2 pub mod on_unimplemented;
6 FulfillmentContext, FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes,
7 Obligation, ObligationCause, ObligationCauseCode, OutputTypeParameterMismatch, Overflow,
8 PredicateObligation, 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::query::evaluate_obligation::InferCtxtExt as _;
14 use crate::traits::query::normalize::AtExt as _;
15 use crate::traits::specialize::to_pretty_impl_header;
16 use on_unimplemented::OnUnimplementedNote;
17 use on_unimplemented::TypeErrCtxtExt as _;
18 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
20 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
24 use rustc_hir::def_id::DefId;
25 use rustc_hir::intravisit::Visitor;
26 use rustc_hir::GenericParam;
29 use rustc_infer::infer::error_reporting::TypeErrCtxt;
30 use rustc_infer::infer::TypeTrace;
31 use rustc_infer::traits::TraitEngine;
32 use rustc_middle::traits::select::OverflowError;
33 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
34 use rustc_middle::ty::error::ExpectedFound;
35 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
36 use rustc_middle::ty::{
37 self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
40 use rustc_session::Limit;
41 use rustc_span::def_id::LOCAL_CRATE;
42 use rustc_span::symbol::{kw, sym};
43 use rustc_span::{ExpnKind, Span, DUMMY_SP};
46 use std::ops::ControlFlow;
47 use suggestions::TypeErrCtxtExt as _;
49 pub use rustc_infer::traits::error_reporting::*;
51 // When outputting impl candidates, prefer showing those that are more similar.
53 // We also compare candidates after skipping lifetimes, which has a lower
54 // priority than exact matches.
55 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
56 pub enum CandidateSimilarity {
57 Exact { ignoring_lifetimes: bool },
58 Fuzzy { ignoring_lifetimes: bool },
61 #[derive(Debug, Clone, Copy)]
62 pub struct ImplCandidate<'tcx> {
63 pub trait_ref: ty::TraitRef<'tcx>,
64 pub similarity: CandidateSimilarity,
67 pub trait InferCtxtExt<'tcx> {
68 /// Given some node representing a fn-like thing in the HIR map,
69 /// returns a span and `ArgKind` information that describes the
70 /// arguments it expects. This can be supplied to
71 /// `report_arg_count_mismatch`.
72 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)>;
74 /// Reports an error when the number of arguments needed by a
75 /// trait match doesn't match the number that the expression
77 fn report_arg_count_mismatch(
80 found_span: Option<Span>,
81 expected_args: Vec<ArgKind>,
82 found_args: Vec<ArgKind>,
84 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
86 /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
87 /// in that order, and returns the generic type corresponding to the
88 /// argument of that trait (corresponding to the closure arguments).
89 fn type_implements_fn_trait(
91 param_env: ty::ParamEnv<'tcx>,
92 ty: ty::Binder<'tcx, Ty<'tcx>>,
93 constness: ty::BoundConstness,
94 polarity: ty::ImplPolarity,
95 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
98 pub trait TypeErrCtxtExt<'tcx> {
99 fn report_fulfillment_errors(
101 errors: &[FulfillmentError<'tcx>],
102 body_id: Option<hir::BodyId>,
103 ) -> ErrorGuaranteed;
105 fn report_overflow_error<T>(
107 obligation: &Obligation<'tcx, T>,
108 suggest_increasing_limit: bool,
111 T: fmt::Display + TypeFoldable<'tcx>;
113 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
115 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
117 /// The `root_obligation` parameter should be the `root_obligation` field
118 /// from a `FulfillmentError`. If no `FulfillmentError` is available,
119 /// then it should be the same as `obligation`.
120 fn report_selection_error(
122 obligation: PredicateObligation<'tcx>,
123 root_obligation: &PredicateObligation<'tcx>,
124 error: &SelectionError<'tcx>,
128 impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
129 /// Given some node representing a fn-like thing in the HIR map,
130 /// returns a span and `ArgKind` information that describes the
131 /// arguments it expects. This can be supplied to
132 /// `report_arg_count_mismatch`.
133 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
134 let sm = self.tcx.sess.source_map();
135 let hir = self.tcx.hir();
137 Node::Expr(&hir::Expr {
138 kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }),
146 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
153 sm.span_to_snippet(pat.span)
155 .map(|snippet| (snippet, "_".to_owned()))
157 .collect::<Option<Vec<_>>>()?,
160 let name = sm.span_to_snippet(arg.pat.span).ok()?;
161 Some(ArgKind::Arg(name, "_".to_owned()))
164 .collect::<Option<Vec<ArgKind>>>()?,
166 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
167 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
168 | Node::TraitItem(&hir::TraitItem {
169 kind: hir::TraitItemKind::Fn(ref sig, _), ..
175 .map(|arg| match arg.kind {
176 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
178 vec![("_".to_owned(), "_".to_owned()); tys.len()],
180 _ => ArgKind::empty(),
182 .collect::<Vec<ArgKind>>(),
184 Node::Ctor(ref variant_data) => {
185 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
186 (span, vec![ArgKind::empty(); variant_data.fields().len()])
188 _ => panic!("non-FnLike node found: {:?}", node),
192 /// Reports an error when the number of arguments needed by a
193 /// trait match doesn't match the number that the expression
195 fn report_arg_count_mismatch(
198 found_span: Option<Span>,
199 expected_args: Vec<ArgKind>,
200 found_args: Vec<ArgKind>,
202 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
203 let kind = if is_closure { "closure" } else { "function" };
205 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
206 let arg_length = arguments.len();
207 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
208 match (arg_length, arguments.get(0)) {
209 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
210 format!("a single {}-tuple as argument", fields.len())
215 if distinct && arg_length > 1 { "distinct " } else { "" },
216 pluralize!(arg_length)
221 let expected_str = args_str(&expected_args, &found_args);
222 let found_str = args_str(&found_args, &expected_args);
224 let mut err = struct_span_err!(
228 "{} is expected to take {}, but it takes {}",
234 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
236 if let Some(found_span) = found_span {
237 err.span_label(found_span, format!("takes {}", found_str));
240 // ^^^^^^^^-- def_span
244 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
248 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
250 // Suggest to take and ignore the arguments with expected_args_length `_`s if
251 // found arguments is empty (assume the user just wants to ignore args in this case).
252 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
253 if found_args.is_empty() && is_closure {
254 let underscores = vec!["_"; expected_args.len()].join(", ");
255 err.span_suggestion_verbose(
258 "consider changing the closure to take and ignore the expected argument{}",
259 pluralize!(expected_args.len())
261 format!("|{}|", underscores),
262 Applicability::MachineApplicable,
266 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
267 if fields.len() == expected_args.len() {
270 .map(|(name, _)| name.to_owned())
271 .collect::<Vec<String>>()
273 err.span_suggestion_verbose(
275 "change the closure to take multiple arguments instead of a single tuple",
276 format!("|{}|", sugg),
277 Applicability::MachineApplicable,
281 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
282 && fields.len() == found_args.len()
289 .map(|arg| match arg {
290 ArgKind::Arg(name, _) => name.to_owned(),
293 .collect::<Vec<String>>()
295 // add type annotations if available
296 if found_args.iter().any(|arg| match arg {
297 ArgKind::Arg(_, ty) => ty != "_",
304 .map(|(_, ty)| ty.to_owned())
305 .collect::<Vec<String>>()
312 err.span_suggestion_verbose(
314 "change the closure to accept a tuple instead of individual arguments",
316 Applicability::MachineApplicable,
324 fn type_implements_fn_trait(
326 param_env: ty::ParamEnv<'tcx>,
327 ty: ty::Binder<'tcx, Ty<'tcx>>,
328 constness: ty::BoundConstness,
329 polarity: ty::ImplPolarity,
330 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
331 self.commit_if_ok(|_| {
332 for trait_def_id in [
333 self.tcx.lang_items().fn_trait(),
334 self.tcx.lang_items().fn_mut_trait(),
335 self.tcx.lang_items().fn_once_trait(),
337 let Some(trait_def_id) = trait_def_id else { continue };
338 // Make a fresh inference variable so we can determine what the substitutions
340 let var = self.next_ty_var(TypeVariableOrigin {
342 kind: TypeVariableOriginKind::MiscVariable,
344 let substs = self.tcx.mk_substs_trait(ty.skip_binder(), &[var.into()]);
345 let obligation = Obligation::new(
346 ObligationCause::dummy(),
348 ty.rebind(ty::TraitPredicate {
349 trait_ref: ty::TraitRef::new(trait_def_id, substs),
353 .to_predicate(self.tcx),
355 let mut fulfill_cx = FulfillmentContext::new_in_snapshot();
356 fulfill_cx.register_predicate_obligation(self, obligation);
357 if fulfill_cx.select_all_or_error(self).is_empty() {
359 ty::ClosureKind::from_def_id(self.tcx, trait_def_id)
360 .expect("expected to map DefId to ClosureKind"),
361 ty.rebind(self.resolve_vars_if_possible(var)),
370 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
371 fn report_fulfillment_errors(
373 errors: &[FulfillmentError<'tcx>],
374 body_id: Option<hir::BodyId>,
375 ) -> ErrorGuaranteed {
377 struct ErrorDescriptor<'tcx> {
378 predicate: ty::Predicate<'tcx>,
379 index: Option<usize>, // None if this is an old error
382 let mut error_map: FxIndexMap<_, Vec<_>> = self
383 .reported_trait_errors
386 .map(|(&span, predicates)| {
391 .map(|&predicate| ErrorDescriptor { predicate, index: None })
397 for (index, error) in errors.iter().enumerate() {
398 // We want to ignore desugarings here: spans are equivalent even
399 // if one is the result of a desugaring and the other is not.
