6 MismatchedProjectionTypes,
11 OnUnimplementedDirective,
13 OutputTypeParameterMismatch,
23 use crate::hir::def_id::DefId;
24 use crate::infer::{self, InferCtxt};
25 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
26 use crate::session::DiagnosticMessageId;
27 use crate::ty::{self, AdtKind, DefIdTree, ToPredicate, ToPolyTraitRef, Ty, TyCtxt, TypeFoldable};
28 use crate::ty::GenericParamDefKind;
29 use crate::ty::error::ExpectedFound;
30 use crate::ty::fast_reject;
31 use crate::ty::fold::TypeFolder;
32 use crate::ty::subst::Subst;
33 use crate::ty::SubtypePredicate;
34 use crate::util::nodemap::{FxHashMap, FxHashSet};
36 use errors::{Applicability, DiagnosticBuilder, pluralize};
39 use syntax::symbol::{sym, kw};
40 use syntax_pos::{DUMMY_SP, Span, ExpnKind, MultiSpan};
42 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
43 pub fn report_fulfillment_errors(
45 errors: &[FulfillmentError<'tcx>],
46 body_id: Option<hir::BodyId>,
47 fallback_has_occurred: bool,
50 struct ErrorDescriptor<'tcx> {
51 predicate: ty::Predicate<'tcx>,
52 index: Option<usize>, // None if this is an old error
55 let mut error_map: FxHashMap<_, Vec<_>> =
56 self.reported_trait_errors.borrow().iter().map(|(&span, predicates)| {
57 (span, predicates.iter().map(|predicate| ErrorDescriptor {
58 predicate: predicate.clone(),
63 for (index, error) in errors.iter().enumerate() {
64 // We want to ignore desugarings here: spans are equivalent even
65 // if one is the result of a desugaring and the other is not.
66 let mut span = error.obligation.cause.span;
67 let expn_data = span.ctxt().outer_expn_data();
68 if let ExpnKind::Desugaring(_) = expn_data.kind {
69 span = expn_data.call_site;
72 error_map.entry(span).or_default().push(
74 predicate: error.obligation.predicate.clone(),
79 self.reported_trait_errors.borrow_mut()
80 .entry(span).or_default()
81 .push(error.obligation.predicate.clone());
84 // We do this in 2 passes because we want to display errors in order, though
85 // maybe it *is* better to sort errors by span or something.
86 let mut is_suppressed = vec![false; errors.len()];
87 for (_, error_set) in error_map.iter() {
88 // We want to suppress "duplicate" errors with the same span.
89 for error in error_set {
90 if let Some(index) = error.index {
91 // Suppress errors that are either:
92 // 1) strictly implied by another error.
93 // 2) implied by an error with a smaller index.
94 for error2 in error_set {
95 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
96 // Avoid errors being suppressed by already-suppressed
97 // errors, to prevent all errors from being suppressed
102 if self.error_implies(&error2.predicate, &error.predicate) &&
103 !(error2.index >= error.index &&
104 self.error_implies(&error.predicate, &error2.predicate))
106 info!("skipping {:?} (implied by {:?})", error, error2);
107 is_suppressed[index] = true;
115 for (error, suppressed) in errors.iter().zip(is_suppressed) {
117 self.report_fulfillment_error(error, body_id, fallback_has_occurred);
122 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
123 // `error` occurring implies that `cond` occurs.
126 cond: &ty::Predicate<'tcx>,
127 error: &ty::Predicate<'tcx>,
133 let (cond, error) = match (cond, error) {
134 (&ty::Predicate::Trait(..), &ty::Predicate::Trait(ref error))
137 // FIXME: make this work in other cases too.
142 for implication in super::elaborate_predicates(self.tcx, vec![cond.clone()]) {
143 if let ty::Predicate::Trait(implication) = implication {
144 let error = error.to_poly_trait_ref();
145 let implication = implication.to_poly_trait_ref();
146 // FIXME: I'm just not taking associated types at all here.
147 // Eventually I'll need to implement param-env-aware
148 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
149 let param_env = ty::ParamEnv::empty();
150 if self.can_sub(param_env, error, implication).is_ok() {
151 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
160 fn report_fulfillment_error(
162 error: &FulfillmentError<'tcx>,
163 body_id: Option<hir::BodyId>,
164 fallback_has_occurred: bool,
166 debug!("report_fulfillment_errors({:?})", error);
168 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
169 self.report_selection_error(
172 fallback_has_occurred,
173 error.points_at_arg_span,
176 FulfillmentErrorCode::CodeProjectionError(ref e) => {
177 self.report_projection_error(&error.obligation, e);
179 FulfillmentErrorCode::CodeAmbiguity => {
180 self.maybe_report_ambiguity(&error.obligation, body_id);
182 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
183 self.report_mismatched_types(
184 &error.obligation.cause,
185 expected_found.expected,
186 expected_found.found,
193 fn report_projection_error(
195 obligation: &PredicateObligation<'tcx>,
196 error: &MismatchedProjectionTypes<'tcx>,
198 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
200 if predicate.references_error() {
206 let mut err = &error.err;
207 let mut values = None;
209 // try to find the mismatched types to report the error with.
