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::{kw, 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,
984 // This is *almost* equivalent to
985 // `obligation.cause.code().peel_derives()`, but it gives us the
986 // trait predicate for that corresponding root obligation. This
987 // lets us get a derived obligation from a type parameter, like
988 // when calling `string.strip_suffix(p)` where `p` is *not* an
989 // implementer of `Pattern<'_>`.
990 let mut code = obligation.cause.code();
991 let mut trait_pred = trait_predicate;
992 let mut peeled = false;
993 while let Some((parent_code, parent_trait_pred)) = code.parent() {
995 if let Some(parent_trait_pred) = parent_trait_pred {
996 trait_pred = parent_trait_pred;
1000 let def_id = trait_pred.def_id();
1001 // Mention *all* the `impl`s for the *top most* obligation, the
1002 // user might have meant to use one of them, if any found. We skip
1003 // auto-traits or fundamental traits that might not be exactly what
1004 // the user might expect to be presented with. Instead this is
1005 // useful for less general traits.
1007 && !self.tcx.trait_is_auto(def_id)
1008 && !self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1010 let trait_ref = trait_pred.to_poly_trait_ref();
1011 let impl_candidates =
1012 self.find_similar_impl_candidates(trait_pred);
1013 self.report_similar_impl_candidates(
1016 obligation.cause.body_id,
1023 // Changing mutability doesn't make a difference to whether we have
1024 // an `Unsize` impl (Fixes ICE in #71036)
1026 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
1029 // If this error is due to `!: Trait` not implemented but `(): Trait` is
1030 // implemented, and fallback has occurred, then it could be due to a
1031 // variable that used to fallback to `()` now falling back to `!`. Issue a
1032 // note informing about the change in behaviour.
1033 if trait_predicate.skip_binder().self_ty().is_never()
1034 && self.fallback_has_occurred
1036 let predicate = trait_predicate.map_bound(|trait_pred| {
1037 trait_pred.with_self_type(self.tcx, self.tcx.mk_unit())
1039 let unit_obligation = obligation.with(tcx, predicate);
1040 if self.predicate_may_hold(&unit_obligation) {
1042 "this error might have been caused by changes to \
1043 Rust's type-inference algorithm (see issue #48950 \
1044 <https://github.com/rust-lang/rust/issues/48950> \
1045 for more information)",
1047 err.help("did you intend to use the type `()` here instead?");
1051 // Return early if the trait is Debug or Display and the invocation
1052 // originates within a standard library macro, because the output
1053 // is otherwise overwhelming and unhelpful (see #85844 for an
1057 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
1058 Some(macro_def_id) => {
1059 let crate_name = tcx.crate_name(macro_def_id.krate);
1060 crate_name == sym::std || crate_name == sym::core
1067 self.tcx.get_diagnostic_name(trait_ref.def_id()),
1068 Some(sym::Debug | sym::Display)
1078 ty::PredicateKind::Subtype(predicate) => {
1079 // Errors for Subtype predicates show up as
1080 // `FulfillmentErrorCode::CodeSubtypeError`,
1081 // not selection error.
1082 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
1085 ty::PredicateKind::Coerce(predicate) => {
1086 // Errors for Coerce predicates show up as
1087 // `FulfillmentErrorCode::CodeSubtypeError`,
1088 // not selection error.
1089 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
1092 ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
1093 | ty::PredicateKind::Clause(ty::Clause::Projection(..))
1094 | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..)) => {
1095 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1100 "the requirement `{}` is not satisfied",
1105 ty::PredicateKind::ObjectSafe(trait_def_id) => {
1106 let violations = self.tcx.object_safety_violations(trait_def_id);
1107 report_object_safety_error(self.tcx, span, trait_def_id, violations)
1110 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
1111 let found_kind = self.closure_kind(closure_substs).unwrap();
1112 let closure_span = self.tcx.def_span(closure_def_id);
1113 let mut err = struct_span_err!(
1117 "expected a closure that implements the `{}` trait, \
1118 but this closure only implements `{}`",
1125 format!("this closure implements `{}`, not `{}`", found_kind, kind),
1128 obligation.cause.span,
1129 format!("the requirement to implement `{}` derives from here", kind),
1132 // Additional context information explaining why the closure only implements
1133 // a particular trait.
1134 if let Some(typeck_results) = &self.typeck_results {
1138 .local_def_id_to_hir_id(closure_def_id.expect_local());
1139 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
1140 (ty::ClosureKind::FnOnce, Some((span, place))) => {
1144 "closure is `FnOnce` because it moves the \
1145 variable `{}` out of its environment",
1146 ty::place_to_string_for_capture(tcx, place)
1150 (ty::ClosureKind::FnMut, Some((span, place))) => {
1154 "closure is `FnMut` because it mutates the \
1155 variable `{}` here",
1156 ty::place_to_string_for_capture(tcx, place)
1167 ty::PredicateKind::WellFormed(ty) => {
1168 if !self.tcx.sess.opts.unstable_opts.chalk {
1169 // WF predicates cannot themselves make
1170 // errors. They can only block due to
1171 // ambiguity; otherwise, they always
1172 // degenerate into other obligations
1173 // (which may fail).
1174 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
1176 // FIXME: we'll need a better message which takes into account
1177 // which bounds actually failed to hold.
1178 self.tcx.sess.struct_span_err(
1180 &format!("the type `{}` is not well-formed (chalk)", ty),
1185 ty::PredicateKind::ConstEvaluatable(..) => {
1186 // Errors for `ConstEvaluatable` predicates show up as
1187 // `SelectionError::ConstEvalFailure`,
1188 // not `Unimplemented`.