400 let mut span = error.obligation.cause.span;
401 let expn_data = span.ctxt().outer_expn_data();
402 if let ExpnKind::Desugaring(_) = expn_data.kind {
403 span = expn_data.call_site;
406 error_map.entry(span).or_default().push(ErrorDescriptor {
407 predicate: error.obligation.predicate,
411 self.reported_trait_errors
415 .push(error.obligation.predicate);
418 // We do this in 2 passes because we want to display errors in order, though
419 // maybe it *is* better to sort errors by span or something.
420 let mut is_suppressed = vec![false; errors.len()];
421 for (_, error_set) in error_map.iter() {
422 // We want to suppress "duplicate" errors with the same span.
423 for error in error_set {
424 if let Some(index) = error.index {
425 // Suppress errors that are either:
426 // 1) strictly implied by another error.
427 // 2) implied by an error with a smaller index.
428 for error2 in error_set {
429 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
430 // Avoid errors being suppressed by already-suppressed
431 // errors, to prevent all errors from being suppressed
436 if self.error_implies(error2.predicate, error.predicate)
437 && !(error2.index >= error.index
438 && self.error_implies(error.predicate, error2.predicate))
440 info!("skipping {:?} (implied by {:?})", error, error2);
441 is_suppressed[index] = true;
449 for (error, suppressed) in iter::zip(errors, is_suppressed) {
451 self.report_fulfillment_error(error, body_id);
455 self.tcx.sess.delay_span_bug(DUMMY_SP, "expected fullfillment errors")
458 /// Reports that an overflow has occurred and halts compilation. We
459 /// halt compilation unconditionally because it is important that
460 /// overflows never be masked -- they basically represent computations
461 /// whose result could not be truly determined and thus we can't say
462 /// if the program type checks or not -- and they are unusual
463 /// occurrences in any case.
464 fn report_overflow_error<T>(
466 obligation: &Obligation<'tcx, T>,
467 suggest_increasing_limit: bool,
470 T: fmt::Display + TypeFoldable<'tcx>,
472 let predicate = self.resolve_vars_if_possible(obligation.predicate.clone());
473 let mut err = struct_span_err!(
475 obligation.cause.span,
477 "overflow evaluating the requirement `{}`",
481 if suggest_increasing_limit {
482 self.suggest_new_overflow_limit(&mut err);
485 self.note_obligation_cause_code(
487 &obligation.predicate,
488 obligation.param_env,
489 obligation.cause.code(),
491 &mut Default::default(),
495 self.tcx.sess.abort_if_errors();
499 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic) {
500 let suggested_limit = match self.tcx.recursion_limit() {
501 Limit(0) => Limit(2),
505 "consider increasing the recursion limit by adding a \
506 `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
508 self.tcx.crate_name(LOCAL_CRATE),
512 /// Reports that a cycle was detected which led to overflow and halts
513 /// compilation. This is equivalent to `report_overflow_error` except
514 /// that we can give a more helpful error message (and, in particular,
515 /// we do not suggest increasing the overflow limit, which is not
517 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
518 let cycle = self.resolve_vars_if_possible(cycle.to_owned());
519 assert!(!cycle.is_empty());
521 debug!(?cycle, "report_overflow_error_cycle");
523 // The 'deepest' obligation is most likely to have a useful
525 self.report_overflow_error(cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(), false);
528 fn report_selection_error(
530 mut obligation: PredicateObligation<'tcx>,
531 root_obligation: &PredicateObligation<'tcx>,
532 error: &SelectionError<'tcx>,
534 self.set_tainted_by_errors();
536 let mut span = obligation.cause.span;
538 let mut err = match *error {
539 SelectionError::Unimplemented => {
540 // If this obligation was generated as a result of well-formedness checking, see if we
541 // can get a better error message by performing HIR-based well-formedness checking.
542 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
543 root_obligation.cause.code().peel_derives()
545 if let Some(cause) = self
547 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
549 obligation.cause = cause.clone();
550 span = obligation.cause.span;
553 if let ObligationCauseCode::CompareImplItemObligation {
557 } = *obligation.cause.code()
559 self.report_extra_impl_obligation(
563 &format!("`{}`", obligation.predicate),
569 let bound_predicate = obligation.predicate.kind();
570 match bound_predicate.skip_binder() {
571 ty::PredicateKind::Trait(trait_predicate) => {
572 let trait_predicate = bound_predicate.rebind(trait_predicate);
573 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
575 trait_predicate.remap_constness_diag(obligation.param_env);
576 let predicate_is_const = ty::BoundConstness::ConstIfConst
577 == trait_predicate.skip_binder().constness;
579 if self.tcx.sess.has_errors().is_some()
580 && trait_predicate.references_error()
584 let trait_ref = trait_predicate.to_poly_trait_ref();
585 let (post_message, pre_message, type_def) = self
586 .get_parent_trait_ref(obligation.cause.code())
589 format!(" in `{}`", t),
590 format!("within `{}`, ", t),
591 s.map(|s| (format!("within this `{}`", t), s)),
594 .unwrap_or_default();
596 let OnUnimplementedNote {
602 } = self.on_unimplemented_note(trait_ref, &obligation);
603 let have_alt_message = message.is_some() || label.is_some();
604 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
606 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
607 let (message, note, append_const_msg) = if is_try_conversion {
610 "`?` couldn't convert the error to `{}`",
611 trait_ref.skip_binder().self_ty(),
614 "the question mark operation (`?`) implicitly performs a \
615 conversion on the error value using the `From` trait"
621 (message, note, append_const_msg)
624 let mut err = struct_span_err!(
630 .and_then(|cannot_do_this| {
631 match (predicate_is_const, append_const_msg) {
632 // do nothing if predicate is not const
633 (false, _) => Some(cannot_do_this),
634 // suggested using default post message
635 (true, Some(None)) => {
636 Some(format!("{cannot_do_this} in const contexts"))
638 // overridden post message
639 (true, Some(Some(post_message))) => {
640 Some(format!("{cannot_do_this}{post_message}"))
642 // fallback to generic message
643 (true, None) => None,
646 .unwrap_or_else(|| format!(
647 "the trait bound `{}` is not satisfied{}",
648 trait_predicate, post_message,
652 if is_try_conversion {
653 let none_error = self
655 .get_diagnostic_item(sym::none_error)
656 .map(|def_id| tcx.type_of(def_id));
657 let should_convert_option_to_result =
658 Some(trait_ref.skip_binder().substs.type_at(1)) == none_error;
659 let should_convert_result_to_option =
660 Some(trait_ref.self_ty().skip_binder()) == none_error;
661 if should_convert_option_to_result {
662 err.span_suggestion_verbose(
664 "consider converting the `Option<T>` into a `Result<T, _>` \
665 using `Option::ok_or` or `Option::ok_or_else`",
666 ".ok_or_else(|| /* error value */)",
667 Applicability::HasPlaceholders,
669 } else if should_convert_result_to_option {
670 err.span_suggestion_verbose(
672 "consider converting the `Result<T, _>` into an `Option<T>` \
675 Applicability::MachineApplicable,
678 if let Some(ret_span) = self.return_type_span(&obligation) {
682 "expected `{}` because of this",
683 trait_ref.skip_binder().self_ty()
689 if Some(trait_ref.def_id()) == tcx.lang_items().tuple_trait() {
690 match obligation.cause.code().peel_derives() {
691 ObligationCauseCode::RustCall => {
692 err.set_primary_message("functions with the \"rust-call\" ABI must take a single non-self tuple argument");
694 ObligationCauseCode::BindingObligation(def_id, _)
695 | ObligationCauseCode::ItemObligation(def_id)
696 if ty::ClosureKind::from_def_id(tcx, *def_id).is_some() =>
698 err.code(rustc_errors::error_code!(E0059));
699 err.set_primary_message(format!(
700 "type parameter to bare `{}` trait must be a tuple",
701 tcx.def_path_str(*def_id)
708 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
709 && predicate_is_const
711 err.note("`~const Drop` was renamed to `~const Destruct`");
712 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
715 let explanation = if let ObligationCauseCode::MainFunctionType =
716 obligation.cause.code()
718 "consider using `()`, or a `Result`".to_owned()
720 let ty_desc = match trait_ref.skip_binder().self_ty().kind() {
721 ty::FnDef(_, _) => Some("fn item"),
722 ty::Closure(_, _) => Some("closure"),
727 Some(desc) => format!(
728 "{}the trait `{}` is not implemented for {} `{}`",
730 trait_predicate.print_modifiers_and_trait_path(),
732 trait_ref.skip_binder().self_ty(),
735 "{}the trait `{}` is not implemented for `{}`",
737 trait_predicate.print_modifiers_and_trait_path(),
738 trait_ref.skip_binder().self_ty(),
743 if self.suggest_add_reference_to_arg(
749 self.note_obligation_cause(&mut err, &obligation);
753 if let Some(ref s) = label {
754 // If it has a custom `#[rustc_on_unimplemented]`
755 // error message, let's display it as the label!