211 // this can fail if the problem was higher-ranked, in which
212 // cause I have no idea for a good error message.
213 if let ty::Predicate::Projection(ref data) = predicate {
214 let mut selcx = SelectionContext::new(self);
215 let (data, _) = self.replace_bound_vars_with_fresh_vars(
216 obligation.cause.span,
217 infer::LateBoundRegionConversionTime::HigherRankedType,
220 let mut obligations = vec![];
221 let normalized_ty = super::normalize_projection_type(
223 obligation.param_env,
225 obligation.cause.clone(),
230 debug!("report_projection_error obligation.cause={:?} obligation.param_env={:?}",
231 obligation.cause, obligation.param_env);
233 debug!("report_projection_error normalized_ty={:?} data.ty={:?}",
234 normalized_ty, data.ty);
236 let is_normalized_ty_expected = match &obligation.cause.code {
237 ObligationCauseCode::ItemObligation(_) |
238 ObligationCauseCode::BindingObligation(_, _) |
239 ObligationCauseCode::ObjectCastObligation(_) => false,
243 if let Err(error) = self.at(&obligation.cause, obligation.param_env)
244 .eq_exp(is_normalized_ty_expected, normalized_ty, data.ty)
246 values = Some(infer::ValuePairs::Types(
247 ExpectedFound::new(is_normalized_ty_expected, normalized_ty, data.ty)));
254 let msg = format!("type mismatch resolving `{}`", predicate);
256 DiagnosticMessageId::ErrorId(271),
257 Some(obligation.cause.span),
260 let fresh = self.tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
262 let mut diag = struct_span_err!(
264 obligation.cause.span,
266 "type mismatch resolving `{}`",
269 self.note_type_err(&mut diag, &obligation.cause, None, values, err);
270 self.note_obligation_cause(&mut diag, obligation);
276 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
277 /// returns the fuzzy category of a given type, or None
278 /// if the type can be equated to any type.
279 fn type_category(t: Ty<'_>) -> Option<u32> {
284 ty::Int(..) | ty::Uint(..) | ty::Infer(ty::IntVar(..)) => Some(3),
285 ty::Float(..) | ty::Infer(ty::FloatVar(..)) => Some(4),
286 ty::Ref(..) | ty::RawPtr(..) => Some(5),
287 ty::Array(..) | ty::Slice(..) => Some(6),
288 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
289 ty::Dynamic(..) => Some(8),
290 ty::Closure(..) => Some(9),
291 ty::Tuple(..) => Some(10),
292 ty::Projection(..) => Some(11),
293 ty::Param(..) => Some(12),
294 ty::Opaque(..) => Some(13),
295 ty::Never => Some(14),
296 ty::Adt(adt, ..) => match adt.adt_kind() {
297 AdtKind::Struct => Some(15),
298 AdtKind::Union => Some(16),
299 AdtKind::Enum => Some(17),
301 ty::Generator(..) => Some(18),
302 ty::Foreign(..) => Some(19),
303 ty::GeneratorWitness(..) => Some(20),
304 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error => None,
305 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
309 match (type_category(a), type_category(b)) {
310 (Some(cat_a), Some(cat_b)) => match (&a.kind, &b.kind) {
311 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => def_a == def_b,
314 // infer and error can be equated to all types
319 fn impl_similar_to(&self,
320 trait_ref: ty::PolyTraitRef<'tcx>,
321 obligation: &PredicateObligation<'tcx>)
325 let param_env = obligation.param_env;
326 let trait_ref = tcx.erase_late_bound_regions(&trait_ref);
327 let trait_self_ty = trait_ref.self_ty();
329 let mut self_match_impls = vec![];
330 let mut fuzzy_match_impls = vec![];
332 self.tcx.for_each_relevant_impl(
333 trait_ref.def_id, trait_self_ty, |def_id| {
334 let impl_substs = self.fresh_substs_for_item(obligation.cause.span, def_id);
335 let impl_trait_ref = tcx
336 .impl_trait_ref(def_id)
338 .subst(tcx, impl_substs);
340 let impl_self_ty = impl_trait_ref.self_ty();
342 if let Ok(..) = self.can_eq(param_env, trait_self_ty, impl_self_ty) {
343 self_match_impls.push(def_id);
345 if trait_ref.substs.types().skip(1)
346 .zip(impl_trait_ref.substs.types().skip(1))
347 .all(|(u,v)| self.fuzzy_match_tys(u, v))
349 fuzzy_match_impls.push(def_id);
354 let impl_def_id = if self_match_impls.len() == 1 {
356 } else if fuzzy_match_impls.len() == 1 {
362 if tcx.has_attr(impl_def_id, sym::rustc_on_unimplemented) {
369 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
370 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| {
372 hir::GeneratorKind::Gen => "a generator",
373 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
374 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
375 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
380 /// Used to set on_unimplemented's `ItemContext`
381 /// to be the enclosing (async) block/function/closure
382 fn describe_enclosure(&self, hir_id: hir::HirId) -> Option<&'static str> {
383 let hir = &self.tcx.hir();
384 let node = hir.find(hir_id)?;
385 if let hir::Node::Item(
386 hir::Item{kind: hir::ItemKind::Fn(sig, _, body_id), .. }) = &node {
387 self.describe_generator(*body_id).or_else(||
388 Some(if let hir::FnHeader{ asyncness: hir::IsAsync::Async, .. } = sig.header {
394 } else if let hir::Node::Expr(hir::Expr {
