2 pub mod on_unimplemented;
6 FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes, Obligation, ObligationCause,
7 ObligationCauseCode, OutputTypeParameterMismatch, Overflow, PredicateObligation,
8 SelectionContext, SelectionError, TraitNotObjectSafe,
10 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
11 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
12 use crate::infer::{self, InferCtxt, TyCtxtInferExt};
13 use crate::traits::engine::TraitEngineExt as _;
14 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
15 use crate::traits::query::normalize::AtExt as _;
16 use crate::traits::specialize::to_pretty_impl_header;
17 use on_unimplemented::OnUnimplementedNote;
18 use on_unimplemented::TypeErrCtxtExt as _;
19 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
21 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
25 use rustc_hir::def_id::DefId;
26 use rustc_hir::intravisit::Visitor;
27 use rustc_hir::GenericParam;
30 use rustc_infer::infer::error_reporting::TypeErrCtxt;
31 use rustc_infer::infer::TypeTrace;
32 use rustc_infer::traits::TraitEngine;
33 use rustc_middle::traits::select::OverflowError;
34 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
35 use rustc_middle::ty::error::ExpectedFound;
36 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
37 use rustc_middle::ty::{
38 self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
41 use rustc_session::Limit;
42 use rustc_span::def_id::LOCAL_CRATE;
43 use rustc_span::symbol::{kw, sym};
44 use rustc_span::{ExpnKind, Span, DUMMY_SP};
47 use std::ops::ControlFlow;
48 use suggestions::TypeErrCtxtExt as _;
50 pub use rustc_infer::traits::error_reporting::*;
52 // When outputting impl candidates, prefer showing those that are more similar.
54 // We also compare candidates after skipping lifetimes, which has a lower
55 // priority than exact matches.
56 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
57 pub enum CandidateSimilarity {
58 Exact { ignoring_lifetimes: bool },
59 Fuzzy { ignoring_lifetimes: bool },
62 #[derive(Debug, Clone, Copy)]
63 pub struct ImplCandidate<'tcx> {
64 pub trait_ref: ty::TraitRef<'tcx>,
65 pub similarity: CandidateSimilarity,
68 pub trait InferCtxtExt<'tcx> {
69 /// Given some node representing a fn-like thing in the HIR map,
70 /// returns a span and `ArgKind` information that describes the
71 /// arguments it expects. This can be supplied to
72 /// `report_arg_count_mismatch`.
73 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)>;
75 /// Reports an error when the number of arguments needed by a
76 /// trait match doesn't match the number that the expression
78 fn report_arg_count_mismatch(
81 found_span: Option<Span>,
82 expected_args: Vec<ArgKind>,
83 found_args: Vec<ArgKind>,
85 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
87 /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
88 /// in that order, and returns the generic type corresponding to the
89 /// argument of that trait (corresponding to the closure arguments).
90 fn type_implements_fn_trait(
92 param_env: ty::ParamEnv<'tcx>,
93 ty: ty::Binder<'tcx, Ty<'tcx>>,
94 constness: ty::BoundConstness,
95 polarity: ty::ImplPolarity,
96 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
99 pub trait TypeErrCtxtExt<'tcx> {
100 fn report_fulfillment_errors(
102 errors: &[FulfillmentError<'tcx>],
103 body_id: Option<hir::BodyId>,
104 ) -> ErrorGuaranteed;
106 fn report_overflow_error<T>(
108 obligation: &Obligation<'tcx, T>,
109 suggest_increasing_limit: bool,
112 T: fmt::Display + TypeFoldable<'tcx>;
114 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
116 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
118 /// The `root_obligation` parameter should be the `root_obligation` field
119 /// from a `FulfillmentError`. If no `FulfillmentError` is available,
120 /// then it should be the same as `obligation`.
121 fn report_selection_error(
123 obligation: PredicateObligation<'tcx>,
124 root_obligation: &PredicateObligation<'tcx>,
125 error: &SelectionError<'tcx>,
129 impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
130 /// Given some node representing a fn-like thing in the HIR map,
131 /// returns a span and `ArgKind` information that describes the
132 /// arguments it expects. This can be supplied to
133 /// `report_arg_count_mismatch`.
134 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
135 let sm = self.tcx.sess.source_map();
136 let hir = self.tcx.hir();
138 Node::Expr(&hir::Expr {
139 kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }),
147 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
154 sm.span_to_snippet(pat.span)
156 .map(|snippet| (snippet, "_".to_owned()))
158 .collect::<Option<Vec<_>>>()?,
161 let name = sm.span_to_snippet(arg.pat.span).ok()?;
162 Some(ArgKind::Arg(name, "_".to_owned()))
165 .collect::<Option<Vec<ArgKind>>>()?,
167 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
168 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
169 | Node::TraitItem(&hir::TraitItem {
170 kind: hir::TraitItemKind::Fn(ref sig, _), ..
176 .map(|arg| match arg.kind {
177 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
179 vec![("_".to_owned(), "_".to_owned()); tys.len()],
181 _ => ArgKind::empty(),
183 .collect::<Vec<ArgKind>>(),
185 Node::Ctor(ref variant_data) => {
186 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
187 (span, vec![ArgKind::empty(); variant_data.fields().len()])
189 _ => panic!("non-FnLike node found: {:?}", node),
193 /// Reports an error when the number of arguments needed by a
194 /// trait match doesn't match the number that the expression
196 fn report_arg_count_mismatch(
199 found_span: Option<Span>,
200 expected_args: Vec<ArgKind>,
201 found_args: Vec<ArgKind>,
203 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
204 let kind = if is_closure { "closure" } else { "function" };
206 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
207 let arg_length = arguments.len();
208 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
209 match (arg_length, arguments.get(0)) {
210 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
211 format!("a single {}-tuple as argument", fields.len())
216 if distinct && arg_length > 1 { "distinct " } else { "" },
217 pluralize!(arg_length)
222 let expected_str = args_str(&expected_args, &found_args);
223 let found_str = args_str(&found_args, &expected_args);
225 let mut err = struct_span_err!(
229 "{} is expected to take {}, but it takes {}",
235 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
237 if let Some(found_span) = found_span {
238 err.span_label(found_span, format!("takes {}", found_str));
241 // ^^^^^^^^-- def_span
245 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
249 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
251 // Suggest to take and ignore the arguments with expected_args_length `_`s if
252 // found arguments is empty (assume the user just wants to ignore args in this case).
253 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
254 if found_args.is_empty() && is_closure {
255 let underscores = vec!["_"; expected_args.len()].join(", ");
256 err.span_suggestion_verbose(
259 "consider changing the closure to take and ignore the expected argument{}",
260 pluralize!(expected_args.len())
262 format!("|{}|", underscores),
263 Applicability::MachineApplicable,
267 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
268 if fields.len() == expected_args.len() {
271 .map(|(name, _)| name.to_owned())
272 .collect::<Vec<String>>()
274 err.span_suggestion_verbose(
276 "change the closure to take multiple arguments instead of a single tuple",
277 format!("|{}|", sugg),
278 Applicability::MachineApplicable,
282 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
283 && fields.len() == found_args.len()
290 .map(|arg| match arg {
291 ArgKind::Arg(name, _) => name.to_owned(),
294 .collect::<Vec<String>>()
296 // add type annotations if available
297 if found_args.iter().any(|arg| match arg {
298 ArgKind::Arg(_, ty) => ty != "_",
305 .map(|(_, ty)| ty.to_owned())
306 .collect::<Vec<String>>()
313 err.span_suggestion_verbose(
315 "change the closure to accept a tuple instead of individual arguments",
317 Applicability::MachineApplicable,
325 fn type_implements_fn_trait(
327 param_env: ty::ParamEnv<'tcx>,
328 ty: ty::Binder<'tcx, Ty<'tcx>>,
329 constness: ty::BoundConstness,
330 polarity: ty::ImplPolarity,
331 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
332 self.commit_if_ok(|_| {
333 for trait_def_id in [
334 self.tcx.lang_items().fn_trait(),
335 self.tcx.lang_items().fn_mut_trait(),
336 self.tcx.lang_items().fn_once_trait(),
338 let Some(trait_def_id) = trait_def_id else { continue };
339 // Make a fresh inference variable so we can determine what the substitutions
341 let var = self.next_ty_var(TypeVariableOrigin {
343 kind: TypeVariableOriginKind::MiscVariable,
345 let substs = self.tcx.mk_substs_trait(ty.skip_binder(), &[var.into()]);
346 let obligation = Obligation::new(
347 ObligationCause::dummy(),
349 ty.rebind(ty::TraitPredicate {
350 trait_ref: ty::TraitRef::new(trait_def_id, substs),
354 .to_predicate(self.tcx),
356 let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new_in_snapshot(self.tcx);
357 fulfill_cx.register_predicate_obligation(self, obligation);
358 if fulfill_cx.select_all_or_error(self).is_empty() {
360 ty::ClosureKind::from_def_id(self.tcx, trait_def_id)
361 .expect("expected to map DefId to ClosureKind"),
362 ty.rebind(self.resolve_vars_if_possible(var)),
371 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
372 fn report_fulfillment_errors(
374 errors: &[FulfillmentError<'tcx>],
375 body_id: Option<hir::BodyId>,
376 ) -> ErrorGuaranteed {
378 struct ErrorDescriptor<'tcx> {
379 predicate: ty::Predicate<'tcx>,
380 index: Option<usize>, // None if this is an old error
383 let mut error_map: FxIndexMap<_, Vec<_>> = self
384 .reported_trait_errors
387 .map(|(&span, predicates)| {
392 .map(|&predicate| ErrorDescriptor { predicate, index: None })
398 for (index, error) in errors.iter().enumerate() {
399 // We want to ignore desugarings here: spans are equivalent even
400 // if one is the result of a desugaring and the other is not.
