1 use super::method::MethodCallee;
2 use super::{DefIdOrName, Expectation, FnCtxt, TupleArgumentsFlag};
3 use crate::type_error_struct;
5 use rustc_errors::{struct_span_err, Applicability, Diagnostic};
7 use rustc_hir::def::{self, Namespace, Res};
8 use rustc_hir::def_id::DefId;
11 traits::{self, Obligation},
14 infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind},
15 traits::ObligationCause,
17 use rustc_middle::ty::adjustment::{
18 Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
20 use rustc_middle::ty::SubstsRef;
21 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};
22 use rustc_span::def_id::LocalDefId;
23 use rustc_span::symbol::{sym, Ident};
25 use rustc_target::spec::abi;
26 use rustc_trait_selection::autoderef::Autoderef;
27 use rustc_trait_selection::infer::InferCtxtExt as _;
28 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
32 /// Checks that it is legal to call methods of the trait corresponding
33 /// to `trait_id` (this only cares about the trait, not the specific
34 /// method that is called).
35 pub fn check_legal_trait_for_method_call(
38 receiver: Option<Span>,
42 if tcx.lang_items().drop_trait() == Some(trait_id) {
43 let mut err = struct_span_err!(tcx.sess, span, E0040, "explicit use of destructor method");
44 err.span_label(span, "explicit destructor calls not allowed");
46 let (sp, suggestion) = receiver
47 .and_then(|s| tcx.sess.source_map().span_to_snippet(s).ok())
48 .filter(|snippet| !snippet.is_empty())
49 .map(|snippet| (expr_span, format!("drop({snippet})")))
50 .unwrap_or_else(|| (span, "drop".to_string()));
54 "consider using `drop` function",
56 Applicability::MaybeIncorrect,
65 DeferredClosure(LocalDefId, ty::FnSig<'tcx>),
66 /// E.g., enum variant constructors.
67 Overloaded(MethodCallee<'tcx>),
70 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
73 call_expr: &'tcx hir::Expr<'tcx>,
74 callee_expr: &'tcx hir::Expr<'tcx>,
75 arg_exprs: &'tcx [hir::Expr<'tcx>],
76 expected: Expectation<'tcx>,
78 let original_callee_ty = match &callee_expr.kind {
79 hir::ExprKind::Path(hir::QPath::Resolved(..) | hir::QPath::TypeRelative(..)) => self
80 .check_expr_with_expectation_and_args(
82 Expectation::NoExpectation,
85 _ => self.check_expr(callee_expr),
88 let expr_ty = self.structurally_resolved_type(call_expr.span, original_callee_ty);
90 let mut autoderef = self.autoderef(callee_expr.span, expr_ty);
91 let mut result = None;
92 while result.is_none() && autoderef.next().is_some() {
93 result = self.try_overloaded_call_step(call_expr, callee_expr, arg_exprs, &autoderef);
95 self.register_predicates(autoderef.into_obligations());
97 let output = match result {
99 // this will report an error since original_callee_ty is not a fn
100 self.confirm_builtin_call(
109 Some(CallStep::Builtin(callee_ty)) => {
110 self.confirm_builtin_call(call_expr, callee_expr, callee_ty, arg_exprs, expected)
113 Some(CallStep::DeferredClosure(def_id, fn_sig)) => {
114 self.confirm_deferred_closure_call(call_expr, arg_exprs, expected, def_id, fn_sig)
117 Some(CallStep::Overloaded(method_callee)) => {
118 self.confirm_overloaded_call(call_expr, arg_exprs, expected, method_callee)
122 // we must check that return type of called functions is WF:
123 self.register_wf_obligation(output.into(), call_expr.span, traits::WellFormed(None));
128 fn try_overloaded_call_step(
130 call_expr: &'tcx hir::Expr<'tcx>,
131 callee_expr: &'tcx hir::Expr<'tcx>,
132 arg_exprs: &'tcx [hir::Expr<'tcx>],
133 autoderef: &Autoderef<'a, 'tcx>,
134 ) -> Option<CallStep<'tcx>> {
136 self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
138 "try_overloaded_call_step(call_expr={:?}, adjusted_ty={:?})",
139 call_expr, adjusted_ty
142 // If the callee is a bare function or a closure, then we're all set.