1191 "const-evaluatable requirement gave wrong error: `{:?}`",
1196 ty::PredicateKind::ConstEquate(..) => {
1197 // Errors for `ConstEquate` predicates show up as
1198 // `SelectionError::ConstEvalFailure`,
1199 // not `Unimplemented`.
1202 "const-equate requirement gave wrong error: `{:?}`",
1207 ty::PredicateKind::Ambiguous => span_bug!(span, "ambiguous"),
1209 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
1211 "TypeWellFormedFromEnv predicate should only exist in the environment"
1216 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
1217 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
1218 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
1220 if expected_trait_ref.self_ty().references_error() {
1224 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
1228 let found_did = match *found_trait_ty.kind() {
1232 | ty::Generator(did, ..) => Some(did),
1233 ty::Adt(def, _) => Some(def.did()),
1237 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
1239 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1240 // We check closures twice, with obligations flowing in different directions,
1241 // but we want to complain about them only once.
1245 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1247 let mut not_tupled = false;
1249 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
1250 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1253 vec![ArgKind::empty()]
1257 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1258 let expected = match expected_ty.kind() {
1259 ty::Tuple(ref tys) => {
1260 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
1264 vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())]
1268 // If this is a `Fn` family trait and either the expected or found
1269 // is not tupled, then fall back to just a regular mismatch error.
1270 // This shouldn't be common unless manually implementing one of the
1271 // traits manually, but don't make it more confusing when it does
1273 if Some(expected_trait_ref.def_id()) != tcx.lang_items().gen_trait() && not_tupled {
1274 self.report_and_explain_type_error(
1275 TypeTrace::poly_trait_refs(
1281 ty::error::TypeError::Mismatch,
1283 } else if found.len() == expected.len() {
1284 self.report_closure_arg_mismatch(
1289 obligation.cause.code(),
1292 let (closure_span, closure_arg_span, found) = found_did
1294 let node = self.tcx.hir().get_if_local(did)?;
1295 let (found_span, closure_arg_span, found) =
1296 self.get_fn_like_arguments(node)?;
1297 Some((Some(found_span), closure_arg_span, found))
1299 .unwrap_or((found_span, None, found));
1301 self.report_arg_count_mismatch(
1306 found_trait_ty.is_closure(),
1312 TraitNotObjectSafe(did) => {
1313 let violations = self.tcx.object_safety_violations(did);
1314 report_object_safety_error(self.tcx, span, did, violations)
1317 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1319 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1322 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1323 if !self.tcx.features().generic_const_exprs {
1324 let mut err = self.tcx.sess.struct_span_err(
1326 "constant expression depends on a generic parameter",
1328 // FIXME(const_generics): we should suggest to the user how they can resolve this
1329 // issue. However, this is currently not actually possible
1330 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1332 // Note that with `feature(generic_const_exprs)` this case should not
1334 err.note("this may fail depending on what value the parameter takes");
1339 match obligation.predicate.kind().skip_binder() {
1340 ty::PredicateKind::ConstEvaluatable(ct) => {
1341 let ty::ConstKind::Unevaluated(uv) = ct.kind() else {
1342 bug!("const evaluatable failed for non-unevaluated const `{ct:?}`");
1345 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1346 let const_span = self.tcx.def_span(uv.def.did);
1347 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1348 Ok(snippet) => err.help(&format!(
1349 "try adding a `where` bound using this expression: `where [(); {}]:`",
1352 _ => err.help("consider adding a `where` bound using this expression"),
1359 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1365 // Already reported in the query.
1366 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1367 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1368 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1371 // Already reported.
1372 Overflow(OverflowError::Error(_)) => {
1373 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1377 bug!("overflow should be handled before the `report_selection_error` path");
1379 SelectionError::ErrorReporting => {
1380 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1384 self.note_obligation_cause(&mut err, &obligation);
1385 self.point_at_returns_when_relevant(&mut err, &obligation);
1391 trait InferCtxtPrivExt<'tcx> {
1392 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1393 // `error` occurring implies that `cond` occurs.
1394 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1396 fn report_fulfillment_error(
1398 error: &FulfillmentError<'tcx>,
1399 body_id: Option<hir::BodyId>,
1402 fn report_projection_error(
1404 obligation: &PredicateObligation<'tcx>,
1405 error: &MismatchedProjectionTypes<'tcx>,
1408 fn maybe_detailed_projection_msg(
1410 pred: ty::ProjectionPredicate<'tcx>,
1411 normalized_ty: ty::Term<'tcx>,
1412 expected_ty: ty::Term<'tcx>,
1413 ) -> Option<String>;
1419 ignoring_lifetimes: bool,
1420 ) -> Option<CandidateSimilarity>;
1422 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1424 fn find_similar_impl_candidates(
1426 trait_pred: ty::PolyTraitPredicate<'tcx>,
1427 ) -> Vec<ImplCandidate<'tcx>>;
1429 fn report_similar_impl_candidates(
1431 impl_candidates: Vec<ImplCandidate<'tcx>>,
1432 trait_ref: ty::PolyTraitRef<'tcx>,
1433 body_id: hir::HirId,
1434 err: &mut Diagnostic,
1437 /// Gets the parent trait chain start
1438 fn get_parent_trait_ref(
1440 code: &ObligationCauseCode<'tcx>,
1441 ) -> Option<(String, Option<Span>)>;
1443 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1444 /// with the same path as `trait_ref`, a help message about
1445 /// a probable version mismatch is added to `err`
1446 fn note_version_mismatch(
1448 err: &mut Diagnostic,
1449 trait_ref: &ty::PolyTraitRef<'tcx>,
1452 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1455 /// For this to work, `new_self_ty` must have no escaping bound variables.