401 let mut span = error.obligation.cause.span;
402 let expn_data = span.ctxt().outer_expn_data();
403 if let ExpnKind::Desugaring(_) = expn_data.kind {
404 span = expn_data.call_site;
407 error_map.entry(span).or_default().push(ErrorDescriptor {
408 predicate: error.obligation.predicate,
412 self.reported_trait_errors
416 .push(error.obligation.predicate);
419 // We do this in 2 passes because we want to display errors in order, though
420 // maybe it *is* better to sort errors by span or something.
421 let mut is_suppressed = vec![false; errors.len()];
422 for (_, error_set) in error_map.iter() {
423 // We want to suppress "duplicate" errors with the same span.
424 for error in error_set {
425 if let Some(index) = error.index {
426 // Suppress errors that are either:
427 // 1) strictly implied by another error.
428 // 2) implied by an error with a smaller index.
429 for error2 in error_set {
430 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
431 // Avoid errors being suppressed by already-suppressed
432 // errors, to prevent all errors from being suppressed
437 if self.error_implies(error2.predicate, error.predicate)
438 && !(error2.index >= error.index
439 && self.error_implies(error.predicate, error2.predicate))
441 info!("skipping {:?} (implied by {:?})", error, error2);
442 is_suppressed[index] = true;
450 for (error, suppressed) in iter::zip(errors, is_suppressed) {
452 self.report_fulfillment_error(error, body_id);
456 self.tcx.sess.delay_span_bug(DUMMY_SP, "expected fullfillment errors")
459 /// Reports that an overflow has occurred and halts compilation. We
460 /// halt compilation unconditionally because it is important that
461 /// overflows never be masked -- they basically represent computations
462 /// whose result could not be truly determined and thus we can't say
463 /// if the program type checks or not -- and they are unusual
464 /// occurrences in any case.
465 fn report_overflow_error<T>(
467 obligation: &Obligation<'tcx, T>,
468 suggest_increasing_limit: bool,
471 T: fmt::Display + TypeFoldable<'tcx>,
473 let predicate = self.resolve_vars_if_possible(obligation.predicate.clone());
474 let mut err = struct_span_err!(
476 obligation.cause.span,
478 "overflow evaluating the requirement `{}`",
482 if suggest_increasing_limit {
483 self.suggest_new_overflow_limit(&mut err);
486 self.note_obligation_cause_code(
488 &obligation.predicate,
489 obligation.param_env,
490 obligation.cause.code(),
492 &mut Default::default(),
496 self.tcx.sess.abort_if_errors();
500 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic) {
501 let suggested_limit = match self.tcx.recursion_limit() {
502 Limit(0) => Limit(2),
506 "consider increasing the recursion limit by adding a \
507 `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
509 self.tcx.crate_name(LOCAL_CRATE),
513 /// Reports that a cycle was detected which led to overflow and halts
514 /// compilation. This is equivalent to `report_overflow_error` except
515 /// that we can give a more helpful error message (and, in particular,
516 /// we do not suggest increasing the overflow limit, which is not
518 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
519 let cycle = self.resolve_vars_if_possible(cycle.to_owned());
520 assert!(!cycle.is_empty());
522 debug!(?cycle, "report_overflow_error_cycle");
524 // The 'deepest' obligation is most likely to have a useful
526 self.report_overflow_error(cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(), false);
529 fn report_selection_error(
531 mut obligation: PredicateObligation<'tcx>,
532 root_obligation: &PredicateObligation<'tcx>,
533 error: &SelectionError<'tcx>,
535 self.set_tainted_by_errors();
537 let mut span = obligation.cause.span;
539 let mut err = match *error {
540 SelectionError::Unimplemented => {
541 // If this obligation was generated as a result of well-formedness checking, see if we
542 // can get a better error message by performing HIR-based well-formedness checking.
543 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
544 root_obligation.cause.code().peel_derives()
546 if let Some(cause) = self
548 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
550 obligation.cause = cause.clone();
551 span = obligation.cause.span;
554 if let ObligationCauseCode::CompareImplItemObligation {
558 } = *obligation.cause.code()
560 self.report_extra_impl_obligation(
564 &format!("`{}`", obligation.predicate),
570 let bound_predicate = obligation.predicate.kind();
571 match bound_predicate.skip_binder() {
572 ty::PredicateKind::Trait(trait_predicate) => {
573 let trait_predicate = bound_predicate.rebind(trait_predicate);
574 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
576 trait_predicate.remap_constness_diag(obligation.param_env);
577 let predicate_is_const = ty::BoundConstness::ConstIfConst
578 == trait_predicate.skip_binder().constness;
580 if self.tcx.sess.has_errors().is_some()
581 && trait_predicate.references_error()
585 let trait_ref = trait_predicate.to_poly_trait_ref();
586 let (post_message, pre_message, type_def) = self
587 .get_parent_trait_ref(obligation.cause.code())
590 format!(" in `{}`", t),
591 format!("within `{}`, ", t),
592 s.map(|s| (format!("within this `{}`", t), s)),
595 .unwrap_or_default();
597 let OnUnimplementedNote {
603 } = self.on_unimplemented_note(trait_ref, &obligation);
604 let have_alt_message = message.is_some() || label.is_some();
605 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
607 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
608 let (message, note, append_const_msg) = if is_try_conversion {
611 "`?` couldn't convert the error to `{}`",
612 trait_ref.skip_binder().self_ty(),
615 "the question mark operation (`?`) implicitly performs a \
616 conversion on the error value using the `From` trait"
622 (message, note, append_const_msg)
625 let mut err = struct_span_err!(
631 .and_then(|cannot_do_this| {
632 match (predicate_is_const, append_const_msg) {
633 // do nothing if predicate is not const
634 (false, _) => Some(cannot_do_this),
635 // suggested using default post message
636 (true, Some(None)) => {
637 Some(format!("{cannot_do_this} in const contexts"))
639 // overridden post message
640 (true, Some(Some(post_message))) => {
641 Some(format!("{cannot_do_this}{post_message}"))
643 // fallback to generic message
644 (true, None) => None,
647 .unwrap_or_else(|| format!(
648 "the trait bound `{}` is not satisfied{}",
649 trait_predicate, post_message,
653 if is_try_conversion {
654 let none_error = self
656 .get_diagnostic_item(sym::none_error)
657 .map(|def_id| tcx.type_of(def_id));
658 let should_convert_option_to_result =
659 Some(trait_ref.skip_binder().substs.type_at(1)) == none_error;
660 let should_convert_result_to_option =
661 Some(trait_ref.self_ty().skip_binder()) == none_error;
662 if should_convert_option_to_result {
663 err.span_suggestion_verbose(
665 "consider converting the `Option<T>` into a `Result<T, _>` \
666 using `Option::ok_or` or `Option::ok_or_else`",
667 ".ok_or_else(|| /* error value */)",
668 Applicability::HasPlaceholders,
670 } else if should_convert_result_to_option {
671 err.span_suggestion_verbose(
673 "consider converting the `Result<T, _>` into an `Option<T>` \
676 Applicability::MachineApplicable,
679 if let Some(ret_span) = self.return_type_span(&obligation) {
683 "expected `{}` because of this",
684 trait_ref.skip_binder().self_ty()
690 if Some(trait_ref.def_id()) == tcx.lang_items().tuple_trait() {
691 match obligation.cause.code().peel_derives() {
692 ObligationCauseCode::RustCall => {
693 err.set_primary_message("functions with the \"rust-call\" ABI must take a single non-self tuple argument");
695 ObligationCauseCode::BindingObligation(def_id, _)
696 | ObligationCauseCode::ItemObligation(def_id)
697 if ty::ClosureKind::from_def_id(tcx, *def_id).is_some() =>
699 err.code(rustc_errors::error_code!(E0059));
700 err.set_primary_message(format!(
701 "type parameter to bare `{}` trait must be a tuple",
702 tcx.def_path_str(*def_id)
709 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
710 && predicate_is_const
712 err.note("`~const Drop` was renamed to `~const Destruct`");
713 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
716 let explanation = if let ObligationCauseCode::MainFunctionType =
717 obligation.cause.code()
719 "consider using `()`, or a `Result`".to_owned()
721 let ty_desc = match trait_ref.skip_binder().self_ty().kind() {
722 ty::FnDef(_, _) => Some("fn item"),
723 ty::Closure(_, _) => Some("closure"),
728 Some(desc) => format!(
729 "{}the trait `{}` is not implemented for {} `{}`",
731 trait_predicate.print_modifiers_and_trait_path(),
733 trait_ref.skip_binder().self_ty(),
736 "{}the trait `{}` is not implemented for `{}`",
738 trait_predicate.print_modifiers_and_trait_path(),
739 trait_ref.skip_binder().self_ty(),
744 if self.suggest_add_reference_to_arg(
750 self.note_obligation_cause(&mut err, &obligation);
754 if let Some(ref s) = label {
755 // If it has a custom `#[rustc_on_unimplemented]`
756 // error message, let's display it as the label!
