1 pub mod on_unimplemented;
5 EvaluationResult, FulfillmentContext, 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;
16 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
20 use rustc_hir::def_id::DefId;
21 use rustc_hir::intravisit::Visitor;
22 use rustc_hir::GenericParam;
25 use rustc_infer::infer::error_reporting::same_type_modulo_infer;
26 use rustc_infer::traits::TraitEngine;
27 use rustc_middle::traits::select::OverflowError;
28 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
29 use rustc_middle::ty::error::ExpectedFound;
30 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
31 use rustc_middle::ty::{
32 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!(?cycle, "report_overflow_error_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,
277 self.set_tainted_by_errors();
279 let mut span = obligation.cause.span;
281 let mut err = match *error {
282 SelectionError::Ambiguous(ref impls) => {
283 let mut err = self.tcx.sess.struct_span_err(
284 obligation.cause.span,
285 &format!("multiple applicable `impl`s for `{}`", obligation.predicate),
287 self.annotate_source_of_ambiguity(&mut err, impls, obligation.predicate);
291 SelectionError::Unimplemented => {
292 // If this obligation was generated as a result of well-formedness checking, see if we
293 // can get a better error message by performing HIR-based well-formedness checking.
294 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
295 root_obligation.cause.code().peel_derives()
297 if let Some(cause) = self
299 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
301 obligation.cause = cause.clone();
302 span = obligation.cause.span;
305 if let ObligationCauseCode::CompareImplMethodObligation {
309 | ObligationCauseCode::CompareImplTypeObligation {
312 } = *obligation.cause.code()
314 self.report_extra_impl_obligation(
318 &format!("`{}`", obligation.predicate),
324 let bound_predicate = obligation.predicate.kind();
325 match bound_predicate.skip_binder() {
326 ty::PredicateKind::Trait(trait_predicate) => {
327 let trait_predicate = bound_predicate.rebind(trait_predicate);
328 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
330 trait_predicate.remap_constness_diag(obligation.param_env);
331 let predicate_is_const = ty::BoundConstness::ConstIfConst
332 == trait_predicate.skip_binder().constness;
334 if self.tcx.sess.has_errors().is_some()
335 && trait_predicate.references_error()
339 let trait_ref = trait_predicate.to_poly_trait_ref();
340 let (post_message, pre_message, type_def) = self
341 .get_parent_trait_ref(obligation.cause.code())
344 format!(" in `{}`", t),
345 format!("within `{}`, ", t),
346 s.map(|s| (format!("within this `{}`", t), s)),
349 .unwrap_or_default();
351 let OnUnimplementedNote {
357 } = self.on_unimplemented_note(trait_ref, &obligation);
358 let have_alt_message = message.is_some() || label.is_some();
359 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
361 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
362 let (message, note, append_const_msg) = if is_try_conversion {
365 "`?` couldn't convert the error to `{}`",
366 trait_ref.skip_binder().self_ty(),
369 "the question mark operation (`?`) implicitly performs a \
370 conversion on the error value using the `From` trait"
376 (message, note, append_const_msg)
379 let mut err = struct_span_err!(
385 .and_then(|cannot_do_this| {
386 match (predicate_is_const, append_const_msg) {
387 // do nothing if predicate is not const
388 (false, _) => Some(cannot_do_this),
389 // suggested using default post message
390 (true, Some(None)) => {
391 Some(format!("{cannot_do_this} in const contexts"))
393 // overridden post message
394 (true, Some(Some(post_message))) => {
395 Some(format!("{cannot_do_this}{post_message}"))
397 // fallback to generic message
398 (true, None) => None,
401 .unwrap_or_else(|| format!(
402 "the trait bound `{}` is not satisfied{}",
403 trait_predicate, post_message,
407 if is_try_conversion {
408 let none_error = self
410 .get_diagnostic_item(sym::none_error)
411 .map(|def_id| tcx.type_of(def_id));
412 let should_convert_option_to_result =
413 Some(trait_ref.skip_binder().substs.type_at(1)) == none_error;
414 let should_convert_result_to_option =
415 Some(trait_ref.self_ty().skip_binder()) == none_error;
416 if should_convert_option_to_result {
417 err.span_suggestion_verbose(
419 "consider converting the `Option<T>` into a `Result<T, _>` \
420 using `Option::ok_or` or `Option::ok_or_else`",
421 ".ok_or_else(|| /* error value */)",
422 Applicability::HasPlaceholders,
424 } else if should_convert_result_to_option {
425 err.span_suggestion_verbose(
427 "consider converting the `Result<T, _>` into an `Option<T>` \
430 Applicability::MachineApplicable,
433 if let Some(ret_span) = self.return_type_span(&obligation) {
437 "expected `{}` because of this",
438 trait_ref.skip_binder().self_ty()
444 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
445 && predicate_is_const
447 err.note("`~const Drop` was renamed to `~const Destruct`");
448 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
451 let explanation = if let ObligationCauseCode::MainFunctionType =
452 obligation.cause.code()
454 "consider using `()`, or a `Result`".to_owned()
457 "{}the trait `{}` is not implemented for `{}`",
459 trait_predicate.print_modifiers_and_trait_path(),
460 trait_ref.skip_binder().self_ty(),
464 if self.suggest_add_reference_to_arg(
470 self.note_obligation_cause(&mut err, &obligation);
474 if let Some(ref s) = label {
475 // If it has a custom `#[rustc_on_unimplemented]`
476 // error message, let's display it as the label!
477 err.span_label(span, s.as_str());
478 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
479 // When the self type is a type param We don't need to "the trait
480 // `std::marker::Sized` is not implemented for `T`" as we will point
481 // at the type param with a label to suggest constraining it.
482 err.help(&explanation);
485 err.span_label(span, explanation);
488 if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
489 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
490 self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_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(
669 obligation.cause.body_id,
671 } else if !suggested {
672 // Can't show anything else useful, try to find similar impls.
673 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
674 if !self.report_similar_impl_candidates(
677 obligation.cause.body_id,
680 // This is *almost* equivalent to
681 // `obligation.cause.code().peel_derives()`, but it gives us the
682 // trait predicate for that corresponding root obligation. This
683 // lets us get a derived obligation from a type parameter, like
684 // when calling `string.strip_suffix(p)` where `p` is *not* an
685 // implementer of `Pattern<'_>`.
