2 pub mod on_unimplemented;
6 FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes, Obligation, ObligationCause,
7 ObligationCauseCode, ObligationCtxt, 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::Namespace;
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_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::print::{FmtPrinter, Print};
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,
114 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
115 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug;
117 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
119 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
121 /// The `root_obligation` parameter should be the `root_obligation` field
122 /// from a `FulfillmentError`. If no `FulfillmentError` is available,
123 /// then it should be the same as `obligation`.
124 fn report_selection_error(
126 obligation: PredicateObligation<'tcx>,
127 root_obligation: &PredicateObligation<'tcx>,
128 error: &SelectionError<'tcx>,
132 impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
133 /// Given some node representing a fn-like thing in the HIR map,
134 /// returns a span and `ArgKind` information that describes the
135 /// arguments it expects. This can be supplied to
136 /// `report_arg_count_mismatch`.
137 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
138 let sm = self.tcx.sess.source_map();
139 let hir = self.tcx.hir();
141 Node::Expr(&hir::Expr {
142 kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }),
150 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
157 sm.span_to_snippet(pat.span)
159 .map(|snippet| (snippet, "_".to_owned()))
161 .collect::<Option<Vec<_>>>()?,
164 let name = sm.span_to_snippet(arg.pat.span).ok()?;
165 Some(ArgKind::Arg(name, "_".to_owned()))
168 .collect::<Option<Vec<ArgKind>>>()?,
170 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
171 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
172 | Node::TraitItem(&hir::TraitItem {
173 kind: hir::TraitItemKind::Fn(ref sig, _), ..
179 .map(|arg| match arg.kind {
180 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
182 vec![("_".to_owned(), "_".to_owned()); tys.len()],
184 _ => ArgKind::empty(),
186 .collect::<Vec<ArgKind>>(),
188 Node::Ctor(ref variant_data) => {
189 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
190 (span, vec![ArgKind::empty(); variant_data.fields().len()])
192 _ => panic!("non-FnLike node found: {:?}", node),
196 /// Reports an error when the number of arguments needed by a
197 /// trait match doesn't match the number that the expression
199 fn report_arg_count_mismatch(
202 found_span: Option<Span>,
203 expected_args: Vec<ArgKind>,
204 found_args: Vec<ArgKind>,
206 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
207 let kind = if is_closure { "closure" } else { "function" };
209 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
210 let arg_length = arguments.len();
211 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
212 match (arg_length, arguments.get(0)) {
213 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
214 format!("a single {}-tuple as argument", fields.len())
219 if distinct && arg_length > 1 { "distinct " } else { "" },
220 pluralize!(arg_length)
225 let expected_str = args_str(&expected_args, &found_args);
226 let found_str = args_str(&found_args, &expected_args);
228 let mut err = struct_span_err!(
232 "{} is expected to take {}, but it takes {}",
238 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
240 if let Some(found_span) = found_span {
241 err.span_label(found_span, format!("takes {}", found_str));
244 // ^^^^^^^^-- def_span
248 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
252 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
254 // Suggest to take and ignore the arguments with expected_args_length `_`s if
255 // found arguments is empty (assume the user just wants to ignore args in this case).
256 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
257 if found_args.is_empty() && is_closure {
258 let underscores = vec!["_"; expected_args.len()].join(", ");
259 err.span_suggestion_verbose(
262 "consider changing the closure to take and ignore the expected argument{}",
263 pluralize!(expected_args.len())
265 format!("|{}|", underscores),
266 Applicability::MachineApplicable,
270 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
271 if fields.len() == expected_args.len() {
274 .map(|(name, _)| name.to_owned())
275 .collect::<Vec<String>>()
277 err.span_suggestion_verbose(
279 "change the closure to take multiple arguments instead of a single tuple",
280 format!("|{}|", sugg),
281 Applicability::MachineApplicable,
285 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
286 && fields.len() == found_args.len()
293 .map(|arg| match arg {
294 ArgKind::Arg(name, _) => name.to_owned(),
297 .collect::<Vec<String>>()
299 // add type annotations if available
300 if found_args.iter().any(|arg| match arg {
301 ArgKind::Arg(_, ty) => ty != "_",
308 .map(|(_, ty)| ty.to_owned())
309 .collect::<Vec<String>>()
316 err.span_suggestion_verbose(
318 "change the closure to accept a tuple instead of individual arguments",
320 Applicability::MachineApplicable,
328 fn type_implements_fn_trait(
330 param_env: ty::ParamEnv<'tcx>,
331 ty: ty::Binder<'tcx, Ty<'tcx>>,
332 constness: ty::BoundConstness,
333 polarity: ty::ImplPolarity,
334 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
335 self.commit_if_ok(|_| {
336 for trait_def_id in [
337 self.tcx.lang_items().fn_trait(),
338 self.tcx.lang_items().fn_mut_trait(),
339 self.tcx.lang_items().fn_once_trait(),
341 let Some(trait_def_id) = trait_def_id else { continue };
342 // Make a fresh inference variable so we can determine what the substitutions
344 let var = self.next_ty_var(TypeVariableOrigin {
346 kind: TypeVariableOriginKind::MiscVariable,
348 let trait_ref = self.tcx.mk_trait_ref(trait_def_id, [ty.skip_binder(), var]);
349 let obligation = Obligation::new(
351 ObligationCause::dummy(),
353 ty.rebind(ty::TraitPredicate { trait_ref, constness, polarity }),
355 let ocx = ObligationCtxt::new_in_snapshot(self);
356 ocx.register_obligation(obligation);
357 if ocx.select_all_or_error().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,
472 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
473 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
475 let predicate = self.resolve_vars_if_possible(obligation.predicate.clone());
476 let mut pred_str = predicate.to_string();
477 if pred_str.len() > 50 {
478 // We don't need to save the type to a file, we will be talking about this type already
479 // in a separate note when we explain the obligation, so it will be available that way.
481 .print(FmtPrinter::new_with_limit(
484 rustc_session::Limit(6),
489 let mut err = struct_span_err!(
491 obligation.cause.span,
493 "overflow evaluating the requirement `{}`",
497 if suggest_increasing_limit {
498 self.suggest_new_overflow_limit(&mut err);
501 self.note_obligation_cause_code(
503 &obligation.predicate,
504 obligation.param_env,
505 obligation.cause.code(),
507 &mut Default::default(),
511 self.tcx.sess.abort_if_errors();
515 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic) {
516 let suggested_limit = match self.tcx.recursion_limit() {
517 Limit(0) => Limit(2),
521 "consider increasing the recursion limit by adding a \
522 `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
524 self.tcx.crate_name(LOCAL_CRATE),
528 /// Reports that a cycle was detected which led to overflow and halts
529 /// compilation. This is equivalent to `report_overflow_error` except
530 /// that we can give a more helpful error message (and, in particular,
531 /// we do not suggest increasing the overflow limit, which is not
533 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
534 let cycle = self.resolve_vars_if_possible(cycle.to_owned());
535 assert!(!cycle.is_empty());
537 debug!(?cycle, "report_overflow_error_cycle");
539 // The 'deepest' obligation is most likely to have a useful
541 self.report_overflow_error(cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(), false);
544 fn report_selection_error(
546 mut obligation: PredicateObligation<'tcx>,
547 root_obligation: &PredicateObligation<'tcx>,
548 error: &SelectionError<'tcx>,
551 let mut span = obligation.cause.span;
552 // FIXME: statically guarantee this by tainting after the diagnostic is emitted
553 self.set_tainted_by_errors(
554 tcx.sess.delay_span_bug(span, "`report_selection_error` did not emit an error"),
557 let mut err = match *error {
558 SelectionError::Unimplemented => {
559 // If this obligation was generated as a result of well-formedness checking, see if we
560 // can get a better error message by performing HIR-based well-formedness checking.
