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, TypeError};
37 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
38 use rustc_middle::ty::print::{with_forced_trimmed_paths, FmtPrinter, Print};
39 use rustc_middle::ty::{
40 self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
43 use rustc_session::config::TraitSolver;
44 use rustc_session::Limit;
45 use rustc_span::def_id::LOCAL_CRATE;
46 use rustc_span::symbol::sym;
47 use rustc_span::{ExpnKind, Span, DUMMY_SP};
50 use std::ops::ControlFlow;
51 use suggestions::TypeErrCtxtExt as _;
53 pub use rustc_infer::traits::error_reporting::*;
55 // When outputting impl candidates, prefer showing those that are more similar.
57 // We also compare candidates after skipping lifetimes, which has a lower
58 // priority than exact matches.
59 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
60 pub enum CandidateSimilarity {
61 Exact { ignoring_lifetimes: bool },
62 Fuzzy { ignoring_lifetimes: bool },
65 #[derive(Debug, Clone, Copy)]
66 pub struct ImplCandidate<'tcx> {
67 pub trait_ref: ty::TraitRef<'tcx>,
68 pub similarity: CandidateSimilarity,
71 pub trait InferCtxtExt<'tcx> {
72 /// Given some node representing a fn-like thing in the HIR map,
73 /// returns a span and `ArgKind` information that describes the
74 /// arguments it expects. This can be supplied to
75 /// `report_arg_count_mismatch`.
76 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)>;
78 /// Reports an error when the number of arguments needed by a
79 /// trait match doesn't match the number that the expression
81 fn report_arg_count_mismatch(
84 found_span: Option<Span>,
85 expected_args: Vec<ArgKind>,
86 found_args: Vec<ArgKind>,
88 closure_pipe_span: Option<Span>,
89 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
91 /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
92 /// in that order, and returns the generic type corresponding to the
93 /// argument of that trait (corresponding to the closure arguments).
94 fn type_implements_fn_trait(
96 param_env: ty::ParamEnv<'tcx>,
97 ty: ty::Binder<'tcx, Ty<'tcx>>,
98 constness: ty::BoundConstness,
99 polarity: ty::ImplPolarity,
100 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
103 pub trait TypeErrCtxtExt<'tcx> {
104 fn report_overflow_error<T>(
108 suggest_increasing_limit: bool,
109 mutate: impl FnOnce(&mut Diagnostic),
114 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
115 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug;
117 fn report_fulfillment_errors(
119 errors: &[FulfillmentError<'tcx>],
120 body_id: Option<hir::BodyId>,
121 ) -> ErrorGuaranteed;
123 fn report_overflow_obligation<T>(
125 obligation: &Obligation<'tcx, T>,
126 suggest_increasing_limit: bool,
129 T: ToPredicate<'tcx> + Clone;
131 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
133 fn report_overflow_obligation_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
135 /// The `root_obligation` parameter should be the `root_obligation` field
136 /// from a `FulfillmentError`. If no `FulfillmentError` is available,
137 /// then it should be the same as `obligation`.
138 fn report_selection_error(
140 obligation: PredicateObligation<'tcx>,
141 root_obligation: &PredicateObligation<'tcx>,
142 error: &SelectionError<'tcx>,
146 impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
147 /// Given some node representing a fn-like thing in the HIR map,
148 /// returns a span and `ArgKind` information that describes the
149 /// arguments it expects. This can be supplied to
150 /// `report_arg_count_mismatch`.
151 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)> {
152 let sm = self.tcx.sess.source_map();
153 let hir = self.tcx.hir();
155 Node::Expr(&hir::Expr {
156 kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, fn_arg_span, .. }),
165 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
172 sm.span_to_snippet(pat.span)
174 .map(|snippet| (snippet, "_".to_owned()))
176 .collect::<Option<Vec<_>>>()?,
179 let name = sm.span_to_snippet(arg.pat.span).ok()?;
180 Some(ArgKind::Arg(name, "_".to_owned()))
183 .collect::<Option<Vec<ArgKind>>>()?,
185 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
186 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
187 | Node::TraitItem(&hir::TraitItem {
188 kind: hir::TraitItemKind::Fn(ref sig, _), ..
195 .map(|arg| match arg.kind {
196 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
198 vec![("_".to_owned(), "_".to_owned()); tys.len()],
200 _ => ArgKind::empty(),
202 .collect::<Vec<ArgKind>>(),
204 Node::Ctor(ref variant_data) => {
205 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
206 (span, None, vec![ArgKind::empty(); variant_data.fields().len()])
208 _ => panic!("non-FnLike node found: {:?}", node),
212 /// Reports an error when the number of arguments needed by a
213 /// trait match doesn't match the number that the expression
215 fn report_arg_count_mismatch(
218 found_span: Option<Span>,
219 expected_args: Vec<ArgKind>,
220 found_args: Vec<ArgKind>,
222 closure_arg_span: Option<Span>,
223 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
224 let kind = if is_closure { "closure" } else { "function" };
226 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
227 let arg_length = arguments.len();
228 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
229 match (arg_length, arguments.get(0)) {
230 (1, Some(ArgKind::Tuple(_, fields))) => {
231 format!("a single {}-tuple as argument", fields.len())
236 if distinct && arg_length > 1 { "distinct " } else { "" },
237 pluralize!(arg_length)
242 let expected_str = args_str(&expected_args, &found_args);
243 let found_str = args_str(&found_args, &expected_args);
245 let mut err = struct_span_err!(
249 "{} is expected to take {}, but it takes {}",
255 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
257 if let Some(found_span) = found_span {
258 err.span_label(found_span, format!("takes {}", found_str));
260 // Suggest to take and ignore the arguments with expected_args_length `_`s if
261 // found arguments is empty (assume the user just wants to ignore args in this case).
262 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
263 if found_args.is_empty() && is_closure {
264 let underscores = vec!["_"; expected_args.len()].join(", ");
265 err.span_suggestion_verbose(
266 closure_arg_span.unwrap_or(found_span),
268 "consider changing the closure to take and ignore the expected argument{}",
269 pluralize!(expected_args.len())
271 format!("|{}|", underscores),
272 Applicability::MachineApplicable,
276 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
277 if fields.len() == expected_args.len() {
280 .map(|(name, _)| name.to_owned())
281 .collect::<Vec<String>>()
283 err.span_suggestion_verbose(
285 "change the closure to take multiple arguments instead of a single tuple",
286 format!("|{}|", sugg),
287 Applicability::MachineApplicable,
291 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
292 && fields.len() == found_args.len()
299 .map(|arg| match arg {
300 ArgKind::Arg(name, _) => name.to_owned(),
303 .collect::<Vec<String>>()
305 // add type annotations if available
306 if found_args.iter().any(|arg| match arg {
307 ArgKind::Arg(_, ty) => ty != "_",
314 .map(|(_, ty)| ty.to_owned())
315 .collect::<Vec<String>>()
322 err.span_suggestion_verbose(
324 "change the closure to accept a tuple instead of individual arguments",
326 Applicability::MachineApplicable,
334 fn type_implements_fn_trait(
336 param_env: ty::ParamEnv<'tcx>,
337 ty: ty::Binder<'tcx, Ty<'tcx>>,
338 constness: ty::BoundConstness,
339 polarity: ty::ImplPolarity,
340 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
341 self.commit_if_ok(|_| {
342 for trait_def_id in [
343 self.tcx.lang_items().fn_trait(),
344 self.tcx.lang_items().fn_mut_trait(),
345 self.tcx.lang_items().fn_once_trait(),
347 let Some(trait_def_id) = trait_def_id else { continue };
348 // Make a fresh inference variable so we can determine what the substitutions
350 let var = self.next_ty_var(TypeVariableOrigin {
352 kind: TypeVariableOriginKind::MiscVariable,
354 let trait_ref = self.tcx.mk_trait_ref(trait_def_id, [ty.skip_binder(), var]);
355 let obligation = Obligation::new(
357 ObligationCause::dummy(),
359 ty.rebind(ty::TraitPredicate { trait_ref, constness, polarity }),
361 let ocx = ObligationCtxt::new_in_snapshot(self);
362 ocx.register_obligation(obligation);
363 if ocx.select_all_or_error().is_empty() {
366 .fn_trait_kind_from_def_id(trait_def_id)
367 .expect("expected to map DefId to ClosureKind"),
368 ty.rebind(self.resolve_vars_if_possible(var)),
377 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
378 fn report_fulfillment_errors(
380 errors: &[FulfillmentError<'tcx>],
381 body_id: Option<hir::BodyId>,
382 ) -> ErrorGuaranteed {
384 struct ErrorDescriptor<'tcx> {
385 predicate: ty::Predicate<'tcx>,
386 index: Option<usize>, // None if this is an old error
389 let mut error_map: FxIndexMap<_, Vec<_>> = self
390 .reported_trait_errors
393 .map(|(&span, predicates)| {
398 .map(|&predicate| ErrorDescriptor { predicate, index: None })
404 for (index, error) in errors.iter().enumerate() {
405 // We want to ignore desugarings here: spans are equivalent even
406 // if one is the result of a desugaring and the other is not.