686 let mut code = obligation.cause.code();
687 let mut trait_pred = trait_predicate;
688 let mut peeled = false;
689 while let Some((parent_code, parent_trait_pred)) = code.parent() {
691 if let Some(parent_trait_pred) = parent_trait_pred {
692 trait_pred = parent_trait_pred;
696 let def_id = trait_pred.def_id();
697 // Mention *all* the `impl`s for the *top most* obligation, the
698 // user might have meant to use one of them, if any found. We skip
699 // auto-traits or fundamental traits that might not be exactly what
700 // the user might expect to be presented with. Instead this is
701 // useful for less general traits.
703 && !self.tcx.trait_is_auto(def_id)
704 && !self.tcx.lang_items().items().contains(&Some(def_id))
706 let trait_ref = trait_pred.to_poly_trait_ref();
707 let impl_candidates =
708 self.find_similar_impl_candidates(trait_ref);
709 self.report_similar_impl_candidates(
712 obligation.cause.body_id,
719 // Changing mutability doesn't make a difference to whether we have
720 // an `Unsize` impl (Fixes ICE in #71036)
722 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
725 // If this error is due to `!: Trait` not implemented but `(): Trait` is
726 // implemented, and fallback has occurred, then it could be due to a
727 // variable that used to fallback to `()` now falling back to `!`. Issue a
728 // note informing about the change in behaviour.
729 if trait_predicate.skip_binder().self_ty().is_never()
730 && fallback_has_occurred
732 let predicate = trait_predicate.map_bound(|mut trait_pred| {
733 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
735 &trait_pred.trait_ref.substs[1..],
739 let unit_obligation = obligation.with(predicate.to_predicate(tcx));
740 if self.predicate_may_hold(&unit_obligation) {
742 "this error might have been caused by changes to \
743 Rust's type-inference algorithm (see issue #48950 \
744 <https://github.com/rust-lang/rust/issues/48950> \
745 for more information)",
747 err.help("did you intend to use the type `()` here instead?");
751 // Return early if the trait is Debug or Display and the invocation
752 // originates within a standard library macro, because the output
753 // is otherwise overwhelming and unhelpful (see #85844 for an
757 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
758 Some(macro_def_id) => {
759 let crate_name = tcx.crate_name(macro_def_id.krate);
760 crate_name == sym::std || crate_name == sym::core
767 self.tcx.get_diagnostic_name(trait_ref.def_id()),
768 Some(sym::Debug | sym::Display)
778 ty::PredicateKind::Subtype(predicate) => {
779 // Errors for Subtype predicates show up as
780 // `FulfillmentErrorCode::CodeSubtypeError`,
781 // not selection error.
782 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
785 ty::PredicateKind::Coerce(predicate) => {
786 // Errors for Coerce predicates show up as
787 // `FulfillmentErrorCode::CodeSubtypeError`,
788 // not selection error.
789 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
792 ty::PredicateKind::RegionOutlives(predicate) => {
793 let predicate = bound_predicate.rebind(predicate);
794 let predicate = self.resolve_vars_if_possible(predicate);
796 .region_outlives_predicate(&obligation.cause, predicate)
803 "the requirement `{}` is not satisfied (`{}`)",
809 ty::PredicateKind::Projection(..) | ty::PredicateKind::TypeOutlives(..) => {
810 let predicate = self.resolve_vars_if_possible(obligation.predicate);
815 "the requirement `{}` is not satisfied",
820 ty::PredicateKind::ObjectSafe(trait_def_id) => {
821 let violations = self.tcx.object_safety_violations(trait_def_id);
822 report_object_safety_error(self.tcx, span, trait_def_id, violations)
825 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
826 let found_kind = self.closure_kind(closure_substs).unwrap();
827 let closure_span = self.tcx.def_span(closure_def_id);
828 let mut err = struct_span_err!(
832 "expected a closure that implements the `{}` trait, \
833 but this closure only implements `{}`",
840 format!("this closure implements `{}`, not `{}`", found_kind, kind),
843 obligation.cause.span,
844 format!("the requirement to implement `{}` derives from here", kind),
847 // Additional context information explaining why the closure only implements
848 // a particular trait.
849 if let Some(typeck_results) = self.in_progress_typeck_results {
853 .local_def_id_to_hir_id(closure_def_id.expect_local());
854 let typeck_results = typeck_results.borrow();
855 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
856 (ty::ClosureKind::FnOnce, Some((span, place))) => {
860 "closure is `FnOnce` because it moves the \
861 variable `{}` out of its environment",
862 ty::place_to_string_for_capture(tcx, place)
866 (ty::ClosureKind::FnMut, Some((span, place))) => {
870 "closure is `FnMut` because it mutates the \
872 ty::place_to_string_for_capture(tcx, place)
884 ty::PredicateKind::WellFormed(ty) => {
885 if !self.tcx.sess.opts.unstable_opts.chalk {
886 // WF predicates cannot themselves make
887 // errors. They can only block due to
888 // ambiguity; otherwise, they always
889 // degenerate into other obligations
891 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
893 // FIXME: we'll need a better message which takes into account
894 // which bounds actually failed to hold.
895 self.tcx.sess.struct_span_err(
897 &format!("the type `{}` is not well-formed (chalk)", ty),
902 ty::PredicateKind::ConstEvaluatable(..) => {
903 // Errors for `ConstEvaluatable` predicates show up as
904 // `SelectionError::ConstEvalFailure`,
905 // not `Unimplemented`.
908 "const-evaluatable requirement gave wrong error: `{:?}`",
913 ty::PredicateKind::ConstEquate(..) => {
914 // Errors for `ConstEquate` predicates show up as
915 // `SelectionError::ConstEvalFailure`,
916 // not `Unimplemented`.
919 "const-equate requirement gave wrong error: `{:?}`",
924 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
926 "TypeWellFormedFromEnv predicate should only exist in the environment"
931 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
932 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
933 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
935 if expected_trait_ref.self_ty().references_error() {
939 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
943 let found_did = match *found_trait_ty.kind() {
947 | ty::Generator(did, ..) => Some(did),
948 ty::Adt(def, _) => Some(def.did()),
952 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
954 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
955 // We check closures twice, with obligations flowing in different directions,
956 // but we want to complain about them only once.