756 err.span_label(span, s);
757 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
758 // When the self type is a type param We don't need to "the trait
759 // `std::marker::Sized` is not implemented for `T`" as we will point
760 // at the type param with a label to suggest constraining it.
761 err.help(&explanation);
764 err.span_label(span, explanation);
767 if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
768 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
769 self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
772 let mut unsatisfied_const = false;
773 if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
774 let non_const_predicate = trait_ref.without_const();
775 let non_const_obligation = Obligation {
776 cause: obligation.cause.clone(),
777 param_env: obligation.param_env.without_const(),
778 predicate: non_const_predicate.to_predicate(tcx),
779 recursion_depth: obligation.recursion_depth,
781 if self.predicate_may_hold(&non_const_obligation) {
782 unsatisfied_const = true;
786 "the trait `{}` is implemented for `{}`, \
787 but that implementation is not `const`",
788 non_const_predicate.print_modifiers_and_trait_path(),
789 trait_ref.skip_binder().self_ty(),
795 if let Some((msg, span)) = type_def {
796 err.span_label(span, &msg);
798 if let Some(ref s) = note {
799 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
800 err.note(s.as_str());
802 if let Some(ref s) = parent_label {
805 .opt_local_def_id(obligation.cause.body_id)
807 tcx.hir().body_owner_def_id(hir::BodyId {
808 hir_id: obligation.cause.body_id,
811 err.span_label(tcx.def_span(body), s);
814 self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
815 self.suggest_dereferencing_index(&obligation, &mut err, trait_predicate);
817 self.suggest_dereferences(&obligation, &mut err, trait_predicate);
818 suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
820 self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
821 suggested |= self.suggest_semicolon_removal(
827 self.note_version_mismatch(&mut err, &trait_ref);
828 self.suggest_remove_await(&obligation, &mut err);
829 self.suggest_derive(&obligation, &mut err, trait_predicate);
831 if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
832 self.suggest_await_before_try(
840 if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
846 // If the obligation failed due to a missing implementation of the
847 // `Unsize` trait, give a pointer to why that might be the case
849 "all implementations of `Unsize` are provided \
850 automatically by the compiler, see \
851 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
852 for more information",
857 ty::ClosureKind::from_def_id(tcx, trait_ref.def_id()).is_some();
858 let is_target_feature_fn = if let ty::FnDef(def_id, _) =
859 *trait_ref.skip_binder().self_ty().kind()
861 !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
865 if is_fn_trait && is_target_feature_fn {
867 "`#[target_feature]` functions do not implement the `Fn` traits",
871 // Try to report a help message
873 && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
874 obligation.param_env,
876 trait_predicate.skip_binder().constness,
877 trait_predicate.skip_binder().polarity,
880 // If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
881 // suggestion to add trait bounds for the type, since we only typically implement
882 // these traits once.
884 // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
887 ty::ClosureKind::from_def_id(self.tcx, trait_ref.def_id())
888 .expect("expected to map DefId to ClosureKind");
889 if !implemented_kind.extends(selected_kind) {
892 "`{}` implements `{}`, but it must implement `{}`, which is more general",
893 trait_ref.skip_binder().self_ty(),
900 // Note any argument mismatches
901 let given_ty = params.skip_binder();
902 let expected_ty = trait_ref.skip_binder().substs.type_at(1);
903 if let ty::Tuple(given) = given_ty.kind()
904 && let ty::Tuple(expected) = expected_ty.kind()
906 if expected.len() != given.len() {
907 // Note number of types that were expected and given
910 "expected a closure taking {} argument{}, but one taking {} argument{} was given",
912 pluralize!(given.len()),
914 pluralize!(expected.len()),
917 } else if !self.same_type_modulo_infer(given_ty, expected_ty) {
918 // Print type mismatch
919 let (expected_args, given_args) =
920 self.cmp(given_ty, expected_ty);
921 err.note_expected_found(
922 &"a closure with arguments",
924 &"a closure with arguments",
929 } else if !trait_ref.has_non_region_infer()
930 && self.predicate_can_apply(obligation.param_env, trait_predicate)
932 // If a where-clause may be useful, remind the
933 // user that they can add it.
935 // don't display an on-unimplemented note, as
936 // these notes will often be of the form
937 // "the type `T` can't be frobnicated"
938 // which is somewhat confusing.
939 self.suggest_restricting_param_bound(
943 obligation.cause.body_id,
945 } else if !suggested && !unsatisfied_const {
946 // Can't show anything else useful, try to find similar impls.
947 let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
948 if !self.report_similar_impl_candidates(
951 obligation.cause.body_id,
954 // This is *almost* equivalent to
955 // `obligation.cause.code().peel_derives()`, but it gives us the
956 // trait predicate for that corresponding root obligation. This
957 // lets us get a derived obligation from a type parameter, like
958 // when calling `string.strip_suffix(p)` where `p` is *not* an
959 // implementer of `Pattern<'_>`.
960 let mut code = obligation.cause.code();
961 let mut trait_pred = trait_predicate;
962 let mut peeled = false;
963 while let Some((parent_code, parent_trait_pred)) = code.parent() {
965 if let Some(parent_trait_pred) = parent_trait_pred {
966 trait_pred = parent_trait_pred;
970 let def_id = trait_pred.def_id();
971 // Mention *all* the `impl`s for the *top most* obligation, the
972 // user might have meant to use one of them, if any found. We skip
973 // auto-traits or fundamental traits that might not be exactly what
974 // the user might expect to be presented with. Instead this is
975 // useful for less general traits.
977 && !self.tcx.trait_is_auto(def_id)
978 && !self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
980 let trait_ref = trait_pred.to_poly_trait_ref();
981 let impl_candidates =
982 self.find_similar_impl_candidates(trait_pred);
983 self.report_similar_impl_candidates(
986 obligation.cause.body_id,
993 // Changing mutability doesn't make a difference to whether we have
994 // an `Unsize` impl (Fixes ICE in #71036)
996 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
999 // If this error is due to `!: Trait` not implemented but `(): Trait` is
1000 // implemented, and fallback has occurred, then it could be due to a
1001 // variable that used to fallback to `()` now falling back to `!`. Issue a
1002 // note informing about the change in behaviour.