561 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
562 root_obligation.cause.code().peel_derives()
564 if let Some(cause) = self
566 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
568 obligation.cause = cause.clone();
569 span = obligation.cause.span;
572 if let ObligationCauseCode::CompareImplItemObligation {
576 } = *obligation.cause.code()
578 self.report_extra_impl_obligation(
582 &format!("`{}`", obligation.predicate),
588 let bound_predicate = obligation.predicate.kind();
589 match bound_predicate.skip_binder() {
590 ty::PredicateKind::Trait(trait_predicate) => {
591 let trait_predicate = bound_predicate.rebind(trait_predicate);
592 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
594 trait_predicate.remap_constness_diag(obligation.param_env);
595 let predicate_is_const = ty::BoundConstness::ConstIfConst
596 == trait_predicate.skip_binder().constness;
598 if self.tcx.sess.has_errors().is_some()
599 && trait_predicate.references_error()
603 let trait_ref = trait_predicate.to_poly_trait_ref();
604 let (post_message, pre_message, type_def) = self
605 .get_parent_trait_ref(obligation.cause.code())
608 format!(" in `{}`", t),
609 format!("within `{}`, ", t),
610 s.map(|s| (format!("within this `{}`", t), s)),
613 .unwrap_or_default();
615 let OnUnimplementedNote {
621 } = self.on_unimplemented_note(trait_ref, &obligation);
622 let have_alt_message = message.is_some() || label.is_some();
623 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
625 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
626 let (message, note, append_const_msg) = if is_try_conversion {
629 "`?` couldn't convert the error to `{}`",
630 trait_ref.skip_binder().self_ty(),
633 "the question mark operation (`?`) implicitly performs a \
634 conversion on the error value using the `From` trait"
640 (message, note, append_const_msg)
643 let mut err = struct_span_err!(
649 .and_then(|cannot_do_this| {
650 match (predicate_is_const, append_const_msg) {
651 // do nothing if predicate is not const
652 (false, _) => Some(cannot_do_this),
653 // suggested using default post message
654 (true, Some(None)) => {
655 Some(format!("{cannot_do_this} in const contexts"))
657 // overridden post message
658 (true, Some(Some(post_message))) => {
659 Some(format!("{cannot_do_this}{post_message}"))
661 // fallback to generic message
662 (true, None) => None,
665 .unwrap_or_else(|| format!(
666 "the trait bound `{}` is not satisfied{}",
667 trait_predicate, post_message,
671 if is_try_conversion && let Some(ret_span) = self.return_type_span(&obligation) {
675 "expected `{}` because of this",
676 trait_ref.skip_binder().self_ty()
681 if Some(trait_ref.def_id()) == tcx.lang_items().tuple_trait() {
682 match obligation.cause.code().peel_derives() {
683 ObligationCauseCode::RustCall => {
684 err.set_primary_message("functions with the \"rust-call\" ABI must take a single non-self tuple argument");
686 ObligationCauseCode::BindingObligation(def_id, _)
687 | ObligationCauseCode::ItemObligation(def_id)
688 if ty::ClosureKind::from_def_id(tcx, *def_id).is_some() =>
690 err.code(rustc_errors::error_code!(E0059));
691 err.set_primary_message(format!(
692 "type parameter to bare `{}` trait must be a tuple",
693 tcx.def_path_str(*def_id)
700 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
701 && predicate_is_const
703 err.note("`~const Drop` was renamed to `~const Destruct`");
704 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
707 let explanation = if let ObligationCauseCode::MainFunctionType =
708 obligation.cause.code()
710 "consider using `()`, or a `Result`".to_owned()
712 let ty_desc = match trait_ref.skip_binder().self_ty().kind() {
713 ty::FnDef(_, _) => Some("fn item"),
714 ty::Closure(_, _) => Some("closure"),
719 Some(desc) => format!(
720 "{}the trait `{}` is not implemented for {} `{}`",
722 trait_predicate.print_modifiers_and_trait_path(),
724 trait_ref.skip_binder().self_ty(),
727 "{}the trait `{}` is not implemented for `{}`",
729 trait_predicate.print_modifiers_and_trait_path(),
730 trait_ref.skip_binder().self_ty(),
735 if self.suggest_add_reference_to_arg(
741 self.note_obligation_cause(&mut err, &obligation);
745 if let Some(ref s) = label {
746 // If it has a custom `#[rustc_on_unimplemented]`
747 // error message, let's display it as the label!
748 err.span_label(span, s);
749 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
750 // When the self type is a type param We don't need to "the trait
751 // `std::marker::Sized` is not implemented for `T`" as we will point
752 // at the type param with a label to suggest constraining it.
753 err.help(&explanation);
756 err.span_label(span, explanation);
759 if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
760 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
761 self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
764 let mut unsatisfied_const = false;
765 if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
766 let non_const_predicate = trait_ref.without_const();
767 let non_const_obligation = Obligation {
768 cause: obligation.cause.clone(),
769 param_env: obligation.param_env.without_const(),
770 predicate: non_const_predicate.to_predicate(tcx),
771 recursion_depth: obligation.recursion_depth,
773 if self.predicate_may_hold(&non_const_obligation) {
774 unsatisfied_const = true;
778 "the trait `{}` is implemented for `{}`, \
779 but that implementation is not `const`",
780 non_const_predicate.print_modifiers_and_trait_path(),
781 trait_ref.skip_binder().self_ty(),
787 if let Some((msg, span)) = type_def {
788 err.span_label(span, &msg);
790 if let Some(ref s) = note {
791 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
792 err.note(s.as_str());
794 if let Some(ref s) = parent_label {
797 .opt_local_def_id(obligation.cause.body_id)
799 tcx.hir().body_owner_def_id(hir::BodyId {
800 hir_id: obligation.cause.body_id,
803 err.span_label(tcx.def_span(body), s);
806 self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
807 self.suggest_dereferencing_index(&obligation, &mut err, trait_predicate);
809 self.suggest_dereferences(&obligation, &mut err, trait_predicate);
810 suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
812 self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
813 suggested |= self.suggest_semicolon_removal(
819 self.note_version_mismatch(&mut err, &trait_ref);
820 self.suggest_remove_await(&obligation, &mut err);
821 self.suggest_derive(&obligation, &mut err, trait_predicate);
823 if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
824 self.suggest_await_before_try(
832 if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
838 // If the obligation failed due to a missing implementation of the
839 // `Unsize` trait, give a pointer to why that might be the case
841 "all implementations of `Unsize` are provided \
842 automatically by the compiler, see \
843 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
844 for more information",
849 ty::ClosureKind::from_def_id(tcx, trait_ref.def_id()).is_some();
850 let is_target_feature_fn = if let ty::FnDef(def_id, _) =
851 *trait_ref.skip_binder().self_ty().kind()
853 !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
857 if is_fn_trait && is_target_feature_fn {
859 "`#[target_feature]` functions do not implement the `Fn` traits",
863 // Try to report a help message
865 && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
866 obligation.param_env,
868 trait_predicate.skip_binder().constness,
869 trait_predicate.skip_binder().polarity,
872 // If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
873 // suggestion to add trait bounds for the type, since we only typically implement
874 // these traits once.
