1 pub mod on_unimplemented;
5 ConstEvalFailure, EvaluationResult, FulfillmentError, FulfillmentErrorCode,
6 MismatchedProjectionTypes, Obligation, ObligationCause, ObligationCauseCode,
7 OnUnimplementedDirective, OnUnimplementedNote, OutputTypeParameterMismatch, Overflow,
8 PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
11 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
12 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
13 use crate::infer::{self, InferCtxt, TyCtxtInferExt};
14 use rustc_data_structures::fx::FxHashMap;
15 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorReported};
17 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
19 use rustc_middle::mir::interpret::ErrorHandled;
20 use rustc_middle::ty::error::ExpectedFound;
21 use rustc_middle::ty::fold::TypeFolder;
22 use rustc_middle::ty::{
23 self, fast_reject, AdtKind, SubtypePredicate, ToPolyTraitRef, ToPredicate, Ty, TyCtxt,
24 TypeFoldable, WithConstness,
26 use rustc_session::DiagnosticMessageId;
27 use rustc_span::{ExpnKind, Span, DUMMY_SP};
30 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
31 use crate::traits::query::normalize::AtExt as _;
32 use on_unimplemented::InferCtxtExt as _;
33 use suggestions::InferCtxtExt as _;
35 pub use rustc_infer::traits::error_reporting::*;
37 pub trait InferCtxtExt<'tcx> {
38 fn report_fulfillment_errors(
40 errors: &[FulfillmentError<'tcx>],
41 body_id: Option<hir::BodyId>,
42 fallback_has_occurred: bool,
45 fn report_overflow_error<T>(
47 obligation: &Obligation<'tcx, T>,
48 suggest_increasing_limit: bool,
51 T: fmt::Display + TypeFoldable<'tcx>;
53 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
55 fn report_selection_error(
57 obligation: &PredicateObligation<'tcx>,
58 error: &SelectionError<'tcx>,
59 fallback_has_occurred: bool,
63 /// Given some node representing a fn-like thing in the HIR map,
64 /// returns a span and `ArgKind` information that describes the
65 /// arguments it expects. This can be supplied to
66 /// `report_arg_count_mismatch`.
67 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)>;
69 /// Reports an error when the number of arguments needed by a
70 /// trait match doesn't match the number that the expression
72 fn report_arg_count_mismatch(
75 found_span: Option<Span>,
76 expected_args: Vec<ArgKind>,
77 found_args: Vec<ArgKind>,
79 ) -> DiagnosticBuilder<'tcx>;
82 impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
83 fn report_fulfillment_errors(
85 errors: &[FulfillmentError<'tcx>],
86 body_id: Option<hir::BodyId>,
87 fallback_has_occurred: bool,
90 struct ErrorDescriptor<'tcx> {
91 predicate: ty::Predicate<'tcx>,
92 index: Option<usize>, // None if this is an old error
95 let mut error_map: FxHashMap<_, Vec<_>> = self
96 .reported_trait_errors
99 .map(|(&span, predicates)| {
104 .map(|&predicate| ErrorDescriptor { predicate, index: None })
110 for (index, error) in errors.iter().enumerate() {
111 // We want to ignore desugarings here: spans are equivalent even
112 // if one is the result of a desugaring and the other is not.
113 let mut span = error.obligation.cause.span;
114 let expn_data = span.ctxt().outer_expn_data();
115 if let ExpnKind::Desugaring(_) = expn_data.kind {
116 span = expn_data.call_site;
119 error_map.entry(span).or_default().push(ErrorDescriptor {
120 predicate: error.obligation.predicate,
124 self.reported_trait_errors
128 .push(error.obligation.predicate);
131 // We do this in 2 passes because we want to display errors in order, though
132 // maybe it *is* better to sort errors by span or something.
133 let mut is_suppressed = vec![false; errors.len()];
134 for (_, error_set) in error_map.iter() {
135 // We want to suppress "duplicate" errors with the same span.
136 for error in error_set {
137 if let Some(index) = error.index {
138 // Suppress errors that are either:
139 // 1) strictly implied by another error.
140 // 2) implied by an error with a smaller index.
141 for error2 in error_set {
142 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
143 // Avoid errors being suppressed by already-suppressed
144 // errors, to prevent all errors from being suppressed
149 if self.error_implies(&error2.predicate, &error.predicate)
150 && !(error2.index >= error.index
151 && self.error_implies(&error.predicate, &error2.predicate))
153 info!("skipping {:?} (implied by {:?})", error, error2);
154 is_suppressed[index] = true;
162 for (error, suppressed) in errors.iter().zip(is_suppressed) {
164 self.report_fulfillment_error(error, body_id, fallback_has_occurred);
169 /// Reports that an overflow has occurred and halts compilation. We
170 /// halt compilation unconditionally because it is important that
171 /// overflows never be masked -- they basically represent computations
172 /// whose result could not be truly determined and thus we can't say
173 /// if the program type checks or not -- and they are unusual
174 /// occurrences in any case.
