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};
13 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
14 use crate::traits::query::normalize::QueryNormalizeExt as _;
15 use crate::traits::specialize::to_pretty_impl_header;
16 use crate::traits::NormalizeExt;
17 use on_unimplemented::OnUnimplementedNote;
18 use on_unimplemented::TypeErrCtxtExt as _;
19 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
21 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
25 use rustc_hir::def::Namespace;
26 use rustc_hir::def_id::DefId;
27 use rustc_hir::intravisit::Visitor;
28 use rustc_hir::GenericParam;
31 use rustc_infer::infer::error_reporting::TypeErrCtxt;
32 use rustc_infer::infer::{InferOk, TypeTrace};
33 use rustc_middle::traits::select::OverflowError;
34 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
35 use rustc_middle::ty::error::ExpectedFound;
36 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
37 use rustc_middle::ty::print::{FmtPrinter, Print};
38 use rustc_middle::ty::{
39 self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
42 use rustc_session::Limit;
43 use rustc_span::def_id::LOCAL_CRATE;
44 use rustc_span::symbol::{kw, sym};
45 use rustc_span::{ExpnKind, Span, DUMMY_SP};
48 use std::ops::ControlFlow;
49 use suggestions::TypeErrCtxtExt as _;
51 pub use rustc_infer::traits::error_reporting::*;
53 // When outputting impl candidates, prefer showing those that are more similar.
55 // We also compare candidates after skipping lifetimes, which has a lower
56 // priority than exact matches.
57 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
58 pub enum CandidateSimilarity {
59 Exact { ignoring_lifetimes: bool },
60 Fuzzy { ignoring_lifetimes: bool },
63 #[derive(Debug, Clone, Copy)]
64 pub struct ImplCandidate<'tcx> {
65 pub trait_ref: ty::TraitRef<'tcx>,
66 pub similarity: CandidateSimilarity,
69 pub trait InferCtxtExt<'tcx> {
70 /// Given some node representing a fn-like thing in the HIR map,
71 /// returns a span and `ArgKind` information that describes the
72 /// arguments it expects. This can be supplied to
73 /// `report_arg_count_mismatch`.
74 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)>;
76 /// Reports an error when the number of arguments needed by a
77 /// trait match doesn't match the number that the expression
79 fn report_arg_count_mismatch(
82 found_span: Option<Span>,
83 expected_args: Vec<ArgKind>,
84 found_args: Vec<ArgKind>,
86 closure_pipe_span: Option<Span>,
87 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
89 /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
90 /// in that order, and returns the generic type corresponding to the
91 /// argument of that trait (corresponding to the closure arguments).
92 fn type_implements_fn_trait(
94 param_env: ty::ParamEnv<'tcx>,
95 ty: ty::Binder<'tcx, Ty<'tcx>>,
96 constness: ty::BoundConstness,
97 polarity: ty::ImplPolarity,
98 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
101 pub trait TypeErrCtxtExt<'tcx> {
102 fn report_overflow_error<T>(
106 suggest_increasing_limit: bool,
107 mutate: impl FnOnce(&mut Diagnostic),
112 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
113 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug;
115 fn report_fulfillment_errors(
117 errors: &[FulfillmentError<'tcx>],
118 body_id: Option<hir::BodyId>,
119 ) -> ErrorGuaranteed;
121 fn report_overflow_obligation<T>(
123 obligation: &Obligation<'tcx, T>,
124 suggest_increasing_limit: bool,
127 T: ToPredicate<'tcx> + Clone;
129 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
131 fn report_overflow_obligation_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
133 /// The `root_obligation` parameter should be the `root_obligation` field
134 /// from a `FulfillmentError`. If no `FulfillmentError` is available,
135 /// then it should be the same as `obligation`.
136 fn report_selection_error(
138 obligation: PredicateObligation<'tcx>,
139 root_obligation: &PredicateObligation<'tcx>,
140 error: &SelectionError<'tcx>,
144 impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
145 /// Given some node representing a fn-like thing in the HIR map,
146 /// returns a span and `ArgKind` information that describes the
147 /// arguments it expects. This can be supplied to
148 /// `report_arg_count_mismatch`.
149 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)> {
150 let sm = self.tcx.sess.source_map();
151 let hir = self.tcx.hir();
153 Node::Expr(&hir::Expr {
154 kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, fn_arg_span, .. }),
163 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
170 sm.span_to_snippet(pat.span)
172 .map(|snippet| (snippet, "_".to_owned()))
174 .collect::<Option<Vec<_>>>()?,
177 let name = sm.span_to_snippet(arg.pat.span).ok()?;
178 Some(ArgKind::Arg(name, "_".to_owned()))
181 .collect::<Option<Vec<ArgKind>>>()?,
183 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
184 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
185 | Node::TraitItem(&hir::TraitItem {
186 kind: hir::TraitItemKind::Fn(ref sig, _), ..
193 .map(|arg| match arg.kind {
194 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
196 vec![("_".to_owned(), "_".to_owned()); tys.len()],
198 _ => ArgKind::empty(),
200 .collect::<Vec<ArgKind>>(),
202 Node::Ctor(ref variant_data) => {
203 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
204 (span, None, vec![ArgKind::empty(); variant_data.fields().len()])
206 _ => panic!("non-FnLike node found: {:?}", node),
210 /// Reports an error when the number of arguments needed by a
211 /// trait match doesn't match the number that the expression
213 fn report_arg_count_mismatch(
216 found_span: Option<Span>,
217 expected_args: Vec<ArgKind>,
218 found_args: Vec<ArgKind>,
220 closure_arg_span: Option<Span>,
221 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
222 let kind = if is_closure { "closure" } else { "function" };
224 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
225 let arg_length = arguments.len();
226 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
227 match (arg_length, arguments.get(0)) {
228 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
229 format!("a single {}-tuple as argument", fields.len())
234 if distinct && arg_length > 1 { "distinct " } else { "" },
235 pluralize!(arg_length)
240 let expected_str = args_str(&expected_args, &found_args);
241 let found_str = args_str(&found_args, &expected_args);
243 let mut err = struct_span_err!(
247 "{} is expected to take {}, but it takes {}",
253 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
255 if let Some(found_span) = found_span {
256 err.span_label(found_span, format!("takes {}", found_str));
258 // Suggest to take and ignore the arguments with expected_args_length `_`s if
259 // found arguments is empty (assume the user just wants to ignore args in this case).
260 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
261 if found_args.is_empty() && is_closure {
262 let underscores = vec!["_"; expected_args.len()].join(", ");
263 err.span_suggestion_verbose(
264 closure_arg_span.unwrap_or(found_span),
266 "consider changing the closure to take and ignore the expected argument{}",
267 pluralize!(expected_args.len())
269 format!("|{}|", underscores),
270 Applicability::MachineApplicable,
274 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
275 if fields.len() == expected_args.len() {
278 .map(|(name, _)| name.to_owned())
279 .collect::<Vec<String>>()
281 err.span_suggestion_verbose(
283 "change the closure to take multiple arguments instead of a single tuple",
284 format!("|{}|", sugg),
285 Applicability::MachineApplicable,
289 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
290 && fields.len() == found_args.len()
297 .map(|arg| match arg {
298 ArgKind::Arg(name, _) => name.to_owned(),
301 .collect::<Vec<String>>()
303 // add type annotations if available
304 if found_args.iter().any(|arg| match arg {
305 ArgKind::Arg(_, ty) => ty != "_",
312 .map(|(_, ty)| ty.to_owned())
313 .collect::<Vec<String>>()
320 err.span_suggestion_verbose(
322 "change the closure to accept a tuple instead of individual arguments",
324 Applicability::MachineApplicable,
332 fn type_implements_fn_trait(
334 param_env: ty::ParamEnv<'tcx>,
335 ty: ty::Binder<'tcx, Ty<'tcx>>,
336 constness: ty::BoundConstness,
337 polarity: ty::ImplPolarity,
338 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
339 self.commit_if_ok(|_| {
340 for trait_def_id in [
341 self.tcx.lang_items().fn_trait(),
342 self.tcx.lang_items().fn_mut_trait(),
343 self.tcx.lang_items().fn_once_trait(),
345 let Some(trait_def_id) = trait_def_id else { continue };
346 // Make a fresh inference variable so we can determine what the substitutions
348 let var = self.next_ty_var(TypeVariableOrigin {
350 kind: TypeVariableOriginKind::MiscVariable,
352 let trait_ref = self.tcx.mk_trait_ref(trait_def_id, [ty.skip_binder(), var]);
353 let obligation = Obligation::new(
355 ObligationCause::dummy(),
357 ty.rebind(ty::TraitPredicate { trait_ref, constness, polarity }),
359 let ocx = ObligationCtxt::new_in_snapshot(self);
360 ocx.register_obligation(obligation);
361 if ocx.select_all_or_error().is_empty() {
364 .fn_trait_kind_from_def_id(trait_def_id)
365 .expect("expected to map DefId to ClosureKind"),
366 ty.rebind(self.resolve_vars_if_possible(var)),
375 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
376 fn report_fulfillment_errors(
378 errors: &[FulfillmentError<'tcx>],
379 body_id: Option<hir::BodyId>,
380 ) -> ErrorGuaranteed {
382 struct ErrorDescriptor<'tcx> {
383 predicate: ty::Predicate<'tcx>,
384 index: Option<usize>, // None if this is an old error
387 let mut error_map: FxIndexMap<_, Vec<_>> = self
388 .reported_trait_errors
391 .map(|(&span, predicates)| {
396 .map(|&predicate| ErrorDescriptor { predicate, index: None })
402 for (index, error) in errors.iter().enumerate() {
403 // We want to ignore desugarings here: spans are equivalent even
404 // if one is the result of a desugaring and the other is not.
