1 pub mod on_unimplemented;
5 DerivedObligationCause, EvaluationResult, FulfillmentContext, FulfillmentError,
6 FulfillmentErrorCode, ImplDerivedObligationCause, MismatchedProjectionTypes, Obligation,
7 ObligationCause, ObligationCauseCode, OnUnimplementedDirective, OnUnimplementedNote,
8 OutputTypeParameterMismatch, Overflow, PredicateObligation, SelectionContext, SelectionError,
12 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
13 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
14 use crate::infer::{self, InferCtxt, TyCtxtInferExt};
15 use rustc_data_structures::fx::FxHashMap;
17 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
21 use rustc_hir::def_id::DefId;
22 use rustc_hir::intravisit::Visitor;
23 use rustc_hir::GenericParam;
26 use rustc_infer::infer::error_reporting::same_type_modulo_infer;
27 use rustc_infer::traits::TraitEngine;
28 use rustc_middle::thir::abstract_const::NotConstEvaluatable;
29 use rustc_middle::traits::select::OverflowError;
30 use rustc_middle::ty::error::ExpectedFound;
31 use rustc_middle::ty::fold::TypeFolder;
32 use rustc_middle::ty::{
33 self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
35 use rustc_span::symbol::{kw, sym};
36 use rustc_span::{ExpnKind, Span, DUMMY_SP};
39 use std::ops::ControlFlow;
41 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
42 use crate::traits::query::normalize::AtExt as _;
43 use crate::traits::specialize::to_pretty_impl_header;
44 use on_unimplemented::InferCtxtExt as _;
45 use suggestions::InferCtxtExt as _;
47 pub use rustc_infer::traits::error_reporting::*;
49 // When outputting impl candidates, prefer showing those that are more similar.
51 // We also compare candidates after skipping lifetimes, which has a lower
52 // priority than exact matches.
53 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
54 pub enum CandidateSimilarity {
55 Exact { ignoring_lifetimes: bool },
56 Fuzzy { ignoring_lifetimes: bool },
59 #[derive(Debug, Clone, Copy)]
60 pub struct ImplCandidate<'tcx> {
61 pub trait_ref: ty::TraitRef<'tcx>,
62 pub similarity: CandidateSimilarity,
65 pub trait InferCtxtExt<'tcx> {
66 fn report_fulfillment_errors(
68 errors: &[FulfillmentError<'tcx>],
69 body_id: Option<hir::BodyId>,
70 fallback_has_occurred: bool,
73 fn report_overflow_error<T>(
75 obligation: &Obligation<'tcx, T>,
76 suggest_increasing_limit: bool,
79 T: fmt::Display + TypeFoldable<'tcx>;
81 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
83 /// The `root_obligation` parameter should be the `root_obligation` field
84 /// from a `FulfillmentError`. If no `FulfillmentError` is available,
85 /// then it should be the same as `obligation`.
86 fn report_selection_error(
88 obligation: PredicateObligation<'tcx>,
89 root_obligation: &PredicateObligation<'tcx>,
90 error: &SelectionError<'tcx>,
91 fallback_has_occurred: bool,
94 /// Given some node representing a fn-like thing in the HIR map,
95 /// returns a span and `ArgKind` information that describes the
96 /// arguments it expects. This can be supplied to
97 /// `report_arg_count_mismatch`.
98 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)>;
100 /// Reports an error when the number of arguments needed by a
101 /// trait match doesn't match the number that the expression
103 fn report_arg_count_mismatch(
106 found_span: Option<Span>,
107 expected_args: Vec<ArgKind>,
108 found_args: Vec<ArgKind>,
110 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
112 /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
113 /// in that order, and returns the generic type corresponding to the
114 /// argument of that trait (corresponding to the closure arguments).
115 fn type_implements_fn_trait(
117 param_env: ty::ParamEnv<'tcx>,
118 ty: ty::Binder<'tcx, Ty<'tcx>>,
119 constness: ty::BoundConstness,
120 polarity: ty::ImplPolarity,
121 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
124 impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
125 fn report_fulfillment_errors(
127 errors: &[FulfillmentError<'tcx>],
128 body_id: Option<hir::BodyId>,
129 fallback_has_occurred: bool,
130 ) -> ErrorGuaranteed {
132 struct ErrorDescriptor<'tcx> {
133 predicate: ty::Predicate<'tcx>,
134 index: Option<usize>, // None if this is an old error
137 let mut error_map: FxHashMap<_, Vec<_>> = self
138 .reported_trait_errors
141 .map(|(&span, predicates)| {
146 .map(|&predicate| ErrorDescriptor { predicate, index: None })
152 for (index, error) in errors.iter().enumerate() {
153 // We want to ignore desugarings here: spans are equivalent even
154 // if one is the result of a desugaring and the other is not.
155 let mut span = error.obligation.cause.span;
156 let expn_data = span.ctxt().outer_expn_data();
157 if let ExpnKind::Desugaring(_) = expn_data.kind {
158 span = expn_data.call_site;
161 error_map.entry(span).or_default().push(ErrorDescriptor {
162 predicate: error.obligation.predicate,
166 self.reported_trait_errors
170 .push(error.obligation.predicate);
173 // We do this in 2 passes because we want to display errors in order, though
174 // maybe it *is* better to sort errors by span or something.
175 let mut is_suppressed = vec![false; errors.len()];
176 for (_, error_set) in error_map.iter() {
177 // We want to suppress "duplicate" errors with the same span.
178 for error in error_set {
179 if let Some(index) = error.index {
180 // Suppress errors that are either:
181 // 1) strictly implied by another error.
182 // 2) implied by an error with a smaller index.
183 for error2 in error_set {
184 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
185 // Avoid errors being suppressed by already-suppressed
186 // errors, to prevent all errors from being suppressed
191 if self.error_implies(error2.predicate, error.predicate)
192 && !(error2.index >= error.index
193 && self.error_implies(error.predicate, error2.predicate))
195 info!("skipping {:?} (implied by {:?})", error, error2);
196 is_suppressed[index] = true;
204 for (error, suppressed) in iter::zip(errors, is_suppressed) {
206 self.report_fulfillment_error(error, body_id, fallback_has_occurred);
210 self.tcx.sess.delay_span_bug(DUMMY_SP, "expected fullfillment errors")
213 /// Reports that an overflow has occurred and halts compilation. We
214 /// halt compilation unconditionally because it is important that
215 /// overflows never be masked -- they basically represent computations
216 /// whose result could not be truly determined and thus we can't say
217 /// if the program type checks or not -- and they are unusual
218 /// occurrences in any case.
219 fn report_overflow_error<T>(
221 obligation: &Obligation<'tcx, T>,
222 suggest_increasing_limit: bool,
225 T: fmt::Display + TypeFoldable<'tcx>,
227 let predicate = self.resolve_vars_if_possible(obligation.predicate.clone());
228 let mut err = struct_span_err!(
230 obligation.cause.span,
232 "overflow evaluating the requirement `{}`",
236 if suggest_increasing_limit {
237 self.suggest_new_overflow_limit(&mut err);
240 self.note_obligation_cause_code(
242 &obligation.predicate,
243 obligation.param_env,
244 obligation.cause.code(),
246 &mut Default::default(),
250 self.tcx.sess.abort_if_errors();
254 /// Reports that a cycle was detected which led to overflow and halts
255 /// compilation. This is equivalent to `report_overflow_error` except
256 /// that we can give a more helpful error message (and, in particular,
257 /// we do not suggest increasing the overflow limit, which is not
259 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
260 let cycle = self.resolve_vars_if_possible(cycle.to_owned());
261 assert!(!cycle.is_empty());
263 debug!("report_overflow_error_cycle: cycle={:?}", cycle);
265 // The 'deepest' obligation is most likely to have a useful
267 self.report_overflow_error(cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(), false);
270 fn report_selection_error(
272 mut obligation: PredicateObligation<'tcx>,
273 root_obligation: &PredicateObligation<'tcx>,
274 error: &SelectionError<'tcx>,
275 fallback_has_occurred: bool,
278 let mut span = obligation.cause.span;
280 let mut err = match *error {
281 SelectionError::Ambiguous(ref impls) => {
282 let mut err = self.tcx.sess.struct_span_err(
283 obligation.cause.span,
284 &format!("multiple applicable `impl`s for `{}`", obligation.predicate),
286 self.annotate_source_of_ambiguity(&mut err, impls, obligation.predicate);
290 SelectionError::Unimplemented => {
291 // If this obligation was generated as a result of well-formedness checking, see if we
292 // can get a better error message by performing HIR-based well-formedness checking.
