3 pub mod on_unimplemented;
7 FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes, Obligation, ObligationCause,
8 ObligationCauseCode, ObligationCtxt, OutputTypeParameterMismatch, Overflow,
9 PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
11 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
12 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
13 use crate::infer::{self, InferCtxt};
14 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
15 use crate::traits::query::normalize::QueryNormalizeExt as _;
16 use crate::traits::specialize::to_pretty_impl_header;
17 use crate::traits::NormalizeExt;
18 use on_unimplemented::OnUnimplementedNote;
19 use on_unimplemented::TypeErrCtxtExt as _;
20 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
22 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
26 use rustc_hir::def::Namespace;
27 use rustc_hir::def_id::DefId;
28 use rustc_hir::intravisit::Visitor;
29 use rustc_hir::GenericParam;
32 use rustc_infer::infer::error_reporting::TypeErrCtxt;
33 use rustc_infer::infer::{InferOk, TypeTrace};
34 use rustc_middle::traits::select::OverflowError;
35 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
36 use rustc_middle::ty::error::ExpectedFound;
37 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
38 use rustc_middle::ty::print::{FmtPrinter, Print};
39 use rustc_middle::ty::{
40 self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
43 use rustc_session::Limit;
44 use rustc_span::def_id::LOCAL_CRATE;
45 use rustc_span::symbol::sym;
46 use rustc_span::{ExpnKind, Span, DUMMY_SP};
49 use std::ops::ControlFlow;
50 use suggestions::TypeErrCtxtExt as _;
52 pub use rustc_infer::traits::error_reporting::*;
54 // When outputting impl candidates, prefer showing those that are more similar.
56 // We also compare candidates after skipping lifetimes, which has a lower
57 // priority than exact matches.
58 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
59 pub enum CandidateSimilarity {
60 Exact { ignoring_lifetimes: bool },
61 Fuzzy { ignoring_lifetimes: bool },
64 #[derive(Debug, Clone, Copy)]
65 pub struct ImplCandidate<'tcx> {
66 pub trait_ref: ty::TraitRef<'tcx>,
67 pub similarity: CandidateSimilarity,
70 pub trait InferCtxtExt<'tcx> {
71 /// Given some node representing a fn-like thing in the HIR map,
72 /// returns a span and `ArgKind` information that describes the
73 /// arguments it expects. This can be supplied to
74 /// `report_arg_count_mismatch`.
75 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)>;
77 /// Reports an error when the number of arguments needed by a
78 /// trait match doesn't match the number that the expression
80 fn report_arg_count_mismatch(
83 found_span: Option<Span>,
84 expected_args: Vec<ArgKind>,
85 found_args: Vec<ArgKind>,
87 closure_pipe_span: Option<Span>,
88 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
90 /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
91 /// in that order, and returns the generic type corresponding to the
92 /// argument of that trait (corresponding to the closure arguments).
93 fn type_implements_fn_trait(
95 param_env: ty::ParamEnv<'tcx>,
96 ty: ty::Binder<'tcx, Ty<'tcx>>,
97 constness: ty::BoundConstness,
98 polarity: ty::ImplPolarity,
99 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
102 pub trait TypeErrCtxtExt<'tcx> {
103 fn report_overflow_error<T>(
107 suggest_increasing_limit: bool,
108 mutate: impl FnOnce(&mut Diagnostic),
113 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
114 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug;
116 fn report_fulfillment_errors(
118 errors: &[FulfillmentError<'tcx>],
119 body_id: Option<hir::BodyId>,
120 ) -> ErrorGuaranteed;
122 fn report_overflow_obligation<T>(
124 obligation: &Obligation<'tcx, T>,
125 suggest_increasing_limit: bool,
128 T: ToPredicate<'tcx> + Clone;
130 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
132 fn report_overflow_obligation_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
134 /// The `root_obligation` parameter should be the `root_obligation` field
135 /// from a `FulfillmentError`. If no `FulfillmentError` is available,
136 /// then it should be the same as `obligation`.
137 fn report_selection_error(
139 obligation: PredicateObligation<'tcx>,
140 root_obligation: &PredicateObligation<'tcx>,
141 error: &SelectionError<'tcx>,
145 impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
146 /// Given some node representing a fn-like thing in the HIR map,
147 /// returns a span and `ArgKind` information that describes the
148 /// arguments it expects. This can be supplied to
149 /// `report_arg_count_mismatch`.
150 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)> {
151 let sm = self.tcx.sess.source_map();
152 let hir = self.tcx.hir();
154 Node::Expr(&hir::Expr {
155 kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, fn_arg_span, .. }),
164 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
171 sm.span_to_snippet(pat.span)
173 .map(|snippet| (snippet, "_".to_owned()))
175 .collect::<Option<Vec<_>>>()?,
178 let name = sm.span_to_snippet(arg.pat.span).ok()?;
179 Some(ArgKind::Arg(name, "_".to_owned()))
182 .collect::<Option<Vec<ArgKind>>>()?,
184 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
185 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
186 | Node::TraitItem(&hir::TraitItem {
187 kind: hir::TraitItemKind::Fn(ref sig, _), ..
194 .map(|arg| match arg.kind {
195 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
197 vec![("_".to_owned(), "_".to_owned()); tys.len()],
199 _ => ArgKind::empty(),
201 .collect::<Vec<ArgKind>>(),
203 Node::Ctor(ref variant_data) => {
204 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
205 (span, None, vec![ArgKind::empty(); variant_data.fields().len()])
207 _ => panic!("non-FnLike node found: {:?}", node),
211 /// Reports an error when the number of arguments needed by a
212 /// trait match doesn't match the number that the expression
214 fn report_arg_count_mismatch(
217 found_span: Option<Span>,
218 expected_args: Vec<ArgKind>,
219 found_args: Vec<ArgKind>,
221 closure_arg_span: Option<Span>,
222 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
223 let kind = if is_closure { "closure" } else { "function" };
225 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
226 let arg_length = arguments.len();
227 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
228 match (arg_length, arguments.get(0)) {
229 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
230 format!("a single {}-tuple as argument", fields.len())
235 if distinct && arg_length > 1 { "distinct " } else { "" },
236 pluralize!(arg_length)
241 let expected_str = args_str(&expected_args, &found_args);
242 let found_str = args_str(&found_args, &expected_args);
244 let mut err = struct_span_err!(
248 "{} is expected to take {}, but it takes {}",
254 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
256 if let Some(found_span) = found_span {
257 err.span_label(found_span, format!("takes {}", found_str));
259 // Suggest to take and ignore the arguments with expected_args_length `_`s if
260 // found arguments is empty (assume the user just wants to ignore args in this case).
261 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
262 if found_args.is_empty() && is_closure {
263 let underscores = vec!["_"; expected_args.len()].join(", ");
264 err.span_suggestion_verbose(
265 closure_arg_span.unwrap_or(found_span),
267 "consider changing the closure to take and ignore the expected argument{}",
268 pluralize!(expected_args.len())
270 format!("|{}|", underscores),
271 Applicability::MachineApplicable,
275 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
276 if fields.len() == expected_args.len() {
279 .map(|(name, _)| name.to_owned())
280 .collect::<Vec<String>>()
282 err.span_suggestion_verbose(
284 "change the closure to take multiple arguments instead of a single tuple",
285 format!("|{}|", sugg),
286 Applicability::MachineApplicable,
290 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
291 && fields.len() == found_args.len()
298 .map(|arg| match arg {
299 ArgKind::Arg(name, _) => name.to_owned(),
302 .collect::<Vec<String>>()
304 // add type annotations if available
305 if found_args.iter().any(|arg| match arg {
306 ArgKind::Arg(_, ty) => ty != "_",
313 .map(|(_, ty)| ty.to_owned())
314 .collect::<Vec<String>>()
321 err.span_suggestion_verbose(
323 "change the closure to accept a tuple instead of individual arguments",
325 Applicability::MachineApplicable,
333 fn type_implements_fn_trait(
335 param_env: ty::ParamEnv<'tcx>,
336 ty: ty::Binder<'tcx, Ty<'tcx>>,
337 constness: ty::BoundConstness,
338 polarity: ty::ImplPolarity,
339 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
340 self.commit_if_ok(|_| {
341 for trait_def_id in [
342 self.tcx.lang_items().fn_trait(),
343 self.tcx.lang_items().fn_mut_trait(),
344 self.tcx.lang_items().fn_once_trait(),
346 let Some(trait_def_id) = trait_def_id else { continue };
347 // Make a fresh inference variable so we can determine what the substitutions
349 let var = self.next_ty_var(TypeVariableOrigin {
351 kind: TypeVariableOriginKind::MiscVariable,
353 let trait_ref = self.tcx.mk_trait_ref(trait_def_id, [ty.skip_binder(), var]);
354 let obligation = Obligation::new(
356 ObligationCause::dummy(),
358 ty.rebind(ty::TraitPredicate { trait_ref, constness, polarity }),
360 let ocx = ObligationCtxt::new_in_snapshot(self);
361 ocx.register_obligation(obligation);
362 if ocx.select_all_or_error().is_empty() {
365 .fn_trait_kind_from_def_id(trait_def_id)
366 .expect("expected to map DefId to ClosureKind"),
367 ty.rebind(self.resolve_vars_if_possible(var)),
376 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
377 fn report_fulfillment_errors(
379 errors: &[FulfillmentError<'tcx>],
380 body_id: Option<hir::BodyId>,
381 ) -> ErrorGuaranteed {
383 struct ErrorDescriptor<'tcx> {
384 predicate: ty::Predicate<'tcx>,
385 index: Option<usize>, // None if this is an old error
388 let mut error_map: FxIndexMap<_, Vec<_>> = self
389 .reported_trait_errors
392 .map(|(&span, predicates)| {
397 .map(|&predicate| ErrorDescriptor { predicate, index: None })
403 for (index, error) in errors.iter().enumerate() {
404 // We want to ignore desugarings here: spans are equivalent even
405 // if one is the result of a desugaring and the other is not.