757 err.span_label(span, s);
758 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
759 // When the self type is a type param We don't need to "the trait
760 // `std::marker::Sized` is not implemented for `T`" as we will point
761 // at the type param with a label to suggest constraining it.
762 err.help(&explanation);
765 err.span_label(span, explanation);
768 if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
769 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
770 self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
773 let mut unsatisfied_const = false;
774 if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
775 let non_const_predicate = trait_ref.without_const();
776 let non_const_obligation = Obligation {
777 cause: obligation.cause.clone(),
778 param_env: obligation.param_env.without_const(),
779 predicate: non_const_predicate.to_predicate(tcx),
780 recursion_depth: obligation.recursion_depth,
782 if self.predicate_may_hold(&non_const_obligation) {
783 unsatisfied_const = true;
787 "the trait `{}` is implemented for `{}`, \
788 but that implementation is not `const`",
789 non_const_predicate.print_modifiers_and_trait_path(),
790 trait_ref.skip_binder().self_ty(),
796 if let Some((msg, span)) = type_def {
797 err.span_label(span, &msg);
799 if let Some(ref s) = note {
800 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
801 err.note(s.as_str());
803 if let Some(ref s) = parent_label {
806 .opt_local_def_id(obligation.cause.body_id)
808 tcx.hir().body_owner_def_id(hir::BodyId {
809 hir_id: obligation.cause.body_id,
812 err.span_label(tcx.def_span(body), s);
815 self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
816 self.suggest_dereferencing_index(&obligation, &mut err, trait_predicate);
818 self.suggest_dereferences(&obligation, &mut err, trait_predicate);
819 suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
821 self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
822 suggested |= self.suggest_semicolon_removal(
828 self.note_version_mismatch(&mut err, &trait_ref);
829 self.suggest_remove_await(&obligation, &mut err);
830 self.suggest_derive(&obligation, &mut err, trait_predicate);
832 if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
833 self.suggest_await_before_try(
841 if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
847 // If the obligation failed due to a missing implementation of the
848 // `Unsize` trait, give a pointer to why that might be the case
850 "all implementations of `Unsize` are provided \
851 automatically by the compiler, see \
852 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
853 for more information",
858 ty::ClosureKind::from_def_id(tcx, trait_ref.def_id()).is_some();
859 let is_target_feature_fn = if let ty::FnDef(def_id, _) =
860 *trait_ref.skip_binder().self_ty().kind()
862 !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
866 if is_fn_trait && is_target_feature_fn {
868 "`#[target_feature]` functions do not implement the `Fn` traits",
872 // Try to report a help message
874 && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
875 obligation.param_env,
877 trait_predicate.skip_binder().constness,
878 trait_predicate.skip_binder().polarity,
881 // If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
882 // suggestion to add trait bounds for the type, since we only typically implement
883 // these traits once.
885 // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
888 ty::ClosureKind::from_def_id(self.tcx, trait_ref.def_id())
889 .expect("expected to map DefId to ClosureKind");
890 if !implemented_kind.extends(selected_kind) {
893 "`{}` implements `{}`, but it must implement `{}`, which is more general",
894 trait_ref.skip_binder().self_ty(),
901 // Note any argument mismatches
902 let given_ty = params.skip_binder();
903 let expected_ty = trait_ref.skip_binder().substs.type_at(1);
904 if let ty::Tuple(given) = given_ty.kind()
905 && let ty::Tuple(expected) = expected_ty.kind()
907 if expected.len() != given.len() {
908 // Note number of types that were expected and given
911 "expected a closure taking {} argument{}, but one taking {} argument{} was given",
913 pluralize!(given.len()),
915 pluralize!(expected.len()),
918 } else if !self.same_type_modulo_infer(given_ty, expected_ty) {
919 // Print type mismatch
920 let (expected_args, given_args) =
921 self.cmp(given_ty, expected_ty);
922 err.note_expected_found(
923 &"a closure with arguments",
925 &"a closure with arguments",
930 } else if !trait_ref.has_non_region_infer()
931 && self.predicate_can_apply(obligation.param_env, trait_predicate)
933 // If a where-clause may be useful, remind the
934 // user that they can add it.
936 // don't display an on-unimplemented note, as
937 // these notes will often be of the form
938 // "the type `T` can't be frobnicated"
939 // which is somewhat confusing.
940 self.suggest_restricting_param_bound(
944 obligation.cause.body_id,
946 } else if !suggested && !unsatisfied_const {
947 // Can't show anything else useful, try to find similar impls.
948 let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
949 if !self.report_similar_impl_candidates(
952 obligation.cause.body_id,
955 // This is *almost* equivalent to
956 // `obligation.cause.code().peel_derives()`, but it gives us the
957 // trait predicate for that corresponding root obligation. This
958 // lets us get a derived obligation from a type parameter, like
959 // when calling `string.strip_suffix(p)` where `p` is *not* an
960 // implementer of `Pattern<'_>`.
961 let mut code = obligation.cause.code();
962 let mut trait_pred = trait_predicate;
963 let mut peeled = false;
964 while let Some((parent_code, parent_trait_pred)) = code.parent() {
966 if let Some(parent_trait_pred) = parent_trait_pred {
967 trait_pred = parent_trait_pred;
971 let def_id = trait_pred.def_id();
972 // Mention *all* the `impl`s for the *top most* obligation, the
973 // user might have meant to use one of them, if any found. We skip
974 // auto-traits or fundamental traits that might not be exactly what
975 // the user might expect to be presented with. Instead this is
976 // useful for less general traits.
978 && !self.tcx.trait_is_auto(def_id)
979 && !self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
981 let trait_ref = trait_pred.to_poly_trait_ref();
982 let impl_candidates =
983 self.find_similar_impl_candidates(trait_pred);
984 self.report_similar_impl_candidates(
987 obligation.cause.body_id,
994 // Changing mutability doesn't make a difference to whether we have
995 // an `Unsize` impl (Fixes ICE in #71036)
997 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
1000 // If this error is due to `!: Trait` not implemented but `(): Trait` is
1001 // implemented, and fallback has occurred, then it could be due to a
1002 // variable that used to fallback to `()` now falling back to `!`. Issue a
1003 // note informing about the change in behaviour.
