2 pub mod on_unimplemented;
6 FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes, Obligation, ObligationCause,
7 ObligationCauseCode, ObligationCtxt, OutputTypeParameterMismatch, Overflow,
8 PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
10 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
11 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
12 use crate::infer::{self, InferCtxt};
13 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
14 use crate::traits::query::normalize::QueryNormalizeExt as _;
15 use crate::traits::specialize::to_pretty_impl_header;
16 use crate::traits::NormalizeExt;
17 use on_unimplemented::OnUnimplementedNote;
18 use on_unimplemented::TypeErrCtxtExt as _;
19 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
21 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
25 use rustc_hir::def::Namespace;
26 use rustc_hir::def_id::DefId;
27 use rustc_hir::intravisit::Visitor;
28 use rustc_hir::GenericParam;
31 use rustc_infer::infer::error_reporting::TypeErrCtxt;
32 use rustc_infer::infer::{InferOk, TypeTrace};
33 use rustc_middle::traits::select::OverflowError;
34 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
35 use rustc_middle::ty::error::ExpectedFound;
36 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
37 use rustc_middle::ty::print::{FmtPrinter, Print};
38 use rustc_middle::ty::{
39 self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
42 use rustc_session::Limit;
43 use rustc_span::def_id::LOCAL_CRATE;
44 use rustc_span::symbol::{kw, sym};
45 use rustc_span::{ExpnKind, Span, DUMMY_SP};
48 use std::ops::ControlFlow;
49 use suggestions::TypeErrCtxtExt as _;
51 pub use rustc_infer::traits::error_reporting::*;
53 // When outputting impl candidates, prefer showing those that are more similar.
55 // We also compare candidates after skipping lifetimes, which has a lower
56 // priority than exact matches.
57 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
58 pub enum CandidateSimilarity {
59 Exact { ignoring_lifetimes: bool },
60 Fuzzy { ignoring_lifetimes: bool },
63 #[derive(Debug, Clone, Copy)]
64 pub struct ImplCandidate<'tcx> {
65 pub trait_ref: ty::TraitRef<'tcx>,
66 pub similarity: CandidateSimilarity,
69 pub trait InferCtxtExt<'tcx> {
70 /// Given some node representing a fn-like thing in the HIR map,
71 /// returns a span and `ArgKind` information that describes the
72 /// arguments it expects. This can be supplied to
73 /// `report_arg_count_mismatch`.
74 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)>;
76 /// Reports an error when the number of arguments needed by a
77 /// trait match doesn't match the number that the expression
79 fn report_arg_count_mismatch(
82 found_span: Option<Span>,
83 expected_args: Vec<ArgKind>,
84 found_args: Vec<ArgKind>,
86 closure_pipe_span: Option<Span>,
87 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
89 /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
90 /// in that order, and returns the generic type corresponding to the
91 /// argument of that trait (corresponding to the closure arguments).
92 fn type_implements_fn_trait(
94 param_env: ty::ParamEnv<'tcx>,
95 ty: ty::Binder<'tcx, Ty<'tcx>>,
96 constness: ty::BoundConstness,
97 polarity: ty::ImplPolarity,
98 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
101 pub trait TypeErrCtxtExt<'tcx> {
102 fn report_fulfillment_errors(
104 errors: &[FulfillmentError<'tcx>],
105 body_id: Option<hir::BodyId>,
106 ) -> ErrorGuaranteed;
108 fn report_overflow_error<T>(
110 obligation: &Obligation<'tcx, T>,
111 suggest_increasing_limit: bool,
116 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
117 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug;
119 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
121 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
123 /// The `root_obligation` parameter should be the `root_obligation` field
124 /// from a `FulfillmentError`. If no `FulfillmentError` is available,
125 /// then it should be the same as `obligation`.
126 fn report_selection_error(
128 obligation: PredicateObligation<'tcx>,
129 root_obligation: &PredicateObligation<'tcx>,
130 error: &SelectionError<'tcx>,
134 impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
135 /// Given some node representing a fn-like thing in the HIR map,
136 /// returns a span and `ArgKind` information that describes the
137 /// arguments it expects. This can be supplied to
138 /// `report_arg_count_mismatch`.
139 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)> {
140 let sm = self.tcx.sess.source_map();
141 let hir = self.tcx.hir();
143 Node::Expr(&hir::Expr {
144 kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, fn_arg_span, .. }),
153 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
160 sm.span_to_snippet(pat.span)
162 .map(|snippet| (snippet, "_".to_owned()))
164 .collect::<Option<Vec<_>>>()?,
167 let name = sm.span_to_snippet(arg.pat.span).ok()?;
168 Some(ArgKind::Arg(name, "_".to_owned()))
171 .collect::<Option<Vec<ArgKind>>>()?,
173 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
174 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
175 | Node::TraitItem(&hir::TraitItem {
176 kind: hir::TraitItemKind::Fn(ref sig, _), ..
183 .map(|arg| match arg.kind {
184 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
186 vec![("_".to_owned(), "_".to_owned()); tys.len()],
188 _ => ArgKind::empty(),
190 .collect::<Vec<ArgKind>>(),
192 Node::Ctor(ref variant_data) => {
193 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
194 (span, None, vec![ArgKind::empty(); variant_data.fields().len()])
196 _ => panic!("non-FnLike node found: {:?}", node),
200 /// Reports an error when the number of arguments needed by a
201 /// trait match doesn't match the number that the expression
203 fn report_arg_count_mismatch(
206 found_span: Option<Span>,
207 expected_args: Vec<ArgKind>,
208 found_args: Vec<ArgKind>,
210 closure_arg_span: Option<Span>,
211 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
212 let kind = if is_closure { "closure" } else { "function" };
214 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
215 let arg_length = arguments.len();
216 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
217 match (arg_length, arguments.get(0)) {
218 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
219 format!("a single {}-tuple as argument", fields.len())
224 if distinct && arg_length > 1 { "distinct " } else { "" },
225 pluralize!(arg_length)
230 let expected_str = args_str(&expected_args, &found_args);
231 let found_str = args_str(&found_args, &expected_args);
233 let mut err = struct_span_err!(
237 "{} is expected to take {}, but it takes {}",
243 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
245 if let Some(found_span) = found_span {
246 err.span_label(found_span, format!("takes {}", found_str));
248 // Suggest to take and ignore the arguments with expected_args_length `_`s if
249 // found arguments is empty (assume the user just wants to ignore args in this case).
250 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
251 if found_args.is_empty() && is_closure {
252 let underscores = vec!["_"; expected_args.len()].join(", ");
253 err.span_suggestion_verbose(
254 closure_arg_span.unwrap_or(found_span),
256 "consider changing the closure to take and ignore the expected argument{}",
257 pluralize!(expected_args.len())
259 format!("|{}|", underscores),
260 Applicability::MachineApplicable,
264 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
265 if fields.len() == expected_args.len() {
268 .map(|(name, _)| name.to_owned())
269 .collect::<Vec<String>>()
271 err.span_suggestion_verbose(
273 "change the closure to take multiple arguments instead of a single tuple",
274 format!("|{}|", sugg),
275 Applicability::MachineApplicable,
279 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
280 && fields.len() == found_args.len()
287 .map(|arg| match arg {
288 ArgKind::Arg(name, _) => name.to_owned(),
291 .collect::<Vec<String>>()
293 // add type annotations if available
294 if found_args.iter().any(|arg| match arg {
295 ArgKind::Arg(_, ty) => ty != "_",
302 .map(|(_, ty)| ty.to_owned())
303 .collect::<Vec<String>>()
310 err.span_suggestion_verbose(
312 "change the closure to accept a tuple instead of individual arguments",
314 Applicability::MachineApplicable,
322 fn type_implements_fn_trait(
324 param_env: ty::ParamEnv<'tcx>,
325 ty: ty::Binder<'tcx, Ty<'tcx>>,
326 constness: ty::BoundConstness,
327 polarity: ty::ImplPolarity,
328 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
329 self.commit_if_ok(|_| {
330 for trait_def_id in [
331 self.tcx.lang_items().fn_trait(),
332 self.tcx.lang_items().fn_mut_trait(),
333 self.tcx.lang_items().fn_once_trait(),
335 let Some(trait_def_id) = trait_def_id else { continue };
336 // Make a fresh inference variable so we can determine what the substitutions
338 let var = self.next_ty_var(TypeVariableOrigin {
340 kind: TypeVariableOriginKind::MiscVariable,
342 let trait_ref = self.tcx.mk_trait_ref(trait_def_id, [ty.skip_binder(), var]);
343 let obligation = Obligation::new(
345 ObligationCause::dummy(),
347 ty.rebind(ty::TraitPredicate { trait_ref, constness, polarity }),
349 let ocx = ObligationCtxt::new_in_snapshot(self);
350 ocx.register_obligation(obligation);
351 if ocx.select_all_or_error().is_empty() {
354 .fn_trait_kind_from_def_id(trait_def_id)
355 .expect("expected to map DefId to ClosureKind"),
356 ty.rebind(self.resolve_vars_if_possible(var)),
365 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
366 fn report_fulfillment_errors(
368 errors: &[FulfillmentError<'tcx>],
369 body_id: Option<hir::BodyId>,
370 ) -> ErrorGuaranteed {
372 struct ErrorDescriptor<'tcx> {
373 predicate: ty::Predicate<'tcx>,
374 index: Option<usize>, // None if this is an old error
377 let mut error_map: FxIndexMap<_, Vec<_>> = self
378 .reported_trait_errors
381 .map(|(&span, predicates)| {
386 .map(|&predicate| ErrorDescriptor { predicate, index: None })
392 for (index, error) in errors.iter().enumerate() {
393 // We want to ignore desugarings here: spans are equivalent even
394 // if one is the result of a desugaring and the other is not.