293 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
294 root_obligation.cause.code().peel_derives()
296 if let Some(cause) = self
298 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
300 obligation.cause = cause.clone();
301 span = obligation.cause.span;
304 if let ObligationCauseCode::CompareImplMethodObligation {
308 | ObligationCauseCode::CompareImplTypeObligation {
311 } = *obligation.cause.code()
313 self.report_extra_impl_obligation(
317 &format!("`{}`", obligation.predicate),
323 let bound_predicate = obligation.predicate.kind();
324 match bound_predicate.skip_binder() {
325 ty::PredicateKind::Trait(trait_predicate) => {
326 let trait_predicate = bound_predicate.rebind(trait_predicate);
327 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
329 trait_predicate.remap_constness_diag(obligation.param_env);
330 let predicate_is_const = ty::BoundConstness::ConstIfConst
331 == trait_predicate.skip_binder().constness;
333 if self.tcx.sess.has_errors().is_some()
334 && trait_predicate.references_error()
338 let trait_ref = trait_predicate.to_poly_trait_ref();
339 let (post_message, pre_message, type_def) = self
340 .get_parent_trait_ref(obligation.cause.code())
343 format!(" in `{}`", t),
344 format!("within `{}`, ", t),
345 s.map(|s| (format!("within this `{}`", t), s)),
348 .unwrap_or_default();
350 let OnUnimplementedNote {
356 } = self.on_unimplemented_note(trait_ref, &obligation);
357 let have_alt_message = message.is_some() || label.is_some();
358 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
360 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
361 let (message, note, append_const_msg) = if is_try_conversion {
364 "`?` couldn't convert the error to `{}`",
365 trait_ref.skip_binder().self_ty(),
368 "the question mark operation (`?`) implicitly performs a \
369 conversion on the error value using the `From` trait"
375 (message, note, append_const_msg)
378 let mut err = struct_span_err!(
384 .and_then(|cannot_do_this| {
385 match (predicate_is_const, append_const_msg) {
386 // do nothing if predicate is not const
387 (false, _) => Some(cannot_do_this),
388 // suggested using default post message
389 (true, Some(None)) => {
390 Some(format!("{cannot_do_this} in const contexts"))
392 // overridden post message
393 (true, Some(Some(post_message))) => {
394 Some(format!("{cannot_do_this}{post_message}"))
396 // fallback to generic message
397 (true, None) => None,
400 .unwrap_or_else(|| format!(
401 "the trait bound `{}` is not satisfied{}",
402 trait_predicate, post_message,
406 if is_try_conversion {
407 let none_error = self
409 .get_diagnostic_item(sym::none_error)
410 .map(|def_id| tcx.type_of(def_id));
411 let should_convert_option_to_result =
412 Some(trait_ref.skip_binder().substs.type_at(1)) == none_error;
413 let should_convert_result_to_option =
414 Some(trait_ref.self_ty().skip_binder()) == none_error;
415 if should_convert_option_to_result {
416 err.span_suggestion_verbose(
418 "consider converting the `Option<T>` into a `Result<T, _>` \
419 using `Option::ok_or` or `Option::ok_or_else`",
420 ".ok_or_else(|| /* error value */)".to_string(),
421 Applicability::HasPlaceholders,
423 } else if should_convert_result_to_option {
424 err.span_suggestion_verbose(
426 "consider converting the `Result<T, _>` into an `Option<T>` \
429 Applicability::MachineApplicable,
432 if let Some(ret_span) = self.return_type_span(&obligation) {
436 "expected `{}` because of this",
437 trait_ref.skip_binder().self_ty()
443 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
444 && predicate_is_const
446 err.note("`~const Drop` was renamed to `~const Destruct`");
447 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
450 let explanation = if let ObligationCauseCode::MainFunctionType =
451 obligation.cause.code()
453 "consider using `()`, or a `Result`".to_owned()
456 "{}the trait `{}` is not implemented for `{}`",
458 trait_predicate.print_modifiers_and_trait_path(),
459 trait_ref.skip_binder().self_ty(),
463 if self.suggest_add_reference_to_arg(
469 self.note_obligation_cause(&mut err, &obligation);
473 if let Some(ref s) = label {
474 // If it has a custom `#[rustc_on_unimplemented]`
475 // error message, let's display it as the label!
476 err.span_label(span, s.as_str());
477 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
478 // When the self type is a type param We don't need to "the trait
479 // `std::marker::Sized` is not implemented for `T`" as we will point
480 // at the type param with a label to suggest constraining it.
481 err.help(&explanation);
484 err.span_label(span, explanation);
487 if let ObligationCauseCode::ObjectCastObligation(obj_ty) = obligation.cause.code().peel_derives() &&
488 let Some(self_ty) = trait_predicate.self_ty().no_bound_vars() &&
489 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
490 self.suggest_borrowing_for_object_cast(&mut err, &obligation, self_ty, *obj_ty);
493 if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
494 let non_const_predicate = trait_ref.without_const();
495 let non_const_obligation = Obligation {
496 cause: obligation.cause.clone(),
497 param_env: obligation.param_env.without_const(),
498 predicate: non_const_predicate.to_predicate(tcx),
499 recursion_depth: obligation.recursion_depth,
501 if self.predicate_may_hold(&non_const_obligation) {
505 "the trait `{}` is implemented for `{}`, \
506 but that implementation is not `const`",
507 non_const_predicate.print_modifiers_and_trait_path(),
508 trait_ref.skip_binder().self_ty(),
514 if let Some((msg, span)) = type_def {
515 err.span_label(span, &msg);
517 if let Some(ref s) = note {
518 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
519 err.note(s.as_str());
521 if let Some(ref s) = enclosing_scope {
524 .opt_local_def_id(obligation.cause.body_id)
526 tcx.hir().body_owner_def_id(hir::BodyId {
527 hir_id: obligation.cause.body_id,
531 let enclosing_scope_span =
532 tcx.hir().span_with_body(tcx.hir().local_def_id_to_hir_id(body));
534 err.span_label(enclosing_scope_span, s.as_str());
537 self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
539 self.suggest_dereferences(&obligation, &mut err, trait_predicate);
540 suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
542 self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
543 suggested |= self.suggest_semicolon_removal(
549 self.note_version_mismatch(&mut err, &trait_ref);
550 self.suggest_remove_await(&obligation, &mut err);
551 self.suggest_derive(&obligation, &mut err, trait_predicate);
553 if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
554 self.suggest_await_before_try(
562 if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
568 // If the obligation failed due to a missing implementation of the
569 // `Unsize` trait, give a pointer to why that might be the case
571 "all implementations of `Unsize` are provided \
572 automatically by the compiler, see \
573 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
574 for more information",
579 self.tcx.lang_items().fn_trait(),
580 self.tcx.lang_items().fn_mut_trait(),
581 self.tcx.lang_items().fn_once_trait(),
583 .contains(&Some(trait_ref.def_id()));
584 let is_target_feature_fn = if let ty::FnDef(def_id, _) =
585 *trait_ref.skip_binder().self_ty().kind()
587 !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
591 if is_fn_trait && is_target_feature_fn {
593 "`#[target_feature]` functions do not implement the `Fn` traits",
597 // Try to report a help message
599 && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
600 obligation.param_env,
602 trait_predicate.skip_binder().constness,
603 trait_predicate.skip_binder().polarity,
606 // If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
607 // suggestion to add trait bounds for the type, since we only typically implement
608 // these traits once.