960 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
962 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
963 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
964 _ => vec![ArgKind::empty()],
967 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
968 let expected = match expected_ty.kind() {
969 ty::Tuple(ref tys) => {
970 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
972 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
975 if found.len() == expected.len() {
976 self.report_closure_arg_mismatch(
983 let (closure_span, found) = found_did
985 let node = self.tcx.hir().get_if_local(did)?;
986 let (found_span, found) = self.get_fn_like_arguments(node)?;
987 Some((Some(found_span), found))
989 .unwrap_or((found_span, found));
991 self.report_arg_count_mismatch(
996 found_trait_ty.is_closure(),
1001 TraitNotObjectSafe(did) => {
1002 let violations = self.tcx.object_safety_violations(did);
1003 report_object_safety_error(self.tcx, span, did, violations)
1006 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1008 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1011 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1012 if !self.tcx.features().generic_const_exprs {
1013 let mut err = self.tcx.sess.struct_span_err(
1015 "constant expression depends on a generic parameter",
1017 // FIXME(const_generics): we should suggest to the user how they can resolve this
1018 // issue. However, this is currently not actually possible
1019 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1021 // Note that with `feature(generic_const_exprs)` this case should not
1023 err.note("this may fail depending on what value the parameter takes");
1028 match obligation.predicate.kind().skip_binder() {
1029 ty::PredicateKind::ConstEvaluatable(uv) => {
1031 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1032 let const_span = self.tcx.def_span(uv.def.did);
1033 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1034 Ok(snippet) => err.help(&format!(
1035 "try adding a `where` bound using this expression: `where [(); {}]:`",
1038 _ => err.help("consider adding a `where` bound using this expression"),
1045 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1051 // Already reported in the query.
1052 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1053 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1054 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1057 // Already reported.
1058 Overflow(OverflowError::Error(_)) => {
1059 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1063 bug!("overflow should be handled before the `report_selection_error` path");
1065 SelectionError::ErrorReporting => {
1066 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1070 self.note_obligation_cause(&mut err, &obligation);
1071 self.point_at_returns_when_relevant(&mut err, &obligation);
1076 /// Given some node representing a fn-like thing in the HIR map,
1077 /// returns a span and `ArgKind` information that describes the
1078 /// arguments it expects. This can be supplied to
1079 /// `report_arg_count_mismatch`.
1080 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
1081 let sm = self.tcx.sess.source_map();
1082 let hir = self.tcx.hir();
1084 Node::Expr(&hir::Expr {
1085 kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }),
1093 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
1096 Some(ArgKind::Tuple(
1100 sm.span_to_snippet(pat.span)
1102 .map(|snippet| (snippet, "_".to_owned()))
1104 .collect::<Option<Vec<_>>>()?,
1107 let name = sm.span_to_snippet(arg.pat.span).ok()?;
1108 Some(ArgKind::Arg(name, "_".to_owned()))
1111 .collect::<Option<Vec<ArgKind>>>()?,
1113 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
1114 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
1115 | Node::TraitItem(&hir::TraitItem {
1116 kind: hir::TraitItemKind::Fn(ref sig, _), ..
1122 .map(|arg| match arg.kind {
1123 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
1125 vec![("_".to_owned(), "_".to_owned()); tys.len()],
1127 _ => ArgKind::empty(),
1129 .collect::<Vec<ArgKind>>(),
1131 Node::Ctor(ref variant_data) => {
1132 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
1133 (span, vec![ArgKind::empty(); variant_data.fields().len()])
1135 _ => panic!("non-FnLike node found: {:?}", node),
1139 /// Reports an error when the number of arguments needed by a
1140 /// trait match doesn't match the number that the expression
1142 fn report_arg_count_mismatch(
1145 found_span: Option<Span>,
1146 expected_args: Vec<ArgKind>,
1147 found_args: Vec<ArgKind>,
1149 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1150 let kind = if is_closure { "closure" } else { "function" };
1152 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
1153 let arg_length = arguments.len();
1154 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
1155 match (arg_length, arguments.get(0)) {
1156 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
1157 format!("a single {}-tuple as argument", fields.len())
1162 if distinct && arg_length > 1 { "distinct " } else { "" },
1163 pluralize!(arg_length)
1168 let expected_str = args_str(&expected_args, &found_args);
1169 let found_str = args_str(&found_args, &expected_args);
1171 let mut err = struct_span_err!(
1175 "{} is expected to take {}, but it takes {}",
1181 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
1183 if let Some(found_span) = found_span {
1184 err.span_label(found_span, format!("takes {}", found_str));
1187 // ^^^^^^^^-- def_span
1191 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
1195 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
1197 // Suggest to take and ignore the arguments with expected_args_length `_`s if
1198 // found arguments is empty (assume the user just wants to ignore args in this case).
1199 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
1200 if found_args.is_empty() && is_closure {
1201 let underscores = vec!["_"; expected_args.len()].join(", ");
1202 err.span_suggestion_verbose(
1205 "consider changing the closure to take and ignore the expected argument{}",
1206 pluralize!(expected_args.len())
1208 format!("|{}|", underscores),
1209 Applicability::MachineApplicable,
1213 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
1214 if fields.len() == expected_args.len() {
1217 .map(|(name, _)| name.to_owned())
1218 .collect::<Vec<String>>()
1220 err.span_suggestion_verbose(
1222 "change the closure to take multiple arguments instead of a single tuple",
1223 format!("|{}|", sugg),
1224 Applicability::MachineApplicable,
1228 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
1229 && fields.len() == found_args.len()
1236 .map(|arg| match arg {
1237 ArgKind::Arg(name, _) => name.to_owned(),
1238 _ => "_".to_owned(),
1240 .collect::<Vec<String>>()
1242 // add type annotations if available
1243 if found_args.iter().any(|arg| match arg {
1244 ArgKind::Arg(_, ty) => ty != "_",
1251 .map(|(_, ty)| ty.to_owned())
1252 .collect::<Vec<String>>()
1259 err.span_suggestion_verbose(
1261 "change the closure to accept a tuple instead of individual arguments",
1263 Applicability::MachineApplicable,
1271 fn type_implements_fn_trait(
1273 param_env: ty::ParamEnv<'tcx>,
1274 ty: ty::Binder<'tcx, Ty<'tcx>>,
1275 constness: ty::BoundConstness,
1276 polarity: ty::ImplPolarity,
1277 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
1278 self.commit_if_ok(|_| {
1279 for trait_def_id in [
1280 self.tcx.lang_items().fn_trait(),
1281 self.tcx.lang_items().fn_mut_trait(),
1282 self.tcx.lang_items().fn_once_trait(),
1284 let Some(trait_def_id) = trait_def_id else { continue };
1285 // Make a fresh inference variable so we can determine what the substitutions
1286 // of the trait are.