1456 fn mk_trait_obligation_with_new_self_ty(
1458 param_env: ty::ParamEnv<'tcx>,
1459 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1460 ) -> PredicateObligation<'tcx>;
1462 fn maybe_report_ambiguity(
1464 obligation: &PredicateObligation<'tcx>,
1465 body_id: Option<hir::BodyId>,
1468 fn predicate_can_apply(
1470 param_env: ty::ParamEnv<'tcx>,
1471 pred: ty::PolyTraitPredicate<'tcx>,
1474 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1476 fn suggest_unsized_bound_if_applicable(
1478 err: &mut Diagnostic,
1479 obligation: &PredicateObligation<'tcx>,
1482 fn annotate_source_of_ambiguity(
1484 err: &mut Diagnostic,
1486 predicate: ty::Predicate<'tcx>,
1489 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>);
1491 fn maybe_indirection_for_unsized(
1493 err: &mut Diagnostic,
1494 item: &'tcx Item<'tcx>,
1495 param: &'tcx GenericParam<'tcx>,
1498 fn is_recursive_obligation(
1500 obligated_types: &mut Vec<Ty<'tcx>>,
1501 cause_code: &ObligationCauseCode<'tcx>,
1505 impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
1506 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1507 // `error` occurring implies that `cond` occurs.
1508 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1513 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1514 let bound_error = error.kind();
1515 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1517 ty::PredicateKind::Clause(ty::Clause::Trait(..)),
1518 ty::PredicateKind::Clause(ty::Clause::Trait(error)),
1519 ) => (cond, bound_error.rebind(error)),
1521 // FIXME: make this work in other cases too.
1526 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1527 let bound_predicate = obligation.predicate.kind();
1528 if let ty::PredicateKind::Clause(ty::Clause::Trait(implication)) =
1529 bound_predicate.skip_binder()
1531 let error = error.to_poly_trait_ref();
1532 let implication = bound_predicate.rebind(implication.trait_ref);
1533 // FIXME: I'm just not taking associated types at all here.
1534 // Eventually I'll need to implement param-env-aware
1535 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1536 let param_env = ty::ParamEnv::empty();
1537 if self.can_sub(param_env, error, implication).is_ok() {
1538 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1547 #[instrument(skip(self), level = "debug")]
1548 fn report_fulfillment_error(
1550 error: &FulfillmentError<'tcx>,
1551 body_id: Option<hir::BodyId>,
1554 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1555 self.report_selection_error(
1556 error.obligation.clone(),
1557 &error.root_obligation,
1561 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1562 self.report_projection_error(&error.obligation, e);
1564 FulfillmentErrorCode::CodeAmbiguity => {
1565 self.maybe_report_ambiguity(&error.obligation, body_id);
1567 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1568 self.report_mismatched_types(
1569 &error.obligation.cause,
1570 expected_found.expected,
1571 expected_found.found,
1576 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1577 let mut diag = self.report_mismatched_consts(
1578 &error.obligation.cause,
1579 expected_found.expected,
1580 expected_found.found,
1583 let code = error.obligation.cause.code().peel_derives().peel_match_impls();
1584 if let ObligationCauseCode::BindingObligation(..)
1585 | ObligationCauseCode::ItemObligation(..)
1586 | ObligationCauseCode::ExprBindingObligation(..)
1587 | ObligationCauseCode::ExprItemObligation(..) = code
1589 self.note_obligation_cause_code(
1591 error.obligation.predicate,
1592 error.obligation.param_env,
1595 &mut Default::default(),
1600 FulfillmentErrorCode::CodeCycle(ref cycle) => {
1601 self.report_overflow_obligation_cycle(cycle);
1606 #[instrument(level = "debug", skip_all)]
1607 fn report_projection_error(
1609 obligation: &PredicateObligation<'tcx>,
1610 error: &MismatchedProjectionTypes<'tcx>,
1612 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1614 if predicate.references_error() {
1619 let ocx = ObligationCtxt::new_in_snapshot(self);
1621 // try to find the mismatched types to report the error with.
1623 // this can fail if the problem was higher-ranked, in which
1624 // cause I have no idea for a good error message.
1625 let bound_predicate = predicate.kind();
1626 let (values, err) = if let ty::PredicateKind::Clause(ty::Clause::Projection(data)) =
1627 bound_predicate.skip_binder()
1629 let data = self.replace_bound_vars_with_fresh_vars(
1630 obligation.cause.span,
1631 infer::LateBoundRegionConversionTime::HigherRankedType,
1632 bound_predicate.rebind(data),
1634 let normalized_ty = ocx.normalize(
1636 obligation.param_env,
1638 .mk_projection(data.projection_ty.item_def_id, data.projection_ty.substs),
1641 debug!(?obligation.cause, ?obligation.param_env);
1643 debug!(?normalized_ty, data.ty = ?data.term);
1645 let is_normalized_ty_expected = !matches!(
1646 obligation.cause.code().peel_derives(),
1647 ObligationCauseCode::ItemObligation(_)
1648 | ObligationCauseCode::BindingObligation(_, _)
1649 | ObligationCauseCode::ExprItemObligation(..)
1650 | ObligationCauseCode::ExprBindingObligation(..)
1651 | ObligationCauseCode::ObjectCastObligation(..)
1652 | ObligationCauseCode::OpaqueType
1654 let expected_ty = data.term.ty().unwrap_or_else(|| self.tcx.ty_error());
1656 // constrain inference variables a bit more to nested obligations from normalize so
1657 // we can have more helpful errors.