1003 if trait_predicate.skip_binder().self_ty().is_never()
1004 && self.fallback_has_occurred
1006 let predicate = trait_predicate.map_bound(|mut trait_pred| {
1007 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
1009 &trait_pred.trait_ref.substs[1..],
1013 let unit_obligation = obligation.with(predicate.to_predicate(tcx));
1014 if self.predicate_may_hold(&unit_obligation) {
1016 "this error might have been caused by changes to \
1017 Rust's type-inference algorithm (see issue #48950 \
1018 <https://github.com/rust-lang/rust/issues/48950> \
1019 for more information)",
1021 err.help("did you intend to use the type `()` here instead?");
1025 // Return early if the trait is Debug or Display and the invocation
1026 // originates within a standard library macro, because the output
1027 // is otherwise overwhelming and unhelpful (see #85844 for an
1031 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
1032 Some(macro_def_id) => {
1033 let crate_name = tcx.crate_name(macro_def_id.krate);
1034 crate_name == sym::std || crate_name == sym::core
1041 self.tcx.get_diagnostic_name(trait_ref.def_id()),
1042 Some(sym::Debug | sym::Display)
1052 ty::PredicateKind::Subtype(predicate) => {
1053 // Errors for Subtype predicates show up as
1054 // `FulfillmentErrorCode::CodeSubtypeError`,
1055 // not selection error.
1056 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
1059 ty::PredicateKind::Coerce(predicate) => {
1060 // Errors for Coerce predicates show up as
1061 // `FulfillmentErrorCode::CodeSubtypeError`,
1062 // not selection error.
1063 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
1066 ty::PredicateKind::RegionOutlives(..)
1067 | ty::PredicateKind::Projection(..)
1068 | ty::PredicateKind::TypeOutlives(..) => {
1069 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1074 "the requirement `{}` is not satisfied",
1079 ty::PredicateKind::ObjectSafe(trait_def_id) => {
1080 let violations = self.tcx.object_safety_violations(trait_def_id);
1081 report_object_safety_error(self.tcx, span, trait_def_id, violations)
1084 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
1085 let found_kind = self.closure_kind(closure_substs).unwrap();
1086 let closure_span = self.tcx.def_span(closure_def_id);
1087 let mut err = struct_span_err!(
1091 "expected a closure that implements the `{}` trait, \
1092 but this closure only implements `{}`",
1099 format!("this closure implements `{}`, not `{}`", found_kind, kind),
1102 obligation.cause.span,
1103 format!("the requirement to implement `{}` derives from here", kind),
1106 // Additional context information explaining why the closure only implements
1107 // a particular trait.
1108 if let Some(typeck_results) = &self.typeck_results {
1112 .local_def_id_to_hir_id(closure_def_id.expect_local());
1113 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
1114 (ty::ClosureKind::FnOnce, Some((span, place))) => {
1118 "closure is `FnOnce` because it moves the \
1119 variable `{}` out of its environment",
1120 ty::place_to_string_for_capture(tcx, place)
1124 (ty::ClosureKind::FnMut, Some((span, place))) => {
1128 "closure is `FnMut` because it mutates the \
1129 variable `{}` here",
1130 ty::place_to_string_for_capture(tcx, place)
1141 ty::PredicateKind::WellFormed(ty) => {
1142 if !self.tcx.sess.opts.unstable_opts.chalk {
1143 // WF predicates cannot themselves make
1144 // errors. They can only block due to
1145 // ambiguity; otherwise, they always
1146 // degenerate into other obligations
1147 // (which may fail).
1148 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
1150 // FIXME: we'll need a better message which takes into account
1151 // which bounds actually failed to hold.
1152 self.tcx.sess.struct_span_err(
1154 &format!("the type `{}` is not well-formed (chalk)", ty),
1159 ty::PredicateKind::ConstEvaluatable(..) => {
1160 // Errors for `ConstEvaluatable` predicates show up as
1161 // `SelectionError::ConstEvalFailure`,
1162 // not `Unimplemented`.
1165 "const-evaluatable requirement gave wrong error: `{:?}`",
1170 ty::PredicateKind::ConstEquate(..) => {
1171 // Errors for `ConstEquate` predicates show up as
1172 // `SelectionError::ConstEvalFailure`,
1173 // not `Unimplemented`.
1176 "const-equate requirement gave wrong error: `{:?}`",
1181 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
1183 "TypeWellFormedFromEnv predicate should only exist in the environment"
1188 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
1189 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
1190 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
1192 if expected_trait_ref.self_ty().references_error() {
1196 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
1200 let found_did = match *found_trait_ty.kind() {
1204 | ty::Generator(did, ..) => Some(did),
1205 ty::Adt(def, _) => Some(def.did()),
1209 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
1211 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1212 // We check closures twice, with obligations flowing in different directions,
1213 // but we want to complain about them only once.
1217 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1219 let mut not_tupled = false;
1221 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
1222 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1225 vec![ArgKind::empty()]
1229 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1230 let expected = match expected_ty.kind() {
1231 ty::Tuple(ref tys) => {
1232 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
1236 vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())]
1240 // If this is a `Fn` family trait and either the expected or found
1241 // is not tupled, then fall back to just a regular mismatch error.
1242 // This shouldn't be common unless manually implementing one of the
1243 // traits manually, but don't make it more confusing when it does
1245 if Some(expected_trait_ref.def_id()) != tcx.lang_items().gen_trait() && not_tupled {
1246 self.report_and_explain_type_error(
1247 TypeTrace::poly_trait_refs(
1253 ty::error::TypeError::Mismatch,
1255 } else if found.len() == expected.len() {
1256 self.report_closure_arg_mismatch(
1261 obligation.cause.code(),
1264 let (closure_span, found) = found_did
1266 let node = self.tcx.hir().get_if_local(did)?;
1267 let (found_span, found) = self.get_fn_like_arguments(node)?;
1268 Some((Some(found_span), found))
1270 .unwrap_or((found_span, found));
1272 self.report_arg_count_mismatch(
1277 found_trait_ty.is_closure(),
1282 TraitNotObjectSafe(did) => {
1283 let violations = self.tcx.object_safety_violations(did);
1284 report_object_safety_error(self.tcx, span, did, violations)
1287 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1289 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1292 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1293 if !self.tcx.features().generic_const_exprs {
1294 let mut err = self.tcx.sess.struct_span_err(
1296 "constant expression depends on a generic parameter",
1298 // FIXME(const_generics): we should suggest to the user how they can resolve this
1299 // issue. However, this is currently not actually possible
1300 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1302 // Note that with `feature(generic_const_exprs)` this case should not
1304 err.note("this may fail depending on what value the parameter takes");
1309 match obligation.predicate.kind().skip_binder() {
1310 ty::PredicateKind::ConstEvaluatable(ct) => {
1311 let ty::ConstKind::Unevaluated(uv) = ct.kind() else {
1312 bug!("const evaluatable failed for non-unevaluated const `{ct:?}`");
1315 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1316 let const_span = self.tcx.def_span(uv.def.did);
1317 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1318 Ok(snippet) => err.help(&format!(
1319 "try adding a `where` bound using this expression: `where [(); {}]:`",
1322 _ => err.help("consider adding a `where` bound using this expression"),
1329 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1335 // Already reported in the query.
1336 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1337 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1338 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1341 // Already reported.
1342 Overflow(OverflowError::Error(_)) => {
1343 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1347 bug!("overflow should be handled before the `report_selection_error` path");
1349 SelectionError::ErrorReporting => {
1350 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1354 self.note_obligation_cause(&mut err, &obligation);
1355 self.point_at_returns_when_relevant(&mut err, &obligation);
1361 trait InferCtxtPrivExt<'tcx> {
1362 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1363 // `error` occurring implies that `cond` occurs.
1364 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1366 fn report_fulfillment_error(
1368 error: &FulfillmentError<'tcx>,
1369 body_id: Option<hir::BodyId>,
1372 fn report_projection_error(
1374 obligation: &PredicateObligation<'tcx>,
1375 error: &MismatchedProjectionTypes<'tcx>,
1378 fn maybe_detailed_projection_msg(
1380 pred: ty::ProjectionPredicate<'tcx>,
1381 normalized_ty: ty::Term<'tcx>,
1382 expected_ty: ty::Term<'tcx>,
1383 ) -> Option<String>;
1389 ignoring_lifetimes: bool,
1390 ) -> Option<CandidateSimilarity>;
1392 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1394 fn find_similar_impl_candidates(
1396 trait_pred: ty::PolyTraitPredicate<'tcx>,
1397 ) -> Vec<ImplCandidate<'tcx>>;
1399 fn report_similar_impl_candidates(
1401 impl_candidates: Vec<ImplCandidate<'tcx>>,
1402 trait_ref: ty::PolyTraitRef<'tcx>,
1403 body_id: hir::HirId,
1404 err: &mut Diagnostic,
1407 /// Gets the parent trait chain start
1408 fn get_parent_trait_ref(
1410 code: &ObligationCauseCode<'tcx>,
1411 ) -> Option<(String, Option<Span>)>;
1413 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1414 /// with the same path as `trait_ref`, a help message about
1415 /// a probable version mismatch is added to `err`
1416 fn note_version_mismatch(
1418 err: &mut Diagnostic,
1419 trait_ref: &ty::PolyTraitRef<'tcx>,
1422 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1425 /// For this to work, `new_self_ty` must have no escaping bound variables.