407 let mut span = error.obligation.cause.span;
408 let expn_data = span.ctxt().outer_expn_data();
409 if let ExpnKind::Desugaring(_) = expn_data.kind {
410 span = expn_data.call_site;
413 error_map.entry(span).or_default().push(ErrorDescriptor {
414 predicate: error.obligation.predicate,
418 self.reported_trait_errors
422 .push(error.obligation.predicate);
425 // We do this in 2 passes because we want to display errors in order, though
426 // maybe it *is* better to sort errors by span or something.
427 let mut is_suppressed = vec![false; errors.len()];
428 for (_, error_set) in error_map.iter() {
429 // We want to suppress "duplicate" errors with the same span.
430 for error in error_set {
431 if let Some(index) = error.index {
432 // Suppress errors that are either:
433 // 1) strictly implied by another error.
434 // 2) implied by an error with a smaller index.
435 for error2 in error_set {
436 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
437 // Avoid errors being suppressed by already-suppressed
438 // errors, to prevent all errors from being suppressed
443 if self.error_implies(error2.predicate, error.predicate)
444 && !(error2.index >= error.index
445 && self.error_implies(error.predicate, error2.predicate))
447 info!("skipping {:?} (implied by {:?})", error, error2);
448 is_suppressed[index] = true;
456 for (error, suppressed) in iter::zip(errors, is_suppressed) {
458 self.report_fulfillment_error(error, body_id);
462 self.tcx.sess.delay_span_bug(DUMMY_SP, "expected fullfillment errors")
465 /// Reports that an overflow has occurred and halts compilation. We
466 /// halt compilation unconditionally because it is important that
467 /// overflows never be masked -- they basically represent computations
468 /// whose result could not be truly determined and thus we can't say
469 /// if the program type checks or not -- and they are unusual
470 /// occurrences in any case.
471 fn report_overflow_error<T>(
475 suggest_increasing_limit: bool,
476 mutate: impl FnOnce(&mut Diagnostic),
481 + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
482 <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
484 let predicate = self.resolve_vars_if_possible(predicate.clone());
485 let mut pred_str = predicate.to_string();
487 if pred_str.len() > 50 {
488 // We don't need to save the type to a file, we will be talking about this type already
489 // in a separate note when we explain the obligation, so it will be available that way.
491 .print(FmtPrinter::new_with_limit(
494 rustc_session::Limit(6),
499 let mut err = struct_span_err!(
503 "overflow evaluating the requirement `{}`",
507 if suggest_increasing_limit {
508 self.suggest_new_overflow_limit(&mut err);
514 self.tcx.sess.abort_if_errors();
518 /// Reports that an overflow has occurred and halts compilation. We
519 /// halt compilation unconditionally because it is important that
520 /// overflows never be masked -- they basically represent computations
521 /// whose result could not be truly determined and thus we can't say
522 /// if the program type checks or not -- and they are unusual
523 /// occurrences in any case.
524 fn report_overflow_obligation<T>(
526 obligation: &Obligation<'tcx, T>,
527 suggest_increasing_limit: bool,
530 T: ToPredicate<'tcx> + Clone,
532 let predicate = obligation.predicate.clone().to_predicate(self.tcx);
533 let predicate = self.resolve_vars_if_possible(predicate);
534 self.report_overflow_error(
536 obligation.cause.span,
537 suggest_increasing_limit,
539 self.note_obligation_cause_code(
542 obligation.param_env,
543 obligation.cause.code(),
545 &mut Default::default(),
551 fn suggest_new_overflow_limit(&self, err: &mut Diagnostic) {
552 let suggested_limit = match self.tcx.recursion_limit() {
553 Limit(0) => Limit(2),
557 "consider increasing the recursion limit by adding a \
558 `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
560 self.tcx.crate_name(LOCAL_CRATE),
564 /// Reports that a cycle was detected which led to overflow and halts
565 /// compilation. This is equivalent to `report_overflow_obligation` except
566 /// that we can give a more helpful error message (and, in particular,
567 /// we do not suggest increasing the overflow limit, which is not
569 fn report_overflow_obligation_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
570 let cycle = self.resolve_vars_if_possible(cycle.to_owned());
571 assert!(!cycle.is_empty());
573 debug!(?cycle, "report_overflow_error_cycle");
575 // The 'deepest' obligation is most likely to have a useful
577 self.report_overflow_obligation(
578 cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(),
583 fn report_selection_error(
585 mut obligation: PredicateObligation<'tcx>,
586 root_obligation: &PredicateObligation<'tcx>,
587 error: &SelectionError<'tcx>,
590 let mut span = obligation.cause.span;
591 // FIXME: statically guarantee this by tainting after the diagnostic is emitted
592 self.set_tainted_by_errors(
593 tcx.sess.delay_span_bug(span, "`report_selection_error` did not emit an error"),
596 let mut err = match *error {
597 SelectionError::Unimplemented => {
598 // If this obligation was generated as a result of well-formedness checking, see if we
599 // can get a better error message by performing HIR-based well-formedness checking.
600 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
601 root_obligation.cause.code().peel_derives()
602 && !obligation.predicate.has_non_region_infer()
604 if let Some(cause) = self
606 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
608 obligation.cause = cause.clone();
609 span = obligation.cause.span;
612 if let ObligationCauseCode::CompareImplItemObligation {
616 } = *obligation.cause.code()
618 self.report_extra_impl_obligation(
622 &format!("`{}`", obligation.predicate),
628 let bound_predicate = obligation.predicate.kind();
629 match bound_predicate.skip_binder() {
630 ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
631 let trait_predicate = bound_predicate.rebind(trait_predicate);
632 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
634 trait_predicate.remap_constness_diag(obligation.param_env);
635 let predicate_is_const = ty::BoundConstness::ConstIfConst
636 == trait_predicate.skip_binder().constness;
638 if self.tcx.sess.has_errors().is_some()
639 && trait_predicate.references_error()
643 let trait_ref = trait_predicate.to_poly_trait_ref();
644 let (post_message, pre_message, type_def) = self
645 .get_parent_trait_ref(obligation.cause.code())
648 format!(" in `{}`", t),
649 format!("within `{}`, ", t),
650 s.map(|s| (format!("within this `{}`", t), s)),
653 .unwrap_or_default();
655 let OnUnimplementedNote {
661 } = self.on_unimplemented_note(trait_ref, &obligation);
662 let have_alt_message = message.is_some() || label.is_some();
663 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
665 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
666 let (message, note, append_const_msg) = if is_try_conversion {
669 "`?` couldn't convert the error to `{}`",
670 trait_ref.skip_binder().self_ty(),
673 "the question mark operation (`?`) implicitly performs a \
674 conversion on the error value using the `From` trait"
680 (message, note, append_const_msg)
683 let mut err = struct_span_err!(
689 .and_then(|cannot_do_this| {
690 match (predicate_is_const, append_const_msg) {
691 // do nothing if predicate is not const
692 (false, _) => Some(cannot_do_this),
693 // suggested using default post message
694 (true, Some(None)) => {
695 Some(format!("{cannot_do_this} in const contexts"))
697 // overridden post message
698 (true, Some(Some(post_message))) => {
699 Some(format!("{cannot_do_this}{post_message}"))
701 // fallback to generic message
702 (true, None) => None,
705 .unwrap_or_else(|| format!(
706 "the trait bound `{}` is not satisfied{}",
707 trait_predicate, post_message,
711 if is_try_conversion && let Some(ret_span) = self.return_type_span(&obligation) {
715 "expected `{}` because of this",
716 trait_ref.skip_binder().self_ty()
721 if Some(trait_ref.def_id()) == tcx.lang_items().tuple_trait() {
722 match obligation.cause.code().peel_derives() {
723 ObligationCauseCode::RustCall => {
724 err.set_primary_message("functions with the \"rust-call\" ABI must take a single non-self tuple argument");
726 ObligationCauseCode::BindingObligation(def_id, _)
727 | ObligationCauseCode::ItemObligation(def_id)
728 if tcx.is_fn_trait(*def_id) =>
730 err.code(rustc_errors::error_code!(E0059));
731 err.set_primary_message(format!(
732 "type parameter to bare `{}` trait must be a tuple",
733 tcx.def_path_str(*def_id)
740 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
741 && predicate_is_const
743 err.note("`~const Drop` was renamed to `~const Destruct`");
744 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
747 let explanation = if let ObligationCauseCode::MainFunctionType =
748 obligation.cause.code()
750 "consider using `()`, or a `Result`".to_owned()
752 let ty_desc = match trait_ref.skip_binder().self_ty().kind() {
753 ty::FnDef(_, _) => Some("fn item"),
754 ty::Closure(_, _) => Some("closure"),
759 Some(desc) => format!(
760 "{}the trait `{}` is not implemented for {} `{}`",
762 trait_predicate.print_modifiers_and_trait_path(),
764 trait_ref.skip_binder().self_ty(),
767 "{}the trait `{}` is not implemented for `{}`",
769 trait_predicate.print_modifiers_and_trait_path(),
770 trait_ref.skip_binder().self_ty(),
775 if self.suggest_add_reference_to_arg(
781 self.note_obligation_cause(&mut err, &obligation);
785 if let Some(ref s) = label {
786 // If it has a custom `#[rustc_on_unimplemented]`
787 // error message, let's display it as the label!