876 // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
879 ty::ClosureKind::from_def_id(self.tcx, trait_ref.def_id())
880 .expect("expected to map DefId to ClosureKind");
881 if !implemented_kind.extends(selected_kind) {
884 "`{}` implements `{}`, but it must implement `{}`, which is more general",
885 trait_ref.skip_binder().self_ty(),
892 // Note any argument mismatches
893 let given_ty = params.skip_binder();
894 let expected_ty = trait_ref.skip_binder().substs.type_at(1);
895 if let ty::Tuple(given) = given_ty.kind()
896 && let ty::Tuple(expected) = expected_ty.kind()
898 if expected.len() != given.len() {
899 // Note number of types that were expected and given
902 "expected a closure taking {} argument{}, but one taking {} argument{} was given",
904 pluralize!(given.len()),
906 pluralize!(expected.len()),
909 } else if !self.same_type_modulo_infer(given_ty, expected_ty) {
910 // Print type mismatch
911 let (expected_args, given_args) =
912 self.cmp(given_ty, expected_ty);
913 err.note_expected_found(
914 &"a closure with arguments",
916 &"a closure with arguments",
921 } else if !trait_ref.has_non_region_infer()
922 && self.predicate_can_apply(obligation.param_env, trait_predicate)
924 // If a where-clause may be useful, remind the
925 // user that they can add it.
927 // don't display an on-unimplemented note, as
928 // these notes will often be of the form
929 // "the type `T` can't be frobnicated"
930 // which is somewhat confusing.
931 self.suggest_restricting_param_bound(
935 obligation.cause.body_id,
937 } else if !suggested && !unsatisfied_const {
938 // Can't show anything else useful, try to find similar impls.
939 let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
940 if !self.report_similar_impl_candidates(
943 obligation.cause.body_id,
946 // This is *almost* equivalent to
947 // `obligation.cause.code().peel_derives()`, but it gives us the
948 // trait predicate for that corresponding root obligation. This
949 // lets us get a derived obligation from a type parameter, like
950 // when calling `string.strip_suffix(p)` where `p` is *not* an
951 // implementer of `Pattern<'_>`.
952 let mut code = obligation.cause.code();
953 let mut trait_pred = trait_predicate;
954 let mut peeled = false;
955 while let Some((parent_code, parent_trait_pred)) = code.parent() {
957 if let Some(parent_trait_pred) = parent_trait_pred {
958 trait_pred = parent_trait_pred;
962 let def_id = trait_pred.def_id();
963 // Mention *all* the `impl`s for the *top most* obligation, the
964 // user might have meant to use one of them, if any found. We skip
965 // auto-traits or fundamental traits that might not be exactly what
966 // the user might expect to be presented with. Instead this is
967 // useful for less general traits.
969 && !self.tcx.trait_is_auto(def_id)
970 && !self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
972 let trait_ref = trait_pred.to_poly_trait_ref();
973 let impl_candidates =
974 self.find_similar_impl_candidates(trait_pred);
975 self.report_similar_impl_candidates(
978 obligation.cause.body_id,
985 // Changing mutability doesn't make a difference to whether we have
986 // an `Unsize` impl (Fixes ICE in #71036)
988 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
991 // If this error is due to `!: Trait` not implemented but `(): Trait` is
992 // implemented, and fallback has occurred, then it could be due to a
993 // variable that used to fallback to `()` now falling back to `!`. Issue a
994 // note informing about the change in behaviour.
995 if trait_predicate.skip_binder().self_ty().is_never()
996 && self.fallback_has_occurred
998 let predicate = trait_predicate.map_bound(|trait_pred| {
999 trait_pred.with_self_type(self.tcx, self.tcx.mk_unit())
1001 let unit_obligation = obligation.with(tcx, predicate);
1002 if self.predicate_may_hold(&unit_obligation) {
1004 "this error might have been caused by changes to \
1005 Rust's type-inference algorithm (see issue #48950 \
1006 <https://github.com/rust-lang/rust/issues/48950> \
1007 for more information)",
1009 err.help("did you intend to use the type `()` here instead?");
1013 // Return early if the trait is Debug or Display and the invocation
1014 // originates within a standard library macro, because the output
1015 // is otherwise overwhelming and unhelpful (see #85844 for an
1019 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
1020 Some(macro_def_id) => {
1021 let crate_name = tcx.crate_name(macro_def_id.krate);
1022 crate_name == sym::std || crate_name == sym::core
1029 self.tcx.get_diagnostic_name(trait_ref.def_id()),
1030 Some(sym::Debug | sym::Display)
1040 ty::PredicateKind::Subtype(predicate) => {
1041 // Errors for Subtype predicates show up as
1042 // `FulfillmentErrorCode::CodeSubtypeError`,
1043 // not selection error.
1044 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
1047 ty::PredicateKind::Coerce(predicate) => {
1048 // Errors for Coerce predicates show up as
1049 // `FulfillmentErrorCode::CodeSubtypeError`,
1050 // not selection error.
1051 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
1054 ty::PredicateKind::RegionOutlives(..)
1055 | ty::PredicateKind::Projection(..)
1056 | ty::PredicateKind::TypeOutlives(..) => {
1057 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1062 "the requirement `{}` is not satisfied",
1067 ty::PredicateKind::ObjectSafe(trait_def_id) => {
1068 let violations = self.tcx.object_safety_violations(trait_def_id);
1069 report_object_safety_error(self.tcx, span, trait_def_id, violations)
1072 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
1073 let found_kind = self.closure_kind(closure_substs).unwrap();
1074 let closure_span = self.tcx.def_span(closure_def_id);
1075 let mut err = struct_span_err!(
1079 "expected a closure that implements the `{}` trait, \
1080 but this closure only implements `{}`",
1087 format!("this closure implements `{}`, not `{}`", found_kind, kind),
1090 obligation.cause.span,
1091 format!("the requirement to implement `{}` derives from here", kind),
1094 // Additional context information explaining why the closure only implements
1095 // a particular trait.
1096 if let Some(typeck_results) = &self.typeck_results {
1100 .local_def_id_to_hir_id(closure_def_id.expect_local());
1101 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
1102 (ty::ClosureKind::FnOnce, Some((span, place))) => {
1106 "closure is `FnOnce` because it moves the \
1107 variable `{}` out of its environment",
1108 ty::place_to_string_for_capture(tcx, place)
1112 (ty::ClosureKind::FnMut, Some((span, place))) => {
1116 "closure is `FnMut` because it mutates the \
1117 variable `{}` here",
1118 ty::place_to_string_for_capture(tcx, place)
1129 ty::PredicateKind::WellFormed(ty) => {
1130 if !self.tcx.sess.opts.unstable_opts.chalk {
1131 // WF predicates cannot themselves make
1132 // errors. They can only block due to
1133 // ambiguity; otherwise, they always
1134 // degenerate into other obligations
1135 // (which may fail).
1136 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
1138 // FIXME: we'll need a better message which takes into account
1139 // which bounds actually failed to hold.
1140 self.tcx.sess.struct_span_err(
1142 &format!("the type `{}` is not well-formed (chalk)", ty),
1147 ty::PredicateKind::ConstEvaluatable(..) => {
1148 // Errors for `ConstEvaluatable` predicates show up as
1149 // `SelectionError::ConstEvalFailure`,
1150 // not `Unimplemented`.
1153 "const-evaluatable requirement gave wrong error: `{:?}`",
1158 ty::PredicateKind::ConstEquate(..) => {
1159 // Errors for `ConstEquate` predicates show up as
1160 // `SelectionError::ConstEvalFailure`,
1161 // not `Unimplemented`.
1164 "const-equate requirement gave wrong error: `{:?}`",
1169 ty::PredicateKind::Ambiguous => span_bug!(span, "ambiguous"),
1171 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
1173 "TypeWellFormedFromEnv predicate should only exist in the environment"
1178 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
1179 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
1180 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
1182 if expected_trait_ref.self_ty().references_error() {
1186 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
1190 let found_did = match *found_trait_ty.kind() {
1194 | ty::Generator(did, ..) => Some(did),
1195 ty::Adt(def, _) => Some(def.did()),
1199 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
1201 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1202 // We check closures twice, with obligations flowing in different directions,
1203 // but we want to complain about them only once.