395 let mut span = error.obligation.cause.span;
396 let expn_data = span.ctxt().outer_expn_data();
397 if let ExpnKind::Desugaring(_) = expn_data.kind {
398 span = expn_data.call_site;
401 error_map.entry(span).or_default().push(ErrorDescriptor {
402 predicate: error.obligation.predicate,
406 self.reported_trait_errors
410 .push(error.obligation.predicate);
413 // We do this in 2 passes because we want to display errors in order, though
414 // maybe it *is* better to sort errors by span or something.
415 let mut is_suppressed = vec![false; errors.len()];
416 for (_, error_set) in error_map.iter() {
417 // We want to suppress "duplicate" errors with the same span.
418 for error in error_set {
419 if let Some(index) = error.index {
420 // Suppress errors that are either:
421 // 1) strictly implied by another error.
422 // 2) implied by an error with a smaller index.
423 for error2 in error_set {
424 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
425 // Avoid errors being suppressed by already-suppressed
426 // errors, to prevent all errors from being suppressed
431 if self.error_implies(error2.predicate, error.predicate)
432 && !(error2.index >= error.index
433 && self.error_implies(error.predicate, error2.predicate))
435 info!("skipping {:?} (implied by {:?})", error, error2);
436 is_suppressed[index] = true;
444 for (error, suppressed) in iter::zip(errors, is_suppressed) {
446 self.report_fulfillment_error(error, body_id);
450 self.tcx.sess.delay_span_bug(DUMMY_SP, "expected fullfillment errors")
453 /// Reports that an overflow has occurred and halts compilation. We
454 /// halt compilation unconditionally because it is important that
455 /// overflows never be masked -- they basically represent computations
456 /// whose result could not be truly determined and thus we can't say
457 /// if the program type checks or not -- and they are unusual
458 /// occurrences in any case.
459 fn report_overflow_error<T>(
461 obligation: &Obligation<'tcx, T>,
462 suggest_increasing_limit: bool,
467 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
468 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
470 let predicate = self.resolve_vars_if_possible(obligation.predicate.clone());
471 let mut pred_str = predicate.to_string();
472 if pred_str.len() > 50 {
473 // We don't need to save the type to a file, we will be talking about this type already
474 // in a separate note when we explain the obligation, so it will be available that way.
476 .print(FmtPrinter::new_with_limit(
479 rustc_session::Limit(6),
484 let mut err = struct_span_err!(
486 obligation.cause.span,
488 "overflow evaluating the requirement `{}`",
492 if suggest_increasing_limit {
493 self.suggest_new_overflow_limit(&mut err);
496 self.note_obligation_cause_code(
498 &obligation.predicate,
499 obligation.param_env,
500 obligation.cause.code(),
502 &mut Default::default(),
506 self.tcx.sess.abort_if_errors();
510 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic) {
511 let suggested_limit = match self.tcx.recursion_limit() {
512 Limit(0) => Limit(2),
516 "consider increasing the recursion limit by adding a \
517 `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
519 self.tcx.crate_name(LOCAL_CRATE),
523 /// Reports that a cycle was detected which led to overflow and halts
524 /// compilation. This is equivalent to `report_overflow_error` except
525 /// that we can give a more helpful error message (and, in particular,
526 /// we do not suggest increasing the overflow limit, which is not
528 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
529 let cycle = self.resolve_vars_if_possible(cycle.to_owned());
530 assert!(!cycle.is_empty());
532 debug!(?cycle, "report_overflow_error_cycle");
534 // The 'deepest' obligation is most likely to have a useful
536 self.report_overflow_error(cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(), false);
539 fn report_selection_error(
541 mut obligation: PredicateObligation<'tcx>,
542 root_obligation: &PredicateObligation<'tcx>,
543 error: &SelectionError<'tcx>,
546 let mut span = obligation.cause.span;
547 // FIXME: statically guarantee this by tainting after the diagnostic is emitted
548 self.set_tainted_by_errors(
549 tcx.sess.delay_span_bug(span, "`report_selection_error` did not emit an error"),
552 let mut err = match *error {
553 SelectionError::Unimplemented => {
554 // If this obligation was generated as a result of well-formedness checking, see if we
555 // can get a better error message by performing HIR-based well-formedness checking.
556 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
557 root_obligation.cause.code().peel_derives()
559 if let Some(cause) = self
561 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
563 obligation.cause = cause.clone();
564 span = obligation.cause.span;
567 if let ObligationCauseCode::CompareImplItemObligation {
571 } = *obligation.cause.code()
573 self.report_extra_impl_obligation(
577 &format!("`{}`", obligation.predicate),
583 let bound_predicate = obligation.predicate.kind();
584 match bound_predicate.skip_binder() {
585 ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
586 let trait_predicate = bound_predicate.rebind(trait_predicate);
587 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
589 trait_predicate.remap_constness_diag(obligation.param_env);
590 let predicate_is_const = ty::BoundConstness::ConstIfConst
591 == trait_predicate.skip_binder().constness;
593 if self.tcx.sess.has_errors().is_some()
594 && trait_predicate.references_error()
598 let trait_ref = trait_predicate.to_poly_trait_ref();
599 let (post_message, pre_message, type_def) = self
600 .get_parent_trait_ref(obligation.cause.code())
603 format!(" in `{}`", t),
604 format!("within `{}`, ", t),
605 s.map(|s| (format!("within this `{}`", t), s)),
608 .unwrap_or_default();
610 let OnUnimplementedNote {
616 } = self.on_unimplemented_note(trait_ref, &obligation);
617 let have_alt_message = message.is_some() || label.is_some();
618 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
620 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
621 let (message, note, append_const_msg) = if is_try_conversion {
624 "`?` couldn't convert the error to `{}`",
625 trait_ref.skip_binder().self_ty(),
628 "the question mark operation (`?`) implicitly performs a \
629 conversion on the error value using the `From` trait"
635 (message, note, append_const_msg)
638 let mut err = struct_span_err!(
644 .and_then(|cannot_do_this| {
645 match (predicate_is_const, append_const_msg) {
646 // do nothing if predicate is not const
647 (false, _) => Some(cannot_do_this),
648 // suggested using default post message
649 (true, Some(None)) => {
650 Some(format!("{cannot_do_this} in const contexts"))
652 // overridden post message
653 (true, Some(Some(post_message))) => {
654 Some(format!("{cannot_do_this}{post_message}"))
656 // fallback to generic message
657 (true, None) => None,
660 .unwrap_or_else(|| format!(
661 "the trait bound `{}` is not satisfied{}",
662 trait_predicate, post_message,
666 if is_try_conversion && let Some(ret_span) = self.return_type_span(&obligation) {
670 "expected `{}` because of this",
671 trait_ref.skip_binder().self_ty()
676 if Some(trait_ref.def_id()) == tcx.lang_items().tuple_trait() {
677 match obligation.cause.code().peel_derives() {
678 ObligationCauseCode::RustCall => {
679 err.set_primary_message("functions with the \"rust-call\" ABI must take a single non-self tuple argument");
681 ObligationCauseCode::BindingObligation(def_id, _)
682 | ObligationCauseCode::ItemObligation(def_id)
683 if tcx.is_fn_trait(*def_id) =>
685 err.code(rustc_errors::error_code!(E0059));
686 err.set_primary_message(format!(
687 "type parameter to bare `{}` trait must be a tuple",
688 tcx.def_path_str(*def_id)
695 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
696 && predicate_is_const
698 err.note("`~const Drop` was renamed to `~const Destruct`");
699 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
702 let explanation = if let ObligationCauseCode::MainFunctionType =
703 obligation.cause.code()
705 "consider using `()`, or a `Result`".to_owned()
707 let ty_desc = match trait_ref.skip_binder().self_ty().kind() {
708 ty::FnDef(_, _) => Some("fn item"),
709 ty::Closure(_, _) => Some("closure"),
714 Some(desc) => format!(
715 "{}the trait `{}` is not implemented for {} `{}`",
717 trait_predicate.print_modifiers_and_trait_path(),
719 trait_ref.skip_binder().self_ty(),
722 "{}the trait `{}` is not implemented for `{}`",
724 trait_predicate.print_modifiers_and_trait_path(),
725 trait_ref.skip_binder().self_ty(),
730 if self.suggest_add_reference_to_arg(
736 self.note_obligation_cause(&mut err, &obligation);
740 if let Some(ref s) = label {
741 // If it has a custom `#[rustc_on_unimplemented]`
742 // error message, let's display it as the label!