395 kind: hir::ExprKind::Closure(_is_move, _, body_id, _, gen_movability), .. }) = &node {
396 self.describe_generator(*body_id).or_else(||
397 Some(if gen_movability.is_some() {
403 } else if let hir::Node::Expr(hir::Expr { .. }) = &node {
404 let parent_hid = hir.get_parent_node(hir_id);
405 if parent_hid != hir_id {
406 return self.describe_enclosure(parent_hid);
415 fn on_unimplemented_note(
417 trait_ref: ty::PolyTraitRef<'tcx>,
418 obligation: &PredicateObligation<'tcx>,
419 ) -> OnUnimplementedNote {
420 let def_id = self.impl_similar_to(trait_ref, obligation)
421 .unwrap_or_else(|| trait_ref.def_id());
422 let trait_ref = *trait_ref.skip_binder();
424 let mut flags = vec![];
425 flags.push((sym::item_context,
426 self.describe_enclosure(obligation.cause.body_id).map(|s|s.to_owned())));
428 match obligation.cause.code {
429 ObligationCauseCode::BuiltinDerivedObligation(..) |
430 ObligationCauseCode::ImplDerivedObligation(..) => {}
432 // this is a "direct", user-specified, rather than derived,
434 flags.push((sym::direct, None));
438 if let ObligationCauseCode::ItemObligation(item) = obligation.cause.code {
439 // FIXME: maybe also have some way of handling methods
440 // from other traits? That would require name resolution,
441 // which we might want to be some sort of hygienic.
443 // Currently I'm leaving it for what I need for `try`.
444 if self.tcx.trait_of_item(item) == Some(trait_ref.def_id) {
445 let method = self.tcx.item_name(item);
446 flags.push((sym::from_method, None));
447 flags.push((sym::from_method, Some(method.to_string())));
450 if let Some(t) = self.get_parent_trait_ref(&obligation.cause.code) {
451 flags.push((sym::parent_trait, Some(t)));
454 if let Some(k) = obligation.cause.span.desugaring_kind() {
455 flags.push((sym::from_desugaring, None));
456 flags.push((sym::from_desugaring, Some(format!("{:?}", k))));
458 let generics = self.tcx.generics_of(def_id);
459 let self_ty = trait_ref.self_ty();
460 // This is also included through the generics list as `Self`,
461 // but the parser won't allow you to use it
462 flags.push((sym::_Self, Some(self_ty.to_string())));
463 if let Some(def) = self_ty.ty_adt_def() {
464 // We also want to be able to select self's original
465 // signature with no type arguments resolved
466 flags.push((sym::_Self, Some(self.tcx.type_of(def.did).to_string())));
469 for param in generics.params.iter() {
470 let value = match param.kind {
471 GenericParamDefKind::Type { .. } |
472 GenericParamDefKind::Const => {
473 trait_ref.substs[param.index as usize].to_string()
475 GenericParamDefKind::Lifetime => continue,
477 let name = param.name;
478 flags.push((name, Some(value)));
481 if let Some(true) = self_ty.ty_adt_def().map(|def| def.did.is_local()) {
482 flags.push((sym::crate_local, None));
485 // Allow targeting all integers using `{integral}`, even if the exact type was resolved
486 if self_ty.is_integral() {
487 flags.push((sym::_Self, Some("{integral}".to_owned())));
490 if let ty::Array(aty, len) = self_ty.kind {
491 flags.push((sym::_Self, Some("[]".to_owned())));
492 flags.push((sym::_Self, Some(format!("[{}]", aty))));
493 if let Some(def) = aty.ty_adt_def() {
494 // We also want to be able to select the array's type's original
495 // signature with no type arguments resolved
498 Some(format!("[{}]", self.tcx.type_of(def.did).to_string())),
501 if let Some(len) = len.try_eval_usize(tcx, ty::ParamEnv::empty()) {
504 Some(format!("[{}; {}]", self.tcx.type_of(def.did).to_string(), len)),
509 Some(format!("[{}; _]", self.tcx.type_of(def.did).to_string())),
515 if let Ok(Some(command)) = OnUnimplementedDirective::of_item(
516 self.tcx, trait_ref.def_id, def_id
518 command.evaluate(self.tcx, trait_ref, &flags[..])
520 OnUnimplementedNote::empty()
524 fn find_similar_impl_candidates(
526 trait_ref: ty::PolyTraitRef<'tcx>,
527 ) -> Vec<ty::TraitRef<'tcx>> {
528 let simp = fast_reject::simplify_type(self.tcx, trait_ref.skip_binder().self_ty(), true);
529 let all_impls = self.tcx.all_impls(trait_ref.def_id());
532 Some(simp) => all_impls.iter().filter_map(|&def_id| {
533 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
534 let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
535 if let Some(imp_simp) = imp_simp {
536 if simp != imp_simp {
543 None => all_impls.iter().map(|&def_id|
544 self.tcx.impl_trait_ref(def_id).unwrap()
549 fn report_similar_impl_candidates(
551 impl_candidates: Vec<ty::TraitRef<'tcx>>,
552 err: &mut DiagnosticBuilder<'_>,
554 if impl_candidates.is_empty() {
558 let len = impl_candidates.len();
559 let end = if impl_candidates.len() <= 5 {
560 impl_candidates.len()
565 let normalize = |candidate| self.tcx.infer_ctxt().enter(|ref infcx| {
566 let normalized = infcx
567 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
568 .normalize(candidate)
571 Some(normalized) => format!("\n {:?}", normalized.value),
572 None => format!("\n {:?}", candidate),
576 // Sort impl candidates so that ordering is consistent for UI tests.