175 fn report_overflow_error<T>(
177 obligation: &Obligation<'tcx, T>,
178 suggest_increasing_limit: bool,
181 T: fmt::Display + TypeFoldable<'tcx>,
183 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
184 let mut err = struct_span_err!(
186 obligation.cause.span,
188 "overflow evaluating the requirement `{}`",
192 if suggest_increasing_limit {
193 self.suggest_new_overflow_limit(&mut err);
196 self.note_obligation_cause_code(
198 &obligation.predicate,
199 &obligation.cause.code,
204 self.tcx.sess.abort_if_errors();
208 /// Reports that a cycle was detected which led to overflow and halts
209 /// compilation. This is equivalent to `report_overflow_error` except
210 /// that we can give a more helpful error message (and, in particular,
211 /// we do not suggest increasing the overflow limit, which is not
213 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
214 let cycle = self.resolve_vars_if_possible(&cycle.to_owned());
215 assert!(!cycle.is_empty());
217 debug!("report_overflow_error_cycle: cycle={:?}", cycle);
219 self.report_overflow_error(&cycle[0], false);
222 fn report_selection_error(
224 obligation: &PredicateObligation<'tcx>,
225 error: &SelectionError<'tcx>,
226 fallback_has_occurred: bool,
230 let span = obligation.cause.span;
232 let mut err = match *error {
233 SelectionError::Unimplemented => {
234 if let ObligationCauseCode::CompareImplMethodObligation {
239 | ObligationCauseCode::CompareImplTypeObligation {
243 } = obligation.cause.code
245 self.report_extra_impl_obligation(
250 &format!("`{}`", obligation.predicate),
255 match obligation.predicate {
256 ty::Predicate::Trait(ref trait_predicate, _) => {
257 let trait_predicate = self.resolve_vars_if_possible(trait_predicate);
259 if self.tcx.sess.has_errors() && trait_predicate.references_error() {
262 let trait_ref = trait_predicate.to_poly_trait_ref();
263 let (post_message, pre_message, type_def) = self
264 .get_parent_trait_ref(&obligation.cause.code)
267 format!(" in `{}`", t),
268 format!("within `{}`, ", t),
269 s.map(|s| (format!("within this `{}`", t), s)),
272 .unwrap_or_default();
274 let OnUnimplementedNote { message, label, note, enclosing_scope } =
275 self.on_unimplemented_note(trait_ref, obligation);
276 let have_alt_message = message.is_some() || label.is_some();
281 .span_to_snippet(span)
284 let is_from = format!("{}", trait_ref.print_only_trait_path())
285 .starts_with("std::convert::From<");
286 let (message, note) = if is_try && is_from {
289 "`?` couldn't convert the error to `{}`",
293 "the question mark operation (`?`) implicitly performs a \
294 conversion on the error value using the `From` trait"
302 let mut err = struct_span_err!(
307 message.unwrap_or_else(|| format!(
308 "the trait bound `{}` is not satisfied{}",
309 trait_ref.without_const().to_predicate(),
314 let should_convert_option_to_result =
315 format!("{}", trait_ref.print_only_trait_path())
316 .starts_with("std::convert::From<std::option::NoneError");
317 let should_convert_result_to_option = format!("{}", trait_ref)
318 .starts_with("<std::option::NoneError as std::convert::From<");
319 if is_try && is_from {
320 if should_convert_option_to_result {
321 err.span_suggestion_verbose(
323 "consider converting the `Option<T>` into a `Result<T, _>` \
324 using `Option::ok_or` or `Option::ok_or_else`",
325 ".ok_or_else(|| /* error value */)".to_string(),
326 Applicability::HasPlaceholders,
328 } else if should_convert_result_to_option {
329 err.span_suggestion_verbose(
331 "consider converting the `Result<T, _>` into an `Option<T>` \
334 Applicability::MachineApplicable,
337 if let Some(ret_span) = self.return_type_span(obligation) {
340 &format!("expected `{}` because of this", trait_ref.self_ty()),
346 if obligation.cause.code == ObligationCauseCode::MainFunctionType {
347 "consider using `()`, or a `Result`".to_owned()
350 "{}the trait `{}` is not implemented for `{}`",
352 trait_ref.print_only_trait_path(),
357 if self.suggest_add_reference_to_arg(
364 self.note_obligation_cause(&mut err, obligation);
368 if let Some(ref s) = label {
369 // If it has a custom `#[rustc_on_unimplemented]`
370 // error message, let's display it as the label!
371 err.span_label(span, s.as_str());
372 err.help(&explanation);
374 err.span_label(span, explanation);
376 if let Some((msg, span)) = type_def {
377 err.span_label(span, &msg);
379 if let Some(ref s) = note {
380 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
381 err.note(s.as_str());
383 if let Some(ref s) = enclosing_scope {
384 let enclosing_scope_span = tcx.def_span(
386 .opt_local_def_id(obligation.cause.body_id)
388 tcx.hir().body_owner_def_id(hir::BodyId {
389 hir_id: obligation.cause.body_id,
395 err.span_label(enclosing_scope_span, s.as_str());
398 self.suggest_borrow_on_unsized_slice(&obligation.cause.code, &mut err);
399 self.suggest_fn_call(&obligation, &mut err, &trait_ref, points_at_arg);
400 self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
401 self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
402 self.note_version_mismatch(&mut err, &trait_ref);
403 if self.suggest_impl_trait(&mut err, span, &obligation, &trait_ref) {
408 // Try to report a help message
409 if !trait_ref.has_infer_types_or_consts()
410 && self.predicate_can_apply(obligation.param_env, trait_ref)
412 // If a where-clause may be useful, remind the
413 // user that they can add it.
415 // don't display an on-unimplemented note, as
416 // these notes will often be of the form
417 // "the type `T` can't be frobnicated"
418 // which is somewhat confusing.
419 self.suggest_restricting_param_bound(
422 obligation.cause.body_id,
425 if !have_alt_message {
426 // Can't show anything else useful, try to find similar impls.