1426 fn mk_trait_obligation_with_new_self_ty(
1428 param_env: ty::ParamEnv<'tcx>,
1429 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1430 ) -> PredicateObligation<'tcx>;
1432 fn maybe_report_ambiguity(
1434 obligation: &PredicateObligation<'tcx>,
1435 body_id: Option<hir::BodyId>,
1438 fn predicate_can_apply(
1440 param_env: ty::ParamEnv<'tcx>,
1441 pred: ty::PolyTraitPredicate<'tcx>,
1444 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1446 fn suggest_unsized_bound_if_applicable(
1448 err: &mut Diagnostic,
1449 obligation: &PredicateObligation<'tcx>,
1452 fn annotate_source_of_ambiguity(
1454 err: &mut Diagnostic,
1456 predicate: ty::Predicate<'tcx>,
1459 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>);
1461 fn maybe_indirection_for_unsized(
1463 err: &mut Diagnostic,
1464 item: &'tcx Item<'tcx>,
1465 param: &'tcx GenericParam<'tcx>,
1468 fn is_recursive_obligation(
1470 obligated_types: &mut Vec<Ty<'tcx>>,
1471 cause_code: &ObligationCauseCode<'tcx>,
1475 impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
1476 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1477 // `error` occurring implies that `cond` occurs.
1478 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1483 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1484 let bound_error = error.kind();
1485 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1486 (ty::PredicateKind::Trait(..), ty::PredicateKind::Trait(error)) => {
1487 (cond, bound_error.rebind(error))
1490 // FIXME: make this work in other cases too.
1495 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1496 let bound_predicate = obligation.predicate.kind();
1497 if let ty::PredicateKind::Trait(implication) = bound_predicate.skip_binder() {
1498 let error = error.to_poly_trait_ref();
1499 let implication = bound_predicate.rebind(implication.trait_ref);
1500 // FIXME: I'm just not taking associated types at all here.
1501 // Eventually I'll need to implement param-env-aware
1502 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1503 let param_env = ty::ParamEnv::empty();
1504 if self.can_sub(param_env, error, implication).is_ok() {
1505 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1514 #[instrument(skip(self), level = "debug")]
1515 fn report_fulfillment_error(
1517 error: &FulfillmentError<'tcx>,
1518 body_id: Option<hir::BodyId>,
1521 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1522 self.report_selection_error(
1523 error.obligation.clone(),
1524 &error.root_obligation,
1528 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1529 self.report_projection_error(&error.obligation, e);
1531 FulfillmentErrorCode::CodeAmbiguity => {
1532 self.maybe_report_ambiguity(&error.obligation, body_id);
1534 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1535 self.report_mismatched_types(
1536 &error.obligation.cause,
1537 expected_found.expected,
1538 expected_found.found,
1543 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1544 let mut diag = self.report_mismatched_consts(
1545 &error.obligation.cause,
1546 expected_found.expected,
1547 expected_found.found,
1550 let code = error.obligation.cause.code().peel_derives().peel_match_impls();
1551 if let ObligationCauseCode::BindingObligation(..)
1552 | ObligationCauseCode::ItemObligation(..)
1553 | ObligationCauseCode::ExprBindingObligation(..)
1554 | ObligationCauseCode::ExprItemObligation(..) = code
1556 self.note_obligation_cause_code(
1558 &error.obligation.predicate,
1559 error.obligation.param_env,
1562 &mut Default::default(),
1567 FulfillmentErrorCode::CodeCycle(ref cycle) => {
1568 self.report_overflow_error_cycle(cycle);
1573 #[instrument(level = "debug", skip_all)]
1574 fn report_projection_error(
1576 obligation: &PredicateObligation<'tcx>,
1577 error: &MismatchedProjectionTypes<'tcx>,
1579 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1581 if predicate.references_error() {
1586 let mut err = error.err;
1587 let mut values = None;
1589 // try to find the mismatched types to report the error with.
1591 // this can fail if the problem was higher-ranked, in which
1592 // cause I have no idea for a good error message.
1593 let bound_predicate = predicate.kind();
1594 if let ty::PredicateKind::Projection(data) = bound_predicate.skip_binder() {
1595 let mut selcx = SelectionContext::new(self);
1596 let data = self.replace_bound_vars_with_fresh_vars(
1597 obligation.cause.span,
1598 infer::LateBoundRegionConversionTime::HigherRankedType,
1599 bound_predicate.rebind(data),
1601 let mut obligations = vec![];
1602 let normalized_ty = super::normalize_projection_type(
1604 obligation.param_env,
1606 obligation.cause.clone(),
1611 debug!(?obligation.cause, ?obligation.param_env);
1613 debug!(?normalized_ty, data.ty = ?data.term);
1615 let is_normalized_ty_expected = !matches!(
1616 obligation.cause.code().peel_derives(),
1617 ObligationCauseCode::ItemObligation(_)
1618 | ObligationCauseCode::BindingObligation(_, _)
1619 | ObligationCauseCode::ExprItemObligation(..)
1620 | ObligationCauseCode::ExprBindingObligation(..)
1621 | ObligationCauseCode::ObjectCastObligation(..)
1622 | ObligationCauseCode::OpaqueType
1624 if let Err(new_err) = self.at(&obligation.cause, obligation.param_env).eq_exp(
1625 is_normalized_ty_expected,
1629 values = Some((data, is_normalized_ty_expected, normalized_ty, data.term));
1635 .and_then(|(predicate, _, normalized_ty, expected_ty)| {
1636 self.maybe_detailed_projection_msg(predicate, normalized_ty, expected_ty)
1638 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
1639 let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
1641 let secondary_span = match predicate.kind().skip_binder() {
1642 ty::PredicateKind::Projection(proj) => self
1644 .opt_associated_item(proj.projection_ty.item_def_id)
1645 .and_then(|trait_assoc_item| {
1647 .trait_of_item(proj.projection_ty.item_def_id)
1648 .map(|id| (trait_assoc_item, id))
1650 .and_then(|(trait_assoc_item, id)| {
1651 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1652 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1654 .associated_items(did)
1655 .in_definition_order()
1656 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1659 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1661 hir::Node::TraitItem(hir::TraitItem {
1662 kind: hir::TraitItemKind::Type(_, Some(ty)),
1665 | hir::Node::ImplItem(hir::ImplItem {
1666 kind: hir::ImplItemKind::Type(ty),
1669 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1678 values.map(|(_, is_normalized_ty_expected, normalized_ty, term)| {
1679 infer::ValuePairs::Terms(ExpectedFound::new(
1680 is_normalized_ty_expected,
1689 self.note_obligation_cause(&mut diag, obligation);
1694 fn maybe_detailed_projection_msg(
1696 pred: ty::ProjectionPredicate<'tcx>,
1697 normalized_ty: ty::Term<'tcx>,
1698 expected_ty: ty::Term<'tcx>,
1699 ) -> Option<String> {
1700 let trait_def_id = pred.projection_ty.trait_def_id(self.tcx);
1701 let self_ty = pred.projection_ty.self_ty();
1703 if Some(pred.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output() {
1705 "expected `{self_ty}` to be a {fn_kind} that returns `{expected_ty}`, but it returns `{normalized_ty}`",
1706 fn_kind = self_ty.prefix_string(self.tcx)
1708 } else if Some(trait_def_id) == self.tcx.lang_items().future_trait() {
1710 "expected `{self_ty}` to be a future that resolves to `{expected_ty}`, but it resolves to `{normalized_ty}`"
1712 } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
1714 "expected `{self_ty}` to be an iterator that yields `{expected_ty}`, but it yields `{normalized_ty}`"
1725 ignoring_lifetimes: bool,
1726 ) -> Option<CandidateSimilarity> {
1727 /// returns the fuzzy category of a given type, or None
1728 /// if the type can be equated to any type.