143 match *adjusted_ty.kind() {
144 ty::FnDef(..) | ty::FnPtr(_) => {
145 let adjustments = self.adjust_steps(autoderef);
146 self.apply_adjustments(callee_expr, adjustments);
147 return Some(CallStep::Builtin(adjusted_ty));
150 ty::Closure(def_id, substs) => {
151 let def_id = def_id.expect_local();
153 // Check whether this is a call to a closure where we
154 // haven't yet decided on whether the closure is fn vs
155 // fnmut vs fnonce. If so, we have to defer further processing.
156 if self.closure_kind(substs).is_none() {
157 let closure_sig = substs.as_closure().sig();
158 let closure_sig = self.replace_bound_vars_with_fresh_vars(
163 let adjustments = self.adjust_steps(autoderef);
164 self.record_deferred_call_resolution(
166 DeferredCallResolution {
172 closure_substs: substs,
175 return Some(CallStep::DeferredClosure(def_id, closure_sig));
179 // Hack: we know that there are traits implementing Fn for &F
180 // where F:Fn and so forth. In the particular case of types
181 // like `x: &mut FnMut()`, if there is a call `x()`, we would
182 // normally translate to `FnMut::call_mut(&mut x, ())`, but
183 // that winds up requiring `mut x: &mut FnMut()`. A little
184 // over the top. The simplest fix by far is to just ignore
185 // this case and deref again, so we wind up with
186 // `FnMut::call_mut(&mut *x, ())`.
187 ty::Ref(..) if autoderef.step_count() == 0 => {
194 // Now, we look for the implementation of a Fn trait on the object's type.
195 // We first do it with the explicit instruction to look for an impl of
196 // `Fn<Tuple>`, with the tuple `Tuple` having an arity corresponding
197 // to the number of call parameters.
198 // If that fails (or_else branch), we try again without specifying the
199 // shape of the tuple (hence the None). This allows to detect an Fn trait
200 // is implemented, and use this information for diagnostic.
201 self.try_overloaded_call_traits(call_expr, adjusted_ty, Some(arg_exprs))
202 .or_else(|| self.try_overloaded_call_traits(call_expr, adjusted_ty, None))
203 .map(|(autoref, method)| {
204 let mut adjustments = self.adjust_steps(autoderef);
205 adjustments.extend(autoref);
206 self.apply_adjustments(callee_expr, adjustments);
207 CallStep::Overloaded(method)
211 fn try_overloaded_call_traits(
213 call_expr: &hir::Expr<'_>,
214 adjusted_ty: Ty<'tcx>,
215 opt_arg_exprs: Option<&'tcx [hir::Expr<'tcx>]>,
216 ) -> Option<(Option<Adjustment<'tcx>>, MethodCallee<'tcx>)> {
217 // Try the options that are least restrictive on the caller first.
218 for (opt_trait_def_id, method_name, borrow) in [
219 (self.tcx.lang_items().fn_trait(), Ident::with_dummy_span(sym::call), true),
220 (self.tcx.lang_items().fn_mut_trait(), Ident::with_dummy_span(sym::call_mut), true),
221 (self.tcx.lang_items().fn_once_trait(), Ident::with_dummy_span(sym::call_once), false),
223 let Some(trait_def_id) = opt_trait_def_id else { continue };
225 let opt_input_types = opt_arg_exprs.map(|arg_exprs| {
226 [self.tcx.mk_tup(arg_exprs.iter().map(|e| {
227 self.next_ty_var(TypeVariableOrigin {
228 kind: TypeVariableOriginKind::TypeInference,
233 let opt_input_types = opt_input_types.as_ref().map(AsRef::as_ref);
235 if let Some(ok) = self.lookup_method_in_trait(
242 let method = self.register_infer_ok_obligations(ok);
243 let mut autoref = None;
245 // Check for &self vs &mut self in the method signature. Since this is either
246 // the Fn or FnMut trait, it should be one of those.
247 let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() else {
248 // The `fn`/`fn_mut` lang item is ill-formed, which should have
249 // caused an error elsewhere.
252 .delay_span_bug(call_expr.span, "input to call/call_mut is not a ref?");
256 let mutbl = match mutbl {
257 hir::Mutability::Not => AutoBorrowMutability::Not,
258 hir::Mutability::Mut => AutoBorrowMutability::Mut {
259 // For initial two-phase borrow
260 // deployment, conservatively omit
261 // overloaded function call ops.