427 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
428 self.report_similar_impl_candidates(impl_candidates, &mut err);
430 self.suggest_change_mut(
438 // If this error is due to `!: Trait` not implemented but `(): Trait` is
439 // implemented, and fallback has occurred, then it could be due to a
440 // variable that used to fallback to `()` now falling back to `!`. Issue a
441 // note informing about the change in behaviour.
442 if trait_predicate.skip_binder().self_ty().is_never()
443 && fallback_has_occurred
445 let predicate = trait_predicate.map_bound(|mut trait_pred| {
446 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
448 &trait_pred.trait_ref.substs[1..],
452 let unit_obligation = Obligation {
453 predicate: ty::Predicate::Trait(
455 hir::Constness::NotConst,
459 if self.predicate_may_hold(&unit_obligation) {
461 "the trait is implemented for `()`. \
462 Possibly this error has been caused by changes to \
463 Rust's type-inference algorithm (see issue #48950 \
464 <https://github.com/rust-lang/rust/issues/48950> \
465 for more information). Consider whether you meant to use \
466 the type `()` here instead.",
474 ty::Predicate::Subtype(ref predicate) => {
475 // Errors for Subtype predicates show up as
476 // `FulfillmentErrorCode::CodeSubtypeError`,
477 // not selection error.
478 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
481 ty::Predicate::RegionOutlives(ref predicate) => {
482 let predicate = self.resolve_vars_if_possible(predicate);
484 .region_outlives_predicate(&obligation.cause, &predicate)
491 "the requirement `{}` is not satisfied (`{}`)",
497 ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
498 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
503 "the requirement `{}` is not satisfied",
508 ty::Predicate::ObjectSafe(trait_def_id) => {
509 let violations = self.tcx.object_safety_violations(trait_def_id);
510 report_object_safety_error(self.tcx, span, trait_def_id, violations)
513 ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
514 let found_kind = self.closure_kind(closure_substs).unwrap();
516 self.tcx.sess.source_map().guess_head_span(
517 self.tcx.hir().span_if_local(closure_def_id).unwrap(),
519 let hir_id = self.tcx.hir().as_local_hir_id(closure_def_id.expect_local());
520 let mut err = struct_span_err!(
524 "expected a closure that implements the `{}` trait, \
525 but this closure only implements `{}`",
532 format!("this closure implements `{}`, not `{}`", found_kind, kind),
535 obligation.cause.span,
536 format!("the requirement to implement `{}` derives from here", kind),
539 // Additional context information explaining why the closure only implements
540 // a particular trait.
541 if let Some(tables) = self.in_progress_tables {
542 let tables = tables.borrow();
543 match (found_kind, tables.closure_kind_origins().get(hir_id)) {
544 (ty::ClosureKind::FnOnce, Some((span, name))) => {
548 "closure is `FnOnce` because it moves the \
549 variable `{}` out of its environment",
554 (ty::ClosureKind::FnMut, Some((span, name))) => {
558 "closure is `FnMut` because it mutates the \
572 ty::Predicate::WellFormed(ty) => {
573 // WF predicates cannot themselves make
574 // errors. They can only block due to
575 // ambiguity; otherwise, they always
576 // degenerate into other obligations
578 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
581 ty::Predicate::ConstEvaluatable(..) => {
582 // Errors for `ConstEvaluatable` predicates show up as
583 // `SelectionError::ConstEvalFailure`,
584 // not `Unimplemented`.
587 "const-evaluatable requirement gave wrong error: `{:?}`",
594 OutputTypeParameterMismatch(ref found_trait_ref, ref expected_trait_ref, _) => {
595 let found_trait_ref = self.resolve_vars_if_possible(&*found_trait_ref);
596 let expected_trait_ref = self.resolve_vars_if_possible(&*expected_trait_ref);
598 if expected_trait_ref.self_ty().references_error() {
602 let found_trait_ty = found_trait_ref.self_ty();
604 let found_did = match found_trait_ty.kind {
605 ty::Closure(did, _) | ty::Foreign(did) | ty::FnDef(did, _) => Some(did),
606 ty::Adt(def, _) => Some(def.did),
610 let found_span = found_did
611 .and_then(|did| self.tcx.hir().span_if_local(did))
612 .map(|sp| self.tcx.sess.source_map().guess_head_span(sp)); // the sp could be an fn def
614 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
615 // We check closures twice, with obligations flowing in different directions,
616 // but we want to complain about them only once.
620 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
622 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind {
623 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
624 _ => vec![ArgKind::empty()],
627 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
628 let expected = match expected_ty.kind {
629 ty::Tuple(ref tys) => tys
631 .map(|t| ArgKind::from_expected_ty(t.expect_ty(), Some(span)))
633 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
636 if found.len() == expected.len() {
637 self.report_closure_arg_mismatch(
644 let (closure_span, found) = found_did
646 let node = self.tcx.hir().get_if_local(did)?;
647 let (found_span, found) = self.get_fn_like_arguments(node)?;
648 Some((Some(found_span), found))
650 .unwrap_or((found_span, found));
652 self.report_arg_count_mismatch(
657 found_trait_ty.is_closure(),
662 TraitNotObjectSafe(did) => {
663 let violations = self.tcx.object_safety_violations(did);
664 report_object_safety_error(self.tcx, span, did, violations)
667 ConstEvalFailure(ErrorHandled::TooGeneric) => {
668 // In this instance, we have a const expression containing an unevaluated
669 // generic parameter. We have no idea whether this expression is valid or
670 // not (e.g. it might result in an error), but we don't want to just assume
671 // that it's okay, because that might result in post-monomorphisation time
672 // errors. The onus is really on the caller to provide values that it can
673 // prove are well-formed.