406 let mut span = error.obligation.cause.span;
407 let expn_data = span.ctxt().outer_expn_data();
408 if let ExpnKind::Desugaring(_) = expn_data.kind {
409 span = expn_data.call_site;
412 error_map.entry(span).or_default().push(ErrorDescriptor {
413 predicate: error.obligation.predicate,
417 self.reported_trait_errors
421 .push(error.obligation.predicate);
424 // We do this in 2 passes because we want to display errors in order, though
425 // maybe it *is* better to sort errors by span or something.
426 let mut is_suppressed = vec![false; errors.len()];
427 for (_, error_set) in error_map.iter() {
428 // We want to suppress "duplicate" errors with the same span.
429 for error in error_set {
430 if let Some(index) = error.index {
431 // Suppress errors that are either:
432 // 1) strictly implied by another error.
433 // 2) implied by an error with a smaller index.
434 for error2 in error_set {
435 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
436 // Avoid errors being suppressed by already-suppressed
437 // errors, to prevent all errors from being suppressed
442 if self.error_implies(error2.predicate, error.predicate)
443 && !(error2.index >= error.index
444 && self.error_implies(error.predicate, error2.predicate))
446 info!("skipping {:?} (implied by {:?})", error, error2);
447 is_suppressed[index] = true;
455 for (error, suppressed) in iter::zip(errors, is_suppressed) {
457 self.report_fulfillment_error(error, body_id);
461 self.tcx.sess.delay_span_bug(DUMMY_SP, "expected fullfillment errors")
464 /// Reports that an overflow has occurred and halts compilation. We
465 /// halt compilation unconditionally because it is important that
466 /// overflows never be masked -- they basically represent computations
467 /// whose result could not be truly determined and thus we can't say
468 /// if the program type checks or not -- and they are unusual
469 /// occurrences in any case.
470 fn report_overflow_error<T>(
474 suggest_increasing_limit: bool,
475 mutate: impl FnOnce(&mut Diagnostic),
480 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
481 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
483 let predicate = self.resolve_vars_if_possible(predicate.clone());
484 let mut pred_str = predicate.to_string();
486 if pred_str.len() > 50 {
487 // We don't need to save the type to a file, we will be talking about this type already
488 // in a separate note when we explain the obligation, so it will be available that way.
490 .print(FmtPrinter::new_with_limit(
493 rustc_session::Limit(6),
498 let mut err = struct_span_err!(
502 "overflow evaluating the requirement `{}`",
506 if suggest_increasing_limit {
507 self.suggest_new_overflow_limit(&mut err);
513 self.tcx.sess.abort_if_errors();
517 /// Reports that an overflow has occurred and halts compilation. We
518 /// halt compilation unconditionally because it is important that
519 /// overflows never be masked -- they basically represent computations
520 /// whose result could not be truly determined and thus we can't say
521 /// if the program type checks or not -- and they are unusual
522 /// occurrences in any case.
523 fn report_overflow_obligation<T>(
525 obligation: &Obligation<'tcx, T>,
526 suggest_increasing_limit: bool,
529 T: ToPredicate<'tcx> + Clone,
531 let predicate = obligation.predicate.clone().to_predicate(self.tcx);
532 let predicate = self.resolve_vars_if_possible(predicate);
533 self.report_overflow_error(
535 obligation.cause.span,
536 suggest_increasing_limit,
538 self.note_obligation_cause_code(
541 obligation.param_env,
542 obligation.cause.code(),
544 &mut Default::default(),
550 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic) {
551 let suggested_limit = match self.tcx.recursion_limit() {
552 Limit(0) => Limit(2),
556 "consider increasing the recursion limit by adding a \
557 `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
559 self.tcx.crate_name(LOCAL_CRATE),
563 /// Reports that a cycle was detected which led to overflow and halts
564 /// compilation. This is equivalent to `report_overflow_obligation` except
565 /// that we can give a more helpful error message (and, in particular,
566 /// we do not suggest increasing the overflow limit, which is not
568 fn report_overflow_obligation_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
569 let cycle = self.resolve_vars_if_possible(cycle.to_owned());
570 assert!(!cycle.is_empty());
572 debug!(?cycle, "report_overflow_error_cycle");
574 // The 'deepest' obligation is most likely to have a useful
576 self.report_overflow_obligation(
577 cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(),
582 fn report_selection_error(
584 mut obligation: PredicateObligation<'tcx>,
585 root_obligation: &PredicateObligation<'tcx>,
586 error: &SelectionError<'tcx>,
589 let mut span = obligation.cause.span;
590 // FIXME: statically guarantee this by tainting after the diagnostic is emitted
591 self.set_tainted_by_errors(
592 tcx.sess.delay_span_bug(span, "`report_selection_error` did not emit an error"),
595 let mut err = match *error {
596 SelectionError::Unimplemented => {
597 // If this obligation was generated as a result of well-formedness checking, see if we
598 // can get a better error message by performing HIR-based well-formedness checking.