1004 if trait_predicate.skip_binder().self_ty().is_never()
1005 && self.fallback_has_occurred
1007 let predicate = trait_predicate.map_bound(|mut trait_pred| {
1008 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
1010 &trait_pred.trait_ref.substs[1..],
1014 let unit_obligation = obligation.with(predicate.to_predicate(tcx));
1015 if self.predicate_may_hold(&unit_obligation) {
1017 "this error might have been caused by changes to \
1018 Rust's type-inference algorithm (see issue #48950 \
1019 <https://github.com/rust-lang/rust/issues/48950> \
1020 for more information)",
1022 err.help("did you intend to use the type `()` here instead?");
1026 // Return early if the trait is Debug or Display and the invocation
1027 // originates within a standard library macro, because the output
1028 // is otherwise overwhelming and unhelpful (see #85844 for an
1032 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
1033 Some(macro_def_id) => {
1034 let crate_name = tcx.crate_name(macro_def_id.krate);
1035 crate_name == sym::std || crate_name == sym::core
1042 self.tcx.get_diagnostic_name(trait_ref.def_id()),
1043 Some(sym::Debug | sym::Display)
1053 ty::PredicateKind::Subtype(predicate) => {
1054 // Errors for Subtype predicates show up as
1055 // `FulfillmentErrorCode::CodeSubtypeError`,
1056 // not selection error.
1057 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
1060 ty::PredicateKind::Coerce(predicate) => {
1061 // Errors for Coerce predicates show up as
1062 // `FulfillmentErrorCode::CodeSubtypeError`,
1063 // not selection error.
1064 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
1067 ty::PredicateKind::RegionOutlives(..)
1068 | ty::PredicateKind::Projection(..)
1069 | ty::PredicateKind::TypeOutlives(..) => {
1070 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1075 "the requirement `{}` is not satisfied",
1080 ty::PredicateKind::ObjectSafe(trait_def_id) => {
1081 let violations = self.tcx.object_safety_violations(trait_def_id);
1082 report_object_safety_error(self.tcx, span, trait_def_id, violations)
1085 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
1086 let found_kind = self.closure_kind(closure_substs).unwrap();
1087 let closure_span = self.tcx.def_span(closure_def_id);
1088 let mut err = struct_span_err!(
1092 "expected a closure that implements the `{}` trait, \
1093 but this closure only implements `{}`",
1100 format!("this closure implements `{}`, not `{}`", found_kind, kind),
1103 obligation.cause.span,
1104 format!("the requirement to implement `{}` derives from here", kind),
1107 // Additional context information explaining why the closure only implements
1108 // a particular trait.
1109 if let Some(typeck_results) = &self.typeck_results {
1113 .local_def_id_to_hir_id(closure_def_id.expect_local());
1114 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
1115 (ty::ClosureKind::FnOnce, Some((span, place))) => {
1119 "closure is `FnOnce` because it moves the \
1120 variable `{}` out of its environment",
1121 ty::place_to_string_for_capture(tcx, place)
1125 (ty::ClosureKind::FnMut, Some((span, place))) => {
1129 "closure is `FnMut` because it mutates the \
1130 variable `{}` here",
1131 ty::place_to_string_for_capture(tcx, place)
1142 ty::PredicateKind::WellFormed(ty) => {
1143 if !self.tcx.sess.opts.unstable_opts.chalk {
1144 // WF predicates cannot themselves make
1145 // errors. They can only block due to
1146 // ambiguity; otherwise, they always
1147 // degenerate into other obligations
1148 // (which may fail).
1149 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
1151 // FIXME: we'll need a better message which takes into account
1152 // which bounds actually failed to hold.
1153 self.tcx.sess.struct_span_err(
1155 &format!("the type `{}` is not well-formed (chalk)", ty),
1160 ty::PredicateKind::ConstEvaluatable(..) => {
1161 // Errors for `ConstEvaluatable` predicates show up as
1162 // `SelectionError::ConstEvalFailure`,
1163 // not `Unimplemented`.
1166 "const-evaluatable requirement gave wrong error: `{:?}`",
1171 ty::PredicateKind::ConstEquate(..) => {
1172 // Errors for `ConstEquate` predicates show up as
1173 // `SelectionError::ConstEvalFailure`,
1174 // not `Unimplemented`.
1177 "const-equate requirement gave wrong error: `{:?}`",
1182 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
1184 "TypeWellFormedFromEnv predicate should only exist in the environment"
1189 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
1190 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
1191 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
1193 if expected_trait_ref.self_ty().references_error() {
1197 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
1201 let found_did = match *found_trait_ty.kind() {
1205 | ty::Generator(did, ..) => Some(did),
1206 ty::Adt(def, _) => Some(def.did()),
1210 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
1212 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1213 // We check closures twice, with obligations flowing in different directions,
1214 // but we want to complain about them only once.
1218 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1220 let mut not_tupled = false;
1222 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
1223 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1226 vec![ArgKind::empty()]
1230 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1231 let expected = match expected_ty.kind() {
1232 ty::Tuple(ref tys) => {
1233 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
1237 vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())]
1241 // If this is a `Fn` family trait and either the expected or found
1242 // is not tupled, then fall back to just a regular mismatch error.
1243 // This shouldn't be common unless manually implementing one of the
1244 // traits manually, but don't make it more confusing when it does
1246 if Some(expected_trait_ref.def_id()) != tcx.lang_items().gen_trait() && not_tupled {
1247 self.report_and_explain_type_error(
1248 TypeTrace::poly_trait_refs(
1254 ty::error::TypeError::Mismatch,
1256 } else if found.len() == expected.len() {
1257 self.report_closure_arg_mismatch(
1262 obligation.cause.code(),
1265 let (closure_span, found) = found_did
1267 let node = self.tcx.hir().get_if_local(did)?;
1268 let (found_span, found) = self.get_fn_like_arguments(node)?;
1269 Some((Some(found_span), found))
1271 .unwrap_or((found_span, found));
1273 self.report_arg_count_mismatch(
1278 found_trait_ty.is_closure(),
1283 TraitNotObjectSafe(did) => {
1284 let violations = self.tcx.object_safety_violations(did);
1285 report_object_safety_error(self.tcx, span, did, violations)
1288 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1290 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1293 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1294 if !self.tcx.features().generic_const_exprs {
1295 let mut err = self.tcx.sess.struct_span_err(
1297 "constant expression depends on a generic parameter",
1299 // FIXME(const_generics): we should suggest to the user how they can resolve this
1300 // issue. However, this is currently not actually possible
1301 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1303 // Note that with `feature(generic_const_exprs)` this case should not
1305 err.note("this may fail depending on what value the parameter takes");
1310 match obligation.predicate.kind().skip_binder() {
1311 ty::PredicateKind::ConstEvaluatable(ct) => {
1312 let ty::ConstKind::Unevaluated(uv) = ct.kind() else {
1313 bug!("const evaluatable failed for non-unevaluated const `{ct:?}`");
1316 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1317 let const_span = self.tcx.def_span(uv.def.did);
1318 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1319 Ok(snippet) => err.help(&format!(
1320 "try adding a `where` bound using this expression: `where [(); {}]:`",
1323 _ => err.help("consider adding a `where` bound using this expression"),
1330 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1336 // Already reported in the query.
1337 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1338 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1339 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1342 // Already reported.
1343 Overflow(OverflowError::Error(_)) => {
1344 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1348 bug!("overflow should be handled before the `report_selection_error` path");
1350 SelectionError::ErrorReporting => {
1351 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1355 self.note_obligation_cause(&mut err, &obligation);
1356 self.point_at_returns_when_relevant(&mut err, &obligation);
1362 trait InferCtxtPrivExt<'tcx> {
1363 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1364 // `error` occurring implies that `cond` occurs.
1365 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1367 fn report_fulfillment_error(
1369 error: &FulfillmentError<'tcx>,
1370 body_id: Option<hir::BodyId>,
1373 fn report_projection_error(
1375 obligation: &PredicateObligation<'tcx>,
1376 error: &MismatchedProjectionTypes<'tcx>,
1379 fn maybe_detailed_projection_msg(
1381 pred: ty::ProjectionPredicate<'tcx>,
1382 normalized_ty: ty::Term<'tcx>,
1383 expected_ty: ty::Term<'tcx>,
1384 ) -> Option<String>;
1390 ignoring_lifetimes: bool,
1391 ) -> Option<CandidateSimilarity>;
1393 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1395 fn find_similar_impl_candidates(
1397 trait_pred: ty::PolyTraitPredicate<'tcx>,
1398 ) -> Vec<ImplCandidate<'tcx>>;
1400 fn report_similar_impl_candidates(
1402 impl_candidates: Vec<ImplCandidate<'tcx>>,
1403 trait_ref: ty::PolyTraitRef<'tcx>,
1404 body_id: hir::HirId,
1405 err: &mut Diagnostic,
1408 /// Gets the parent trait chain start
1409 fn get_parent_trait_ref(
1411 code: &ObligationCauseCode<'tcx>,
1412 ) -> Option<(String, Option<Span>)>;
1414 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1415 /// with the same path as `trait_ref`, a help message about
1416 /// a probable version mismatch is added to `err`
1417 fn note_version_mismatch(
1419 err: &mut Diagnostic,
1420 trait_ref: &ty::PolyTraitRef<'tcx>,
1423 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1426 /// For this to work, `new_self_ty` must have no escaping bound variables.