610 // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
613 ty::ClosureKind::from_def_id(self.tcx, trait_ref.def_id())
614 .expect("expected to map DefId to ClosureKind");
615 if !implemented_kind.extends(selected_kind) {
618 "`{}` implements `{}`, but it must implement `{}`, which is more general",
619 trait_ref.skip_binder().self_ty(),
626 // Note any argument mismatches
627 let given_ty = params.skip_binder();
628 let expected_ty = trait_ref.skip_binder().substs.type_at(1);
629 if let ty::Tuple(given) = given_ty.kind()
630 && let ty::Tuple(expected) = expected_ty.kind()
632 if expected.len() != given.len() {
633 // Note number of types that were expected and given
636 "expected a closure taking {} argument{}, but one taking {} argument{} was given",
638 if given.len() == 1 { "" } else { "s" },
640 if expected.len() == 1 { "" } else { "s" },
643 } else if !same_type_modulo_infer(given_ty, expected_ty) {
644 // Print type mismatch
645 let (expected_args, given_args) =
646 self.cmp(given_ty, expected_ty);
647 err.note_expected_found(
648 &"a closure with arguments",
650 &"a closure with arguments",
655 } else if !trait_ref.has_infer_types_or_consts()
656 && self.predicate_can_apply(obligation.param_env, trait_ref)
658 // If a where-clause may be useful, remind the
659 // user that they can add it.
661 // don't display an on-unimplemented note, as
662 // these notes will often be of the form
663 // "the type `T` can't be frobnicated"
664 // which is somewhat confusing.
665 self.suggest_restricting_param_bound(
668 obligation.cause.body_id,
670 } else if !suggested {
671 // Can't show anything else useful, try to find similar impls.
672 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
673 if !self.report_similar_impl_candidates(
678 // This is *almost* equivalent to
679 // `obligation.cause.code().peel_derives()`, but it gives us the
680 // trait predicate for that corresponding root obligation. This
681 // lets us get a derived obligation from a type parameter, like
682 // when calling `string.strip_suffix(p)` where `p` is *not* an
683 // implementer of `Pattern<'_>`.
684 let mut code = obligation.cause.code();
685 let mut trait_pred = trait_predicate;
686 let mut peeled = false;
689 ObligationCauseCode::FunctionArgumentObligation {
695 ObligationCauseCode::ImplDerivedObligation(
696 box ImplDerivedObligationCause {
698 DerivedObligationCause {
705 | ObligationCauseCode::BuiltinDerivedObligation(
706 DerivedObligationCause {
711 | ObligationCauseCode::DerivedObligation(
712 DerivedObligationCause {
719 trait_pred = *parent_trait_pred;
724 let def_id = trait_pred.def_id();
725 // Mention *all* the `impl`s for the *top most* obligation, the
726 // user might have meant to use one of them, if any found. We skip
727 // auto-traits or fundamental traits that might not be exactly what
728 // the user might expect to be presented with. Instead this is
729 // useful for less general traits.
731 && !self.tcx.trait_is_auto(def_id)
732 && !self.tcx.lang_items().items().contains(&Some(def_id))
734 let trait_ref = trait_pred.to_poly_trait_ref();
735 let impl_candidates =
736 self.find_similar_impl_candidates(trait_ref);
737 self.report_similar_impl_candidates(
746 // Changing mutability doesn't make a difference to whether we have
747 // an `Unsize` impl (Fixes ICE in #71036)
749 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
752 // If this error is due to `!: Trait` not implemented but `(): Trait` is
753 // implemented, and fallback has occurred, then it could be due to a
754 // variable that used to fallback to `()` now falling back to `!`. Issue a
755 // note informing about the change in behaviour.
756 if trait_predicate.skip_binder().self_ty().is_never()
757 && fallback_has_occurred
759 let predicate = trait_predicate.map_bound(|mut trait_pred| {
760 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
762 &trait_pred.trait_ref.substs[1..],
766 let unit_obligation = obligation.with(predicate.to_predicate(tcx));
767 if self.predicate_may_hold(&unit_obligation) {
769 "this error might have been caused by changes to \
770 Rust's type-inference algorithm (see issue #48950 \
771 <https://github.com/rust-lang/rust/issues/48950> \
772 for more information)",
774 err.help("did you intend to use the type `()` here instead?");
778 // Return early if the trait is Debug or Display and the invocation
779 // originates within a standard library macro, because the output
780 // is otherwise overwhelming and unhelpful (see #85844 for an
784 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
785 Some(macro_def_id) => {
786 let crate_name = tcx.crate_name(macro_def_id.krate);
787 crate_name == sym::std || crate_name == sym::core
794 self.tcx.get_diagnostic_name(trait_ref.def_id()),
795 Some(sym::Debug | sym::Display)
805 ty::PredicateKind::Subtype(predicate) => {
806 // Errors for Subtype predicates show up as
807 // `FulfillmentErrorCode::CodeSubtypeError`,
808 // not selection error.
809 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
812 ty::PredicateKind::Coerce(predicate) => {
813 // Errors for Coerce predicates show up as
814 // `FulfillmentErrorCode::CodeSubtypeError`,
815 // not selection error.
816 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
819 ty::PredicateKind::RegionOutlives(predicate) => {
820 let predicate = bound_predicate.rebind(predicate);
821 let predicate = self.resolve_vars_if_possible(predicate);
823 .region_outlives_predicate(&obligation.cause, predicate)
830 "the requirement `{}` is not satisfied (`{}`)",
836 ty::PredicateKind::Projection(..) | ty::PredicateKind::TypeOutlives(..) => {
837 let predicate = self.resolve_vars_if_possible(obligation.predicate);
842 "the requirement `{}` is not satisfied",
847 ty::PredicateKind::ObjectSafe(trait_def_id) => {
848 let violations = self.tcx.object_safety_violations(trait_def_id);
849 report_object_safety_error(self.tcx, span, trait_def_id, violations)
852 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
853 let found_kind = self.closure_kind(closure_substs).unwrap();
855 self.tcx.sess.source_map().guess_head_span(
856 self.tcx.hir().span_if_local(closure_def_id).unwrap(),
858 let mut err = struct_span_err!(
862 "expected a closure that implements the `{}` trait, \
863 but this closure only implements `{}`",
870 format!("this closure implements `{}`, not `{}`", found_kind, kind),
873 obligation.cause.span,
874 format!("the requirement to implement `{}` derives from here", kind),
877 // Additional context information explaining why the closure only implements
878 // a particular trait.
879 if let Some(typeck_results) = self.in_progress_typeck_results {
883 .local_def_id_to_hir_id(closure_def_id.expect_local());
884 let typeck_results = typeck_results.borrow();
885 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
886 (ty::ClosureKind::FnOnce, Some((span, place))) => {
890 "closure is `FnOnce` because it moves the \
891 variable `{}` out of its environment",
892 ty::place_to_string_for_capture(tcx, place)
896 (ty::ClosureKind::FnMut, Some((span, place))) => {
900 "closure is `FnMut` because it mutates the \
902 ty::place_to_string_for_capture(tcx, place)
914 ty::PredicateKind::WellFormed(ty) => {
915 if !self.tcx.sess.opts.debugging_opts.chalk {
916 // WF predicates cannot themselves make
917 // errors. They can only block due to
918 // ambiguity; otherwise, they always
919 // degenerate into other obligations
921 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
923 // FIXME: we'll need a better message which takes into account
924 // which bounds actually failed to hold.
925 self.tcx.sess.struct_span_err(
927 &format!("the type `{}` is not well-formed (chalk)", ty),
932 ty::PredicateKind::ConstEvaluatable(..) => {
933 // Errors for `ConstEvaluatable` predicates show up as
934 // `SelectionError::ConstEvalFailure`,
935 // not `Unimplemented`.
938 "const-evaluatable requirement gave wrong error: `{:?}`",
943 ty::PredicateKind::ConstEquate(..) => {
944 // Errors for `ConstEquate` predicates show up as
945 // `SelectionError::ConstEvalFailure`,
946 // not `Unimplemented`.
949 "const-equate requirement gave wrong error: `{:?}`",
954 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
956 "TypeWellFormedFromEnv predicate should only exist in the environment"
961 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
962 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
963 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
965 if expected_trait_ref.self_ty().references_error() {
969 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
973 let found_did = match *found_trait_ty.kind() {
977 | ty::Generator(did, ..) => Some(did),
978 ty::Adt(def, _) => Some(def.did()),
982 let found_span = found_did
983 .and_then(|did| self.tcx.hir().span_if_local(did))
984 .map(|sp| self.tcx.sess.source_map().guess_head_span(sp)); // the sp could be an fn def
986 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
987 // We check closures twice, with obligations flowing in different directions,
988 // but we want to complain about them only once.