743 err.span_label(span, s);
744 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
745 // When the self type is a type param We don't need to "the trait
746 // `std::marker::Sized` is not implemented for `T`" as we will point
747 // at the type param with a label to suggest constraining it.
748 err.help(&explanation);
751 err.span_label(span, explanation);
754 if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
755 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
756 self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
759 let mut unsatisfied_const = false;
760 if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
761 let non_const_predicate = trait_ref.without_const();
762 let non_const_obligation = Obligation {
763 cause: obligation.cause.clone(),
764 param_env: obligation.param_env.without_const(),
765 predicate: non_const_predicate.to_predicate(tcx),
766 recursion_depth: obligation.recursion_depth,
768 if self.predicate_may_hold(&non_const_obligation) {
769 unsatisfied_const = true;
773 "the trait `{}` is implemented for `{}`, \
774 but that implementation is not `const`",
775 non_const_predicate.print_modifiers_and_trait_path(),
776 trait_ref.skip_binder().self_ty(),
782 if let Some((msg, span)) = type_def {
783 err.span_label(span, &msg);
785 if let Some(ref s) = note {
786 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
787 err.note(s.as_str());
789 if let Some(ref s) = parent_label {
792 .opt_local_def_id(obligation.cause.body_id)
794 tcx.hir().body_owner_def_id(hir::BodyId {
795 hir_id: obligation.cause.body_id,
798 err.span_label(tcx.def_span(body), s);
801 self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
802 self.suggest_dereferencing_index(&obligation, &mut err, trait_predicate);
804 self.suggest_dereferences(&obligation, &mut err, trait_predicate);
805 suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
807 self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
808 suggested |= self.suggest_semicolon_removal(
814 self.note_version_mismatch(&mut err, &trait_ref);
815 self.suggest_remove_await(&obligation, &mut err);
816 self.suggest_derive(&obligation, &mut err, trait_predicate);
818 if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
819 self.suggest_await_before_try(
827 if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
833 // If the obligation failed due to a missing implementation of the
834 // `Unsize` trait, give a pointer to why that might be the case
836 "all implementations of `Unsize` are provided \
837 automatically by the compiler, see \
838 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
839 for more information",
843 let is_fn_trait = tcx.is_fn_trait(trait_ref.def_id());
844 let is_target_feature_fn = if let ty::FnDef(def_id, _) =
845 *trait_ref.skip_binder().self_ty().kind()
847 !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
851 if is_fn_trait && is_target_feature_fn {
853 "`#[target_feature]` functions do not implement the `Fn` traits",
857 // Try to report a help message
859 && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
860 obligation.param_env,
862 trait_predicate.skip_binder().constness,
863 trait_predicate.skip_binder().polarity,
866 // If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
867 // suggestion to add trait bounds for the type, since we only typically implement
868 // these traits once.
870 // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
873 self.tcx.fn_trait_kind_from_def_id(trait_ref.def_id())
874 .expect("expected to map DefId to ClosureKind");
875 if !implemented_kind.extends(selected_kind) {
878 "`{}` implements `{}`, but it must implement `{}`, which is more general",
879 trait_ref.skip_binder().self_ty(),
886 // Note any argument mismatches
887 let given_ty = params.skip_binder();
888 let expected_ty = trait_ref.skip_binder().substs.type_at(1);
889 if let ty::Tuple(given) = given_ty.kind()
890 && let ty::Tuple(expected) = expected_ty.kind()
892 if expected.len() != given.len() {
893 // Note number of types that were expected and given
896 "expected a closure taking {} argument{}, but one taking {} argument{} was given",
898 pluralize!(given.len()),
900 pluralize!(expected.len()),
903 } else if !self.same_type_modulo_infer(given_ty, expected_ty) {
904 // Print type mismatch
905 let (expected_args, given_args) =
906 self.cmp(given_ty, expected_ty);
907 err.note_expected_found(
908 &"a closure with arguments",
910 &"a closure with arguments",
915 } else if !trait_ref.has_non_region_infer()
916 && self.predicate_can_apply(obligation.param_env, trait_predicate)
918 // If a where-clause may be useful, remind the
919 // user that they can add it.
921 // don't display an on-unimplemented note, as
922 // these notes will often be of the form
923 // "the type `T` can't be frobnicated"
924 // which is somewhat confusing.
925 self.suggest_restricting_param_bound(
929 obligation.cause.body_id,
931 } else if !suggested && !unsatisfied_const {
932 // Can't show anything else useful, try to find similar impls.
933 let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
934 if !self.report_similar_impl_candidates(
937 obligation.cause.body_id,
940 // This is *almost* equivalent to
941 // `obligation.cause.code().peel_derives()`, but it gives us the
942 // trait predicate for that corresponding root obligation. This
943 // lets us get a derived obligation from a type parameter, like
944 // when calling `string.strip_suffix(p)` where `p` is *not* an
945 // implementer of `Pattern<'_>`.
946 let mut code = obligation.cause.code();
947 let mut trait_pred = trait_predicate;
948 let mut peeled = false;
949 while let Some((parent_code, parent_trait_pred)) = code.parent() {
951 if let Some(parent_trait_pred) = parent_trait_pred {
952 trait_pred = parent_trait_pred;
956 let def_id = trait_pred.def_id();
957 // Mention *all* the `impl`s for the *top most* obligation, the
958 // user might have meant to use one of them, if any found. We skip
959 // auto-traits or fundamental traits that might not be exactly what
960 // the user might expect to be presented with. Instead this is
961 // useful for less general traits.
963 && !self.tcx.trait_is_auto(def_id)
964 && !self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
966 let trait_ref = trait_pred.to_poly_trait_ref();
967 let impl_candidates =
968 self.find_similar_impl_candidates(trait_pred);
969 self.report_similar_impl_candidates(
972 obligation.cause.body_id,
979 // Changing mutability doesn't make a difference to whether we have
980 // an `Unsize` impl (Fixes ICE in #71036)
982 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
985 // If this error is due to `!: Trait` not implemented but `(): Trait` is
986 // implemented, and fallback has occurred, then it could be due to a
987 // variable that used to fallback to `()` now falling back to `!`. Issue a
988 // note informing about the change in behaviour.
989 if trait_predicate.skip_binder().self_ty().is_never()
990 && self.fallback_has_occurred
992 let predicate = trait_predicate.map_bound(|trait_pred| {
993 trait_pred.with_self_type(self.tcx, self.tcx.mk_unit())
995 let unit_obligation = obligation.with(tcx, predicate);
996 if self.predicate_may_hold(&unit_obligation) {
998 "this error might have been caused by changes to \
999 Rust's type-inference algorithm (see issue #48950 \
1000 <https://github.com/rust-lang/rust/issues/48950> \
1001 for more information)",
1003 err.help("did you intend to use the type `()` here instead?");
1007 // Return early if the trait is Debug or Display and the invocation
1008 // originates within a standard library macro, because the output
1009 // is otherwise overwhelming and unhelpful (see #85844 for an
1013 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
1014 Some(macro_def_id) => {
1015 let crate_name = tcx.crate_name(macro_def_id.krate);
1016 crate_name == sym::std || crate_name == sym::core
1023 self.tcx.get_diagnostic_name(trait_ref.def_id()),
1024 Some(sym::Debug | sym::Display)
1034 ty::PredicateKind::Subtype(predicate) => {
1035 // Errors for Subtype predicates show up as
1036 // `FulfillmentErrorCode::CodeSubtypeError`,
1037 // not selection error.
