1 pub mod on_unimplemented;
5 EvaluationResult, FulfillmentContext, FulfillmentError, FulfillmentErrorCode,
6 MismatchedProjectionTypes, Obligation, ObligationCause, ObligationCauseCode,
7 OnUnimplementedDirective, OnUnimplementedNote, OutputTypeParameterMismatch, Overflow,
8 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, TyCtxtInferExt};
14 use rustc_data_structures::fx::FxHashMap;
16 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
20 use rustc_hir::def_id::DefId;
21 use rustc_hir::intravisit::Visitor;
22 use rustc_hir::GenericParam;
25 use rustc_infer::traits::TraitEngine;
26 use rustc_middle::traits::select::OverflowError;
27 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
28 use rustc_middle::ty::error::ExpectedFound;
29 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
30 use rustc_middle::ty::{
31 self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
34 use rustc_span::symbol::{kw, sym};
35 use rustc_span::{ExpnKind, Span, DUMMY_SP};
38 use std::ops::ControlFlow;
40 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
41 use crate::traits::query::normalize::AtExt as _;
42 use crate::traits::specialize::to_pretty_impl_header;
43 use on_unimplemented::InferCtxtExt as _;
44 use suggestions::InferCtxtExt as _;
46 pub use rustc_infer::traits::error_reporting::*;
48 // When outputting impl candidates, prefer showing those that are more similar.
50 // We also compare candidates after skipping lifetimes, which has a lower
51 // priority than exact matches.
52 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
53 pub enum CandidateSimilarity {
54 Exact { ignoring_lifetimes: bool },
55 Fuzzy { ignoring_lifetimes: bool },
58 #[derive(Debug, Clone, Copy)]
59 pub struct ImplCandidate<'tcx> {
60 pub trait_ref: ty::TraitRef<'tcx>,
61 pub similarity: CandidateSimilarity,
64 pub trait InferCtxtExt<'tcx> {
65 fn report_fulfillment_errors(
67 errors: &[FulfillmentError<'tcx>],
68 body_id: Option<hir::BodyId>,
69 fallback_has_occurred: bool,
72 fn report_overflow_error<T>(
74 obligation: &Obligation<'tcx, T>,
75 suggest_increasing_limit: bool,
78 T: fmt::Display + TypeFoldable<'tcx>;
80 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
82 /// The `root_obligation` parameter should be the `root_obligation` field
83 /// from a `FulfillmentError`. If no `FulfillmentError` is available,
84 /// then it should be the same as `obligation`.
85 fn report_selection_error(
87 obligation: PredicateObligation<'tcx>,
88 root_obligation: &PredicateObligation<'tcx>,
89 error: &SelectionError<'tcx>,
90 fallback_has_occurred: bool,
93 /// Given some node representing a fn-like thing in the HIR map,
94 /// returns a span and `ArgKind` information that describes the
95 /// arguments it expects. This can be supplied to
96 /// `report_arg_count_mismatch`.
97 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)>;
99 /// Reports an error when the number of arguments needed by a
100 /// trait match doesn't match the number that the expression
102 fn report_arg_count_mismatch(
105 found_span: Option<Span>,
106 expected_args: Vec<ArgKind>,
107 found_args: Vec<ArgKind>,
109 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
111 /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
112 /// in that order, and returns the generic type corresponding to the
113 /// argument of that trait (corresponding to the closure arguments).
114 fn type_implements_fn_trait(
116 param_env: ty::ParamEnv<'tcx>,
117 ty: ty::Binder<'tcx, Ty<'tcx>>,
118 constness: ty::BoundConstness,
119 polarity: ty::ImplPolarity,
120 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
123 impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
124 fn report_fulfillment_errors(
126 errors: &[FulfillmentError<'tcx>],
127 body_id: Option<hir::BodyId>,
128 fallback_has_occurred: bool,
129 ) -> ErrorGuaranteed {
131 struct ErrorDescriptor<'tcx> {
132 predicate: ty::Predicate<'tcx>,
133 index: Option<usize>, // None if this is an old error
136 let mut error_map: FxHashMap<_, Vec<_>> = self
137 .reported_trait_errors
140 .map(|(&span, predicates)| {
145 .map(|&predicate| ErrorDescriptor { predicate, index: None })
151 for (index, error) in errors.iter().enumerate() {
152 // We want to ignore desugarings here: spans are equivalent even
153 // if one is the result of a desugaring and the other is not.
154 let mut span = error.obligation.cause.span;
155 let expn_data = span.ctxt().outer_expn_data();
156 if let ExpnKind::Desugaring(_) = expn_data.kind {
157 span = expn_data.call_site;
160 error_map.entry(span).or_default().push(ErrorDescriptor {
161 predicate: error.obligation.predicate,
165 self.reported_trait_errors
169 .push(error.obligation.predicate);
172 // We do this in 2 passes because we want to display errors in order, though
173 // maybe it *is* better to sort errors by span or something.
174 let mut is_suppressed = vec![false; errors.len()];
175 for (_, error_set) in error_map.iter() {
176 // We want to suppress "duplicate" errors with the same span.
177 for error in error_set {
178 if let Some(index) = error.index {
179 // Suppress errors that are either:
180 // 1) strictly implied by another error.
181 // 2) implied by an error with a smaller index.
182 for error2 in error_set {
183 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
184 // Avoid errors being suppressed by already-suppressed
185 // errors, to prevent all errors from being suppressed
190 if self.error_implies(error2.predicate, error.predicate)
191 && !(error2.index >= error.index
192 && self.error_implies(error.predicate, error2.predicate))
194 info!("skipping {:?} (implied by {:?})", error, error2);
195 is_suppressed[index] = true;
203 for (error, suppressed) in iter::zip(errors, is_suppressed) {
205 self.report_fulfillment_error(error, body_id, fallback_has_occurred);
209 self.tcx.sess.delay_span_bug(DUMMY_SP, "expected fullfillment errors")
212 /// Reports that an overflow has occurred and halts compilation. We
213 /// halt compilation unconditionally because it is important that
214 /// overflows never be masked -- they basically represent computations
215 /// whose result could not be truly determined and thus we can't say
216 /// if the program type checks or not -- and they are unusual
217 /// occurrences in any case.
218 fn report_overflow_error<T>(
220 obligation: &Obligation<'tcx, T>,
221 suggest_increasing_limit: bool,
224 T: fmt::Display + TypeFoldable<'tcx>,
226 let predicate = self.resolve_vars_if_possible(obligation.predicate.clone());
227 let mut err = struct_span_err!(
229 obligation.cause.span,
231 "overflow evaluating the requirement `{}`",
235 if suggest_increasing_limit {
236 self.suggest_new_overflow_limit(&mut err);
239 self.note_obligation_cause_code(
241 &obligation.predicate,
242 obligation.param_env,
243 obligation.cause.code(),
245 &mut Default::default(),
249 self.tcx.sess.abort_if_errors();
253 /// Reports that a cycle was detected which led to overflow and halts
254 /// compilation. This is equivalent to `report_overflow_error` except
255 /// that we can give a more helpful error message (and, in particular,
256 /// we do not suggest increasing the overflow limit, which is not
258 fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
259 let cycle = self.resolve_vars_if_possible(cycle.to_owned());
260 assert!(!cycle.is_empty());
262 debug!(?cycle, "report_overflow_error_cycle");
264 // The 'deepest' obligation is most likely to have a useful
266 self.report_overflow_error(cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(), false);
269 fn report_selection_error(
271 mut obligation: PredicateObligation<'tcx>,
272 root_obligation: &PredicateObligation<'tcx>,
273 error: &SelectionError<'tcx>,
274 fallback_has_occurred: bool,
276 self.set_tainted_by_errors();
278 let mut span = obligation.cause.span;
280 let mut err = match *error {
281 SelectionError::Ambiguous(ref impls) => {
282 let mut err = self.tcx.sess.struct_span_err(
283 obligation.cause.span,
284 &format!("multiple applicable `impl`s for `{}`", obligation.predicate),
286 self.annotate_source_of_ambiguity(&mut err, impls, obligation.predicate);
290 SelectionError::Unimplemented => {
291 // If this obligation was generated as a result of well-formedness checking, see if we
292 // can get a better error message by performing HIR-based well-formedness checking.