1427 fn mk_trait_obligation_with_new_self_ty(
1429 param_env: ty::ParamEnv<'tcx>,
1430 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1431 ) -> PredicateObligation<'tcx>;
1433 fn maybe_report_ambiguity(
1435 obligation: &PredicateObligation<'tcx>,
1436 body_id: Option<hir::BodyId>,
1439 fn predicate_can_apply(
1441 param_env: ty::ParamEnv<'tcx>,
1442 pred: ty::PolyTraitPredicate<'tcx>,
1445 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1447 fn suggest_unsized_bound_if_applicable(
1449 err: &mut Diagnostic,
1450 obligation: &PredicateObligation<'tcx>,
1453 fn annotate_source_of_ambiguity(
1455 err: &mut Diagnostic,
1457 predicate: ty::Predicate<'tcx>,
1460 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>);
1462 fn maybe_indirection_for_unsized(
1464 err: &mut Diagnostic,
1465 item: &'tcx Item<'tcx>,
1466 param: &'tcx GenericParam<'tcx>,
1469 fn is_recursive_obligation(
1471 obligated_types: &mut Vec<Ty<'tcx>>,
1472 cause_code: &ObligationCauseCode<'tcx>,
1476 impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
1477 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1478 // `error` occurring implies that `cond` occurs.
1479 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1484 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1485 let bound_error = error.kind();
1486 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1487 (ty::PredicateKind::Trait(..), ty::PredicateKind::Trait(error)) => {
1488 (cond, bound_error.rebind(error))
1491 // FIXME: make this work in other cases too.
1496 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1497 let bound_predicate = obligation.predicate.kind();
1498 if let ty::PredicateKind::Trait(implication) = bound_predicate.skip_binder() {
1499 let error = error.to_poly_trait_ref();
1500 let implication = bound_predicate.rebind(implication.trait_ref);
1501 // FIXME: I'm just not taking associated types at all here.
1502 // Eventually I'll need to implement param-env-aware
1503 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1504 let param_env = ty::ParamEnv::empty();
1505 if self.can_sub(param_env, error, implication).is_ok() {
1506 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1515 #[instrument(skip(self), level = "debug")]
1516 fn report_fulfillment_error(
1518 error: &FulfillmentError<'tcx>,
1519 body_id: Option<hir::BodyId>,
1522 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1523 self.report_selection_error(
1524 error.obligation.clone(),
1525 &error.root_obligation,
1529 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1530 self.report_projection_error(&error.obligation, e);
1532 FulfillmentErrorCode::CodeAmbiguity => {
1533 self.maybe_report_ambiguity(&error.obligation, body_id);
1535 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1536 self.report_mismatched_types(
1537 &error.obligation.cause,
1538 expected_found.expected,
1539 expected_found.found,
1544 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1545 let mut diag = self.report_mismatched_consts(
1546 &error.obligation.cause,
1547 expected_found.expected,
1548 expected_found.found,
1551 let code = error.obligation.cause.code().peel_derives().peel_match_impls();
1552 if let ObligationCauseCode::BindingObligation(..)
1553 | ObligationCauseCode::ItemObligation(..)
1554 | ObligationCauseCode::ExprBindingObligation(..)
1555 | ObligationCauseCode::ExprItemObligation(..) = code
1557 self.note_obligation_cause_code(
1559 &error.obligation.predicate,
1560 error.obligation.param_env,
1563 &mut Default::default(),
1568 FulfillmentErrorCode::CodeCycle(ref cycle) => {
1569 self.report_overflow_error_cycle(cycle);
1574 #[instrument(level = "debug", skip_all)]
1575 fn report_projection_error(
1577 obligation: &PredicateObligation<'tcx>,
1578 error: &MismatchedProjectionTypes<'tcx>,
1580 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1582 if predicate.references_error() {
1587 let mut err = error.err;
1588 let mut values = None;
1590 // try to find the mismatched types to report the error with.
1592 // this can fail if the problem was higher-ranked, in which
1593 // cause I have no idea for a good error message.
1594 let bound_predicate = predicate.kind();
1595 if let ty::PredicateKind::Projection(data) = bound_predicate.skip_binder() {
1596 let mut selcx = SelectionContext::new(self);
1597 let data = self.replace_bound_vars_with_fresh_vars(
1598 obligation.cause.span,
1599 infer::LateBoundRegionConversionTime::HigherRankedType,
1600 bound_predicate.rebind(data),
1602 let mut obligations = vec![];
1603 let normalized_ty = super::normalize_projection_type(
1605 obligation.param_env,
1607 obligation.cause.clone(),
1612 debug!(?obligation.cause, ?obligation.param_env);
1614 debug!(?normalized_ty, data.ty = ?data.term);
1616 let is_normalized_ty_expected = !matches!(
1617 obligation.cause.code().peel_derives(),
1618 ObligationCauseCode::ItemObligation(_)
1619 | ObligationCauseCode::BindingObligation(_, _)
1620 | ObligationCauseCode::ExprItemObligation(..)
1621 | ObligationCauseCode::ExprBindingObligation(..)
1622 | ObligationCauseCode::ObjectCastObligation(..)
1623 | ObligationCauseCode::OpaqueType
1625 if let Err(new_err) = self.at(&obligation.cause, obligation.param_env).eq_exp(
1626 is_normalized_ty_expected,
1630 values = Some((data, is_normalized_ty_expected, normalized_ty, data.term));
1636 .and_then(|(predicate, _, normalized_ty, expected_ty)| {
1637 self.maybe_detailed_projection_msg(predicate, normalized_ty, expected_ty)
1639 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
1640 let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
1642 let secondary_span = match predicate.kind().skip_binder() {
1643 ty::PredicateKind::Projection(proj) => self
1645 .opt_associated_item(proj.projection_ty.item_def_id)
1646 .and_then(|trait_assoc_item| {
1648 .trait_of_item(proj.projection_ty.item_def_id)
1649 .map(|id| (trait_assoc_item, id))
1651 .and_then(|(trait_assoc_item, id)| {
1652 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1653 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1655 .associated_items(did)
1656 .in_definition_order()
1657 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1660 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1662 hir::Node::TraitItem(hir::TraitItem {
1663 kind: hir::TraitItemKind::Type(_, Some(ty)),
1666 | hir::Node::ImplItem(hir::ImplItem {
1667 kind: hir::ImplItemKind::Type(ty),
1670 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1679 values.map(|(_, is_normalized_ty_expected, normalized_ty, term)| {
1680 infer::ValuePairs::Terms(ExpectedFound::new(
1681 is_normalized_ty_expected,
1690 self.note_obligation_cause(&mut diag, obligation);
1695 fn maybe_detailed_projection_msg(
1697 pred: ty::ProjectionPredicate<'tcx>,
1698 normalized_ty: ty::Term<'tcx>,
1699 expected_ty: ty::Term<'tcx>,
1700 ) -> Option<String> {
1701 let trait_def_id = pred.projection_ty.trait_def_id(self.tcx);
1702 let self_ty = pred.projection_ty.self_ty();
1704 if Some(pred.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output() {
1706 "expected `{self_ty}` to be a {fn_kind} that returns `{expected_ty}`, but it returns `{normalized_ty}`",
1707 fn_kind = self_ty.prefix_string(self.tcx)
1709 } else if Some(trait_def_id) == self.tcx.lang_items().future_trait() {
1711 "expected `{self_ty}` to be a future that resolves to `{expected_ty}`, but it resolves to `{normalized_ty}`"
1713 } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
1715 "expected `{self_ty}` to be an iterator that yields `{expected_ty}`, but it yields `{normalized_ty}`"
1726 ignoring_lifetimes: bool,
1727 ) -> Option<CandidateSimilarity> {
1728 /// returns the fuzzy category of a given type, or None
1729 /// if the type can be equated to any type.