1287 let var = self.next_ty_var(TypeVariableOrigin {
1289 kind: TypeVariableOriginKind::MiscVariable,
1291 let substs = self.tcx.mk_substs_trait(ty.skip_binder(), &[var.into()]);
1292 let obligation = Obligation::new(
1293 ObligationCause::dummy(),
1295 ty.rebind(ty::TraitPredicate {
1296 trait_ref: ty::TraitRef::new(trait_def_id, substs),
1300 .to_predicate(self.tcx),
1302 let mut fulfill_cx = FulfillmentContext::new_in_snapshot();
1303 fulfill_cx.register_predicate_obligation(self, obligation);
1304 if fulfill_cx.select_all_or_error(self).is_empty() {
1306 ty::ClosureKind::from_def_id(self.tcx, trait_def_id)
1307 .expect("expected to map DefId to ClosureKind"),
1308 ty.rebind(self.resolve_vars_if_possible(var)),
1318 trait InferCtxtPrivExt<'hir, 'tcx> {
1319 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1320 // `error` occurring implies that `cond` occurs.
1321 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1323 fn report_fulfillment_error(
1325 error: &FulfillmentError<'tcx>,
1326 body_id: Option<hir::BodyId>,
1327 fallback_has_occurred: bool,
1330 fn report_projection_error(
1332 obligation: &PredicateObligation<'tcx>,
1333 error: &MismatchedProjectionTypes<'tcx>,
1340 ignoring_lifetimes: bool,
1341 ) -> Option<CandidateSimilarity>;
1343 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1345 fn find_similar_impl_candidates(
1347 trait_ref: ty::PolyTraitRef<'tcx>,
1348 ) -> Vec<ImplCandidate<'tcx>>;
1350 fn report_similar_impl_candidates(
1352 impl_candidates: Vec<ImplCandidate<'tcx>>,
1353 trait_ref: ty::PolyTraitRef<'tcx>,
1354 body_id: hir::HirId,
1355 err: &mut Diagnostic,
1358 /// Gets the parent trait chain start
1359 fn get_parent_trait_ref(
1361 code: &ObligationCauseCode<'tcx>,
1362 ) -> Option<(String, Option<Span>)>;
1364 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1365 /// with the same path as `trait_ref`, a help message about
1366 /// a probable version mismatch is added to `err`
1367 fn note_version_mismatch(
1369 err: &mut Diagnostic,
1370 trait_ref: &ty::PolyTraitRef<'tcx>,
1373 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1376 /// For this to work, `new_self_ty` must have no escaping bound variables.
1377 fn mk_trait_obligation_with_new_self_ty(
1379 param_env: ty::ParamEnv<'tcx>,
1380 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1381 ) -> PredicateObligation<'tcx>;
1383 fn maybe_report_ambiguity(
1385 obligation: &PredicateObligation<'tcx>,
1386 body_id: Option<hir::BodyId>,
1389 fn predicate_can_apply(
1391 param_env: ty::ParamEnv<'tcx>,
1392 pred: ty::PolyTraitRef<'tcx>,
1395 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1397 fn suggest_unsized_bound_if_applicable(
1399 err: &mut Diagnostic,
1400 obligation: &PredicateObligation<'tcx>,
1403 fn annotate_source_of_ambiguity(
1405 err: &mut Diagnostic,
1407 predicate: ty::Predicate<'tcx>,
1410 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'hir>);
1412 fn maybe_indirection_for_unsized(
1414 err: &mut Diagnostic,
1415 item: &'hir Item<'hir>,
1416 param: &'hir GenericParam<'hir>,
1419 fn is_recursive_obligation(
1421 obligated_types: &mut Vec<Ty<'tcx>>,
1422 cause_code: &ObligationCauseCode<'tcx>,
1426 impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
1427 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1428 // `error` occurring implies that `cond` occurs.
1429 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1434 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1435 let bound_error = error.kind();
1436 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1437 (ty::PredicateKind::Trait(..), ty::PredicateKind::Trait(error)) => {
1438 (cond, bound_error.rebind(error))
1441 // FIXME: make this work in other cases too.
1446 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1447 let bound_predicate = obligation.predicate.kind();
1448 if let ty::PredicateKind::Trait(implication) = bound_predicate.skip_binder() {
1449 let error = error.to_poly_trait_ref();
1450 let implication = bound_predicate.rebind(implication.trait_ref);
1451 // FIXME: I'm just not taking associated types at all here.
1452 // Eventually I'll need to implement param-env-aware
1453 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1454 let param_env = ty::ParamEnv::empty();
1455 if self.can_sub(param_env, error, implication).is_ok() {
1456 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1465 #[instrument(skip(self), level = "debug")]
1466 fn report_fulfillment_error(
1468 error: &FulfillmentError<'tcx>,
1469 body_id: Option<hir::BodyId>,
1470 fallback_has_occurred: bool,
1473 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1474 self.report_selection_error(
1475 error.obligation.clone(),
1476 &error.root_obligation,
1478 fallback_has_occurred,
1481 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1482 self.report_projection_error(&error.obligation, e);
1484 FulfillmentErrorCode::CodeAmbiguity => {
1485 self.maybe_report_ambiguity(&error.obligation, body_id);
1487 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1488 self.report_mismatched_types(
1489 &error.obligation.cause,
1490 expected_found.expected,
1491 expected_found.found,
1496 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1497 self.report_mismatched_consts(
1498 &error.obligation.cause,
1499 expected_found.expected,
1500 expected_found.found,
1508 #[instrument(level = "debug", skip_all)]
1509 fn report_projection_error(
1511 obligation: &PredicateObligation<'tcx>,
1512 error: &MismatchedProjectionTypes<'tcx>,
1514 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1516 if predicate.references_error() {
1522 let mut err = &error.err;
1523 let mut values = None;
1525 // try to find the mismatched types to report the error with.
1527 // this can fail if the problem was higher-ranked, in which
1528 // cause I have no idea for a good error message.
1529 let bound_predicate = predicate.kind();
1530 if let ty::PredicateKind::Projection(data) = bound_predicate.skip_binder() {
1531 let mut selcx = SelectionContext::new(self);
1532 let data = self.replace_bound_vars_with_fresh_vars(
1533 obligation.cause.span,
1534 infer::LateBoundRegionConversionTime::HigherRankedType,
1535 bound_predicate.rebind(data),
1537 let mut obligations = vec![];
1538 let normalized_ty = super::normalize_projection_type(
1540 obligation.param_env,
1542 obligation.cause.clone(),
1547 debug!(?obligation.cause, ?obligation.param_env);
1549 debug!(?normalized_ty, data.ty = ?data.term);
1551 let is_normalized_ty_expected = !matches!(
1552 obligation.cause.code().peel_derives(),
1553 ObligationCauseCode::ItemObligation(_)
1554 | ObligationCauseCode::BindingObligation(_, _)
1555 | ObligationCauseCode::ObjectCastObligation(..)