293 if let ObligationCauseCode::WellFormed(Some(wf_loc)) =
294 root_obligation.cause.code().peel_derives()
296 if let Some(cause) = self
298 .diagnostic_hir_wf_check((tcx.erase_regions(obligation.predicate), *wf_loc))
300 obligation.cause = cause.clone();
301 span = obligation.cause.span;
304 if let ObligationCauseCode::CompareImplMethodObligation {
308 | ObligationCauseCode::CompareImplTypeObligation {
311 } = *obligation.cause.code()
313 self.report_extra_impl_obligation(
317 &format!("`{}`", obligation.predicate),
323 let bound_predicate = obligation.predicate.kind();
324 match bound_predicate.skip_binder() {
325 ty::PredicateKind::Trait(trait_predicate) => {
326 let trait_predicate = bound_predicate.rebind(trait_predicate);
327 let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
329 trait_predicate.remap_constness_diag(obligation.param_env);
330 let predicate_is_const = ty::BoundConstness::ConstIfConst
331 == trait_predicate.skip_binder().constness;
333 if self.tcx.sess.has_errors().is_some()
334 && trait_predicate.references_error()
338 let trait_ref = trait_predicate.to_poly_trait_ref();
339 let (post_message, pre_message, type_def) = self
340 .get_parent_trait_ref(obligation.cause.code())
343 format!(" in `{}`", t),
344 format!("within `{}`, ", t),
345 s.map(|s| (format!("within this `{}`", t), s)),
348 .unwrap_or_default();
350 let OnUnimplementedNote {
356 } = self.on_unimplemented_note(trait_ref, &obligation);
357 let have_alt_message = message.is_some() || label.is_some();
358 let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id());
360 Some(trait_ref.def_id()) == self.tcx.lang_items().unsize_trait();
361 let (message, note, append_const_msg) = if is_try_conversion {
364 "`?` couldn't convert the error to `{}`",
365 trait_ref.skip_binder().self_ty(),
368 "the question mark operation (`?`) implicitly performs a \
369 conversion on the error value using the `From` trait"
375 (message, note, append_const_msg)
378 let mut err = struct_span_err!(
384 .and_then(|cannot_do_this| {
385 match (predicate_is_const, append_const_msg) {
386 // do nothing if predicate is not const
387 (false, _) => Some(cannot_do_this),
388 // suggested using default post message
389 (true, Some(None)) => {
390 Some(format!("{cannot_do_this} in const contexts"))
392 // overridden post message
393 (true, Some(Some(post_message))) => {
394 Some(format!("{cannot_do_this}{post_message}"))
396 // fallback to generic message
397 (true, None) => None,
400 .unwrap_or_else(|| format!(
401 "the trait bound `{}` is not satisfied{}",
402 trait_predicate, post_message,
406 if is_try_conversion {
407 let none_error = self
409 .get_diagnostic_item(sym::none_error)
410 .map(|def_id| tcx.type_of(def_id));
411 let should_convert_option_to_result =
412 Some(trait_ref.skip_binder().substs.type_at(1)) == none_error;
413 let should_convert_result_to_option =
414 Some(trait_ref.self_ty().skip_binder()) == none_error;
415 if should_convert_option_to_result {
416 err.span_suggestion_verbose(
418 "consider converting the `Option<T>` into a `Result<T, _>` \
419 using `Option::ok_or` or `Option::ok_or_else`",
420 ".ok_or_else(|| /* error value */)",
421 Applicability::HasPlaceholders,
423 } else if should_convert_result_to_option {
424 err.span_suggestion_verbose(
426 "consider converting the `Result<T, _>` into an `Option<T>` \
429 Applicability::MachineApplicable,
432 if let Some(ret_span) = self.return_type_span(&obligation) {
436 "expected `{}` because of this",
437 trait_ref.skip_binder().self_ty()
443 if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
444 && predicate_is_const
446 err.note("`~const Drop` was renamed to `~const Destruct`");
447 err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
450 let explanation = if let ObligationCauseCode::MainFunctionType =
451 obligation.cause.code()
453 "consider using `()`, or a `Result`".to_owned()
456 "{}the trait `{}` is not implemented for `{}`",
458 trait_predicate.print_modifiers_and_trait_path(),
459 trait_ref.skip_binder().self_ty(),
463 if self.suggest_add_reference_to_arg(
469 self.note_obligation_cause(&mut err, &obligation);
473 if let Some(ref s) = label {
474 // If it has a custom `#[rustc_on_unimplemented]`
475 // error message, let's display it as the label!
476 err.span_label(span, s);
477 if !matches!(trait_ref.skip_binder().self_ty().kind(), ty::Param(_)) {
478 // When the self type is a type param We don't need to "the trait
479 // `std::marker::Sized` is not implemented for `T`" as we will point
480 // at the type param with a label to suggest constraining it.
481 err.help(&explanation);
484 err.span_label(span, explanation);
487 if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
488 Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
489 self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
492 if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
493 let non_const_predicate = trait_ref.without_const();
494 let non_const_obligation = Obligation {
495 cause: obligation.cause.clone(),
496 param_env: obligation.param_env.without_const(),
497 predicate: non_const_predicate.to_predicate(tcx),
498 recursion_depth: obligation.recursion_depth,
500 if self.predicate_may_hold(&non_const_obligation) {
504 "the trait `{}` is implemented for `{}`, \
505 but that implementation is not `const`",
506 non_const_predicate.print_modifiers_and_trait_path(),
507 trait_ref.skip_binder().self_ty(),
513 if let Some((msg, span)) = type_def {
514 err.span_label(span, &msg);
516 if let Some(ref s) = note {
517 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
518 err.note(s.as_str());
520 if let Some(ref s) = enclosing_scope {
523 .opt_local_def_id(obligation.cause.body_id)
525 tcx.hir().body_owner_def_id(hir::BodyId {
526 hir_id: obligation.cause.body_id,
530 let enclosing_scope_span =
531 tcx.hir().span_with_body(tcx.hir().local_def_id_to_hir_id(body));
533 err.span_label(enclosing_scope_span, s);
536 self.suggest_floating_point_literal(&obligation, &mut err, &trait_ref);
538 self.suggest_dereferences(&obligation, &mut err, trait_predicate);
539 suggested |= self.suggest_fn_call(&obligation, &mut err, trait_predicate);
541 self.suggest_remove_reference(&obligation, &mut err, trait_predicate);
542 suggested |= self.suggest_semicolon_removal(
548 self.note_version_mismatch(&mut err, &trait_ref);
549 self.suggest_remove_await(&obligation, &mut err);
550 self.suggest_derive(&obligation, &mut err, trait_predicate);
552 if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
553 self.suggest_await_before_try(
561 if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
567 // If the obligation failed due to a missing implementation of the
568 // `Unsize` trait, give a pointer to why that might be the case
570 "all implementations of `Unsize` are provided \
571 automatically by the compiler, see \
572 <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> \
573 for more information",
578 self.tcx.lang_items().fn_trait(),
579 self.tcx.lang_items().fn_mut_trait(),
580 self.tcx.lang_items().fn_once_trait(),
582 .contains(&Some(trait_ref.def_id()));
583 let is_target_feature_fn = if let ty::FnDef(def_id, _) =
584 *trait_ref.skip_binder().self_ty().kind()
586 !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
590 if is_fn_trait && is_target_feature_fn {
592 "`#[target_feature]` functions do not implement the `Fn` traits",
596 // Try to report a help message
598 && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
599 obligation.param_env,
601 trait_predicate.skip_binder().constness,
602 trait_predicate.skip_binder().polarity,
605 // If the type implements `Fn`, `FnMut`, or `FnOnce`, suppress the following
606 // suggestion to add trait bounds for the type, since we only typically implement
607 // these traits once.
609 // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
612 ty::ClosureKind::from_def_id(self.tcx, trait_ref.def_id())
613 .expect("expected to map DefId to ClosureKind");
614 if !implemented_kind.extends(selected_kind) {
617 "`{}` implements `{}`, but it must implement `{}`, which is more general",
618 trait_ref.skip_binder().self_ty(),
625 // Note any argument mismatches
626 let given_ty = params.skip_binder();
627 let expected_ty = trait_ref.skip_binder().substs.type_at(1);
628 if let ty::Tuple(given) = given_ty.kind()
629 && let ty::Tuple(expected) = expected_ty.kind()
631 if expected.len() != given.len() {
632 // Note number of types that were expected and given
635 "expected a closure taking {} argument{}, but one taking {} argument{} was given",
637 if given.len() == 1 { "" } else { "s" },
639 if expected.len() == 1 { "" } else { "s" },
642 } else if !self.same_type_modulo_infer(given_ty, expected_ty) {
643 // Print type mismatch
644 let (expected_args, given_args) =
645 self.cmp(given_ty, expected_ty);
646 err.note_expected_found(
647 &"a closure with arguments",
649 &"a closure with arguments",
654 } else if !trait_ref.has_infer_types_or_consts()
655 && self.predicate_can_apply(obligation.param_env, trait_ref)
657 // If a where-clause may be useful, remind the
658 // user that they can add it.
660 // don't display an on-unimplemented note, as
661 // these notes will often be of the form
662 // "the type `T` can't be frobnicated"
663 // which is somewhat confusing.
664 self.suggest_restricting_param_bound(
668 obligation.cause.body_id,
670 } else if !suggested {
671 // Can't show anything else useful, try to find similar impls.
672 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
673 if !self.report_similar_impl_candidates(
676 obligation.cause.body_id,
679 // This is *almost* equivalent to
680 // `obligation.cause.code().peel_derives()`, but it gives us the
681 // trait predicate for that corresponding root obligation. This
682 // lets us get a derived obligation from a type parameter, like
683 // when calling `string.strip_suffix(p)` where `p` is *not* an
684 // implementer of `Pattern<'_>`.