992 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
994 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
995 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
996 _ => vec![ArgKind::empty()],
999 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1000 let expected = match expected_ty.kind() {
1001 ty::Tuple(ref tys) => {
1002 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
1004 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
1007 if found.len() == expected.len() {
1008 self.report_closure_arg_mismatch(
1015 let (closure_span, found) = found_did
1017 let node = self.tcx.hir().get_if_local(did)?;
1018 let (found_span, found) = self.get_fn_like_arguments(node)?;
1019 Some((Some(found_span), found))
1021 .unwrap_or((found_span, found));
1023 self.report_arg_count_mismatch(
1028 found_trait_ty.is_closure(),
1033 TraitNotObjectSafe(did) => {
1034 let violations = self.tcx.object_safety_violations(did);
1035 report_object_safety_error(self.tcx, span, did, violations)
1038 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1040 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1043 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1044 if !self.tcx.features().generic_const_exprs {
1045 let mut err = self.tcx.sess.struct_span_err(
1047 "constant expression depends on a generic parameter",
1049 // FIXME(const_generics): we should suggest to the user how they can resolve this
1050 // issue. However, this is currently not actually possible
1051 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1053 // Note that with `feature(generic_const_exprs)` this case should not
1055 err.note("this may fail depending on what value the parameter takes");
1060 match obligation.predicate.kind().skip_binder() {
1061 ty::PredicateKind::ConstEvaluatable(uv) => {
1063 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1064 let const_span = self.tcx.def_span(uv.def.did);
1065 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1066 Ok(snippet) => err.help(&format!(
1067 "try adding a `where` bound using this expression: `where [(); {}]:`",
1070 _ => err.help("consider adding a `where` bound using this expression"),
1077 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1083 // Already reported in the query.
1084 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1085 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1086 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1089 // Already reported.
1090 Overflow(OverflowError::Error(_)) => {
1091 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1095 bug!("overflow should be handled before the `report_selection_error` path");
1097 SelectionError::ErrorReporting => {
1098 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1102 self.note_obligation_cause(&mut err, &obligation);
1103 self.point_at_returns_when_relevant(&mut err, &obligation);
1108 /// Given some node representing a fn-like thing in the HIR map,
1109 /// returns a span and `ArgKind` information that describes the
1110 /// arguments it expects. This can be supplied to
1111 /// `report_arg_count_mismatch`.
1112 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
1113 let sm = self.tcx.sess.source_map();
1114 let hir = self.tcx.hir();
1116 Node::Expr(&hir::Expr {
1117 kind: hir::ExprKind::Closure(_, ref _decl, id, span, _),
1120 sm.guess_head_span(span),
1125 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
1128 Some(ArgKind::Tuple(
1132 sm.span_to_snippet(pat.span)
1134 .map(|snippet| (snippet, "_".to_owned()))
1136 .collect::<Option<Vec<_>>>()?,
1139 let name = sm.span_to_snippet(arg.pat.span).ok()?;
1140 Some(ArgKind::Arg(name, "_".to_owned()))
1143 .collect::<Option<Vec<ArgKind>>>()?,
1145 Node::Item(&hir::Item { span, kind: hir::ItemKind::Fn(ref sig, ..), .. })
1146 | Node::ImplItem(&hir::ImplItem {
1148 kind: hir::ImplItemKind::Fn(ref sig, _),
1151 | Node::TraitItem(&hir::TraitItem {
1153 kind: hir::TraitItemKind::Fn(ref sig, _),
1156 sm.guess_head_span(span),
1160 .map(|arg| match arg.kind {
1161 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
1163 vec![("_".to_owned(), "_".to_owned()); tys.len()],
1165 _ => ArgKind::empty(),
1167 .collect::<Vec<ArgKind>>(),
1169 Node::Ctor(ref variant_data) => {
1170 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
1171 let span = sm.guess_head_span(span);
1172 (span, vec![ArgKind::empty(); variant_data.fields().len()])
1174 _ => panic!("non-FnLike node found: {:?}", node),
1178 /// Reports an error when the number of arguments needed by a
1179 /// trait match doesn't match the number that the expression
1181 fn report_arg_count_mismatch(
1184 found_span: Option<Span>,
1185 expected_args: Vec<ArgKind>,
1186 found_args: Vec<ArgKind>,
1188 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1189 let kind = if is_closure { "closure" } else { "function" };
1191 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
1192 let arg_length = arguments.len();
1193 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
1194 match (arg_length, arguments.get(0)) {
1195 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
1196 format!("a single {}-tuple as argument", fields.len())
1201 if distinct && arg_length > 1 { "distinct " } else { "" },
1202 pluralize!(arg_length)
1207 let expected_str = args_str(&expected_args, &found_args);
1208 let found_str = args_str(&found_args, &expected_args);
1210 let mut err = struct_span_err!(
1214 "{} is expected to take {}, but it takes {}",
1220 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
1222 if let Some(found_span) = found_span {
1223 err.span_label(found_span, format!("takes {}", found_str));
1226 // ^^^^^^^^-- def_span
1230 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
1234 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
1236 // Suggest to take and ignore the arguments with expected_args_length `_`s if
1237 // found arguments is empty (assume the user just wants to ignore args in this case).
1238 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
1239 if found_args.is_empty() && is_closure {
1240 let underscores = vec!["_"; expected_args.len()].join(", ");
1241 err.span_suggestion_verbose(
1244 "consider changing the closure to take and ignore the expected argument{}",
1245 pluralize!(expected_args.len())
1247 format!("|{}|", underscores),
1248 Applicability::MachineApplicable,
1252 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
1253 if fields.len() == expected_args.len() {
1256 .map(|(name, _)| name.to_owned())
1257 .collect::<Vec<String>>()
1259 err.span_suggestion_verbose(
1261 "change the closure to take multiple arguments instead of a single tuple",
1262 format!("|{}|", sugg),
1263 Applicability::MachineApplicable,
1267 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
1268 && fields.len() == found_args.len()
1275 .map(|arg| match arg {
1276 ArgKind::Arg(name, _) => name.to_owned(),
1277 _ => "_".to_owned(),
1279 .collect::<Vec<String>>()
1281 // add type annotations if available
1282 if found_args.iter().any(|arg| match arg {
1283 ArgKind::Arg(_, ty) => ty != "_",
1290 .map(|(_, ty)| ty.to_owned())
1291 .collect::<Vec<String>>()
1298 err.span_suggestion_verbose(
1300 "change the closure to accept a tuple instead of individual arguments",
1302 Applicability::MachineApplicable,
1310 fn type_implements_fn_trait(
1312 param_env: ty::ParamEnv<'tcx>,
1313 ty: ty::Binder<'tcx, Ty<'tcx>>,
1314 constness: ty::BoundConstness,
1315 polarity: ty::ImplPolarity,
1316 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
1317 self.commit_if_ok(|_| {
1318 for trait_def_id in [
1319 self.tcx.lang_items().fn_trait(),
1320 self.tcx.lang_items().fn_mut_trait(),
1321 self.tcx.lang_items().fn_once_trait(),
1323 let Some(trait_def_id) = trait_def_id else { continue };
1324 // Make a fresh inference variable so we can determine what the substitutions
1325 // of the trait are.
1326 let var = self.next_ty_var(TypeVariableOrigin {
1328 kind: TypeVariableOriginKind::MiscVariable,
1330 let substs = self.tcx.mk_substs_trait(ty.skip_binder(), &[var.into()]);
1331 let obligation = Obligation::new(
1332 ObligationCause::dummy(),
1334 ty.rebind(ty::TraitPredicate {
1335 trait_ref: ty::TraitRef::new(trait_def_id, substs),
1339 .to_predicate(self.tcx),
1341 let mut fulfill_cx = FulfillmentContext::new_in_snapshot();
1342 fulfill_cx.register_predicate_obligation(self, obligation);
1343 if fulfill_cx.select_all_or_error(self).is_empty() {
1345 ty::ClosureKind::from_def_id(self.tcx, trait_def_id)
1346 .expect("expected to map DefId to ClosureKind"),
1347 ty.rebind(self.resolve_vars_if_possible(var)),
1357 trait InferCtxtPrivExt<'hir, 'tcx> {
1358 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1359 // `error` occurring implies that `cond` occurs.