405 let mut span = error.obligation.cause.span;
406 let expn_data = span.ctxt().outer_expn_data();
407 if let ExpnKind::Desugaring(_) = expn_data.kind {
408 span = expn_data.call_site;
411 error_map.entry(span).or_default().push(ErrorDescriptor {
412 predicate: error.obligation.predicate,
416 self.reported_trait_errors
420 .push(error.obligation.predicate);
423 // We do this in 2 passes because we want to display errors in order, though
424 // maybe it *is* better to sort errors by span or something.
425 let mut is_suppressed = vec![false; errors.len()];
426 for (_, error_set) in error_map.iter() {
427 // We want to suppress "duplicate" errors with the same span.
428 for error in error_set {
429 if let Some(index) = error.index {
430 // Suppress errors that are either:
431 // 1) strictly implied by another error.
432 // 2) implied by an error with a smaller index.
433 for error2 in error_set {
434 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
435 // Avoid errors being suppressed by already-suppressed
436 // errors, to prevent all errors from being suppressed
441 if self.error_implies(error2.predicate, error.predicate)
442 && !(error2.index >= error.index
443 && self.error_implies(error.predicate, error2.predicate))
445 info!("skipping {:?} (implied by {:?})", error, error2);
446 is_suppressed[index] = true;
454 for (error, suppressed) in iter::zip(errors, is_suppressed) {
456 self.report_fulfillment_error(error, body_id);
460 self.tcx.sess.delay_span_bug(DUMMY_SP, "expected fullfillment errors")
463 /// Reports that an overflow has occurred and halts compilation. We
464 /// halt compilation unconditionally because it is important that
465 /// overflows never be masked -- they basically represent computations
466 /// whose result could not be truly determined and thus we can't say
467 /// if the program type checks or not -- and they are unusual
468 /// occurrences in any case.
469 fn report_overflow_error<T>(
473 suggest_increasing_limit: bool,
474 mutate: impl FnOnce(&mut Diagnostic),
479 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
480 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
482 let predicate = self.resolve_vars_if_possible(predicate.clone());
483 let mut pred_str = predicate.to_string();
485 if pred_str.len() > 50 {
486 // We don't need to save the type to a file, we will be talking about this type already
487 // in a separate note when we explain the obligation, so it will be available that way.
489 .print(FmtPrinter::new_with_limit(
492 rustc_session::Limit(6),
497 let mut err = struct_span_err!(
501 "overflow evaluating the requirement `{}`",
505 if suggest_increasing_limit {
506 self.suggest_new_overflow_limit(&mut err);
512 self.tcx.sess.abort_if_errors();
516 /// Reports that an overflow has occurred and halts compilation. We
517 /// halt compilation unconditionally because it is important that
518 /// overflows never be masked -- they basically represent computations
519 /// whose result could not be truly determined and thus we can't say
520 /// if the program type checks or not -- and they are unusual
521 /// occurrences in any case.
522 fn report_overflow_obligation<T>(
524 obligation: &Obligation<'tcx, T>,
525 suggest_increasing_limit: bool,
528 T: ToPredicate<'tcx> + Clone,
530 let predicate = obligation.predicate.clone().to_predicate(self.tcx);
531 let predicate = self.resolve_vars_if_possible(predicate);
532 self.report_overflow_error(
534 obligation.cause.span,
535 suggest_increasing_limit,
537 self.note_obligation_cause_code(
540 obligation.param_env,
541 obligation.cause.code(),
543 &mut Default::default(),
549 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic) {
550 let suggested_limit = match self.tcx.recursion_limit() {
551 Limit(0) => Limit(2),
555 "consider increasing the recursion limit by adding a \
556 `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
558 self.tcx.crate_name(LOCAL_CRATE),
562 /// Reports that a cycle was detected which led to overflow and halts
563 /// compilation. This is equivalent to `report_overflow_obligation` except
564 /// that we can give a more helpful error message (and, in particular,
565 /// we do not suggest increasing the overflow limit, which is not
567 fn report_overflow_obligation_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
568 let cycle = self.resolve_vars_if_possible(cycle.to_owned());
569 assert!(!cycle.is_empty());
571 debug!(?cycle, "report_overflow_error_cycle");
573 // The 'deepest' obligation is most likely to have a useful
575 self.report_overflow_obligation(
576 cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(),
581 fn report_selection_error(
583 mut obligation: PredicateObligation<'tcx>,
584 root_obligation: &PredicateObligation<'tcx>,
585 error: &SelectionError<'tcx>,
588 let mut span = obligation.cause.span;
589 // FIXME: statically guarantee this by tainting after the diagnostic is emitted
590 self.set_tainted_by_errors(
591 tcx.sess.delay_span_bug(span, "`report_selection_error` did not emit an error"),
594 let mut err = match *error {
595 SelectionError::Unimplemented => {
596 // If this obligation was generated as a result of well-formedness checking, see if we
597 // can get a better error message by performing HIR-based well-formedness checking.
598 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
599 root_obligation.cause.code().peel_derives()
600 && !obligation.predicate.has_non_region_infer()
602 if let Some(cause) = self
604 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
606 obligation.cause = cause.clone();
607 span = obligation.cause.span;
610 if let ObligationCauseCode::CompareImplItemObligation {
614 } = *obligation.cause.code()
616 self.report_extra_impl_obligation(
620 &format!("`{}`", obligation.predicate),
626 let bound_predicate = obligation.predicate.kind();
627 match bound_predicate.skip_binder() {
628 ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
629 let trait_predicate = bound_predicate.rebind(trait_predicate);
630 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
632 trait_predicate.remap_constness_diag(obligation.param_env);
633 let predicate_is_const = ty::BoundConstness::ConstIfConst
634 == trait_predicate.skip_binder().constness;
636 if self.tcx.sess.has_errors().is_some()
637 && trait_predicate.references_error()
641 let trait_ref = trait_predicate.to_poly_trait_ref();
642 let (post_message, pre_message, type_def) = self
643 .get_parent_trait_ref(obligation.cause.code())
646 format!(" in `{}`", t),
647 format!("within `{}`, ", t),
648 s.map(|s| (format!("within this `{}`", t), s)),
651 .unwrap_or_default();
653 let OnUnimplementedNote {
659 } = self.on_unimplemented_note(trait_ref, &obligation);
660 let have_alt_message = message.is_some() || label.is_some();
661 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
663 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
664 let (message, note, append_const_msg) = if is_try_conversion {
667 "`?` couldn't convert the error to `{}`",
668 trait_ref.skip_binder().self_ty(),
671 "the question mark operation (`?`) implicitly performs a \
672 conversion on the error value using the `From` trait"
678 (message, note, append_const_msg)
681 let mut err = struct_span_err!(
687 .and_then(|cannot_do_this| {
688 match (predicate_is_const, append_const_msg) {
689 // do nothing if predicate is not const
690 (false, _) => Some(cannot_do_this),
691 // suggested using default post message
692 (true, Some(None)) => {
693 Some(format!("{cannot_do_this} in const contexts"))
695 // overridden post message
696 (true, Some(Some(post_message))) => {
697 Some(format!("{cannot_do_this}{post_message}"))
699 // fallback to generic message
700 (true, None) => None,
703 .unwrap_or_else(|| format!(
704 "the trait bound `{}` is not satisfied{}",
705 trait_predicate, post_message,
709 if is_try_conversion && let Some(ret_span) = self.return_type_span(&obligation) {
713 "expected `{}` because of this",
714 trait_ref.skip_binder().self_ty()
719 if Some(trait_ref.def_id()) == tcx.lang_items().tuple_trait() {
720 match obligation.cause.code().peel_derives() {
721 ObligationCauseCode::RustCall => {
722 err.set_primary_message("functions with the \"rust-call\" ABI must take a single non-self tuple argument");
724 ObligationCauseCode::BindingObligation(def_id, _)
725 | ObligationCauseCode::ItemObligation(def_id)
726 if tcx.is_fn_trait(*def_id) =>
728 err.code(rustc_errors::error_code!(E0059));
729 err.set_primary_message(format!(
730 "type parameter to bare `{}` trait must be a tuple",
731 tcx.def_path_str(*def_id)
738 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
739 && predicate_is_const
741 err.note("`~const Drop` was renamed to `~const Destruct`");
742 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
745 let explanation = if let ObligationCauseCode::MainFunctionType =
746 obligation.cause.code()
748 "consider using `()`, or a `Result`".to_owned()
750 let ty_desc = match trait_ref.skip_binder().self_ty().kind() {
751 ty::FnDef(_, _) => Some("fn item"),
752 ty::Closure(_, _) => Some("closure"),
757 Some(desc) => format!(
758 "{}the trait `{}` is not implemented for {} `{}`",
760 trait_predicate.print_modifiers_and_trait_path(),
762 trait_ref.skip_binder().self_ty(),
765 "{}the trait `{}` is not implemented for `{}`",
767 trait_predicate.print_modifiers_and_trait_path(),
768 trait_ref.skip_binder().self_ty(),
773 if self.suggest_add_reference_to_arg(
779 self.note_obligation_cause(&mut err, &obligation);
783 if let Some(ref s) = label {
784 // If it has a custom `#[rustc_on_unimplemented]`
785 // error message, let's display it as the label!