577 let mut normalized_impl_candidates = impl_candidates
580 .collect::<Vec<String>>();
582 // Sort before taking the `..end` range,
583 // because the ordering of `impl_candidates` may not be deterministic:
584 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
585 normalized_impl_candidates.sort();
587 err.help(&format!("the following implementations were found:{}{}",
588 normalized_impl_candidates[..end].join(""),
590 format!("\nand {} others", len - 4)
597 /// Reports that an overflow has occurred and halts compilation. We
598 /// halt compilation unconditionally because it is important that
599 /// overflows never be masked -- they basically represent computations
600 /// whose result could not be truly determined and thus we can't say
601 /// if the program type checks or not -- and they are unusual
602 /// occurrences in any case.
603 pub fn report_overflow_error<T>(
605 obligation: &Obligation<'tcx, T>,
606 suggest_increasing_limit: bool,
608 where T: fmt::Display + TypeFoldable<'tcx>
611 self.resolve_vars_if_possible(&obligation.predicate);
612 let mut err = struct_span_err!(
614 obligation.cause.span,
616 "overflow evaluating the requirement `{}`",
620 if suggest_increasing_limit {
621 self.suggest_new_overflow_limit(&mut err);
624 self.note_obligation_cause_code(
626 &obligation.predicate,
627 &obligation.cause.code,
632 self.tcx.sess.abort_if_errors();
636 /// Reports that a cycle was detected which led to overflow and halts
637 /// compilation. This is equivalent to `report_overflow_error` except
638 /// that we can give a more helpful error message (and, in particular,
639 /// we do not suggest increasing the overflow limit, which is not
641 pub fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
642 let cycle = self.resolve_vars_if_possible(&cycle.to_owned());
643 assert!(cycle.len() > 0);
645 debug!("report_overflow_error_cycle: cycle={:?}", cycle);
647 self.report_overflow_error(&cycle[0], false);
650 pub fn report_extra_impl_obligation(&self,
652 item_name: ast::Name,
653 _impl_item_def_id: DefId,
654 trait_item_def_id: DefId,
655 requirement: &dyn fmt::Display)
656 -> DiagnosticBuilder<'tcx>
658 let msg = "impl has stricter requirements than trait";
659 let sp = self.tcx.sess.source_map().def_span(error_span);
661 let mut err = struct_span_err!(self.tcx.sess, sp, E0276, "{}", msg);
663 if let Some(trait_item_span) = self.tcx.hir().span_if_local(trait_item_def_id) {
664 let span = self.tcx.sess.source_map().def_span(trait_item_span);
665 err.span_label(span, format!("definition of `{}` from trait", item_name));
668 err.span_label(sp, format!("impl has extra requirement {}", requirement));
674 /// Gets the parent trait chain start
675 fn get_parent_trait_ref(&self, code: &ObligationCauseCode<'tcx>) -> Option<String> {
677 &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
678 let parent_trait_ref = self.resolve_vars_if_possible(
679 &data.parent_trait_ref);
680 match self.get_parent_trait_ref(&data.parent_code) {
682 None => Some(parent_trait_ref.skip_binder().self_ty().to_string()),
689 pub fn report_selection_error(
691 obligation: &PredicateObligation<'tcx>,
692 error: &SelectionError<'tcx>,
693 fallback_has_occurred: bool,
696 let span = obligation.cause.span;
698 let mut err = match *error {
699 SelectionError::Unimplemented => {
700 if let ObligationCauseCode::CompareImplMethodObligation {
701 item_name, impl_item_def_id, trait_item_def_id,
702 } = obligation.cause.code {
703 self.report_extra_impl_obligation(
708 &format!("`{}`", obligation.predicate))
712 match obligation.predicate {
713 ty::Predicate::Trait(ref trait_predicate) => {
714 let trait_predicate =
715 self.resolve_vars_if_possible(trait_predicate);
717 if self.tcx.sess.has_errors() && trait_predicate.references_error() {
720 let trait_ref = trait_predicate.to_poly_trait_ref();
721 let (post_message, pre_message) =
722 self.get_parent_trait_ref(&obligation.cause.code)
723 .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
724 .unwrap_or_default();
726 let OnUnimplementedNote { message, label, note }
727 = self.on_unimplemented_note(trait_ref, obligation);
728 let have_alt_message = message.is_some() || label.is_some();
729 let is_try = self.tcx.sess.source_map().span_to_snippet(span)
732 let is_from = format!("{}", trait_ref).starts_with("std::convert::From<");
733 let (message, note) = if is_try && is_from {
735 "`?` couldn't convert the error to `{}`",
738 "the question mark operation (`?`) implicitly performs a \
739 conversion on the error value using the `From` trait".to_owned()
745 let mut err = struct_span_err!(
750 message.unwrap_or_else(|| format!(
751 "the trait bound `{}` is not satisfied{}",
752 trait_ref.to_predicate(),
757 if obligation.cause.code == ObligationCauseCode::MainFunctionType {
758 "consider using `()`, or a `Result`".to_owned()
761 "{}the trait `{}` is not implemented for `{}`",
768 if let Some(ref s) = label {
769 // If it has a custom `#[rustc_on_unimplemented]`
770 // error message, let's display it as the label!