1038 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
1041 ty::PredicateKind::Coerce(predicate) => {
1042 // Errors for Coerce predicates show up as
1043 // `FulfillmentErrorCode::CodeSubtypeError`,
1044 // not selection error.
1045 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
1048 ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
1049 | ty::PredicateKind::Clause(ty::Clause::Projection(..))
1050 | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..)) => {
1051 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1056 "the requirement `{}` is not satisfied",
1061 ty::PredicateKind::ObjectSafe(trait_def_id) => {
1062 let violations = self.tcx.object_safety_violations(trait_def_id);
1063 report_object_safety_error(self.tcx, span, trait_def_id, violations)
1066 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
1067 let found_kind = self.closure_kind(closure_substs).unwrap();
1068 let closure_span = self.tcx.def_span(closure_def_id);
1069 let mut err = struct_span_err!(
1073 "expected a closure that implements the `{}` trait, \
1074 but this closure only implements `{}`",
1081 format!("this closure implements `{}`, not `{}`", found_kind, kind),
1084 obligation.cause.span,
1085 format!("the requirement to implement `{}` derives from here", kind),
1088 // Additional context information explaining why the closure only implements
1089 // a particular trait.
1090 if let Some(typeck_results) = &self.typeck_results {
1094 .local_def_id_to_hir_id(closure_def_id.expect_local());
1095 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
1096 (ty::ClosureKind::FnOnce, Some((span, place))) => {
1100 "closure is `FnOnce` because it moves the \
1101 variable `{}` out of its environment",
1102 ty::place_to_string_for_capture(tcx, place)
1106 (ty::ClosureKind::FnMut, Some((span, place))) => {
1110 "closure is `FnMut` because it mutates the \
1111 variable `{}` here",
1112 ty::place_to_string_for_capture(tcx, place)
1123 ty::PredicateKind::WellFormed(ty) => {
1124 if !self.tcx.sess.opts.unstable_opts.chalk {
1125 // WF predicates cannot themselves make
1126 // errors. They can only block due to
1127 // ambiguity; otherwise, they always
1128 // degenerate into other obligations
1129 // (which may fail).
1130 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
1132 // FIXME: we'll need a better message which takes into account
1133 // which bounds actually failed to hold.
1134 self.tcx.sess.struct_span_err(
1136 &format!("the type `{}` is not well-formed (chalk)", ty),
1141 ty::PredicateKind::ConstEvaluatable(..) => {
1142 // Errors for `ConstEvaluatable` predicates show up as
1143 // `SelectionError::ConstEvalFailure`,
1144 // not `Unimplemented`.
1147 "const-evaluatable requirement gave wrong error: `{:?}`",
1152 ty::PredicateKind::ConstEquate(..) => {
1153 // Errors for `ConstEquate` predicates show up as
1154 // `SelectionError::ConstEvalFailure`,
1155 // not `Unimplemented`.
1158 "const-equate requirement gave wrong error: `{:?}`",
1163 ty::PredicateKind::Ambiguous => span_bug!(span, "ambiguous"),
1165 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
1167 "TypeWellFormedFromEnv predicate should only exist in the environment"
1172 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
1173 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
1174 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
1176 if expected_trait_ref.self_ty().references_error() {
1180 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
1184 let found_did = match *found_trait_ty.kind() {
1188 | ty::Generator(did, ..) => Some(did),
1189 ty::Adt(def, _) => Some(def.did()),
1193 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
1195 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1196 // We check closures twice, with obligations flowing in different directions,
1197 // but we want to complain about them only once.
1201 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1203 let mut not_tupled = false;
1205 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
1206 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1209 vec![ArgKind::empty()]
1213 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1214 let expected = match expected_ty.kind() {
1215 ty::Tuple(ref tys) => {
1216 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
1220 vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())]
1224 // If this is a `Fn` family trait and either the expected or found
1225 // is not tupled, then fall back to just a regular mismatch error.
1226 // This shouldn't be common unless manually implementing one of the
1227 // traits manually, but don't make it more confusing when it does
1229 if Some(expected_trait_ref.def_id()) != tcx.lang_items().gen_trait() && not_tupled {
1230 self.report_and_explain_type_error(
1231 TypeTrace::poly_trait_refs(
1237 ty::error::TypeError::Mismatch,
1239 } else if found.len() == expected.len() {
1240 self.report_closure_arg_mismatch(
1245 obligation.cause.code(),
1248 let (closure_span, closure_arg_span, found) = found_did
1250 let node = self.tcx.hir().get_if_local(did)?;
1251 let (found_span, closure_arg_span, found) =
1252 self.get_fn_like_arguments(node)?;
1253 Some((Some(found_span), closure_arg_span, found))
1255 .unwrap_or((found_span, None, found));
1257 self.report_arg_count_mismatch(
1262 found_trait_ty.is_closure(),
1268 TraitNotObjectSafe(did) => {
1269 let violations = self.tcx.object_safety_violations(did);
1270 report_object_safety_error(self.tcx, span, did, violations)
1273 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1275 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1278 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1279 if !self.tcx.features().generic_const_exprs {
1280 let mut err = self.tcx.sess.struct_span_err(
1282 "constant expression depends on a generic parameter",
1284 // FIXME(const_generics): we should suggest to the user how they can resolve this
1285 // issue. However, this is currently not actually possible
1286 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1288 // Note that with `feature(generic_const_exprs)` this case should not
1290 err.note("this may fail depending on what value the parameter takes");
1295 match obligation.predicate.kind().skip_binder() {
1296 ty::PredicateKind::ConstEvaluatable(ct) => {
1297 let ty::ConstKind::Unevaluated(uv) = ct.kind() else {
1298 bug!("const evaluatable failed for non-unevaluated const `{ct:?}`");
1301 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1302 let const_span = self.tcx.def_span(uv.def.did);
1303 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1304 Ok(snippet) => err.help(&format!(
1305 "try adding a `where` bound using this expression: `where [(); {}]:`",
1308 _ => err.help("consider adding a `where` bound using this expression"),
1315 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1321 // Already reported in the query.
1322 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1323 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1324 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1327 // Already reported.
1328 Overflow(OverflowError::Error(_)) => {
1329 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1333 bug!("overflow should be handled before the `report_selection_error` path");
1335 SelectionError::ErrorReporting => {
1336 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1340 self.note_obligation_cause(&mut err, &obligation);
1341 self.point_at_returns_when_relevant(&mut err, &obligation);
1347 trait InferCtxtPrivExt<'tcx> {
1348 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1349 // `error` occurring implies that `cond` occurs.
1350 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1352 fn report_fulfillment_error(
1354 error: &FulfillmentError<'tcx>,
1355 body_id: Option<hir::BodyId>,
1358 fn report_projection_error(
1360 obligation: &PredicateObligation<'tcx>,
1361 error: &MismatchedProjectionTypes<'tcx>,
1364 fn maybe_detailed_projection_msg(
1366 pred: ty::ProjectionPredicate<'tcx>,
1367 normalized_ty: ty::Term<'tcx>,
1368 expected_ty: ty::Term<'tcx>,
1369 ) -> Option<String>;
1375 ignoring_lifetimes: bool,
1376 ) -> Option<CandidateSimilarity>;
1378 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1380 fn find_similar_impl_candidates(
1382 trait_pred: ty::PolyTraitPredicate<'tcx>,
1383 ) -> Vec<ImplCandidate<'tcx>>;
1385 fn report_similar_impl_candidates(
1387 impl_candidates: Vec<ImplCandidate<'tcx>>,
1388 trait_ref: ty::PolyTraitRef<'tcx>,
1389 body_id: hir::HirId,
1390 err: &mut Diagnostic,
1393 /// Gets the parent trait chain start
1394 fn get_parent_trait_ref(
1396 code: &ObligationCauseCode<'tcx>,
1397 ) -> Option<(String, Option<Span>)>;
1399 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1400 /// with the same path as `trait_ref`, a help message about
1401 /// a probable version mismatch is added to `err`
1402 fn note_version_mismatch(
1404 err: &mut Diagnostic,
1405 trait_ref: &ty::PolyTraitRef<'tcx>,
1408 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1411 /// For this to work, `new_self_ty` must have no escaping bound variables.