1207 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1209 let mut not_tupled = false;
1211 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
1212 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1215 vec![ArgKind::empty()]
1219 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1220 let expected = match expected_ty.kind() {
1221 ty::Tuple(ref tys) => {
1222 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
1226 vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())]
1230 // If this is a `Fn` family trait and either the expected or found
1231 // is not tupled, then fall back to just a regular mismatch error.
1232 // This shouldn't be common unless manually implementing one of the
1233 // traits manually, but don't make it more confusing when it does
1235 if Some(expected_trait_ref.def_id()) != tcx.lang_items().gen_trait() && not_tupled {
1236 self.report_and_explain_type_error(
1237 TypeTrace::poly_trait_refs(
1243 ty::error::TypeError::Mismatch,
1245 } else if found.len() == expected.len() {
1246 self.report_closure_arg_mismatch(
1251 obligation.cause.code(),
1254 let (closure_span, found) = found_did
1256 let node = self.tcx.hir().get_if_local(did)?;
1257 let (found_span, found) = self.get_fn_like_arguments(node)?;
1258 Some((Some(found_span), found))
1260 .unwrap_or((found_span, found));
1262 self.report_arg_count_mismatch(
1267 found_trait_ty.is_closure(),
1272 TraitNotObjectSafe(did) => {
1273 let violations = self.tcx.object_safety_violations(did);
1274 report_object_safety_error(self.tcx, span, did, violations)
1277 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1279 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1282 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1283 if !self.tcx.features().generic_const_exprs {
1284 let mut err = self.tcx.sess.struct_span_err(
1286 "constant expression depends on a generic parameter",
1288 // FIXME(const_generics): we should suggest to the user how they can resolve this
1289 // issue. However, this is currently not actually possible
1290 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1292 // Note that with `feature(generic_const_exprs)` this case should not
1294 err.note("this may fail depending on what value the parameter takes");
1299 match obligation.predicate.kind().skip_binder() {
1300 ty::PredicateKind::ConstEvaluatable(ct) => {
1301 let ty::ConstKind::Unevaluated(uv) = ct.kind() else {
1302 bug!("const evaluatable failed for non-unevaluated const `{ct:?}`");
1305 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1306 let const_span = self.tcx.def_span(uv.def.did);
1307 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1308 Ok(snippet) => err.help(&format!(
1309 "try adding a `where` bound using this expression: `where [(); {}]:`",
1312 _ => err.help("consider adding a `where` bound using this expression"),
1319 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1325 // Already reported in the query.
1326 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1327 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1328 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1331 // Already reported.
1332 Overflow(OverflowError::Error(_)) => {
1333 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1337 bug!("overflow should be handled before the `report_selection_error` path");
1339 SelectionError::ErrorReporting => {
1340 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1344 self.note_obligation_cause(&mut err, &obligation);
1345 self.point_at_returns_when_relevant(&mut err, &obligation);
1351 trait InferCtxtPrivExt<'tcx> {
1352 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1353 // `error` occurring implies that `cond` occurs.
1354 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1356 fn report_fulfillment_error(
1358 error: &FulfillmentError<'tcx>,
1359 body_id: Option<hir::BodyId>,
1362 fn report_projection_error(
1364 obligation: &PredicateObligation<'tcx>,
1365 error: &MismatchedProjectionTypes<'tcx>,
1368 fn maybe_detailed_projection_msg(
1370 pred: ty::ProjectionPredicate<'tcx>,
1371 normalized_ty: ty::Term<'tcx>,
1372 expected_ty: ty::Term<'tcx>,
1373 ) -> Option<String>;
1379 ignoring_lifetimes: bool,
1380 ) -> Option<CandidateSimilarity>;
1382 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1384 fn find_similar_impl_candidates(
1386 trait_pred: ty::PolyTraitPredicate<'tcx>,
1387 ) -> Vec<ImplCandidate<'tcx>>;
1389 fn report_similar_impl_candidates(
1391 impl_candidates: Vec<ImplCandidate<'tcx>>,
1392 trait_ref: ty::PolyTraitRef<'tcx>,
1393 body_id: hir::HirId,
1394 err: &mut Diagnostic,
1397 /// Gets the parent trait chain start
1398 fn get_parent_trait_ref(
1400 code: &ObligationCauseCode<'tcx>,
1401 ) -> Option<(String, Option<Span>)>;
1403 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1404 /// with the same path as `trait_ref`, a help message about
1405 /// a probable version mismatch is added to `err`
1406 fn note_version_mismatch(
1408 err: &mut Diagnostic,
1409 trait_ref: &ty::PolyTraitRef<'tcx>,
1412 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1415 /// For this to work, `new_self_ty` must have no escaping bound variables.
1416 fn mk_trait_obligation_with_new_self_ty(
1418 param_env: ty::ParamEnv<'tcx>,
1419 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1420 ) -> PredicateObligation<'tcx>;
1422 fn maybe_report_ambiguity(
1424 obligation: &PredicateObligation<'tcx>,
1425 body_id: Option<hir::BodyId>,
1428 fn predicate_can_apply(
1430 param_env: ty::ParamEnv<'tcx>,
1431 pred: ty::PolyTraitPredicate<'tcx>,
1434 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1436 fn suggest_unsized_bound_if_applicable(
1438 err: &mut Diagnostic,
1439 obligation: &PredicateObligation<'tcx>,
1442 fn annotate_source_of_ambiguity(
1444 err: &mut Diagnostic,
1446 predicate: ty::Predicate<'tcx>,
1449 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>);
1451 fn maybe_indirection_for_unsized(
1453 err: &mut Diagnostic,
1454 item: &'tcx Item<'tcx>,
1455 param: &'tcx GenericParam<'tcx>,
1458 fn is_recursive_obligation(
1460 obligated_types: &mut Vec<Ty<'tcx>>,
1461 cause_code: &ObligationCauseCode<'tcx>,
1465 impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
1466 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1467 // `error` occurring implies that `cond` occurs.
1468 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1473 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1474 let bound_error = error.kind();
1475 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1476 (ty::PredicateKind::Trait(..), ty::PredicateKind::Trait(error)) => {
1477 (cond, bound_error.rebind(error))
1480 // FIXME: make this work in other cases too.
1485 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1486 let bound_predicate = obligation.predicate.kind();
1487 if let ty::PredicateKind::Trait(implication) = bound_predicate.skip_binder() {
1488 let error = error.to_poly_trait_ref();
1489 let implication = bound_predicate.rebind(implication.trait_ref);
1490 // FIXME: I'm just not taking associated types at all here.
1491 // Eventually I'll need to implement param-env-aware
1492 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1493 let param_env = ty::ParamEnv::empty();
1494 if self.can_sub(param_env, error, implication).is_ok() {
1495 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1504 #[instrument(skip(self), level = "debug")]
1505 fn report_fulfillment_error(
1507 error: &FulfillmentError<'tcx>,
1508 body_id: Option<hir::BodyId>,
1511 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1512 self.report_selection_error(
1513 error.obligation.clone(),
1514 &error.root_obligation,
1518 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1519 self.report_projection_error(&error.obligation, e);
1521 FulfillmentErrorCode::CodeAmbiguity => {
1522 self.maybe_report_ambiguity(&error.obligation, body_id);
1524 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1525 self.report_mismatched_types(
1526 &error.obligation.cause,
1527 expected_found.expected,
1528 expected_found.found,
1533 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1534 let mut diag = self.report_mismatched_consts(
1535 &error.obligation.cause,
1536 expected_found.expected,
1537 expected_found.found,
1540 let code = error.obligation.cause.code().peel_derives().peel_match_impls();
1541 if let ObligationCauseCode::BindingObligation(..)