788 err.span_label(span, s);
789 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
790 // When the self type is a type param We don't need to "the trait
791 // `std::marker::Sized` is not implemented for `T`" as we will point
792 // at the type param with a label to suggest constraining it.
793 err.help(&explanation);
796 err.span_label(span, explanation);
799 if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
800 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
801 self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
804 let mut unsatisfied_const = false;
805 if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
806 let non_const_predicate = trait_ref.without_const();
807 let non_const_obligation = Obligation {
808 cause: obligation.cause.clone(),
809 param_env: obligation.param_env.without_const(),
810 predicate: non_const_predicate.to_predicate(tcx),
811 recursion_depth: obligation.recursion_depth,
813 if self.predicate_may_hold(&non_const_obligation) {
814 unsatisfied_const = true;
818 "the trait `{}` is implemented for `{}`, \
819 but that implementation is not `const`",
820 non_const_predicate.print_modifiers_and_trait_path(),
821 trait_ref.skip_binder().self_ty(),
827 if let Some((msg, span)) = type_def {
828 err.span_label(span, &msg);
830 if let Some(ref s) = note {
831 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
832 err.note(s.as_str());
834 if let Some(ref s) = parent_label {
837 .opt_local_def_id(obligation.cause.body_id)
839 tcx.hir().body_owner_def_id(hir::BodyId {
840 hir_id: obligation.cause.body_id,
843 err.span_label(tcx.def_span(body), s);
846 self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
847 self.suggest_dereferencing_index(&obligation, &mut err, trait_predicate);
849 self.suggest_dereferences(&obligation, &mut err, trait_predicate);
850 suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
852 self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
853 suggested |= self.suggest_semicolon_removal(
859 self.note_version_mismatch(&mut err, &trait_ref);
860 self.suggest_remove_await(&obligation, &mut err);
861 self.suggest_derive(&obligation, &mut err, trait_predicate);
863 if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
864 self.suggest_await_before_try(
872 if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
878 // If the obligation failed due to a missing implementation of the
879 // `Unsize` trait, give a pointer to why that might be the case
881 "all implementations of `Unsize` are provided \
882 automatically by the compiler, see \
883 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
884 for more information",
888 let is_fn_trait = tcx.is_fn_trait(trait_ref.def_id());
889 let is_target_feature_fn = if let ty::FnDef(def_id, _) =
890 *trait_ref.skip_binder().self_ty().kind()
892 !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
896 if is_fn_trait && is_target_feature_fn {
898 "`#[target_feature]` functions do not implement the `Fn` traits",
902 // Try to report a help message
904 && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
905 obligation.param_env,
907 trait_predicate.skip_binder().constness,
908 trait_predicate.skip_binder().polarity,
911 // If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
912 // suggestion to add trait bounds for the type, since we only typically implement
913 // these traits once.
915 // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
918 self.tcx.fn_trait_kind_from_def_id(trait_ref.def_id())
919 .expect("expected to map DefId to ClosureKind");
920 if !implemented_kind.extends(selected_kind) {
923 "`{}` implements `{}`, but it must implement `{}`, which is more general",
924 trait_ref.skip_binder().self_ty(),
931 // Note any argument mismatches
932 let given_ty = params.skip_binder();
933 let expected_ty = trait_ref.skip_binder().substs.type_at(1);
934 if let ty::Tuple(given) = given_ty.kind()
935 && let ty::Tuple(expected) = expected_ty.kind()
937 if expected.len() != given.len() {
938 // Note number of types that were expected and given
941 "expected a closure taking {} argument{}, but one taking {} argument{} was given",
943 pluralize!(given.len()),
945 pluralize!(expected.len()),
948 } else if !self.same_type_modulo_infer(given_ty, expected_ty) {
949 // Print type mismatch
950 let (expected_args, given_args) =
951 self.cmp(given_ty, expected_ty);
952 err.note_expected_found(
953 &"a closure with arguments",
955 &"a closure with arguments",
960 } else if !trait_ref.has_non_region_infer()
961 && self.predicate_can_apply(obligation.param_env, trait_predicate)
963 // If a where-clause may be useful, remind the
964 // user that they can add it.
966 // don't display an on-unimplemented note, as
967 // these notes will often be of the form
968 // "the type `T` can't be frobnicated"
969 // which is somewhat confusing.
970 self.suggest_restricting_param_bound(
974 obligation.cause.body_id,
976 } else if !suggested && !unsatisfied_const {
977 // Can't show anything else useful, try to find similar impls.
978 let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
979 if !self.report_similar_impl_candidates(
982 obligation.cause.body_id,
986 // This is *almost* equivalent to
987 // `obligation.cause.code().peel_derives()`, but it gives us the
988 // trait predicate for that corresponding root obligation. This
989 // lets us get a derived obligation from a type parameter, like
990 // when calling `string.strip_suffix(p)` where `p` is *not* an
991 // implementer of `Pattern<'_>`.
992 let mut code = obligation.cause.code();
993 let mut trait_pred = trait_predicate;
994 let mut peeled = false;
995 while let Some((parent_code, parent_trait_pred)) = code.parent() {
997 if let Some(parent_trait_pred) = parent_trait_pred {
998 trait_pred = parent_trait_pred;
1002 let def_id = trait_pred.def_id();
1003 // Mention *all* the `impl`s for the *top most* obligation, the
1004 // user might have meant to use one of them, if any found. We skip
1005 // auto-traits or fundamental traits that might not be exactly what
1006 // the user might expect to be presented with. Instead this is
1007 // useful for less general traits.
1009 && !self.tcx.trait_is_auto(def_id)
1010 && !self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1012 let trait_ref = trait_pred.to_poly_trait_ref();
1013 let impl_candidates =
1014 self.find_similar_impl_candidates(trait_pred);
1015 self.report_similar_impl_candidates(
1018 obligation.cause.body_id,
1026 // Changing mutability doesn't make a difference to whether we have
1027 // an `Unsize` impl (Fixes ICE in #71036)
1029 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
1032 // If this error is due to `!: Trait` not implemented but `(): Trait` is
1033 // implemented, and fallback has occurred, then it could be due to a
1034 // variable that used to fallback to `()` now falling back to `!`. Issue a
1035 // note informing about the change in behaviour.
1036 if trait_predicate.skip_binder().self_ty().is_never()
1037 && self.fallback_has_occurred
1039 let predicate = trait_predicate.map_bound(|trait_pred| {
1040 trait_pred.with_self_ty(self.tcx, self.tcx.mk_unit())
1042 let unit_obligation = obligation.with(tcx, predicate);
1043 if self.predicate_may_hold(&unit_obligation) {
1045 "this error might have been caused by changes to \
1046 Rust's type-inference algorithm (see issue #48950 \
1047 <https://github.com/rust-lang/rust/issues/48950> \
1048 for more information)",
1050 err.help("did you intend to use the type `()` here instead?");
1054 // Return early if the trait is Debug or Display and the invocation
1055 // originates within a standard library macro, because the output
1056 // is otherwise overwhelming and unhelpful (see #85844 for an
1060 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
1061 Some(macro_def_id) => {
1062 let crate_name = tcx.crate_name(macro_def_id.krate);
1063 crate_name == sym::std || crate_name == sym::core
1070 self.tcx.get_diagnostic_name(trait_ref.def_id()),
1071 Some(sym::Debug | sym::Display)
1081 ty::PredicateKind::Subtype(predicate) => {
1082 // Errors for Subtype predicates show up as
1083 // `FulfillmentErrorCode::CodeSubtypeError`,
1084 // not selection error.