1412 fn mk_trait_obligation_with_new_self_ty(
1414 param_env: ty::ParamEnv<'tcx>,
1415 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1416 ) -> PredicateObligation<'tcx>;
1418 fn maybe_report_ambiguity(
1420 obligation: &PredicateObligation<'tcx>,
1421 body_id: Option<hir::BodyId>,
1424 fn predicate_can_apply(
1426 param_env: ty::ParamEnv<'tcx>,
1427 pred: ty::PolyTraitPredicate<'tcx>,
1430 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1432 fn suggest_unsized_bound_if_applicable(
1434 err: &mut Diagnostic,
1435 obligation: &PredicateObligation<'tcx>,
1438 fn annotate_source_of_ambiguity(
1440 err: &mut Diagnostic,
1442 predicate: ty::Predicate<'tcx>,
1445 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>);
1447 fn maybe_indirection_for_unsized(
1449 err: &mut Diagnostic,
1450 item: &'tcx Item<'tcx>,
1451 param: &'tcx GenericParam<'tcx>,
1454 fn is_recursive_obligation(
1456 obligated_types: &mut Vec<Ty<'tcx>>,
1457 cause_code: &ObligationCauseCode<'tcx>,
1461 impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
1462 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1463 // `error` occurring implies that `cond` occurs.
1464 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1469 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1470 let bound_error = error.kind();
1471 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1473 ty::PredicateKind::Clause(ty::Clause::Trait(..)),
1474 ty::PredicateKind::Clause(ty::Clause::Trait(error)),
1475 ) => (cond, bound_error.rebind(error)),
1477 // FIXME: make this work in other cases too.
1482 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1483 let bound_predicate = obligation.predicate.kind();
1484 if let ty::PredicateKind::Clause(ty::Clause::Trait(implication)) =
1485 bound_predicate.skip_binder()
1487 let error = error.to_poly_trait_ref();
1488 let implication = bound_predicate.rebind(implication.trait_ref);
1489 // FIXME: I'm just not taking associated types at all here.
1490 // Eventually I'll need to implement param-env-aware
1491 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1492 let param_env = ty::ParamEnv::empty();
1493 if self.can_sub(param_env, error, implication).is_ok() {
1494 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1503 #[instrument(skip(self), level = "debug")]
1504 fn report_fulfillment_error(
1506 error: &FulfillmentError<'tcx>,
1507 body_id: Option<hir::BodyId>,
1510 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1511 self.report_selection_error(
1512 error.obligation.clone(),
1513 &error.root_obligation,
1517 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1518 self.report_projection_error(&error.obligation, e);
1520 FulfillmentErrorCode::CodeAmbiguity => {
1521 self.maybe_report_ambiguity(&error.obligation, body_id);
1523 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1524 self.report_mismatched_types(
1525 &error.obligation.cause,
1526 expected_found.expected,
1527 expected_found.found,
1532 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1533 let mut diag = self.report_mismatched_consts(
1534 &error.obligation.cause,
1535 expected_found.expected,
1536 expected_found.found,
1539 let code = error.obligation.cause.code().peel_derives().peel_match_impls();
1540 if let ObligationCauseCode::BindingObligation(..)
1541 | ObligationCauseCode::ItemObligation(..)
1542 | ObligationCauseCode::ExprBindingObligation(..)
1543 | ObligationCauseCode::ExprItemObligation(..) = code
1545 self.note_obligation_cause_code(
1547 &error.obligation.predicate,
1548 error.obligation.param_env,
1551 &mut Default::default(),
1556 FulfillmentErrorCode::CodeCycle(ref cycle) => {
1557 self.report_overflow_error_cycle(cycle);
1562 #[instrument(level = "debug", skip_all)]
1563 fn report_projection_error(
1565 obligation: &PredicateObligation<'tcx>,
1566 error: &MismatchedProjectionTypes<'tcx>,
1568 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1570 if predicate.references_error() {
1575 let ocx = ObligationCtxt::new_in_snapshot(self);
1577 // try to find the mismatched types to report the error with.
1579 // this can fail if the problem was higher-ranked, in which
1580 // cause I have no idea for a good error message.
1581 let bound_predicate = predicate.kind();
1582 let (values, err) = if let ty::PredicateKind::Clause(ty::Clause::Projection(data)) =
1583 bound_predicate.skip_binder()
1585 let data = self.replace_bound_vars_with_fresh_vars(
1586 obligation.cause.span,
1587 infer::LateBoundRegionConversionTime::HigherRankedType,
1588 bound_predicate.rebind(data),
1590 let normalized_ty = ocx.normalize(
1592 obligation.param_env,
1594 .mk_projection(data.projection_ty.item_def_id, data.projection_ty.substs),
1597 debug!(?obligation.cause, ?obligation.param_env);
1599 debug!(?normalized_ty, data.ty = ?data.term);
1601 let is_normalized_ty_expected = !matches!(
1602 obligation.cause.code().peel_derives(),
1603 ObligationCauseCode::ItemObligation(_)
1604 | ObligationCauseCode::BindingObligation(_, _)
1605 | ObligationCauseCode::ExprItemObligation(..)
1606 | ObligationCauseCode::ExprBindingObligation(..)
1607 | ObligationCauseCode::ObjectCastObligation(..)
1608 | ObligationCauseCode::OpaqueType
1610 let expected_ty = data.term.ty().unwrap();
1612 // constrain inference variables a bit more to nested obligations from normalize so
1613 // we can have more helpful errors.
1614 ocx.select_where_possible();
1616 if let Err(new_err) = ocx.eq_exp(
1618 obligation.param_env,
1619 is_normalized_ty_expected,
1623 (Some((data, is_normalized_ty_expected, normalized_ty, expected_ty)), new_err)
1632 .and_then(|(predicate, _, normalized_ty, expected_ty)| {
1633 self.maybe_detailed_projection_msg(
1635 normalized_ty.into(),
1639 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
1640 let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
1642 let secondary_span = match predicate.kind().skip_binder() {
1643 ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => self
1645 .opt_associated_item(proj.projection_ty.item_def_id)
1646 .and_then(|trait_assoc_item| {
1648 .trait_of_item(proj.projection_ty.item_def_id)
1649 .map(|id| (trait_assoc_item, id))
1651 .and_then(|(trait_assoc_item, id)| {
1652 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1653 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1655 .associated_items(did)
1656 .in_definition_order()
1657 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1660 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1662 hir::Node::TraitItem(hir::TraitItem {
1663 kind: hir::TraitItemKind::Type(_, Some(ty)),
1666 | hir::Node::ImplItem(hir::ImplItem {
1667 kind: hir::ImplItemKind::Type(ty),
1670 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1679 values.map(|(_, is_normalized_ty_expected, normalized_ty, expected_ty)| {
1680 infer::ValuePairs::Terms(ExpectedFound::new(
1681 is_normalized_ty_expected,
1682 normalized_ty.into(),
1690 self.note_obligation_cause(&mut diag, obligation);
1695 fn maybe_detailed_projection_msg(
1697 pred: ty::ProjectionPredicate<'tcx>,
1698 normalized_ty: ty::Term<'tcx>,
1699 expected_ty: ty::Term<'tcx>,
1700 ) -> Option<String> {
1701 let trait_def_id = pred.projection_ty.trait_def_id(self.tcx);
1702 let self_ty = pred.projection_ty.self_ty();
1704 if Some(pred.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output() {
1706 "expected `{self_ty}` to be a {fn_kind} that returns `{expected_ty}`, but it returns `{normalized_ty}`",
1707 fn_kind = self_ty.prefix_string(self.tcx)
1709 } else if Some(trait_def_id) == self.tcx.lang_items().future_trait() {
1711 "expected `{self_ty}` to be a future that resolves to `{expected_ty}`, but it resolves to `{normalized_ty}`"
1713 } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
1715 "expected `{self_ty}` to be an iterator that yields `{expected_ty}`, but it yields `{normalized_ty}`"
1726 ignoring_lifetimes: bool,
1727 ) -> Option<CandidateSimilarity> {
1728 /// returns the fuzzy category of a given type, or None
1729 /// if the type can be equated to any type.