599 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
600 root_obligation.cause.code().peel_derives()
601 && !obligation.predicate.has_non_region_infer()
603 if let Some(cause) = self
605 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
607 obligation.cause = cause.clone();
608 span = obligation.cause.span;
611 if let ObligationCauseCode::CompareImplItemObligation {
615 } = *obligation.cause.code()
617 self.report_extra_impl_obligation(
621 &format!("`{}`", obligation.predicate),
627 let bound_predicate = obligation.predicate.kind();
628 match bound_predicate.skip_binder() {
629 ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
630 let trait_predicate = bound_predicate.rebind(trait_predicate);
631 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
633 trait_predicate.remap_constness_diag(obligation.param_env);
634 let predicate_is_const = ty::BoundConstness::ConstIfConst
635 == trait_predicate.skip_binder().constness;
637 if self.tcx.sess.has_errors().is_some()
638 && trait_predicate.references_error()
642 let trait_ref = trait_predicate.to_poly_trait_ref();
643 let (post_message, pre_message, type_def) = self
644 .get_parent_trait_ref(obligation.cause.code())
647 format!(" in `{}`", t),
648 format!("within `{}`, ", t),
649 s.map(|s| (format!("within this `{}`", t), s)),
652 .unwrap_or_default();
654 let OnUnimplementedNote {
660 } = self.on_unimplemented_note(trait_ref, &obligation);
661 let have_alt_message = message.is_some() || label.is_some();
662 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
664 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
665 let (message, note, append_const_msg) = if is_try_conversion {
668 "`?` couldn't convert the error to `{}`",
669 trait_ref.skip_binder().self_ty(),
672 "the question mark operation (`?`) implicitly performs a \
673 conversion on the error value using the `From` trait"
679 (message, note, append_const_msg)
682 let mut err = struct_span_err!(
688 .and_then(|cannot_do_this| {
689 match (predicate_is_const, append_const_msg) {
690 // do nothing if predicate is not const
691 (false, _) => Some(cannot_do_this),
692 // suggested using default post message
693 (true, Some(None)) => {
694 Some(format!("{cannot_do_this} in const contexts"))
696 // overridden post message
697 (true, Some(Some(post_message))) => {
698 Some(format!("{cannot_do_this}{post_message}"))
700 // fallback to generic message
701 (true, None) => None,
704 .unwrap_or_else(|| format!(
705 "the trait bound `{}` is not satisfied{}",
706 trait_predicate, post_message,
710 if is_try_conversion && let Some(ret_span) = self.return_type_span(&obligation) {
714 "expected `{}` because of this",
715 trait_ref.skip_binder().self_ty()
720 if Some(trait_ref.def_id()) == tcx.lang_items().tuple_trait() {
721 match obligation.cause.code().peel_derives() {
722 ObligationCauseCode::RustCall => {
723 err.set_primary_message("functions with the \"rust-call\" ABI must take a single non-self tuple argument");
725 ObligationCauseCode::BindingObligation(def_id, _)
726 | ObligationCauseCode::ItemObligation(def_id)
727 if tcx.is_fn_trait(*def_id) =>
729 err.code(rustc_errors::error_code!(E0059));
730 err.set_primary_message(format!(
731 "type parameter to bare `{}` trait must be a tuple",
732 tcx.def_path_str(*def_id)
739 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
740 && predicate_is_const
742 err.note("`~const Drop` was renamed to `~const Destruct`");
743 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
746 let explanation = if let ObligationCauseCode::MainFunctionType =
747 obligation.cause.code()
749 "consider using `()`, or a `Result`".to_owned()
751 let ty_desc = match trait_ref.skip_binder().self_ty().kind() {
752 ty::FnDef(_, _) => Some("fn item"),
753 ty::Closure(_, _) => Some("closure"),
758 Some(desc) => format!(
759 "{}the trait `{}` is not implemented for {} `{}`",
761 trait_predicate.print_modifiers_and_trait_path(),
763 trait_ref.skip_binder().self_ty(),
766 "{}the trait `{}` is not implemented for `{}`",
768 trait_predicate.print_modifiers_and_trait_path(),
769 trait_ref.skip_binder().self_ty(),
774 if self.suggest_add_reference_to_arg(
780 self.note_obligation_cause(&mut err, &obligation);
784 if let Some(ref s) = label {
785 // If it has a custom `#[rustc_on_unimplemented]`
786 // error message, let's display it as the label!
787 err.span_label(span, s);
788 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
789 // When the self type is a type param We don't need to "the trait
790 // `std::marker::Sized` is not implemented for `T`" as we will point
791 // at the type param with a label to suggest constraining it.
792 err.help(&explanation);
795 err.span_label(span, explanation);
798 if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
799 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
800 self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
803 let mut unsatisfied_const = false;
804 if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
805 let non_const_predicate = trait_ref.without_const();
806 let non_const_obligation = Obligation {
807 cause: obligation.cause.clone(),
808 param_env: obligation.param_env.without_const(),
809 predicate: non_const_predicate.to_predicate(tcx),
810 recursion_depth: obligation.recursion_depth,
812 if self.predicate_may_hold(&non_const_obligation) {
813 unsatisfied_const = true;
817 "the trait `{}` is implemented for `{}`, \
818 but that implementation is not `const`",
819 non_const_predicate.print_modifiers_and_trait_path(),
820 trait_ref.skip_binder().self_ty(),
826 if let Some((msg, span)) = type_def {
827 err.span_label(span, &msg);
829 if let Some(ref s) = note {
830 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
831 err.note(s.as_str());
833 if let Some(ref s) = parent_label {
836 .opt_local_def_id(obligation.cause.body_id)
838 tcx.hir().body_owner_def_id(hir::BodyId {
839 hir_id: obligation.cause.body_id,
842 err.span_label(tcx.def_span(body), s);
845 self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
846 self.suggest_dereferencing_index(&obligation, &mut err, trait_predicate);
848 self.suggest_dereferences(&obligation, &mut err, trait_predicate);
849 suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
851 self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
852 suggested |= self.suggest_semicolon_removal(
858 self.note_version_mismatch(&mut err, &trait_ref);
859 self.suggest_remove_await(&obligation, &mut err);
860 self.suggest_derive(&obligation, &mut err, trait_predicate);
862 if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
863 self.suggest_await_before_try(
871 if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
877 // If the obligation failed due to a missing implementation of the
878 // `Unsize` trait, give a pointer to why that might be the case
880 "all implementations of `Unsize` are provided \
881 automatically by the compiler, see \
882 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
883 for more information",
887 let is_fn_trait = tcx.is_fn_trait(trait_ref.def_id());
888 let is_target_feature_fn = if let ty::FnDef(def_id, _) =
889 *trait_ref.skip_binder().self_ty().kind()
891 !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
895 if is_fn_trait && is_target_feature_fn {
897 "`#[target_feature]` functions do not implement the `Fn` traits",
901 // Try to report a help message
903 && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
904 obligation.param_env,
906 trait_predicate.skip_binder().constness,
907 trait_predicate.skip_binder().polarity,
910 // If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
911 // suggestion to add trait bounds for the type, since we only typically implement
912 // these traits once.
914 // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
917 self.tcx.fn_trait_kind_from_def_id(trait_ref.def_id())
918 .expect("expected to map DefId to ClosureKind");
919 if !implemented_kind.extends(selected_kind) {
922 "`{}` implements `{}`, but it must implement `{}`, which is more general",
923 trait_ref.skip_binder().self_ty(),
930 // Note any argument mismatches
931 let given_ty = params.skip_binder();
932 let expected_ty = trait_ref.skip_binder().substs.type_at(1);
933 if let ty::Tuple(given) = given_ty.kind()
934 && let ty::Tuple(expected) = expected_ty.kind()
936 if expected.len() != given.len() {
937 // Note number of types that were expected and given
940 "expected a closure taking {} argument{}, but one taking {} argument{} was given",
942 pluralize!(given.len()),
944 pluralize!(expected.len()),
947 } else if !self.same_type_modulo_infer(given_ty, expected_ty) {
948 // Print type mismatch
949 let (expected_args, given_args) =
950 self.cmp(given_ty, expected_ty);
951 err.note_expected_found(
952 &"a closure with arguments",
954 &"a closure with arguments",
959 } else if !trait_ref.has_non_region_infer()
960 && self.predicate_can_apply(obligation.param_env, trait_predicate)
962 // If a where-clause may be useful, remind the
963 // user that they can add it.
965 // don't display an on-unimplemented note, as
966 // these notes will often be of the form
967 // "the type `T` can't be frobnicated"
968 // which is somewhat confusing.
969 self.suggest_restricting_param_bound(
973 obligation.cause.body_id,
975 } else if !suggested && !unsatisfied_const {
976 // Can't show anything else useful, try to find similar impls.
977 let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
978 if !self.report_similar_impl_candidates(
981 obligation.cause.body_id,
985 // This is *almost* equivalent to
986 // `obligation.cause.code().peel_derives()`, but it gives us the
987 // trait predicate for that corresponding root obligation. This
988 // lets us get a derived obligation from a type parameter, like
989 // when calling `string.strip_suffix(p)` where `p` is *not* an
990 // implementer of `Pattern<'_>`.
991 let mut code = obligation.cause.code();
992 let mut trait_pred = trait_predicate;
993 let mut peeled = false;
994 while let Some((parent_code, parent_trait_pred)) = code.parent() {
996 if let Some(parent_trait_pred) = parent_trait_pred {
997 trait_pred = parent_trait_pred;
1001 let def_id = trait_pred.def_id();
1002 // Mention *all* the `impl`s for the *top most* obligation, the
1003 // user might have meant to use one of them, if any found. We skip
1004 // auto-traits or fundamental traits that might not be exactly what
1005 // the user might expect to be presented with. Instead this is
1006 // useful for less general traits.
1008 && !self.tcx.trait_is_auto(def_id)
1009 && !self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1011 let trait_ref = trait_pred.to_poly_trait_ref();
1012 let impl_candidates =
1013 self.find_similar_impl_candidates(trait_pred);
1014 self.report_similar_impl_candidates(
1017 obligation.cause.body_id,
1025 // Changing mutability doesn't make a difference to whether we have
1026 // an `Unsize` impl (Fixes ICE in #71036)
1028 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
1031 // If this error is due to `!: Trait` not implemented but `(): Trait` is
1032 // implemented, and fallback has occurred, then it could be due to a
1033 // variable that used to fallback to `()` now falling back to `!`. Issue a
1034 // note informing about the change in behaviour.