1360 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1362 fn report_fulfillment_error(
1364 error: &FulfillmentError<'tcx>,
1365 body_id: Option<hir::BodyId>,
1366 fallback_has_occurred: bool,
1369 fn report_projection_error(
1371 obligation: &PredicateObligation<'tcx>,
1372 error: &MismatchedProjectionTypes<'tcx>,
1379 ignoring_lifetimes: bool,
1380 ) -> Option<CandidateSimilarity>;
1382 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1384 fn find_similar_impl_candidates(
1386 trait_ref: ty::PolyTraitRef<'tcx>,
1387 ) -> Vec<ImplCandidate<'tcx>>;
1389 fn report_similar_impl_candidates(
1391 impl_candidates: Vec<ImplCandidate<'tcx>>,
1392 trait_ref: ty::PolyTraitRef<'tcx>,
1393 err: &mut Diagnostic,
1396 /// Gets the parent trait chain start
1397 fn get_parent_trait_ref(
1399 code: &ObligationCauseCode<'tcx>,
1400 ) -> Option<(String, Option<Span>)>;
1402 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1403 /// with the same path as `trait_ref`, a help message about
1404 /// a probable version mismatch is added to `err`
1405 fn note_version_mismatch(
1407 err: &mut Diagnostic,
1408 trait_ref: &ty::PolyTraitRef<'tcx>,
1411 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1414 /// For this to work, `new_self_ty` must have no escaping bound variables.
1415 fn mk_trait_obligation_with_new_self_ty(
1417 param_env: ty::ParamEnv<'tcx>,
1418 trait_ref: ty::PolyTraitPredicate<'tcx>,
1419 new_self_ty: Ty<'tcx>,
1420 ) -> PredicateObligation<'tcx>;
1422 fn maybe_report_ambiguity(
1424 obligation: &PredicateObligation<'tcx>,
1425 body_id: Option<hir::BodyId>,
1428 fn predicate_can_apply(
1430 param_env: ty::ParamEnv<'tcx>,
1431 pred: ty::PolyTraitRef<'tcx>,
1434 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1436 fn suggest_unsized_bound_if_applicable(
1438 err: &mut Diagnostic,
1439 obligation: &PredicateObligation<'tcx>,
1442 fn annotate_source_of_ambiguity(
1444 err: &mut Diagnostic,
1446 predicate: ty::Predicate<'tcx>,
1449 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'hir>);
1451 fn maybe_indirection_for_unsized(
1453 err: &mut Diagnostic,
1454 item: &'hir Item<'hir>,
1455 param: &'hir GenericParam<'hir>,
1458 fn is_recursive_obligation(
1460 obligated_types: &mut Vec<Ty<'tcx>>,
1461 cause_code: &ObligationCauseCode<'tcx>,
1465 impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
1466 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1467 // `error` occurring implies that `cond` occurs.
1468 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1473 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1474 let bound_error = error.kind();
1475 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1476 (ty::PredicateKind::Trait(..), ty::PredicateKind::Trait(error)) => {
1477 (cond, bound_error.rebind(error))
1480 // FIXME: make this work in other cases too.
1485 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1486 let bound_predicate = obligation.predicate.kind();
1487 if let ty::PredicateKind::Trait(implication) = bound_predicate.skip_binder() {
1488 let error = error.to_poly_trait_ref();
1489 let implication = bound_predicate.rebind(implication.trait_ref);
1490 // FIXME: I'm just not taking associated types at all here.
1491 // Eventually I'll need to implement param-env-aware
1492 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1493 let param_env = ty::ParamEnv::empty();
1494 if self.can_sub(param_env, error, implication).is_ok() {
1495 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1504 #[instrument(skip(self), level = "debug")]
1505 fn report_fulfillment_error(
1507 error: &FulfillmentError<'tcx>,
1508 body_id: Option<hir::BodyId>,
1509 fallback_has_occurred: bool,
1512 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1513 self.report_selection_error(
1514 error.obligation.clone(),
1515 &error.root_obligation,
1517 fallback_has_occurred,
1520 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1521 self.report_projection_error(&error.obligation, e);
1523 FulfillmentErrorCode::CodeAmbiguity => {
1524 self.maybe_report_ambiguity(&error.obligation, body_id);
1526 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1527 self.report_mismatched_types(
1528 &error.obligation.cause,
1529 expected_found.expected,
1530 expected_found.found,
1535 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1536 self.report_mismatched_consts(
1537 &error.obligation.cause,
1538 expected_found.expected,
1539 expected_found.found,
1547 fn report_projection_error(
1549 obligation: &PredicateObligation<'tcx>,
1550 error: &MismatchedProjectionTypes<'tcx>,
1552 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1554 if predicate.references_error() {
1560 let mut err = &error.err;
1561 let mut values = None;
1563 // try to find the mismatched types to report the error with.
1565 // this can fail if the problem was higher-ranked, in which
1566 // cause I have no idea for a good error message.
1567 let bound_predicate = predicate.kind();
1568 if let ty::PredicateKind::Projection(data) = bound_predicate.skip_binder() {
1569 let mut selcx = SelectionContext::new(self);
1570 let (data, _) = self.replace_bound_vars_with_fresh_vars(
1571 obligation.cause.span,
1572 infer::LateBoundRegionConversionTime::HigherRankedType,
1573 bound_predicate.rebind(data),
1575 let mut obligations = vec![];
1576 let normalized_ty = super::normalize_projection_type(
1578 obligation.param_env,
1580 obligation.cause.clone(),
1586 "report_projection_error obligation.cause={:?} obligation.param_env={:?}",
1587 obligation.cause, obligation.param_env
1591 "report_projection_error normalized_ty={:?} data.ty={:?}",
1592 normalized_ty, data.term,
1595 let is_normalized_ty_expected = !matches!(
1596 obligation.cause.code().peel_derives(),
1597 ObligationCauseCode::ItemObligation(_)
1598 | ObligationCauseCode::BindingObligation(_, _)
1599 | ObligationCauseCode::ObjectCastObligation(_)
1600 | ObligationCauseCode::OpaqueType
1602 if let Err(error) = self.at(&obligation.cause, obligation.param_env).eq_exp(
1603 is_normalized_ty_expected,
1607 values = Some(infer::ValuePairs::Terms(ExpectedFound::new(
1608 is_normalized_ty_expected,
1617 let mut diag = struct_span_err!(
1619 obligation.cause.span,
1621 "type mismatch resolving `{}`",
1624 let secondary_span = match predicate.kind().skip_binder() {
1625 ty::PredicateKind::Projection(proj) => self
1627 .opt_associated_item(proj.projection_ty.item_def_id)
1628 .and_then(|trait_assoc_item| {
1630 .trait_of_item(proj.projection_ty.item_def_id)
1631 .map(|id| (trait_assoc_item, id))
1633 .and_then(|(trait_assoc_item, id)| {
1634 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1635 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1637 .associated_items(did)
1638 .in_definition_order()
1639 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1642 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1644 hir::Node::TraitItem(hir::TraitItem {
1645 kind: hir::TraitItemKind::Type(_, Some(ty)),
1648 | hir::Node::ImplItem(hir::ImplItem {
1649 kind: hir::ImplItemKind::TyAlias(ty),
1652 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1666 self.note_obligation_cause(&mut diag, obligation);
1675 ignoring_lifetimes: bool,
1676 ) -> Option<CandidateSimilarity> {
1677 /// returns the fuzzy category of a given type, or None
1678 /// if the type can be equated to any type.