786 err.span_label(span, s);
787 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
788 // When the self type is a type param We don't need to "the trait
789 // `std::marker::Sized` is not implemented for `T`" as we will point
790 // at the type param with a label to suggest constraining it.
791 err.help(&explanation);
794 err.span_label(span, explanation);
797 if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
798 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
799 self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
802 let mut unsatisfied_const = false;
803 if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
804 let non_const_predicate = trait_ref.without_const();
805 let non_const_obligation = Obligation {
806 cause: obligation.cause.clone(),
807 param_env: obligation.param_env.without_const(),
808 predicate: non_const_predicate.to_predicate(tcx),
809 recursion_depth: obligation.recursion_depth,
811 if self.predicate_may_hold(&non_const_obligation) {
812 unsatisfied_const = true;
816 "the trait `{}` is implemented for `{}`, \
817 but that implementation is not `const`",
818 non_const_predicate.print_modifiers_and_trait_path(),
819 trait_ref.skip_binder().self_ty(),
825 if let Some((msg, span)) = type_def {
826 err.span_label(span, &msg);
828 if let Some(ref s) = note {
829 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
830 err.note(s.as_str());
832 if let Some(ref s) = parent_label {
835 .opt_local_def_id(obligation.cause.body_id)
837 tcx.hir().body_owner_def_id(hir::BodyId {
838 hir_id: obligation.cause.body_id,
841 err.span_label(tcx.def_span(body), s);
844 self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
845 self.suggest_dereferencing_index(&obligation, &mut err, trait_predicate);
847 self.suggest_dereferences(&obligation, &mut err, trait_predicate);
848 suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
850 self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
851 suggested |= self.suggest_semicolon_removal(
857 self.note_version_mismatch(&mut err, &trait_ref);
858 self.suggest_remove_await(&obligation, &mut err);
859 self.suggest_derive(&obligation, &mut err, trait_predicate);
861 if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
862 self.suggest_await_before_try(
870 if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
876 // If the obligation failed due to a missing implementation of the
877 // `Unsize` trait, give a pointer to why that might be the case
879 "all implementations of `Unsize` are provided \
880 automatically by the compiler, see \
881 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
882 for more information",
886 let is_fn_trait = tcx.is_fn_trait(trait_ref.def_id());
887 let is_target_feature_fn = if let ty::FnDef(def_id, _) =
888 *trait_ref.skip_binder().self_ty().kind()
890 !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
894 if is_fn_trait && is_target_feature_fn {
896 "`#[target_feature]` functions do not implement the `Fn` traits",
900 // Try to report a help message
902 && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
903 obligation.param_env,
905 trait_predicate.skip_binder().constness,
906 trait_predicate.skip_binder().polarity,
909 // If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
910 // suggestion to add trait bounds for the type, since we only typically implement
911 // these traits once.
913 // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
916 self.tcx.fn_trait_kind_from_def_id(trait_ref.def_id())
917 .expect("expected to map DefId to ClosureKind");
918 if !implemented_kind.extends(selected_kind) {
921 "`{}` implements `{}`, but it must implement `{}`, which is more general",
922 trait_ref.skip_binder().self_ty(),
929 // Note any argument mismatches
930 let given_ty = params.skip_binder();
931 let expected_ty = trait_ref.skip_binder().substs.type_at(1);
932 if let ty::Tuple(given) = given_ty.kind()
933 && let ty::Tuple(expected) = expected_ty.kind()
935 if expected.len() != given.len() {
936 // Note number of types that were expected and given
939 "expected a closure taking {} argument{}, but one taking {} argument{} was given",
941 pluralize!(given.len()),
943 pluralize!(expected.len()),
946 } else if !self.same_type_modulo_infer(given_ty, expected_ty) {
947 // Print type mismatch
948 let (expected_args, given_args) =
949 self.cmp(given_ty, expected_ty);
950 err.note_expected_found(
951 &"a closure with arguments",
953 &"a closure with arguments",
958 } else if !trait_ref.has_non_region_infer()
959 && self.predicate_can_apply(obligation.param_env, trait_predicate)
961 // If a where-clause may be useful, remind the
962 // user that they can add it.
964 // don't display an on-unimplemented note, as
965 // these notes will often be of the form
966 // "the type `T` can't be frobnicated"
967 // which is somewhat confusing.
968 self.suggest_restricting_param_bound(
972 obligation.cause.body_id,
974 } else if !suggested && !unsatisfied_const {
975 // Can't show anything else useful, try to find similar impls.
976 let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
977 if !self.report_similar_impl_candidates(
980 obligation.cause.body_id,
983 // This is *almost* equivalent to
984 // `obligation.cause.code().peel_derives()`, but it gives us the
985 // trait predicate for that corresponding root obligation. This
986 // lets us get a derived obligation from a type parameter, like
987 // when calling `string.strip_suffix(p)` where `p` is *not* an
988 // implementer of `Pattern<'_>`.
989 let mut code = obligation.cause.code();
990 let mut trait_pred = trait_predicate;
991 let mut peeled = false;
992 while let Some((parent_code, parent_trait_pred)) = code.parent() {
994 if let Some(parent_trait_pred) = parent_trait_pred {
995 trait_pred = parent_trait_pred;
999 let def_id = trait_pred.def_id();
1000 // Mention *all* the `impl`s for the *top most* obligation, the
1001 // user might have meant to use one of them, if any found. We skip
1002 // auto-traits or fundamental traits that might not be exactly what
1003 // the user might expect to be presented with. Instead this is
1004 // useful for less general traits.
1006 && !self.tcx.trait_is_auto(def_id)
1007 && !self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1009 let trait_ref = trait_pred.to_poly_trait_ref();
1010 let impl_candidates =
1011 self.find_similar_impl_candidates(trait_pred);
1012 self.report_similar_impl_candidates(
1015 obligation.cause.body_id,
1022 // Changing mutability doesn't make a difference to whether we have
1023 // an `Unsize` impl (Fixes ICE in #71036)
1025 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
1028 // If this error is due to `!: Trait` not implemented but `(): Trait` is
1029 // implemented, and fallback has occurred, then it could be due to a
1030 // variable that used to fallback to `()` now falling back to `!`. Issue a
1031 // note informing about the change in behaviour.