1542 | ObligationCauseCode::ItemObligation(..)
1543 | ObligationCauseCode::ExprBindingObligation(..)
1544 | ObligationCauseCode::ExprItemObligation(..) = code
1546 self.note_obligation_cause_code(
1548 &error.obligation.predicate,
1549 error.obligation.param_env,
1552 &mut Default::default(),
1557 FulfillmentErrorCode::CodeCycle(ref cycle) => {
1558 self.report_overflow_error_cycle(cycle);
1563 #[instrument(level = "debug", skip_all)]
1564 fn report_projection_error(
1566 obligation: &PredicateObligation<'tcx>,
1567 error: &MismatchedProjectionTypes<'tcx>,
1569 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1571 if predicate.references_error() {
1576 let mut err = error.err;
1577 let mut values = None;
1579 // try to find the mismatched types to report the error with.
1581 // this can fail if the problem was higher-ranked, in which
1582 // cause I have no idea for a good error message.
1583 let bound_predicate = predicate.kind();
1584 if let ty::PredicateKind::Projection(data) = bound_predicate.skip_binder() {
1585 let mut selcx = SelectionContext::new(self);
1586 let data = self.replace_bound_vars_with_fresh_vars(
1587 obligation.cause.span,
1588 infer::LateBoundRegionConversionTime::HigherRankedType,
1589 bound_predicate.rebind(data),
1591 let mut obligations = vec![];
1592 let normalized_ty = super::normalize_projection_type(
1594 obligation.param_env,
1596 obligation.cause.clone(),
1601 debug!(?obligation.cause, ?obligation.param_env);
1603 debug!(?normalized_ty, data.ty = ?data.term);
1605 let is_normalized_ty_expected = !matches!(
1606 obligation.cause.code().peel_derives(),
1607 ObligationCauseCode::ItemObligation(_)
1608 | ObligationCauseCode::BindingObligation(_, _)
1609 | ObligationCauseCode::ExprItemObligation(..)
1610 | ObligationCauseCode::ExprBindingObligation(..)
1611 | ObligationCauseCode::ObjectCastObligation(..)
1612 | ObligationCauseCode::OpaqueType
1614 if let Err(new_err) = self.at(&obligation.cause, obligation.param_env).eq_exp(
1615 is_normalized_ty_expected,
1619 values = Some((data, is_normalized_ty_expected, normalized_ty, data.term));
1625 .and_then(|(predicate, _, normalized_ty, expected_ty)| {
1626 self.maybe_detailed_projection_msg(predicate, normalized_ty, expected_ty)
1628 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
1629 let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
1631 let secondary_span = match predicate.kind().skip_binder() {
1632 ty::PredicateKind::Projection(proj) => self
1634 .opt_associated_item(proj.projection_ty.item_def_id)
1635 .and_then(|trait_assoc_item| {
1637 .trait_of_item(proj.projection_ty.item_def_id)
1638 .map(|id| (trait_assoc_item, id))
1640 .and_then(|(trait_assoc_item, id)| {
1641 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1642 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1644 .associated_items(did)
1645 .in_definition_order()
1646 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1649 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1651 hir::Node::TraitItem(hir::TraitItem {
1652 kind: hir::TraitItemKind::Type(_, Some(ty)),
1655 | hir::Node::ImplItem(hir::ImplItem {
1656 kind: hir::ImplItemKind::Type(ty),
1659 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1668 values.map(|(_, is_normalized_ty_expected, normalized_ty, term)| {
1669 infer::ValuePairs::Terms(ExpectedFound::new(
1670 is_normalized_ty_expected,
1679 self.note_obligation_cause(&mut diag, obligation);
1684 fn maybe_detailed_projection_msg(
1686 pred: ty::ProjectionPredicate<'tcx>,
1687 normalized_ty: ty::Term<'tcx>,
1688 expected_ty: ty::Term<'tcx>,
1689 ) -> Option<String> {
1690 let trait_def_id = pred.projection_ty.trait_def_id(self.tcx);
1691 let self_ty = pred.projection_ty.self_ty();
1693 if Some(pred.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output() {
1695 "expected `{self_ty}` to be a {fn_kind} that returns `{expected_ty}`, but it returns `{normalized_ty}`",
1696 fn_kind = self_ty.prefix_string(self.tcx)
1698 } else if Some(trait_def_id) == self.tcx.lang_items().future_trait() {
1700 "expected `{self_ty}` to be a future that resolves to `{expected_ty}`, but it resolves to `{normalized_ty}`"
1702 } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
1704 "expected `{self_ty}` to be an iterator that yields `{expected_ty}`, but it yields `{normalized_ty}`"
1715 ignoring_lifetimes: bool,
1716 ) -> Option<CandidateSimilarity> {
1717 /// returns the fuzzy category of a given type, or None
1718 /// if the type can be equated to any type.
1719 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1721 ty::Bool => Some(0),
1722 ty::Char => Some(1),
1724 ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => Some(2),
1728 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1729 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1730 ty::Array(..) | ty::Slice(..) => Some(6),
1731 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1732 ty::Dynamic(..) => Some(8),
1733 ty::Closure(..) => Some(9),
1734 ty::Tuple(..) => Some(10),
1735 ty::Param(..) => Some(11),
1736 ty::Projection(..) => Some(12),
1737 ty::Opaque(..) => Some(13),
1738 ty::Never => Some(14),
1739 ty::Adt(..) => Some(15),
1740 ty::Generator(..) => Some(16),
1741 ty::Foreign(..) => Some(17),
1742 ty::GeneratorWitness(..) => Some(18),
1743 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1747 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1750 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1758 if !ignoring_lifetimes {
1759 a = strip_references(a);
1760 b = strip_references(b);
1763 let cat_a = type_category(self.tcx, a)?;
1764 let cat_b = type_category(self.tcx, b)?;
1766 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1767 } else if cat_a == cat_b {
1768 match (a.kind(), b.kind()) {
1769 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1770 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1771 // Matching on references results in a lot of unhelpful
1772 // suggestions, so let's just not do that for now.
1774 // We still upgrade successful matches to `ignoring_lifetimes: true`
1775 // to prioritize that impl.
1776 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1777 self.fuzzy_match_tys(a, b, true).is_some()
1781 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1782 } else if ignoring_lifetimes {
1785 self.fuzzy_match_tys(a, b, true)
1789 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1790 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1791 hir::GeneratorKind::Gen => "a generator",
1792 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1793 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1794 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1798 fn find_similar_impl_candidates(
1800 trait_pred: ty::PolyTraitPredicate<'tcx>,
1801 ) -> Vec<ImplCandidate<'tcx>> {
1803 .all_impls(trait_pred.def_id())
1804 .filter_map(|def_id| {
1805 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
1808 .is_constness_satisfied_by(self.tcx.constness(def_id))
1813 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1815 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
1816 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1821 fn report_similar_impl_candidates(
1823 impl_candidates: Vec<ImplCandidate<'tcx>>,
1824 trait_ref: ty::PolyTraitRef<'tcx>,
1825 body_id: hir::HirId,
1826 err: &mut Diagnostic,
1828 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1831 let len = candidates.len();
1832 if candidates.len() == 0 {
1835 if candidates.len() == 1 {
1836 let ty_desc = match candidates[0].self_ty().kind() {
1837 ty::FnPtr(_) => Some("fn pointer"),
1840 let the_desc = match ty_desc {
1841 Some(desc) => format!(" implemented for {} `", desc),
1842 None => " implemented for `".to_string(),
1844 err.highlighted_help(vec![
1846 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1849 ("is".to_string(), Style::Highlight),
1850 (the_desc, Style::NoStyle),
1851 (candidates[0].self_ty().to_string(), Style::Highlight),
1852 ("`".to_string(), Style::NoStyle),
1856 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1857 // Check if the trait is the same in all cases. If so, we'll only show the type.