1658 ocx.select_where_possible();
1660 if let Err(new_err) = ocx.eq_exp(
1662 obligation.param_env,
1663 is_normalized_ty_expected,
1667 (Some((data, is_normalized_ty_expected, normalized_ty, expected_ty)), new_err)
1676 .and_then(|(predicate, _, normalized_ty, expected_ty)| {
1677 self.maybe_detailed_projection_msg(
1679 normalized_ty.into(),
1683 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
1684 let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
1686 let secondary_span = match predicate.kind().skip_binder() {
1687 ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => self
1689 .opt_associated_item(proj.projection_ty.item_def_id)
1690 .and_then(|trait_assoc_item| {
1692 .trait_of_item(proj.projection_ty.item_def_id)
1693 .map(|id| (trait_assoc_item, id))
1695 .and_then(|(trait_assoc_item, id)| {
1696 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1697 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1699 .associated_items(did)
1700 .in_definition_order()
1701 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1704 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1706 hir::Node::TraitItem(hir::TraitItem {
1707 kind: hir::TraitItemKind::Type(_, Some(ty)),
1710 | hir::Node::ImplItem(hir::ImplItem {
1711 kind: hir::ImplItemKind::Type(ty),
1714 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1723 values.map(|(_, is_normalized_ty_expected, normalized_ty, expected_ty)| {
1724 infer::ValuePairs::Terms(ExpectedFound::new(
1725 is_normalized_ty_expected,
1726 normalized_ty.into(),
1734 self.note_obligation_cause(&mut diag, obligation);
1739 fn maybe_detailed_projection_msg(
1741 pred: ty::ProjectionPredicate<'tcx>,
1742 normalized_ty: ty::Term<'tcx>,
1743 expected_ty: ty::Term<'tcx>,
1744 ) -> Option<String> {
1745 let trait_def_id = pred.projection_ty.trait_def_id(self.tcx);
1746 let self_ty = pred.projection_ty.self_ty();
1748 if Some(pred.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output() {
1750 "expected `{self_ty}` to be a {fn_kind} that returns `{expected_ty}`, but it returns `{normalized_ty}`",
1751 fn_kind = self_ty.prefix_string(self.tcx)
1753 } else if Some(trait_def_id) == self.tcx.lang_items().future_trait() {
1755 "expected `{self_ty}` to be a future that resolves to `{expected_ty}`, but it resolves to `{normalized_ty}`"
1757 } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
1759 "expected `{self_ty}` to be an iterator that yields `{expected_ty}`, but it yields `{normalized_ty}`"
1770 ignoring_lifetimes: bool,
1771 ) -> Option<CandidateSimilarity> {
1772 /// returns the fuzzy category of a given type, or None
1773 /// if the type can be equated to any type.
1774 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1776 ty::Bool => Some(0),
1777 ty::Char => Some(1),
1779 ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => Some(2),
1783 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1784 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1785 ty::Array(..) | ty::Slice(..) => Some(6),
1786 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1787 ty::Dynamic(..) => Some(8),
1788 ty::Closure(..) => Some(9),
1789 ty::Tuple(..) => Some(10),
1790 ty::Param(..) => Some(11),
1791 ty::Projection(..) => Some(12),
1792 ty::Opaque(..) => Some(13),
1793 ty::Never => Some(14),
1794 ty::Adt(..) => Some(15),
1795 ty::Generator(..) => Some(16),
1796 ty::Foreign(..) => Some(17),
1797 ty::GeneratorWitness(..) => Some(18),
1798 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1802 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1805 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1813 if !ignoring_lifetimes {
1814 a = strip_references(a);
1815 b = strip_references(b);
1818 let cat_a = type_category(self.tcx, a)?;
1819 let cat_b = type_category(self.tcx, b)?;
1821 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1822 } else if cat_a == cat_b {
1823 match (a.kind(), b.kind()) {
1824 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1825 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1826 // Matching on references results in a lot of unhelpful
1827 // suggestions, so let's just not do that for now.
1829 // We still upgrade successful matches to `ignoring_lifetimes: true`
1830 // to prioritize that impl.
1831 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1832 self.fuzzy_match_tys(a, b, true).is_some()
1836 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1837 } else if ignoring_lifetimes {
1840 self.fuzzy_match_tys(a, b, true)
1844 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1845 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1846 hir::GeneratorKind::Gen => "a generator",
1847 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1848 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1849 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1853 fn find_similar_impl_candidates(
1855 trait_pred: ty::PolyTraitPredicate<'tcx>,
1856 ) -> Vec<ImplCandidate<'tcx>> {
1857 let mut candidates: Vec<_> = self
1859 .all_impls(trait_pred.def_id())
1860 .filter_map(|def_id| {
1861 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
1864 .is_constness_satisfied_by(self.tcx.constness(def_id))
1869 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1871 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
1872 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1875 if candidates.iter().any(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. })) {
1876 // If any of the candidates is a perfect match, we don't want to show all of them.
1877 // This is particularly relevant for the case of numeric types (as they all have the
1879 candidates.retain(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. }));
1884 fn report_similar_impl_candidates(
1886 impl_candidates: Vec<ImplCandidate<'tcx>>,
1887 trait_ref: ty::PolyTraitRef<'tcx>,
1888 body_id: hir::HirId,
1889 err: &mut Diagnostic,
1891 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1894 let len = candidates.len();
1895 if candidates.len() == 0 {
1898 if candidates.len() == 1 {
1899 let ty_desc = match candidates[0].self_ty().kind() {
1900 ty::FnPtr(_) => Some("fn pointer"),
1903 let the_desc = match ty_desc {
1904 Some(desc) => format!(" implemented for {} `", desc),
1905 None => " implemented for `".to_string(),
1907 err.highlighted_help(vec![
1909 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1912 ("is".to_string(), Style::Highlight),
1913 (the_desc, Style::NoStyle),
1914 (candidates[0].self_ty().to_string(), Style::Highlight),
1915 ("`".to_string(), Style::NoStyle),
1919 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1920 // Check if the trait is the same in all cases. If so, we'll only show the type.