262 allow_two_phase_borrow: AllowTwoPhase::No,
265 autoref = Some(Adjustment {
266 kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
267 target: method.sig.inputs()[0],
270 return Some((autoref, method));
277 /// Give appropriate suggestion when encountering `||{/* not callable */}()`, where the
278 /// likely intention is to call the closure, suggest `(||{})()`. (#55851)
279 fn identify_bad_closure_def_and_call(
281 err: &mut Diagnostic,
283 callee_node: &hir::ExprKind<'_>,
286 let hir = self.tcx.hir();
287 let parent_hir_id = hir.get_parent_node(hir_id);
288 let parent_node = hir.get(parent_hir_id);
290 hir::Node::Expr(hir::Expr {
291 kind: hir::ExprKind::Closure(&hir::Closure { fn_decl_span, body, .. }),
294 hir::ExprKind::Block(..),
295 ) = (parent_node, callee_node)
297 let fn_decl_span = if hir.body(body).generator_kind
298 == Some(hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure))
300 // Actually need to unwrap a few more layers of HIR to get to
301 // the _real_ closure...
302 let async_closure = hir.get_parent_node(hir.get_parent_node(parent_hir_id));
303 if let hir::Node::Expr(hir::Expr {
304 kind: hir::ExprKind::Closure(&hir::Closure { fn_decl_span, .. }),
306 }) = hir.get(async_closure)
316 let start = fn_decl_span.shrink_to_lo();
317 let end = callee_span.shrink_to_hi();
318 err.multipart_suggestion(
319 "if you meant to create this closure and immediately call it, surround the \
320 closure with parentheses",
321 vec![(start, "(".to_string()), (end, ")".to_string())],
322 Applicability::MaybeIncorrect,
327 /// Give appropriate suggestion when encountering `[("a", 0) ("b", 1)]`, where the
328 /// likely intention is to create an array containing tuples.
329 fn maybe_suggest_bad_array_definition(
331 err: &mut Diagnostic,
332 call_expr: &'tcx hir::Expr<'tcx>,
333 callee_expr: &'tcx hir::Expr<'tcx>,
335 let hir_id = self.tcx.hir().get_parent_node(call_expr.hir_id);
336 let parent_node = self.tcx.hir().get(hir_id);
338 hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Array(_), .. }),
339 hir::ExprKind::Tup(exp),
340 hir::ExprKind::Call(_, args),
341 ) = (parent_node, &callee_expr.kind, &call_expr.kind)
342 && args.len() == exp.len()
344 let start = callee_expr.span.shrink_to_hi();
347 "consider separating array elements with a comma",
349 Applicability::MaybeIncorrect,
356 fn confirm_builtin_call(
358 call_expr: &'tcx hir::Expr<'tcx>,
359 callee_expr: &'tcx hir::Expr<'tcx>,
361 arg_exprs: &'tcx [hir::Expr<'tcx>],
362 expected: Expectation<'tcx>,
364 let (fn_sig, def_id) = match *callee_ty.kind() {
365 ty::FnDef(def_id, subst) => {
366 let fn_sig = self.tcx.bound_fn_sig(def_id).subst(self.tcx, subst);
368 // Unit testing: function items annotated with
369 // `#[rustc_evaluate_where_clauses]` trigger special output
370 // to let us test the trait evaluation system.