685 let mut code = obligation.cause.code();
686 let mut trait_pred = trait_predicate;
687 let mut peeled = false;
688 while let Some((parent_code, parent_trait_pred)) = code.parent() {
690 if let Some(parent_trait_pred) = parent_trait_pred {
691 trait_pred = parent_trait_pred;
695 let def_id = trait_pred.def_id();
696 // Mention *all* the `impl`s for the *top most* obligation, the
697 // user might have meant to use one of them, if any found. We skip
698 // auto-traits or fundamental traits that might not be exactly what
699 // the user might expect to be presented with. Instead this is
700 // useful for less general traits.
702 && !self.tcx.trait_is_auto(def_id)
703 && !self.tcx.lang_items().items().contains(&Some(def_id))
705 let trait_ref = trait_pred.to_poly_trait_ref();
706 let impl_candidates =
707 self.find_similar_impl_candidates(trait_ref);
708 self.report_similar_impl_candidates(
711 obligation.cause.body_id,
718 // Changing mutability doesn't make a difference to whether we have
719 // an `Unsize` impl (Fixes ICE in #71036)
721 self.suggest_change_mut(&obligation, &mut err, trait_predicate);
724 // If this error is due to `!: Trait` not implemented but `(): Trait` is
725 // implemented, and fallback has occurred, then it could be due to a
726 // variable that used to fallback to `()` now falling back to `!`. Issue a
727 // note informing about the change in behaviour.
728 if trait_predicate.skip_binder().self_ty().is_never()
729 && fallback_has_occurred
731 let predicate = trait_predicate.map_bound(|mut trait_pred| {
732 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
734 &trait_pred.trait_ref.substs[1..],
738 let unit_obligation = obligation.with(predicate.to_predicate(tcx));
739 if self.predicate_may_hold(&unit_obligation) {
741 "this error might have been caused by changes to \
742 Rust's type-inference algorithm (see issue #48950 \
743 <https://github.com/rust-lang/rust/issues/48950> \
744 for more information)",
746 err.help("did you intend to use the type `()` here instead?");
750 // Return early if the trait is Debug or Display and the invocation
751 // originates within a standard library macro, because the output
752 // is otherwise overwhelming and unhelpful (see #85844 for an
756 match obligation.cause.span.ctxt().outer_expn_data().macro_def_id {
757 Some(macro_def_id) => {
758 let crate_name = tcx.crate_name(macro_def_id.krate);
759 crate_name == sym::std || crate_name == sym::core
766 self.tcx.get_diagnostic_name(trait_ref.def_id()),
767 Some(sym::Debug | sym::Display)
777 ty::PredicateKind::Subtype(predicate) => {
778 // Errors for Subtype predicates show up as
779 // `FulfillmentErrorCode::CodeSubtypeError`,
780 // not selection error.
781 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
784 ty::PredicateKind::Coerce(predicate) => {
785 // Errors for Coerce predicates show up as
786 // `FulfillmentErrorCode::CodeSubtypeError`,
787 // not selection error.
788 span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
791 ty::PredicateKind::RegionOutlives(..)
792 | ty::PredicateKind::Projection(..)
793 | ty::PredicateKind::TypeOutlives(..) => {
794 let predicate = self.resolve_vars_if_possible(obligation.predicate);
799 "the requirement `{}` is not satisfied",
804 ty::PredicateKind::ObjectSafe(trait_def_id) => {
805 let violations = self.tcx.object_safety_violations(trait_def_id);
806 report_object_safety_error(self.tcx, span, trait_def_id, violations)
809 ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
810 let found_kind = self.closure_kind(closure_substs).unwrap();
811 let closure_span = self.tcx.def_span(closure_def_id);
812 let mut err = struct_span_err!(
816 "expected a closure that implements the `{}` trait, \
817 but this closure only implements `{}`",
824 format!("this closure implements `{}`, not `{}`", found_kind, kind),
827 obligation.cause.span,
828 format!("the requirement to implement `{}` derives from here", kind),
831 // Additional context information explaining why the closure only implements
832 // a particular trait.
833 if let Some(typeck_results) = self.in_progress_typeck_results {
837 .local_def_id_to_hir_id(closure_def_id.expect_local());
838 let typeck_results = typeck_results.borrow();
839 match (found_kind, typeck_results.closure_kind_origins().get(hir_id)) {
840 (ty::ClosureKind::FnOnce, Some((span, place))) => {
844 "closure is `FnOnce` because it moves the \
845 variable `{}` out of its environment",
846 ty::place_to_string_for_capture(tcx, place)
850 (ty::ClosureKind::FnMut, Some((span, place))) => {
854 "closure is `FnMut` because it mutates the \
856 ty::place_to_string_for_capture(tcx, place)
868 ty::PredicateKind::WellFormed(ty) => {
869 if !self.tcx.sess.opts.unstable_opts.chalk {
870 // WF predicates cannot themselves make
871 // errors. They can only block due to
872 // ambiguity; otherwise, they always
873 // degenerate into other obligations
875 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
877 // FIXME: we'll need a better message which takes into account
878 // which bounds actually failed to hold.
879 self.tcx.sess.struct_span_err(
881 &format!("the type `{}` is not well-formed (chalk)", ty),
886 ty::PredicateKind::ConstEvaluatable(..) => {
887 // Errors for `ConstEvaluatable` predicates show up as
888 // `SelectionError::ConstEvalFailure`,
889 // not `Unimplemented`.
892 "const-evaluatable requirement gave wrong error: `{:?}`",
897 ty::PredicateKind::ConstEquate(..) => {
898 // Errors for `ConstEquate` predicates show up as
899 // `SelectionError::ConstEvalFailure`,
900 // not `Unimplemented`.
903 "const-equate requirement gave wrong error: `{:?}`",
908 ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
910 "TypeWellFormedFromEnv predicate should only exist in the environment"
915 OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
916 let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
917 let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
919 if expected_trait_ref.self_ty().references_error() {
923 let Some(found_trait_ty) = found_trait_ref.self_ty().no_bound_vars() else {
927 let found_did = match *found_trait_ty.kind() {
931 | ty::Generator(did, ..) => Some(did),
932 ty::Adt(def, _) => Some(def.did()),
936 let found_span = found_did.and_then(|did| self.tcx.hir().span_if_local(did));
938 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
939 // We check closures twice, with obligations flowing in different directions,
940 // but we want to complain about them only once.
944 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
946 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
947 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
948 _ => vec![ArgKind::empty()],
951 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
952 let expected = match expected_ty.kind() {
953 ty::Tuple(ref tys) => {
954 tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
956 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
959 if found.len() == expected.len() {
960 self.report_closure_arg_mismatch(
967 let (closure_span, found) = found_did
969 let node = self.tcx.hir().get_if_local(did)?;
970 let (found_span, found) = self.get_fn_like_arguments(node)?;
971 Some((Some(found_span), found))
973 .unwrap_or((found_span, found));
975 self.report_arg_count_mismatch(
980 found_trait_ty.is_closure(),
985 TraitNotObjectSafe(did) => {
986 let violations = self.tcx.object_safety_violations(did);
987 report_object_safety_error(self.tcx, span, did, violations)
990 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsInfer) => {
992 "MentionsInfer should have been handled in `traits/fulfill.rs` or `traits/select/mod.rs`"
995 SelectionError::NotConstEvaluatable(NotConstEvaluatable::MentionsParam) => {
996 if !self.tcx.features().generic_const_exprs {
997 let mut err = self.tcx.sess.struct_span_err(
999 "constant expression depends on a generic parameter",
1001 // FIXME(const_generics): we should suggest to the user how they can resolve this
1002 // issue. However, this is currently not actually possible
1003 // (see https://github.com/rust-lang/rust/issues/66962#issuecomment-575907083).
1005 // Note that with `feature(generic_const_exprs)` this case should not
1007 err.note("this may fail depending on what value the parameter takes");
1012 match obligation.predicate.kind().skip_binder() {
1013 ty::PredicateKind::ConstEvaluatable(uv) => {
1015 self.tcx.sess.struct_span_err(span, "unconstrained generic constant");
1016 let const_span = self.tcx.def_span(uv.def.did);
1017 match self.tcx.sess.source_map().span_to_snippet(const_span) {
1018 Ok(snippet) => err.help(&format!(
1019 "try adding a `where` bound using this expression: `where [(); {}]:`",
1022 _ => err.help("consider adding a `where` bound using this expression"),
1029 "unexpected non-ConstEvaluatable predicate, this should not be reachable"
1035 // Already reported in the query.
1036 SelectionError::NotConstEvaluatable(NotConstEvaluatable::Error(_)) => {
1037 // FIXME(eddyb) remove this once `ErrorGuaranteed` becomes a proof token.
1038 self.tcx.sess.delay_span_bug(span, "`ErrorGuaranteed` without an error");
1041 // Already reported.