1032 if trait_predicate.skip_binder().self_ty().is_never()
1033 && self.fallback_has_occurred
1035 let predicate = trait_predicate.map_bound(|trait_pred| {
1036 trait_pred.with_self_type(self.tcx, self.tcx.mk_unit())
1038 let unit_obligation = obligation.with(tcx, predicate);
1039 if self.predicate_may_hold(&unit_obligation) {
1041 "this error might have been caused by changes to \
1042 Rust's type-inference algorithm (see issue #48950 \
1043 <https://github.com/rust-lang/rust/issues/48950> \
1044 for more information)",
1046 err.help("did you intend to use the type `()` here instead?");
1050 // Return early if the trait is Debug or Display and the invocation
1051 // originates within a standard library macro, because the output
1052 // is otherwise overwhelming and unhelpful (see #85844 for an
1056 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
1057 Some(macro_def_id) => {
1058 let crate_name = tcx.crate_name(macro_def_id.krate);
1059 crate_name == sym::std || crate_name == sym::core
1066 self.tcx.get_diagnostic_name(trait_ref.def_id()),
1067 Some(sym::Debug | sym::Display)
1077 ty::PredicateKind::Subtype(predicate) => {
1078 // Errors for Subtype predicates show up as
1079 // `FulfillmentErrorCode::CodeSubtypeError`,
1080 // not selection error.
1081 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
1084 ty::PredicateKind::Coerce(predicate) => {
1085 // Errors for Coerce predicates show up as
1086 // `FulfillmentErrorCode::CodeSubtypeError`,
1087 // not selection error.
1088 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
1091 ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
1092 | ty::PredicateKind::Clause(ty::Clause::Projection(..))
1093 | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..)) => {
1094 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1099 "the requirement `{}` is not satisfied",
1104 ty::PredicateKind::ObjectSafe(trait_def_id) => {
1105 let violations = self.tcx.object_safety_violations(trait_def_id);
1106 report_object_safety_error(self.tcx, span, trait_def_id, violations)
1109 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
1110 let found_kind = self.closure_kind(closure_substs).unwrap();
1111 let closure_span = self.tcx.def_span(closure_def_id);
1112 let mut err = struct_span_err!(
1116 "expected a closure that implements the `{}` trait, \
1117 but this closure only implements `{}`",
1124 format!("this closure implements `{}`, not `{}`", found_kind, kind),
1127 obligation.cause.span,
1128 format!("the requirement to implement `{}` derives from here", kind),
1131 // Additional context information explaining why the closure only implements
1132 // a particular trait.
1133 if let Some(typeck_results) = &self.typeck_results {
1137 .local_def_id_to_hir_id(closure_def_id.expect_local());
1138 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
1139 (ty::ClosureKind::FnOnce, Some((span, place))) => {
1143 "closure is `FnOnce` because it moves the \
1144 variable `{}` out of its environment",
1145 ty::place_to_string_for_capture(tcx, place)
1149 (ty::ClosureKind::FnMut, Some((span, place))) => {
1153 "closure is `FnMut` because it mutates the \
1154 variable `{}` here",
1155 ty::place_to_string_for_capture(tcx, place)
1166 ty::PredicateKind::WellFormed(ty) => {
1167 if !self.tcx.sess.opts.unstable_opts.chalk {
1168 // WF predicates cannot themselves make
1169 // errors. They can only block due to
1170 // ambiguity; otherwise, they always
1171 // degenerate into other obligations
1172 // (which may fail).
1173 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
1175 // FIXME: we'll need a better message which takes into account
1176 // which bounds actually failed to hold.
1177 self.tcx.sess.struct_span_err(
1179 &format!("the type `{}` is not well-formed (chalk)", ty),
1184 ty::PredicateKind::ConstEvaluatable(..) => {
1185 // Errors for `ConstEvaluatable` predicates show up as
1186 // `SelectionError::ConstEvalFailure`,
1187 // not `Unimplemented`.
1190 "const-evaluatable requirement gave wrong error: `{:?}`",
1195 ty::PredicateKind::ConstEquate(..) => {
1196 // Errors for `ConstEquate` predicates show up as
1197 // `SelectionError::ConstEvalFailure`,
1198 // not `Unimplemented`.
1201 "const-equate requirement gave wrong error: `{:?}`",
1206 ty::PredicateKind::Ambiguous => span_bug!(span, "ambiguous"),
1208 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
1210 "TypeWellFormedFromEnv predicate should only exist in the environment"
1215 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
1216 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
1217 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
1219 if expected_trait_ref.self_ty().references_error() {
1223 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
1227 let found_did = match *found_trait_ty.kind() {
1231 | ty::Generator(did, ..) => Some(did),
1232 ty::Adt(def, _) => Some(def.did()),
1236 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
1238 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1239 // We check closures twice, with obligations flowing in different directions,
1240 // but we want to complain about them only once.
1244 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1246 let mut not_tupled = false;
1248 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
1249 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1252 vec![ArgKind::empty()]
1256 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1257 let expected = match expected_ty.kind() {
1258 ty::Tuple(ref tys) => {
1259 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
1263 vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())]
1267 // If this is a `Fn` family trait and either the expected or found
1268 // is not tupled, then fall back to just a regular mismatch error.
1269 // This shouldn't be common unless manually implementing one of the
1270 // traits manually, but don't make it more confusing when it does
1272 if Some(expected_trait_ref.def_id()) != tcx.lang_items().gen_trait() && not_tupled {
1273 self.report_and_explain_type_error(
1274 TypeTrace::poly_trait_refs(
1280 ty::error::TypeError::Mismatch,
1282 } else if found.len() == expected.len() {
1283 self.report_closure_arg_mismatch(
1288 obligation.cause.code(),
1291 let (closure_span, closure_arg_span, found) = found_did
1293 let node = self.tcx.hir().get_if_local(did)?;
1294 let (found_span, closure_arg_span, found) =
1295 self.get_fn_like_arguments(node)?;
1296 Some((Some(found_span), closure_arg_span, found))
1298 .unwrap_or((found_span, None, found));
1300 self.report_arg_count_mismatch(
1305 found_trait_ty.is_closure(),
1311 TraitNotObjectSafe(did) => {
1312 let violations = self.tcx.object_safety_violations(did);
1313 report_object_safety_error(self.tcx, span, did, violations)
1316 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1318 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1321 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1322 if !self.tcx.features().generic_const_exprs {
1323 let mut err = self.tcx.sess.struct_span_err(
1325 "constant expression depends on a generic parameter",
1327 // FIXME(const_generics): we should suggest to the user how they can resolve this
1328 // issue. However, this is currently not actually possible
1329 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1331 // Note that with `feature(generic_const_exprs)` this case should not
1333 err.note("this may fail depending on what value the parameter takes");
1338 match obligation.predicate.kind().skip_binder() {
1339 ty::PredicateKind::ConstEvaluatable(ct) => {
1340 let ty::ConstKind::Unevaluated(uv) = ct.kind() else {
1341 bug!("const evaluatable failed for non-unevaluated const `{ct:?}`");
1344 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1345 let const_span = self.tcx.def_span(uv.def.did);
1346 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1347 Ok(snippet) => err.help(&format!(
1348 "try adding a `where` bound using this expression: `where [(); {}]:`",
1351 _ => err.help("consider adding a `where` bound using this expression"),
1358 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1364 // Already reported in the query.
1365 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1366 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1367 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1370 // Already reported.
1371 Overflow(OverflowError::Error(_)) => {
1372 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1376 bug!("overflow should be handled before the `report_selection_error` path");
1378 SelectionError::ErrorReporting => {
1379 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1383 self.note_obligation_cause(&mut err, &obligation);
1384 self.point_at_returns_when_relevant(&mut err, &obligation);
1390 trait InferCtxtPrivExt<'tcx> {
1391 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1392 // `error` occurring implies that `cond` occurs.
1393 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1395 fn report_fulfillment_error(
1397 error: &FulfillmentError<'tcx>,
1398 body_id: Option<hir::BodyId>,
1401 fn report_projection_error(
1403 obligation: &PredicateObligation<'tcx>,
1404 error: &MismatchedProjectionTypes<'tcx>,
1407 fn maybe_detailed_projection_msg(
1409 pred: ty::ProjectionPredicate<'tcx>,
1410 normalized_ty: ty::Term<'tcx>,
1411 expected_ty: ty::Term<'tcx>,
1412 ) -> Option<String>;
1418 ignoring_lifetimes: bool,
1419 ) -> Option<CandidateSimilarity>;
1421 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1423 fn find_similar_impl_candidates(
1425 trait_pred: ty::PolyTraitPredicate<'tcx>,
1426 ) -> Vec<ImplCandidate<'tcx>>;
1428 fn report_similar_impl_candidates(
1430 impl_candidates: Vec<ImplCandidate<'tcx>>,
1431 trait_ref: ty::PolyTraitRef<'tcx>,
1432 body_id: hir::HirId,
1433 err: &mut Diagnostic,
1436 /// Gets the parent trait chain start
1437 fn get_parent_trait_ref(
1439 code: &ObligationCauseCode<'tcx>,
1440 ) -> Option<(String, Option<Span>)>;
1442 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1443 /// with the same path as `trait_ref`, a help message about
1444 /// a probable version mismatch is added to `err`
1445 fn note_version_mismatch(
1447 err: &mut Diagnostic,
1448 trait_ref: &ty::PolyTraitRef<'tcx>,
1451 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1454 /// For this to work, `new_self_ty` must have no escaping bound variables.