1858 let mut traits: Vec<_> =
1859 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1863 let mut candidates: Vec<String> = candidates
1866 if traits.len() == 1 {
1867 format!("\n {}", c.self_ty())
1876 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1878 "the following other types implement trait `{}`:{}{}",
1879 trait_ref.print_only_trait_path(),
1880 candidates[..end].join(""),
1881 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1886 let def_id = trait_ref.def_id();
1887 if impl_candidates.is_empty() {
1888 if self.tcx.trait_is_auto(def_id)
1889 || self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1890 || self.tcx.get_diagnostic_name(def_id).is_some()
1892 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1895 let normalized_impl_candidates: Vec<_> = self
1898 // Ignore automatically derived impls and `!Trait` impls.
1900 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1901 || self.tcx.is_builtin_derive(def_id)
1903 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1904 .filter(|trait_ref| {
1905 let self_ty = trait_ref.self_ty();
1906 // Avoid mentioning type parameters.
1907 if let ty::Param(_) = self_ty.kind() {
1910 // Avoid mentioning types that are private to another crate
1911 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
1912 // FIXME(compiler-errors): This could be generalized, both to
1913 // be more granular, and probably look past other `#[fundamental]`
1916 .visibility(def.did())
1917 .is_accessible_from(body_id.owner.def_id, self.tcx)
1923 return report(normalized_impl_candidates, err);
1926 let normalize = |candidate| {
1927 let infcx = self.tcx.infer_ctxt().build();
1929 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1930 .normalize(candidate)
1931 .map_or(candidate, |normalized| normalized.value)
1934 // Sort impl candidates so that ordering is consistent for UI tests.
1935 // because the ordering of `impl_candidates` may not be deterministic:
1936 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1938 // Prefer more similar candidates first, then sort lexicographically
1939 // by their normalized string representation.
1940 let mut normalized_impl_candidates_and_similarities = impl_candidates
1942 .map(|ImplCandidate { trait_ref, similarity }| {
1943 let normalized = normalize(trait_ref);
1944 (similarity, normalized)
1946 .collect::<Vec<_>>();
1947 normalized_impl_candidates_and_similarities.sort();
1948 normalized_impl_candidates_and_similarities.dedup();
1950 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
1952 .map(|(_, normalized)| normalized)
1953 .collect::<Vec<_>>();
1955 report(normalized_impl_candidates, err)
1958 /// Gets the parent trait chain start
1959 fn get_parent_trait_ref(
1961 code: &ObligationCauseCode<'tcx>,
1962 ) -> Option<(String, Option<Span>)> {
1964 ObligationCauseCode::BuiltinDerivedObligation(data) => {
1965 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
1966 match self.get_parent_trait_ref(&data.parent_code) {
1969 let ty = parent_trait_ref.skip_binder().self_ty();
1970 let span = TyCategory::from_ty(self.tcx, ty)
1971 .map(|(_, def_id)| self.tcx.def_span(def_id));
1972 Some((ty.to_string(), span))
1976 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
1977 self.get_parent_trait_ref(&parent_code)
1983 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1984 /// with the same path as `trait_ref`, a help message about
1985 /// a probable version mismatch is added to `err`
1986 fn note_version_mismatch(
1988 err: &mut Diagnostic,
1989 trait_ref: &ty::PolyTraitRef<'tcx>,
1991 let get_trait_impl = |trait_def_id| {
1992 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
1994 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
1995 let traits_with_same_path: std::collections::BTreeSet<_> = self
1998 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
1999 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
2001 let mut suggested = false;
2002 for trait_with_same_path in traits_with_same_path {
2003 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
2004 let impl_span = self.tcx.def_span(impl_def_id);
2005 err.span_help(impl_span, "trait impl with same name found");
2006 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
2007 let crate_msg = format!(
2008 "perhaps two different versions of crate `{}` are being used?",
2011 err.note(&crate_msg);
2018 fn mk_trait_obligation_with_new_self_ty(
2020 param_env: ty::ParamEnv<'tcx>,
2021 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
2022 ) -> PredicateObligation<'tcx> {
2023 let trait_pred = trait_ref_and_ty
2024 .map_bound(|(tr, new_self_ty)| tr.with_self_type(self.tcx, new_self_ty));
2026 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, trait_pred)
2029 #[instrument(skip(self), level = "debug")]
2030 fn maybe_report_ambiguity(
2032 obligation: &PredicateObligation<'tcx>,
2033 body_id: Option<hir::BodyId>,
2035 // Unable to successfully determine, probably means
2036 // insufficient type information, but could mean
2037 // ambiguous impls. The latter *ought* to be a
2038 // coherence violation, so we don't report it here.
2040 let predicate = self.resolve_vars_if_possible(obligation.predicate);
2041 let span = obligation.cause.span;
2043 debug!(?predicate, obligation.cause.code = ?obligation.cause.code());
2045 // Ambiguity errors are often caused as fallout from earlier errors.
2046 // We ignore them if this `infcx` is tainted in some cases below.
2048 let bound_predicate = predicate.kind();
2049 let mut err = match bound_predicate.skip_binder() {
2050 ty::PredicateKind::Trait(data) => {
2051 let trait_ref = bound_predicate.rebind(data.trait_ref);
2054 if predicate.references_error() {
2058 // This is kind of a hack: it frequently happens that some earlier
2059 // error prevents types from being fully inferred, and then we get
2060 // a bunch of uninteresting errors saying something like "<generic
2061 // #0> doesn't implement Sized". It may even be true that we
2062 // could just skip over all checks where the self-ty is an
2063 // inference variable, but I was afraid that there might be an
2064 // inference variable created, registered as an obligation, and
2065 // then never forced by writeback, and hence by skipping here we'd
2066 // be ignoring the fact that we don't KNOW the type works
2067 // out. Though even that would probably be harmless, given that
2068 // we're only talking about builtin traits, which are known to be
2069 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2070 // avoid inundating the user with unnecessary errors, but we now
2071 // check upstream for type errors and don't add the obligations to
2072 // begin with in those cases.
2073 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
2074 if let None = self.tainted_by_errors() {
2075 self.emit_inference_failure_err(
2078 trait_ref.self_ty().skip_binder().into(),
2087 // Typically, this ambiguity should only happen if
2088 // there are unresolved type inference variables
2089 // (otherwise it would suggest a coherence
2090 // failure). But given #21974 that is not necessarily
2091 // the case -- we can have multiple where clauses that
2092 // are only distinguished by a region, which results
2093 // in an ambiguity even when all types are fully
2094 // known, since we don't dispatch based on region
2097 // Pick the first substitution that still contains inference variables as the one
2098 // we're going to emit an error for. If there are none (see above), fall back to
2099 // a more general error.
2100 let subst = data.trait_ref.substs.iter().find(|s| s.has_non_region_infer());
2102 let mut err = if let Some(subst) = subst {
2103 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2109 "type annotations needed: cannot satisfy `{}`",
2114 let obligation = obligation.with(self.tcx, trait_ref.to_poly_trait_predicate());
2115 let mut selcx = SelectionContext::with_query_mode(
2117 crate::traits::TraitQueryMode::Standard,
2119 match selcx.select_from_obligation(&obligation) {
2121 let impls = ambiguity::recompute_applicable_impls(self.infcx, &obligation);
2122 let has_non_region_infer =
2123 trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_infer());
2124 // It doesn't make sense to talk about applicable impls if there are more
2125 // than a handful of them.