1042 Overflow(OverflowError::Error(_)) => {
1043 self.tcx.sess.delay_span_bug(span, "`OverflowError` has been reported");
1047 bug!("overflow should be handled before the `report_selection_error` path");
1049 SelectionError::ErrorReporting => {
1050 bug!("ErrorReporting Overflow should not reach `report_selection_err` call")
1054 self.note_obligation_cause(&mut err, &obligation);
1055 self.point_at_returns_when_relevant(&mut err, &obligation);
1060 /// Given some node representing a fn-like thing in the HIR map,
1061 /// returns a span and `ArgKind` information that describes the
1062 /// arguments it expects. This can be supplied to
1063 /// `report_arg_count_mismatch`.
1064 fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
1065 let sm = self.tcx.sess.source_map();
1066 let hir = self.tcx.hir();
1068 Node::Expr(&hir::Expr {
1069 kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }),
1077 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
1080 Some(ArgKind::Tuple(
1084 sm.span_to_snippet(pat.span)
1086 .map(|snippet| (snippet, "_".to_owned()))
1088 .collect::<Option<Vec<_>>>()?,
1091 let name = sm.span_to_snippet(arg.pat.span).ok()?;
1092 Some(ArgKind::Arg(name, "_".to_owned()))
1095 .collect::<Option<Vec<ArgKind>>>()?,
1097 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
1098 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
1099 | Node::TraitItem(&hir::TraitItem {
1100 kind: hir::TraitItemKind::Fn(ref sig, _), ..
1106 .map(|arg| match arg.kind {
1107 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
1109 vec![("_".to_owned(), "_".to_owned()); tys.len()],
1111 _ => ArgKind::empty(),
1113 .collect::<Vec<ArgKind>>(),
1115 Node::Ctor(ref variant_data) => {
1116 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
1117 (span, vec![ArgKind::empty(); variant_data.fields().len()])
1119 _ => panic!("non-FnLike node found: {:?}", node),
1123 /// Reports an error when the number of arguments needed by a
1124 /// trait match doesn't match the number that the expression
1126 fn report_arg_count_mismatch(
1129 found_span: Option<Span>,
1130 expected_args: Vec<ArgKind>,
1131 found_args: Vec<ArgKind>,
1133 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1134 let kind = if is_closure { "closure" } else { "function" };
1136 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
1137 let arg_length = arguments.len();
1138 let distinct = matches!(other, &[ArgKind::Tuple(..)]);
1139 match (arg_length, arguments.get(0)) {
1140 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
1141 format!("a single {}-tuple as argument", fields.len())
1146 if distinct && arg_length > 1 { "distinct " } else { "" },
1147 pluralize!(arg_length)
1152 let expected_str = args_str(&expected_args, &found_args);
1153 let found_str = args_str(&found_args, &expected_args);
1155 let mut err = struct_span_err!(
1159 "{} is expected to take {}, but it takes {}",
1165 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
1167 if let Some(found_span) = found_span {
1168 err.span_label(found_span, format!("takes {}", found_str));
1171 // ^^^^^^^^-- def_span
1175 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
1179 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
1181 // Suggest to take and ignore the arguments with expected_args_length `_`s if
1182 // found arguments is empty (assume the user just wants to ignore args in this case).
1183 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
1184 if found_args.is_empty() && is_closure {
1185 let underscores = vec!["_"; expected_args.len()].join(", ");
1186 err.span_suggestion_verbose(
1189 "consider changing the closure to take and ignore the expected argument{}",
1190 pluralize!(expected_args.len())
1192 format!("|{}|", underscores),
1193 Applicability::MachineApplicable,
1197 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
1198 if fields.len() == expected_args.len() {
1201 .map(|(name, _)| name.to_owned())
1202 .collect::<Vec<String>>()
1204 err.span_suggestion_verbose(
1206 "change the closure to take multiple arguments instead of a single tuple",
1207 format!("|{}|", sugg),
1208 Applicability::MachineApplicable,
1212 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
1213 && fields.len() == found_args.len()
1220 .map(|arg| match arg {
1221 ArgKind::Arg(name, _) => name.to_owned(),
1222 _ => "_".to_owned(),
1224 .collect::<Vec<String>>()
1226 // add type annotations if available
1227 if found_args.iter().any(|arg| match arg {
1228 ArgKind::Arg(_, ty) => ty != "_",
1235 .map(|(_, ty)| ty.to_owned())
1236 .collect::<Vec<String>>()
1243 err.span_suggestion_verbose(
1245 "change the closure to accept a tuple instead of individual arguments",
1247 Applicability::MachineApplicable,
1255 fn type_implements_fn_trait(
1257 param_env: ty::ParamEnv<'tcx>,
1258 ty: ty::Binder<'tcx, Ty<'tcx>>,
1259 constness: ty::BoundConstness,
1260 polarity: ty::ImplPolarity,
1261 ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
1262 self.commit_if_ok(|_| {
1263 for trait_def_id in [
1264 self.tcx.lang_items().fn_trait(),
1265 self.tcx.lang_items().fn_mut_trait(),
1266 self.tcx.lang_items().fn_once_trait(),
1268 let Some(trait_def_id) = trait_def_id else { continue };
1269 // Make a fresh inference variable so we can determine what the substitutions
1270 // of the trait are.
1271 let var = self.next_ty_var(TypeVariableOrigin {
1273 kind: TypeVariableOriginKind::MiscVariable,
1275 let substs = self.tcx.mk_substs_trait(ty.skip_binder(), &[var.into()]);
1276 let obligation = Obligation::new(
1277 ObligationCause::dummy(),
1279 ty.rebind(ty::TraitPredicate {
1280 trait_ref: ty::TraitRef::new(trait_def_id, substs),
1284 .to_predicate(self.tcx),
1286 let mut fulfill_cx = FulfillmentContext::new_in_snapshot();
1287 fulfill_cx.register_predicate_obligation(self, obligation);
1288 if fulfill_cx.select_all_or_error(self).is_empty() {
1290 ty::ClosureKind::from_def_id(self.tcx, trait_def_id)
1291 .expect("expected to map DefId to ClosureKind"),
1292 ty.rebind(self.resolve_vars_if_possible(var)),
1302 trait InferCtxtPrivExt<'hir, 'tcx> {
1303 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1304 // `error` occurring implies that `cond` occurs.
1305 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
1307 fn report_fulfillment_error(
1309 error: &FulfillmentError<'tcx>,
1310 body_id: Option<hir::BodyId>,
1311 fallback_has_occurred: bool,
1314 fn report_projection_error(
1316 obligation: &PredicateObligation<'tcx>,
1317 error: &MismatchedProjectionTypes<'tcx>,
1324 ignoring_lifetimes: bool,
1325 ) -> Option<CandidateSimilarity>;
1327 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str>;
1329 fn find_similar_impl_candidates(
1331 trait_ref: ty::PolyTraitRef<'tcx>,
1332 ) -> Vec<ImplCandidate<'tcx>>;
1334 fn report_similar_impl_candidates(
1336 impl_candidates: Vec<ImplCandidate<'tcx>>,
1337 trait_ref: ty::PolyTraitRef<'tcx>,
1338 body_id: hir::HirId,
1339 err: &mut Diagnostic,
1342 /// Gets the parent trait chain start
1343 fn get_parent_trait_ref(
1345 code: &ObligationCauseCode<'tcx>,
1346 ) -> Option<(String, Option<Span>)>;
1348 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1349 /// with the same path as `trait_ref`, a help message about
1350 /// a probable version mismatch is added to `err`
1351 fn note_version_mismatch(
1353 err: &mut Diagnostic,
1354 trait_ref: &ty::PolyTraitRef<'tcx>,
1357 /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
1360 /// For this to work, `new_self_ty` must have no escaping bound variables.
1361 fn mk_trait_obligation_with_new_self_ty(
1363 param_env: ty::ParamEnv<'tcx>,
1364 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1365 ) -> PredicateObligation<'tcx>;
1367 fn maybe_report_ambiguity(
1369 obligation: &PredicateObligation<'tcx>,
1370 body_id: Option<hir::BodyId>,
1373 fn predicate_can_apply(
1375 param_env: ty::ParamEnv<'tcx>,
1376 pred: ty::PolyTraitRef<'tcx>,
1379 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
1381 fn suggest_unsized_bound_if_applicable(
1383 err: &mut Diagnostic,
1384 obligation: &PredicateObligation<'tcx>,
1387 fn annotate_source_of_ambiguity(
1389 err: &mut Diagnostic,
1391 predicate: ty::Predicate<'tcx>,
1394 fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'hir>);
1396 fn maybe_indirection_for_unsized(
1398 err: &mut Diagnostic,
1399 item: &'hir Item<'hir>,
1400 param: &'hir GenericParam<'hir>,
1403 fn is_recursive_obligation(
1405 obligated_types: &mut Vec<Ty<'tcx>>,
1406 cause_code: &ObligationCauseCode<'tcx>,
1410 impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
1411 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
1412 // `error` occurring implies that `cond` occurs.
1413 fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
1418 // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
1419 let bound_error = error.kind();
1420 let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
1421 (ty::PredicateKind::Trait(..), ty::PredicateKind::Trait(error)) => {
1422 (cond, bound_error.rebind(error))
1425 // FIXME: make this work in other cases too.