1085 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
1088 ty::PredicateKind::Coerce(predicate) => {
1089 // Errors for Coerce predicates show up as
1090 // `FulfillmentErrorCode::CodeSubtypeError`,
1091 // not selection error.
1092 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
1095 ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
1096 | ty::PredicateKind::Clause(ty::Clause::Projection(..))
1097 | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..)) => {
1098 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1103 "the requirement `{}` is not satisfied",
1108 ty::PredicateKind::ObjectSafe(trait_def_id) => {
1109 let violations = self.tcx.object_safety_violations(trait_def_id);
1110 report_object_safety_error(self.tcx, span, trait_def_id, violations)
1113 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
1114 let found_kind = self.closure_kind(closure_substs).unwrap();
1115 let closure_span = self.tcx.def_span(closure_def_id);
1116 let mut err = struct_span_err!(
1120 "expected a closure that implements the `{}` trait, \
1121 but this closure only implements `{}`",
1128 format!("this closure implements `{}`, not `{}`", found_kind, kind),
1131 obligation.cause.span,
1132 format!("the requirement to implement `{}` derives from here", kind),
1135 // Additional context information explaining why the closure only implements
1136 // a particular trait.
1137 if let Some(typeck_results) = &self.typeck_results {
1141 .local_def_id_to_hir_id(closure_def_id.expect_local());
1142 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
1143 (ty::ClosureKind::FnOnce, Some((span, place))) => {
1147 "closure is `FnOnce` because it moves the \
1148 variable `{}` out of its environment",
1149 ty::place_to_string_for_capture(tcx, place)
1153 (ty::ClosureKind::FnMut, Some((span, place))) => {
1157 "closure is `FnMut` because it mutates the \
1158 variable `{}` here",
1159 ty::place_to_string_for_capture(tcx, place)
1170 ty::PredicateKind::WellFormed(ty) => {
1171 if self.tcx.sess.opts.unstable_opts.trait_solver != TraitSolver::Chalk {
1172 // WF predicates cannot themselves make
1173 // errors. They can only block due to
1174 // ambiguity; otherwise, they always
1175 // degenerate into other obligations
1176 // (which may fail).
1177 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
1179 // FIXME: we'll need a better message which takes into account
1180 // which bounds actually failed to hold.
1181 self.tcx.sess.struct_span_err(
1183 &format!("the type `{}` is not well-formed (chalk)", ty),
1188 ty::PredicateKind::ConstEvaluatable(..) => {
1189 // Errors for `ConstEvaluatable` predicates show up as
1190 // `SelectionError::ConstEvalFailure`,
1191 // not `Unimplemented`.
1194 "const-evaluatable requirement gave wrong error: `{:?}`",
1199 ty::PredicateKind::ConstEquate(..) => {
1200 // Errors for `ConstEquate` predicates show up as
1201 // `SelectionError::ConstEvalFailure`,
1202 // not `Unimplemented`.
1205 "const-equate requirement gave wrong error: `{:?}`",
1210 ty::PredicateKind::Ambiguous => span_bug!(span, "ambiguous"),
1212 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
1214 "TypeWellFormedFromEnv predicate should only exist in the environment"
1219 OutputTypeParameterMismatch(
1222 terr @ TypeError::CyclicTy(_),
1224 let self_ty = found_trait_ref.self_ty().skip_binder();
1225 let (cause, terr) = if let ty::Closure(def_id, _) = self_ty.kind() {
1227 ObligationCause::dummy_with_span(tcx.def_span(def_id)),
1228 TypeError::CyclicTy(self_ty),
1231 (obligation.cause.clone(), terr)
1233 self.report_and_explain_type_error(
1234 TypeTrace::poly_trait_refs(&cause, true, expected_trait_ref, found_trait_ref),
1238 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
1239 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
1240 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
1242 if expected_trait_ref.self_ty().references_error() {
1246 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
1250 let found_did = match *found_trait_ty.kind() {
1254 | ty::Generator(did, ..) => Some(did),
1255 ty::Adt(def, _) => Some(def.did()),
1259 let found_node = found_did.and_then(|did| self.tcx.hir().get_if_local(did));
1260 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
1262 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1263 // We check closures twice, with obligations flowing in different directions,
1264 // but we want to complain about them only once.
1268 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1270 let mut not_tupled = false;
1272 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
1273 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1276 vec![ArgKind::empty()]
1280 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1281 let expected = match expected_ty.kind() {
1282 ty::Tuple(ref tys) => {
1283 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
1287 vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())]
1291 // If this is a `Fn` family trait and either the expected or found
1292 // is not tupled, then fall back to just a regular mismatch error.
1293 // This shouldn't be common unless manually implementing one of the
1294 // traits manually, but don't make it more confusing when it does
1296 if Some(expected_trait_ref.def_id()) != tcx.lang_items().gen_trait() && not_tupled {
1297 self.report_and_explain_type_error(
1298 TypeTrace::poly_trait_refs(
1304 ty::error::TypeError::Mismatch,
1306 } else if found.len() == expected.len() {
1307 self.report_closure_arg_mismatch(
1312 obligation.cause.code(),
1316 let (closure_span, closure_arg_span, found) = found_did
1318 let node = self.tcx.hir().get_if_local(did)?;
1319 let (found_span, closure_arg_span, found) =
1320 self.get_fn_like_arguments(node)?;
1321 Some((Some(found_span), closure_arg_span, found))
1323 .unwrap_or((found_span, None, found));
1325 self.report_arg_count_mismatch(
1330 found_trait_ty.is_closure(),
1336 TraitNotObjectSafe(did) => {
1337 let violations = self.tcx.object_safety_violations(did);
1338 report_object_safety_error(self.tcx, span, did, violations)
1341 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
1343 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
1346 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
1347 if !self.tcx.features().generic_const_exprs {
1348 let mut err = self.tcx.sess.struct_span_err(
1350 "constant expression depends on a generic parameter",
1352 // FIXME(const_generics): we should suggest to the user how they can resolve this
1353 // issue. However, this is currently not actually possible
1354 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1356 // Note that with `feature(generic_const_exprs)` this case should not
1358 err.note("this may fail depending on what value the parameter takes");
1363 match obligation.predicate.kind().skip_binder() {
1364 ty::PredicateKind::ConstEvaluatable(ct) => {
1365 let ty::ConstKind::Unevaluated(uv) = ct.kind() else {
1366 bug!("const evaluatable failed for non-unevaluated const `{ct:?}`");
1369 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1370 let const_span = self.tcx.def_span(uv.def.did);
1371 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1372 Ok(snippet) => err.help(&format!(
1373 "try adding a `where` bound using this expression: `where [(); {}]:`",
1376 _ => err.help("consider adding a `where` bound using this expression"),
1383 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1389 // Already reported in the query.
1390 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1391 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1392 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1395 // Already reported.
1396 Overflow(OverflowError::Error(_)) => {
1397 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1401 bug!("overflow should be handled before the `report_selection_error` path");
1403 SelectionError::ErrorReporting => {
1404 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1408 self.note_obligation_cause(&mut err, &obligation);
1409 self.point_at_returns_when_relevant(&mut err, &obligation);
1415 trait InferCtxtPrivExt<'tcx> {
1416 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1417 // `error` occurring implies that `cond` occurs.
1418 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1420 fn report_fulfillment_error(
1422 error: &FulfillmentError<'tcx>,
1423 body_id: Option<hir::BodyId>,
1426 fn report_projection_error(
1428 obligation: &PredicateObligation<'tcx>,
1429 error: &MismatchedProjectionTypes<'tcx>,
1432 fn maybe_detailed_projection_msg(
1434 pred: ty::ProjectionPredicate<'tcx>,
1435 normalized_ty: ty::Term<'tcx>,
1436 expected_ty: ty::Term<'tcx>,
1437 ) -> Option<String>;
1443 ignoring_lifetimes: bool,
1444 ) -> Option<CandidateSimilarity>;
1446 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1448 fn find_similar_impl_candidates(
1450 trait_pred: ty::PolyTraitPredicate<'tcx>,
1451 ) -> Vec<ImplCandidate<'tcx>>;
1453 fn report_similar_impl_candidates(
1455 impl_candidates: Vec<ImplCandidate<'tcx>>,
1456 trait_ref: ty::PolyTraitRef<'tcx>,
1457 body_id: hir::HirId,
1458 err: &mut Diagnostic,
1462 /// Gets the parent trait chain start
1463 fn get_parent_trait_ref(
1465 code: &ObligationCauseCode<'tcx>,
1466 ) -> Option<(String, Option<Span>)>;
1468 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1469 /// with the same path as `trait_ref`, a help message about
1470 /// a probable version mismatch is added to `err`
1471 fn note_version_mismatch(
1473 err: &mut Diagnostic,
1474 trait_ref: &ty::PolyTraitRef<'tcx>,
1477 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1480 /// For this to work, `new_self_ty` must have no escaping bound variables.