1729 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1731 ty::Bool => Some(0),
1732 ty::Char => Some(1),
1734 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::String, def.did()) => Some(2),
1738 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1739 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1740 ty::Array(..) | ty::Slice(..) => Some(6),
1741 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1742 ty::Dynamic(..) => Some(8),
1743 ty::Closure(..) => Some(9),
1744 ty::Tuple(..) => Some(10),
1745 ty::Param(..) => Some(11),
1746 ty::Projection(..) => Some(12),
1747 ty::Opaque(..) => Some(13),
1748 ty::Never => Some(14),
1749 ty::Adt(..) => Some(15),
1750 ty::Generator(..) => Some(16),
1751 ty::Foreign(..) => Some(17),
1752 ty::GeneratorWitness(..) => Some(18),
1753 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1757 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1760 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1768 if !ignoring_lifetimes {
1769 a = strip_references(a);
1770 b = strip_references(b);
1773 let cat_a = type_category(self.tcx, a)?;
1774 let cat_b = type_category(self.tcx, b)?;
1776 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1777 } else if cat_a == cat_b {
1778 match (a.kind(), b.kind()) {
1779 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1780 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1781 // Matching on references results in a lot of unhelpful
1782 // suggestions, so let's just not do that for now.
1784 // We still upgrade successful matches to `ignoring_lifetimes: true`
1785 // to prioritize that impl.
1786 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1787 self.fuzzy_match_tys(a, b, true).is_some()
1791 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1792 } else if ignoring_lifetimes {
1795 self.fuzzy_match_tys(a, b, true)
1799 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1800 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1801 hir::GeneratorKind::Gen => "a generator",
1802 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1803 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1804 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1808 fn find_similar_impl_candidates(
1810 trait_pred: ty::PolyTraitPredicate<'tcx>,
1811 ) -> Vec<ImplCandidate<'tcx>> {
1813 .all_impls(trait_pred.def_id())
1814 .filter_map(|def_id| {
1815 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
1818 .is_constness_satisfied_by(self.tcx.constness(def_id))
1823 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1825 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
1826 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1831 fn report_similar_impl_candidates(
1833 impl_candidates: Vec<ImplCandidate<'tcx>>,
1834 trait_ref: ty::PolyTraitRef<'tcx>,
1835 body_id: hir::HirId,
1836 err: &mut Diagnostic,
1838 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1841 let len = candidates.len();
1842 if candidates.len() == 0 {
1845 if candidates.len() == 1 {
1846 let ty_desc = match candidates[0].self_ty().kind() {
1847 ty::FnPtr(_) => Some("fn pointer"),
1850 let the_desc = match ty_desc {
1851 Some(desc) => format!(" implemented for {} `", desc),
1852 None => " implemented for `".to_string(),
1854 err.highlighted_help(vec![
1856 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1859 ("is".to_string(), Style::Highlight),
1860 (the_desc, Style::NoStyle),
1861 (candidates[0].self_ty().to_string(), Style::Highlight),
1862 ("`".to_string(), Style::NoStyle),
1866 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1867 // Check if the trait is the same in all cases. If so, we'll only show the type.
1868 let mut traits: Vec<_> =
1869 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1873 let mut candidates: Vec<String> = candidates
1876 if traits.len() == 1 {
1877 format!("\n {}", c.self_ty())
1886 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1888 "the following other types implement trait `{}`:{}{}",
1889 trait_ref.print_only_trait_path(),
1890 candidates[..end].join(""),
1891 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1896 let def_id = trait_ref.def_id();
1897 if impl_candidates.is_empty() {
1898 if self.tcx.trait_is_auto(def_id)
1899 || self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1900 || self.tcx.get_diagnostic_name(def_id).is_some()
1902 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1905 let normalized_impl_candidates: Vec<_> = self
1908 // Ignore automatically derived impls and `!Trait` impls.
1910 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1911 || self.tcx.is_builtin_derive(def_id)
1913 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1914 .filter(|trait_ref| {
1915 let self_ty = trait_ref.self_ty();
1916 // Avoid mentioning type parameters.
1917 if let ty::Param(_) = self_ty.kind() {
1920 // Avoid mentioning types that are private to another crate
1921 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
1922 // FIXME(compiler-errors): This could be generalized, both to
1923 // be more granular, and probably look past other `#[fundamental]`
1926 .visibility(def.did())
1927 .is_accessible_from(body_id.owner.def_id, self.tcx)
1933 return report(normalized_impl_candidates, err);
1936 let normalize = |candidate| {
1937 let infcx = self.tcx.infer_ctxt().build();
1939 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1940 .normalize(candidate)
1941 .map_or(candidate, |normalized| normalized.value)
1944 // Sort impl candidates so that ordering is consistent for UI tests.
1945 // because the ordering of `impl_candidates` may not be deterministic:
1946 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1948 // Prefer more similar candidates first, then sort lexicographically
1949 // by their normalized string representation.
1950 let mut normalized_impl_candidates_and_similarities = impl_candidates
1952 .map(|ImplCandidate { trait_ref, similarity }| {
1953 let normalized = normalize(trait_ref);
1954 (similarity, normalized)
1956 .collect::<Vec<_>>();
1957 normalized_impl_candidates_and_similarities.sort();
1958 normalized_impl_candidates_and_similarities.dedup();
1960 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
1962 .map(|(_, normalized)| normalized)
1963 .collect::<Vec<_>>();
1965 report(normalized_impl_candidates, err)
1968 /// Gets the parent trait chain start
1969 fn get_parent_trait_ref(
1971 code: &ObligationCauseCode<'tcx>,
1972 ) -> Option<(String, Option<Span>)> {
1974 ObligationCauseCode::BuiltinDerivedObligation(data) => {
1975 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
1976 match self.get_parent_trait_ref(&data.parent_code) {
1979 let ty = parent_trait_ref.skip_binder().self_ty();
1980 let span = TyCategory::from_ty(self.tcx, ty)
1981 .map(|(_, def_id)| self.tcx.def_span(def_id));
1982 Some((ty.to_string(), span))
1986 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
1987 self.get_parent_trait_ref(&parent_code)
1993 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1994 /// with the same path as `trait_ref`, a help message about
1995 /// a probable version mismatch is added to `err`
1996 fn note_version_mismatch(
1998 err: &mut Diagnostic,
1999 trait_ref: &ty::PolyTraitRef<'tcx>,
2001 let get_trait_impl = |trait_def_id| {
2002 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
2004 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
2005 let traits_with_same_path: std::collections::BTreeSet<_> = self
2008 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
2009 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
2011 let mut suggested = false;
2012 for trait_with_same_path in traits_with_same_path {
2013 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
2014 let impl_span = self.tcx.def_span(impl_def_id);
2015 err.span_help(impl_span, "trait impl with same name found");
2016 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
2017 let crate_msg = format!(
2018 "perhaps two different versions of crate `{}` are being used?",
2021 err.note(&crate_msg);
2028 fn mk_trait_obligation_with_new_self_ty(
2030 param_env: ty::ParamEnv<'tcx>,
2031 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
2032 ) -> PredicateObligation<'tcx> {
2033 let trait_pred = trait_ref_and_ty.map_bound_ref(|(tr, new_self_ty)| ty::TraitPredicate {
2034 trait_ref: ty::TraitRef {
2035 substs: self.tcx.mk_substs_trait(*new_self_ty, &tr.trait_ref.substs[1..]),
2041 Obligation::new(ObligationCause::dummy(), param_env, trait_pred.to_predicate(self.tcx))
2044 #[instrument(skip(self), level = "debug")]
2045 fn maybe_report_ambiguity(
2047 obligation: &PredicateObligation<'tcx>,
2048 body_id: Option<hir::BodyId>,
2050 // Unable to successfully determine, probably means
2051 // insufficient type information, but could mean
2052 // ambiguous impls. The latter *ought* to be a
2053 // coherence violation, so we don't report it here.
2055 let predicate = self.resolve_vars_if_possible(obligation.predicate);
2056 let span = obligation.cause.span;
2058 debug!(?predicate, obligation.cause.code = ?obligation.cause.code());
2060 // Ambiguity errors are often caused as fallout from earlier errors.
2061 // We ignore them if this `infcx` is tainted in some cases below.
2063 let bound_predicate = predicate.kind();
2064 let mut err = match bound_predicate.skip_binder() {
2065 ty::PredicateKind::Trait(data) => {
2066 let trait_ref = bound_predicate.rebind(data.trait_ref);
2069 if predicate.references_error() {
2073 // This is kind of a hack: it frequently happens that some earlier
2074 // error prevents types from being fully inferred, and then we get
2075 // a bunch of uninteresting errors saying something like "<generic
2076 // #0> doesn't implement Sized". It may even be true that we
2077 // could just skip over all checks where the self-ty is an
2078 // inference variable, but I was afraid that there might be an
2079 // inference variable created, registered as an obligation, and
2080 // then never forced by writeback, and hence by skipping here we'd
2081 // be ignoring the fact that we don't KNOW the type works
2082 // out. Though even that would probably be harmless, given that
2083 // we're only talking about builtin traits, which are known to be
2084 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2085 // avoid inundating the user with unnecessary errors, but we now
2086 // check upstream for type errors and don't add the obligations to
2087 // begin with in those cases.