371 if self.tcx.has_attr(def_id, sym::rustc_evaluate_where_clauses) {
372 let predicates = self.tcx.predicates_of(def_id);
373 let predicates = predicates.instantiate(self.tcx, subst);
374 for (predicate, predicate_span) in
375 predicates.predicates.iter().zip(&predicates.spans)
377 let obligation = Obligation::new(
378 ObligationCause::dummy_with_span(callee_expr.span),
382 let result = self.evaluate_obligation(&obligation);
387 &format!("evaluate({:?}) = {:?}", predicate, result),
389 .span_label(*predicate_span, "predicate")
393 (fn_sig, Some(def_id))
395 ty::FnPtr(sig) => (sig, None),
397 let mut unit_variant = None;
398 if let hir::ExprKind::Path(qpath) = &callee_expr.kind
399 && let Res::Def(def::DefKind::Ctor(kind, def::CtorKind::Const), _)
400 = self.typeck_results.borrow().qpath_res(qpath, callee_expr.hir_id)
401 // Only suggest removing parens if there are no arguments
402 && arg_exprs.is_empty()
404 let descr = match kind {
405 def::CtorOf::Struct => "struct",
406 def::CtorOf::Variant => "enum variant",
409 callee_expr.span.shrink_to_hi().to(call_expr.span.shrink_to_hi());
411 Some((removal_span, descr, rustc_hir_pretty::qpath_to_string(qpath)));
414 let callee_ty = self.resolve_vars_if_possible(callee_ty);
415 let mut err = type_error_struct!(
420 "expected function, found {}",
421 match &unit_variant {
422 Some((_, kind, path)) => format!("{kind} `{path}`"),
423 None => format!("`{callee_ty}`"),
427 self.identify_bad_closure_def_and_call(
434 if let Some((removal_span, kind, path)) = &unit_variant {
435 err.span_suggestion_verbose(
438 "`{path}` is a unit {kind}, and does not take parentheses to be constructed",
441 Applicability::MachineApplicable,
445 let mut inner_callee_path = None;
446 let def = match callee_expr.kind {
447 hir::ExprKind::Path(ref qpath) => {
448 self.typeck_results.borrow().qpath_res(qpath, callee_expr.hir_id)
450 hir::ExprKind::Call(ref inner_callee, _) => {
451 // If the call spans more than one line and the callee kind is
452 // itself another `ExprCall`, that's a clue that we might just be
453 // missing a semicolon (Issue #51055)
454 let call_is_multiline =
455 self.tcx.sess.source_map().is_multiline(call_expr.span);
456 if call_is_multiline {
458 callee_expr.span.shrink_to_hi(),
459 "consider using a semicolon here",
461 Applicability::MaybeIncorrect,
464 if let hir::ExprKind::Path(ref inner_qpath) = inner_callee.kind {
465 inner_callee_path = Some(inner_qpath);
466 self.typeck_results.borrow().qpath_res(inner_qpath, inner_callee.hir_id)
474 if !self.maybe_suggest_bad_array_definition(&mut err, call_expr, callee_expr) {
475 if let Some((maybe_def, output_ty, _)) = self.extract_callable_info(callee_expr, callee_ty)
476 && !self.type_is_sized_modulo_regions(self.param_env, output_ty, callee_expr.span)
478 let descr = match maybe_def {
479 DefIdOrName::DefId(def_id) => self.tcx.def_kind(def_id).descr(def_id),
480 DefIdOrName::Name(name) => name,
484 format!("this {descr} returns an unsized value `{output_ty}`, so it cannot be called")
486 if let DefIdOrName::DefId(def_id) = maybe_def
487 && let Some(def_span) = self.tcx.hir().span_if_local(def_id)
489 err.span_label(def_span, "the callable type is defined here");
492 err.span_label(call_expr.span, "call expression requires function");
496 if let Some(span) = self.tcx.hir().res_span(def) {
497 let callee_ty = callee_ty.to_string();
498 let label = match (unit_variant, inner_callee_path) {
499 (Some((_, kind, path)), _) => Some(format!("{kind} `{path}` defined here")),
500 (_, Some(hir::QPath::Resolved(_, path))) => self
504 .span_to_snippet(path.span)
506 .map(|p| format!("`{p}` defined here returns `{callee_ty}`")),
509 // Emit a different diagnostic for local variables, as they are not
510 // type definitions themselves, but rather variables *of* that type.
511 Res::Local(hir_id) => Some(format!(
512 "`{}` has type `{}`",
513 self.tcx.hir().name(hir_id),
516 Res::Def(kind, def_id) if kind.ns() == Some(Namespace::ValueNS) => {
519 self.tcx.def_path_str(def_id),
522 _ => Some(format!("`{callee_ty}` defined here")),
526 if let Some(label) = label {
527 err.span_label(span, label);
532 // This is the "default" function signature, used in case of error.
533 // In that case, we check each argument against "error" in order to
534 // set up all the node type bindings.