1481 fn mk_trait_obligation_with_new_self_ty(
1483 param_env: ty::ParamEnv<'tcx>,
1484 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1485 ) -> PredicateObligation<'tcx>;
1487 fn maybe_report_ambiguity(
1489 obligation: &PredicateObligation<'tcx>,
1490 body_id: Option<hir::BodyId>,
1493 fn predicate_can_apply(
1495 param_env: ty::ParamEnv<'tcx>,
1496 pred: ty::PolyTraitPredicate<'tcx>,
1499 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1501 fn suggest_unsized_bound_if_applicable(
1503 err: &mut Diagnostic,
1504 obligation: &PredicateObligation<'tcx>,
1507 fn annotate_source_of_ambiguity(
1509 err: &mut Diagnostic,
1510 impls: &[ambiguity::Ambiguity],
1511 predicate: ty::Predicate<'tcx>,
1514 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>);
1516 fn maybe_indirection_for_unsized(
1518 err: &mut Diagnostic,
1519 item: &'tcx Item<'tcx>,
1520 param: &'tcx GenericParam<'tcx>,
1523 fn is_recursive_obligation(
1525 obligated_types: &mut Vec<Ty<'tcx>>,
1526 cause_code: &ObligationCauseCode<'tcx>,
1530 impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
1531 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1532 // `error` occurring implies that `cond` occurs.
1533 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1538 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1539 let bound_error = error.kind();
1540 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1542 ty::PredicateKind::Clause(ty::Clause::Trait(..)),
1543 ty::PredicateKind::Clause(ty::Clause::Trait(error)),
1544 ) => (cond, bound_error.rebind(error)),
1546 // FIXME: make this work in other cases too.
1551 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1552 let bound_predicate = obligation.predicate.kind();
1553 if let ty::PredicateKind::Clause(ty::Clause::Trait(implication)) =
1554 bound_predicate.skip_binder()
1556 let error = error.to_poly_trait_ref();
1557 let implication = bound_predicate.rebind(implication.trait_ref);
1558 // FIXME: I'm just not taking associated types at all here.
1559 // Eventually I'll need to implement param-env-aware
1560 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1561 let param_env = ty::ParamEnv::empty();
1562 if self.can_sub(param_env, error, implication).is_ok() {
1563 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1572 #[instrument(skip(self), level = "debug")]
1573 fn report_fulfillment_error(
1575 error: &FulfillmentError<'tcx>,
1576 body_id: Option<hir::BodyId>,
1579 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1580 self.report_selection_error(
1581 error.obligation.clone(),
1582 &error.root_obligation,
1586 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1587 self.report_projection_error(&error.obligation, e);
1589 FulfillmentErrorCode::CodeAmbiguity => {
1590 self.maybe_report_ambiguity(&error.obligation, body_id);
1592 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1593 self.report_mismatched_types(
1594 &error.obligation.cause,
1595 expected_found.expected,
1596 expected_found.found,
1601 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1602 let mut diag = self.report_mismatched_consts(
1603 &error.obligation.cause,
1604 expected_found.expected,
1605 expected_found.found,
1608 let code = error.obligation.cause.code().peel_derives().peel_match_impls();
1609 if let ObligationCauseCode::BindingObligation(..)
1610 | ObligationCauseCode::ItemObligation(..)
1611 | ObligationCauseCode::ExprBindingObligation(..)
1612 | ObligationCauseCode::ExprItemObligation(..) = code
1614 self.note_obligation_cause_code(
1616 error.obligation.predicate,
1617 error.obligation.param_env,
1620 &mut Default::default(),
1625 FulfillmentErrorCode::CodeCycle(ref cycle) => {
1626 self.report_overflow_obligation_cycle(cycle);
1631 #[instrument(level = "debug", skip_all)]
1632 fn report_projection_error(
1634 obligation: &PredicateObligation<'tcx>,
1635 error: &MismatchedProjectionTypes<'tcx>,
1637 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1639 if predicate.references_error() {
1644 let ocx = ObligationCtxt::new_in_snapshot(self);
1646 // try to find the mismatched types to report the error with.
1648 // this can fail if the problem was higher-ranked, in which
1649 // cause I have no idea for a good error message.
1650 let bound_predicate = predicate.kind();
1651 let (values, err) = if let ty::PredicateKind::Clause(ty::Clause::Projection(data)) =
1652 bound_predicate.skip_binder()
1654 let data = self.replace_bound_vars_with_fresh_vars(
1655 obligation.cause.span,
1656 infer::LateBoundRegionConversionTime::HigherRankedType,
1657 bound_predicate.rebind(data),
1659 let unnormalized_term = match data.term.unpack() {
1660 ty::TermKind::Ty(_) => self
1662 .mk_projection(data.projection_ty.def_id, data.projection_ty.substs)
1664 ty::TermKind::Const(ct) => self
1667 ty::UnevaluatedConst {
1668 def: ty::WithOptConstParam::unknown(data.projection_ty.def_id),
1669 substs: data.projection_ty.substs,
1675 let normalized_term =
1676 ocx.normalize(&obligation.cause, obligation.param_env, unnormalized_term);
1678 debug!(?obligation.cause, ?obligation.param_env);
1680 debug!(?normalized_term, data.ty = ?data.term);
1682 let is_normalized_term_expected = !matches!(
1683 obligation.cause.code().peel_derives(),
1684 ObligationCauseCode::ItemObligation(_)
1685 | ObligationCauseCode::BindingObligation(_, _)
1686 | ObligationCauseCode::ExprItemObligation(..)
1687 | ObligationCauseCode::ExprBindingObligation(..)
1688 | ObligationCauseCode::ObjectCastObligation(..)
1689 | ObligationCauseCode::OpaqueType
1692 // constrain inference variables a bit more to nested obligations from normalize so
1693 // we can have more helpful errors.
1694 ocx.select_where_possible();
1696 if let Err(new_err) = ocx.eq_exp(
1698 obligation.param_env,
1699 is_normalized_term_expected,
1703 (Some((data, is_normalized_term_expected, normalized_term, data.term)), new_err)
1712 .and_then(|(predicate, _, normalized_term, expected_term)| {
1713 self.maybe_detailed_projection_msg(predicate, normalized_term, expected_term)
1715 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
1716 let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
1718 let secondary_span = match predicate.kind().skip_binder() {
1719 ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => self
1721 .opt_associated_item(proj.projection_ty.def_id)
1722 .and_then(|trait_assoc_item| {
1724 .trait_of_item(proj.projection_ty.def_id)
1725 .map(|id| (trait_assoc_item, id))
1727 .and_then(|(trait_assoc_item, id)| {
1728 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1729 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1731 .associated_items(did)
1732 .in_definition_order()
1733 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1736 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1738 hir::Node::TraitItem(hir::TraitItem {
1739 kind: hir::TraitItemKind::Type(_, Some(ty)),
1742 | hir::Node::ImplItem(hir::ImplItem {
1743 kind: hir::ImplItemKind::Type(ty),
1746 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1755 values.map(|(_, is_normalized_ty_expected, normalized_ty, expected_ty)| {
1756 infer::ValuePairs::Terms(ExpectedFound::new(
1757 is_normalized_ty_expected,
1766 self.note_obligation_cause(&mut diag, obligation);
1771 fn maybe_detailed_projection_msg(
1773 pred: ty::ProjectionPredicate<'tcx>,
1774 normalized_ty: ty::Term<'tcx>,
1775 expected_ty: ty::Term<'tcx>,
1776 ) -> Option<String> {
1777 let trait_def_id = pred.projection_ty.trait_def_id(self.tcx);
1778 let self_ty = pred.projection_ty.self_ty();
1780 with_forced_trimmed_paths! {
1781 if Some(pred.projection_ty.def_id) == self.tcx.lang_items().fn_once_output() {
1783 "expected `{self_ty}` to be a {fn_kind} that returns `{expected_ty}`, but it \
1784 returns `{normalized_ty}`",
1785 fn_kind = self_ty.prefix_string(self.tcx)
1787 } else if Some(trait_def_id) == self.tcx.lang_items().future_trait() {
1789 "expected `{self_ty}` to be a future that resolves to `{expected_ty}`, but it \
1790 resolves to `{normalized_ty}`"
1792 } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
1794 "expected `{self_ty}` to be an iterator that yields `{expected_ty}`, but it \
1795 yields `{normalized_ty}`"
1807 ignoring_lifetimes: bool,
1808 ) -> Option<CandidateSimilarity> {
1809 /// returns the fuzzy category of a given type, or None
1810 /// if the type can be equated to any type.