677 .struct_span_err(span, "constant expression depends on a generic parameter");
678 // FIXME(const_generics): we should suggest to the user how they can resolve this
679 // issue. However, this is currently not actually possible
680 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
681 err.note("this may fail depending on what value the parameter takes");
685 // Already reported in the query.
686 ConstEvalFailure(ErrorHandled::Reported(ErrorReported)) => {
687 // FIXME(eddyb) remove this once `ErrorReported` becomes a proof token.
688 self.tcx.sess.delay_span_bug(span, "`ErrorReported` without an error");
692 // Already reported in the query, but only as a lint.
693 // This shouldn't actually happen for constants used in types, modulo
694 // bugs. The `delay_span_bug` here ensures it won't be ignored.
695 ConstEvalFailure(ErrorHandled::Linted) => {
696 self.tcx.sess.delay_span_bug(span, "constant in type had error reported as lint");
701 bug!("overflow should be handled before the `report_selection_error` path");
705 self.note_obligation_cause(&mut err, obligation);
706 self.point_at_returns_when_relevant(&mut err, &obligation);
711 /// Given some node representing a fn-like thing in the HIR map,
712 /// returns a span and `ArgKind` information that describes the
713 /// arguments it expects. This can be supplied to
714 /// `report_arg_count_mismatch`.
715 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
716 let sm = self.tcx.sess.source_map();
717 let hir = self.tcx.hir();
719 Node::Expr(&hir::Expr {
720 kind: hir::ExprKind::Closure(_, ref _decl, id, span, _),
723 sm.guess_head_span(span),
728 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
735 sm.span_to_snippet(pat.span)
737 .map(|snippet| (snippet, "_".to_owned()))
739 .collect::<Option<Vec<_>>>()?,
742 let name = sm.span_to_snippet(arg.pat.span).ok()?;
743 Some(ArgKind::Arg(name, "_".to_owned()))
746 .collect::<Option<Vec<ArgKind>>>()?,
748 Node::Item(&hir::Item { span, kind: hir::ItemKind::Fn(ref sig, ..), .. })
749 | Node::ImplItem(&hir::ImplItem {
751 kind: hir::ImplItemKind::Fn(ref sig, _),
754 | Node::TraitItem(&hir::TraitItem {
756 kind: hir::TraitItemKind::Fn(ref sig, _),
759 sm.guess_head_span(span),
763 .map(|arg| match arg.clone().kind {
764 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
766 vec![("_".to_owned(), "_".to_owned()); tys.len()],
768 _ => ArgKind::empty(),
770 .collect::<Vec<ArgKind>>(),
772 Node::Ctor(ref variant_data) => {
773 let span = variant_data.ctor_hir_id().map(|id| hir.span(id)).unwrap_or(DUMMY_SP);
774 let span = sm.guess_head_span(span);
775 (span, vec![ArgKind::empty(); variant_data.fields().len()])
777 _ => panic!("non-FnLike node found: {:?}", node),
781 /// Reports an error when the number of arguments needed by a
782 /// trait match doesn't match the number that the expression
784 fn report_arg_count_mismatch(
787 found_span: Option<Span>,
788 expected_args: Vec<ArgKind>,
789 found_args: Vec<ArgKind>,
791 ) -> DiagnosticBuilder<'tcx> {
792 let kind = if is_closure { "closure" } else { "function" };
794 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
795 let arg_length = arguments.len();
796 let distinct = match &other[..] {
797 &[ArgKind::Tuple(..)] => true,
800 match (arg_length, arguments.get(0)) {
801 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
802 format!("a single {}-tuple as argument", fields.len())
807 if distinct && arg_length > 1 { "distinct " } else { "" },
808 pluralize!(arg_length)
813 let expected_str = args_str(&expected_args, &found_args);
814 let found_str = args_str(&found_args, &expected_args);
816 let mut err = struct_span_err!(
820 "{} is expected to take {}, but it takes {}",
826 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
828 if let Some(found_span) = found_span {
829 err.span_label(found_span, format!("takes {}", found_str));
832 // ^^^^^^^^-- def_span
836 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
840 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
842 // Suggest to take and ignore the arguments with expected_args_length `_`s if
843 // found arguments is empty (assume the user just wants to ignore args in this case).
844 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
845 if found_args.is_empty() && is_closure {
846 let underscores = vec!["_"; expected_args.len()].join(", ");
847 err.span_suggestion_verbose(
850 "consider changing the closure to take and ignore the expected argument{}",
851 pluralize!(expected_args.len())
853 format!("|{}|", underscores),
854 Applicability::MachineApplicable,
858 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
859 if fields.len() == expected_args.len() {
862 .map(|(name, _)| name.to_owned())
863 .collect::<Vec<String>>()
865 err.span_suggestion_verbose(
867 "change the closure to take multiple arguments instead of a single tuple",
868 format!("|{}|", sugg),
869 Applicability::MachineApplicable,
873 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..] {
874 if fields.len() == found_args.len() && is_closure {
879 .map(|arg| match arg {
880 ArgKind::Arg(name, _) => name.to_owned(),
883 .collect::<Vec<String>>()
885 // add type annotations if available
886 if found_args.iter().any(|arg| match arg {
887 ArgKind::Arg(_, ty) => ty != "_",
894 .map(|(_, ty)| ty.to_owned())
895 .collect::<Vec<String>>()
902 err.span_suggestion_verbose(
904 "change the closure to accept a tuple instead of individual arguments",
906 Applicability::MachineApplicable,
916 trait InferCtxtPrivExt<'tcx> {
917 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
918 // `error` occurring implies that `cond` occurs.