1730 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1732 ty::Bool => Some(0),
1733 ty::Char => Some(1),
1735 ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => Some(2),
1739 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1740 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1741 ty::Array(..) | ty::Slice(..) => Some(6),
1742 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1743 ty::Dynamic(..) => Some(8),
1744 ty::Closure(..) => Some(9),
1745 ty::Tuple(..) => Some(10),
1746 ty::Param(..) => Some(11),
1747 ty::Projection(..) => Some(12),
1748 ty::Opaque(..) => Some(13),
1749 ty::Never => Some(14),
1750 ty::Adt(..) => Some(15),
1751 ty::Generator(..) => Some(16),
1752 ty::Foreign(..) => Some(17),
1753 ty::GeneratorWitness(..) => Some(18),
1754 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1758 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1761 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1769 if !ignoring_lifetimes {
1770 a = strip_references(a);
1771 b = strip_references(b);
1774 let cat_a = type_category(self.tcx, a)?;
1775 let cat_b = type_category(self.tcx, b)?;
1777 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1778 } else if cat_a == cat_b {
1779 match (a.kind(), b.kind()) {
1780 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1781 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1782 // Matching on references results in a lot of unhelpful
1783 // suggestions, so let's just not do that for now.
1785 // We still upgrade successful matches to `ignoring_lifetimes: true`
1786 // to prioritize that impl.
1787 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1788 self.fuzzy_match_tys(a, b, true).is_some()
1792 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1793 } else if ignoring_lifetimes {
1796 self.fuzzy_match_tys(a, b, true)
1800 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1801 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1802 hir::GeneratorKind::Gen => "a generator",
1803 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1804 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1805 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1809 fn find_similar_impl_candidates(
1811 trait_pred: ty::PolyTraitPredicate<'tcx>,
1812 ) -> Vec<ImplCandidate<'tcx>> {
1813 let mut candidates: Vec<_> = self
1815 .all_impls(trait_pred.def_id())
1816 .filter_map(|def_id| {
1817 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
1820 .is_constness_satisfied_by(self.tcx.constness(def_id))
1825 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1827 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
1828 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1831 if candidates.iter().any(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. })) {
1832 // If any of the candidates is a perfect match, we don't want to show all of them.
1833 // This is particularly relevant for the case of numeric types (as they all have the
1835 candidates.retain(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. }));
1840 fn report_similar_impl_candidates(
1842 impl_candidates: Vec<ImplCandidate<'tcx>>,
1843 trait_ref: ty::PolyTraitRef<'tcx>,
1844 body_id: hir::HirId,
1845 err: &mut Diagnostic,
1847 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1850 let len = candidates.len();
1851 if candidates.len() == 0 {
1854 if candidates.len() == 1 {
1855 let ty_desc = match candidates[0].self_ty().kind() {
1856 ty::FnPtr(_) => Some("fn pointer"),
1859 let the_desc = match ty_desc {
1860 Some(desc) => format!(" implemented for {} `", desc),
1861 None => " implemented for `".to_string(),
1863 err.highlighted_help(vec![
1865 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1868 ("is".to_string(), Style::Highlight),
1869 (the_desc, Style::NoStyle),
1870 (candidates[0].self_ty().to_string(), Style::Highlight),
1871 ("`".to_string(), Style::NoStyle),
1875 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1876 // Check if the trait is the same in all cases. If so, we'll only show the type.
1877 let mut traits: Vec<_> =
1878 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1882 let mut candidates: Vec<String> = candidates
1885 if traits.len() == 1 {
1886 format!("\n {}", c.self_ty())
1895 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1897 "the following other types implement trait `{}`:{}{}",
1898 trait_ref.print_only_trait_path(),
1899 candidates[..end].join(""),
1900 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1905 let def_id = trait_ref.def_id();
1906 if impl_candidates.is_empty() {
1907 if self.tcx.trait_is_auto(def_id)
1908 || self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1909 || self.tcx.get_diagnostic_name(def_id).is_some()
1911 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1914 let normalized_impl_candidates: Vec<_> = self
1917 // Ignore automatically derived impls and `!Trait` impls.
1919 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1920 || self.tcx.is_builtin_derive(def_id)
1922 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1923 .filter(|trait_ref| {
1924 let self_ty = trait_ref.self_ty();
1925 // Avoid mentioning type parameters.
1926 if let ty::Param(_) = self_ty.kind() {
1929 // Avoid mentioning types that are private to another crate
1930 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
1931 // FIXME(compiler-errors): This could be generalized, both to
1932 // be more granular, and probably look past other `#[fundamental]`
1935 .visibility(def.did())
1936 .is_accessible_from(body_id.owner.def_id, self.tcx)
1942 return report(normalized_impl_candidates, err);
1945 // Sort impl candidates so that ordering is consistent for UI tests.
1946 // because the ordering of `impl_candidates` may not be deterministic:
1947 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1949 // Prefer more similar candidates first, then sort lexicographically
1950 // by their normalized string representation.
1951 let mut normalized_impl_candidates_and_similarities = impl_candidates
1953 .map(|ImplCandidate { trait_ref, similarity }| {
1954 // FIXME(compiler-errors): This should be using `NormalizeExt::normalize`
1955 let normalized = self
1956 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1957 .query_normalize(trait_ref)
1958 .map_or(trait_ref, |normalized| normalized.value);
1959 (similarity, normalized)
1961 .collect::<Vec<_>>();
1962 normalized_impl_candidates_and_similarities.sort();
1963 normalized_impl_candidates_and_similarities.dedup();
1965 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
1967 .map(|(_, normalized)| normalized)
1968 .collect::<Vec<_>>();
1970 report(normalized_impl_candidates, err)
1973 /// Gets the parent trait chain start
1974 fn get_parent_trait_ref(
1976 code: &ObligationCauseCode<'tcx>,
1977 ) -> Option<(String, Option<Span>)> {
1979 ObligationCauseCode::BuiltinDerivedObligation(data) => {
1980 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
1981 match self.get_parent_trait_ref(&data.parent_code) {
1984 let ty = parent_trait_ref.skip_binder().self_ty();
1985 let span = TyCategory::from_ty(self.tcx, ty)
1986 .map(|(_, def_id)| self.tcx.def_span(def_id));
1987 Some((ty.to_string(), span))
1991 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
1992 self.get_parent_trait_ref(&parent_code)
1998 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1999 /// with the same path as `trait_ref`, a help message about
2000 /// a probable version mismatch is added to `err`
2001 fn note_version_mismatch(
2003 err: &mut Diagnostic,
2004 trait_ref: &ty::PolyTraitRef<'tcx>,
2006 let get_trait_impl = |trait_def_id| {
2007 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
2009 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
2010 let traits_with_same_path: std::collections::BTreeSet<_> = self
2013 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
2014 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
2016 let mut suggested = false;
2017 for trait_with_same_path in traits_with_same_path {
2018 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
2019 let impl_span = self.tcx.def_span(impl_def_id);
2020 err.span_help(impl_span, "trait impl with same name found");
2021 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
2022 let crate_msg = format!(
2023 "perhaps two different versions of crate `{}` are being used?",
2026 err.note(&crate_msg);
2033 fn mk_trait_obligation_with_new_self_ty(
2035 param_env: ty::ParamEnv<'tcx>,
2036 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
2037 ) -> PredicateObligation<'tcx> {
2038 let trait_pred = trait_ref_and_ty
2039 .map_bound(|(tr, new_self_ty)| tr.with_self_type(self.tcx, new_self_ty));
2041 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, trait_pred)
2044 #[instrument(skip(self), level = "debug")]
2045 fn maybe_report_ambiguity(
2047 obligation: &PredicateObligation<'tcx>,
2048 body_id: Option<hir::BodyId>,
2050 // Unable to successfully determine, probably means
2051 // insufficient type information, but could mean
2052 // ambiguous impls. The latter *ought* to be a
2053 // coherence violation, so we don't report it here.
2055 let predicate = self.resolve_vars_if_possible(obligation.predicate);
2056 let span = obligation.cause.span;
2058 debug!(?predicate, obligation.cause.code = ?obligation.cause.code());
2060 // Ambiguity errors are often caused as fallout from earlier errors.
2061 // We ignore them if this `infcx` is tainted in some cases below.