1455 fn mk_trait_obligation_with_new_self_ty(
1457 param_env: ty::ParamEnv<'tcx>,
1458 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1459 ) -> PredicateObligation<'tcx>;
1461 fn maybe_report_ambiguity(
1463 obligation: &PredicateObligation<'tcx>,
1464 body_id: Option<hir::BodyId>,
1467 fn predicate_can_apply(
1469 param_env: ty::ParamEnv<'tcx>,
1470 pred: ty::PolyTraitPredicate<'tcx>,
1473 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1475 fn suggest_unsized_bound_if_applicable(
1477 err: &mut Diagnostic,
1478 obligation: &PredicateObligation<'tcx>,
1481 fn annotate_source_of_ambiguity(
1483 err: &mut Diagnostic,
1485 predicate: ty::Predicate<'tcx>,
1488 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>);
1490 fn maybe_indirection_for_unsized(
1492 err: &mut Diagnostic,
1493 item: &'tcx Item<'tcx>,
1494 param: &'tcx GenericParam<'tcx>,
1497 fn is_recursive_obligation(
1499 obligated_types: &mut Vec<Ty<'tcx>>,
1500 cause_code: &ObligationCauseCode<'tcx>,
1504 impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
1505 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1506 // `error` occurring implies that `cond` occurs.
1507 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1512 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1513 let bound_error = error.kind();
1514 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1516 ty::PredicateKind::Clause(ty::Clause::Trait(..)),
1517 ty::PredicateKind::Clause(ty::Clause::Trait(error)),
1518 ) => (cond, bound_error.rebind(error)),
1520 // FIXME: make this work in other cases too.
1525 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1526 let bound_predicate = obligation.predicate.kind();
1527 if let ty::PredicateKind::Clause(ty::Clause::Trait(implication)) =
1528 bound_predicate.skip_binder()
1530 let error = error.to_poly_trait_ref();
1531 let implication = bound_predicate.rebind(implication.trait_ref);
1532 // FIXME: I'm just not taking associated types at all here.
1533 // Eventually I'll need to implement param-env-aware
1534 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1535 let param_env = ty::ParamEnv::empty();
1536 if self.can_sub(param_env, error, implication).is_ok() {
1537 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1546 #[instrument(skip(self), level = "debug")]
1547 fn report_fulfillment_error(
1549 error: &FulfillmentError<'tcx>,
1550 body_id: Option<hir::BodyId>,
1553 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1554 self.report_selection_error(
1555 error.obligation.clone(),
1556 &error.root_obligation,
1560 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1561 self.report_projection_error(&error.obligation, e);
1563 FulfillmentErrorCode::CodeAmbiguity => {
1564 self.maybe_report_ambiguity(&error.obligation, body_id);
1566 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1567 self.report_mismatched_types(
1568 &error.obligation.cause,
1569 expected_found.expected,
1570 expected_found.found,
1575 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1576 let mut diag = self.report_mismatched_consts(
1577 &error.obligation.cause,
1578 expected_found.expected,
1579 expected_found.found,
1582 let code = error.obligation.cause.code().peel_derives().peel_match_impls();
1583 if let ObligationCauseCode::BindingObligation(..)
1584 | ObligationCauseCode::ItemObligation(..)
1585 | ObligationCauseCode::ExprBindingObligation(..)
1586 | ObligationCauseCode::ExprItemObligation(..) = code
1588 self.note_obligation_cause_code(
1590 &error.obligation.predicate,
1591 error.obligation.param_env,
1594 &mut Default::default(),
1599 FulfillmentErrorCode::CodeCycle(ref cycle) => {
1600 self.report_overflow_obligation_cycle(cycle);
1605 #[instrument(level = "debug", skip_all)]
1606 fn report_projection_error(
1608 obligation: &PredicateObligation<'tcx>,
1609 error: &MismatchedProjectionTypes<'tcx>,
1611 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1613 if predicate.references_error() {
1618 let ocx = ObligationCtxt::new_in_snapshot(self);
1620 // try to find the mismatched types to report the error with.
1622 // this can fail if the problem was higher-ranked, in which
1623 // cause I have no idea for a good error message.
1624 let bound_predicate = predicate.kind();
1625 let (values, err) = if let ty::PredicateKind::Clause(ty::Clause::Projection(data)) =
1626 bound_predicate.skip_binder()
1628 let data = self.replace_bound_vars_with_fresh_vars(
1629 obligation.cause.span,
1630 infer::LateBoundRegionConversionTime::HigherRankedType,
1631 bound_predicate.rebind(data),
1633 let normalized_ty = ocx.normalize(
1635 obligation.param_env,
1637 .mk_projection(data.projection_ty.item_def_id, data.projection_ty.substs),
1640 debug!(?obligation.cause, ?obligation.param_env);
1642 debug!(?normalized_ty, data.ty = ?data.term);
1644 let is_normalized_ty_expected = !matches!(
1645 obligation.cause.code().peel_derives(),
1646 ObligationCauseCode::ItemObligation(_)
1647 | ObligationCauseCode::BindingObligation(_, _)
1648 | ObligationCauseCode::ExprItemObligation(..)
1649 | ObligationCauseCode::ExprBindingObligation(..)
1650 | ObligationCauseCode::ObjectCastObligation(..)
1651 | ObligationCauseCode::OpaqueType
1653 let expected_ty = data.term.ty().unwrap_or_else(|| self.tcx.ty_error());
1655 // constrain inference variables a bit more to nested obligations from normalize so
1656 // we can have more helpful errors.
1657 ocx.select_where_possible();
1659 if let Err(new_err) = ocx.eq_exp(
1661 obligation.param_env,
1662 is_normalized_ty_expected,
1666 (Some((data, is_normalized_ty_expected, normalized_ty, expected_ty)), new_err)
1675 .and_then(|(predicate, _, normalized_ty, expected_ty)| {
1676 self.maybe_detailed_projection_msg(
1678 normalized_ty.into(),
1682 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
1683 let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
1685 let secondary_span = match predicate.kind().skip_binder() {
1686 ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => self
1688 .opt_associated_item(proj.projection_ty.item_def_id)
1689 .and_then(|trait_assoc_item| {
1691 .trait_of_item(proj.projection_ty.item_def_id)
1692 .map(|id| (trait_assoc_item, id))
1694 .and_then(|(trait_assoc_item, id)| {
1695 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1696 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1698 .associated_items(did)
1699 .in_definition_order()
1700 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1703 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1705 hir::Node::TraitItem(hir::TraitItem {
1706 kind: hir::TraitItemKind::Type(_, Some(ty)),
1709 | hir::Node::ImplItem(hir::ImplItem {
1710 kind: hir::ImplItemKind::Type(ty),
1713 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1722 values.map(|(_, is_normalized_ty_expected, normalized_ty, expected_ty)| {
1723 infer::ValuePairs::Terms(ExpectedFound::new(
1724 is_normalized_ty_expected,
1725 normalized_ty.into(),
1733 self.note_obligation_cause(&mut diag, obligation);
1738 fn maybe_detailed_projection_msg(
1740 pred: ty::ProjectionPredicate<'tcx>,
1741 normalized_ty: ty::Term<'tcx>,
1742 expected_ty: ty::Term<'tcx>,
1743 ) -> Option<String> {
1744 let trait_def_id = pred.projection_ty.trait_def_id(self.tcx);
1745 let self_ty = pred.projection_ty.self_ty();
1747 if Some(pred.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output() {
1749 "expected `{self_ty}` to be a {fn_kind} that returns `{expected_ty}`, but it returns `{normalized_ty}`",
1750 fn_kind = self_ty.prefix_string(self.tcx)
1752 } else if Some(trait_def_id) == self.tcx.lang_items().future_trait() {
1754 "expected `{self_ty}` to be a future that resolves to `{expected_ty}`, but it resolves to `{normalized_ty}`"
1756 } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
1758 "expected `{self_ty}` to be an iterator that yields `{expected_ty}`, but it yields `{normalized_ty}`"
1769 ignoring_lifetimes: bool,
1770 ) -> Option<CandidateSimilarity> {
1771 /// returns the fuzzy category of a given type, or None
1772 /// if the type can be equated to any type.