1730 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1732 ty::Bool => Some(0),
1733 ty::Char => Some(1),
1735 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::String, def.did()) => Some(2),
1739 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1740 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1741 ty::Array(..) | ty::Slice(..) => Some(6),
1742 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1743 ty::Dynamic(..) => Some(8),
1744 ty::Closure(..) => Some(9),
1745 ty::Tuple(..) => Some(10),
1746 ty::Param(..) => Some(11),
1747 ty::Projection(..) => Some(12),
1748 ty::Opaque(..) => Some(13),
1749 ty::Never => Some(14),
1750 ty::Adt(..) => Some(15),
1751 ty::Generator(..) => Some(16),
1752 ty::Foreign(..) => Some(17),
1753 ty::GeneratorWitness(..) => Some(18),
1754 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1758 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1761 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1769 if !ignoring_lifetimes {
1770 a = strip_references(a);
1771 b = strip_references(b);
1774 let cat_a = type_category(self.tcx, a)?;
1775 let cat_b = type_category(self.tcx, b)?;
1777 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1778 } else if cat_a == cat_b {
1779 match (a.kind(), b.kind()) {
1780 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1781 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1782 // Matching on references results in a lot of unhelpful
1783 // suggestions, so let's just not do that for now.
1785 // We still upgrade successful matches to `ignoring_lifetimes: true`
1786 // to prioritize that impl.
1787 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1788 self.fuzzy_match_tys(a, b, true).is_some()
1792 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1793 } else if ignoring_lifetimes {
1796 self.fuzzy_match_tys(a, b, true)
1800 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1801 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1802 hir::GeneratorKind::Gen => "a generator",
1803 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1804 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1805 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1809 fn find_similar_impl_candidates(
1811 trait_pred: ty::PolyTraitPredicate<'tcx>,
1812 ) -> Vec<ImplCandidate<'tcx>> {
1814 .all_impls(trait_pred.def_id())
1815 .filter_map(|def_id| {
1816 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
1819 .is_constness_satisfied_by(self.tcx.constness(def_id))
1824 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1826 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
1827 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1832 fn report_similar_impl_candidates(
1834 impl_candidates: Vec<ImplCandidate<'tcx>>,
1835 trait_ref: ty::PolyTraitRef<'tcx>,
1836 body_id: hir::HirId,
1837 err: &mut Diagnostic,
1839 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1842 let len = candidates.len();
1843 if candidates.len() == 0 {
1846 if candidates.len() == 1 {
1847 let ty_desc = match candidates[0].self_ty().kind() {
1848 ty::FnPtr(_) => Some("fn pointer"),
1851 let the_desc = match ty_desc {
1852 Some(desc) => format!(" implemented for {} `", desc),
1853 None => " implemented for `".to_string(),
1855 err.highlighted_help(vec![
1857 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1860 ("is".to_string(), Style::Highlight),
1861 (the_desc, Style::NoStyle),
1862 (candidates[0].self_ty().to_string(), Style::Highlight),
1863 ("`".to_string(), Style::NoStyle),
1867 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1868 // Check if the trait is the same in all cases. If so, we'll only show the type.
1869 let mut traits: Vec<_> =
1870 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1874 let mut candidates: Vec<String> = candidates
1877 if traits.len() == 1 {
1878 format!("\n {}", c.self_ty())
1887 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1889 "the following other types implement trait `{}`:{}{}",
1890 trait_ref.print_only_trait_path(),
1891 candidates[..end].join(""),
1892 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1897 let def_id = trait_ref.def_id();
1898 if impl_candidates.is_empty() {
1899 if self.tcx.trait_is_auto(def_id)
1900 || self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1901 || self.tcx.get_diagnostic_name(def_id).is_some()
1903 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1906 let normalized_impl_candidates: Vec<_> = self
1909 // Ignore automatically derived impls and `!Trait` impls.
1911 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1912 || self.tcx.is_builtin_derive(def_id)
1914 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1915 .filter(|trait_ref| {
1916 let self_ty = trait_ref.self_ty();
1917 // Avoid mentioning type parameters.
1918 if let ty::Param(_) = self_ty.kind() {
1921 // Avoid mentioning types that are private to another crate
1922 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
1923 // FIXME(compiler-errors): This could be generalized, both to
1924 // be more granular, and probably look past other `#[fundamental]`
1927 .visibility(def.did())
1928 .is_accessible_from(body_id.owner.def_id, self.tcx)
1934 return report(normalized_impl_candidates, err);
1937 let normalize = |candidate| {
1938 let infcx = self.tcx.infer_ctxt().build();
1940 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1941 .normalize(candidate)
1942 .map_or(candidate, |normalized| normalized.value)
1945 // Sort impl candidates so that ordering is consistent for UI tests.
1946 // because the ordering of `impl_candidates` may not be deterministic:
1947 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1949 // Prefer more similar candidates first, then sort lexicographically
1950 // by their normalized string representation.
1951 let mut normalized_impl_candidates_and_similarities = impl_candidates
1953 .map(|ImplCandidate { trait_ref, similarity }| {
1954 let normalized = normalize(trait_ref);
1955 (similarity, normalized)
1957 .collect::<Vec<_>>();
1958 normalized_impl_candidates_and_similarities.sort();
1959 normalized_impl_candidates_and_similarities.dedup();
1961 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
1963 .map(|(_, normalized)| normalized)
1964 .collect::<Vec<_>>();
1966 report(normalized_impl_candidates, err)
1969 /// Gets the parent trait chain start
1970 fn get_parent_trait_ref(
1972 code: &ObligationCauseCode<'tcx>,
1973 ) -> Option<(String, Option<Span>)> {
1975 ObligationCauseCode::BuiltinDerivedObligation(data) => {
1976 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
1977 match self.get_parent_trait_ref(&data.parent_code) {
1980 let ty = parent_trait_ref.skip_binder().self_ty();
1981 let span = TyCategory::from_ty(self.tcx, ty)
1982 .map(|(_, def_id)| self.tcx.def_span(def_id));
1983 Some((ty.to_string(), span))
1987 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
1988 self.get_parent_trait_ref(&parent_code)
1994 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1995 /// with the same path as `trait_ref`, a help message about
1996 /// a probable version mismatch is added to `err`
1997 fn note_version_mismatch(
1999 err: &mut Diagnostic,
2000 trait_ref: &ty::PolyTraitRef<'tcx>,
2002 let get_trait_impl = |trait_def_id| {
2003 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
2005 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
2006 let traits_with_same_path: std::collections::BTreeSet<_> = self
2009 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
2010 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
2012 let mut suggested = false;
2013 for trait_with_same_path in traits_with_same_path {
2014 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
2015 let impl_span = self.tcx.def_span(impl_def_id);
2016 err.span_help(impl_span, "trait impl with same name found");
2017 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
2018 let crate_msg = format!(
2019 "perhaps two different versions of crate `{}` are being used?",
2022 err.note(&crate_msg);
2029 fn mk_trait_obligation_with_new_self_ty(
2031 param_env: ty::ParamEnv<'tcx>,
2032 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
2033 ) -> PredicateObligation<'tcx> {
2034 let trait_pred = trait_ref_and_ty.map_bound_ref(|(tr, new_self_ty)| ty::TraitPredicate {
2035 trait_ref: ty::TraitRef {
2036 substs: self.tcx.mk_substs_trait(*new_self_ty, &tr.trait_ref.substs[1..]),
2042 Obligation::new(ObligationCause::dummy(), param_env, trait_pred.to_predicate(self.tcx))
2045 #[instrument(skip(self), level = "debug")]
2046 fn maybe_report_ambiguity(
2048 obligation: &PredicateObligation<'tcx>,
2049 body_id: Option<hir::BodyId>,
2051 // Unable to successfully determine, probably means
2052 // insufficient type information, but could mean
2053 // ambiguous impls. The latter *ought* to be a
2054 // coherence violation, so we don't report it here.
2056 let predicate = self.resolve_vars_if_possible(obligation.predicate);
2057 let span = obligation.cause.span;
2059 debug!(?predicate, obligation.cause.code = ?obligation.cause.code());
2061 // Ambiguity errors are often caused as fallout from earlier errors.
2062 // We ignore them if this `infcx` is tainted in some cases below.
2064 let bound_predicate = predicate.kind();
2065 let mut err = match bound_predicate.skip_binder() {
2066 ty::PredicateKind::Trait(data) => {
2067 let trait_ref = bound_predicate.rebind(data.trait_ref);
2070 if predicate.references_error() {
2074 // This is kind of a hack: it frequently happens that some earlier
2075 // error prevents types from being fully inferred, and then we get
2076 // a bunch of uninteresting errors saying something like "<generic
2077 // #0> doesn't implement Sized". It may even be true that we
2078 // could just skip over all checks where the self-ty is an
2079 // inference variable, but I was afraid that there might be an
2080 // inference variable created, registered as an obligation, and
2081 // then never forced by writeback, and hence by skipping here we'd
2082 // be ignoring the fact that we don't KNOW the type works
2083 // out. Though even that would probably be harmless, given that
2084 // we're only talking about builtin traits, which are known to be
2085 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2086 // avoid inundating the user with unnecessary errors, but we now
2087 // check upstream for type errors and don't add the obligations to
2088 // begin with in those cases.