2063 let bound_predicate = predicate.kind();
2064 let mut err = match bound_predicate.skip_binder() {
2065 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
2066 let trait_ref = bound_predicate.rebind(data.trait_ref);
2069 if predicate.references_error() {
2073 // This is kind of a hack: it frequently happens that some earlier
2074 // error prevents types from being fully inferred, and then we get
2075 // a bunch of uninteresting errors saying something like "<generic
2076 // #0> doesn't implement Sized". It may even be true that we
2077 // could just skip over all checks where the self-ty is an
2078 // inference variable, but I was afraid that there might be an
2079 // inference variable created, registered as an obligation, and
2080 // then never forced by writeback, and hence by skipping here we'd
2081 // be ignoring the fact that we don't KNOW the type works
2082 // out. Though even that would probably be harmless, given that
2083 // we're only talking about builtin traits, which are known to be
2084 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2085 // avoid inundating the user with unnecessary errors, but we now
2086 // check upstream for type errors and don't add the obligations to
2087 // begin with in those cases.
2088 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
2089 if let None = self.tainted_by_errors() {
2090 self.emit_inference_failure_err(
2093 trait_ref.self_ty().skip_binder().into(),
2102 // Typically, this ambiguity should only happen if
2103 // there are unresolved type inference variables
2104 // (otherwise it would suggest a coherence
2105 // failure). But given #21974 that is not necessarily
2106 // the case -- we can have multiple where clauses that
2107 // are only distinguished by a region, which results
2108 // in an ambiguity even when all types are fully
2109 // known, since we don't dispatch based on region
2112 // Pick the first substitution that still contains inference variables as the one
2113 // we're going to emit an error for. If there are none (see above), fall back to
2114 // a more general error.
2115 let subst = data.trait_ref.substs.iter().find(|s| s.has_non_region_infer());
2117 let mut err = if let Some(subst) = subst {
2118 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2124 "type annotations needed: cannot satisfy `{}`",
2129 let obligation = obligation.with(self.tcx, trait_ref);
2130 let mut selcx = SelectionContext::new(&self);
2131 match selcx.select_from_obligation(&obligation) {
2133 let impls = ambiguity::recompute_applicable_impls(self.infcx, &obligation);
2134 let has_non_region_infer =
2135 trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_infer());
2136 // It doesn't make sense to talk about applicable impls if there are more
2137 // than a handful of them.
2138 if impls.len() > 1 && impls.len() < 5 && has_non_region_infer {
2139 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2141 if self.tainted_by_errors().is_some() {
2145 err.note(&format!("cannot satisfy `{}`", predicate));
2149 if self.tainted_by_errors().is_some() {
2153 err.note(&format!("cannot satisfy `{}`", predicate));
2157 if let ObligationCauseCode::ItemObligation(def_id) | ObligationCauseCode::ExprItemObligation(def_id, ..) = *obligation.cause.code() {
2158 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2159 } else if let Ok(snippet) = &self.tcx.sess.source_map().span_to_snippet(span)
2160 && let ObligationCauseCode::BindingObligation(def_id, _) | ObligationCauseCode::ExprBindingObligation(def_id, ..)
2161 = *obligation.cause.code()
2163 let generics = self.tcx.generics_of(def_id);
2164 if generics.params.iter().any(|p| p.name != kw::SelfUpper)
2165 && !snippet.ends_with('>')
2166 && !generics.has_impl_trait()
2167 && !self.tcx.is_fn_trait(def_id)
2169 // FIXME: To avoid spurious suggestions in functions where type arguments
2170 // where already supplied, we check the snippet to make sure it doesn't
2171 // end with a turbofish. Ideally we would have access to a `PathSegment`
2172 // instead. Otherwise we would produce the following output:
2174 // error[E0283]: type annotations needed
2175 // --> $DIR/issue-54954.rs:3:24
2177 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2178 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2180 // | cannot infer type
2181 // | help: consider specifying the type argument
2182 // | in the function call:
2183 // | `Tt::const_val::<[i8; 123]>::<T>`
2185 // LL | const fn const_val<T: Sized>() -> usize {
2186 // | - required by this bound in `Tt::const_val`
2188 // = note: cannot satisfy `_: Tt`
2190 // Clear any more general suggestions in favor of our specific one
2191 err.clear_suggestions();
2193 err.span_suggestion_verbose(
2194 span.shrink_to_hi(),
2196 "consider specifying the type argument{} in the function call",
2197 pluralize!(generics.params.len()),
2204 .map(|p| p.name.to_string())
2205 .collect::<Vec<String>>()
2208 Applicability::HasPlaceholders,
2213 if let (Some(body_id), Some(ty::subst::GenericArgKind::Type(_))) =
2214 (body_id, subst.map(|subst| subst.unpack()))
2216 struct FindExprBySpan<'hir> {
2218 result: Option<&'hir hir::Expr<'hir>>,
2221 impl<'v> hir::intravisit::Visitor<'v> for FindExprBySpan<'v> {
2222 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2223 if self.span == ex.span {
2224 self.result = Some(ex);
2226 hir::intravisit::walk_expr(self, ex);
2231 let mut expr_finder = FindExprBySpan { span, result: None };
2233 expr_finder.visit_expr(&self.tcx.hir().body(body_id).value);
2235 if let Some(hir::Expr {
2236 kind: hir::ExprKind::Path(hir::QPath::Resolved(None, path)), .. }
2237 ) = expr_finder.result
2240 trait_path_segment @ hir::PathSegment {
2241 res: rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id),
2245 ident: assoc_item_name,
2246 res: rustc_hir::def::Res::Def(_, item_id),
2250 && data.trait_ref.def_id == *trait_id
2251 && self.tcx.trait_of_item(*item_id) == Some(*trait_id)
2252 && let None = self.tainted_by_errors()
2254 let (verb, noun) = match self.tcx.associated_item(item_id).kind {
2255 ty::AssocKind::Const => ("refer to the", "constant"),
2256 ty::AssocKind::Fn => ("call", "function"),
2257 ty::AssocKind::Type => ("refer to the", "type"), // this is already covered by E0223, but this single match arm doesn't hurt here
2260 // Replace the more general E0283 with a more specific error
2262 err = self.tcx.sess.struct_span_err_with_code(
2265 "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type",
2267 rustc_errors::error_code!(E0790),
2270 if let Some(local_def_id) = data.trait_ref.def_id.as_local()
2271 && 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)
2272 && let Some(method_ref) = trait_item_refs.iter().find(|item_ref| item_ref.ident == *assoc_item_name) {
2273 err.span_label(method_ref.span, format!("`{}::{}` defined here", trait_name, assoc_item_name));
2276 err.span_label(span, format!("cannot {verb} associated {noun} of trait"));
2278 let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
2280 if trait_impls.blanket_impls().is_empty()
2281 && let Some((impl_ty, _)) = trait_impls.non_blanket_impls().iter().next()
2282 && let Some(impl_def_id) = impl_ty.def() {
2283 let message = if trait_impls.non_blanket_impls().len() == 1 {
2284 "use the fully-qualified path to the only available implementation".to_string()
2287 "use a fully-qualified path to a specific available implementation ({} found)",
2288 trait_impls.non_blanket_impls().len()
2291 let mut suggestions = vec![(
2292 trait_path_segment.ident.span.shrink_to_lo(),
2293 format!("<{} as ", self.tcx.type_of(impl_def_id))
2295 if let Some(generic_arg) = trait_path_segment.args {
2296 let between_span = trait_path_segment.ident.span.between(generic_arg.span_ext);
2297 // get rid of :: between Trait and <type>
2298 // must be '::' between them, otherwise the parser won't accept the code
2299 suggestions.push((between_span, "".to_string(),));
2300 suggestions.push((generic_arg.span_ext.shrink_to_hi(), format!(">")));
2302 suggestions.push((trait_path_segment.ident.span.shrink_to_hi(), format!(">")));
2304 err.multipart_suggestion(
2307 Applicability::MaybeIncorrect
2316 ty::PredicateKind::WellFormed(arg) => {
2317 // Same hacky approach as above to avoid deluging user
2318 // with error messages.