771 err.span_label(span, s.as_str());
772 err.help(&explanation);
774 err.span_label(span, explanation);
776 if let Some(ref s) = note {
777 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
778 err.note(s.as_str());
781 self.suggest_borrow_on_unsized_slice(&obligation.cause.code, &mut err);
782 self.suggest_fn_call(&obligation, &mut err, &trait_ref, points_at_arg);
783 self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
784 self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
786 // Try to report a help message
787 if !trait_ref.has_infer_types() &&
788 self.predicate_can_apply(obligation.param_env, trait_ref) {
789 // If a where-clause may be useful, remind the
790 // user that they can add it.
792 // don't display an on-unimplemented note, as
793 // these notes will often be of the form
794 // "the type `T` can't be frobnicated"
795 // which is somewhat confusing.
796 self.suggest_restricting_param_bound(
799 obligation.cause.body_id,
802 if !have_alt_message {
803 // Can't show anything else useful, try to find similar impls.
804 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
805 self.report_similar_impl_candidates(impl_candidates, &mut err);
807 self.suggest_change_mut(
815 // If this error is due to `!: Trait` not implemented but `(): Trait` is
816 // implemented, and fallback has occurred, then it could be due to a
817 // variable that used to fallback to `()` now falling back to `!`. Issue a
818 // note informing about the change in behaviour.
819 if trait_predicate.skip_binder().self_ty().is_never()
820 && fallback_has_occurred
822 let predicate = trait_predicate.map_bound(|mut trait_pred| {
823 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
825 &trait_pred.trait_ref.substs[1..],
829 let unit_obligation = Obligation {
830 predicate: ty::Predicate::Trait(predicate),
831 .. obligation.clone()
833 if self.predicate_may_hold(&unit_obligation) {
834 err.note("the trait is implemented for `()`. \
835 Possibly this error has been caused by changes to \
836 Rust's type-inference algorithm \
837 (see: https://github.com/rust-lang/rust/issues/48950 \
838 for more info). Consider whether you meant to use the \
839 type `()` here instead.");
846 ty::Predicate::Subtype(ref predicate) => {
847 // Errors for Subtype predicates show up as
848 // `FulfillmentErrorCode::CodeSubtypeError`,
849 // not selection error.
850 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
853 ty::Predicate::RegionOutlives(ref predicate) => {
854 let predicate = self.resolve_vars_if_possible(predicate);
855 let err = self.region_outlives_predicate(&obligation.cause,
856 &predicate).err().unwrap();
858 self.tcx.sess, span, E0279,
859 "the requirement `{}` is not satisfied (`{}`)",
864 ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
866 self.resolve_vars_if_possible(&obligation.predicate);
867 struct_span_err!(self.tcx.sess, span, E0280,
868 "the requirement `{}` is not satisfied",
872 ty::Predicate::ObjectSafe(trait_def_id) => {
873 let violations = self.tcx.object_safety_violations(trait_def_id);
874 self.tcx.report_object_safety_error(
881 ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
882 let found_kind = self.closure_kind(closure_def_id, closure_substs).unwrap();
883 let closure_span = self.tcx.sess.source_map()
884 .def_span(self.tcx.hir().span_if_local(closure_def_id).unwrap());
885 let hir_id = self.tcx.hir().as_local_hir_id(closure_def_id).unwrap();
886 let mut err = struct_span_err!(
887 self.tcx.sess, closure_span, E0525,
888 "expected a closure that implements the `{}` trait, \
889 but this closure only implements `{}`",
895 format!("this closure implements `{}`, not `{}`", found_kind, kind));
897 obligation.cause.span,
898 format!("the requirement to implement `{}` derives from here", kind));
900 // Additional context information explaining why the closure only implements
901 // a particular trait.
902 if let Some(tables) = self.in_progress_tables {
903 let tables = tables.borrow();
904 match (found_kind, tables.closure_kind_origins().get(hir_id)) {
905 (ty::ClosureKind::FnOnce, Some((span, name))) => {
906 err.span_label(*span, format!(
907 "closure is `FnOnce` because it moves the \
908 variable `{}` out of its environment", name));
910 (ty::ClosureKind::FnMut, Some((span, name))) => {
911 err.span_label(*span, format!(
912 "closure is `FnMut` because it mutates the \
913 variable `{}` here", name));
923 ty::Predicate::WellFormed(ty) => {
924 if !self.tcx.sess.opts.debugging_opts.chalk {
925 // WF predicates cannot themselves make
926 // errors. They can only block due to
927 // ambiguity; otherwise, they always
928 // degenerate into other obligations
930 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
932 // FIXME: we'll need a better message which takes into account
933 // which bounds actually failed to hold.