919 fn error_implies(&self, cond: &ty::Predicate<'tcx>, error: &ty::Predicate<'tcx>) -> bool;
921 fn report_fulfillment_error(
923 error: &FulfillmentError<'tcx>,
924 body_id: Option<hir::BodyId>,
925 fallback_has_occurred: bool,
928 fn report_projection_error(
930 obligation: &PredicateObligation<'tcx>,
931 error: &MismatchedProjectionTypes<'tcx>,
934 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool;
936 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
938 fn find_similar_impl_candidates(
940 trait_ref: ty::PolyTraitRef<'tcx>,
941 ) -> Vec<ty::TraitRef<'tcx>>;
943 fn report_similar_impl_candidates(
945 impl_candidates: Vec<ty::TraitRef<'tcx>>,
946 err: &mut DiagnosticBuilder<'_>,
949 /// Gets the parent trait chain start
950 fn get_parent_trait_ref(
952 code: &ObligationCauseCode<'tcx>,
953 ) -> Option<(String, Option<Span>)>;
955 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
956 /// with the same path as `trait_ref`, a help message about
957 /// a probable version mismatch is added to `err`
958 fn note_version_mismatch(
960 err: &mut DiagnosticBuilder<'_>,
961 trait_ref: &ty::PolyTraitRef<'tcx>,
964 fn mk_obligation_for_def_id(
968 cause: ObligationCause<'tcx>,
969 param_env: ty::ParamEnv<'tcx>,
970 ) -> PredicateObligation<'tcx>;
972 fn maybe_report_ambiguity(
974 obligation: &PredicateObligation<'tcx>,
975 body_id: Option<hir::BodyId>,
978 fn predicate_can_apply(
980 param_env: ty::ParamEnv<'tcx>,
981 pred: ty::PolyTraitRef<'tcx>,
984 fn note_obligation_cause(
986 err: &mut DiagnosticBuilder<'_>,
987 obligation: &PredicateObligation<'tcx>,
990 fn suggest_unsized_bound_if_applicable(
992 err: &mut DiagnosticBuilder<'_>,
993 obligation: &PredicateObligation<'tcx>,
996 fn is_recursive_obligation(
998 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
999 cause_code: &ObligationCauseCode<'tcx>,
1003 impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
1004 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1005 // `error` occurring implies that `cond` occurs.
1006 fn error_implies(&self, cond: &ty::Predicate<'tcx>, error: &ty::Predicate<'tcx>) -> bool {
1011 let (cond, error) = match (cond, error) {
1012 (&ty::Predicate::Trait(..), &ty::Predicate::Trait(ref error, _)) => (cond, error),
1014 // FIXME: make this work in other cases too.
1019 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(*cond)) {
1020 if let ty::Predicate::Trait(implication, _) = obligation.predicate {
1021 let error = error.to_poly_trait_ref();
1022 let implication = implication.to_poly_trait_ref();
1023 // FIXME: I'm just not taking associated types at all here.
1024 // Eventually I'll need to implement param-env-aware
1025 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1026 let param_env = ty::ParamEnv::empty();
1027 if self.can_sub(param_env, error, implication).is_ok() {
1028 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1037 fn report_fulfillment_error(
1039 error: &FulfillmentError<'tcx>,
1040 body_id: Option<hir::BodyId>,
1041 fallback_has_occurred: bool,
1043 debug!("report_fulfillment_error({:?})", error);
1045 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1046 self.report_selection_error(
1049 fallback_has_occurred,
1050 error.points_at_arg_span,
1053 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1054 self.report_projection_error(&error.obligation, e);
1056 FulfillmentErrorCode::CodeAmbiguity => {
1057 self.maybe_report_ambiguity(&error.obligation, body_id);
1059 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1060 self.report_mismatched_types(
1061 &error.obligation.cause,
1062 expected_found.expected,
1063 expected_found.found,
1071 fn report_projection_error(
1073 obligation: &PredicateObligation<'tcx>,
1074 error: &MismatchedProjectionTypes<'tcx>,
1076 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
1078 if predicate.references_error() {
1084 let mut err = &error.err;
1085 let mut values = None;
1087 // try to find the mismatched types to report the error with.
1089 // this can fail if the problem was higher-ranked, in which
1090 // cause I have no idea for a good error message.
1091 if let ty::Predicate::Projection(ref data) = predicate {
1092 let mut selcx = SelectionContext::new(self);
1093 let (data, _) = self.replace_bound_vars_with_fresh_vars(
1094 obligation.cause.span,
1095 infer::LateBoundRegionConversionTime::HigherRankedType,
1098 let mut obligations = vec![];
1099 let normalized_ty = super::normalize_projection_type(
1101 obligation.param_env,
1103 obligation.cause.clone(),
1109 "report_projection_error obligation.cause={:?} obligation.param_env={:?}",
1110 obligation.cause, obligation.param_env
1114 "report_projection_error normalized_ty={:?} data.ty={:?}",
1115 normalized_ty, data.ty
1118 let is_normalized_ty_expected = match &obligation.cause.code {
1119 ObligationCauseCode::ItemObligation(_)
1120 | ObligationCauseCode::BindingObligation(_, _)
1121 | ObligationCauseCode::ObjectCastObligation(_) => false,
1125 if let Err(error) = self.at(&obligation.cause, obligation.param_env).eq_exp(
1126 is_normalized_ty_expected,
1130 values = Some(infer::ValuePairs::Types(ExpectedFound::new(
1131 is_normalized_ty_expected,
1141 let msg = format!("type mismatch resolving `{}`", predicate);
1142 let error_id = (DiagnosticMessageId::ErrorId(271), Some(obligation.cause.span), msg);
1143 let fresh = self.tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
1145 let mut diag = struct_span_err!(
1147 obligation.cause.span,
1149 "type mismatch resolving `{}`",
1152 self.note_type_err(&mut diag, &obligation.cause, None, values, err);
1153 self.note_obligation_cause(&mut diag, obligation);
1159 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
1160 /// returns the fuzzy category of a given type, or None
1161 /// if the type can be equated to any type.