1035 if trait_predicate.skip_binder().self_ty().is_never()
1036 && self.fallback_has_occurred
1038 let predicate = trait_predicate.map_bound(|trait_pred| {
1039 trait_pred.with_self_ty(self.tcx, self.tcx.mk_unit())
1041 let unit_obligation = obligation.with(tcx, predicate);
1042 if self.predicate_may_hold(&unit_obligation) {
1044 "this error might have been caused by changes to \
1045 Rust's type-inference algorithm (see issue #48950 \
1046 <https://github.com/rust-lang/rust/issues/48950> \
1047 for more information)",
1049 err.help("did you intend to use the type `()` here instead?");
1053 // Return early if the trait is Debug or Display and the invocation
1054 // originates within a standard library macro, because the output
1055 // is otherwise overwhelming and unhelpful (see #85844 for an
1059 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
1060 Some(macro_def_id) => {
1061 let crate_name = tcx.crate_name(macro_def_id.krate);
1062 crate_name == sym::std || crate_name == sym::core
1069 self.tcx.get_diagnostic_name(trait_ref.def_id()),
1070 Some(sym::Debug | sym::Display)
1080 ty::PredicateKind::Subtype(predicate) => {
1081 // Errors for Subtype predicates show up as
1082 // `FulfillmentErrorCode::CodeSubtypeError`,
1083 // not selection error.
1084 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
1087 ty::PredicateKind::Coerce(predicate) => {
1088 // Errors for Coerce predicates show up as
1089 // `FulfillmentErrorCode::CodeSubtypeError`,
1090 // not selection error.
1091 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
1094 ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
1095 | ty::PredicateKind::Clause(ty::Clause::Projection(..))
1096 | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..)) => {
1097 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1102 "the requirement `{}` is not satisfied",
1107 ty::PredicateKind::ObjectSafe(trait_def_id) => {
1108 let violations = self.tcx.object_safety_violations(trait_def_id);
1109 report_object_safety_error(self.tcx, span, trait_def_id, violations)
1112 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
1113 let found_kind = self.closure_kind(closure_substs).unwrap();
1114 let closure_span = self.tcx.def_span(closure_def_id);
1115 let mut err = struct_span_err!(
1119 "expected a closure that implements the `{}` trait, \
1120 but this closure only implements `{}`",
1127 format!("this closure implements `{}`, not `{}`", found_kind, kind),
1130 obligation.cause.span,
1131 format!("the requirement to implement `{}` derives from here", kind),
1134 // Additional context information explaining why the closure only implements
1135 // a particular trait.
1136 if let Some(typeck_results) = &self.typeck_results {
1140 .local_def_id_to_hir_id(closure_def_id.expect_local());
1141 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
1142 (ty::ClosureKind::FnOnce, Some((span, place))) => {
1146 "closure is `FnOnce` because it moves the \
1147 variable `{}` out of its environment",
1148 ty::place_to_string_for_capture(tcx, place)
1152 (ty::ClosureKind::FnMut, Some((span, place))) => {
1156 "closure is `FnMut` because it mutates the \
1157 variable `{}` here",
1158 ty::place_to_string_for_capture(tcx, place)
1169 ty::PredicateKind::WellFormed(ty) => {
1170 if !self.tcx.sess.opts.unstable_opts.chalk {
1171 // WF predicates cannot themselves make
1172 // errors. They can only block due to
1173 // ambiguity; otherwise, they always
1174 // degenerate into other obligations
1175 // (which may fail).
1176 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
1178 // FIXME: we'll need a better message which takes into account
1179 // which bounds actually failed to hold.
1180 self.tcx.sess.struct_span_err(
1182 &format!("the type `{}` is not well-formed (chalk)", ty),
1187 ty::PredicateKind::ConstEvaluatable(..) => {
1188 // Errors for `ConstEvaluatable` predicates show up as
1189 // `SelectionError::ConstEvalFailure`,
1190 // not `Unimplemented`.
1193 "const-evaluatable requirement gave wrong error: `{:?}`",
1198 ty::PredicateKind::ConstEquate(..) => {
1199 // Errors for `ConstEquate` predicates show up as
1200 // `SelectionError::ConstEvalFailure`,
1201 // not `Unimplemented`.
1204 "const-equate requirement gave wrong error: `{:?}`",
1209 ty::PredicateKind::Ambiguous => span_bug!(span, "ambiguous"),
1211 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
1213 "TypeWellFormedFromEnv predicate should only exist in the environment"
1218 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
1219 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
1220 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
1222 if expected_trait_ref.self_ty().references_error() {
1226 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
1230 let found_did = match *found_trait_ty.kind() {
1234 | ty::Generator(did, ..) => Some(did),
1235 ty::Adt(def, _) => Some(def.did()),
1239 let found_node = found_did.and_then(|did| self.tcx.hir().get_if_local(did));
1240 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
1242 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1243 // We check closures twice, with obligations flowing in different directions,
1244 // but we want to complain about them only once.
1248 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1250 let mut not_tupled = false;
1252 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
1253 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1256 vec![ArgKind::empty()]
1260 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1261 let expected = match expected_ty.kind() {
1262 ty::Tuple(ref tys) => {
1263 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
1267 vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())]
1271 // If this is a `Fn` family trait and either the expected or found
1272 // is not tupled, then fall back to just a regular mismatch error.
1273 // This shouldn't be common unless manually implementing one of the
1274 // traits manually, but don't make it more confusing when it does
1276 if Some(expected_trait_ref.def_id()) != tcx.lang_items().gen_trait() && not_tupled {
1277 self.report_and_explain_type_error(
1278 TypeTrace::poly_trait_refs(
1284 ty::error::TypeError::Mismatch,
1286 } else if found.len() == expected.len() {
1287 self.report_closure_arg_mismatch(
1292 obligation.cause.code(),
1296 let (closure_span, closure_arg_span, found) = found_did
1298 let node = self.tcx.hir().get_if_local(did)?;
1299 let (found_span, closure_arg_span, found) =
1300 self.get_fn_like_arguments(node)?;
1301 Some((Some(found_span), closure_arg_span, found))
1303 .unwrap_or((found_span, None, found));
1305 self.report_arg_count_mismatch(
1310 found_trait_ty.is_closure(),
1316 TraitNotObjectSafe(did) => {
1317 let violations = self.tcx.object_safety_violations(did);
1318 report_object_safety_error(self.tcx, span, did, violations)
1321 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1323 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1326 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1327 if !self.tcx.features().generic_const_exprs {
1328 let mut err = self.tcx.sess.struct_span_err(
1330 "constant expression depends on a generic parameter",
1332 // FIXME(const_generics): we should suggest to the user how they can resolve this
1333 // issue. However, this is currently not actually possible
1334 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1336 // Note that with `feature(generic_const_exprs)` this case should not
1338 err.note("this may fail depending on what value the parameter takes");
1343 match obligation.predicate.kind().skip_binder() {
1344 ty::PredicateKind::ConstEvaluatable(ct) => {
1345 let ty::ConstKind::Unevaluated(uv) = ct.kind() else {
1346 bug!("const evaluatable failed for non-unevaluated const `{ct:?}`");
1349 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1350 let const_span = self.tcx.def_span(uv.def.did);
1351 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1352 Ok(snippet) => err.help(&format!(
1353 "try adding a `where` bound using this expression: `where [(); {}]:`",
1356 _ => err.help("consider adding a `where` bound using this expression"),
1363 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1369 // Already reported in the query.
1370 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1371 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1372 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1375 // Already reported.
1376 Overflow(OverflowError::Error(_)) => {
1377 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1381 bug!("overflow should be handled before the `report_selection_error` path");
1383 SelectionError::ErrorReporting => {
1384 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1388 self.note_obligation_cause(&mut err, &obligation);
1389 self.point_at_returns_when_relevant(&mut err, &obligation);
1395 trait InferCtxtPrivExt<'tcx> {
1396 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1397 // `error` occurring implies that `cond` occurs.