1811 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1813 ty::Bool => Some(0),
1814 ty::Char => Some(1),
1816 ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => Some(2),
1820 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1821 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1822 ty::Array(..) | ty::Slice(..) => Some(6),
1823 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1824 ty::Dynamic(..) => Some(8),
1825 ty::Closure(..) => Some(9),
1826 ty::Tuple(..) => Some(10),
1827 ty::Param(..) => Some(11),
1828 ty::Alias(ty::Projection, ..) => Some(12),
1829 ty::Alias(ty::Opaque, ..) => Some(13),
1830 ty::Never => Some(14),
1831 ty::Adt(..) => Some(15),
1832 ty::Generator(..) => Some(16),
1833 ty::Foreign(..) => Some(17),
1834 ty::GeneratorWitness(..) => Some(18),
1835 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1839 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1842 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1850 if !ignoring_lifetimes {
1851 a = strip_references(a);
1852 b = strip_references(b);
1855 let cat_a = type_category(self.tcx, a)?;
1856 let cat_b = type_category(self.tcx, b)?;
1858 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1859 } else if cat_a == cat_b {
1860 match (a.kind(), b.kind()) {
1861 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1862 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1863 // Matching on references results in a lot of unhelpful
1864 // suggestions, so let's just not do that for now.
1866 // We still upgrade successful matches to `ignoring_lifetimes: true`
1867 // to prioritize that impl.
1868 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1869 self.fuzzy_match_tys(a, b, true).is_some()
1873 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1874 } else if ignoring_lifetimes {
1877 self.fuzzy_match_tys(a, b, true)
1881 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1882 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1883 hir::GeneratorKind::Gen => "a generator",
1884 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1885 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1886 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1890 fn find_similar_impl_candidates(
1892 trait_pred: ty::PolyTraitPredicate<'tcx>,
1893 ) -> Vec<ImplCandidate<'tcx>> {
1894 let mut candidates: Vec<_> = self
1896 .all_impls(trait_pred.def_id())
1897 .filter_map(|def_id| {
1898 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
1901 .is_constness_satisfied_by(self.tcx.constness(def_id))
1906 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1908 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
1909 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1912 if candidates.iter().any(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. })) {
1913 // If any of the candidates is a perfect match, we don't want to show all of them.
1914 // This is particularly relevant for the case of numeric types (as they all have the
1916 candidates.retain(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. }));
1921 fn report_similar_impl_candidates(
1923 impl_candidates: Vec<ImplCandidate<'tcx>>,
1924 trait_ref: ty::PolyTraitRef<'tcx>,
1925 body_id: hir::HirId,
1926 err: &mut Diagnostic,
1929 let other = if other { "other " } else { "" };
1930 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1933 let len = candidates.len();
1934 if candidates.len() == 0 {
1937 if candidates.len() == 1 {
1938 let ty_desc = match candidates[0].self_ty().kind() {
1939 ty::FnPtr(_) => Some("fn pointer"),
1942 let the_desc = match ty_desc {
1943 Some(desc) => format!(" implemented for {} `", desc),
1944 None => " implemented for `".to_string(),
1946 err.highlighted_help(vec![
1948 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1951 ("is".to_string(), Style::Highlight),
1952 (the_desc, Style::NoStyle),
1953 (candidates[0].self_ty().to_string(), Style::Highlight),
1954 ("`".to_string(), Style::NoStyle),
1958 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1959 // Check if the trait is the same in all cases. If so, we'll only show the type.
1960 let mut traits: Vec<_> =
1961 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1965 let mut candidates: Vec<String> = candidates
1968 if traits.len() == 1 {
1969 format!("\n {}", c.self_ty())
1978 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1980 "the following {other}types implement trait `{}`:{}{}",
1981 trait_ref.print_only_trait_path(),
1982 candidates[..end].join(""),
1983 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1988 let def_id = trait_ref.def_id();
1989 if impl_candidates.is_empty() {
1990 if self.tcx.trait_is_auto(def_id)
1991 || self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
1992 || self.tcx.get_diagnostic_name(def_id).is_some()
1994 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1997 let normalized_impl_candidates: Vec<_> = self
2000 // Ignore automatically derived impls and `!Trait` impls.
2002 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
2003 || self.tcx.is_builtin_derive(def_id)
2005 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
2006 .filter(|trait_ref| {
2007 let self_ty = trait_ref.self_ty();
2008 // Avoid mentioning type parameters.
2009 if let ty::Param(_) = self_ty.kind() {
2012 // Avoid mentioning types that are private to another crate
2013 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
2014 // FIXME(compiler-errors): This could be generalized, both to
2015 // be more granular, and probably look past other `#[fundamental]`
2018 .visibility(def.did())
2019 .is_accessible_from(body_id.owner.def_id, self.tcx)
2025 return report(normalized_impl_candidates, err);
2028 // Sort impl candidates so that ordering is consistent for UI tests.
2029 // because the ordering of `impl_candidates` may not be deterministic:
2030 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
2032 // Prefer more similar candidates first, then sort lexicographically
2033 // by their normalized string representation.
2034 let mut normalized_impl_candidates_and_similarities = impl_candidates
2036 .map(|ImplCandidate { trait_ref, similarity }| {
2037 // FIXME(compiler-errors): This should be using `NormalizeExt::normalize`
2038 let normalized = self
2039 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
2040 .query_normalize(trait_ref)
2041 .map_or(trait_ref, |normalized| normalized.value);
2042 (similarity, normalized)
2044 .collect::<Vec<_>>();
2045 normalized_impl_candidates_and_similarities.sort();
2046 normalized_impl_candidates_and_similarities.dedup();
2048 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
2050 .map(|(_, normalized)| normalized)
2051 .collect::<Vec<_>>();
2053 report(normalized_impl_candidates, err)
2056 /// Gets the parent trait chain start
2057 fn get_parent_trait_ref(
2059 code: &ObligationCauseCode<'tcx>,
2060 ) -> Option<(String, Option<Span>)> {
2062 ObligationCauseCode::BuiltinDerivedObligation(data) => {
2063 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2064 match self.get_parent_trait_ref(&data.parent_code) {
2067 let ty = parent_trait_ref.skip_binder().self_ty();
2068 let span = TyCategory::from_ty(self.tcx, ty)
2069 .map(|(_, def_id)| self.tcx.def_span(def_id));
2070 Some((ty.to_string(), span))
2074 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
2075 self.get_parent_trait_ref(&parent_code)
2081 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
2082 /// with the same path as `trait_ref`, a help message about
2083 /// a probable version mismatch is added to `err`
2084 fn note_version_mismatch(
2086 err: &mut Diagnostic,
2087 trait_ref: &ty::PolyTraitRef<'tcx>,
2089 let get_trait_impl = |trait_def_id| {
2090 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
2092 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
2093 let traits_with_same_path: std::collections::BTreeSet<_> = self
2096 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
2097 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
2099 let mut suggested = false;
2100 for trait_with_same_path in traits_with_same_path {
2101 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
2102 let impl_span = self.tcx.def_span(impl_def_id);
2103 err.span_help(impl_span, "trait impl with same name found");
2104 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
2105 let crate_msg = format!(
2106 "perhaps two different versions of crate `{}` are being used?",
2109 err.note(&crate_msg);
2116 fn mk_trait_obligation_with_new_self_ty(
2118 param_env: ty::ParamEnv<'tcx>,
2119 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
2120 ) -> PredicateObligation<'tcx> {
2122 trait_ref_and_ty.map_bound(|(tr, new_self_ty)| tr.with_self_ty(self.tcx, new_self_ty));
2124 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, trait_pred)
2127 #[instrument(skip(self), level = "debug")]
2128 fn maybe_report_ambiguity(
2130 obligation: &PredicateObligation<'tcx>,
2131 body_id: Option<hir::BodyId>,
2133 // Unable to successfully determine, probably means
2134 // insufficient type information, but could mean
2135 // ambiguous impls. The latter *ought* to be a
2136 // coherence violation, so we don't report it here.