1679 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1681 ty::Bool => Some(0),
1682 ty::Char => Some(1),
1684 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::String, def.did()) => Some(2),
1688 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1689 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1690 ty::Array(..) | ty::Slice(..) => Some(6),
1691 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1692 ty::Dynamic(..) => Some(8),
1693 ty::Closure(..) => Some(9),
1694 ty::Tuple(..) => Some(10),
1695 ty::Param(..) => Some(11),
1696 ty::Projection(..) => Some(12),
1697 ty::Opaque(..) => Some(13),
1698 ty::Never => Some(14),
1699 ty::Adt(..) => Some(15),
1700 ty::Generator(..) => Some(16),
1701 ty::Foreign(..) => Some(17),
1702 ty::GeneratorWitness(..) => Some(18),
1703 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1707 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1710 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1718 if !ignoring_lifetimes {
1719 a = strip_references(a);
1720 b = strip_references(b);
1723 let cat_a = type_category(self.tcx, a)?;
1724 let cat_b = type_category(self.tcx, b)?;
1726 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1727 } else if cat_a == cat_b {
1728 match (a.kind(), b.kind()) {
1729 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1730 // Matching on references results in a lot of unhelpful
1731 // suggestions, so let's just not do that for now.
1733 // We still upgrade successful matches to `ignoring_lifetimes: true`
1734 // to prioritize that impl.
1735 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1736 self.fuzzy_match_tys(a, b, true).is_some()
1740 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1741 } else if ignoring_lifetimes {
1744 self.fuzzy_match_tys(a, b, true)
1748 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1749 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1750 hir::GeneratorKind::Gen => "a generator",
1751 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1752 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1753 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1757 fn find_similar_impl_candidates(
1759 trait_ref: ty::PolyTraitRef<'tcx>,
1760 ) -> Vec<ImplCandidate<'tcx>> {
1762 .all_impls(trait_ref.def_id())
1763 .filter_map(|def_id| {
1764 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative {
1768 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1770 self.fuzzy_match_tys(trait_ref.skip_binder().self_ty(), imp.self_ty(), false)
1771 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1776 fn report_similar_impl_candidates(
1778 impl_candidates: Vec<ImplCandidate<'tcx>>,
1779 trait_ref: ty::PolyTraitRef<'tcx>,
1780 err: &mut Diagnostic,
1782 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1785 let len = candidates.len();
1786 if candidates.len() == 0 {
1789 if candidates.len() == 1 {
1790 err.highlighted_help(vec![
1792 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1795 ("is".to_string(), Style::Highlight),
1796 (" implemented for `".to_string(), Style::NoStyle),
1797 (candidates[0].self_ty().to_string(), Style::Highlight),
1798 ("`".to_string(), Style::NoStyle),
1802 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1803 // Check if the trait is the same in all cases. If so, we'll only show the type.
1804 let mut traits: Vec<_> =
1805 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1809 let mut candidates: Vec<String> = candidates
1812 if traits.len() == 1 {
1813 format!("\n {}", c.self_ty())
1822 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1824 "the following other types implement trait `{}`:{}{}",
1825 trait_ref.print_only_trait_path(),
1826 candidates[..end].join(""),
1827 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1832 let def_id = trait_ref.def_id();
1833 if impl_candidates.is_empty() {
1834 if self.tcx.trait_is_auto(def_id)
1835 || self.tcx.lang_items().items().contains(&Some(def_id))
1836 || self.tcx.get_diagnostic_name(def_id).is_some()
1838 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1841 let normalized_impl_candidates: Vec<_> = self
1844 // Ignore automatically derived impls and `!Trait` impls.
1846 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1847 || self.tcx.is_builtin_derive(def_id)
1849 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1850 // Avoid mentioning type parameters.
1851 .filter(|trait_ref| !matches!(trait_ref.self_ty().kind(), ty::Param(_)))
1853 return report(normalized_impl_candidates, err);
1856 let normalize = |candidate| {
1857 self.tcx.infer_ctxt().enter(|ref infcx| {
1858 let normalized = infcx
1859 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1860 .normalize(candidate)
1863 Some(normalized) => normalized.value,
1869 // Sort impl candidates so that ordering is consistent for UI tests.
1870 // because the ordering of `impl_candidates` may not be deterministic:
1871 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1873 // Prefer more similar candidates first, then sort lexicographically
1874 // by their normalized string representation.
1875 let mut normalized_impl_candidates_and_similarities = impl_candidates
1877 .map(|ImplCandidate { trait_ref, similarity }| {
1878 let normalized = normalize(trait_ref);
1879 (similarity, normalized)
1881 .collect::<Vec<_>>();
1882 normalized_impl_candidates_and_similarities.sort();
1883 normalized_impl_candidates_and_similarities.dedup();
1885 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
1887 .map(|(_, normalized)| normalized)
1888 .collect::<Vec<_>>();
1890 report(normalized_impl_candidates, err)
1893 /// Gets the parent trait chain start
1894 fn get_parent_trait_ref(
1896 code: &ObligationCauseCode<'tcx>,
1897 ) -> Option<(String, Option<Span>)> {
1899 ObligationCauseCode::BuiltinDerivedObligation(data) => {
1900 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
1901 match self.get_parent_trait_ref(&data.parent_code) {
1904 let ty = parent_trait_ref.skip_binder().self_ty();
1905 let span = TyCategory::from_ty(self.tcx, ty)
1906 .map(|(_, def_id)| self.tcx.def_span(def_id));
1907 Some((ty.to_string(), span))
1911 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
1912 self.get_parent_trait_ref(&parent_code)
1918 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1919 /// with the same path as `trait_ref`, a help message about
1920 /// a probable version mismatch is added to `err`
1921 fn note_version_mismatch(
1923 err: &mut Diagnostic,
1924 trait_ref: &ty::PolyTraitRef<'tcx>,
1926 let get_trait_impl = |trait_def_id| {
1927 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
1929 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
1930 let traits_with_same_path: std::collections::BTreeSet<_> = self
1933 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
1934 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
1936 let mut suggested = false;
1937 for trait_with_same_path in traits_with_same_path {
1938 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
1939 let impl_span = self.tcx.def_span(impl_def_id);
1940 err.span_help(impl_span, "trait impl with same name found");
1941 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
1942 let crate_msg = format!(
1943 "perhaps two different versions of crate `{}` are being used?",
1946 err.note(&crate_msg);
1953 fn mk_trait_obligation_with_new_self_ty(
1955 param_env: ty::ParamEnv<'tcx>,
1956 trait_ref: ty::PolyTraitPredicate<'tcx>,
1957 new_self_ty: Ty<'tcx>,
1958 ) -> PredicateObligation<'tcx> {
1959 assert!(!new_self_ty.has_escaping_bound_vars());
1961 let trait_pred = trait_ref.map_bound_ref(|tr| ty::TraitPredicate {
1962 trait_ref: ty::TraitRef {
1963 substs: self.tcx.mk_substs_trait(new_self_ty, &tr.trait_ref.substs[1..]),
1969 Obligation::new(ObligationCause::dummy(), param_env, trait_pred.to_predicate(self.tcx))
1972 #[instrument(skip(self), level = "debug")]
1973 fn maybe_report_ambiguity(
1975 obligation: &PredicateObligation<'tcx>,
1976 body_id: Option<hir::BodyId>,
1978 // Unable to successfully determine, probably means
1979 // insufficient type information, but could mean
1980 // ambiguous impls. The latter *ought* to be a
1981 // coherence violation, so we don't report it here.
1983 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1984 let span = obligation.cause.span;
1986 debug!(?predicate, obligation.cause.code = tracing::field::debug(&obligation.cause.code()));
1988 // Ambiguity errors are often caused as fallout from earlier errors.
1989 // We ignore them if this `infcx` is tainted in some cases below.
1991 let bound_predicate = predicate.kind();
1992 let mut err = match bound_predicate.skip_binder() {
1993 ty::PredicateKind::Trait(data) => {
1994 let trait_ref = bound_predicate.rebind(data.trait_ref);
1997 if predicate.references_error() {
2000 // Typically, this ambiguity should only happen if
2001 // there are unresolved type inference variables
2002 // (otherwise it would suggest a coherence
2003 // failure). But given #21974 that is not necessarily
2004 // the case -- we can have multiple where clauses that
2005 // are only distinguished by a region, which results
2006 // in an ambiguity even when all types are fully
2007 // known, since we don't dispatch based on region
2010 // Pick the first substitution that still contains inference variables as the one
2011 // we're going to emit an error for. If there are none (see above), fall back to
2012 // the substitution for `Self`.