1398 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1400 fn report_fulfillment_error(
1402 error: &FulfillmentError<'tcx>,
1403 body_id: Option<hir::BodyId>,
1406 fn report_projection_error(
1408 obligation: &PredicateObligation<'tcx>,
1409 error: &MismatchedProjectionTypes<'tcx>,
1412 fn maybe_detailed_projection_msg(
1414 pred: ty::ProjectionPredicate<'tcx>,
1415 normalized_ty: ty::Term<'tcx>,
1416 expected_ty: ty::Term<'tcx>,
1417 ) -> Option<String>;
1423 ignoring_lifetimes: bool,
1424 ) -> Option<CandidateSimilarity>;
1426 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1428 fn find_similar_impl_candidates(
1430 trait_pred: ty::PolyTraitPredicate<'tcx>,
1431 ) -> Vec<ImplCandidate<'tcx>>;
1433 fn report_similar_impl_candidates(
1435 impl_candidates: Vec<ImplCandidate<'tcx>>,
1436 trait_ref: ty::PolyTraitRef<'tcx>,
1437 body_id: hir::HirId,
1438 err: &mut Diagnostic,
1442 /// Gets the parent trait chain start
1443 fn get_parent_trait_ref(
1445 code: &ObligationCauseCode<'tcx>,
1446 ) -> Option<(String, Option<Span>)>;
1448 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1449 /// with the same path as `trait_ref`, a help message about
1450 /// a probable version mismatch is added to `err`
1451 fn note_version_mismatch(
1453 err: &mut Diagnostic,
1454 trait_ref: &ty::PolyTraitRef<'tcx>,
1457 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1460 /// For this to work, `new_self_ty` must have no escaping bound variables.
1461 fn mk_trait_obligation_with_new_self_ty(
1463 param_env: ty::ParamEnv<'tcx>,
1464 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1465 ) -> PredicateObligation<'tcx>;
1467 fn maybe_report_ambiguity(
1469 obligation: &PredicateObligation<'tcx>,
1470 body_id: Option<hir::BodyId>,
1473 fn predicate_can_apply(
1475 param_env: ty::ParamEnv<'tcx>,
1476 pred: ty::PolyTraitPredicate<'tcx>,
1479 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1481 fn suggest_unsized_bound_if_applicable(
1483 err: &mut Diagnostic,
1484 obligation: &PredicateObligation<'tcx>,
1487 fn annotate_source_of_ambiguity(
1489 err: &mut Diagnostic,
1491 predicate: ty::Predicate<'tcx>,
1494 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>);
1496 fn maybe_indirection_for_unsized(
1498 err: &mut Diagnostic,
1499 item: &'tcx Item<'tcx>,
1500 param: &'tcx GenericParam<'tcx>,
1503 fn is_recursive_obligation(
1505 obligated_types: &mut Vec<Ty<'tcx>>,
1506 cause_code: &ObligationCauseCode<'tcx>,
1510 impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
1511 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1512 // `error` occurring implies that `cond` occurs.
1513 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1518 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1519 let bound_error = error.kind();
1520 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1522 ty::PredicateKind::Clause(ty::Clause::Trait(..)),
1523 ty::PredicateKind::Clause(ty::Clause::Trait(error)),
1524 ) => (cond, bound_error.rebind(error)),
1526 // FIXME: make this work in other cases too.
1531 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1532 let bound_predicate = obligation.predicate.kind();
1533 if let ty::PredicateKind::Clause(ty::Clause::Trait(implication)) =
1534 bound_predicate.skip_binder()
1536 let error = error.to_poly_trait_ref();
1537 let implication = bound_predicate.rebind(implication.trait_ref);
1538 // FIXME: I'm just not taking associated types at all here.
1539 // Eventually I'll need to implement param-env-aware
1540 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1541 let param_env = ty::ParamEnv::empty();
1542 if self.can_sub(param_env, error, implication).is_ok() {
1543 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1552 #[instrument(skip(self), level = "debug")]
1553 fn report_fulfillment_error(
1555 error: &FulfillmentError<'tcx>,
1556 body_id: Option<hir::BodyId>,
1559 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1560 self.report_selection_error(
1561 error.obligation.clone(),
1562 &error.root_obligation,
1566 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1567 self.report_projection_error(&error.obligation, e);
1569 FulfillmentErrorCode::CodeAmbiguity => {
1570 self.maybe_report_ambiguity(&error.obligation, body_id);
1572 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1573 self.report_mismatched_types(
1574 &error.obligation.cause,
1575 expected_found.expected,
1576 expected_found.found,
1581 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1582 let mut diag = self.report_mismatched_consts(
1583 &error.obligation.cause,
1584 expected_found.expected,
1585 expected_found.found,
1588 let code = error.obligation.cause.code().peel_derives().peel_match_impls();
1589 if let ObligationCauseCode::BindingObligation(..)
1590 | ObligationCauseCode::ItemObligation(..)
1591 | ObligationCauseCode::ExprBindingObligation(..)
1592 | ObligationCauseCode::ExprItemObligation(..) = code
1594 self.note_obligation_cause_code(
1596 error.obligation.predicate,
1597 error.obligation.param_env,
1600 &mut Default::default(),
1605 FulfillmentErrorCode::CodeCycle(ref cycle) => {
1606 self.report_overflow_obligation_cycle(cycle);
1611 #[instrument(level = "debug", skip_all)]
1612 fn report_projection_error(
1614 obligation: &PredicateObligation<'tcx>,
1615 error: &MismatchedProjectionTypes<'tcx>,
1617 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1619 if predicate.references_error() {
1624 let ocx = ObligationCtxt::new_in_snapshot(self);
1626 // try to find the mismatched types to report the error with.
1628 // this can fail if the problem was higher-ranked, in which
1629 // cause I have no idea for a good error message.
1630 let bound_predicate = predicate.kind();
1631 let (values, err) = if let ty::PredicateKind::Clause(ty::Clause::Projection(data)) =
1632 bound_predicate.skip_binder()
1634 let data = self.replace_bound_vars_with_fresh_vars(
1635 obligation.cause.span,
1636 infer::LateBoundRegionConversionTime::HigherRankedType,
1637 bound_predicate.rebind(data),
1639 let normalized_ty = ocx.normalize(
1641 obligation.param_env,
1642 self.tcx.mk_projection(data.projection_ty.def_id, data.projection_ty.substs),
1645 debug!(?obligation.cause, ?obligation.param_env);
1647 debug!(?normalized_ty, data.ty = ?data.term);
1649 let is_normalized_ty_expected = !matches!(
1650 obligation.cause.code().peel_derives(),
1651 ObligationCauseCode::ItemObligation(_)
1652 | ObligationCauseCode::BindingObligation(_, _)
1653 | ObligationCauseCode::ExprItemObligation(..)
1654 | ObligationCauseCode::ExprBindingObligation(..)
1655 | ObligationCauseCode::ObjectCastObligation(..)
1656 | ObligationCauseCode::OpaqueType
1658 let expected_ty = data.term.ty().unwrap_or_else(|| self.tcx.ty_error());
1660 // constrain inference variables a bit more to nested obligations from normalize so
1661 // we can have more helpful errors.
1662 ocx.select_where_possible();
1664 if let Err(new_err) = ocx.eq_exp(
1666 obligation.param_env,
1667 is_normalized_ty_expected,
1671 (Some((data, is_normalized_ty_expected, normalized_ty, expected_ty)), new_err)
1680 .and_then(|(predicate, _, normalized_ty, expected_ty)| {
1681 self.maybe_detailed_projection_msg(
1683 normalized_ty.into(),
1687 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
1688 let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
1690 let secondary_span = match predicate.kind().skip_binder() {
1691 ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => self
1693 .opt_associated_item(proj.projection_ty.def_id)
1694 .and_then(|trait_assoc_item| {
1696 .trait_of_item(proj.projection_ty.def_id)
1697 .map(|id| (trait_assoc_item, id))
1699 .and_then(|(trait_assoc_item, id)| {
1700 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1701 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1703 .associated_items(did)
1704 .in_definition_order()
1705 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1708 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1710 hir::Node::TraitItem(hir::TraitItem {
1711 kind: hir::TraitItemKind::Type(_, Some(ty)),
1714 | hir::Node::ImplItem(hir::ImplItem {
1715 kind: hir::ImplItemKind::Type(ty),
1718 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1727 values.map(|(_, is_normalized_ty_expected, normalized_ty, expected_ty)| {
1728 infer::ValuePairs::Terms(ExpectedFound::new(
1729 is_normalized_ty_expected,
1730 normalized_ty.into(),
1738 self.note_obligation_cause(&mut diag, obligation);
1743 fn maybe_detailed_projection_msg(
1745 pred: ty::ProjectionPredicate<'tcx>,
1746 normalized_ty: ty::Term<'tcx>,
1747 expected_ty: ty::Term<'tcx>,
1748 ) -> Option<String> {
1749 let trait_def_id = pred.projection_ty.trait_def_id(self.tcx);
1750 let self_ty = pred.projection_ty.self_ty();
1752 if Some(pred.projection_ty.def_id) == self.tcx.lang_items().fn_once_output() {
1754 "expected `{self_ty}` to be a {fn_kind} that returns `{expected_ty}`, but it returns `{normalized_ty}`",
1755 fn_kind = self_ty.prefix_string(self.tcx)
1757 } else if Some(trait_def_id) == self.tcx.lang_items().future_trait() {
1759 "expected `{self_ty}` to be a future that resolves to `{expected_ty}`, but it resolves to `{normalized_ty}`"
1761 } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
1763 "expected `{self_ty}` to be an iterator that yields `{expected_ty}`, but it yields `{normalized_ty}`"
1774 ignoring_lifetimes: bool,
1775 ) -> Option<CandidateSimilarity> {
1776 /// returns the fuzzy category of a given type, or None
1777 /// if the type can be equated to any type.