536 ty::Binder::dummy(self.tcx.mk_fn_sig(
537 self.err_args(arg_exprs.len()).into_iter(),
540 hir::Unsafety::Normal,
548 // Replace any late-bound regions that appear in the function
549 // signature with region variables. We also have to
550 // renormalize the associated types at this point, since they
551 // previously appeared within a `Binder<>` and hence would not
552 // have been normalized before.
553 let fn_sig = self.replace_bound_vars_with_fresh_vars(call_expr.span, infer::FnCall, fn_sig);
554 let fn_sig = self.normalize_associated_types_in(call_expr.span, fn_sig);
556 // Call the generic checker.
557 let expected_arg_tys = self.expected_inputs_for_expected_output(
563 self.check_argument_types(
570 TupleArgumentsFlag::DontTupleArguments,
577 fn confirm_deferred_closure_call(
579 call_expr: &'tcx hir::Expr<'tcx>,
580 arg_exprs: &'tcx [hir::Expr<'tcx>],
581 expected: Expectation<'tcx>,
582 closure_def_id: LocalDefId,
583 fn_sig: ty::FnSig<'tcx>,
585 // `fn_sig` is the *signature* of the closure being called. We
586 // don't know the full details yet (`Fn` vs `FnMut` etc), but we
587 // do know the types expected for each argument and the return
590 let expected_arg_tys = self.expected_inputs_for_expected_output(
597 self.check_argument_types(
604 TupleArgumentsFlag::TupleArguments,
605 Some(closure_def_id.to_def_id()),
611 fn confirm_overloaded_call(
613 call_expr: &'tcx hir::Expr<'tcx>,
614 arg_exprs: &'tcx [hir::Expr<'tcx>],
615 expected: Expectation<'tcx>,
616 method_callee: MethodCallee<'tcx>,
618 let output_type = self.check_method_argument_types(
623 TupleArgumentsFlag::TupleArguments,
627 self.write_method_call(call_expr.hir_id, method_callee);
633 pub struct DeferredCallResolution<'tcx> {
634 call_expr: &'tcx hir::Expr<'tcx>,
635 callee_expr: &'tcx hir::Expr<'tcx>,
636 adjusted_ty: Ty<'tcx>,
637 adjustments: Vec<Adjustment<'tcx>>,
638 fn_sig: ty::FnSig<'tcx>,
639 closure_substs: SubstsRef<'tcx>,
642 impl<'a, 'tcx> DeferredCallResolution<'tcx> {
643 pub fn resolve(self, fcx: &FnCtxt<'a, 'tcx>) {
644 debug!("DeferredCallResolution::resolve() {:?}", self);
646 // we should not be invoked until the closure kind has been
647 // determined by upvar inference
648 assert!(fcx.closure_kind(self.closure_substs).is_some());
650 // We may now know enough to figure out fn vs fnmut etc.
651 match fcx.try_overloaded_call_traits(self.call_expr, self.adjusted_ty, None) {
652 Some((autoref, method_callee)) => {
653 // One problem is that when we get here, we are going
654 // to have a newly instantiated function signature
655 // from the call trait. This has to be reconciled with
656 // the older function signature we had before. In
657 // principle we *should* be able to fn_sigs(), but we
658 // can't because of the annoying need for a TypeTrace.
659 // (This always bites me, should find a way to
661 let method_sig = method_callee.sig;
663 debug!("attempt_resolution: method_callee={:?}", method_callee);
665 for (method_arg_ty, self_arg_ty) in
666 iter::zip(method_sig.inputs().iter().skip(1), self.fn_sig.inputs())
668 fcx.demand_eqtype(self.call_expr.span, *self_arg_ty, *method_arg_ty);
671 fcx.demand_eqtype(self.call_expr.span, method_sig.output(), self.fn_sig.output());
673 let mut adjustments = self.adjustments;
674 adjustments.extend(autoref);
675 fcx.apply_adjustments(self.callee_expr, adjustments);
677 fcx.write_method_call(self.call_expr.hir_id, method_callee);
680 // This can happen if `#![no_core]` is used and the `fn/fn_mut/fn_once`
681 // lang items are not defined (issue #86238).
682 let mut err = fcx.inh.tcx.sess.struct_span_err(
684 "failed to find an overloaded call trait for closure call",
687 "make sure the `fn`/`fn_mut`/`fn_once` lang items are defined \
688 and have associated `call`/`call_mut`/`call_once` functions",