2089 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
2090 if !self.is_tainted_by_errors() {
2091 self.emit_inference_failure_err(
2094 trait_ref.self_ty().skip_binder().into(),
2103 // Typically, this ambiguity should only happen if
2104 // there are unresolved type inference variables
2105 // (otherwise it would suggest a coherence
2106 // failure). But given #21974 that is not necessarily
2107 // the case -- we can have multiple where clauses that
2108 // are only distinguished by a region, which results
2109 // in an ambiguity even when all types are fully
2110 // known, since we don't dispatch based on region
2113 // Pick the first substitution that still contains inference variables as the one
2114 // we're going to emit an error for. If there are none (see above), fall back to
2115 // a more general error.
2116 let subst = data.trait_ref.substs.iter().find(|s| s.has_non_region_infer());
2118 let mut err = if let Some(subst) = subst {
2119 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2125 "type annotations needed: cannot satisfy `{}`",
2130 let obligation = Obligation::new(
2131 obligation.cause.clone(),
2132 obligation.param_env,
2133 trait_ref.to_poly_trait_predicate(),
2135 let mut selcx = SelectionContext::with_query_mode(
2137 crate::traits::TraitQueryMode::Standard,
2139 match selcx.select_from_obligation(&obligation) {
2141 let impls = ambiguity::recompute_applicable_impls(self.infcx, &obligation);
2142 let has_non_region_infer =
2143 trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_infer());
2144 // It doesn't make sense to talk about applicable impls if there are more
2145 // than a handful of them.
2146 if impls.len() > 1 && impls.len() < 5 && has_non_region_infer {
2147 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2149 if self.is_tainted_by_errors() {
2153 err.note(&format!("cannot satisfy `{}`", predicate));
2157 if self.is_tainted_by_errors() {
2161 err.note(&format!("cannot satisfy `{}`", predicate));
2165 if let ObligationCauseCode::ItemObligation(def_id) | ObligationCauseCode::ExprItemObligation(def_id, ..) = *obligation.cause.code() {
2166 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2167 } else if let Ok(snippet) = &self.tcx.sess.source_map().span_to_snippet(span)
2168 && let ObligationCauseCode::BindingObligation(def_id, _) | ObligationCauseCode::ExprBindingObligation(def_id, ..)
2169 = *obligation.cause.code()
2171 let generics = self.tcx.generics_of(def_id);
2172 if generics.params.iter().any(|p| p.name != kw::SelfUpper)
2173 && !snippet.ends_with('>')
2174 && !generics.has_impl_trait()
2175 && !self.tcx.fn_trait_kind_from_lang_item(def_id).is_some()
2177 // FIXME: To avoid spurious suggestions in functions where type arguments
2178 // where already supplied, we check the snippet to make sure it doesn't
2179 // end with a turbofish. Ideally we would have access to a `PathSegment`
2180 // instead. Otherwise we would produce the following output:
2182 // error[E0283]: type annotations needed
2183 // --> $DIR/issue-54954.rs:3:24
2185 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2186 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2188 // | cannot infer type
2189 // | help: consider specifying the type argument
2190 // | in the function call:
2191 // | `Tt::const_val::<[i8; 123]>::<T>`
2193 // LL | const fn const_val<T: Sized>() -> usize {
2194 // | - required by this bound in `Tt::const_val`
2196 // = note: cannot satisfy `_: Tt`
2198 // Clear any more general suggestions in favor of our specific one
2199 err.clear_suggestions();
2201 err.span_suggestion_verbose(
2202 span.shrink_to_hi(),
2204 "consider specifying the type argument{} in the function call",
2205 pluralize!(generics.params.len()),
2212 .map(|p| p.name.to_string())
2213 .collect::<Vec<String>>()
2216 Applicability::HasPlaceholders,
2221 if let (Some(body_id), Some(ty::subst::GenericArgKind::Type(_))) =
2222 (body_id, subst.map(|subst| subst.unpack()))
2224 struct FindExprBySpan<'hir> {
2226 result: Option<&'hir hir::Expr<'hir>>,
2229 impl<'v> hir::intravisit::Visitor<'v> for FindExprBySpan<'v> {
2230 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2231 if self.span == ex.span {
2232 self.result = Some(ex);
2234 hir::intravisit::walk_expr(self, ex);
2239 let mut expr_finder = FindExprBySpan { span, result: None };
2241 expr_finder.visit_expr(&self.tcx.hir().body(body_id).value);
2243 if let Some(hir::Expr {
2244 kind: hir::ExprKind::Path(hir::QPath::Resolved(None, path)), .. }
2245 ) = expr_finder.result
2248 trait_path_segment @ hir::PathSegment {
2249 res: rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id),
2253 ident: assoc_item_name,
2254 res: rustc_hir::def::Res::Def(_, item_id),
2258 && data.trait_ref.def_id == *trait_id
2259 && self.tcx.trait_of_item(*item_id) == Some(*trait_id)
2260 && !self.is_tainted_by_errors()
2262 let (verb, noun) = match self.tcx.associated_item(item_id).kind {
2263 ty::AssocKind::Const => ("refer to the", "constant"),
2264 ty::AssocKind::Fn => ("call", "function"),
2265 ty::AssocKind::Type => ("refer to the", "type"), // this is already covered by E0223, but this single match arm doesn't hurt here
2268 // Replace the more general E0283 with a more specific error
2270 err = self.tcx.sess.struct_span_err_with_code(
2273 "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type",
2275 rustc_errors::error_code!(E0790),
2278 if let Some(local_def_id) = data.trait_ref.def_id.as_local()
2279 && let Some(hir::Node::Item(hir::Item { ident: trait_name, kind: hir::ItemKind::Trait(_, _, _, _, trait_item_refs), .. })) = self.tcx.hir().find_by_def_id(local_def_id)
2280 && let Some(method_ref) = trait_item_refs.iter().find(|item_ref| item_ref.ident == *assoc_item_name) {
2281 err.span_label(method_ref.span, format!("`{}::{}` defined here", trait_name, assoc_item_name));
2284 err.span_label(span, format!("cannot {verb} associated {noun} of trait"));
2286 let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
2288 if trait_impls.blanket_impls().is_empty()
2289 && let Some((impl_ty, _)) = trait_impls.non_blanket_impls().iter().next()
2290 && let Some(impl_def_id) = impl_ty.def() {
2291 let message = if trait_impls.non_blanket_impls().len() == 1 {
2292 "use the fully-qualified path to the only available implementation".to_string()
2295 "use a fully-qualified path to a specific available implementation ({} found)",
2296 trait_impls.non_blanket_impls().len()
2299 let mut suggestions = vec![(
2300 trait_path_segment.ident.span.shrink_to_lo(),
2301 format!("<{} as ", self.tcx.type_of(impl_def_id))
2303 if let Some(generic_arg) = trait_path_segment.args {
2304 let between_span = trait_path_segment.ident.span.between(generic_arg.span_ext);
2305 // get rid of :: between Trait and <type>
2306 // must be '::' between them, otherwise the parser won't accept the code
2307 suggestions.push((between_span, "".to_string(),));
2308 suggestions.push((generic_arg.span_ext.shrink_to_hi(), format!(">")));
2310 suggestions.push((trait_path_segment.ident.span.shrink_to_hi(), format!(">")));
2312 err.multipart_suggestion(
2315 Applicability::MaybeIncorrect
2324 ty::PredicateKind::WellFormed(arg) => {
2325 // Same hacky approach as above to avoid deluging user
2326 // with error messages.