1430 for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
1431 let bound_predicate = obligation.predicate.kind();
1432 if let ty::PredicateKind::Trait(implication) = bound_predicate.skip_binder() {
1433 let error = error.to_poly_trait_ref();
1434 let implication = bound_predicate.rebind(implication.trait_ref);
1435 // FIXME: I'm just not taking associated types at all here.
1436 // Eventually I'll need to implement param-env-aware
1437 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
1438 let param_env = ty::ParamEnv::empty();
1439 if self.can_sub(param_env, error, implication).is_ok() {
1440 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
1449 #[instrument(skip(self), level = "debug")]
1450 fn report_fulfillment_error(
1452 error: &FulfillmentError<'tcx>,
1453 body_id: Option<hir::BodyId>,
1454 fallback_has_occurred: bool,
1457 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
1458 self.report_selection_error(
1459 error.obligation.clone(),
1460 &error.root_obligation,
1462 fallback_has_occurred,
1465 FulfillmentErrorCode::CodeProjectionError(ref e) => {
1466 self.report_projection_error(&error.obligation, e);
1468 FulfillmentErrorCode::CodeAmbiguity => {
1469 self.maybe_report_ambiguity(&error.obligation, body_id);
1471 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
1472 self.report_mismatched_types(
1473 &error.obligation.cause,
1474 expected_found.expected,
1475 expected_found.found,
1480 FulfillmentErrorCode::CodeConstEquateError(ref expected_found, ref err) => {
1481 self.report_mismatched_consts(
1482 &error.obligation.cause,
1483 expected_found.expected,
1484 expected_found.found,
1492 #[instrument(level = "debug", skip_all)]
1493 fn report_projection_error(
1495 obligation: &PredicateObligation<'tcx>,
1496 error: &MismatchedProjectionTypes<'tcx>,
1498 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1500 if predicate.references_error() {
1506 let mut err = &error.err;
1507 let mut values = None;
1509 // try to find the mismatched types to report the error with.
1511 // this can fail if the problem was higher-ranked, in which
1512 // cause I have no idea for a good error message.
1513 let bound_predicate = predicate.kind();
1514 if let ty::PredicateKind::Projection(data) = bound_predicate.skip_binder() {
1515 let mut selcx = SelectionContext::new(self);
1516 let data = self.replace_bound_vars_with_fresh_vars(
1517 obligation.cause.span,
1518 infer::LateBoundRegionConversionTime::HigherRankedType,
1519 bound_predicate.rebind(data),
1521 let mut obligations = vec![];
1522 let normalized_ty = super::normalize_projection_type(
1524 obligation.param_env,
1526 obligation.cause.clone(),
1531 debug!(?obligation.cause, ?obligation.param_env);
1533 debug!(?normalized_ty, data.ty = ?data.term);
1535 let is_normalized_ty_expected = !matches!(
1536 obligation.cause.code().peel_derives(),
1537 ObligationCauseCode::ItemObligation(_)
1538 | ObligationCauseCode::BindingObligation(_, _)
1539 | ObligationCauseCode::ObjectCastObligation(..)
1540 | ObligationCauseCode::OpaqueType
1542 if let Err(error) = self.at(&obligation.cause, obligation.param_env).eq_exp(
1543 is_normalized_ty_expected,
1547 values = Some(infer::ValuePairs::Terms(ExpectedFound::new(
1548 is_normalized_ty_expected,
1557 let mut diag = struct_span_err!(
1559 obligation.cause.span,
1561 "type mismatch resolving `{}`",
1564 let secondary_span = match predicate.kind().skip_binder() {
1565 ty::PredicateKind::Projection(proj) => self
1567 .opt_associated_item(proj.projection_ty.item_def_id)
1568 .and_then(|trait_assoc_item| {
1570 .trait_of_item(proj.projection_ty.item_def_id)
1571 .map(|id| (trait_assoc_item, id))
1573 .and_then(|(trait_assoc_item, id)| {
1574 let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
1575 self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
1577 .associated_items(did)
1578 .in_definition_order()
1579 .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
1582 .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
1584 hir::Node::TraitItem(hir::TraitItem {
1585 kind: hir::TraitItemKind::Type(_, Some(ty)),
1588 | hir::Node::ImplItem(hir::ImplItem {
1589 kind: hir::ImplItemKind::TyAlias(ty),
1592 ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
1606 self.note_obligation_cause(&mut diag, obligation);
1615 ignoring_lifetimes: bool,
1616 ) -> Option<CandidateSimilarity> {
1617 /// returns the fuzzy category of a given type, or None
1618 /// if the type can be equated to any type.
1619 fn type_category(tcx: TyCtxt<'_>, t: Ty<'_>) -> Option<u32> {
1621 ty::Bool => Some(0),
1622 ty::Char => Some(1),
1624 ty::Adt(def, _) if tcx.is_diagnostic_item(sym::String, def.did()) => Some(2),
1628 | ty::Infer(ty::IntVar(..) | ty::FloatVar(..)) => Some(4),
1629 ty::Ref(..) | ty::RawPtr(..) => Some(5),
1630 ty::Array(..) | ty::Slice(..) => Some(6),
1631 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
1632 ty::Dynamic(..) => Some(8),
1633 ty::Closure(..) => Some(9),
1634 ty::Tuple(..) => Some(10),
1635 ty::Param(..) => Some(11),
1636 ty::Projection(..) => Some(12),
1637 ty::Opaque(..) => Some(13),
1638 ty::Never => Some(14),
1639 ty::Adt(..) => Some(15),
1640 ty::Generator(..) => Some(16),
1641 ty::Foreign(..) => Some(17),
1642 ty::GeneratorWitness(..) => Some(18),
1643 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => None,
1647 let strip_references = |mut t: Ty<'tcx>| -> Ty<'tcx> {
1650 ty::Ref(_, inner, _) | ty::RawPtr(ty::TypeAndMut { ty: inner, .. }) => {
1658 if !ignoring_lifetimes {
1659 a = strip_references(a);
1660 b = strip_references(b);
1663 let cat_a = type_category(self.tcx, a)?;
1664 let cat_b = type_category(self.tcx, b)?;
1666 Some(CandidateSimilarity::Exact { ignoring_lifetimes })
1667 } else if cat_a == cat_b {
1668 match (a.kind(), b.kind()) {
1669 (ty::Adt(def_a, _), ty::Adt(def_b, _)) => def_a == def_b,
1670 (ty::Foreign(def_a), ty::Foreign(def_b)) => def_a == def_b,
1671 // Matching on references results in a lot of unhelpful
1672 // suggestions, so let's just not do that for now.
1674 // We still upgrade successful matches to `ignoring_lifetimes: true`
1675 // to prioritize that impl.
1676 (ty::Ref(..) | ty::RawPtr(..), ty::Ref(..) | ty::RawPtr(..)) => {
1677 self.fuzzy_match_tys(a, b, true).is_some()
1681 .then_some(CandidateSimilarity::Fuzzy { ignoring_lifetimes })
1682 } else if ignoring_lifetimes {
1685 self.fuzzy_match_tys(a, b, true)
1689 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
1690 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
1691 hir::GeneratorKind::Gen => "a generator",
1692 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
1693 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
1694 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
1698 fn find_similar_impl_candidates(
1700 trait_ref: ty::PolyTraitRef<'tcx>,
1701 ) -> Vec<ImplCandidate<'tcx>> {
1703 .all_impls(trait_ref.def_id())
1704 .filter_map(|def_id| {
1705 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative {
1709 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
1711 self.fuzzy_match_tys(trait_ref.skip_binder().self_ty(), imp.self_ty(), false)
1712 .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
1717 fn report_similar_impl_candidates(
1719 impl_candidates: Vec<ImplCandidate<'tcx>>,
1720 trait_ref: ty::PolyTraitRef<'tcx>,
1721 body_id: hir::HirId,
1722 err: &mut Diagnostic,
1724 let report = |mut candidates: Vec<TraitRef<'tcx>>, err: &mut Diagnostic| {
1727 let len = candidates.len();
1728 if candidates.len() == 0 {
1731 if candidates.len() == 1 {
1732 err.highlighted_help(vec![
1734 format!("the trait `{}` ", candidates[0].print_only_trait_path()),
1737 ("is".to_string(), Style::Highlight),
1738 (" implemented for `".to_string(), Style::NoStyle),
1739 (candidates[0].self_ty().to_string(), Style::Highlight),
1740 ("`".to_string(), Style::NoStyle),
1744 let trait_ref = TraitRef::identity(self.tcx, candidates[0].def_id);
1745 // Check if the trait is the same in all cases. If so, we'll only show the type.