2014 let substs = data.trait_ref.substs;
2017 .find(|s| s.has_infer_types_or_consts())
2018 .unwrap_or_else(|| substs[0])
2021 // This is kind of a hack: it frequently happens that some earlier
2022 // error prevents types from being fully inferred, and then we get
2023 // a bunch of uninteresting errors saying something like "<generic
2024 // #0> doesn't implement Sized". It may even be true that we
2025 // could just skip over all checks where the self-ty is an
2026 // inference variable, but I was afraid that there might be an
2027 // inference variable created, registered as an obligation, and
2028 // then never forced by writeback, and hence by skipping here we'd
2029 // be ignoring the fact that we don't KNOW the type works
2030 // out. Though even that would probably be harmless, given that
2031 // we're only talking about builtin traits, which are known to be
2032 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2033 // avoid inundating the user with unnecessary errors, but we now
2034 // check upstream for type errors and don't add the obligations to
2035 // begin with in those cases.
2036 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
2037 if !self.is_tainted_by_errors() {
2038 self.emit_inference_failure_err(
2050 let impl_candidates = self
2051 .find_similar_impl_candidates(trait_ref)
2053 .map(|candidate| candidate.trait_ref)
2055 let mut err = self.emit_inference_failure_err(
2063 let obligation = Obligation::new(
2064 obligation.cause.clone(),
2065 obligation.param_env,
2066 trait_ref.to_poly_trait_predicate(),
2068 let mut selcx = SelectionContext::with_query_mode(
2070 crate::traits::TraitQueryMode::Standard,
2072 match selcx.select_from_obligation(&obligation) {
2073 Err(SelectionError::Ambiguous(impls)) if impls.len() > 1 => {
2074 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2077 if self.is_tainted_by_errors() {
2081 err.note(&format!("cannot satisfy `{}`", predicate));
2085 if let ObligationCauseCode::ItemObligation(def_id) = *obligation.cause.code() {
2086 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2089 &ObligationCauseCode::BindingObligation(def_id, _),
2091 (self.tcx.sess.source_map().span_to_snippet(span), obligation.cause.code())
2093 let generics = self.tcx.generics_of(def_id);
2094 if generics.params.iter().any(|p| p.name != kw::SelfUpper)
2095 && !snippet.ends_with('>')
2096 && !generics.has_impl_trait()
2097 && !self.tcx.fn_trait_kind_from_lang_item(def_id).is_some()
2099 // FIXME: To avoid spurious suggestions in functions where type arguments
2100 // where already supplied, we check the snippet to make sure it doesn't
2101 // end with a turbofish. Ideally we would have access to a `PathSegment`
2102 // instead. Otherwise we would produce the following output:
2104 // error[E0283]: type annotations needed
2105 // --> $DIR/issue-54954.rs:3:24
2107 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2108 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2110 // | cannot infer type
2111 // | help: consider specifying the type argument
2112 // | in the function call:
2113 // | `Tt::const_val::<[i8; 123]>::<T>`
2115 // LL | const fn const_val<T: Sized>() -> usize {
2116 // | - required by this bound in `Tt::const_val`
2118 // = note: cannot satisfy `_: Tt`
2120 err.span_suggestion_verbose(
2121 span.shrink_to_hi(),
2123 "consider specifying the type argument{} in the function call",
2124 pluralize!(generics.params.len()),
2131 .map(|p| p.name.to_string())
2132 .collect::<Vec<String>>()
2135 Applicability::HasPlaceholders,
2142 ty::PredicateKind::WellFormed(arg) => {
2143 // Same hacky approach as above to avoid deluging user
2144 // with error messages.
2145 if arg.references_error()
2146 || self.tcx.sess.has_errors().is_some()
2147 || self.is_tainted_by_errors()
2152 self.emit_inference_failure_err(body_id, span, arg, vec![], ErrorCode::E0282)
2155 ty::PredicateKind::Subtype(data) => {
2156 if data.references_error()
2157 || self.tcx.sess.has_errors().is_some()
2158 || self.is_tainted_by_errors()
2160 // no need to overload user in such cases
2163 let SubtypePredicate { a_is_expected: _, a, b } = data;
2164 // both must be type variables, or the other would've been instantiated
2165 assert!(a.is_ty_var() && b.is_ty_var());
2166 self.emit_inference_failure_err(body_id, span, a.into(), vec![], ErrorCode::E0282)
2168 ty::PredicateKind::Projection(data) => {
2169 let self_ty = data.projection_ty.self_ty();
2170 let term = data.term;
2171 if predicate.references_error() || self.is_tainted_by_errors() {
2174 if self_ty.needs_infer() && term.needs_infer() {
2175 // We do this for the `foo.collect()?` case to produce a suggestion.
2176 let mut err = self.emit_inference_failure_err(
2183 err.note(&format!("cannot satisfy `{}`", predicate));
2186 let mut err = struct_span_err!(
2190 "type annotations needed: cannot satisfy `{}`",
2193 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2199 if self.tcx.sess.has_errors().is_some() || self.is_tainted_by_errors() {
2202 let mut err = struct_span_err!(
2206 "type annotations needed: cannot satisfy `{}`",
2209 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2213 self.note_obligation_cause(&mut err, obligation);
2217 fn annotate_source_of_ambiguity(
2219 err: &mut Diagnostic,
2221 predicate: ty::Predicate<'tcx>,
2223 let mut spans = vec![];
2224 let mut crates = vec![];
2225 let mut post = vec![];
2226 for def_id in impls {
2227 match self.tcx.span_of_impl(*def_id) {
2228 Ok(span) => spans.push(self.tcx.sess.source_map().guess_head_span(span)),
2231 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2237 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2238 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2240 crate_names.dedup();
2244 if self.is_tainted_by_errors()
2245 && (crate_names.len() == 1
2247 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2248 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2250 // Avoid complaining about other inference issues for expressions like
2251 // `42 >> 1`, where the types are still `{integer}`, but we want to
2252 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2253 // NOTE(eddyb) this was `.cancel()`, but `err`
2254 // is borrowed, so we can't fully defuse it.
2255 err.downgrade_to_delayed_bug();
2258 let post = if post.len() > 4 {
2260 ":\n{}\nand {} more",
2261 post.iter().map(|p| format!("- {}", p)).take(4).collect::<Vec<_>>().join("\n"),
2264 } else if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2265 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2266 } else if post.len() == 1 {
2267 format!(": `{}`", post[0])
2272 match (spans.len(), crates.len(), crate_names.len()) {
2274 err.note(&format!("cannot satisfy `{}`", predicate));
2277 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2281 "{} in the following crates: {}{}",
2283 crate_names.join(", "),
2288 let span: MultiSpan = spans.into();
2289 err.span_note(span, &msg);
2292 let span: MultiSpan = spans.into();
2293 err.span_note(span, &msg);
2295 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2299 let span: MultiSpan = spans.into();
2300 err.span_note(span, &msg);
2302 "and more `impl`s found in the following crates: {}{}",
2303 crate_names.join(", "),
2310 /// Returns `true` if the trait predicate may apply for *some* assignment
2311 /// to the type parameters.
2312 fn predicate_can_apply(
2314 param_env: ty::ParamEnv<'tcx>,
2315 pred: ty::PolyTraitRef<'tcx>,
2317 struct ParamToVarFolder<'a, 'tcx> {
2318 infcx: &'a InferCtxt<'a, 'tcx>,
2319 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2322 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2323 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2327 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2328 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2329 let infcx = self.infcx;
2330 *self.var_map.entry(ty).or_insert_with(|| {
2331 infcx.next_ty_var(TypeVariableOrigin {
2332 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2337 ty.super_fold_with(self)
2343 let mut selcx = SelectionContext::new(self);
2346 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2348 let cleaned_pred = super::project::normalize(
2351 ObligationCause::dummy(),
2356 let obligation = Obligation::new(
2357 ObligationCause::dummy(),
2359 cleaned_pred.without_const().to_predicate(selcx.tcx()),
2362 self.predicate_may_hold(&obligation)
2366 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2367 // First, attempt to add note to this error with an async-await-specific
2368 // message, and fall back to regular note otherwise.