2126 if impls.len() > 1 && impls.len() < 5 && has_non_region_infer {
2127 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2129 if self.tainted_by_errors().is_some() {
2133 err.note(&format!("cannot satisfy `{}`", predicate));
2137 if self.tainted_by_errors().is_some() {
2141 err.note(&format!("cannot satisfy `{}`", predicate));
2145 if let ObligationCauseCode::ItemObligation(def_id) | ObligationCauseCode::ExprItemObligation(def_id, ..) = *obligation.cause.code() {
2146 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2147 } else if let Ok(snippet) = &self.tcx.sess.source_map().span_to_snippet(span)
2148 && let ObligationCauseCode::BindingObligation(def_id, _) | ObligationCauseCode::ExprBindingObligation(def_id, ..)
2149 = *obligation.cause.code()
2151 let generics = self.tcx.generics_of(def_id);
2152 if generics.params.iter().any(|p| p.name != kw::SelfUpper)
2153 && !snippet.ends_with('>')
2154 && !generics.has_impl_trait()
2155 && !self.tcx.fn_trait_kind_from_lang_item(def_id).is_some()
2157 // FIXME: To avoid spurious suggestions in functions where type arguments
2158 // where already supplied, we check the snippet to make sure it doesn't
2159 // end with a turbofish. Ideally we would have access to a `PathSegment`
2160 // instead. Otherwise we would produce the following output:
2162 // error[E0283]: type annotations needed
2163 // --> $DIR/issue-54954.rs:3:24
2165 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2166 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2168 // | cannot infer type
2169 // | help: consider specifying the type argument
2170 // | in the function call:
2171 // | `Tt::const_val::<[i8; 123]>::<T>`
2173 // LL | const fn const_val<T: Sized>() -> usize {
2174 // | - required by this bound in `Tt::const_val`
2176 // = note: cannot satisfy `_: Tt`
2178 // Clear any more general suggestions in favor of our specific one
2179 err.clear_suggestions();
2181 err.span_suggestion_verbose(
2182 span.shrink_to_hi(),
2184 "consider specifying the type argument{} in the function call",
2185 pluralize!(generics.params.len()),
2192 .map(|p| p.name.to_string())
2193 .collect::<Vec<String>>()
2196 Applicability::HasPlaceholders,
2201 if let (Some(body_id), Some(ty::subst::GenericArgKind::Type(_))) =
2202 (body_id, subst.map(|subst| subst.unpack()))
2204 struct FindExprBySpan<'hir> {
2206 result: Option<&'hir hir::Expr<'hir>>,
2209 impl<'v> hir::intravisit::Visitor<'v> for FindExprBySpan<'v> {
2210 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2211 if self.span == ex.span {
2212 self.result = Some(ex);
2214 hir::intravisit::walk_expr(self, ex);
2219 let mut expr_finder = FindExprBySpan { span, result: None };
2221 expr_finder.visit_expr(&self.tcx.hir().body(body_id).value);
2223 if let Some(hir::Expr {
2224 kind: hir::ExprKind::Path(hir::QPath::Resolved(None, path)), .. }
2225 ) = expr_finder.result
2228 trait_path_segment @ hir::PathSegment {
2229 res: rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id),
2233 ident: assoc_item_name,
2234 res: rustc_hir::def::Res::Def(_, item_id),
2238 && data.trait_ref.def_id == *trait_id
2239 && self.tcx.trait_of_item(*item_id) == Some(*trait_id)
2240 && let None = self.tainted_by_errors()
2242 let (verb, noun) = match self.tcx.associated_item(item_id).kind {
2243 ty::AssocKind::Const => ("refer to the", "constant"),
2244 ty::AssocKind::Fn => ("call", "function"),
2245 ty::AssocKind::Type => ("refer to the", "type"), // this is already covered by E0223, but this single match arm doesn't hurt here
2248 // Replace the more general E0283 with a more specific error
2250 err = self.tcx.sess.struct_span_err_with_code(
2253 "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type",
2255 rustc_errors::error_code!(E0790),
2258 if let Some(local_def_id) = data.trait_ref.def_id.as_local()
2259 && 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)
2260 && let Some(method_ref) = trait_item_refs.iter().find(|item_ref| item_ref.ident == *assoc_item_name) {
2261 err.span_label(method_ref.span, format!("`{}::{}` defined here", trait_name, assoc_item_name));
2264 err.span_label(span, format!("cannot {verb} associated {noun} of trait"));
2266 let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
2268 if trait_impls.blanket_impls().is_empty()
2269 && let Some((impl_ty, _)) = trait_impls.non_blanket_impls().iter().next()
2270 && let Some(impl_def_id) = impl_ty.def() {
2271 let message = if trait_impls.non_blanket_impls().len() == 1 {
2272 "use the fully-qualified path to the only available implementation".to_string()
2275 "use a fully-qualified path to a specific available implementation ({} found)",
2276 trait_impls.non_blanket_impls().len()
2279 let mut suggestions = vec![(
2280 trait_path_segment.ident.span.shrink_to_lo(),
2281 format!("<{} as ", self.tcx.type_of(impl_def_id))
2283 if let Some(generic_arg) = trait_path_segment.args {
2284 let between_span = trait_path_segment.ident.span.between(generic_arg.span_ext);
2285 // get rid of :: between Trait and <type>
2286 // must be '::' between them, otherwise the parser won't accept the code
2287 suggestions.push((between_span, "".to_string(),));
2288 suggestions.push((generic_arg.span_ext.shrink_to_hi(), format!(">")));
2290 suggestions.push((trait_path_segment.ident.span.shrink_to_hi(), format!(">")));
2292 err.multipart_suggestion(
2295 Applicability::MaybeIncorrect
2304 ty::PredicateKind::WellFormed(arg) => {
2305 // Same hacky approach as above to avoid deluging user
2306 // with error messages.
2307 if arg.references_error()
2308 || self.tcx.sess.has_errors().is_some()
2309 || self.tainted_by_errors().is_some()
2314 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2317 ty::PredicateKind::Subtype(data) => {
2318 if data.references_error()
2319 || self.tcx.sess.has_errors().is_some()
2320 || self.tainted_by_errors().is_some()
2322 // no need to overload user in such cases
2325 let SubtypePredicate { a_is_expected: _, a, b } = data;
2326 // both must be type variables, or the other would've been instantiated
2327 assert!(a.is_ty_var() && b.is_ty_var());
2328 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2330 ty::PredicateKind::Projection(data) => {
2331 if predicate.references_error() || self.tainted_by_errors().is_some() {
2338 .chain(Some(data.term.into_arg()))
2339 .find(|g| g.has_non_region_infer());
2340 if let Some(subst) = subst {
2341 let mut err = self.emit_inference_failure_err(
2348 err.note(&format!("cannot satisfy `{}`", predicate));
2351 // If we can't find a substitution, just print a generic error
2352 let mut err = struct_span_err!(
2356 "type annotations needed: cannot satisfy `{}`",
2359 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2364 ty::PredicateKind::ConstEvaluatable(data) => {
2365 if predicate.references_error() || self.tainted_by_errors().is_some() {
2368 let subst = data.walk().find(|g| g.is_non_region_infer());
2369 if let Some(subst) = subst {
2370 let err = self.emit_inference_failure_err(
2379 // If we can't find a substitution, just print a generic error
2380 let mut err = struct_span_err!(
2384 "type annotations needed: cannot satisfy `{}`",
2387 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2392 if self.tcx.sess.has_errors().is_some() || self.tainted_by_errors().is_some() {
2395 let mut err = struct_span_err!(
2399 "type annotations needed: cannot satisfy `{}`",
2402 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2406 self.note_obligation_cause(&mut err, obligation);
2410 fn annotate_source_of_ambiguity(
2412 err: &mut Diagnostic,
2414 predicate: ty::Predicate<'tcx>,
2416 let mut spans = vec![];
2417 let mut crates = vec![];
2418 let mut post = vec![];
2419 for def_id in impls {
2420 match self.tcx.span_of_impl(*def_id) {
2421 Ok(span) => spans.push(span),
2424 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2430 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2432 crate_names.dedup();
2436 if self.tainted_by_errors().is_some()
2437 && (crate_names.len() == 1
2439 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2440 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2442 // Avoid complaining about other inference issues for expressions like
2443 // `42 >> 1`, where the types are still `{integer}`, but we want to
2444 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2445 // NOTE(eddyb) this was `.cancel()`, but `err`
2446 // is borrowed, so we can't fully defuse it.