1162 fn type_category(t: Ty<'_>) -> Option<u32> {
1164 ty::Bool => Some(0),
1165 ty::Char => Some(1),
1167 ty::Int(..) | ty::Uint(..) | ty::Infer(ty::IntVar(..)) => Some(3),
1168 ty::Float(..) | ty::Infer(ty::FloatVar(..)) => Some(4),
1169 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1170 ty::Array(..) | ty::Slice(..) => Some(6),
1171 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1172 ty::Dynamic(..) => Some(8),
1173 ty::Closure(..) => Some(9),
1174 ty::Tuple(..) => Some(10),
1175 ty::Projection(..) => Some(11),
1176 ty::Param(..) => Some(12),
1177 ty::Opaque(..) => Some(13),
1178 ty::Never => Some(14),
1179 ty::Adt(adt, ..) => match adt.adt_kind() {
1180 AdtKind::Struct => Some(15),
1181 AdtKind::Union => Some(16),
1182 AdtKind::Enum => Some(17),
1184 ty::Generator(..) => Some(18),
1185 ty::Foreign(..) => Some(19),
1186 ty::GeneratorWitness(..) => Some(20),
1187 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error => None,
1188 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
1192 match (type_category(a), type_category(b)) {
1193 (Some(cat_a), Some(cat_b)) => match (&a.kind, &b.kind) {
1194 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => def_a == def_b,
1195 _ => cat_a == cat_b,
1197 // infer and error can be equated to all types
1202 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1203 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1204 hir::GeneratorKind::Gen => "a generator",
1205 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1206 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1207 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1211 fn find_similar_impl_candidates(
1213 trait_ref: ty::PolyTraitRef<'tcx>,
1214 ) -> Vec<ty::TraitRef<'tcx>> {
1215 let simp = fast_reject::simplify_type(self.tcx, trait_ref.skip_binder().self_ty(), true);
1216 let all_impls = self.tcx.all_impls(trait_ref.def_id());
1219 Some(simp) => all_impls
1220 .filter_map(|def_id| {
1221 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1222 let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
1223 if let Some(imp_simp) = imp_simp {
1224 if simp != imp_simp {
1231 None => all_impls.map(|def_id| self.tcx.impl_trait_ref(def_id).unwrap()).collect(),
1235 fn report_similar_impl_candidates(
1237 impl_candidates: Vec<ty::TraitRef<'tcx>>,
1238 err: &mut DiagnosticBuilder<'_>,
1240 if impl_candidates.is_empty() {
1244 let len = impl_candidates.len();
1245 let end = if impl_candidates.len() <= 5 { impl_candidates.len() } else { 4 };
1247 let normalize = |candidate| {
1248 self.tcx.infer_ctxt().enter(|ref infcx| {
1249 let normalized = infcx
1250 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1251 .normalize(candidate)
1254 Some(normalized) => format!("\n {:?}", normalized.value),
1255 None => format!("\n {:?}", candidate),
1260 // Sort impl candidates so that ordering is consistent for UI tests.
1261 let mut normalized_impl_candidates =
1262 impl_candidates.iter().map(normalize).collect::<Vec<String>>();
1264 // Sort before taking the `..end` range,
1265 // because the ordering of `impl_candidates` may not be deterministic:
1266 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1267 normalized_impl_candidates.sort();
1270 "the following implementations were found:{}{}",
1271 normalized_impl_candidates[..end].join(""),
1272 if len > 5 { format!("\nand {} others", len - 4) } else { String::new() }
1276 /// Gets the parent trait chain start
1277 fn get_parent_trait_ref(
1279 code: &ObligationCauseCode<'tcx>,
1280 ) -> Option<(String, Option<Span>)> {
1282 &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
1283 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
1284 match self.get_parent_trait_ref(&data.parent_code) {
1287 let ty = parent_trait_ref.skip_binder().self_ty();
1289 TyCategory::from_ty(ty).map(|(_, def_id)| self.tcx.def_span(def_id));
1290 Some((ty.to_string(), span))
1298 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1299 /// with the same path as `trait_ref`, a help message about
1300 /// a probable version mismatch is added to `err`
1301 fn note_version_mismatch(
1303 err: &mut DiagnosticBuilder<'_>,
1304 trait_ref: &ty::PolyTraitRef<'tcx>,
1306 let get_trait_impl = |trait_def_id| {
1307 let mut trait_impl = None;
1308 self.tcx.for_each_relevant_impl(trait_def_id, trait_ref.self_ty(), |impl_def_id| {
1309 if trait_impl.is_none() {
1310 trait_impl = Some(impl_def_id);
1315 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
1316 let all_traits = self.tcx.all_traits(LOCAL_CRATE);
1317 let traits_with_same_path: std::collections::BTreeSet<_> = all_traits
1319 .filter(|trait_def_id| **trait_def_id != trait_ref.def_id())
1320 .filter(|trait_def_id| self.tcx.def_path_str(**trait_def_id) == required_trait_path)
1322 for trait_with_same_path in traits_with_same_path {
1323 if let Some(impl_def_id) = get_trait_impl(*trait_with_same_path) {
1324 let impl_span = self.tcx.def_span(impl_def_id);
1325 err.span_help(impl_span, "trait impl with same name found");
1326 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
1327 let crate_msg = format!(
1328 "perhaps two different versions of crate `{}` are being used?",
1331 err.note(&crate_msg);
1336 fn mk_obligation_for_def_id(
1339 output_ty: Ty<'tcx>,
1340 cause: ObligationCause<'tcx>,
1341 param_env: ty::ParamEnv<'tcx>,
1342 ) -> PredicateObligation<'tcx> {
1344 ty::TraitRef { def_id, substs: self.tcx.mk_substs_trait(output_ty, &[]) };
1345 Obligation::new(cause, param_env, new_trait_ref.without_const().to_predicate())
1348 fn maybe_report_ambiguity(
1350 obligation: &PredicateObligation<'tcx>,
1351 body_id: Option<hir::BodyId>,
1353 // Unable to successfully determine, probably means
1354 // insufficient type information, but could mean
1355 // ambiguous impls. The latter *ought* to be a
1356 // coherence violation, so we don't report it here.