2369 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2370 self.note_obligation_cause_code(
2372 &obligation.predicate,
2373 obligation.param_env,
2374 obligation.cause.code(),
2376 &mut Default::default(),
2378 self.suggest_unsized_bound_if_applicable(err, obligation);
2382 fn suggest_unsized_bound_if_applicable(
2384 err: &mut Diagnostic,
2385 obligation: &PredicateObligation<'tcx>,
2388 ty::PredicateKind::Trait(pred),
2389 &ObligationCauseCode::BindingObligation(item_def_id, span),
2391 obligation.predicate.kind().skip_binder(),
2392 obligation.cause.code().peel_derives(),
2397 "suggest_unsized_bound_if_applicable: pred={:?} item_def_id={:?} span={:?}",
2398 pred, item_def_id, span
2401 let (Some(node), true) = (
2402 self.tcx.hir().get_if_local(item_def_id),
2403 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2407 self.maybe_suggest_unsized_generics(err, span, node);
2410 fn maybe_suggest_unsized_generics<'hir>(
2412 err: &mut Diagnostic,
2416 let Some(generics) = node.generics() else {
2419 let sized_trait = self.tcx.lang_items().sized_trait();
2420 debug!("maybe_suggest_unsized_generics: generics.params={:?}", generics.params);
2421 debug!("maybe_suggest_unsized_generics: generics.where_clause={:?}", generics.where_clause);
2422 let param = generics.params.iter().filter(|param| param.span == span).find(|param| {
2423 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2424 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2428 .all(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) != sized_trait)
2430 let Some(param) = param else {
2433 let param_def_id = self.tcx.hir().local_def_id(param.hir_id).to_def_id();
2434 let preds = generics.where_clause.predicates.iter();
2435 let explicitly_sized = preds
2436 .filter_map(|pred| match pred {
2437 hir::WherePredicate::BoundPredicate(bp) => Some(bp),
2440 .filter(|bp| bp.is_param_bound(param_def_id))
2441 .flat_map(|bp| bp.bounds)
2442 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2443 if explicitly_sized {
2446 debug!("maybe_suggest_unsized_generics: param={:?}", param);
2450 // Only suggest indirection for uses of type parameters in ADTs.
2452 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2456 if self.maybe_indirection_for_unsized(err, item, param) {
2462 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2463 let (span, separator) = match param.bounds {
2464 [] => (span.shrink_to_hi(), ":"),
2465 [.., bound] => (bound.span().shrink_to_hi(), " +"),
2467 err.span_suggestion_verbose(
2469 "consider relaxing the implicit `Sized` restriction",
2470 format!("{} ?Sized", separator),
2471 Applicability::MachineApplicable,
2475 fn maybe_indirection_for_unsized<'hir>(
2477 err: &mut Diagnostic,
2478 item: &'hir Item<'hir>,
2479 param: &'hir GenericParam<'hir>,
2481 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2482 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2483 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2485 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2486 visitor.visit_item(item);
2487 if visitor.invalid_spans.is_empty() {
2490 let mut multispan: MultiSpan = param.span.into();
2491 multispan.push_span_label(
2493 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2495 for sp in visitor.invalid_spans {
2496 multispan.push_span_label(
2498 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2504 "you could relax the implicit `Sized` bound on `{T}` if it were \
2505 used through indirection like `&{T}` or `Box<{T}>`",
2506 T = param.name.ident(),
2512 fn is_recursive_obligation(
2514 obligated_types: &mut Vec<Ty<'tcx>>,
2515 cause_code: &ObligationCauseCode<'tcx>,
2517 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2518 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2519 let self_ty = parent_trait_ref.skip_binder().self_ty();
2520 if obligated_types.iter().any(|ot| ot == &self_ty) {
2523 if let ty::Adt(def, substs) = self_ty.kind()
2524 && let [arg] = &substs[..]
2525 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2526 && let ty::Adt(inner_def, _) = ty.kind()
2536 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2537 /// `param: ?Sized` would be a valid constraint.
2538 struct FindTypeParam {
2539 param: rustc_span::Symbol,
2540 invalid_spans: Vec<Span>,
2544 impl<'v> Visitor<'v> for FindTypeParam {
2545 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2546 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2549 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2550 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2551 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2552 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2553 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2554 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2555 // in that case should make what happened clear enough.
2557 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2558 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2559 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2562 debug!("FindTypeParam::visit_ty: ty={:?}", ty);
2563 self.invalid_spans.push(ty.span);
2566 hir::TyKind::Path(_) => {
2567 let prev = self.nested;
2569 hir::intravisit::walk_ty(self, ty);
2573 hir::intravisit::walk_ty(self, ty);
2579 pub fn recursive_type_with_infinite_size_error<'tcx>(
2582 spans: Vec<(Span, Option<hir::HirId>)>,
2584 assert!(type_def_id.is_local());
2585 let span = tcx.hir().span_if_local(type_def_id).unwrap();
2586 let span = tcx.sess.source_map().guess_head_span(span);
2587 let path = tcx.def_path_str(type_def_id);
2589 struct_span_err!(tcx.sess, span, E0072, "recursive type `{}` has infinite size", path);
2590 err.span_label(span, "recursive type has infinite size");
2591 for &(span, _) in &spans {
2592 err.span_label(span, "recursive without indirection");
2595 "insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `{}` representable",
2598 if spans.len() <= 4 {
2599 // FIXME(compiler-errors): This suggestion might be erroneous if Box is shadowed
2600 err.multipart_suggestion(
2604 .flat_map(|(span, field_id)| {
2605 if let Some(generic_span) = get_option_generic_from_field_id(tcx, field_id) {
2606 // If we match an `Option` and can grab the span of the Option's generic, then
2607 // suggest boxing the generic arg for a non-null niche optimization.
2609 (generic_span.shrink_to_lo(), "Box<".to_string()),
2610 (generic_span.shrink_to_hi(), ">".to_string()),
2614 (span.shrink_to_lo(), "Box<".to_string()),
2615 (span.shrink_to_hi(), ">".to_string()),
2620 Applicability::HasPlaceholders,
2628 /// Extract the span for the generic type `T` of `Option<T>` in a field definition
2629 fn get_option_generic_from_field_id(tcx: TyCtxt<'_>, field_id: Option<hir::HirId>) -> Option<Span> {
2630 let node = tcx.hir().find(field_id?);
2632 // Expect a field from our field_id
2633 let Some(hir::Node::Field(field_def)) = node
2634 else { bug!("Expected HirId corresponding to FieldDef, found: {:?}", node) };
2636 // Match a type that is a simple QPath with no Self
2637 let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = &field_def.ty.kind
2638 else { return None };
2640 // Check if the path we're checking resolves to Option
2641 let hir::def::Res::Def(_, did) = path.res
2642 else { return None };
2644 // Bail if this path doesn't describe `::core::option::Option`
2645 if !tcx.is_diagnostic_item(sym::Option, did) {
2649 // Match a single generic arg in the 0th path segment
2650 let generic_arg = path.segments.last()?.args?.args.get(0)?;
2652 // Take the span out of the type, if it's a type
2653 if let hir::GenericArg::Type(generic_ty) = generic_arg { Some(generic_ty.span) } else { None }
2656 /// Summarizes information
2659 /// An argument of non-tuple type. Parameters are (name, ty)
2660 Arg(String, String),
2662 /// An argument of tuple type. For a "found" argument, the span is
2663 /// the location in the source of the pattern. For an "expected"
2664 /// argument, it will be None. The vector is a list of (name, ty)
2665 /// strings for the components of the tuple.
2666 Tuple(Option<Span>, Vec<(String, String)>),
2670 fn empty() -> ArgKind {
2671 ArgKind::Arg("_".to_owned(), "_".to_owned())
2674 /// Creates an `ArgKind` from the expected type of an
2675 /// argument. It has no name (`_`) and an optional source span.
2676 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2678 ty::Tuple(tys) => ArgKind::Tuple(
2680 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2682 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2687 struct HasNumericInferVisitor;
2689 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2692 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2693 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2694 ControlFlow::Break(())
2696 ControlFlow::CONTINUE