2088 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
2089 if !self.is_tainted_by_errors() {
2090 self.emit_inference_failure_err(
2093 trait_ref.self_ty().skip_binder().into(),
2102 // Typically, this ambiguity should only happen if
2103 // there are unresolved type inference variables
2104 // (otherwise it would suggest a coherence
2105 // failure). But given #21974 that is not necessarily
2106 // the case -- we can have multiple where clauses that
2107 // are only distinguished by a region, which results
2108 // in an ambiguity even when all types are fully
2109 // known, since we don't dispatch based on region
2112 // Pick the first substitution that still contains inference variables as the one
2113 // we're going to emit an error for. If there are none (see above), fall back to
2114 // a more general error.
2115 let subst = data.trait_ref.substs.iter().find(|s| s.has_non_region_infer());
2117 let mut err = if let Some(subst) = subst {
2118 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2124 "type annotations needed: cannot satisfy `{}`",
2129 let obligation = Obligation::new(
2130 obligation.cause.clone(),
2131 obligation.param_env,
2132 trait_ref.to_poly_trait_predicate(),
2134 let mut selcx = SelectionContext::with_query_mode(
2136 crate::traits::TraitQueryMode::Standard,
2138 match selcx.select_from_obligation(&obligation) {
2140 let impls = ambiguity::recompute_applicable_impls(self.infcx, &obligation);
2141 let has_non_region_infer =
2142 trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_infer());
2143 // It doesn't make sense to talk about applicable impls if there are more
2144 // than a handful of them.
2145 if impls.len() > 1 && impls.len() < 5 && has_non_region_infer {
2146 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2148 if self.is_tainted_by_errors() {
2152 err.note(&format!("cannot satisfy `{}`", predicate));
2156 if self.is_tainted_by_errors() {
2160 err.note(&format!("cannot satisfy `{}`", predicate));
2164 if let ObligationCauseCode::ItemObligation(def_id) | ObligationCauseCode::ExprItemObligation(def_id, ..) = *obligation.cause.code() {
2165 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2166 } else if let Ok(snippet) = &self.tcx.sess.source_map().span_to_snippet(span)
2167 && let ObligationCauseCode::BindingObligation(def_id, _) | ObligationCauseCode::ExprBindingObligation(def_id, ..)
2168 = *obligation.cause.code()
2170 let generics = self.tcx.generics_of(def_id);
2171 if generics.params.iter().any(|p| p.name != kw::SelfUpper)
2172 && !snippet.ends_with('>')
2173 && !generics.has_impl_trait()
2174 && !self.tcx.fn_trait_kind_from_lang_item(def_id).is_some()
2176 // FIXME: To avoid spurious suggestions in functions where type arguments
2177 // where already supplied, we check the snippet to make sure it doesn't
2178 // end with a turbofish. Ideally we would have access to a `PathSegment`
2179 // instead. Otherwise we would produce the following output:
2181 // error[E0283]: type annotations needed
2182 // --> $DIR/issue-54954.rs:3:24
2184 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2185 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2187 // | cannot infer type
2188 // | help: consider specifying the type argument
2189 // | in the function call:
2190 // | `Tt::const_val::<[i8; 123]>::<T>`
2192 // LL | const fn const_val<T: Sized>() -> usize {
2193 // | - required by this bound in `Tt::const_val`
2195 // = note: cannot satisfy `_: Tt`
2197 // Clear any more general suggestions in favor of our specific one
2198 err.clear_suggestions();
2200 err.span_suggestion_verbose(
2201 span.shrink_to_hi(),
2203 "consider specifying the type argument{} in the function call",
2204 pluralize!(generics.params.len()),
2211 .map(|p| p.name.to_string())
2212 .collect::<Vec<String>>()
2215 Applicability::HasPlaceholders,
2220 if let (Some(body_id), Some(ty::subst::GenericArgKind::Type(_))) =
2221 (body_id, subst.map(|subst| subst.unpack()))
2223 struct FindExprBySpan<'hir> {
2225 result: Option<&'hir hir::Expr<'hir>>,
2228 impl<'v> hir::intravisit::Visitor<'v> for FindExprBySpan<'v> {
2229 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2230 if self.span == ex.span {
2231 self.result = Some(ex);
2233 hir::intravisit::walk_expr(self, ex);
2238 let mut expr_finder = FindExprBySpan { span, result: None };
2240 expr_finder.visit_expr(&self.tcx.hir().body(body_id).value);
2242 if let Some(hir::Expr {
2243 kind: hir::ExprKind::Path(hir::QPath::Resolved(None, path)), .. }
2244 ) = expr_finder.result
2247 trait_path_segment @ hir::PathSegment {
2248 res: rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id),
2252 ident: assoc_item_name,
2253 res: rustc_hir::def::Res::Def(_, item_id),
2257 && data.trait_ref.def_id == *trait_id
2258 && self.tcx.trait_of_item(*item_id) == Some(*trait_id)
2259 && !self.is_tainted_by_errors()
2261 let (verb, noun) = match self.tcx.associated_item(item_id).kind {
2262 ty::AssocKind::Const => ("refer to the", "constant"),
2263 ty::AssocKind::Fn => ("call", "function"),
2264 ty::AssocKind::Type => ("refer to the", "type"), // this is already covered by E0223, but this single match arm doesn't hurt here
2267 // Replace the more general E0283 with a more specific error
2269 err = self.tcx.sess.struct_span_err_with_code(
2272 "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type",
2274 rustc_errors::error_code!(E0790),
2277 if let Some(local_def_id) = data.trait_ref.def_id.as_local()
2278 && 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)
2279 && let Some(method_ref) = trait_item_refs.iter().find(|item_ref| item_ref.ident == *assoc_item_name) {
2280 err.span_label(method_ref.span, format!("`{}::{}` defined here", trait_name, assoc_item_name));
2283 err.span_label(span, format!("cannot {verb} associated {noun} of trait"));
2285 let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
2287 if trait_impls.blanket_impls().is_empty()
2288 && let Some((impl_ty, _)) = trait_impls.non_blanket_impls().iter().next()
2289 && let Some(impl_def_id) = impl_ty.def() {
2290 let message = if trait_impls.non_blanket_impls().len() == 1 {
2291 "use the fully-qualified path to the only available implementation".to_string()
2294 "use a fully-qualified path to a specific available implementation ({} found)",
2295 trait_impls.non_blanket_impls().len()
2298 let mut suggestions = vec![(
2299 trait_path_segment.ident.span.shrink_to_lo(),
2300 format!("<{} as ", self.tcx.type_of(impl_def_id))
2302 if let Some(generic_arg) = trait_path_segment.args {
2303 let between_span = trait_path_segment.ident.span.between(generic_arg.span_ext);
2304 // get rid of :: between Trait and <type>
2305 // must be '::' between them, otherwise the parser won't accept the code
2306 suggestions.push((between_span, "".to_string(),));
2307 suggestions.push((generic_arg.span_ext.shrink_to_hi(), format!(">")));
2309 suggestions.push((trait_path_segment.ident.span.shrink_to_hi(), format!(">")));
2311 err.multipart_suggestion(
2314 Applicability::MaybeIncorrect
2323 ty::PredicateKind::WellFormed(arg) => {
2324 // Same hacky approach as above to avoid deluging user
2325 // with error messages.