2138 let predicate = self.resolve_vars_if_possible(obligation.predicate);
2139 let span = obligation.cause.span;
2141 debug!(?predicate, obligation.cause.code = ?obligation.cause.code());
2143 // Ambiguity errors are often caused as fallout from earlier errors.
2144 // We ignore them if this `infcx` is tainted in some cases below.
2146 let bound_predicate = predicate.kind();
2147 let mut err = match bound_predicate.skip_binder() {
2148 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
2149 let trait_ref = bound_predicate.rebind(data.trait_ref);
2152 if predicate.references_error() {
2156 // This is kind of a hack: it frequently happens that some earlier
2157 // error prevents types from being fully inferred, and then we get
2158 // a bunch of uninteresting errors saying something like "<generic
2159 // #0> doesn't implement Sized". It may even be true that we
2160 // could just skip over all checks where the self-ty is an
2161 // inference variable, but I was afraid that there might be an
2162 // inference variable created, registered as an obligation, and
2163 // then never forced by writeback, and hence by skipping here we'd
2164 // be ignoring the fact that we don't KNOW the type works
2165 // out. Though even that would probably be harmless, given that
2166 // we're only talking about builtin traits, which are known to be
2167 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2168 // avoid inundating the user with unnecessary errors, but we now
2169 // check upstream for type errors and don't add the obligations to
2170 // begin with in those cases.
2171 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
2172 if let None = self.tainted_by_errors() {
2173 self.emit_inference_failure_err(
2176 trait_ref.self_ty().skip_binder().into(),
2185 // Typically, this ambiguity should only happen if
2186 // there are unresolved type inference variables
2187 // (otherwise it would suggest a coherence
2188 // failure). But given #21974 that is not necessarily
2189 // the case -- we can have multiple where clauses that
2190 // are only distinguished by a region, which results
2191 // in an ambiguity even when all types are fully
2192 // known, since we don't dispatch based on region
2195 // Pick the first substitution that still contains inference variables as the one
2196 // we're going to emit an error for. If there are none (see above), fall back to
2197 // a more general error.
2198 let subst = data.trait_ref.substs.iter().find(|s| s.has_non_region_infer());
2200 let mut err = if let Some(subst) = subst {
2201 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2207 "type annotations needed: cannot satisfy `{}`",
2212 let obligation = obligation.with(self.tcx, trait_ref);
2213 let mut selcx = SelectionContext::new(&self);
2214 match selcx.select_from_obligation(&obligation) {
2217 ambiguity::recompute_applicable_impls(self.infcx, &obligation);
2218 let has_non_region_infer =
2219 trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_infer());
2220 // It doesn't make sense to talk about applicable impls if there are more
2221 // than a handful of them.
2222 if ambiguities.len() > 1 && ambiguities.len() < 10 && has_non_region_infer {
2223 if self.tainted_by_errors().is_some() && subst.is_none() {
2224 // If `subst.is_none()`, then this is probably two param-env
2225 // candidates or impl candidates that are equal modulo lifetimes.
2226 // Therefore, if we've already emitted an error, just skip this
2227 // one, since it's not particularly actionable.
2231 self.annotate_source_of_ambiguity(&mut err, &ambiguities, predicate);
2233 if self.tainted_by_errors().is_some() {
2237 err.note(&format!("cannot satisfy `{}`", predicate));
2238 let impl_candidates = self.find_similar_impl_candidates(
2239 predicate.to_opt_poly_trait_pred().unwrap(),
2241 if impl_candidates.len() < 10 {
2242 self.report_similar_impl_candidates(
2245 body_id.map(|id| id.hir_id).unwrap_or(obligation.cause.body_id),
2253 if self.tainted_by_errors().is_some() {
2257 err.note(&format!("cannot satisfy `{}`", predicate));
2261 if let ObligationCauseCode::ItemObligation(def_id)
2262 | ObligationCauseCode::ExprItemObligation(def_id, ..) = *obligation.cause.code()
2264 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2267 if let (Some(body_id), Some(ty::subst::GenericArgKind::Type(_))) =
2268 (body_id, subst.map(|subst| subst.unpack()))
2270 struct FindExprBySpan<'hir> {
2272 result: Option<&'hir hir::Expr<'hir>>,
2275 impl<'v> hir::intravisit::Visitor<'v> for FindExprBySpan<'v> {
2276 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2277 if self.span == ex.span {
2278 self.result = Some(ex);
2280 hir::intravisit::walk_expr(self, ex);
2285 let mut expr_finder = FindExprBySpan { span, result: None };
2287 expr_finder.visit_expr(&self.tcx.hir().body(body_id).value);
2289 if let Some(hir::Expr {
2290 kind: hir::ExprKind::Path(hir::QPath::Resolved(None, path)), .. }
2291 ) = expr_finder.result
2294 trait_path_segment @ hir::PathSegment {
2295 res: rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id),
2299 ident: assoc_item_name,
2300 res: rustc_hir::def::Res::Def(_, item_id),
2304 && data.trait_ref.def_id == *trait_id
2305 && self.tcx.trait_of_item(*item_id) == Some(*trait_id)
2306 && let None = self.tainted_by_errors()
2308 let (verb, noun) = match self.tcx.associated_item(item_id).kind {
2309 ty::AssocKind::Const => ("refer to the", "constant"),
2310 ty::AssocKind::Fn => ("call", "function"),
2311 ty::AssocKind::Type => ("refer to the", "type"), // this is already covered by E0223, but this single match arm doesn't hurt here
2314 // Replace the more general E0283 with a more specific error
2316 err = self.tcx.sess.struct_span_err_with_code(
2319 "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type",
2321 rustc_errors::error_code!(E0790),
2324 if let Some(local_def_id) = data.trait_ref.def_id.as_local()
2325 && 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)
2326 && let Some(method_ref) = trait_item_refs.iter().find(|item_ref| item_ref.ident == *assoc_item_name) {
2327 err.span_label(method_ref.span, format!("`{}::{}` defined here", trait_name, assoc_item_name));
2330 err.span_label(span, format!("cannot {verb} associated {noun} of trait"));
2332 let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
2334 if trait_impls.blanket_impls().is_empty()
2335 && let Some(impl_def_id) = trait_impls.non_blanket_impls().values().flatten().next()
2337 let non_blanket_impl_count = trait_impls.non_blanket_impls().values().flatten().count();
2338 let message = if non_blanket_impl_count == 1 {
2339 "use the fully-qualified path to the only available implementation".to_string()
2342 "use a fully-qualified path to a specific available implementation ({} found)",
2343 non_blanket_impl_count
2346 let mut suggestions = vec![(
2347 path.span.shrink_to_lo(),
2348 format!("<{} as ", self.tcx.type_of(impl_def_id))
2350 if let Some(generic_arg) = trait_path_segment.args {
2351 let between_span = trait_path_segment.ident.span.between(generic_arg.span_ext);
2352 // get rid of :: between Trait and <type>
2353 // must be '::' between them, otherwise the parser won't accept the code
2354 suggestions.push((between_span, "".to_string(),));
2355 suggestions.push((generic_arg.span_ext.shrink_to_hi(), ">".to_string()));
2357 suggestions.push((trait_path_segment.ident.span.shrink_to_hi(), ">".to_string()));
2359 err.multipart_suggestion(
2362 Applicability::MaybeIncorrect
2371 ty::PredicateKind::WellFormed(arg) => {
2372 // Same hacky approach as above to avoid deluging user
2373 // with error messages.