2447 err.downgrade_to_delayed_bug();
2451 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2452 let post = if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2453 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2454 } else if post.len() == 1 {
2455 format!(": `{}`", post[0])
2460 match (spans.len(), crates.len(), crate_names.len()) {
2462 err.note(&format!("cannot satisfy `{}`", predicate));
2465 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2469 "{} in the following crates: {}{}",
2471 crate_names.join(", "),
2476 let span: MultiSpan = spans.into();
2477 err.span_note(span, &msg);
2480 let span: MultiSpan = spans.into();
2481 err.span_note(span, &msg);
2483 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2487 let span: MultiSpan = spans.into();
2488 err.span_note(span, &msg);
2490 "and more `impl`s found in the following crates: {}{}",
2491 crate_names.join(", "),
2498 /// Returns `true` if the trait predicate may apply for *some* assignment
2499 /// to the type parameters.
2500 fn predicate_can_apply(
2502 param_env: ty::ParamEnv<'tcx>,
2503 pred: ty::PolyTraitPredicate<'tcx>,
2505 struct ParamToVarFolder<'a, 'tcx> {
2506 infcx: &'a InferCtxt<'tcx>,
2507 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2510 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2511 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2515 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2516 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2517 let infcx = self.infcx;
2518 *self.var_map.entry(ty).or_insert_with(|| {
2519 infcx.next_ty_var(TypeVariableOrigin {
2520 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2525 ty.super_fold_with(self)
2531 let mut selcx = SelectionContext::new(self);
2534 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2536 let cleaned_pred = super::project::normalize(
2539 ObligationCause::dummy(),
2545 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, cleaned_pred);
2547 // We don't use `InferCtxt::predicate_may_hold` because that
2548 // will re-run predicates that overflow locally, which ends up
2549 // taking a really long time to compute.
2550 self.evaluate_obligation(&obligation).map_or(false, |eval| eval.may_apply())
2554 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2555 // First, attempt to add note to this error with an async-await-specific
2556 // message, and fall back to regular note otherwise.
2557 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2558 self.note_obligation_cause_code(
2560 &obligation.predicate,
2561 obligation.param_env,
2562 obligation.cause.code(),
2564 &mut Default::default(),
2566 self.suggest_unsized_bound_if_applicable(err, obligation);
2570 #[instrument(level = "debug", skip_all)]
2571 fn suggest_unsized_bound_if_applicable(
2573 err: &mut Diagnostic,
2574 obligation: &PredicateObligation<'tcx>,
2576 let ty::PredicateKind::Trait(pred) = obligation.predicate.kind().skip_binder() else { return; };
2577 let (ObligationCauseCode::BindingObligation(item_def_id, span)
2578 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..))
2579 = *obligation.cause.code().peel_derives() else { return; };
2580 debug!(?pred, ?item_def_id, ?span);
2582 let (Some(node), true) = (
2583 self.tcx.hir().get_if_local(item_def_id),
2584 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2588 self.maybe_suggest_unsized_generics(err, span, node);
2591 #[instrument(level = "debug", skip_all)]
2592 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>) {
2593 let Some(generics) = node.generics() else {
2596 let sized_trait = self.tcx.lang_items().sized_trait();
2597 debug!(?generics.params);
2598 debug!(?generics.predicates);
2599 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2602 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2603 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2604 let explicitly_sized = generics
2605 .bounds_for_param(param.def_id)
2606 .flat_map(|bp| bp.bounds)
2607 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2608 if explicitly_sized {
2615 // Only suggest indirection for uses of type parameters in ADTs.
2617 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2621 if self.maybe_indirection_for_unsized(err, item, param) {
2627 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2628 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param.def_id)
2632 (span.shrink_to_hi(), ":")
2634 err.span_suggestion_verbose(
2636 "consider relaxing the implicit `Sized` restriction",
2637 format!("{} ?Sized", separator),
2638 Applicability::MachineApplicable,
2642 fn maybe_indirection_for_unsized(
2644 err: &mut Diagnostic,
2646 param: &GenericParam<'tcx>,
2648 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2649 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2650 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2652 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2653 visitor.visit_item(item);
2654 if visitor.invalid_spans.is_empty() {
2657 let mut multispan: MultiSpan = param.span.into();
2658 multispan.push_span_label(
2660 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2662 for sp in visitor.invalid_spans {
2663 multispan.push_span_label(
2665 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2671 "you could relax the implicit `Sized` bound on `{T}` if it were \
2672 used through indirection like `&{T}` or `Box<{T}>`",
2673 T = param.name.ident(),
2679 fn is_recursive_obligation(
2681 obligated_types: &mut Vec<Ty<'tcx>>,
2682 cause_code: &ObligationCauseCode<'tcx>,
2684 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2685 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2686 let self_ty = parent_trait_ref.skip_binder().self_ty();
2687 if obligated_types.iter().any(|ot| ot == &self_ty) {
2690 if let ty::Adt(def, substs) = self_ty.kind()
2691 && let [arg] = &substs[..]
2692 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2693 && let ty::Adt(inner_def, _) = ty.kind()
2703 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2704 /// `param: ?Sized` would be a valid constraint.
2705 struct FindTypeParam {
2706 param: rustc_span::Symbol,
2707 invalid_spans: Vec<Span>,
2711 impl<'v> Visitor<'v> for FindTypeParam {
2712 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2713 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2716 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2717 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2718 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2719 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2720 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2721 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2722 // in that case should make what happened clear enough.
2724 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2725 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2726 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2729 debug!(?ty, "FindTypeParam::visit_ty");
2730 self.invalid_spans.push(ty.span);
2733 hir::TyKind::Path(_) => {
2734 let prev = self.nested;
2736 hir::intravisit::walk_ty(self, ty);
2740 hir::intravisit::walk_ty(self, ty);
2746 /// Summarizes information
2749 /// An argument of non-tuple type. Parameters are (name, ty)
2750 Arg(String, String),
2752 /// An argument of tuple type. For a "found" argument, the span is
2753 /// the location in the source of the pattern. For an "expected"
2754 /// argument, it will be None. The vector is a list of (name, ty)
2755 /// strings for the components of the tuple.
2756 Tuple(Option<Span>, Vec<(String, String)>),
2760 fn empty() -> ArgKind {
2761 ArgKind::Arg("_".to_owned(), "_".to_owned())
2764 /// Creates an `ArgKind` from the expected type of an
2765 /// argument. It has no name (`_`) and an optional source span.
2766 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2768 ty::Tuple(tys) => ArgKind::Tuple(
2770 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2772 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2777 struct HasNumericInferVisitor;
2779 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2782 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2783 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2784 ControlFlow::Break(())
2786 ControlFlow::CONTINUE
2791 pub enum DefIdOrName {