2326 if arg.references_error()
2327 || self.tcx.sess.has_errors().is_some()
2328 || self.is_tainted_by_errors()
2333 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2336 ty::PredicateKind::Subtype(data) => {
2337 if data.references_error()
2338 || self.tcx.sess.has_errors().is_some()
2339 || self.is_tainted_by_errors()
2341 // no need to overload user in such cases
2344 let SubtypePredicate { a_is_expected: _, a, b } = data;
2345 // both must be type variables, or the other would've been instantiated
2346 assert!(a.is_ty_var() && b.is_ty_var());
2347 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2349 ty::PredicateKind::Projection(data) => {
2350 if predicate.references_error() || self.is_tainted_by_errors() {
2357 .chain(Some(data.term.into_arg()))
2358 .find(|g| g.has_non_region_infer());
2359 if let Some(subst) = subst {
2360 let mut err = self.emit_inference_failure_err(
2367 err.note(&format!("cannot satisfy `{}`", predicate));
2370 // If we can't find a substitution, just print a generic error
2371 let mut err = struct_span_err!(
2375 "type annotations needed: cannot satisfy `{}`",
2378 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2383 ty::PredicateKind::ConstEvaluatable(data) => {
2384 if predicate.references_error() || self.is_tainted_by_errors() {
2387 let subst = data.walk().find(|g| g.is_non_region_infer());
2388 if let Some(subst) = subst {
2389 let err = self.emit_inference_failure_err(
2398 // If we can't find a substitution, just print a generic error
2399 let mut err = struct_span_err!(
2403 "type annotations needed: cannot satisfy `{}`",
2406 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2411 if self.tcx.sess.has_errors().is_some() || self.is_tainted_by_errors() {
2414 let mut err = struct_span_err!(
2418 "type annotations needed: cannot satisfy `{}`",
2421 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2425 self.note_obligation_cause(&mut err, obligation);
2429 fn annotate_source_of_ambiguity(
2431 err: &mut Diagnostic,
2433 predicate: ty::Predicate<'tcx>,
2435 let mut spans = vec![];
2436 let mut crates = vec![];
2437 let mut post = vec![];
2438 for def_id in impls {
2439 match self.tcx.span_of_impl(*def_id) {
2440 Ok(span) => spans.push(span),
2443 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2449 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2451 crate_names.dedup();
2455 if self.is_tainted_by_errors()
2456 && (crate_names.len() == 1
2458 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2459 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2461 // Avoid complaining about other inference issues for expressions like
2462 // `42 >> 1`, where the types are still `{integer}`, but we want to
2463 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2464 // NOTE(eddyb) this was `.cancel()`, but `err`
2465 // is borrowed, so we can't fully defuse it.
2466 err.downgrade_to_delayed_bug();
2470 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2471 let post = if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2472 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2473 } else if post.len() == 1 {
2474 format!(": `{}`", post[0])
2479 match (spans.len(), crates.len(), crate_names.len()) {
2481 err.note(&format!("cannot satisfy `{}`", predicate));
2484 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2488 "{} in the following crates: {}{}",
2490 crate_names.join(", "),
2495 let span: MultiSpan = spans.into();
2496 err.span_note(span, &msg);
2499 let span: MultiSpan = spans.into();
2500 err.span_note(span, &msg);
2502 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2506 let span: MultiSpan = spans.into();
2507 err.span_note(span, &msg);
2509 "and more `impl`s found in the following crates: {}{}",
2510 crate_names.join(", "),
2517 /// Returns `true` if the trait predicate may apply for *some* assignment
2518 /// to the type parameters.
2519 fn predicate_can_apply(
2521 param_env: ty::ParamEnv<'tcx>,
2522 pred: ty::PolyTraitPredicate<'tcx>,
2524 struct ParamToVarFolder<'a, 'tcx> {
2525 infcx: &'a InferCtxt<'tcx>,
2526 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2529 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2530 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2534 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2535 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2536 let infcx = self.infcx;
2537 *self.var_map.entry(ty).or_insert_with(|| {
2538 infcx.next_ty_var(TypeVariableOrigin {
2539 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2544 ty.super_fold_with(self)
2550 let mut selcx = SelectionContext::new(self);
2553 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2555 let cleaned_pred = super::project::normalize(
2558 ObligationCause::dummy(),
2563 let obligation = Obligation::new(
2564 ObligationCause::dummy(),
2566 cleaned_pred.to_predicate(selcx.tcx()),
2569 self.predicate_may_hold(&obligation)
2573 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2574 // First, attempt to add note to this error with an async-await-specific
2575 // message, and fall back to regular note otherwise.
2576 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2577 self.note_obligation_cause_code(
2579 &obligation.predicate,
2580 obligation.param_env,
2581 obligation.cause.code(),
2583 &mut Default::default(),
2585 self.suggest_unsized_bound_if_applicable(err, obligation);
2589 #[instrument(level = "debug", skip_all)]
2590 fn suggest_unsized_bound_if_applicable(
2592 err: &mut Diagnostic,
2593 obligation: &PredicateObligation<'tcx>,
2595 let ty::PredicateKind::Trait(pred) = obligation.predicate.kind().skip_binder() else { return; };
2596 let (ObligationCauseCode::BindingObligation(item_def_id, span)
2597 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..))
2598 = *obligation.cause.code().peel_derives() else { return; };
2599 debug!(?pred, ?item_def_id, ?span);
2601 let (Some(node), true) = (
2602 self.tcx.hir().get_if_local(item_def_id),
2603 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2607 self.maybe_suggest_unsized_generics(err, span, node);
2610 #[instrument(level = "debug", skip_all)]
2611 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>) {
2612 let Some(generics) = node.generics() else {
2615 let sized_trait = self.tcx.lang_items().sized_trait();
2616 debug!(?generics.params);
2617 debug!(?generics.predicates);
2618 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2621 let param_def_id = self.tcx.hir().local_def_id(param.hir_id);
2622 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2623 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2624 let explicitly_sized = generics
2625 .bounds_for_param(param_def_id)
2626 .flat_map(|bp| bp.bounds)
2627 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2628 if explicitly_sized {
2635 // Only suggest indirection for uses of type parameters in ADTs.
2637 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2641 if self.maybe_indirection_for_unsized(err, item, param) {
2647 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2648 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param_def_id)
2652 (span.shrink_to_hi(), ":")
2654 err.span_suggestion_verbose(
2656 "consider relaxing the implicit `Sized` restriction",
2657 format!("{} ?Sized", separator),
2658 Applicability::MachineApplicable,
2662 fn maybe_indirection_for_unsized(
2664 err: &mut Diagnostic,
2666 param: &GenericParam<'tcx>,
2668 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2669 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2670 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2672 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2673 visitor.visit_item(item);
2674 if visitor.invalid_spans.is_empty() {
2677 let mut multispan: MultiSpan = param.span.into();
2678 multispan.push_span_label(
2680 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2682 for sp in visitor.invalid_spans {
2683 multispan.push_span_label(
2685 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2691 "you could relax the implicit `Sized` bound on `{T}` if it were \
2692 used through indirection like `&{T}` or `Box<{T}>`",
2693 T = param.name.ident(),
2699 fn is_recursive_obligation(
2701 obligated_types: &mut Vec<Ty<'tcx>>,
2702 cause_code: &ObligationCauseCode<'tcx>,
2704 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2705 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2706 let self_ty = parent_trait_ref.skip_binder().self_ty();
2707 if obligated_types.iter().any(|ot| ot == &self_ty) {
2710 if let ty::Adt(def, substs) = self_ty.kind()
2711 && let [arg] = &substs[..]
2712 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2713 && let ty::Adt(inner_def, _) = ty.kind()
2723 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2724 /// `param: ?Sized` would be a valid constraint.
2725 struct FindTypeParam {
2726 param: rustc_span::Symbol,
2727 invalid_spans: Vec<Span>,
2731 impl<'v> Visitor<'v> for FindTypeParam {
2732 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2733 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2736 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2737 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2738 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2739 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2740 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2741 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2742 // in that case should make what happened clear enough.
2744 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2745 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2746 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2749 debug!(?ty, "FindTypeParam::visit_ty");
2750 self.invalid_spans.push(ty.span);
2753 hir::TyKind::Path(_) => {
2754 let prev = self.nested;
2756 hir::intravisit::walk_ty(self, ty);
2760 hir::intravisit::walk_ty(self, ty);
2766 /// Summarizes information
2769 /// An argument of non-tuple type. Parameters are (name, ty)
2770 Arg(String, String),
2772 /// An argument of tuple type. For a "found" argument, the span is
2773 /// the location in the source of the pattern. For an "expected"
2774 /// argument, it will be None. The vector is a list of (name, ty)
2775 /// strings for the components of the tuple.
2776 Tuple(Option<Span>, Vec<(String, String)>),
2780 fn empty() -> ArgKind {
2781 ArgKind::Arg("_".to_owned(), "_".to_owned())
2784 /// Creates an `ArgKind` from the expected type of an
2785 /// argument. It has no name (`_`) and an optional source span.
2786 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2788 ty::Tuple(tys) => ArgKind::Tuple(
2790 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2792 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2797 struct HasNumericInferVisitor;
2799 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2802 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2803 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2804 ControlFlow::Break(())
2806 ControlFlow::CONTINUE
2811 pub enum DefIdOrName {