1556 | ObligationCauseCode::OpaqueType
1558 if let Err(error) = self.at(&obligation.cause, obligation.param_env).eq_exp(
1559 is_normalized_ty_expected,
1563 values = Some(infer::ValuePairs::Terms(ExpectedFound::new(
1564 is_normalized_ty_expected,
1573 let mut diag = struct_span_err!(
1575 obligation.cause.span,
1577 "type mismatch resolving `{}`",
1580 let secondary_span = match predicate.kind().skip_binder() {
1581 ty::PredicateKind::Projection(proj) => self
1583 .opt_associated_item(proj.projection_ty.item_def_id)
1584 .and_then(|trait_assoc_item| {
1586 .trait_of_item(proj.projection_ty.item_def_id)
1587 .map(|id| (trait_assoc_item, id))
1589 .and_then(|(trait_assoc_item, id)| {
1590 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1591 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1593 .associated_items(did)
1594 .in_definition_order()
1595 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1598 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1600 hir::Node::TraitItem(hir::TraitItem {
1601 kind: hir::TraitItemKind::Type(_, Some(ty)),
1604 | hir::Node::ImplItem(hir::ImplItem {
1605 kind: hir::ImplItemKind::TyAlias(ty),
1608 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1622 self.note_obligation_cause(&mut diag, obligation);
1631 ignoring_lifetimes: bool,
1632 ) -> Option<CandidateSimilarity> {
1633 /// returns the fuzzy category of a given type, or None
1634 /// if the type can be equated to any type.
1635 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1637 ty::Bool => Some(0),
1638 ty::Char => Some(1),
1640 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::String, def.did()) => Some(2),
1644 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1645 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1646 ty::Array(..) | ty::Slice(..) => Some(6),
1647 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1648 ty::Dynamic(..) => Some(8),
1649 ty::Closure(..) => Some(9),
1650 ty::Tuple(..) => Some(10),
1651 ty::Param(..) => Some(11),
1652 ty::Projection(..) => Some(12),
1653 ty::Opaque(..) => Some(13),
1654 ty::Never => Some(14),
1655 ty::Adt(..) => Some(15),
1656 ty::Generator(..) => Some(16),
1657 ty::Foreign(..) => Some(17),
1658 ty::GeneratorWitness(..) => Some(18),
1659 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1663 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1666 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1674 if !ignoring_lifetimes {
1675 a = strip_references(a);
1676 b = strip_references(b);
1679 let cat_a = type_category(self.tcx, a)?;
1680 let cat_b = type_category(self.tcx, b)?;
1682 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1683 } else if cat_a == cat_b {
1684 match (a.kind(), b.kind()) {
1685 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1686 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1687 // Matching on references results in a lot of unhelpful
1688 // suggestions, so let's just not do that for now.
1690 // We still upgrade successful matches to `ignoring_lifetimes: true`
1691 // to prioritize that impl.
1692 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1693 self.fuzzy_match_tys(a, b, true).is_some()
1697 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1698 } else if ignoring_lifetimes {
1701 self.fuzzy_match_tys(a, b, true)
1705 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1706 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1707 hir::GeneratorKind::Gen => "a generator",
1708 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1709 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1710 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1714 fn find_similar_impl_candidates(
1716 trait_ref: ty::PolyTraitRef<'tcx>,
1717 ) -> Vec<ImplCandidate<'tcx>> {
1719 .all_impls(trait_ref.def_id())
1720 .filter_map(|def_id| {
1721 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative {
1725 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1727 self.fuzzy_match_tys(trait_ref.skip_binder().self_ty(), imp.self_ty(), false)
1728 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1733 fn report_similar_impl_candidates(
1735 impl_candidates: Vec<ImplCandidate<'tcx>>,
1736 trait_ref: ty::PolyTraitRef<'tcx>,
1737 body_id: hir::HirId,
1738 err: &mut Diagnostic,
1740 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1743 let len = candidates.len();
1744 if candidates.len() == 0 {
1747 if candidates.len() == 1 {
1748 err.highlighted_help(vec![
1750 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1753 ("is".to_string(), Style::Highlight),
1754 (" implemented for `".to_string(), Style::NoStyle),
1755 (candidates[0].self_ty().to_string(), Style::Highlight),
1756 ("`".to_string(), Style::NoStyle),
1760 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1761 // Check if the trait is the same in all cases. If so, we'll only show the type.
1762 let mut traits: Vec<_> =
1763 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1767 let mut candidates: Vec<String> = candidates
1770 if traits.len() == 1 {
1771 format!("\n {}", c.self_ty())
1780 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1782 "the following other types implement trait `{}`:{}{}",
1783 trait_ref.print_only_trait_path(),
1784 candidates[..end].join(""),
1785 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1790 let def_id = trait_ref.def_id();
1791 if impl_candidates.is_empty() {
1792 if self.tcx.trait_is_auto(def_id)
1793 || self.tcx.lang_items().items().contains(&Some(def_id))
1794 || self.tcx.get_diagnostic_name(def_id).is_some()
1796 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1799 let normalized_impl_candidates: Vec<_> = self
1802 // Ignore automatically derived impls and `!Trait` impls.
1804 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1805 || self.tcx.is_builtin_derive(def_id)
1807 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1808 .filter(|trait_ref| {
1809 let self_ty = trait_ref.self_ty();
1810 // Avoid mentioning type parameters.
1811 if let ty::Param(_) = self_ty.kind() {
1814 // Avoid mentioning types that are private to another crate
1815 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
1816 // FIXME(compiler-errors): This could be generalized, both to
1817 // be more granular, and probably look past other `#[fundamental]`
1820 .visibility(def.did())
1821 .is_accessible_from(body_id.owner.to_def_id(), self.tcx)
1827 return report(normalized_impl_candidates, err);
1830 let normalize = |candidate| {
1831 self.tcx.infer_ctxt().enter(|ref infcx| {
1832 let normalized = infcx
1833 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1834 .normalize(candidate)
1837 Some(normalized) => normalized.value,
1843 // Sort impl candidates so that ordering is consistent for UI tests.
1844 // because the ordering of `impl_candidates` may not be deterministic:
1845 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1847 // Prefer more similar candidates first, then sort lexicographically
1848 // by their normalized string representation.