1746 let mut traits: Vec<_> =
1747 candidates.iter().map(|c| c.print_only_trait_path().to_string()).collect();
1751 let mut candidates: Vec<String> = candidates
1754 if traits.len() == 1 {
1755 format!("\n {}", c.self_ty())
1764 let end = if candidates.len() <= 9 { candidates.len() } else { 8 };
1766 "the following other types implement trait `{}`:{}{}",
1767 trait_ref.print_only_trait_path(),
1768 candidates[..end].join(""),
1769 if len > 9 { format!("\nand {} others", len - 8) } else { String::new() }
1774 let def_id = trait_ref.def_id();
1775 if impl_candidates.is_empty() {
1776 if self.tcx.trait_is_auto(def_id)
1777 || self.tcx.lang_items().items().contains(&Some(def_id))
1778 || self.tcx.get_diagnostic_name(def_id).is_some()
1780 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
1783 let normalized_impl_candidates: Vec<_> = self
1786 // Ignore automatically derived impls and `!Trait` impls.
1788 self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
1789 || self.tcx.is_builtin_derive(def_id)
1791 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
1792 .filter(|trait_ref| {
1793 let self_ty = trait_ref.self_ty();
1794 // Avoid mentioning type parameters.
1795 if let ty::Param(_) = self_ty.kind() {
1798 // Avoid mentioning types that are private to another crate
1799 else if let ty::Adt(def, _) = self_ty.peel_refs().kind() {
1800 // FIXME(compiler-errors): This could be generalized, both to
1801 // be more granular, and probably look past other `#[fundamental]`
1804 .visibility(def.did())
1805 .is_accessible_from(body_id.owner.to_def_id(), self.tcx)
1811 return report(normalized_impl_candidates, err);
1814 let normalize = |candidate| {
1815 self.tcx.infer_ctxt().enter(|ref infcx| {
1816 let normalized = infcx
1817 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
1818 .normalize(candidate)
1821 Some(normalized) => normalized.value,
1827 // Sort impl candidates so that ordering is consistent for UI tests.
1828 // because the ordering of `impl_candidates` may not be deterministic:
1829 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
1831 // Prefer more similar candidates first, then sort lexicographically
1832 // by their normalized string representation.
1833 let mut normalized_impl_candidates_and_similarities = impl_candidates
1835 .map(|ImplCandidate { trait_ref, similarity }| {
1836 let normalized = normalize(trait_ref);
1837 (similarity, normalized)
1839 .collect::<Vec<_>>();
1840 normalized_impl_candidates_and_similarities.sort();
1841 normalized_impl_candidates_and_similarities.dedup();
1843 let normalized_impl_candidates = normalized_impl_candidates_and_similarities
1845 .map(|(_, normalized)| normalized)
1846 .collect::<Vec<_>>();
1848 report(normalized_impl_candidates, err)
1851 /// Gets the parent trait chain start
1852 fn get_parent_trait_ref(
1854 code: &ObligationCauseCode<'tcx>,
1855 ) -> Option<(String, Option<Span>)> {
1857 ObligationCauseCode::BuiltinDerivedObligation(data) => {
1858 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
1859 match self.get_parent_trait_ref(&data.parent_code) {
1862 let ty = parent_trait_ref.skip_binder().self_ty();
1863 let span = TyCategory::from_ty(self.tcx, ty)
1864 .map(|(_, def_id)| self.tcx.def_span(def_id));
1865 Some((ty.to_string(), span))
1869 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
1870 self.get_parent_trait_ref(&parent_code)
1876 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1877 /// with the same path as `trait_ref`, a help message about
1878 /// a probable version mismatch is added to `err`
1879 fn note_version_mismatch(
1881 err: &mut Diagnostic,
1882 trait_ref: &ty::PolyTraitRef<'tcx>,
1884 let get_trait_impl = |trait_def_id| {
1885 self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
1887 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
1888 let traits_with_same_path: std::collections::BTreeSet<_> = self
1891 .filter(|trait_def_id| *trait_def_id != trait_ref.def_id())
1892 .filter(|trait_def_id| self.tcx.def_path_str(*trait_def_id) == required_trait_path)
1894 let mut suggested = false;
1895 for trait_with_same_path in traits_with_same_path {
1896 if let Some(impl_def_id) = get_trait_impl(trait_with_same_path) {
1897 let impl_span = self.tcx.def_span(impl_def_id);
1898 err.span_help(impl_span, "trait impl with same name found");
1899 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
1900 let crate_msg = format!(
1901 "perhaps two different versions of crate `{}` are being used?",
1904 err.note(&crate_msg);
1911 fn mk_trait_obligation_with_new_self_ty(
1913 param_env: ty::ParamEnv<'tcx>,
1914 trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
1915 ) -> PredicateObligation<'tcx> {
1916 let trait_pred = trait_ref_and_ty.map_bound_ref(|(tr, new_self_ty)| ty::TraitPredicate {
1917 trait_ref: ty::TraitRef {
1918 substs: self.tcx.mk_substs_trait(*new_self_ty, &tr.trait_ref.substs[1..]),
1924 Obligation::new(ObligationCause::dummy(), param_env, trait_pred.to_predicate(self.tcx))
1927 #[instrument(skip(self), level = "debug")]
1928 fn maybe_report_ambiguity(
1930 obligation: &PredicateObligation<'tcx>,
1931 body_id: Option<hir::BodyId>,
1933 // Unable to successfully determine, probably means
1934 // insufficient type information, but could mean
1935 // ambiguous impls. The latter *ought* to be a
1936 // coherence violation, so we don't report it here.
1938 let predicate = self.resolve_vars_if_possible(obligation.predicate);
1939 let span = obligation.cause.span;
1941 debug!(?predicate, obligation.cause.code = tracing::field::debug(&obligation.cause.code()));
1943 // Ambiguity errors are often caused as fallout from earlier errors.
1944 // We ignore them if this `infcx` is tainted in some cases below.
1946 let bound_predicate = predicate.kind();
1947 let mut err = match bound_predicate.skip_binder() {
1948 ty::PredicateKind::Trait(data) => {
1949 let trait_ref = bound_predicate.rebind(data.trait_ref);
1952 if predicate.references_error() {
1956 // This is kind of a hack: it frequently happens that some earlier
1957 // error prevents types from being fully inferred, and then we get
1958 // a bunch of uninteresting errors saying something like "<generic
1959 // #0> doesn't implement Sized". It may even be true that we
1960 // could just skip over all checks where the self-ty is an
1961 // inference variable, but I was afraid that there might be an
1962 // inference variable created, registered as an obligation, and
1963 // then never forced by writeback, and hence by skipping here we'd
1964 // be ignoring the fact that we don't KNOW the type works
1965 // out. Though even that would probably be harmless, given that
1966 // we're only talking about builtin traits, which are known to be
1967 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
1968 // avoid inundating the user with unnecessary errors, but we now
1969 // check upstream for type errors and don't add the obligations to
1970 // begin with in those cases.
1971 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
1972 if !self.is_tainted_by_errors() {
1973 self.emit_inference_failure_err(
1976 trait_ref.self_ty().skip_binder().into(),
1985 // Typically, this ambiguity should only happen if
1986 // there are unresolved type inference variables
1987 // (otherwise it would suggest a coherence
1988 // failure). But given #21974 that is not necessarily
1989 // the case -- we can have multiple where clauses that
1990 // are only distinguished by a region, which results
1991 // in an ambiguity even when all types are fully
1992 // known, since we don't dispatch based on region
1995 // Pick the first substitution that still contains inference variables as the one
1996 // we're going to emit an error for. If there are none (see above), fall back to
1997 // a more general error.