1921 let mut traits: Vec<_> =
1922 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1926 let mut candidates: Vec<String> = candidates
1929 if traits.len() == 1 {
1930 format!("\n {}", c.self_ty())
1939 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1941 "the following other types implement trait `{}`:{}{}",
1942 trait_ref.print_only_trait_path(),
1943 candidates[..end].join(""),
1944 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1949 let def_id = trait_ref.def_id();
1950 if impl_candidates.is_empty() {
1951 if self.tcx.trait_is_auto(def_id)
1952 || self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1953 || self.tcx.get_diagnostic_name(def_id).is_some()
1955 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1958 let normalized_impl_candidates: Vec<_> = self
1961 // Ignore automatically derived impls and `!Trait` impls.
1963 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1964 || self.tcx.is_builtin_derive(def_id)
1966 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1967 .filter(|trait_ref| {
1968 let self_ty = trait_ref.self_ty();
1969 // Avoid mentioning type parameters.
1970 if let ty::Param(_) = self_ty.kind() {
1973 // Avoid mentioning types that are private to another crate
1974 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
1975 // FIXME(compiler-errors): This could be generalized, both to
1976 // be more granular, and probably look past other `#[fundamental]`
1979 .visibility(def.did())
1980 .is_accessible_from(body_id.owner.def_id, self.tcx)
1986 return report(normalized_impl_candidates, err);
1989 // Sort impl candidates so that ordering is consistent for UI tests.
1990 // because the ordering of `impl_candidates` may not be deterministic:
1991 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1993 // Prefer more similar candidates first, then sort lexicographically
1994 // by their normalized string representation.
1995 let mut normalized_impl_candidates_and_similarities = impl_candidates
1997 .map(|ImplCandidate { trait_ref, similarity }| {
1998 // FIXME(compiler-errors): This should be using `NormalizeExt::normalize`
1999 let normalized = self
2000 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
2001 .query_normalize(trait_ref)
2002 .map_or(trait_ref, |normalized| normalized.value);
2003 (similarity, normalized)
2005 .collect::<Vec<_>>();
2006 normalized_impl_candidates_and_similarities.sort();
2007 normalized_impl_candidates_and_similarities.dedup();
2009 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
2011 .map(|(_, normalized)| normalized)
2012 .collect::<Vec<_>>();
2014 report(normalized_impl_candidates, err)
2017 /// Gets the parent trait chain start
2018 fn get_parent_trait_ref(
2020 code: &ObligationCauseCode<'tcx>,
2021 ) -> Option<(String, Option<Span>)> {
2023 ObligationCauseCode::BuiltinDerivedObligation(data) => {
2024 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2025 match self.get_parent_trait_ref(&data.parent_code) {
2028 let ty = parent_trait_ref.skip_binder().self_ty();
2029 let span = TyCategory::from_ty(self.tcx, ty)
2030 .map(|(_, def_id)| self.tcx.def_span(def_id));
2031 Some((ty.to_string(), span))
2035 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
2036 self.get_parent_trait_ref(&parent_code)
2042 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
2043 /// with the same path as `trait_ref`, a help message about
2044 /// a probable version mismatch is added to `err`
2045 fn note_version_mismatch(
2047 err: &mut Diagnostic,
2048 trait_ref: &ty::PolyTraitRef<'tcx>,
2050 let get_trait_impl = |trait_def_id| {
2051 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
2053 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
2054 let traits_with_same_path: std::collections::BTreeSet<_> = self
2057 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
2058 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
2060 let mut suggested = false;
2061 for trait_with_same_path in traits_with_same_path {
2062 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
2063 let impl_span = self.tcx.def_span(impl_def_id);
2064 err.span_help(impl_span, "trait impl with same name found");
2065 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
2066 let crate_msg = format!(
2067 "perhaps two different versions of crate `{}` are being used?",
2070 err.note(&crate_msg);
2077 fn mk_trait_obligation_with_new_self_ty(
2079 param_env: ty::ParamEnv<'tcx>,
2080 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
2081 ) -> PredicateObligation<'tcx> {
2082 let trait_pred = trait_ref_and_ty
2083 .map_bound(|(tr, new_self_ty)| tr.with_self_type(self.tcx, new_self_ty));
2085 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, trait_pred)
2088 #[instrument(skip(self), level = "debug")]
2089 fn maybe_report_ambiguity(
2091 obligation: &PredicateObligation<'tcx>,
2092 body_id: Option<hir::BodyId>,
2094 // Unable to successfully determine, probably means
2095 // insufficient type information, but could mean
2096 // ambiguous impls. The latter *ought* to be a
2097 // coherence violation, so we don't report it here.
2099 let predicate = self.resolve_vars_if_possible(obligation.predicate);
2100 let span = obligation.cause.span;
2102 debug!(?predicate, obligation.cause.code = ?obligation.cause.code());
2104 // Ambiguity errors are often caused as fallout from earlier errors.
2105 // We ignore them if this `infcx` is tainted in some cases below.