1849 let mut normalized_impl_candidates_and_similarities = impl_candidates
1851 .map(|ImplCandidate { trait_ref, similarity }| {
1852 let normalized = normalize(trait_ref);
1853 (similarity, normalized)
1855 .collect::<Vec<_>>();
1856 normalized_impl_candidates_and_similarities.sort();
1857 normalized_impl_candidates_and_similarities.dedup();
1859 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
1861 .map(|(_, normalized)| normalized)
1862 .collect::<Vec<_>>();
1864 report(normalized_impl_candidates, err)
1867 /// Gets the parent trait chain start
1868 fn get_parent_trait_ref(
1870 code: &ObligationCauseCode<'tcx>,
1871 ) -> Option<(String, Option<Span>)> {
1873 ObligationCauseCode::BuiltinDerivedObligation(data) => {
1874 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
1875 match self.get_parent_trait_ref(&data.parent_code) {
1878 let ty = parent_trait_ref.skip_binder().self_ty();
1879 let span = TyCategory::from_ty(self.tcx, ty)
1880 .map(|(_, def_id)| self.tcx.def_span(def_id));
1881 Some((ty.to_string(), span))
1885 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
1886 self.get_parent_trait_ref(&parent_code)
1892 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1893 /// with the same path as `trait_ref`, a help message about
1894 /// a probable version mismatch is added to `err`
1895 fn note_version_mismatch(
1897 err: &mut Diagnostic,
1898 trait_ref: &ty::PolyTraitRef<'tcx>,
1900 let get_trait_impl = |trait_def_id| {
1901 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
1903 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
1904 let traits_with_same_path: std::collections::BTreeSet<_> = self
1907 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
1908 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
1910 let mut suggested = false;
1911 for trait_with_same_path in traits_with_same_path {
1912 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
1913 let impl_span = self.tcx.def_span(impl_def_id);
1914 err.span_help(impl_span, "trait impl with same name found");
1915 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
1916 let crate_msg = format!(
1917 "perhaps two different versions of crate `{}` are being used?",
1920 err.note(&crate_msg);
1927 fn mk_trait_obligation_with_new_self_ty(
1929 param_env: ty::ParamEnv<'tcx>,
1930 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1931 ) -> PredicateObligation<'tcx> {
1932 let trait_pred = trait_ref_and_ty.map_bound_ref(|(tr, new_self_ty)| ty::TraitPredicate {
1933 trait_ref: ty::TraitRef {
1934 substs: self.tcx.mk_substs_trait(*new_self_ty, &tr.trait_ref.substs[1..]),
1940 Obligation::new(ObligationCause::dummy(), param_env, trait_pred.to_predicate(self.tcx))
1943 #[instrument(skip(self), level = "debug")]
1944 fn maybe_report_ambiguity(
1946 obligation: &PredicateObligation<'tcx>,
1947 body_id: Option<hir::BodyId>,
1949 // Unable to successfully determine, probably means
1950 // insufficient type information, but could mean
1951 // ambiguous impls. The latter *ought* to be a
1952 // coherence violation, so we don't report it here.
1954 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1955 let span = obligation.cause.span;
1957 debug!(?predicate, obligation.cause.code = tracing::field::debug(&obligation.cause.code()));
1959 // Ambiguity errors are often caused as fallout from earlier errors.
1960 // We ignore them if this `infcx` is tainted in some cases below.
1962 let bound_predicate = predicate.kind();
1963 let mut err = match bound_predicate.skip_binder() {
1964 ty::PredicateKind::Trait(data) => {
1965 let trait_ref = bound_predicate.rebind(data.trait_ref);
1968 if predicate.references_error() {
1972 // This is kind of a hack: it frequently happens that some earlier
1973 // error prevents types from being fully inferred, and then we get
1974 // a bunch of uninteresting errors saying something like "<generic
1975 // #0> doesn't implement Sized". It may even be true that we
1976 // could just skip over all checks where the self-ty is an
1977 // inference variable, but I was afraid that there might be an
1978 // inference variable created, registered as an obligation, and
1979 // then never forced by writeback, and hence by skipping here we'd
1980 // be ignoring the fact that we don't KNOW the type works
1981 // out. Though even that would probably be harmless, given that
1982 // we're only talking about builtin traits, which are known to be
1983 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
1984 // avoid inundating the user with unnecessary errors, but we now
1985 // check upstream for type errors and don't add the obligations to
1986 // begin with in those cases.
1987 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
1988 if !self.is_tainted_by_errors() {
1989 self.emit_inference_failure_err(
1992 trait_ref.self_ty().skip_binder().into(),
2001 // Typically, this ambiguity should only happen if
2002 // there are unresolved type inference variables
2003 // (otherwise it would suggest a coherence
2004 // failure). But given #21974 that is not necessarily
2005 // the case -- we can have multiple where clauses that
2006 // are only distinguished by a region, which results
2007 // in an ambiguity even when all types are fully
2008 // known, since we don't dispatch based on region
2011 // Pick the first substitution that still contains inference variables as the one
2012 // we're going to emit an error for. If there are none (see above), fall back to
2013 // a more general error.
2014 let subst = data.trait_ref.substs.iter().find(|s| s.has_infer_types_or_consts());
2016 let mut err = if let Some(subst) = subst {
2017 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2023 "type annotations needed: cannot satisfy `{}`",
2028 let obligation = Obligation::new(
2029 obligation.cause.clone(),
2030 obligation.param_env,
2031 trait_ref.to_poly_trait_predicate(),
2033 let mut selcx = SelectionContext::with_query_mode(
2035 crate::traits::TraitQueryMode::Standard,
2037 match selcx.select_from_obligation(&obligation) {
2038 Err(SelectionError::Ambiguous(impls)) if impls.len() > 1 => {
2039 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2042 if self.is_tainted_by_errors() {
2046 err.note(&format!("cannot satisfy `{}`", predicate));
2050 if let ObligationCauseCode::ItemObligation(def_id) = *obligation.cause.code() {
2051 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2054 &ObligationCauseCode::BindingObligation(def_id, _),
2056 (self.tcx.sess.source_map().span_to_snippet(span), obligation.cause.code())
2058 let generics = self.tcx.generics_of(def_id);
2059 if generics.params.iter().any(|p| p.name != kw::SelfUpper)
2060 && !snippet.ends_with('>')
2061 && !generics.has_impl_trait()
2062 && !self.tcx.fn_trait_kind_from_lang_item(def_id).is_some()
2064 // FIXME: To avoid spurious suggestions in functions where type arguments
2065 // where already supplied, we check the snippet to make sure it doesn't
2066 // end with a turbofish. Ideally we would have access to a `PathSegment`
2067 // instead. Otherwise we would produce the following output:
2069 // error[E0283]: type annotations needed
2070 // --> $DIR/issue-54954.rs:3:24
2072 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2073 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2075 // | cannot infer type
2076 // | help: consider specifying the type argument
2077 // | in the function call:
2078 // | `Tt::const_val::<[i8; 123]>::<T>`
2080 // LL | const fn const_val<T: Sized>() -> usize {
2081 // | - required by this bound in `Tt::const_val`
2083 // = note: cannot satisfy `_: Tt`
2085 // Clear any more general suggestions in favor of our specific one
2086 err.clear_suggestions();
2088 err.span_suggestion_verbose(
2089 span.shrink_to_hi(),
2091 "consider specifying the type argument{} in the function call",
2092 pluralize!(generics.params.len()),
2099 .map(|p| p.name.to_string())
2100 .collect::<Vec<String>>()
2103 Applicability::HasPlaceholders,
2110 ty::PredicateKind::WellFormed(arg) => {
2111 // Same hacky approach as above to avoid deluging user
2112 // with error messages.