1358 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
1359 let span = obligation.cause.span;
1362 "maybe_report_ambiguity(predicate={:?}, obligation={:?} body_id={:?}, code={:?})",
1363 predicate, obligation, body_id, obligation.cause.code,
1366 // Ambiguity errors are often caused as fallout from earlier
1367 // errors. So just ignore them if this infcx is tainted.
1368 if self.is_tainted_by_errors() {
1372 let mut err = match predicate {
1373 ty::Predicate::Trait(ref data, _) => {
1374 let trait_ref = data.to_poly_trait_ref();
1375 let self_ty = trait_ref.self_ty();
1376 debug!("self_ty {:?} {:?} trait_ref {:?}", self_ty, self_ty.kind, trait_ref);
1378 if predicate.references_error() {
1381 // Typically, this ambiguity should only happen if
1382 // there are unresolved type inference variables
1383 // (otherwise it would suggest a coherence
1384 // failure). But given #21974 that is not necessarily
1385 // the case -- we can have multiple where clauses that
1386 // are only distinguished by a region, which results
1387 // in an ambiguity even when all types are fully
1388 // known, since we don't dispatch based on region
1391 // This is kind of a hack: it frequently happens that some earlier
1392 // error prevents types from being fully inferred, and then we get
1393 // a bunch of uninteresting errors saying something like "<generic
1394 // #0> doesn't implement Sized". It may even be true that we
1395 // could just skip over all checks where the self-ty is an
1396 // inference variable, but I was afraid that there might be an
1397 // inference variable created, registered as an obligation, and
1398 // then never forced by writeback, and hence by skipping here we'd
1399 // be ignoring the fact that we don't KNOW the type works
1400 // out. Though even that would probably be harmless, given that
1401 // we're only talking about builtin traits, which are known to be
1402 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
1403 // avoid inundating the user with unnecessary errors, but we now
1404 // check upstream for type errors and don't add the obligations to
1405 // begin with in those cases.
1410 .map_or(false, |sized_id| sized_id == trait_ref.def_id())
1412 self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0282).emit();
1415 let mut err = self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0283);
1416 err.note(&format!("cannot satisfy `{}`", predicate));
1417 if let ObligationCauseCode::ItemObligation(def_id) = obligation.cause.code {
1418 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
1421 ObligationCauseCode::BindingObligation(ref def_id, _),
1423 (self.tcx.sess.source_map().span_to_snippet(span), &obligation.cause.code)
1425 let generics = self.tcx.generics_of(*def_id);
1426 if generics.params.iter().any(|p| p.name.as_str() != "Self")
1427 && !snippet.ends_with('>')
1429 // FIXME: To avoid spurious suggestions in functions where type arguments
1430 // where already supplied, we check the snippet to make sure it doesn't
1431 // end with a turbofish. Ideally we would have access to a `PathSegment`
1432 // instead. Otherwise we would produce the following output:
1434 // error[E0283]: type annotations needed
1435 // --> $DIR/issue-54954.rs:3:24
1437 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
1438 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
1440 // | cannot infer type
1441 // | help: consider specifying the type argument
1442 // | in the function call:
1443 // | `Tt::const_val::<[i8; 123]>::<T>`
1445 // LL | const fn const_val<T: Sized>() -> usize {
1446 // | - required by this bound in `Tt::const_val`
1448 // = note: cannot satisfy `_: Tt`
1450 err.span_suggestion_verbose(
1451 span.shrink_to_hi(),
1453 "consider specifying the type argument{} in the function call",
1454 pluralize!(generics.params.len()),
1461 .map(|p| p.name.to_string())
1462 .collect::<Vec<String>>()
1465 Applicability::HasPlaceholders,
1472 ty::Predicate::WellFormed(ty) => {
1473 // Same hacky approach as above to avoid deluging user
1474 // with error messages.
