is_none() {
                    let closure_ty = self.closure_type(def_id, substs);
                    let fn_sig = self.replace_late_bound_regions_with_fresh_var(call_expr.span,
                                                                   infer::FnCall,
                                                                   &closure_ty.sig)
                        .0;
                    self.record_deferred_call_resolution(def_id,
                                                         Box::new(CallResolution {
                                                             call_expr: call_expr,
                                                             callee_expr: callee_expr,
                                                             adjusted_ty: adjusted_ty,
                                                             autoderefs: autoderefs,
                                                             fn_sig: fn_sig.clone(),
                                                             closure_def_id: def_id,
                                                         }));
                    return Some(CallStep::DeferredClosure(fn_sig));
                }
            }

            // Hack: we know that there are traits implementing Fn for &F
            // where F:Fn and so forth. In the particular case of types
            // like `x: &mut FnMut()`, if there is a call `x()`, we would
            // normally translate to `FnMut::call_mut(&mut x, ())`, but
            // that winds up requiring `mut x: &mut FnMut()`. A little
            // over the top. The simplest fix by far is to just ignore
            // this case and deref again, so we wind up with
            // `FnMut::call_mut(&mut *x, ())`.
            ty::TyRef(..) if autoderefs == 0 => {
                return None;
            }

            _ => {}
        }

        self.try_overloaded_call_traits(call_expr, callee_expr, adjusted_ty, autoderefs)
            .map(|method_callee| CallStep::Overloaded(method_callee))
    }

    fn try_overloaded_call_traits(&self,
                                  call_expr: &hir::Expr,
                                  callee_expr: &hir::Expr,
                                  adjusted_ty: Ty<'tcx>,
                                  autoderefs: usize)
                                  -> Option<ty::MethodCallee<'tcx>> {
        // Try the options that are least restrictive on the caller first.
        for &(opt_trait_def_id, method_name) in
            &[(self.tcx.lang_items.fn_trait(), Symbol::intern("call")),
              (self.tcx.lang_items.fn_mut_trait(), Symbol::intern("call_mut")),
              (self.tcx.lang_items.fn_once_trait(), Symbol::intern("call_once"))] {
            let trait_def_id = match opt_trait_def_id {
                Some(def_id) => def_id,
                None => continue,
            };

            match self.lookup_method_in_trait_adjusted(call_expr.span,
                                                       Some(&callee_expr),
                                                       method_name,
                                                       trait_def_id,
                                                       autoderefs,
                                                       false,
                                                       adjusted_ty,
                                                       None) {
                None => continue,
                Some(method_callee) => {
                    return Some(method_callee);
                }
            }
        }

        None
    }

    fn confirm_builtin_call(&self,
                            call_expr: &hir::Expr,
                            callee_ty: Ty<'tcx>,
                            arg_exprs: &'gcx [hir::Expr],
                            expected: Expectation<'tcx>)
                            -> Ty<'tcx> {
        let error_fn_sig;

        let (fn_sig, def_span) = match callee_ty.sty {
            ty::TyFnDef(def_id, .., &ty::BareFnTy {ref sig, ..}) => {
                (sig, self.tcx.map.span_if_local(def_id))
            }
            ty::TyFnPtr(&ty::BareFnTy {ref sig, ..}) => (sig, None),
            ref t => {
                let mut unit_variant = None;
                if let &ty::TyAdt(adt_def, ..) = t {
                    if adt_def.is_enum() {
                        if let hir::ExprCall(ref expr, _) = call_expr.node {
                            unit_variant = Some(print::expr_to_string(expr))
                        }
                    }
                }
                let mut err = if let Some(path) = unit_variant {
                    let mut err = self.type_error_struct(call_expr.span, |_| {
                        format!("`{}` is being called, but it is not a function", path)
                    }, callee_ty);
                    err.help(&format!("did you mean to write `{}`?", path));
                    err
                } else {
                    self.type_error_struct(call_expr.span, |actual| {
                        format!("expected function, found `{}`", actual)
                    }, callee_ty)
                };

                if let hir::ExprCall(ref expr, _) = call_expr.node {
                    let def = if let hir::ExprPath(ref qpath) = expr.node {
                        self.tables.borrow().qpath_def(qpath, expr.id)
                    } else {
                        Def::Err
                    };
                    if def != Def::Err {
                        if let Some(span) = self.tcx.map.span_if_local(def.def_id()) {
                            err.span_note(span, "defined here");
                        }
                    }
                }

                err.emit();

                // This is the "default" function signature, used in case of error.
                // In that case, we check each argument against "error" in order to
                // set up all the node type bindings.
                error_fn_sig = ty::Binder(self.tcx.mk_fn_sig(
                    self.err_args(arg_exprs.len()).into_iter(),
                    self.tcx.types.err,
                    false,
                ));

                (&error_fn_sig, None)
            }
        };