2113 if arg.references_error()
2114 || self.tcx.sess.has_errors().is_some()
2115 || self.is_tainted_by_errors()
2120 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2123 ty::PredicateKind::Subtype(data) => {
2124 if data.references_error()
2125 || self.tcx.sess.has_errors().is_some()
2126 || self.is_tainted_by_errors()
2128 // no need to overload user in such cases
2131 let SubtypePredicate { a_is_expected: _, a, b } = data;
2132 // both must be type variables, or the other would've been instantiated
2133 assert!(a.is_ty_var() && b.is_ty_var());
2134 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2136 ty::PredicateKind::Projection(data) => {
2137 if predicate.references_error() || self.is_tainted_by_errors() {
2144 .chain(Some(data.term.into_arg()))
2145 .find(|g| g.has_infer_types_or_consts());
2146 if let Some(subst) = subst {
2147 let mut err = self.emit_inference_failure_err(
2154 err.note(&format!("cannot satisfy `{}`", predicate));
2157 // If we can't find a substitution, just print a generic error
2158 let mut err = struct_span_err!(
2162 "type annotations needed: cannot satisfy `{}`",
2165 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2170 ty::PredicateKind::ConstEvaluatable(data) => {
2171 if predicate.references_error() || self.is_tainted_by_errors() {
2174 let subst = data.substs.iter().find(|g| g.has_infer_types_or_consts());
2175 if let Some(subst) = subst {
2176 let err = self.emit_inference_failure_err(
2185 // If we can't find a substitution, just print a generic error
2186 let mut err = struct_span_err!(
2190 "type annotations needed: cannot satisfy `{}`",
2193 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2198 if self.tcx.sess.has_errors().is_some() || self.is_tainted_by_errors() {
2201 let mut err = struct_span_err!(
2205 "type annotations needed: cannot satisfy `{}`",
2208 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2212 self.note_obligation_cause(&mut err, obligation);
2216 fn annotate_source_of_ambiguity(
2218 err: &mut Diagnostic,
2220 predicate: ty::Predicate<'tcx>,
2222 let mut spans = vec![];
2223 let mut crates = vec![];
2224 let mut post = vec![];
2225 for def_id in impls {
2226 match self.tcx.span_of_impl(*def_id) {
2227 Ok(span) => spans.push(span),
2230 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2236 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2237 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2239 crate_names.dedup();
2243 if self.is_tainted_by_errors()
2244 && (crate_names.len() == 1
2246 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2247 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2249 // Avoid complaining about other inference issues for expressions like
2250 // `42 >> 1`, where the types are still `{integer}`, but we want to
2251 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2252 // NOTE(eddyb) this was `.cancel()`, but `err`
2253 // is borrowed, so we can't fully defuse it.
2254 err.downgrade_to_delayed_bug();
2257 let post = if post.len() > 4 {
2259 ":\n{}\nand {} more",
2260 post.iter().map(|p| format!("- {}", p)).take(4).collect::<Vec<_>>().join("\n"),
2263 } else if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2264 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2265 } else if post.len() == 1 {
2266 format!(": `{}`", post[0])
2271 match (spans.len(), crates.len(), crate_names.len()) {
2273 err.note(&format!("cannot satisfy `{}`", predicate));
2276 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2280 "{} in the following crates: {}{}",
2282 crate_names.join(", "),
2287 let span: MultiSpan = spans.into();
2288 err.span_note(span, &msg);
2291 let span: MultiSpan = spans.into();
2292 err.span_note(span, &msg);
2294 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2298 let span: MultiSpan = spans.into();
2299 err.span_note(span, &msg);
2301 "and more `impl`s found in the following crates: {}{}",
2302 crate_names.join(", "),
2309 /// Returns `true` if the trait predicate may apply for *some* assignment
2310 /// to the type parameters.
2311 fn predicate_can_apply(
2313 param_env: ty::ParamEnv<'tcx>,
2314 pred: ty::PolyTraitRef<'tcx>,
2316 struct ParamToVarFolder<'a, 'tcx> {
2317 infcx: &'a InferCtxt<'a, 'tcx>,
2318 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2321 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2322 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2326 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2327 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2328 let infcx = self.infcx;
2329 *self.var_map.entry(ty).or_insert_with(|| {
2330 infcx.next_ty_var(TypeVariableOrigin {
2331 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2336 ty.super_fold_with(self)
2342 let mut selcx = SelectionContext::new(self);
2345 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2347 let cleaned_pred = super::project::normalize(
2350 ObligationCause::dummy(),
2355 let obligation = Obligation::new(
2356 ObligationCause::dummy(),
2358 cleaned_pred.without_const().to_predicate(selcx.tcx()),
2361 self.predicate_may_hold(&obligation)
2365 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2366 // First, attempt to add note to this error with an async-await-specific
2367 // message, and fall back to regular note otherwise.