1773 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1775 ty::Bool => Some(0),
1776 ty::Char => Some(1),
1778 ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => Some(2),
1782 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1783 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1784 ty::Array(..) | ty::Slice(..) => Some(6),
1785 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1786 ty::Dynamic(..) => Some(8),
1787 ty::Closure(..) => Some(9),
1788 ty::Tuple(..) => Some(10),
1789 ty::Param(..) => Some(11),
1790 ty::Projection(..) => Some(12),
1791 ty::Opaque(..) => Some(13),
1792 ty::Never => Some(14),
1793 ty::Adt(..) => Some(15),
1794 ty::Generator(..) => Some(16),
1795 ty::Foreign(..) => Some(17),
1796 ty::GeneratorWitness(..) => Some(18),
1797 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1801 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1804 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1812 if !ignoring_lifetimes {
1813 a = strip_references(a);
1814 b = strip_references(b);
1817 let cat_a = type_category(self.tcx, a)?;
1818 let cat_b = type_category(self.tcx, b)?;
1820 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1821 } else if cat_a == cat_b {
1822 match (a.kind(), b.kind()) {
1823 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1824 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1825 // Matching on references results in a lot of unhelpful
1826 // suggestions, so let's just not do that for now.
1828 // We still upgrade successful matches to `ignoring_lifetimes: true`
1829 // to prioritize that impl.
1830 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1831 self.fuzzy_match_tys(a, b, true).is_some()
1835 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1836 } else if ignoring_lifetimes {
1839 self.fuzzy_match_tys(a, b, true)
1843 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1844 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1845 hir::GeneratorKind::Gen => "a generator",
1846 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1847 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1848 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1852 fn find_similar_impl_candidates(
1854 trait_pred: ty::PolyTraitPredicate<'tcx>,
1855 ) -> Vec<ImplCandidate<'tcx>> {
1856 let mut candidates: Vec<_> = self
1858 .all_impls(trait_pred.def_id())
1859 .filter_map(|def_id| {
1860 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
1863 .is_constness_satisfied_by(self.tcx.constness(def_id))
1868 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1870 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
1871 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1874 if candidates.iter().any(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. })) {
1875 // If any of the candidates is a perfect match, we don't want to show all of them.
1876 // This is particularly relevant for the case of numeric types (as they all have the
1878 candidates.retain(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. }));
1883 fn report_similar_impl_candidates(
1885 impl_candidates: Vec<ImplCandidate<'tcx>>,
1886 trait_ref: ty::PolyTraitRef<'tcx>,
1887 body_id: hir::HirId,
1888 err: &mut Diagnostic,
1890 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1893 let len = candidates.len();
1894 if candidates.len() == 0 {
1897 if candidates.len() == 1 {
1898 let ty_desc = match candidates[0].self_ty().kind() {
1899 ty::FnPtr(_) => Some("fn pointer"),
1902 let the_desc = match ty_desc {
1903 Some(desc) => format!(" implemented for {} `", desc),
1904 None => " implemented for `".to_string(),
1906 err.highlighted_help(vec![
1908 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1911 ("is".to_string(), Style::Highlight),
1912 (the_desc, Style::NoStyle),
1913 (candidates[0].self_ty().to_string(), Style::Highlight),
1914 ("`".to_string(), Style::NoStyle),
1918 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1919 // Check if the trait is the same in all cases. If so, we'll only show the type.
1920 let mut traits: Vec<_> =
1921 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1925 let mut candidates: Vec<String> = candidates
1928 if traits.len() == 1 {
1929 format!("\n {}", c.self_ty())
1938 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1940 "the following other types implement trait `{}`:{}{}",
1941 trait_ref.print_only_trait_path(),
1942 candidates[..end].join(""),
1943 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1948 let def_id = trait_ref.def_id();
1949 if impl_candidates.is_empty() {
1950 if self.tcx.trait_is_auto(def_id)
1951 || self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1952 || self.tcx.get_diagnostic_name(def_id).is_some()
1954 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1957 let normalized_impl_candidates: Vec<_> = self
1960 // Ignore automatically derived impls and `!Trait` impls.
1962 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1963 || self.tcx.is_builtin_derive(def_id)
1965 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1966 .filter(|trait_ref| {
1967 let self_ty = trait_ref.self_ty();
1968 // Avoid mentioning type parameters.
1969 if let ty::Param(_) = self_ty.kind() {
1972 // Avoid mentioning types that are private to another crate
1973 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
1974 // FIXME(compiler-errors): This could be generalized, both to
1975 // be more granular, and probably look past other `#[fundamental]`
1978 .visibility(def.did())
1979 .is_accessible_from(body_id.owner.def_id, self.tcx)
1985 return report(normalized_impl_candidates, err);
1988 // Sort impl candidates so that ordering is consistent for UI tests.
1989 // because the ordering of `impl_candidates` may not be deterministic:
1990 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1992 // Prefer more similar candidates first, then sort lexicographically
1993 // by their normalized string representation.
1994 let mut normalized_impl_candidates_and_similarities = impl_candidates
1996 .map(|ImplCandidate { trait_ref, similarity }| {
1997 // FIXME(compiler-errors): This should be using `NormalizeExt::normalize`
1998 let normalized = self
1999 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
2000 .query_normalize(trait_ref)
2001 .map_or(trait_ref, |normalized| normalized.value);
2002 (similarity, normalized)
2004 .collect::<Vec<_>>();
2005 normalized_impl_candidates_and_similarities.sort();
2006 normalized_impl_candidates_and_similarities.dedup();
2008 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
2010 .map(|(_, normalized)| normalized)
2011 .collect::<Vec<_>>();
2013 report(normalized_impl_candidates, err)
2016 /// Gets the parent trait chain start
2017 fn get_parent_trait_ref(
2019 code: &ObligationCauseCode<'tcx>,
2020 ) -> Option<(String, Option<Span>)> {
2022 ObligationCauseCode::BuiltinDerivedObligation(data) => {
2023 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2024 match self.get_parent_trait_ref(&data.parent_code) {
2027 let ty = parent_trait_ref.skip_binder().self_ty();
2028 let span = TyCategory::from_ty(self.tcx, ty)
2029 .map(|(_, def_id)| self.tcx.def_span(def_id));
2030 Some((ty.to_string(), span))
2034 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
2035 self.get_parent_trait_ref(&parent_code)
2041 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
2042 /// with the same path as `trait_ref`, a help message about
2043 /// a probable version mismatch is added to `err`
2044 fn note_version_mismatch(
2046 err: &mut Diagnostic,
2047 trait_ref: &ty::PolyTraitRef<'tcx>,
2049 let get_trait_impl = |trait_def_id| {
2050 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
2052 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
2053 let traits_with_same_path: std::collections::BTreeSet<_> = self
2056 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
2057 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
2059 let mut suggested = false;
2060 for trait_with_same_path in traits_with_same_path {
2061 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
2062 let impl_span = self.tcx.def_span(impl_def_id);
2063 err.span_help(impl_span, "trait impl with same name found");
2064 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
2065 let crate_msg = format!(
2066 "perhaps two different versions of crate `{}` are being used?",
2069 err.note(&crate_msg);
2076 fn mk_trait_obligation_with_new_self_ty(
2078 param_env: ty::ParamEnv<'tcx>,
2079 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
2080 ) -> PredicateObligation<'tcx> {
2081 let trait_pred = trait_ref_and_ty
2082 .map_bound(|(tr, new_self_ty)| tr.with_self_type(self.tcx, new_self_ty));
2084 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, trait_pred)
2087 #[instrument(skip(self), level = "debug")]
2088 fn maybe_report_ambiguity(
2090 obligation: &PredicateObligation<'tcx>,
2091 body_id: Option<hir::BodyId>,
2093 // Unable to successfully determine, probably means
2094 // insufficient type information, but could mean
2095 // ambiguous impls. The latter *ought* to be a
2096 // coherence violation, so we don't report it here.
2098 let predicate = self.resolve_vars_if_possible(obligation.predicate);
2099 let span = obligation.cause.span;
2101 debug!(?predicate, obligation.cause.code = ?obligation.cause.code());
2103 // Ambiguity errors are often caused as fallout from earlier errors.
2104 // We ignore them if this `infcx` is tainted in some cases below.