1475 if ty.references_error() || self.tcx.sess.has_errors() {
1478 self.need_type_info_err(body_id, span, ty, ErrorCode::E0282)
1481 ty::Predicate::Subtype(ref data) => {
1482 if data.references_error() || self.tcx.sess.has_errors() {
1483 // no need to overload user in such cases
1486 let &SubtypePredicate { a_is_expected: _, a, b } = data.skip_binder();
1487 // both must be type variables, or the other would've been instantiated
1488 assert!(a.is_ty_var() && b.is_ty_var());
1489 self.need_type_info_err(body_id, span, a, ErrorCode::E0282)
1491 ty::Predicate::Projection(ref data) => {
1492 let trait_ref = data.to_poly_trait_ref(self.tcx);
1493 let self_ty = trait_ref.self_ty();
1494 if predicate.references_error() {
1497 let mut err = self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0284);
1498 err.note(&format!("cannot satisfy `{}`", predicate));
1503 if self.tcx.sess.has_errors() {
1506 let mut err = struct_span_err!(
1510 "type annotations needed: cannot satisfy `{}`",
1513 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
1517 self.note_obligation_cause(&mut err, obligation);
1521 /// Returns `true` if the trait predicate may apply for *some* assignment
1522 /// to the type parameters.
1523 fn predicate_can_apply(
1525 param_env: ty::ParamEnv<'tcx>,
1526 pred: ty::PolyTraitRef<'tcx>,
1528 struct ParamToVarFolder<'a, 'tcx> {
1529 infcx: &'a InferCtxt<'a, 'tcx>,
1530 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
1533 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
1534 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1538 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1539 if let ty::Param(ty::ParamTy { name, .. }) = ty.kind {
1540 let infcx = self.infcx;
1541 self.var_map.entry(ty).or_insert_with(|| {
1542 infcx.next_ty_var(TypeVariableOrigin {
1543 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
1548 ty.super_fold_with(self)
1554 let mut selcx = SelectionContext::new(self);
1557 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
1559 let cleaned_pred = super::project::normalize(
1562 ObligationCause::dummy(),
1567 let obligation = Obligation::new(
1568 ObligationCause::dummy(),
1570 cleaned_pred.without_const().to_predicate(),
1573 self.predicate_may_hold(&obligation)
1577 fn note_obligation_cause(
1579 err: &mut DiagnosticBuilder<'_>,
1580 obligation: &PredicateObligation<'tcx>,
1582 // First, attempt to add note to this error with an async-await-specific
1583 // message, and fall back to regular note otherwise.
1584 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
1585 self.note_obligation_cause_code(
1587 &obligation.predicate,
1588 &obligation.cause.code,
1591 self.suggest_unsized_bound_if_applicable(err, obligation);
1595 fn suggest_unsized_bound_if_applicable(
1597 err: &mut DiagnosticBuilder<'_>,
1598 obligation: &PredicateObligation<'tcx>,
1601 ty::Predicate::Trait(pred, _),
1602 ObligationCauseCode::BindingObligation(item_def_id, span),
1603 ) = (&obligation.predicate, &obligation.cause.code)
1605 if let (Some(generics), true) = (
1606 self.tcx.hir().get_if_local(*item_def_id).as_ref().and_then(|n| n.generics()),
1607 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
1609 for param in generics.params {
1610 if param.span == *span
1611 && !param.bounds.iter().any(|bound| {
1612 bound.trait_ref().and_then(|trait_ref| trait_ref.trait_def_id())
1613 == self.tcx.lang_items().sized_trait()
1616 let (span, separator) = match param.bounds {
1617 [] => (span.shrink_to_hi(), ":"),
1618 [.., bound] => (bound.span().shrink_to_hi(), " + "),
1620 err.span_suggestion_verbose(
1622 "consider relaxing the implicit `Sized` restriction",
1623 format!("{} ?Sized", separator),
1624 Applicability::MachineApplicable,
1633 fn is_recursive_obligation(
1635 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
1636 cause_code: &ObligationCauseCode<'tcx>,
1638 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
1639 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
1641 if obligated_types.iter().any(|ot| ot == &parent_trait_ref.skip_binder().self_ty()) {
1649 pub fn recursive_type_with_infinite_size_error(
1652 ) -> DiagnosticBuilder<'tcx> {
1653 assert!(type_def_id.is_local());
1654 let span = tcx.hir().span_if_local(type_def_id).unwrap();
1655 let span = tcx.sess.source_map().guess_head_span(span);
1656 let mut err = struct_span_err!(
1660 "recursive type `{}` has infinite size",
1661 tcx.def_path_str(type_def_id)
1663 err.span_label(span, "recursive type has infinite size");
1665 "insert indirection (e.g., a `Box`, `Rc`, or `&`) \
1666 at some point to make `{}` representable",
1667 tcx.def_path_str(type_def_id)
1672 /// Summarizes information
1675 /// An argument of non-tuple type. Parameters are (name, ty)
1676 Arg(String, String),
1678 /// An argument of tuple type. For a "found" argument, the span is
1679 /// the locationo in the source of the pattern. For a "expected"
1680 /// argument, it will be None. The vector is a list of (name, ty)
1681 /// strings for the components of the tuple.
1682 Tuple(Option<Span>, Vec<(String, String)>),
1686 fn empty() -> ArgKind {
1687 ArgKind::Arg("_".to_owned(), "_".to_owned())
1690 /// Creates an `ArgKind` from the expected type of an
1691 /// argument. It has no name (`_`) and an optional source span.
1692 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
1694 ty::Tuple(ref tys) => ArgKind::Tuple(
1696 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
1698 _ => ArgKind::Arg("_".to_owned(), t.to_string()),