2107 let bound_predicate = predicate.kind();
2108 let mut err = match bound_predicate.skip_binder() {
2109 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
2110 let trait_ref = bound_predicate.rebind(data.trait_ref);
2113 if predicate.references_error() {
2117 // This is kind of a hack: it frequently happens that some earlier
2118 // error prevents types from being fully inferred, and then we get
2119 // a bunch of uninteresting errors saying something like "<generic
2120 // #0> doesn't implement Sized". It may even be true that we
2121 // could just skip over all checks where the self-ty is an
2122 // inference variable, but I was afraid that there might be an
2123 // inference variable created, registered as an obligation, and
2124 // then never forced by writeback, and hence by skipping here we'd
2125 // be ignoring the fact that we don't KNOW the type works
2126 // out. Though even that would probably be harmless, given that
2127 // we're only talking about builtin traits, which are known to be
2128 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2129 // avoid inundating the user with unnecessary errors, but we now
2130 // check upstream for type errors and don't add the obligations to
2131 // begin with in those cases.
2132 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
2133 if let None = self.tainted_by_errors() {
2134 self.emit_inference_failure_err(
2137 trait_ref.self_ty().skip_binder().into(),
2146 // Typically, this ambiguity should only happen if
2147 // there are unresolved type inference variables
2148 // (otherwise it would suggest a coherence
2149 // failure). But given #21974 that is not necessarily
2150 // the case -- we can have multiple where clauses that
2151 // are only distinguished by a region, which results
2152 // in an ambiguity even when all types are fully
2153 // known, since we don't dispatch based on region
2156 // Pick the first substitution that still contains inference variables as the one
2157 // we're going to emit an error for. If there are none (see above), fall back to
2158 // a more general error.
2159 let subst = data.trait_ref.substs.iter().find(|s| s.has_non_region_infer());
2161 let mut err = if let Some(subst) = subst {
2162 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2168 "type annotations needed: cannot satisfy `{}`",
2173 let obligation = obligation.with(self.tcx, trait_ref);
2174 let mut selcx = SelectionContext::new(&self);
2175 match selcx.select_from_obligation(&obligation) {
2177 let impls = ambiguity::recompute_applicable_impls(self.infcx, &obligation);
2178 let has_non_region_infer =
2179 trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_infer());
2180 // It doesn't make sense to talk about applicable impls if there are more
2181 // than a handful of them.
2182 if impls.len() > 1 && impls.len() < 5 && has_non_region_infer {
2183 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2185 if self.tainted_by_errors().is_some() {
2189 err.note(&format!("cannot satisfy `{}`", predicate));
2193 if self.tainted_by_errors().is_some() {
2197 err.note(&format!("cannot satisfy `{}`", predicate));
2201 if let ObligationCauseCode::ItemObligation(def_id) | ObligationCauseCode::ExprItemObligation(def_id, ..) = *obligation.cause.code() {
2202 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2203 } else if let Ok(snippet) = &self.tcx.sess.source_map().span_to_snippet(span)
2204 && let ObligationCauseCode::BindingObligation(def_id, _) | ObligationCauseCode::ExprBindingObligation(def_id, ..)
2205 = *obligation.cause.code()
2207 let generics = self.tcx.generics_of(def_id);
2208 if generics.params.iter().any(|p| p.name != kw::SelfUpper)
2209 && !snippet.ends_with('>')
2210 && !generics.has_impl_trait()
2211 && !self.tcx.is_fn_trait(def_id)
2213 // FIXME: To avoid spurious suggestions in functions where type arguments
2214 // where already supplied, we check the snippet to make sure it doesn't
2215 // end with a turbofish. Ideally we would have access to a `PathSegment`
2216 // instead. Otherwise we would produce the following output:
2218 // error[E0283]: type annotations needed
2219 // --> $DIR/issue-54954.rs:3:24
2221 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2222 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2224 // | cannot infer type
2225 // | help: consider specifying the type argument
2226 // | in the function call:
2227 // | `Tt::const_val::<[i8; 123]>::<T>`
2229 // LL | const fn const_val<T: Sized>() -> usize {
2230 // | - required by this bound in `Tt::const_val`
2232 // = note: cannot satisfy `_: Tt`
2234 // Clear any more general suggestions in favor of our specific one
2235 err.clear_suggestions();
2237 err.span_suggestion_verbose(
2238 span.shrink_to_hi(),
2240 "consider specifying the type argument{} in the function call",
2241 pluralize!(generics.params.len()),
2248 .map(|p| p.name.to_string())
2249 .collect::<Vec<String>>()
2252 Applicability::HasPlaceholders,
2257 if let (Some(body_id), Some(ty::subst::GenericArgKind::Type(_))) =
2258 (body_id, subst.map(|subst| subst.unpack()))
2260 struct FindExprBySpan<'hir> {
2262 result: Option<&'hir hir::Expr<'hir>>,
2265 impl<'v> hir::intravisit::Visitor<'v> for FindExprBySpan<'v> {
2266 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2267 if self.span == ex.span {
2268 self.result = Some(ex);
2270 hir::intravisit::walk_expr(self, ex);
2275 let mut expr_finder = FindExprBySpan { span, result: None };
2277 expr_finder.visit_expr(&self.tcx.hir().body(body_id).value);
2279 if let Some(hir::Expr {
2280 kind: hir::ExprKind::Path(hir::QPath::Resolved(None, path)), .. }
2281 ) = expr_finder.result
2284 trait_path_segment @ hir::PathSegment {
2285 res: rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id),
2289 ident: assoc_item_name,
2290 res: rustc_hir::def::Res::Def(_, item_id),
2294 && data.trait_ref.def_id == *trait_id
2295 && self.tcx.trait_of_item(*item_id) == Some(*trait_id)
2296 && let None = self.tainted_by_errors()
2298 let (verb, noun) = match self.tcx.associated_item(item_id).kind {
2299 ty::AssocKind::Const => ("refer to the", "constant"),