1778 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1780 ty::Bool => Some(0),
1781 ty::Char => Some(1),
1783 ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => Some(2),
1787 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1788 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1789 ty::Array(..) | ty::Slice(..) => Some(6),
1790 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1791 ty::Dynamic(..) => Some(8),
1792 ty::Closure(..) => Some(9),
1793 ty::Tuple(..) => Some(10),
1794 ty::Param(..) => Some(11),
1795 ty::Alias(ty::Projection, ..) => Some(12),
1796 ty::Alias(ty::Opaque, ..) => Some(13),
1797 ty::Never => Some(14),
1798 ty::Adt(..) => Some(15),
1799 ty::Generator(..) => Some(16),
1800 ty::Foreign(..) => Some(17),
1801 ty::GeneratorWitness(..) => Some(18),
1802 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1806 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1809 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1817 if !ignoring_lifetimes {
1818 a = strip_references(a);
1819 b = strip_references(b);
1822 let cat_a = type_category(self.tcx, a)?;
1823 let cat_b = type_category(self.tcx, b)?;
1825 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1826 } else if cat_a == cat_b {
1827 match (a.kind(), b.kind()) {
1828 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1829 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1830 // Matching on references results in a lot of unhelpful
1831 // suggestions, so let's just not do that for now.
1833 // We still upgrade successful matches to `ignoring_lifetimes: true`
1834 // to prioritize that impl.
1835 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1836 self.fuzzy_match_tys(a, b, true).is_some()
1840 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1841 } else if ignoring_lifetimes {
1844 self.fuzzy_match_tys(a, b, true)
1848 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1849 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1850 hir::GeneratorKind::Gen => "a generator",
1851 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1852 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1853 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1857 fn find_similar_impl_candidates(
1859 trait_pred: ty::PolyTraitPredicate<'tcx>,
1860 ) -> Vec<ImplCandidate<'tcx>> {
1861 let mut candidates: Vec<_> = self
1863 .all_impls(trait_pred.def_id())
1864 .filter_map(|def_id| {
1865 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
1868 .is_constness_satisfied_by(self.tcx.constness(def_id))
1873 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1875 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
1876 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1879 if candidates.iter().any(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. })) {
1880 // If any of the candidates is a perfect match, we don't want to show all of them.
1881 // This is particularly relevant for the case of numeric types (as they all have the
1883 candidates.retain(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. }));
1888 fn report_similar_impl_candidates(
1890 impl_candidates: Vec<ImplCandidate<'tcx>>,
1891 trait_ref: ty::PolyTraitRef<'tcx>,
1892 body_id: hir::HirId,
1893 err: &mut Diagnostic,
1896 let other = if other { "other " } else { "" };
1897 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1900 let len = candidates.len();
1901 if candidates.len() == 0 {
1904 if candidates.len() == 1 {
1905 let ty_desc = match candidates[0].self_ty().kind() {
1906 ty::FnPtr(_) => Some("fn pointer"),
1909 let the_desc = match ty_desc {
1910 Some(desc) => format!(" implemented for {} `", desc),
1911 None => " implemented for `".to_string(),
1913 err.highlighted_help(vec![
1915 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1918 ("is".to_string(), Style::Highlight),
1919 (the_desc, Style::NoStyle),
1920 (candidates[0].self_ty().to_string(), Style::Highlight),
1921 ("`".to_string(), Style::NoStyle),
1925 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1926 // Check if the trait is the same in all cases. If so, we'll only show the type.
1927 let mut traits: Vec<_> =
1928 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1932 let mut candidates: Vec<String> = candidates
1935 if traits.len() == 1 {
1936 format!("\n {}", c.self_ty())
1945 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1947 "the following {other}types implement trait `{}`:{}{}",
1948 trait_ref.print_only_trait_path(),
1949 candidates[..end].join(""),
1950 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1955 let def_id = trait_ref.def_id();
1956 if impl_candidates.is_empty() {
1957 if self.tcx.trait_is_auto(def_id)
1958 || self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1959 || self.tcx.get_diagnostic_name(def_id).is_some()
1961 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1964 let normalized_impl_candidates: Vec<_> = self
1967 // Ignore automatically derived impls and `!Trait` impls.
1969 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1970 || self.tcx.is_builtin_derive(def_id)
1972 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1973 .filter(|trait_ref| {
1974 let self_ty = trait_ref.self_ty();
1975 // Avoid mentioning type parameters.
1976 if let ty::Param(_) = self_ty.kind() {
1979 // Avoid mentioning types that are private to another crate
1980 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
1981 // FIXME(compiler-errors): This could be generalized, both to
1982 // be more granular, and probably look past other `#[fundamental]`
1985 .visibility(def.did())
1986 .is_accessible_from(body_id.owner.def_id, self.tcx)
1992 return report(normalized_impl_candidates, err);
1995 // Sort impl candidates so that ordering is consistent for UI tests.
1996 // because the ordering of `impl_candidates` may not be deterministic:
1997 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1999 // Prefer more similar candidates first, then sort lexicographically
2000 // by their normalized string representation.
2001 let mut normalized_impl_candidates_and_similarities = impl_candidates
2003 .map(|ImplCandidate { trait_ref, similarity }| {
2004 // FIXME(compiler-errors): This should be using `NormalizeExt::normalize`
2005 let normalized = self
2006 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
2007 .query_normalize(trait_ref)
2008 .map_or(trait_ref, |normalized| normalized.value);
2009 (similarity, normalized)
2011 .collect::<Vec<_>>();
2012 normalized_impl_candidates_and_similarities.sort();
2013 normalized_impl_candidates_and_similarities.dedup();
2015 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
2017 .map(|(_, normalized)| normalized)
2018 .collect::<Vec<_>>();
2020 report(normalized_impl_candidates, err)
2023 /// Gets the parent trait chain start
2024 fn get_parent_trait_ref(
2026 code: &ObligationCauseCode<'tcx>,
2027 ) -> Option<(String, Option<Span>)> {
2029 ObligationCauseCode::BuiltinDerivedObligation(data) => {
2030 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2031 match self.get_parent_trait_ref(&data.parent_code) {
2034 let ty = parent_trait_ref.skip_binder().self_ty();
2035 let span = TyCategory::from_ty(self.tcx, ty)
2036 .map(|(_, def_id)| self.tcx.def_span(def_id));
2037 Some((ty.to_string(), span))
2041 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
2042 self.get_parent_trait_ref(&parent_code)
2048 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
2049 /// with the same path as `trait_ref`, a help message about
2050 /// a probable version mismatch is added to `err`
2051 fn note_version_mismatch(
2053 err: &mut Diagnostic,
2054 trait_ref: &ty::PolyTraitRef<'tcx>,
2056 let get_trait_impl = |trait_def_id| {
2057 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
2059 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
2060 let traits_with_same_path: std::collections::BTreeSet<_> = self
2063 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
2064 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
2066 let mut suggested = false;
2067 for trait_with_same_path in traits_with_same_path {
2068 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
2069 let impl_span = self.tcx.def_span(impl_def_id);
2070 err.span_help(impl_span, "trait impl with same name found");
2071 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
2072 let crate_msg = format!(
2073 "perhaps two different versions of crate `{}` are being used?",
2076 err.note(&crate_msg);
2083 fn mk_trait_obligation_with_new_self_ty(
2085 param_env: ty::ParamEnv<'tcx>,
2086 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
2087 ) -> PredicateObligation<'tcx> {
2089 trait_ref_and_ty.map_bound(|(tr, new_self_ty)| tr.with_self_ty(self.tcx, new_self_ty));
2091 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, trait_pred)
2094 #[instrument(skip(self), level = "debug")]
2095 fn maybe_report_ambiguity(
2097 obligation: &PredicateObligation<'tcx>,
2098 body_id: Option<hir::BodyId>,
2100 // Unable to successfully determine, probably means
2101 // insufficient type information, but could mean
2102 // ambiguous impls. The latter *ought* to be a
2103 // coherence violation, so we don't report it here.