934 self.tcx.sess.struct_span_err(
936 &format!("the type `{}` is not well-formed (chalk)", ty)
941 ty::Predicate::ConstEvaluatable(..) => {
942 // Errors for `ConstEvaluatable` predicates show up as
943 // `SelectionError::ConstEvalFailure`,
944 // not `Unimplemented`.
946 "const-evaluatable requirement gave wrong error: `{:?}`", obligation)
951 OutputTypeParameterMismatch(ref found_trait_ref, ref expected_trait_ref, _) => {
952 let found_trait_ref = self.resolve_vars_if_possible(&*found_trait_ref);
953 let expected_trait_ref = self.resolve_vars_if_possible(&*expected_trait_ref);
955 if expected_trait_ref.self_ty().references_error() {
959 let found_trait_ty = found_trait_ref.self_ty();
961 let found_did = match found_trait_ty.kind {
962 ty::Closure(did, _) | ty::Foreign(did) | ty::FnDef(did, _) => Some(did),
963 ty::Adt(def, _) => Some(def.did),
967 let found_span = found_did.and_then(|did|
968 self.tcx.hir().span_if_local(did)
969 ).map(|sp| self.tcx.sess.source_map().def_span(sp)); // the sp could be an fn def
971 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
972 // We check closures twice, with obligations flowing in different directions,
973 // but we want to complain about them only once.
977 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
979 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind {
980 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
981 _ => vec![ArgKind::empty()],
984 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
985 let expected = match expected_ty.kind {
986 ty::Tuple(ref tys) => tys.iter()
987 .map(|t| ArgKind::from_expected_ty(t.expect_ty(), Some(span))).collect(),
988 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
991 if found.len() == expected.len() {
992 self.report_closure_arg_mismatch(span,
997 let (closure_span, found) = found_did
998 .and_then(|did| self.tcx.hir().get_if_local(did))
1000 let (found_span, found) = self.get_fn_like_arguments(node);
1001 (Some(found_span), found)
1002 }).unwrap_or((found_span, found));
1004 self.report_arg_count_mismatch(span,
1008 found_trait_ty.is_closure())
1012 TraitNotObjectSafe(did) => {
1013 let violations = self.tcx.object_safety_violations(did);
1014 self.tcx.report_object_safety_error(span, did, violations)
1017 // already reported in the query
1018 ConstEvalFailure(err) => {
1019 self.tcx.sess.delay_span_bug(
1021 &format!("constant in type had an ignored error: {:?}", err),
1027 bug!("overflow should be handled before the `report_selection_error` path");
1031 self.note_obligation_cause(&mut err, obligation);
1036 fn suggest_restricting_param_bound(
1038 err: &mut DiagnosticBuilder<'_>,
1039 trait_ref: &ty::PolyTraitRef<'_>,
1040 body_id: hir::HirId,
1042 let self_ty = trait_ref.self_ty();
1043 let (param_ty, projection) = match &self_ty.kind {
1044 ty::Param(_) => (true, None),
1045 ty::Projection(projection) => (false, Some(projection)),
1049 let mut suggest_restriction = |generics: &hir::Generics, msg| {
1050 let span = generics.where_clause.span_for_predicates_or_empty_place();
1051 if !span.from_expansion() && span.desugaring_kind().is_none() {
1052 err.span_suggestion(
1053 generics.where_clause.span_for_predicates_or_empty_place().shrink_to_hi(),
1054 &format!("consider further restricting {}", msg),
1057 if !generics.where_clause.predicates.is_empty() {
1062 trait_ref.to_predicate(),
1064 Applicability::MachineApplicable,
1069 // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
1070 // don't suggest `T: Sized + ?Sized`.
1071 let mut hir_id = body_id;
1072 while let Some(node) = self.tcx.hir().find(hir_id) {
1074 hir::Node::TraitItem(hir::TraitItem {
1076 kind: hir::TraitItemKind::Method(..), ..
1077 }) if param_ty && self_ty == self.tcx.types.self_param => {
1078 // Restricting `Self` for a single method.
1079 suggest_restriction(&generics, "`Self`");
1083 hir::Node::Item(hir::Item {
1084 kind: hir::ItemKind::Fn(_, generics, _), ..
1086 hir::Node::TraitItem(hir::TraitItem {
1088 kind: hir::TraitItemKind::Method(..), ..
1090 hir::Node::ImplItem(hir::ImplItem {
1092 kind: hir::ImplItemKind::Method(..), ..
1094 hir::Node::Item(hir::Item {
1095 kind: hir::ItemKind::Trait(_, _, generics, _, _), ..
1097 hir::Node::Item(hir::Item {
1098 kind: hir::ItemKind::Impl(_, _, _, generics, ..), ..
1099 }) if projection.is_some() => {
1100 // Missing associated type bound.
1101 suggest_restriction(&generics, "the associated type");
1105 hir::Node::Item(hir::Item { kind: hir::ItemKind::Struct(_, generics), span, .. }) |
1106 hir::Node::Item(hir::Item { kind: hir::ItemKind::Enum(_, generics), span, .. }) |
1107 hir::Node::Item(hir::Item { kind: hir::ItemKind::Union(_, generics), span, .. }) |
1108 hir::Node::Item(hir::Item {
1109 kind: hir::ItemKind::Trait(_, _, generics, ..), span, ..