2319 if arg.references_error()
2320 || self.tcx.sess.has_errors().is_some()
2321 || self.tainted_by_errors().is_some()
2326 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2329 ty::PredicateKind::Subtype(data) => {
2330 if data.references_error()
2331 || self.tcx.sess.has_errors().is_some()
2332 || self.tainted_by_errors().is_some()
2334 // no need to overload user in such cases
2337 let SubtypePredicate { a_is_expected: _, a, b } = data;
2338 // both must be type variables, or the other would've been instantiated
2339 assert!(a.is_ty_var() && b.is_ty_var());
2340 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2342 ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
2343 if predicate.references_error() || self.tainted_by_errors().is_some() {
2350 .chain(Some(data.term.into_arg()))
2351 .find(|g| g.has_non_region_infer());
2352 if let Some(subst) = subst {
2353 let mut err = self.emit_inference_failure_err(
2360 err.note(&format!("cannot satisfy `{}`", predicate));
2363 // If we can't find a substitution, just print a generic error
2364 let mut err = struct_span_err!(
2368 "type annotations needed: cannot satisfy `{}`",
2371 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2376 ty::PredicateKind::ConstEvaluatable(data) => {
2377 if predicate.references_error() || self.tainted_by_errors().is_some() {
2380 let subst = data.walk().find(|g| g.is_non_region_infer());
2381 if let Some(subst) = subst {
2382 let err = self.emit_inference_failure_err(
2391 // If we can't find a substitution, just print a generic error
2392 let mut err = struct_span_err!(
2396 "type annotations needed: cannot satisfy `{}`",
2399 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2404 if self.tcx.sess.has_errors().is_some() || self.tainted_by_errors().is_some() {
2407 let mut err = struct_span_err!(
2411 "type annotations needed: cannot satisfy `{}`",
2414 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2418 self.note_obligation_cause(&mut err, obligation);
2422 fn annotate_source_of_ambiguity(
2424 err: &mut Diagnostic,
2426 predicate: ty::Predicate<'tcx>,
2428 let mut spans = vec![];
2429 let mut crates = vec![];
2430 let mut post = vec![];
2431 for def_id in impls {
2432 match self.tcx.span_of_impl(*def_id) {
2433 Ok(span) => spans.push(span),
2436 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2442 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2444 crate_names.dedup();
2448 if self.tainted_by_errors().is_some()
2449 && (crate_names.len() == 1
2451 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2452 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2454 // Avoid complaining about other inference issues for expressions like
2455 // `42 >> 1`, where the types are still `{integer}`, but we want to
2456 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2457 // NOTE(eddyb) this was `.cancel()`, but `err`
2458 // is borrowed, so we can't fully defuse it.
2459 err.downgrade_to_delayed_bug();
2463 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2464 let post = if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2465 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2466 } else if post.len() == 1 {
2467 format!(": `{}`", post[0])
2472 match (spans.len(), crates.len(), crate_names.len()) {
2474 err.note(&format!("cannot satisfy `{}`", predicate));
2477 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2481 "{} in the following crates: {}{}",
2483 crate_names.join(", "),
2488 let span: MultiSpan = spans.into();
2489 err.span_note(span, &msg);
2492 let span: MultiSpan = spans.into();
2493 err.span_note(span, &msg);
2495 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2499 let span: MultiSpan = spans.into();
2500 err.span_note(span, &msg);
2502 "and more `impl`s found in the following crates: {}{}",
2503 crate_names.join(", "),
2510 /// Returns `true` if the trait predicate may apply for *some* assignment
2511 /// to the type parameters.
2512 fn predicate_can_apply(
2514 param_env: ty::ParamEnv<'tcx>,
2515 pred: ty::PolyTraitPredicate<'tcx>,
2517 struct ParamToVarFolder<'a, 'tcx> {
2518 infcx: &'a InferCtxt<'tcx>,
2519 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2522 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2523 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2527 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2528 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2529 let infcx = self.infcx;
2530 *self.var_map.entry(ty).or_insert_with(|| {
2531 infcx.next_ty_var(TypeVariableOrigin {
2532 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2537 ty.super_fold_with(self)
2544 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2546 let InferOk { value: cleaned_pred, .. } =
2547 self.infcx.at(&ObligationCause::dummy(), param_env).normalize(cleaned_pred);
2550 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, cleaned_pred);
2552 self.predicate_may_hold(&obligation)
2556 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2557 // First, attempt to add note to this error with an async-await-specific
2558 // message, and fall back to regular note otherwise.
2559 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2560 self.note_obligation_cause_code(
2562 &obligation.predicate,
2563 obligation.param_env,
2564 obligation.cause.code(),
2566 &mut Default::default(),
2568 self.suggest_unsized_bound_if_applicable(err, obligation);
2572 #[instrument(level = "debug", skip_all)]
2573 fn suggest_unsized_bound_if_applicable(
2575 err: &mut Diagnostic,
2576 obligation: &PredicateObligation<'tcx>,
2578 let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = obligation.predicate.kind().skip_binder() else { return; };
2579 let (ObligationCauseCode::BindingObligation(item_def_id, span)
2580 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..))
2581 = *obligation.cause.code().peel_derives() else { return; };
2582 debug!(?pred, ?item_def_id, ?span);
2584 let (Some(node), true) = (
2585 self.tcx.hir().get_if_local(item_def_id),
2586 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2590 self.maybe_suggest_unsized_generics(err, span, node);
2593 #[instrument(level = "debug", skip_all)]
2594 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>) {
2595 let Some(generics) = node.generics() else {
2598 let sized_trait = self.tcx.lang_items().sized_trait();
2599 debug!(?generics.params);
2600 debug!(?generics.predicates);
2601 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2604 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2605 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2606 let explicitly_sized = generics
2607 .bounds_for_param(param.def_id)
2608 .flat_map(|bp| bp.bounds)
2609 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2610 if explicitly_sized {
2617 // Only suggest indirection for uses of type parameters in ADTs.
2619 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2623 if self.maybe_indirection_for_unsized(err, item, param) {
2629 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2630 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param.def_id)
2634 (span.shrink_to_hi(), ":")
2636 err.span_suggestion_verbose(
2638 "consider relaxing the implicit `Sized` restriction",
2639 format!("{} ?Sized", separator),
2640 Applicability::MachineApplicable,
2644 fn maybe_indirection_for_unsized(
2646 err: &mut Diagnostic,
2648 param: &GenericParam<'tcx>,
2650 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2651 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2652 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2654 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2655 visitor.visit_item(item);
2656 if visitor.invalid_spans.is_empty() {
2659 let mut multispan: MultiSpan = param.span.into();
2660 multispan.push_span_label(
2662 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2664 for sp in visitor.invalid_spans {
2665 multispan.push_span_label(
2667 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2673 "you could relax the implicit `Sized` bound on `{T}` if it were \
2674 used through indirection like `&{T}` or `Box<{T}>`",
2675 T = param.name.ident(),
2681 fn is_recursive_obligation(
2683 obligated_types: &mut Vec<Ty<'tcx>>,
2684 cause_code: &ObligationCauseCode<'tcx>,
2686 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2687 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2688 let self_ty = parent_trait_ref.skip_binder().self_ty();
2689 if obligated_types.iter().any(|ot| ot == &self_ty) {
2692 if let ty::Adt(def, substs) = self_ty.kind()
2693 && let [arg] = &substs[..]
2694 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2695 && let ty::Adt(inner_def, _) = ty.kind()
2705 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2706 /// `param: ?Sized` would be a valid constraint.
2707 struct FindTypeParam {
2708 param: rustc_span::Symbol,
2709 invalid_spans: Vec<Span>,
2713 impl<'v> Visitor<'v> for FindTypeParam {
2714 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2715 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2718 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2719 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2720 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2721 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2722 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2723 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2724 // in that case should make what happened clear enough.
2726 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2727 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2728 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2731 debug!(?ty, "FindTypeParam::visit_ty");
2732 self.invalid_spans.push(ty.span);
2735 hir::TyKind::Path(_) => {
2736 let prev = self.nested;
2738 hir::intravisit::walk_ty(self, ty);
2742 hir::intravisit::walk_ty(self, ty);
2748 /// Summarizes information
2751 /// An argument of non-tuple type. Parameters are (name, ty)
2752 Arg(String, String),
2754 /// An argument of tuple type. For a "found" argument, the span is
2755 /// the location in the source of the pattern. For an "expected"
2756 /// argument, it will be None. The vector is a list of (name, ty)
2757 /// strings for the components of the tuple.
2758 Tuple(Option<Span>, Vec<(String, String)>),
2762 fn empty() -> ArgKind {
2763 ArgKind::Arg("_".to_owned(), "_".to_owned())
2766 /// Creates an `ArgKind` from the expected type of an
2767 /// argument. It has no name (`_`) and an optional source span.
2768 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2770 ty::Tuple(tys) => ArgKind::Tuple(
2772 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2774 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2779 struct HasNumericInferVisitor;
2781 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2784 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2785 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2786 ControlFlow::Break(())
2788 ControlFlow::CONTINUE
2793 pub enum DefIdOrName {