2374 if arg.references_error()
2375 || self.tcx.sess.has_errors().is_some()
2376 || self.tainted_by_errors().is_some()
2381 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2384 ty::PredicateKind::Subtype(data) => {
2385 if data.references_error()
2386 || self.tcx.sess.has_errors().is_some()
2387 || self.tainted_by_errors().is_some()
2389 // no need to overload user in such cases
2392 let SubtypePredicate { a_is_expected: _, a, b } = data;
2393 // both must be type variables, or the other would've been instantiated
2394 assert!(a.is_ty_var() && b.is_ty_var());
2395 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2397 ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
2398 if predicate.references_error() || self.tainted_by_errors().is_some() {
2405 .chain(Some(data.term.into_arg()))
2406 .find(|g| g.has_non_region_infer());
2407 if let Some(subst) = subst {
2408 let mut err = self.emit_inference_failure_err(
2415 err.note(&format!("cannot satisfy `{}`", predicate));
2418 // If we can't find a substitution, just print a generic error
2419 let mut err = struct_span_err!(
2423 "type annotations needed: cannot satisfy `{}`",
2426 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2431 ty::PredicateKind::ConstEvaluatable(data) => {
2432 if predicate.references_error() || self.tainted_by_errors().is_some() {
2435 let subst = data.walk().find(|g| g.is_non_region_infer());
2436 if let Some(subst) = subst {
2437 let err = self.emit_inference_failure_err(
2446 // If we can't find a substitution, just print a generic error
2447 let mut err = struct_span_err!(
2451 "type annotations needed: cannot satisfy `{}`",
2454 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2459 if self.tcx.sess.has_errors().is_some() || self.tainted_by_errors().is_some() {
2462 let mut err = struct_span_err!(
2466 "type annotations needed: cannot satisfy `{}`",
2469 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2473 self.note_obligation_cause(&mut err, obligation);
2477 fn annotate_source_of_ambiguity(
2479 err: &mut Diagnostic,
2480 ambiguities: &[ambiguity::Ambiguity],
2481 predicate: ty::Predicate<'tcx>,
2483 let mut spans = vec![];
2484 let mut crates = vec![];
2485 let mut post = vec![];
2486 let mut has_param_env = false;
2487 for ambiguity in ambiguities {
2489 ambiguity::Ambiguity::DefId(impl_def_id) => {
2490 match self.tcx.span_of_impl(*impl_def_id) {
2491 Ok(span) => spans.push(span),
2494 if let Some(header) = to_pretty_impl_header(self.tcx, *impl_def_id) {
2500 ambiguity::Ambiguity::ParamEnv(span) => {
2501 has_param_env = true;
2506 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2508 crate_names.dedup();
2512 if self.tainted_by_errors().is_some()
2513 && (crate_names.len() == 1
2515 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2516 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2518 // Avoid complaining about other inference issues for expressions like
2519 // `42 >> 1`, where the types are still `{integer}`, but we want to
2520 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2521 // NOTE(eddyb) this was `.cancel()`, but `err`
2522 // is borrowed, so we can't fully defuse it.
2523 err.downgrade_to_delayed_bug();
2528 "multiple `impl`s{} satisfying `{}` found",
2529 if has_param_env { " or `where` clauses" } else { "" },
2532 let post = if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2533 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2534 } else if post.len() == 1 {
2535 format!(": `{}`", post[0])
2540 match (spans.len(), crates.len(), crate_names.len()) {
2542 err.note(&format!("cannot satisfy `{}`", predicate));
2545 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2549 "{} in the following crates: {}{}",
2551 crate_names.join(", "),
2556 let span: MultiSpan = spans.into();
2557 err.span_note(span, &msg);
2560 let span: MultiSpan = spans.into();
2561 err.span_note(span, &msg);
2563 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2567 let span: MultiSpan = spans.into();
2568 err.span_note(span, &msg);
2570 "and more `impl`s found in the following crates: {}{}",
2571 crate_names.join(", "),
2578 /// Returns `true` if the trait predicate may apply for *some* assignment
2579 /// to the type parameters.
2580 fn predicate_can_apply(
2582 param_env: ty::ParamEnv<'tcx>,
2583 pred: ty::PolyTraitPredicate<'tcx>,
2585 struct ParamToVarFolder<'a, 'tcx> {
2586 infcx: &'a InferCtxt<'tcx>,
2587 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2590 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2591 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2595 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2596 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2597 let infcx = self.infcx;
2598 *self.var_map.entry(ty).or_insert_with(|| {
2599 infcx.next_ty_var(TypeVariableOrigin {
2600 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2605 ty.super_fold_with(self)
2612 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2614 let InferOk { value: cleaned_pred, .. } =
2615 self.infcx.at(&ObligationCause::dummy(), param_env).normalize(cleaned_pred);
2618 Obligation::new(self.tcx, ObligationCause::dummy(), param_env, cleaned_pred);
2620 self.predicate_may_hold(&obligation)
2624 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2625 // First, attempt to add note to this error with an async-await-specific
2626 // message, and fall back to regular note otherwise.
2627 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2628 self.note_obligation_cause_code(
2630 obligation.predicate,
2631 obligation.param_env,
2632 obligation.cause.code(),
2634 &mut Default::default(),
2636 self.suggest_unsized_bound_if_applicable(err, obligation);
2640 #[instrument(level = "debug", skip_all)]
2641 fn suggest_unsized_bound_if_applicable(
2643 err: &mut Diagnostic,
2644 obligation: &PredicateObligation<'tcx>,
2646 let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = obligation.predicate.kind().skip_binder() else { return; };
2647 let (ObligationCauseCode::BindingObligation(item_def_id, span)
2648 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..))
2649 = *obligation.cause.code().peel_derives() else { return; };
2650 debug!(?pred, ?item_def_id, ?span);
2652 let (Some(node), true) = (
2653 self.tcx.hir().get_if_local(item_def_id),
2654 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2658 self.maybe_suggest_unsized_generics(err, span, node);
2661 #[instrument(level = "debug", skip_all)]
2662 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>) {
2663 let Some(generics) = node.generics() else {
2666 let sized_trait = self.tcx.lang_items().sized_trait();
2667 debug!(?generics.params);
2668 debug!(?generics.predicates);
2669 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2672 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2673 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2674 let explicitly_sized = generics
2675 .bounds_for_param(param.def_id)
2676 .flat_map(|bp| bp.bounds)
2677 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2678 if explicitly_sized {
2685 // Only suggest indirection for uses of type parameters in ADTs.
2687 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2691 if self.maybe_indirection_for_unsized(err, item, param) {
2697 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2698 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param.def_id)
2702 (span.shrink_to_hi(), ":")
2704 err.span_suggestion_verbose(
2706 "consider relaxing the implicit `Sized` restriction",
2707 format!("{} ?Sized", separator),
2708 Applicability::MachineApplicable,
2712 fn maybe_indirection_for_unsized(
2714 err: &mut Diagnostic,
2716 param: &GenericParam<'tcx>,
2718 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2719 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2720 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2722 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2723 visitor.visit_item(item);
2724 if visitor.invalid_spans.is_empty() {
2727 let mut multispan: MultiSpan = param.span.into();
2728 multispan.push_span_label(
2730 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2732 for sp in visitor.invalid_spans {
2733 multispan.push_span_label(
2735 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2741 "you could relax the implicit `Sized` bound on `{T}` if it were \
2742 used through indirection like `&{T}` or `Box<{T}>`",
2743 T = param.name.ident(),
2749 fn is_recursive_obligation(
2751 obligated_types: &mut Vec<Ty<'tcx>>,
2752 cause_code: &ObligationCauseCode<'tcx>,
2754 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2755 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2756 let self_ty = parent_trait_ref.skip_binder().self_ty();
2757 if obligated_types.iter().any(|ot| ot == &self_ty) {
2760 if let ty::Adt(def, substs) = self_ty.kind()
2761 && let [arg] = &substs[..]
2762 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2763 && let ty::Adt(inner_def, _) = ty.kind()
2773 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2774 /// `param: ?Sized` would be a valid constraint.
2775 struct FindTypeParam {
2776 param: rustc_span::Symbol,
2777 invalid_spans: Vec<Span>,
2781 impl<'v> Visitor<'v> for FindTypeParam {
2782 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2783 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2786 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2787 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2788 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2789 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2790 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2791 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2792 // in that case should make what happened clear enough.
2794 hir::TyKind::Ptr(_) | hir::TyKind::Ref(..) | hir::TyKind::TraitObject(..) => {}
2795 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2796 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2799 debug!(?ty, "FindTypeParam::visit_ty");
2800 self.invalid_spans.push(ty.span);
2803 hir::TyKind::Path(_) => {
2804 let prev = self.nested;
2806 hir::intravisit::walk_ty(self, ty);
2810 hir::intravisit::walk_ty(self, ty);
2816 /// Summarizes information
2819 /// An argument of non-tuple type. Parameters are (name, ty)
2820 Arg(String, String),
2822 /// An argument of tuple type. For a "found" argument, the span is
2823 /// the location in the source of the pattern. For an "expected"
2824 /// argument, it will be None. The vector is a list of (name, ty)
2825 /// strings for the components of the tuple.
2826 Tuple(Option<Span>, Vec<(String, String)>),
2830 fn empty() -> ArgKind {
2831 ArgKind::Arg("_".to_owned(), "_".to_owned())
2834 /// Creates an `ArgKind` from the expected type of an
2835 /// argument. It has no name (`_`) and an optional source span.
2836 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2838 ty::Tuple(tys) => ArgKind::Tuple(
2840 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2842 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2847 struct HasNumericInferVisitor;
2849 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2852 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2853 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2854 ControlFlow::Break(())
2856 ControlFlow::CONTINUE
2861 pub enum DefIdOrName {