1111 hir::Node::Item(hir::Item {
1112 kind: hir::ItemKind::Impl(_, _, _, generics, ..), span, ..
1114 hir::Node::Item(hir::Item {
1115 kind: hir::ItemKind::Fn(_, generics, _), span, ..
1117 hir::Node::Item(hir::Item {
1118 kind: hir::ItemKind::TyAlias(_, generics), span, ..
1120 hir::Node::Item(hir::Item {
1121 kind: hir::ItemKind::TraitAlias(generics, _), span, ..
1123 hir::Node::Item(hir::Item {
1124 kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }), span, ..
1126 hir::Node::TraitItem(hir::TraitItem { generics, span, .. }) |
1127 hir::Node::ImplItem(hir::ImplItem { generics, span, .. })
1129 // Missing generic type parameter bound.
1130 let restrict_msg = "consider further restricting this bound";
1131 let param_name = self_ty.to_string();
1132 for param in generics.params.iter().filter(|p| {
1133 p.name.ident().as_str() == param_name
1135 if param_name.starts_with("impl ") {
1136 // `impl Trait` in argument:
1137 // `fn foo(x: impl Trait) {}` → `fn foo(t: impl Trait + Trait2) {}`
1138 err.span_suggestion(
1141 // `impl CurrentTrait + MissingTrait`
1142 format!("{} + {}", param.name.ident(), trait_ref),
1143 Applicability::MachineApplicable,
1145 } else if generics.where_clause.predicates.is_empty() &&
1146 param.bounds.is_empty()
1148 // If there are no bounds whatsoever, suggest adding a constraint
1149 // to the type parameter:
1150 // `fn foo<T>(t: T) {}` → `fn foo<T: Trait>(t: T) {}`
1151 err.span_suggestion(
1153 "consider restricting this bound",
1154 format!("{}", trait_ref.to_predicate()),
1155 Applicability::MachineApplicable,
1157 } else if !generics.where_clause.predicates.is_empty() {
1158 // There is a `where` clause, so suggest expanding it:
1159 // `fn foo<T>(t: T) where T: Debug {}` →
1160 // `fn foo<T>(t: T) where T: Debug, T: Trait {}`
1161 err.span_suggestion(
1162 generics.where_clause.span().unwrap().shrink_to_hi(),
1164 "consider further restricting type parameter `{}`",
1167 format!(", {}", trait_ref.to_predicate()),
1168 Applicability::MachineApplicable,
1171 // If there is no `where` clause lean towards constraining to the
1173 // `fn foo<X: Bar, T>(t: T, x: X) {}` → `fn foo<T: Trait>(t: T) {}`
1174 // `fn foo<T: Bar>(t: T) {}` → `fn foo<T: Bar + Trait>(t: T) {}`
1175 let sp = param.span.with_hi(span.hi());
1176 let span = self.tcx.sess.source_map()
1177 .span_through_char(sp, ':');
1178 if sp != param.span && sp != span {
1179 // Only suggest if we have high certainty that the span
1180 // covers the colon in `foo<T: Trait>`.
1181 err.span_suggestion(span, restrict_msg, format!(
1183 trait_ref.to_predicate(),
1184 ), Applicability::MachineApplicable);
1186 err.span_label(param.span, &format!(
1187 "consider adding a `where {}` bound",
1188 trait_ref.to_predicate(),
1196 hir::Node::Crate => return,
1201 hir_id = self.tcx.hir().get_parent_item(hir_id);
1205 /// When encountering an assignment of an unsized trait, like `let x = ""[..];`, provide a
1206 /// suggestion to borrow the initializer in order to use have a slice instead.