2105 let predicate = self.resolve_vars_if_possible(obligation.predicate);
2106 let span = obligation.cause.span;
2108 debug!(?predicate, obligation.cause.code = ?obligation.cause.code());
2110 // Ambiguity errors are often caused as fallout from earlier errors.
2111 // We ignore them if this `infcx` is tainted in some cases below.
2113 let bound_predicate = predicate.kind();
2114 let mut err = match bound_predicate.skip_binder() {
2115 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
2116 let trait_ref = bound_predicate.rebind(data.trait_ref);
2119 if predicate.references_error() {
2123 // This is kind of a hack: it frequently happens that some earlier
2124 // error prevents types from being fully inferred, and then we get
2125 // a bunch of uninteresting errors saying something like "<generic
2126 // #0> doesn't implement Sized". It may even be true that we
2127 // could just skip over all checks where the self-ty is an
2128 // inference variable, but I was afraid that there might be an
2129 // inference variable created, registered as an obligation, and
2130 // then never forced by writeback, and hence by skipping here we'd
2131 // be ignoring the fact that we don't KNOW the type works
2132 // out. Though even that would probably be harmless, given that
2133 // we're only talking about builtin traits, which are known to be
2134 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2135 // avoid inundating the user with unnecessary errors, but we now
2136 // check upstream for type errors and don't add the obligations to
2137 // begin with in those cases.
2138 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
2139 if let None = self.tainted_by_errors() {
2140 self.emit_inference_failure_err(
2143 trait_ref.self_ty().skip_binder().into(),
2152 // Typically, this ambiguity should only happen if
2153 // there are unresolved type inference variables
2154 // (otherwise it would suggest a coherence
2155 // failure). But given #21974 that is not necessarily
2156 // the case -- we can have multiple where clauses that
2157 // are only distinguished by a region, which results
2158 // in an ambiguity even when all types are fully
2159 // known, since we don't dispatch based on region
2162 // Pick the first substitution that still contains inference variables as the one
2163 // we're going to emit an error for. If there are none (see above), fall back to
2164 // a more general error.
2165 let subst = data.trait_ref.substs.iter().find(|s| s.has_non_region_infer());
2167 let mut err = if let Some(subst) = subst {
2168 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2174 "type annotations needed: cannot satisfy `{}`",
2179 let obligation = obligation.with(self.tcx, trait_ref);
2180 let mut selcx = SelectionContext::new(&self);
2181 match selcx.select_from_obligation(&obligation) {
2183 let impls = ambiguity::recompute_applicable_impls(self.infcx, &obligation);
2184 let has_non_region_infer =
2185 trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_infer());
2186 // It doesn't make sense to talk about applicable impls if there are more
2187 // than a handful of them.
2188 if impls.len() > 1 && impls.len() < 10 && has_non_region_infer {
2189 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2191 if self.tainted_by_errors().is_some() {
2195 err.note(&format!("cannot satisfy `{}`", predicate));
2196 let impl_candidates = self.find_similar_impl_candidates(
2197 predicate.to_opt_poly_trait_pred().unwrap(),
2199 if impl_candidates.len() < 10 {
2200 self.report_similar_impl_candidates(
2203 body_id.map(|id| id.hir_id).unwrap_or(obligation.cause.body_id),
2211 if self.tainted_by_errors().is_some() {
2215 err.note(&format!("cannot satisfy `{}`", predicate));
2219 if let ObligationCauseCode::ItemObligation(def_id)
2220 | ObligationCauseCode::ExprItemObligation(def_id, ..) = *obligation.cause.code()
2222 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2225 if let (Some(body_id), Some(ty::subst::GenericArgKind::Type(_))) =
2226 (body_id, subst.map(|subst| subst.unpack()))
2228 struct FindExprBySpan<'hir> {
2230 result: Option<&'hir hir::Expr<'hir>>,
2233 impl<'v> hir::intravisit::Visitor<'v> for FindExprBySpan<'v> {
2234 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2235 if self.span == ex.span {
2236 self.result = Some(ex);
2238 hir::intravisit::walk_expr(self, ex);
2243 let mut expr_finder = FindExprBySpan { span, result: None };
2245 expr_finder.visit_expr(&self.tcx.hir().body(body_id).value);
2247 if let Some(hir::Expr {
2248 kind: hir::ExprKind::Path(hir::QPath::Resolved(None, path)), .. }
2249 ) = expr_finder.result
2252 trait_path_segment @ hir::PathSegment {
2253 res: rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id),
2257 ident: assoc_item_name,
2258 res: rustc_hir::def::Res::Def(_, item_id),
2262 && data.trait_ref.def_id == *trait_id
2263 && self.tcx.trait_of_item(*item_id) == Some(*trait_id)
2264 && let None = self.tainted_by_errors()
2266 let (verb, noun) = match self.tcx.associated_item(item_id).kind {
2267 ty::AssocKind::Const => ("refer to the", "constant"),
2268 ty::AssocKind::Fn => ("call", "function"),
2269 ty::AssocKind::Type => ("refer to the", "type"), // this is already covered by E0223, but this single match arm doesn't hurt here
2272 // Replace the more general E0283 with a more specific error
2274 err = self.tcx.sess.struct_span_err_with_code(
2277 "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type",
2279 rustc_errors::error_code!(E0790),
2282 if let Some(local_def_id) = data.trait_ref.def_id.as_local()
2283 && 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)
2284 && let Some(method_ref) = trait_item_refs.iter().find(|item_ref| item_ref.ident == *assoc_item_name) {
2285 err.span_label(method_ref.span, format!("`{}::{}` defined here", trait_name, assoc_item_name));
2288 err.span_label(span, format!("cannot {verb} associated {noun} of trait"));
2290 let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
2292 if trait_impls.blanket_impls().is_empty()
2293 && let Some((impl_ty, _)) = trait_impls.non_blanket_impls().iter().next()
2294 && let Some(impl_def_id) = impl_ty.def() {
2295 let message = if trait_impls.non_blanket_impls().len() == 1 {
2296 "use the fully-qualified path to the only available implementation".to_string()
2299 "use a fully-qualified path to a specific available implementation ({} found)",
2300 trait_impls.non_blanket_impls().len()
2303 let mut suggestions = vec![(
2304 trait_path_segment.ident.span.shrink_to_lo(),
2305 format!("<{} as ", self.tcx.type_of(impl_def_id))
2307 if let Some(generic_arg) = trait_path_segment.args {
2308 let between_span = trait_path_segment.ident.span.between(generic_arg.span_ext);
2309 // get rid of :: between Trait and <type>
2310 // must be '::' between them, otherwise the parser won't accept the code
2311 suggestions.push((between_span, "".to_string(),));
2312 suggestions.push((generic_arg.span_ext.shrink_to_hi(), format!(">")));
2314 suggestions.push((trait_path_segment.ident.span.shrink_to_hi(), format!(">")));
2316 err.multipart_suggestion(
2319 Applicability::MaybeIncorrect
2328 ty::PredicateKind::WellFormed(arg) => {
2329 // Same hacky approach as above to avoid deluging user
2330 // with error messages.