2300 ty::AssocKind::Fn => ("call", "function"),
2301 ty::AssocKind::Type => ("refer to the", "type"), // this is already covered by E0223, but this single match arm doesn't hurt here
2304 // Replace the more general E0283 with a more specific error
2306 err = self.tcx.sess.struct_span_err_with_code(
2309 "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type",
2311 rustc_errors::error_code!(E0790),
2314 if let Some(local_def_id) = data.trait_ref.def_id.as_local()
2315 && 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)
2316 && let Some(method_ref) = trait_item_refs.iter().find(|item_ref| item_ref.ident == *assoc_item_name) {
2317 err.span_label(method_ref.span, format!("`{}::{}` defined here", trait_name, assoc_item_name));
2320 err.span_label(span, format!("cannot {verb} associated {noun} of trait"));
2322 let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
2324 if trait_impls.blanket_impls().is_empty()
2325 && let Some((impl_ty, _)) = trait_impls.non_blanket_impls().iter().next()
2326 && let Some(impl_def_id) = impl_ty.def() {
2327 let message = if trait_impls.non_blanket_impls().len() == 1 {
2328 "use the fully-qualified path to the only available implementation".to_string()
2331 "use a fully-qualified path to a specific available implementation ({} found)",
2332 trait_impls.non_blanket_impls().len()
2335 let mut suggestions = vec![(
2336 trait_path_segment.ident.span.shrink_to_lo(),
2337 format!("<{} as ", self.tcx.type_of(impl_def_id))
2339 if let Some(generic_arg) = trait_path_segment.args {
2340 let between_span = trait_path_segment.ident.span.between(generic_arg.span_ext);
2341 // get rid of :: between Trait and <type>
2342 // must be '::' between them, otherwise the parser won't accept the code
2343 suggestions.push((between_span, "".to_string(),));
2344 suggestions.push((generic_arg.span_ext.shrink_to_hi(), format!(">")));
2346 suggestions.push((trait_path_segment.ident.span.shrink_to_hi(), format!(">")));
2348 err.multipart_suggestion(
2351 Applicability::MaybeIncorrect
2360 ty::PredicateKind::WellFormed(arg) => {
2361 // Same hacky approach as above to avoid deluging user
2362 // with error messages.
2363 if arg.references_error()
2364 || self.tcx.sess.has_errors().is_some()
2365 || self.tainted_by_errors().is_some()
2370 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2373 ty::PredicateKind::Subtype(data) => {
2374 if data.references_error()
2375 || self.tcx.sess.has_errors().is_some()
2376 || self.tainted_by_errors().is_some()
2378 // no need to overload user in such cases
2381 let SubtypePredicate { a_is_expected: _, a, b } = data;
2382 // both must be type variables, or the other would've been instantiated
2383 assert!(a.is_ty_var() && b.is_ty_var());
2384 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2386 ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
2387 if predicate.references_error() || self.tainted_by_errors().is_some() {
2394 .chain(Some(data.term.into_arg()))
2395 .find(|g| g.has_non_region_infer());
2396 if let Some(subst) = subst {
2397 let mut err = self.emit_inference_failure_err(
2404 err.note(&format!("cannot satisfy `{}`", predicate));
2407 // If we can't find a substitution, just print a generic error
2408 let mut err = struct_span_err!(
2412 "type annotations needed: cannot satisfy `{}`",
2415 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2420 ty::PredicateKind::ConstEvaluatable(data) => {
2421 if predicate.references_error() || self.tainted_by_errors().is_some() {
2424 let subst = data.walk().find(|g| g.is_non_region_infer());
2425 if let Some(subst) = subst {
2426 let err = self.emit_inference_failure_err(
2435 // If we can't find a substitution, just print a generic error
2436 let mut err = struct_span_err!(
2440 "type annotations needed: cannot satisfy `{}`",
2443 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2448 if self.tcx.sess.has_errors().is_some() || self.tainted_by_errors().is_some() {
2451 let mut err = struct_span_err!(
2455 "type annotations needed: cannot satisfy `{}`",
2458 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2462 self.note_obligation_cause(&mut err, obligation);
2466 fn annotate_source_of_ambiguity(
2468 err: &mut Diagnostic,
2470 predicate: ty::Predicate<'tcx>,
2472 let mut spans = vec![];
2473 let mut crates = vec![];
2474 let mut post = vec![];
2475 for def_id in impls {
2476 match self.tcx.span_of_impl(*def_id) {
2477 Ok(span) => spans.push(span),
2480 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2486 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2488 crate_names.dedup();
2492 if self.tainted_by_errors().is_some()
2493 && (crate_names.len() == 1
2495 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2496 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2498 // Avoid complaining about other inference issues for expressions like
2499 // `42 >> 1`, where the types are still `{integer}`, but we want to
2500 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2501 // NOTE(eddyb) this was `.cancel()`, but `err`
2502 // is borrowed, so we can't fully defuse it.
2503 err.downgrade_to_delayed_bug();
2507 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2508 let post = if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2509 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2510 } else if post.len() == 1 {
2511 format!(": `{}`", post[0])
2516 match (spans.len(), crates.len(), crate_names.len()) {
2518 err.note(&format!("cannot satisfy `{}`", predicate));
2521 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2525 "{} in the following crates: {}{}",
2527 crate_names.join(", "),
2532 let span: MultiSpan = spans.into();
2533 err.span_note(span, &msg);
2536 let span: MultiSpan = spans.into();
2537 err.span_note(span, &msg);
2539 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2543 let span: MultiSpan = spans.into();
2544 err.span_note(span, &msg);
2546 "and more `impl`s found in the following crates: {}{}",
2547 crate_names.join(", "),
2554 /// Returns `true` if the trait predicate may apply for *some* assignment
2555 /// to the type parameters.