1998 let subst = data.trait_ref.substs.iter().find(|s| s.has_infer_types_or_consts());
2000 let mut err = if let Some(subst) = subst {
2001 self.emit_inference_failure_err(body_id, span, subst, ErrorCode::E0283, true)
2007 "type annotations needed: cannot satisfy `{}`",
2012 let obligation = Obligation::new(
2013 obligation.cause.clone(),
2014 obligation.param_env,
2015 trait_ref.to_poly_trait_predicate(),
2017 let mut selcx = SelectionContext::with_query_mode(
2019 crate::traits::TraitQueryMode::Standard,
2021 match selcx.select_from_obligation(&obligation) {
2022 Err(SelectionError::Ambiguous(impls)) if impls.len() > 1 => {
2023 self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
2026 if self.is_tainted_by_errors() {
2030 err.note(&format!("cannot satisfy `{}`", predicate));
2034 if let ObligationCauseCode::ItemObligation(def_id) = *obligation.cause.code() {
2035 self.suggest_fully_qualified_path(&mut err, def_id, span, trait_ref.def_id());
2038 &ObligationCauseCode::BindingObligation(def_id, _),
2040 (self.tcx.sess.source_map().span_to_snippet(span), obligation.cause.code())
2042 let generics = self.tcx.generics_of(def_id);
2043 if generics.params.iter().any(|p| p.name != kw::SelfUpper)
2044 && !snippet.ends_with('>')
2045 && !generics.has_impl_trait()
2046 && !self.tcx.fn_trait_kind_from_lang_item(def_id).is_some()
2048 // FIXME: To avoid spurious suggestions in functions where type arguments
2049 // where already supplied, we check the snippet to make sure it doesn't
2050 // end with a turbofish. Ideally we would have access to a `PathSegment`
2051 // instead. Otherwise we would produce the following output:
2053 // error[E0283]: type annotations needed
2054 // --> $DIR/issue-54954.rs:3:24
2056 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2057 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2059 // | cannot infer type
2060 // | help: consider specifying the type argument
2061 // | in the function call:
2062 // | `Tt::const_val::<[i8; 123]>::<T>`
2064 // LL | const fn const_val<T: Sized>() -> usize {
2065 // | - required by this bound in `Tt::const_val`
2067 // = note: cannot satisfy `_: Tt`
2069 // Clear any more general suggestions in favor of our specific one
2070 err.clear_suggestions();
2072 err.span_suggestion_verbose(
2073 span.shrink_to_hi(),
2075 "consider specifying the type argument{} in the function call",
2076 pluralize!(generics.params.len()),
2083 .map(|p| p.name.to_string())
2084 .collect::<Vec<String>>()
2087 Applicability::HasPlaceholders,
2092 if let (Some(body_id), Some(ty::subst::GenericArgKind::Type(_))) =
2093 (body_id, subst.map(|subst| subst.unpack()))
2095 struct FindExprBySpan<'hir> {
2097 result: Option<&'hir hir::Expr<'hir>>,
2100 impl<'v> hir::intravisit::Visitor<'v> for FindExprBySpan<'v> {
2101 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2102 if self.span == ex.span {
2103 self.result = Some(ex);
2105 hir::intravisit::walk_expr(self, ex);
2110 let mut expr_finder = FindExprBySpan { span, result: None };
2112 expr_finder.visit_expr(&self.tcx.hir().body(body_id).value);
2114 if let Some(hir::Expr {
2115 kind: hir::ExprKind::Path(hir::QPath::Resolved(None, path)), .. }
2116 ) = expr_finder.result
2119 trait_path_segment @ hir::PathSegment {
2120 res: Some(rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id)),
2124 ident: assoc_item_name,
2125 res: Some(rustc_hir::def::Res::Def(_, item_id)),
2129 && data.trait_ref.def_id == *trait_id
2130 && self.tcx.trait_of_item(item_id) == Some(*trait_id)
2131 && !self.is_tainted_by_errors()
2133 let (verb, noun) = match self.tcx.associated_item(item_id).kind {
2134 ty::AssocKind::Const => ("refer to the", "constant"),
2135 ty::AssocKind::Fn => ("call", "function"),
2136 ty::AssocKind::Type => ("refer to the", "type"), // this is already covered by E0223, but this single match arm doesn't hurt here
2139 // Replace the more general E0283 with a more specific error
2141 err = self.tcx.sess.struct_span_err_with_code(
2144 "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type",
2146 rustc_errors::error_code!(E0790),
2149 if let Some(local_def_id) = data.trait_ref.def_id.as_local()
2150 && 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)
2151 && let Some(method_ref) = trait_item_refs.iter().find(|item_ref| item_ref.ident == *assoc_item_name) {
2152 err.span_label(method_ref.span, format!("`{}::{}` defined here", trait_name, assoc_item_name));
2155 err.span_label(span, format!("cannot {verb} associated {noun} of trait"));
2157 let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
2159 if trait_impls.blanket_impls().is_empty()
2160 && let Some((impl_ty, _)) = trait_impls.non_blanket_impls().iter().next()
2161 && let Some(impl_def_id) = impl_ty.def() {
2162 let message = if trait_impls.non_blanket_impls().len() == 1 {
2163 "use the fully-qualified path to the only available implementation".to_string()
2166 "use a fully-qualified path to a specific available implementation ({} found)",
2167 trait_impls.non_blanket_impls().len()
2171 err.multipart_suggestion(
2174 (trait_path_segment.ident.span.shrink_to_lo(), format!("<{} as ", self.tcx.def_path(impl_def_id).to_string_no_crate_verbose())),
2175 (trait_path_segment.ident.span.shrink_to_hi(), format!(">"))
2177 Applicability::MaybeIncorrect
2186 ty::PredicateKind::WellFormed(arg) => {
2187 // Same hacky approach as above to avoid deluging user
2188 // with error messages.
2189 if arg.references_error()
2190 || self.tcx.sess.has_errors().is_some()
2191 || self.is_tainted_by_errors()
2196 self.emit_inference_failure_err(body_id, span, arg, ErrorCode::E0282, false)
2199 ty::PredicateKind::Subtype(data) => {
2200 if data.references_error()
2201 || self.tcx.sess.has_errors().is_some()
2202 || self.is_tainted_by_errors()
2204 // no need to overload user in such cases
2207 let SubtypePredicate { a_is_expected: _, a, b } = data;
2208 // both must be type variables, or the other would've been instantiated
2209 assert!(a.is_ty_var() && b.is_ty_var());
2210 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
2212 ty::PredicateKind::Projection(data) => {
2213 if predicate.references_error() || self.is_tainted_by_errors() {
2220 .chain(Some(data.term.into_arg()))
2221 .find(|g| g.has_infer_types_or_consts());
2222 if let Some(subst) = subst {
2223 let mut err = self.emit_inference_failure_err(
2230 err.note(&format!("cannot satisfy `{}`", predicate));
2233 // If we can't find a substitution, just print a generic error
2234 let mut err = struct_span_err!(
2238 "type annotations needed: cannot satisfy `{}`",
2241 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2246 ty::PredicateKind::ConstEvaluatable(data) => {
2247 if predicate.references_error() || self.is_tainted_by_errors() {
2250 let subst = data.substs.iter().find(|g| g.has_infer_types_or_consts());
2251 if let Some(subst) = subst {
2252 let err = self.emit_inference_failure_err(
2261 // If we can't find a substitution, just print a generic error
2262 let mut err = struct_span_err!(
2266 "type annotations needed: cannot satisfy `{}`",
2269 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2274 if self.tcx.sess.has_errors().is_some() || self.is_tainted_by_errors() {
2277 let mut err = struct_span_err!(
2281 "type annotations needed: cannot satisfy `{}`",
2284 err.span_label(span, &format!("cannot satisfy `{}`", predicate));
2288 self.note_obligation_cause(&mut err, obligation);
2292 fn annotate_source_of_ambiguity(
2294 err: &mut Diagnostic,
2296 predicate: ty::Predicate<'tcx>,
2298 let mut spans = vec![];
2299 let mut crates = vec![];
2300 let mut post = vec![];
2301 for def_id in impls {
2302 match self.tcx.span_of_impl(*def_id) {
2303 Ok(span) => spans.push(span),
2306 if let Some(header) = to_pretty_impl_header(self.tcx, *def_id) {
2312 let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
2313 let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
2315 crate_names.dedup();
2319 if self.is_tainted_by_errors()
2320 && (crate_names.len() == 1
2322 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
2323 || predicate.visit_with(&mut HasNumericInferVisitor).is_break())
2325 // Avoid complaining about other inference issues for expressions like
2326 // `42 >> 1`, where the types are still `{integer}`, but we want to
2327 // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
2328 // NOTE(eddyb) this was `.cancel()`, but `err`
2329 // is borrowed, so we can't fully defuse it.
2330 err.downgrade_to_delayed_bug();
2333 let post = if post.len() > 4 {
2335 ":\n{}\nand {} more",
2336 post.iter().map(|p| format!("- {}", p)).take(4).collect::<Vec<_>>().join("\n"),
2339 } else if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
2340 format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
2341 } else if post.len() == 1 {
2342 format!(": `{}`", post[0])
2347 match (spans.len(), crates.len(), crate_names.len()) {
2349 err.note(&format!("cannot satisfy `{}`", predicate));
2352 err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,));
2356 "{} in the following crates: {}{}",
2358 crate_names.join(", "),
2363 let span: MultiSpan = spans.into();
2364 err.span_note(span, &msg);
2367 let span: MultiSpan = spans.into();
2368 err.span_note(span, &msg);
2370 &format!("and another `impl` found in the `{}` crate{}", crates[0], post,),
2374 let span: MultiSpan = spans.into();
2375 err.span_note(span, &msg);
2377 "and more `impl`s found in the following crates: {}{}",
2378 crate_names.join(", "),
2385 /// Returns `true` if the trait predicate may apply for *some* assignment
2386 /// to the type parameters.
2387 fn predicate_can_apply(
2389 param_env: ty::ParamEnv<'tcx>,
2390 pred: ty::PolyTraitRef<'tcx>,
2392 struct ParamToVarFolder<'a, 'tcx> {
2393 infcx: &'a InferCtxt<'a, 'tcx>,
2394 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2397 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2398 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2402 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2403 if let ty::Param(ty::ParamTy { name, .. }) = *ty.kind() {
2404 let infcx = self.infcx;
2405 *self.var_map.entry(ty).or_insert_with(|| {
2406 infcx.next_ty_var(TypeVariableOrigin {
2407 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2412 ty.super_fold_with(self)
2418 let mut selcx = SelectionContext::new(self);
2421 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2423 let cleaned_pred = super::project::normalize(
2426 ObligationCause::dummy(),
2431 let obligation = Obligation::new(
2432 ObligationCause::dummy(),
2434 cleaned_pred.without_const().to_predicate(selcx.tcx()),
2437 self.predicate_may_hold(&obligation)
2441 fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>) {
2442 // First, attempt to add note to this error with an async-await-specific
2443 // message, and fall back to regular note otherwise.