2106 let bound_predicate = predicate.kind();
2107 let mut err = match bound_predicate.skip_binder() {
2108 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
2109 let trait_ref = bound_predicate.rebind(data.trait_ref);
2112 if predicate.references_error() {
2116 // This is kind of a hack: it frequently happens that some earlier
2117 // error prevents types from being fully inferred, and then we get
2118 // a bunch of uninteresting errors saying something like "<generic
2119 // #0> doesn't implement Sized". It may even be true that we
2120 // could just skip over all checks where the self-ty is an
2121 // inference variable, but I was afraid that there might be an
2122 // inference variable created, registered as an obligation, and
2123 // then never forced by writeback, and hence by skipping here we'd
2124 // be ignoring the fact that we don't KNOW the type works
2125 // out. Though even that would probably be harmless, given that
2126 // we're only talking about builtin traits, which are known to be
2127 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2128 // avoid inundating the user with unnecessary errors, but we now
2129 // check upstream for type errors and don't add the obligations to
2130 // begin with in those cases.
2131 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
2132 if let None = self.tainted_by_errors() {
2133 self.emit_inference_failure_err(
2136 trait_ref.self_ty().skip_binder().into(),
2145 // Typically, this ambiguity should only happen if
2146 // there are unresolved type inference variables
2147 // (otherwise it would suggest a coherence
2148 // failure). But given #21974 that is not necessarily
2149 // the case -- we can have multiple where clauses that
2150 // are only distinguished by a region, which results
2151 // in an ambiguity even when all types are fully
2152 // known, since we don't dispatch based on region
2155 // Pick the first substitution that still contains inference variables as the one
2156 // we're going to emit an error for. If there are none (see above), fall back to
2157 // a more general error.
2158 let subst = data.trait_ref.substs.iter().find(|s| s.has_non_region_infer());
2160 let mut err = if let Some(subst) = subst {
2161 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2167 "type annotations needed: cannot satisfy `{}`",
2172 let obligation = obligation.with(self.tcx, trait_ref);
2173 let mut selcx = SelectionContext::new(&self);
2174 match selcx.select_from_obligation(&obligation) {
2176 let impls = ambiguity::recompute_applicable_impls(self.infcx, &obligation);
2177 let has_non_region_infer =
2178 trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_infer());
2179 // It doesn't make sense to talk about applicable impls if there are more
2180 // than a handful of them.
2181 if impls.len() > 1 && impls.len() < 5 && has_non_region_infer {
2182 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2184 if self.tainted_by_errors().is_some() {
2188 err.note(&format!("cannot satisfy `{}`", predicate));
2192 if self.tainted_by_errors().is_some() {
2196 err.note(&format!("cannot satisfy `{}`", predicate));
2200 if let ObligationCauseCode::ItemObligation(def_id) | ObligationCauseCode::ExprItemObligation(def_id, ..) = *obligation.cause.code() {
2201 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2202 } else if let Ok(snippet) = &self.tcx.sess.source_map().span_to_snippet(span)
2203 && let ObligationCauseCode::BindingObligation(def_id, _) | ObligationCauseCode::ExprBindingObligation(def_id, ..)
2204 = *obligation.cause.code()
2206 let generics = self.tcx.generics_of(def_id);
2207 if generics.params.iter().any(|p| p.name != kw::SelfUpper)
2208 && !snippet.ends_with('>')
2209 && !generics.has_impl_trait()
2210 && !self.tcx.is_fn_trait(def_id)
2212 // FIXME: To avoid spurious suggestions in functions where type arguments
2213 // where already supplied, we check the snippet to make sure it doesn't
2214 // end with a turbofish. Ideally we would have access to a `PathSegment`
2215 // instead. Otherwise we would produce the following output:
2217 // error[E0283]: type annotations needed
2218 // --> $DIR/issue-54954.rs:3:24
2220 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2221 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2223 // | cannot infer type
2224 // | help: consider specifying the type argument
2225 // | in the function call:
2226 // | `Tt::const_val::<[i8; 123]>::<T>`
2228 // LL | const fn const_val<T: Sized>() -> usize {
2229 // | - required by this bound in `Tt::const_val`
2231 // = note: cannot satisfy `_: Tt`
2233 // Clear any more general suggestions in favor of our specific one
2234 err.clear_suggestions();
2236 err.span_suggestion_verbose(
2237 span.shrink_to_hi(),
2239 "consider specifying the type argument{} in the function call",
2240 pluralize!(generics.params.len()),
2247 .map(|p| p.name.to_string())
2248 .collect::<Vec<String>>()
2251 Applicability::HasPlaceholders,
2256 if let (Some(body_id), Some(ty::subst::GenericArgKind::Type(_))) =
2257 (body_id, subst.map(|subst| subst.unpack()))
2259 struct FindExprBySpan<'hir> {
2261 result: Option<&'hir hir::Expr<'hir>>,
2264 impl<'v> hir::intravisit::Visitor<'v> for FindExprBySpan<'v> {
2265 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2266 if self.span == ex.span {
2267 self.result = Some(ex);
2269 hir::intravisit::walk_expr(self, ex);
2274 let mut expr_finder = FindExprBySpan { span, result: None };
2276 expr_finder.visit_expr(&self.tcx.hir().body(body_id).value);
2278 if let Some(hir::Expr {
2279 kind: hir::ExprKind::Path(hir::QPath::Resolved(None, path)), .. }
2280 ) = expr_finder.result
2283 trait_path_segment @ hir::PathSegment {
2284 res: rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id),
2288 ident: assoc_item_name,
2289 res: rustc_hir::def::Res::Def(_, item_id),
2293 && data.trait_ref.def_id == *trait_id
2294 && self.tcx.trait_of_item(*item_id) == Some(*trait_id)
2295 && let None = self.tainted_by_errors()
2297 let (verb, noun) = match self.tcx.associated_item(item_id).kind {
2298 ty::AssocKind::Const => ("refer to the", "constant"),
2299 ty::AssocKind::Fn => ("call", "function"),
2300 ty::AssocKind::Type => ("refer to the", "type"), // this is already covered by E0223, but this single match arm doesn't hurt here
2303 // Replace the more general E0283 with a more specific error
2305 err = self.tcx.sess.struct_span_err_with_code(
2308 "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type",
2310 rustc_errors::error_code!(E0790),
2313 if let Some(local_def_id) = data.trait_ref.def_id.as_local()
2314 && 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)
2315 && let Some(method_ref) = trait_item_refs.iter().find(|item_ref| item_ref.ident == *assoc_item_name) {
2316 err.span_label(method_ref.span, format!("`{}::{}` defined here", trait_name, assoc_item_name));
2319 err.span_label(span, format!("cannot {verb} associated {noun} of trait"));
2321 let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
2323 if trait_impls.blanket_impls().is_empty()
2324 && let Some((impl_ty, _)) = trait_impls.non_blanket_impls().iter().next()
2325 && let Some(impl_def_id) = impl_ty.def() {
2326 let message = if trait_impls.non_blanket_impls().len() == 1 {
2327 "use the fully-qualified path to the only available implementation".to_string()
2330 "use a fully-qualified path to a specific available implementation ({} found)",
2331 trait_impls.non_blanket_impls().len()
2334 let mut suggestions = vec![(
2335 trait_path_segment.ident.span.shrink_to_lo(),
2336 format!("<{} as ", self.tcx.type_of(impl_def_id))
2338 if let Some(generic_arg) = trait_path_segment.args {
2339 let between_span = trait_path_segment.ident.span.between(generic_arg.span_ext);
2340 // get rid of :: between Trait and <type>
2341 // must be '::' between them, otherwise the parser won't accept the code
2342 suggestions.push((between_span, "".to_string(),));
2343 suggestions.push((generic_arg.span_ext.shrink_to_hi(), format!(">")));
2345 suggestions.push((trait_path_segment.ident.span.shrink_to_hi(), format!(">")));
2347 err.multipart_suggestion(
2350 Applicability::MaybeIncorrect
2359 ty::PredicateKind::WellFormed(arg) => {
2360 // Same hacky approach as above to avoid deluging user
2361 // with error messages.