2556 fn predicate_can_apply(
2558 param_env: ty::ParamEnv<'tcx>,
2559 pred: ty::PolyTraitPredicate<'tcx>,
2561 struct ParamToVarFolder<'a, 'tcx> {
2562 infcx: &'a InferCtxt<'tcx>,
2563 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2566 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2567 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2571 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2572 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2573 let infcx = self.infcx;
2574 *self.var_map.entry(ty).or_insert_with(|| {
2575 infcx.next_ty_var(TypeVariableOrigin {
2576 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2581 ty.super_fold_with(self)
2588 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2590 let InferOk { value: cleaned_pred, .. } =
2591 self.infcx.at(&ObligationCause::dummy(), param_env).normalize(cleaned_pred);
2594 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, cleaned_pred);
2596 self.predicate_may_hold(&obligation)
2600 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2601 // First, attempt to add note to this error with an async-await-specific
2602 // message, and fall back to regular note otherwise.
2603 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2604 self.note_obligation_cause_code(
2606 obligation.predicate,
2607 obligation.param_env,
2608 obligation.cause.code(),
2610 &mut Default::default(),
2612 self.suggest_unsized_bound_if_applicable(err, obligation);
2616 #[instrument(level = "debug", skip_all)]
2617 fn suggest_unsized_bound_if_applicable(
2619 err: &mut Diagnostic,
2620 obligation: &PredicateObligation<'tcx>,
2622 let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = obligation.predicate.kind().skip_binder() else { return; };
2623 let (ObligationCauseCode::BindingObligation(item_def_id, span)
2624 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..))
2625 = *obligation.cause.code().peel_derives() else { return; };
2626 debug!(?pred, ?item_def_id, ?span);
2628 let (Some(node), true) = (
2629 self.tcx.hir().get_if_local(item_def_id),
2630 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2634 self.maybe_suggest_unsized_generics(err, span, node);
2637 #[instrument(level = "debug", skip_all)]
2638 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>) {
2639 let Some(generics) = node.generics() else {
2642 let sized_trait = self.tcx.lang_items().sized_trait();
2643 debug!(?generics.params);
2644 debug!(?generics.predicates);
2645 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2648 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2649 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2650 let explicitly_sized = generics
2651 .bounds_for_param(param.def_id)
2652 .flat_map(|bp| bp.bounds)
2653 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2654 if explicitly_sized {
2661 // Only suggest indirection for uses of type parameters in ADTs.
2663 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2667 if self.maybe_indirection_for_unsized(err, item, param) {
2673 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2674 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param.def_id)
2678 (span.shrink_to_hi(), ":")
2680 err.span_suggestion_verbose(
2682 "consider relaxing the implicit `Sized` restriction",
2683 format!("{} ?Sized", separator),
2684 Applicability::MachineApplicable,
2688 fn maybe_indirection_for_unsized(
2690 err: &mut Diagnostic,
2692 param: &GenericParam<'tcx>,
2694 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2695 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2696 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2698 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2699 visitor.visit_item(item);
2700 if visitor.invalid_spans.is_empty() {
2703 let mut multispan: MultiSpan = param.span.into();
2704 multispan.push_span_label(
2706 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2708 for sp in visitor.invalid_spans {
2709 multispan.push_span_label(
2711 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2717 "you could relax the implicit `Sized` bound on `{T}` if it were \
2718 used through indirection like `&{T}` or `Box<{T}>`",
2719 T = param.name.ident(),
2725 fn is_recursive_obligation(
2727 obligated_types: &mut Vec<Ty<'tcx>>,
2728 cause_code: &ObligationCauseCode<'tcx>,
2730 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2731 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2732 let self_ty = parent_trait_ref.skip_binder().self_ty();
2733 if obligated_types.iter().any(|ot| ot == &self_ty) {
2736 if let ty::Adt(def, substs) = self_ty.kind()
2737 && let [arg] = &substs[..]
2738 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2739 && let ty::Adt(inner_def, _) = ty.kind()
2749 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2750 /// `param: ?Sized` would be a valid constraint.
2751 struct FindTypeParam {
2752 param: rustc_span::Symbol,
2753 invalid_spans: Vec<Span>,
2757 impl<'v> Visitor<'v> for FindTypeParam {
2758 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2759 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2762 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2763 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2764 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2765 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2766 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2767 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2768 // in that case should make what happened clear enough.
2770 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2771 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2772 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2775 debug!(?ty, "FindTypeParam::visit_ty");
2776 self.invalid_spans.push(ty.span);
2779 hir::TyKind::Path(_) => {
2780 let prev = self.nested;
2782 hir::intravisit::walk_ty(self, ty);
2786 hir::intravisit::walk_ty(self, ty);
2792 /// Summarizes information
2795 /// An argument of non-tuple type. Parameters are (name, ty)
2796 Arg(String, String),
2798 /// An argument of tuple type. For a "found" argument, the span is
2799 /// the location in the source of the pattern. For an "expected"
2800 /// argument, it will be None. The vector is a list of (name, ty)
2801 /// strings for the components of the tuple.
2802 Tuple(Option<Span>, Vec<(String, String)>),
2806 fn empty() -> ArgKind {
2807 ArgKind::Arg("_".to_owned(), "_".to_owned())
2810 /// Creates an `ArgKind` from the expected type of an
2811 /// argument. It has no name (`_`) and an optional source span.
2812 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2814 ty::Tuple(tys) => ArgKind::Tuple(
2816 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2818 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2823 struct HasNumericInferVisitor;
2825 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2828 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2829 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2830 ControlFlow::Break(())
2832 ControlFlow::CONTINUE
2837 pub enum DefIdOrName {