2327 if arg.references_error()
2328 || self.tcx.sess.has_errors().is_some()
2329 || self.is_tainted_by_errors()
2334 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2337 ty::PredicateKind::Subtype(data) => {
2338 if data.references_error()
2339 || self.tcx.sess.has_errors().is_some()
2340 || self.is_tainted_by_errors()
2342 // no need to overload user in such cases
2345 let SubtypePredicate { a_is_expected: _, a, b } = data;
2346 // both must be type variables, or the other would've been instantiated
2347 assert!(a.is_ty_var() && b.is_ty_var());
2348 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2350 ty::PredicateKind::Projection(data) => {
2351 if predicate.references_error() || self.is_tainted_by_errors() {
2358 .chain(Some(data.term.into_arg()))
2359 .find(|g| g.has_non_region_infer());
2360 if let Some(subst) = subst {
2361 let mut err = self.emit_inference_failure_err(
2368 err.note(&format!("cannot satisfy `{}`", predicate));
2371 // If we can't find a substitution, just print a generic error
2372 let mut err = struct_span_err!(
2376 "type annotations needed: cannot satisfy `{}`",
2379 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2384 ty::PredicateKind::ConstEvaluatable(data) => {
2385 if predicate.references_error() || self.is_tainted_by_errors() {
2388 let subst = data.walk().find(|g| g.is_non_region_infer());
2389 if let Some(subst) = subst {
2390 let err = self.emit_inference_failure_err(
2399 // If we can't find a substitution, just print a generic error
2400 let mut err = struct_span_err!(
2404 "type annotations needed: cannot satisfy `{}`",
2407 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2412 if self.tcx.sess.has_errors().is_some() || self.is_tainted_by_errors() {
2415 let mut err = struct_span_err!(
2419 "type annotations needed: cannot satisfy `{}`",
2422 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2426 self.note_obligation_cause(&mut err, obligation);
2430 fn annotate_source_of_ambiguity(
2432 err: &mut Diagnostic,
2434 predicate: ty::Predicate<'tcx>,
2436 let mut spans = vec![];
2437 let mut crates = vec![];
2438 let mut post = vec![];
2439 for def_id in impls {
2440 match self.tcx.span_of_impl(*def_id) {
2441 Ok(span) => spans.push(span),
2444 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2450 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2452 crate_names.dedup();
2456 if self.is_tainted_by_errors()
2457 && (crate_names.len() == 1
2459 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2460 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2462 // Avoid complaining about other inference issues for expressions like
2463 // `42 >> 1`, where the types are still `{integer}`, but we want to
2464 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2465 // NOTE(eddyb) this was `.cancel()`, but `err`
2466 // is borrowed, so we can't fully defuse it.
2467 err.downgrade_to_delayed_bug();
2471 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2472 let post = if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2473 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2474 } else if post.len() == 1 {
2475 format!(": `{}`", post[0])
2480 match (spans.len(), crates.len(), crate_names.len()) {
2482 err.note(&format!("cannot satisfy `{}`", predicate));
2485 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2489 "{} in the following crates: {}{}",
2491 crate_names.join(", "),
2496 let span: MultiSpan = spans.into();
2497 err.span_note(span, &msg);
2500 let span: MultiSpan = spans.into();
2501 err.span_note(span, &msg);
2503 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2507 let span: MultiSpan = spans.into();
2508 err.span_note(span, &msg);
2510 "and more `impl`s found in the following crates: {}{}",
2511 crate_names.join(", "),
2518 /// Returns `true` if the trait predicate may apply for *some* assignment
2519 /// to the type parameters.
2520 fn predicate_can_apply(
2522 param_env: ty::ParamEnv<'tcx>,
2523 pred: ty::PolyTraitPredicate<'tcx>,
2525 struct ParamToVarFolder<'a, 'tcx> {
2526 infcx: &'a InferCtxt<'tcx>,
2527 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2530 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2531 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2535 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2536 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2537 let infcx = self.infcx;
2538 *self.var_map.entry(ty).or_insert_with(|| {
2539 infcx.next_ty_var(TypeVariableOrigin {
2540 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2545 ty.super_fold_with(self)
2551 let mut selcx = SelectionContext::new(self);
2554 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2556 let cleaned_pred = super::project::normalize(
2559 ObligationCause::dummy(),
2564 let obligation = Obligation::new(
2565 ObligationCause::dummy(),
2567 cleaned_pred.to_predicate(selcx.tcx()),
2570 self.predicate_may_hold(&obligation)
2574 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2575 // First, attempt to add note to this error with an async-await-specific
2576 // message, and fall back to regular note otherwise.
2577 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2578 self.note_obligation_cause_code(
2580 &obligation.predicate,
2581 obligation.param_env,
2582 obligation.cause.code(),
2584 &mut Default::default(),
2586 self.suggest_unsized_bound_if_applicable(err, obligation);
2590 #[instrument(level = "debug", skip_all)]
2591 fn suggest_unsized_bound_if_applicable(
2593 err: &mut Diagnostic,
2594 obligation: &PredicateObligation<'tcx>,
2596 let ty::PredicateKind::Trait(pred) = obligation.predicate.kind().skip_binder() else { return; };
2597 let (ObligationCauseCode::BindingObligation(item_def_id, span)
2598 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..))
2599 = *obligation.cause.code().peel_derives() else { return; };
2600 debug!(?pred, ?item_def_id, ?span);
2602 let (Some(node), true) = (
2603 self.tcx.hir().get_if_local(item_def_id),
2604 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2608 self.maybe_suggest_unsized_generics(err, span, node);
2611 #[instrument(level = "debug", skip_all)]
2612 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>) {
2613 let Some(generics) = node.generics() else {
2616 let sized_trait = self.tcx.lang_items().sized_trait();
2617 debug!(?generics.params);
2618 debug!(?generics.predicates);
2619 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2622 let param_def_id = self.tcx.hir().local_def_id(param.hir_id);
2623 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2624 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2625 let explicitly_sized = generics
2626 .bounds_for_param(param_def_id)
2627 .flat_map(|bp| bp.bounds)
2628 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2629 if explicitly_sized {
2636 // Only suggest indirection for uses of type parameters in ADTs.
2638 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2642 if self.maybe_indirection_for_unsized(err, item, param) {
2648 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2649 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param_def_id)
2653 (span.shrink_to_hi(), ":")
2655 err.span_suggestion_verbose(
2657 "consider relaxing the implicit `Sized` restriction",
2658 format!("{} ?Sized", separator),
2659 Applicability::MachineApplicable,
2663 fn maybe_indirection_for_unsized(
2665 err: &mut Diagnostic,
2667 param: &GenericParam<'tcx>,
2669 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2670 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2671 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2673 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2674 visitor.visit_item(item);
2675 if visitor.invalid_spans.is_empty() {
2678 let mut multispan: MultiSpan = param.span.into();
2679 multispan.push_span_label(
2681 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2683 for sp in visitor.invalid_spans {
2684 multispan.push_span_label(
2686 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2692 "you could relax the implicit `Sized` bound on `{T}` if it were \
2693 used through indirection like `&{T}` or `Box<{T}>`",
2694 T = param.name.ident(),
2700 fn is_recursive_obligation(
2702 obligated_types: &mut Vec<Ty<'tcx>>,
2703 cause_code: &ObligationCauseCode<'tcx>,
2705 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2706 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2707 let self_ty = parent_trait_ref.skip_binder().self_ty();
2708 if obligated_types.iter().any(|ot| ot == &self_ty) {
2711 if let ty::Adt(def, substs) = self_ty.kind()
2712 && let [arg] = &substs[..]
2713 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2714 && let ty::Adt(inner_def, _) = ty.kind()
2724 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2725 /// `param: ?Sized` would be a valid constraint.
2726 struct FindTypeParam {
2727 param: rustc_span::Symbol,
2728 invalid_spans: Vec<Span>,
2732 impl<'v> Visitor<'v> for FindTypeParam {
2733 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2734 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2737 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2738 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2739 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2740 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2741 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2742 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2743 // in that case should make what happened clear enough.
2745 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2746 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2747 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2750 debug!(?ty, "FindTypeParam::visit_ty");
2751 self.invalid_spans.push(ty.span);
2754 hir::TyKind::Path(_) => {
2755 let prev = self.nested;
2757 hir::intravisit::walk_ty(self, ty);
2761 hir::intravisit::walk_ty(self, ty);
2767 /// Summarizes information
2770 /// An argument of non-tuple type. Parameters are (name, ty)
2771 Arg(String, String),
2773 /// An argument of tuple type. For a "found" argument, the span is
2774 /// the location in the source of the pattern. For an "expected"
2775 /// argument, it will be None. The vector is a list of (name, ty)
2776 /// strings for the components of the tuple.
2777 Tuple(Option<Span>, Vec<(String, String)>),
2781 fn empty() -> ArgKind {
2782 ArgKind::Arg("_".to_owned(), "_".to_owned())
2785 /// Creates an `ArgKind` from the expected type of an
2786 /// argument. It has no name (`_`) and an optional source span.
2787 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2789 ty::Tuple(tys) => ArgKind::Tuple(
2791 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2793 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2798 struct HasNumericInferVisitor;
2800 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2803 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2804 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2805 ControlFlow::Break(())
2807 ControlFlow::CONTINUE
2812 pub enum DefIdOrName {