2368 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2369 self.note_obligation_cause_code(
2371 &obligation.predicate,
2372 obligation.param_env,
2373 obligation.cause.code(),
2375 &mut Default::default(),
2377 self.suggest_unsized_bound_if_applicable(err, obligation);
2381 #[instrument(level = "debug", skip_all)]
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(),
2396 debug!(?pred, ?item_def_id, ?span);
2398 let (Some(node), true) = (
2399 self.tcx.hir().get_if_local(item_def_id),
2400 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2404 self.maybe_suggest_unsized_generics(err, span, node);
2407 #[instrument(level = "debug", skip_all)]
2408 fn maybe_suggest_unsized_generics<'hir>(
2410 err: &mut Diagnostic,
2414 let Some(generics) = node.generics() else {
2417 let sized_trait = self.tcx.lang_items().sized_trait();
2418 debug!(?generics.params);
2419 debug!(?generics.predicates);
2420 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2423 let param_def_id = self.tcx.hir().local_def_id(param.hir_id);
2424 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2425 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2426 let explicitly_sized = generics
2427 .bounds_for_param(param_def_id)
2428 .flat_map(|bp| bp.bounds)
2429 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2430 if explicitly_sized {
2437 // Only suggest indirection for uses of type parameters in ADTs.
2439 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2443 if self.maybe_indirection_for_unsized(err, item, param) {
2449 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2450 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param_def_id)
2454 (span.shrink_to_hi(), ":")
2456 err.span_suggestion_verbose(
2458 "consider relaxing the implicit `Sized` restriction",
2459 format!("{} ?Sized", separator),
2460 Applicability::MachineApplicable,
2464 fn maybe_indirection_for_unsized<'hir>(
2466 err: &mut Diagnostic,
2467 item: &'hir Item<'hir>,
2468 param: &'hir GenericParam<'hir>,
2470 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2471 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2472 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2474 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2475 visitor.visit_item(item);
2476 if visitor.invalid_spans.is_empty() {
2479 let mut multispan: MultiSpan = param.span.into();
2480 multispan.push_span_label(
2482 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2484 for sp in visitor.invalid_spans {
2485 multispan.push_span_label(
2487 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2493 "you could relax the implicit `Sized` bound on `{T}` if it were \
2494 used through indirection like `&{T}` or `Box<{T}>`",
2495 T = param.name.ident(),
2501 fn is_recursive_obligation(
2503 obligated_types: &mut Vec<Ty<'tcx>>,
2504 cause_code: &ObligationCauseCode<'tcx>,
2506 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2507 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2508 let self_ty = parent_trait_ref.skip_binder().self_ty();
2509 if obligated_types.iter().any(|ot| ot == &self_ty) {
2512 if let ty::Adt(def, substs) = self_ty.kind()
2513 && let [arg] = &substs[..]
2514 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2515 && let ty::Adt(inner_def, _) = ty.kind()
2525 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2526 /// `param: ?Sized` would be a valid constraint.
2527 struct FindTypeParam {
2528 param: rustc_span::Symbol,
2529 invalid_spans: Vec<Span>,
2533 impl<'v> Visitor<'v> for FindTypeParam {
2534 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2535 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2538 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2539 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2540 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2541 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2542 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2543 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2544 // in that case should make what happened clear enough.
2546 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2547 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2548 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2551 debug!(?ty, "FindTypeParam::visit_ty");
2552 self.invalid_spans.push(ty.span);
2555 hir::TyKind::Path(_) => {
2556 let prev = self.nested;
2558 hir::intravisit::walk_ty(self, ty);
2562 hir::intravisit::walk_ty(self, ty);
2568 pub fn recursive_type_with_infinite_size_error<'tcx>(
2571 spans: Vec<(Span, Option<hir::HirId>)>,
2573 assert!(type_def_id.is_local());
2574 let span = tcx.def_span(type_def_id);
2575 let path = tcx.def_path_str(type_def_id);
2577 struct_span_err!(tcx.sess, span, E0072, "recursive type `{}` has infinite size", path);
2578 err.span_label(span, "recursive type has infinite size");
2579 for &(span, _) in &spans {
2580 err.span_label(span, "recursive without indirection");
2583 "insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `{}` representable",
2586 if spans.len() <= 4 {
2587 // FIXME(compiler-errors): This suggestion might be erroneous if Box is shadowed
2588 err.multipart_suggestion(
2592 .flat_map(|(span, field_id)| {
2593 if let Some(generic_span) = get_option_generic_from_field_id(tcx, field_id) {
2594 // If we match an `Option` and can grab the span of the Option's generic, then
2595 // suggest boxing the generic arg for a non-null niche optimization.
2597 (generic_span.shrink_to_lo(), "Box<".to_string()),
2598 (generic_span.shrink_to_hi(), ">".to_string()),
2602 (span.shrink_to_lo(), "Box<".to_string()),
2603 (span.shrink_to_hi(), ">".to_string()),
2608 Applicability::HasPlaceholders,
2616 /// Extract the span for the generic type `T` of `Option<T>` in a field definition
2617 fn get_option_generic_from_field_id(tcx: TyCtxt<'_>, field_id: Option<hir::HirId>) -> Option<Span> {
2618 let node = tcx.hir().find(field_id?);
2620 // Expect a field from our field_id
2621 let Some(hir::Node::Field(field_def)) = node
2622 else { bug!("Expected HirId corresponding to FieldDef, found: {:?}", node) };
2624 // Match a type that is a simple QPath with no Self
2625 let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = &field_def.ty.kind
2626 else { return None };
2628 // Check if the path we're checking resolves to Option
2629 let hir::def::Res::Def(_, did) = path.res
2630 else { return None };
2632 // Bail if this path doesn't describe `::core::option::Option`
2633 if !tcx.is_diagnostic_item(sym::Option, did) {
2637 // Match a single generic arg in the 0th path segment
2638 let generic_arg = path.segments.last()?.args?.args.get(0)?;
2640 // Take the span out of the type, if it's a type
2641 if let hir::GenericArg::Type(generic_ty) = generic_arg { Some(generic_ty.span) } else { None }
2644 /// Summarizes information
2647 /// An argument of non-tuple type. Parameters are (name, ty)
2648 Arg(String, String),
2650 /// An argument of tuple type. For a "found" argument, the span is
2651 /// the location in the source of the pattern. For an "expected"
2652 /// argument, it will be None. The vector is a list of (name, ty)
2653 /// strings for the components of the tuple.
2654 Tuple(Option<Span>, Vec<(String, String)>),
2658 fn empty() -> ArgKind {
2659 ArgKind::Arg("_".to_owned(), "_".to_owned())
2662 /// Creates an `ArgKind` from the expected type of an
2663 /// argument. It has no name (`_`) and an optional source span.
2664 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2666 ty::Tuple(tys) => ArgKind::Tuple(
2668 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2670 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2675 struct HasNumericInferVisitor;
2677 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2680 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2681 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2682 ControlFlow::Break(())
2684 ControlFlow::CONTINUE