        // Replace any late-bound regions that appear in the function
        // signature with region variables. We also have to
        // renormalize the associated types at this point, since they
        // previously appeared within a `Binder<>` and hence would not
        // have been normalized before.
        let fn_sig =
            self.replace_late_bound_regions_with_fresh_var(call_expr.span, infer::FnCall, fn_sig)
                .0;
        let fn_sig = self.normalize_associated_types_in(call_expr.span, &fn_sig);

        // Call the generic checker.
        let expected_arg_tys =
            self.expected_types_for_fn_args(call_expr.span,
                                            expected,
                                            fn_sig.output(),
                                            fn_sig.inputs());
        self.check_argument_types(call_expr.span,
                                  fn_sig.inputs(),
                                  &expected_arg_tys[..],
                                  arg_exprs,
                                  fn_sig.variadic,
                                  TupleArgumentsFlag::DontTupleArguments,
                                  def_span);

        fn_sig.output()
    }

    fn confirm_deferred_closure_call(&self,
                                     call_expr: &hir::Expr,
                                     arg_exprs: &'gcx [hir::Expr],
                                     expected: Expectation<'tcx>,
                                     fn_sig: ty::FnSig<'tcx>)
                                     -> Ty<'tcx> {
        // `fn_sig` is the *signature* of the cosure being called. We
        // don't know the full details yet (`Fn` vs `FnMut` etc), but we
        // do know the types expected for each argument and the return
        // type.

        let expected_arg_tys = self.expected_types_for_fn_args(call_expr.span,
                                                               expected,
                                                               fn_sig.output().clone(),
                                                               fn_sig.inputs());

        self.check_argument_types(call_expr.span,
                                  fn_sig.inputs(),
                                  &expected_arg_tys,
                                  arg_exprs,
                                  fn_sig.variadic,
                                  TupleArgumentsFlag::TupleArguments,
                                  None);

        fn_sig.output()
    }

    fn confirm_overloaded_call(&self,
                               call_expr: &hir::Expr,
                               callee_expr: &'gcx hir::Expr,
                               arg_exprs: &'gcx [hir::Expr],
                               expected: Expectation<'tcx>,
                               method_callee: ty::MethodCallee<'tcx>)
                               -> Ty<'tcx> {
        let output_type = self.check_method_argument_types(call_expr.span,
                                                           method_callee.ty,
                                                           callee_expr,
                                                           arg_exprs,
                                                           TupleArgumentsFlag::TupleArguments,
                                                           expected);

        self.write_overloaded_call_method_map(call_expr, method_callee);
        output_type
    }

    fn write_overloaded_call_method_map(&self,
                                        call_expr: &hir::Expr,
                                        method_callee: ty::MethodCallee<'tcx>) {
        let method_call = ty::MethodCall::expr(call_expr.id);
        self.tables.borrow_mut().method_map.insert(method_call, method_callee);
    }
}

#[derive(Debug)]
struct CallResolution<'gcx: 'tcx, 'tcx> {
    call_expr: &'gcx hir::Expr,
    callee_expr: &'gcx hir::Expr,
    adjusted_ty: Ty<'tcx>,
    autoderefs: usize,
    fn_sig: ty::FnSig<'tcx>,
    closure_def_id: DefId,
}

impl<'gcx, 'tcx> DeferredCallResolution<'gcx, 'tcx> for CallResolution<'gcx, 'tcx> {
    fn resolve<'a>(&mut self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) {
        debug!("DeferredCallResolution::resolve() {:?}", self);

        // we should not be invoked until the closure kind has been
        // determined by upvar inference
        assert!(fcx.closure_kind(self.closure_def_id).is_some());

        // We may now know enough to figure out fn vs fnmut etc.
        match fcx.try_overloaded_call_traits(self.call_expr,
                                             self.callee_expr,
                                             self.adjusted_ty,
                                             self.autoderefs) {
            Some(method_callee) => {
                // One problem is that when we get here, we are going
                // to have a newly instantiated function signature
                // from the call trait. This has to be reconciled with
                // the older function signature we had before. In
                // principle we *should* be able to fn_sigs(), but we
                // can't because of the annoying need for a TypeTrace.
                // (This always bites me, should find a way to
                // refactor it.)
                let method_sig = fcx.tcx
                    .no_late_bound_regions(method_callee.ty.fn_sig())
                    .unwrap();

                debug!("attempt_resolution: method_callee={:?}", method_callee);

                for (method_arg_ty, self_arg_ty) in
                    method_sig.inputs().iter().skip(1).zip(self.fn_sig.inputs()) {
                    fcx.demand_eqtype(self.call_expr.span, &self_arg_ty, &method_arg_ty);
                }

                fcx.demand_eqtype(self.call_expr.span, method_sig.output(), self.fn_sig.output());

                fcx.write_overloaded_call_method_map(self.call_expr, method_callee);
            }
            None => {
                span_bug!(self.call_expr.span,
                          "failed to find an overloaded call trait for closure call");
            }
        }
    }
}