2331 if arg.references_error()
2332 || self.tcx.sess.has_errors().is_some()
2333 || self.tainted_by_errors().is_some()
2338 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2341 ty::PredicateKind::Subtype(data) => {
2342 if data.references_error()
2343 || self.tcx.sess.has_errors().is_some()
2344 || self.tainted_by_errors().is_some()
2346 // no need to overload user in such cases
2349 let SubtypePredicate { a_is_expected: _, a, b } = data;
2350 // both must be type variables, or the other would've been instantiated
2351 assert!(a.is_ty_var() && b.is_ty_var());
2352 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2354 ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
2355 if predicate.references_error() || self.tainted_by_errors().is_some() {
2362 .chain(Some(data.term.into_arg()))
2363 .find(|g| g.has_non_region_infer());
2364 if let Some(subst) = subst {
2365 let mut err = self.emit_inference_failure_err(
2372 err.note(&format!("cannot satisfy `{}`", predicate));
2375 // If we can't find a substitution, just print a generic error
2376 let mut err = struct_span_err!(
2380 "type annotations needed: cannot satisfy `{}`",
2383 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2388 ty::PredicateKind::ConstEvaluatable(data) => {
2389 if predicate.references_error() || self.tainted_by_errors().is_some() {
2392 let subst = data.walk().find(|g| g.is_non_region_infer());
2393 if let Some(subst) = subst {
2394 let err = self.emit_inference_failure_err(
2403 // If we can't find a substitution, just print a generic error
2404 let mut err = struct_span_err!(
2408 "type annotations needed: cannot satisfy `{}`",
2411 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2416 if self.tcx.sess.has_errors().is_some() || self.tainted_by_errors().is_some() {
2419 let mut err = struct_span_err!(
2423 "type annotations needed: cannot satisfy `{}`",
2426 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2430 self.note_obligation_cause(&mut err, obligation);
2434 fn annotate_source_of_ambiguity(
2436 err: &mut Diagnostic,
2438 predicate: ty::Predicate<'tcx>,
2440 let mut spans = vec![];
2441 let mut crates = vec![];
2442 let mut post = vec![];
2443 for def_id in impls {
2444 match self.tcx.span_of_impl(*def_id) {
2445 Ok(span) => spans.push(span),
2448 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2454 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2456 crate_names.dedup();
2460 if self.tainted_by_errors().is_some()
2461 && (crate_names.len() == 1
2463 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2464 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2466 // Avoid complaining about other inference issues for expressions like
2467 // `42 >> 1`, where the types are still `{integer}`, but we want to
2468 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2469 // NOTE(eddyb) this was `.cancel()`, but `err`
2470 // is borrowed, so we can't fully defuse it.
2471 err.downgrade_to_delayed_bug();
2475 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2476 let post = if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2477 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2478 } else if post.len() == 1 {
2479 format!(": `{}`", post[0])
2484 match (spans.len(), crates.len(), crate_names.len()) {
2486 err.note(&format!("cannot satisfy `{}`", predicate));
2489 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2493 "{} in the following crates: {}{}",
2495 crate_names.join(", "),
2500 let span: MultiSpan = spans.into();
2501 err.span_note(span, &msg);
2504 let span: MultiSpan = spans.into();
2505 err.span_note(span, &msg);
2507 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2511 let span: MultiSpan = spans.into();
2512 err.span_note(span, &msg);
2514 "and more `impl`s found in the following crates: {}{}",
2515 crate_names.join(", "),
2522 /// Returns `true` if the trait predicate may apply for *some* assignment
2523 /// to the type parameters.
2524 fn predicate_can_apply(
2526 param_env: ty::ParamEnv<'tcx>,
2527 pred: ty::PolyTraitPredicate<'tcx>,
2529 struct ParamToVarFolder<'a, 'tcx> {
2530 infcx: &'a InferCtxt<'tcx>,
2531 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2534 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2535 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2539 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2540 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2541 let infcx = self.infcx;
2542 *self.var_map.entry(ty).or_insert_with(|| {
2543 infcx.next_ty_var(TypeVariableOrigin {
2544 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2549 ty.super_fold_with(self)
2556 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2558 let InferOk { value: cleaned_pred, .. } =
2559 self.infcx.at(&ObligationCause::dummy(), param_env).normalize(cleaned_pred);
2562 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, cleaned_pred);
2564 self.predicate_may_hold(&obligation)
2568 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2569 // First, attempt to add note to this error with an async-await-specific
2570 // message, and fall back to regular note otherwise.
2571 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2572 self.note_obligation_cause_code(
2574 obligation.predicate,
2575 obligation.param_env,
2576 obligation.cause.code(),
2578 &mut Default::default(),
2580 self.suggest_unsized_bound_if_applicable(err, obligation);
2584 #[instrument(level = "debug", skip_all)]
2585 fn suggest_unsized_bound_if_applicable(
2587 err: &mut Diagnostic,
2588 obligation: &PredicateObligation<'tcx>,
2590 let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = obligation.predicate.kind().skip_binder() else { return; };
2591 let (ObligationCauseCode::BindingObligation(item_def_id, span)
2592 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..))
2593 = *obligation.cause.code().peel_derives() else { return; };
2594 debug!(?pred, ?item_def_id, ?span);
2596 let (Some(node), true) = (
2597 self.tcx.hir().get_if_local(item_def_id),
2598 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2602 self.maybe_suggest_unsized_generics(err, span, node);
2605 #[instrument(level = "debug", skip_all)]
2606 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>) {
2607 let Some(generics) = node.generics() else {
2610 let sized_trait = self.tcx.lang_items().sized_trait();
2611 debug!(?generics.params);
2612 debug!(?generics.predicates);
2613 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2616 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2617 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2618 let explicitly_sized = generics
2619 .bounds_for_param(param.def_id)
2620 .flat_map(|bp| bp.bounds)
2621 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2622 if explicitly_sized {
2629 // Only suggest indirection for uses of type parameters in ADTs.
2631 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2635 if self.maybe_indirection_for_unsized(err, item, param) {
2641 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2642 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param.def_id)
2646 (span.shrink_to_hi(), ":")
2648 err.span_suggestion_verbose(
2650 "consider relaxing the implicit `Sized` restriction",
2651 format!("{} ?Sized", separator),
2652 Applicability::MachineApplicable,
2656 fn maybe_indirection_for_unsized(
2658 err: &mut Diagnostic,
2660 param: &GenericParam<'tcx>,
2662 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2663 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2664 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2666 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2667 visitor.visit_item(item);
2668 if visitor.invalid_spans.is_empty() {
2671 let mut multispan: MultiSpan = param.span.into();
2672 multispan.push_span_label(
2674 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2676 for sp in visitor.invalid_spans {
2677 multispan.push_span_label(
2679 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2685 "you could relax the implicit `Sized` bound on `{T}` if it were \
2686 used through indirection like `&{T}` or `Box<{T}>`",
2687 T = param.name.ident(),
2693 fn is_recursive_obligation(
2695 obligated_types: &mut Vec<Ty<'tcx>>,
2696 cause_code: &ObligationCauseCode<'tcx>,
2698 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2699 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2700 let self_ty = parent_trait_ref.skip_binder().self_ty();
2701 if obligated_types.iter().any(|ot| ot == &self_ty) {
2704 if let ty::Adt(def, substs) = self_ty.kind()
2705 && let [arg] = &substs[..]
2706 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2707 && let ty::Adt(inner_def, _) = ty.kind()
2717 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2718 /// `param: ?Sized` would be a valid constraint.
2719 struct FindTypeParam {
2720 param: rustc_span::Symbol,
2721 invalid_spans: Vec<Span>,
2725 impl<'v> Visitor<'v> for FindTypeParam {
2726 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2727 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2730 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2731 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2732 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2733 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2734 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2735 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2736 // in that case should make what happened clear enough.
2738 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2739 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2740 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2743 debug!(?ty, "FindTypeParam::visit_ty");
2744 self.invalid_spans.push(ty.span);
2747 hir::TyKind::Path(_) => {
2748 let prev = self.nested;
2750 hir::intravisit::walk_ty(self, ty);
2754 hir::intravisit::walk_ty(self, ty);
2760 /// Summarizes information
2763 /// An argument of non-tuple type. Parameters are (name, ty)
2764 Arg(String, String),
2766 /// An argument of tuple type. For a "found" argument, the span is
2767 /// the location in the source of the pattern. For an "expected"
2768 /// argument, it will be None. The vector is a list of (name, ty)
2769 /// strings for the components of the tuple.
2770 Tuple(Option<Span>, Vec<(String, String)>),
2774 fn empty() -> ArgKind {
2775 ArgKind::Arg("_".to_owned(), "_".to_owned())
2778 /// Creates an `ArgKind` from the expected type of an
2779 /// argument. It has no name (`_`) and an optional source span.
2780 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2782 ty::Tuple(tys) => ArgKind::Tuple(
2784 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2786 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2791 struct HasNumericInferVisitor;
2793 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2796 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2797 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2798 ControlFlow::Break(())
2800 ControlFlow::CONTINUE
2805 pub enum DefIdOrName {