2444 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2445 self.note_obligation_cause_code(
2447 &obligation.predicate,
2448 obligation.param_env,
2449 obligation.cause.code(),
2451 &mut Default::default(),
2453 self.suggest_unsized_bound_if_applicable(err, obligation);
2457 #[instrument(level = "debug", skip_all)]
2458 fn suggest_unsized_bound_if_applicable(
2460 err: &mut Diagnostic,
2461 obligation: &PredicateObligation<'tcx>,
2464 ty::PredicateKind::Trait(pred),
2465 &ObligationCauseCode::BindingObligation(item_def_id, span),
2467 obligation.predicate.kind().skip_binder(),
2468 obligation.cause.code().peel_derives(),
2472 debug!(?pred, ?item_def_id, ?span);
2474 let (Some(node), true) = (
2475 self.tcx.hir().get_if_local(item_def_id),
2476 Some(pred.def_id()) == self.tcx.lang_items().sized_trait(),
2480 self.maybe_suggest_unsized_generics(err, span, node);
2483 #[instrument(level = "debug", skip_all)]
2484 fn maybe_suggest_unsized_generics<'hir>(
2486 err: &mut Diagnostic,
2490 let Some(generics) = node.generics() else {
2493 let sized_trait = self.tcx.lang_items().sized_trait();
2494 debug!(?generics.params);
2495 debug!(?generics.predicates);
2496 let Some(param) = generics.params.iter().find(|param| param.span == span) else {
2499 let param_def_id = self.tcx.hir().local_def_id(param.hir_id);
2500 // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
2501 // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
2502 let explicitly_sized = generics
2503 .bounds_for_param(param_def_id)
2504 .flat_map(|bp| bp.bounds)
2505 .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
2506 if explicitly_sized {
2513 // Only suggest indirection for uses of type parameters in ADTs.
2515 hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) | hir::ItemKind::Union(..),
2519 if self.maybe_indirection_for_unsized(err, item, param) {
2525 // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
2526 let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param_def_id)
2530 (span.shrink_to_hi(), ":")
2532 err.span_suggestion_verbose(
2534 "consider relaxing the implicit `Sized` restriction",
2535 format!("{} ?Sized", separator),
2536 Applicability::MachineApplicable,
2540 fn maybe_indirection_for_unsized<'hir>(
2542 err: &mut Diagnostic,
2543 item: &'hir Item<'hir>,
2544 param: &'hir GenericParam<'hir>,
2546 // Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
2547 // borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
2548 // is not. Look for invalid "bare" parameter uses, and suggest using indirection.
2550 FindTypeParam { param: param.name.ident().name, invalid_spans: vec![], nested: false };
2551 visitor.visit_item(item);
2552 if visitor.invalid_spans.is_empty() {
2555 let mut multispan: MultiSpan = param.span.into();
2556 multispan.push_span_label(
2558 format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
2560 for sp in visitor.invalid_spans {
2561 multispan.push_span_label(
2563 format!("...if indirection were used here: `Box<{}>`", param.name.ident()),
2569 "you could relax the implicit `Sized` bound on `{T}` if it were \
2570 used through indirection like `&{T}` or `Box<{T}>`",
2571 T = param.name.ident(),
2577 fn is_recursive_obligation(
2579 obligated_types: &mut Vec<Ty<'tcx>>,
2580 cause_code: &ObligationCauseCode<'tcx>,
2582 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2583 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2584 let self_ty = parent_trait_ref.skip_binder().self_ty();
2585 if obligated_types.iter().any(|ot| ot == &self_ty) {
2588 if let ty::Adt(def, substs) = self_ty.kind()
2589 && let [arg] = &substs[..]
2590 && let ty::subst::GenericArgKind::Type(ty) = arg.unpack()
2591 && let ty::Adt(inner_def, _) = ty.kind()
2601 /// Look for type `param` in an ADT being used only through a reference to confirm that suggesting
2602 /// `param: ?Sized` would be a valid constraint.
2603 struct FindTypeParam {
2604 param: rustc_span::Symbol,
2605 invalid_spans: Vec<Span>,
2609 impl<'v> Visitor<'v> for FindTypeParam {
2610 fn visit_where_predicate(&mut self, _: &'v hir::WherePredicate<'v>) {
2611 // Skip where-clauses, to avoid suggesting indirection for type parameters found there.
2614 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2615 // We collect the spans of all uses of the "bare" type param, like in `field: T` or
2616 // `field: (T, T)` where we could make `T: ?Sized` while skipping cases that are known to be
2617 // valid like `field: &'a T` or `field: *mut T` and cases that *might* have further `Sized`
2618 // obligations like `Box<T>` and `Vec<T>`, but we perform no extra analysis for those cases
2619 // and suggest `T: ?Sized` regardless of their obligations. This is fine because the errors
2620 // in that case should make what happened clear enough.
2622 hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
2623 hir::TyKind::Path(hir::QPath::Resolved(None, path))
2624 if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
2627 debug!(?ty, "FindTypeParam::visit_ty");
2628 self.invalid_spans.push(ty.span);
2631 hir::TyKind::Path(_) => {
2632 let prev = self.nested;
2634 hir::intravisit::walk_ty(self, ty);
2638 hir::intravisit::walk_ty(self, ty);
2644 pub fn recursive_type_with_infinite_size_error<'tcx>(
2647 spans: Vec<(Span, Option<hir::HirId>)>,
2649 assert!(type_def_id.is_local());
2650 let span = tcx.def_span(type_def_id);
2651 let path = tcx.def_path_str(type_def_id);
2653 struct_span_err!(tcx.sess, span, E0072, "recursive type `{}` has infinite size", path);
2654 err.span_label(span, "recursive type has infinite size");
2655 for &(span, _) in &spans {
2656 err.span_label(span, "recursive without indirection");
2659 "insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `{}` representable",
2662 if spans.len() <= 4 {
2663 // FIXME(compiler-errors): This suggestion might be erroneous if Box is shadowed
2664 err.multipart_suggestion(
2668 .flat_map(|(span, field_id)| {
2669 if let Some(generic_span) = get_option_generic_from_field_id(tcx, field_id) {
2670 // If we match an `Option` and can grab the span of the Option's generic, then
2671 // suggest boxing the generic arg for a non-null niche optimization.
2673 (generic_span.shrink_to_lo(), "Box<".to_string()),
2674 (generic_span.shrink_to_hi(), ">".to_string()),
2678 (span.shrink_to_lo(), "Box<".to_string()),
2679 (span.shrink_to_hi(), ">".to_string()),
2684 Applicability::HasPlaceholders,
2692 /// Extract the span for the generic type `T` of `Option<T>` in a field definition
2693 fn get_option_generic_from_field_id(tcx: TyCtxt<'_>, field_id: Option<hir::HirId>) -> Option<Span> {
2694 let node = tcx.hir().find(field_id?);
2696 // Expect a field from our field_id
2697 let Some(hir::Node::Field(field_def)) = node
2698 else { bug!("Expected HirId corresponding to FieldDef, found: {:?}", node) };
2700 // Match a type that is a simple QPath with no Self
2701 let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = &field_def.ty.kind
2702 else { return None };
2704 // Check if the path we're checking resolves to Option
2705 let hir::def::Res::Def(_, did) = path.res
2706 else { return None };
2708 // Bail if this path doesn't describe `::core::option::Option`
2709 if !tcx.is_diagnostic_item(sym::Option, did) {
2713 // Match a single generic arg in the 0th path segment
2714 let generic_arg = path.segments.last()?.args?.args.get(0)?;
2716 // Take the span out of the type, if it's a type
2717 if let hir::GenericArg::Type(generic_ty) = generic_arg { Some(generic_ty.span) } else { None }
2720 /// Summarizes information
2723 /// An argument of non-tuple type. Parameters are (name, ty)
2724 Arg(String, String),
2726 /// An argument of tuple type. For a "found" argument, the span is
2727 /// the location in the source of the pattern. For an "expected"
2728 /// argument, it will be None. The vector is a list of (name, ty)
2729 /// strings for the components of the tuple.
2730 Tuple(Option<Span>, Vec<(String, String)>),
2734 fn empty() -> ArgKind {
2735 ArgKind::Arg("_".to_owned(), "_".to_owned())
2738 /// Creates an `ArgKind` from the expected type of an
2739 /// argument. It has no name (`_`) and an optional source span.
2740 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2742 ty::Tuple(tys) => ArgKind::Tuple(
2744 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2746 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2751 struct HasNumericInferVisitor;
2753 impl<'tcx> ty::TypeVisitor<'tcx> for HasNumericInferVisitor {
2756 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
2757 if matches!(ty.kind(), ty::Infer(ty::FloatVar(_) | ty::IntVar(_))) {
2758 ControlFlow::Break(())
2760 ControlFlow::CONTINUE