2362 if arg.references_error()
2363 || self.tcx.sess.has_errors().is_some()
2364 || self.tainted_by_errors().is_some()
2369 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2372 ty::PredicateKind::Subtype(data) => {
2373 if data.references_error()
2374 || self.tcx.sess.has_errors().is_some()
2375 || self.tainted_by_errors().is_some()
2377 // no need to overload user in such cases
2380 let SubtypePredicate { a_is_expected: _, a, b } = data;
2381 // both must be type variables, or the other would've been instantiated
2382 assert!(a.is_ty_var() && b.is_ty_var());
2383 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2385 ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
2386 if predicate.references_error() || self.tainted_by_errors().is_some() {
2393 .chain(Some(data.term.into_arg()))
2394 .find(|g| g.has_non_region_infer());
2395 if let Some(subst) = subst {
2396 let mut err = self.emit_inference_failure_err(
2403 err.note(&format!("cannot satisfy `{}`", predicate));
2406 // If we can't find a substitution, just print a generic error
2407 let mut err = struct_span_err!(
2411 "type annotations needed: cannot satisfy `{}`",
2414 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2419 ty::PredicateKind::ConstEvaluatable(data) => {
2420 if predicate.references_error() || self.tainted_by_errors().is_some() {
2423 let subst = data.walk().find(|g| g.is_non_region_infer());
2424 if let Some(subst) = subst {
2425 let err = self.emit_inference_failure_err(
2434 // If we can't find a substitution, just print a generic error
2435 let mut err = struct_span_err!(
2439 "type annotations needed: cannot satisfy `{}`",
2442 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2447 if self.tcx.sess.has_errors().is_some() || self.tainted_by_errors().is_some() {
2450 let mut err = struct_span_err!(
2454 "type annotations needed: cannot satisfy `{}`",
2457 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2461 self.note_obligation_cause(&mut err, obligation);
2465 fn annotate_source_of_ambiguity(
2467 err: &mut Diagnostic,
2469 predicate: ty::Predicate<'tcx>,
2471 let mut spans = vec![];
2472 let mut crates = vec![];
2473 let mut post = vec![];
2474 for def_id in impls {
2475 match self.tcx.span_of_impl(*def_id) {
2476 Ok(span) => spans.push(span),
2479 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2485 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2487 crate_names.dedup();
2491 if self.tainted_by_errors().is_some()
2492 && (crate_names.len() == 1
2494 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2495 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2497 // Avoid complaining about other inference issues for expressions like
2498 // `42 >> 1`, where the types are still `{integer}`, but we want to
2499 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2500 // NOTE(eddyb) this was `.cancel()`, but `err`
2501 // is borrowed, so we can't fully defuse it.
2502 err.downgrade_to_delayed_bug();
2506 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2507 let post = if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2508 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2509 } else if post.len() == 1 {
2510 format!(": `{}`", post[0])
2515 match (spans.len(), crates.len(), crate_names.len()) {
2517 err.note(&format!("cannot satisfy `{}`", predicate));
2520 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2524 "{} in the following crates: {}{}",
2526 crate_names.join(", "),
2531 let span: MultiSpan = spans.into();
2532 err.span_note(span, &msg);
2535 let span: MultiSpan = spans.into();
2536 err.span_note(span, &msg);
2538 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2542 let span: MultiSpan = spans.into();
2543 err.span_note(span, &msg);
2545 "and more `impl`s found in the following crates: {}{}",
2546 crate_names.join(", "),
2553 /// Returns `true` if the trait predicate may apply for *some* assignment
2554 /// to the type parameters.
2555 fn predicate_can_apply(
2557 param_env: ty::ParamEnv<'tcx>,
2558 pred: ty::PolyTraitPredicate<'tcx>,
2560 struct ParamToVarFolder<'a, 'tcx> {
2561 infcx: &'a InferCtxt<'tcx>,
2562 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2565 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2566 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2570 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2571 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2572 let infcx = self.infcx;
2573 *self.var_map.entry(ty).or_insert_with(|| {
2574 infcx.next_ty_var(TypeVariableOrigin {
2575 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2580 ty.super_fold_with(self)
2587 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2589 let InferOk { value: cleaned_pred, .. } =
2590 self.infcx.at(&ObligationCause::dummy(), param_env).normalize(cleaned_pred);
2593 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, cleaned_pred);
2595 self.predicate_may_hold(&obligation)
2599 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2600 // First, attempt to add note to this error with an async-await-specific
2601 // message, and fall back to regular note otherwise.
2602 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2603 self.note_obligation_cause_code(
2605 &obligation.predicate,
2606 obligation.param_env,
2607 obligation.cause.code(),
2609 &mut Default::default(),
2611 self.suggest_unsized_bound_if_applicable(err, obligation);
2615 #[instrument(level = "debug", skip_all)]
2616 fn suggest_unsized_bound_if_applicable(
2618 err: &mut Diagnostic,
2619 obligation: &PredicateObligation<'tcx>,
2621 let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = obligation.predicate.kind().skip_binder() else { return; };
2622 let (ObligationCauseCode::BindingObligation(item_def_id, span)
2623 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..))
2624 = *obligation.cause.code().peel_derives() else { return; };
2625 debug!(?pred, ?item_def_id, ?span);
2627 let (Some(node), true) = (
2628 self.tcx.hir().get_if_local(item_def_id),
2629 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2633 self.maybe_suggest_unsized_generics(err, span, node);
2636 #[instrument(level = "debug", skip_all)]
2637 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>) {
2638 let Some(generics) = node.generics() else {
2641 let sized_trait = self.tcx.lang_items().sized_trait();
2642 debug!(?generics.params);
2643 debug!(?generics.predicates);
2644 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2647 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2648 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2649 let explicitly_sized = generics
2650 .bounds_for_param(param.def_id)
2651 .flat_map(|bp| bp.bounds)
2652 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2653 if explicitly_sized {
2660 // Only suggest indirection for uses of type parameters in ADTs.
2662 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2666 if self.maybe_indirection_for_unsized(err, item, param) {
2672 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2673 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param.def_id)
2677 (span.shrink_to_hi(), ":")
2679 err.span_suggestion_verbose(
2681 "consider relaxing the implicit `Sized` restriction",
2682 format!("{} ?Sized", separator),
2683 Applicability::MachineApplicable,
2687 fn maybe_indirection_for_unsized(
2689 err: &mut Diagnostic,
2691 param: &GenericParam<'tcx>,
2693 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2694 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2695 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2697 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2698 visitor.visit_item(item);
2699 if visitor.invalid_spans.is_empty() {
2702 let mut multispan: MultiSpan = param.span.into();
2703 multispan.push_span_label(
2705 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2707 for sp in visitor.invalid_spans {
2708 multispan.push_span_label(
2710 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2716 "you could relax the implicit `Sized` bound on `{T}` if it were \
2717 used through indirection like `&{T}` or `Box<{T}>`",
2718 T = param.name.ident(),
2724 fn is_recursive_obligation(
2726 obligated_types: &mut Vec<Ty<'tcx>>,
2727 cause_code: &ObligationCauseCode<'tcx>,
2729 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2730 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2731 let self_ty = parent_trait_ref.skip_binder().self_ty();
2732 if obligated_types.iter().any(|ot| ot == &self_ty) {
2735 if let ty::Adt(def, substs) = self_ty.kind()
2736 && let [arg] = &substs[..]
2737 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2738 && let ty::Adt(inner_def, _) = ty.kind()
2748 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2749 /// `param: ?Sized` would be a valid constraint.
2750 struct FindTypeParam {
2751 param: rustc_span::Symbol,
2752 invalid_spans: Vec<Span>,
2756 impl<'v> Visitor<'v> for FindTypeParam {
2757 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2758 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2761 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2762 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2763 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2764 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2765 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2766 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2767 // in that case should make what happened clear enough.
2769 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2770 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2771 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2774 debug!(?ty, "FindTypeParam::visit_ty");
2775 self.invalid_spans.push(ty.span);
2778 hir::TyKind::Path(_) => {
2779 let prev = self.nested;
2781 hir::intravisit::walk_ty(self, ty);
2785 hir::intravisit::walk_ty(self, ty);
2791 /// Summarizes information
2794 /// An argument of non-tuple type. Parameters are (name, ty)
2795 Arg(String, String),
2797 /// An argument of tuple type. For a "found" argument, the span is
2798 /// the location in the source of the pattern. For an "expected"
2799 /// argument, it will be None. The vector is a list of (name, ty)
2800 /// strings for the components of the tuple.
2801 Tuple(Option<Span>, Vec<(String, String)>),
2805 fn empty() -> ArgKind {
2806 ArgKind::Arg("_".to_owned(), "_".to_owned())
2809 /// Creates an `ArgKind` from the expected type of an
2810 /// argument. It has no name (`_`) and an optional source span.
2811 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2813 ty::Tuple(tys) => ArgKind::Tuple(
2815 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2817 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2822 struct HasNumericInferVisitor;
2824 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2827 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2828 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2829 ControlFlow::Break(())
2831 ControlFlow::CONTINUE
2836 pub enum DefIdOrName {