1207 fn suggest_borrow_on_unsized_slice(
1209 code: &ObligationCauseCode<'tcx>,
1210 err: &mut DiagnosticBuilder<'tcx>,
1212 if let &ObligationCauseCode::VariableType(hir_id) = code {
1213 let parent_node = self.tcx.hir().get_parent_node(hir_id);
1214 if let Some(Node::Local(ref local)) = self.tcx.hir().find(parent_node) {
1215 if let Some(ref expr) = local.init {
1216 if let hir::ExprKind::Index(_, _) = expr.kind {
1217 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
1218 err.span_suggestion(
1220 "consider borrowing here",
1221 format!("&{}", snippet),
1222 Applicability::MachineApplicable
1233 obligation: &PredicateObligation<'tcx>,
1234 err: &mut DiagnosticBuilder<'_>,
1235 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1236 points_at_arg: bool,
1238 let self_ty = trait_ref.self_ty();
1239 match self_ty.kind {
1240 ty::FnDef(def_id, _) => {
1241 // We tried to apply the bound to an `fn`. Check whether calling it would evaluate
1242 // to a type that *would* satisfy the trait binding. If it would, suggest calling
1243 // it: `bar(foo)` -> `bar(foo)`. This case is *very* likely to be hit if `foo` is
1245 let output_ty = self_ty.fn_sig(self.tcx).output();
1246 let new_trait_ref = ty::TraitRef {
1247 def_id: trait_ref.def_id(),
1248 substs: self.tcx.mk_substs_trait(output_ty.skip_binder(), &[]),
1250 let obligation = Obligation::new(
1251 obligation.cause.clone(),
1252 obligation.param_env,
1253 new_trait_ref.to_predicate(),
1255 match self.evaluate_obligation(&obligation) {
1256 Ok(EvaluationResult::EvaluatedToOk) |
1257 Ok(EvaluationResult::EvaluatedToOkModuloRegions) |
1258 Ok(EvaluationResult::EvaluatedToAmbig) => {
1259 if let Some(hir::Node::Item(hir::Item {
1261 kind: hir::ItemKind::Fn(.., body_id),
1263 })) = self.tcx.hir().get_if_local(def_id) {
1264 let body = self.tcx.hir().body(*body_id);
1265 let msg = "use parentheses to call the function";
1266 let snippet = format!(
1270 .map(|arg| match &arg.pat.kind {
1271 hir::PatKind::Binding(_, _, ident, None)
1272 if ident.name != kw::SelfLower => ident.to_string(),
1273 _ => "_".to_string(),
1274 }).collect::<Vec<_>>().join(", "),
1276 // When the obligation error has been ensured to have been caused by
1277 // an argument, the `obligation.cause.span` points at the expression
1278 // of the argument, so we can provide a suggestion. This is signaled
1279 // by `points_at_arg`. Otherwise, we give a more general note.
1281 err.span_suggestion(
1282 obligation.cause.span,
1285 Applicability::HasPlaceholders,
1288 err.help(&format!("{}: `{}`", msg, snippet));
1299 /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
1300 /// suggest removing these references until we reach a type that implements the trait.
1301 fn suggest_remove_reference(
1303 obligation: &PredicateObligation<'tcx>,
1304 err: &mut DiagnosticBuilder<'tcx>,
1305 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1307 let trait_ref = trait_ref.skip_binder();
1308 let span = obligation.cause.span;
1310 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1311 let refs_number = snippet.chars()
1312 .filter(|c| !c.is_whitespace())
1313 .take_while(|c| *c == '&')
1315 if let Some('\'') = snippet.chars()
1316 .filter(|c| !c.is_whitespace())
1319 { // Do not suggest removal of borrow from type arguments.
1323 let mut trait_type = trait_ref.self_ty();
1325 for refs_remaining in 0..refs_number {
1326 if let ty::Ref(_, t_type, _) = trait_type.kind {
1327 trait_type = t_type;
1329 let substs = self.tcx.mk_substs_trait(trait_type, &[]);
1330 let new_trait_ref = ty::TraitRef::new(trait_ref.def_id, substs);
1331 let new_obligation = Obligation::new(
1332 ObligationCause::dummy(),
1333 obligation.param_env,
1334 new_trait_ref.to_predicate(),
1337 if self.predicate_may_hold(&new_obligation) {
1338 let sp = self.tcx.sess.source_map()
1339 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1341 let remove_refs = refs_remaining + 1;
1342 let format_str = format!("consider removing {} leading `&`-references",
1345 err.span_suggestion_short(
1346 sp, &format_str, String::new(), Applicability::MachineApplicable
1357 /// Check if the trait bound is implemented for a different mutability and note it in the
1359 fn suggest_change_mut(
1361 obligation: &PredicateObligation<'tcx>,
1362 err: &mut DiagnosticBuilder<'tcx>,
1363 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1364 points_at_arg: bool,
1366 let span = obligation.cause.span;
1367 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1368 let refs_number = snippet.chars()
1369 .filter(|c| !c.is_whitespace())
1370 .take_while(|c| *c == '&')
1372 if let Some('\'') = snippet.chars()
1373 .filter(|c| !c.is_whitespace())
1376 { // Do not suggest removal of borrow from type arguments.
1379 let trait_ref = self.resolve_vars_if_possible(trait_ref);
1380 if trait_ref.has_infer_types() {
1381 // Do not ICE while trying to find if a reborrow would succeed on a trait with
1382 // unresolved bindings.
1386 if let ty::Ref(region, t_type, mutability) = trait_ref.skip_binder().self_ty().kind {
1387 let trait_type = match mutability {
1388 hir::Mutability::Mutable => self.tcx.mk_imm_ref(region, t_type),
1389 hir::Mutability::Immutable => self.tcx.mk_mut_ref(region, t_type),
1392 let substs = self.tcx.mk_substs_trait(&trait_type, &[]);
1393 let new_trait_ref = ty::TraitRef::new(trait_ref.skip_binder().def_id, substs);
1394 let new_obligation = Obligation::new(
1395 ObligationCause::dummy(),
1396 obligation.param_env,
1397 new_trait_ref.to_predicate(),
1400 if self.evaluate_obligation_no_overflow(
1402 ).must_apply_modulo_regions() {
1403 let sp = self.tcx.sess.source_map()
1404 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1406 mutability == hir::Mutability::Immutable &&
1409 err.span_suggestion(
1411 "consider changing this borrow's mutability",
1412 "&mut ".to_string(),
1413 Applicability::MachineApplicable,
1417 "`{}` is implemented for `{:?}`, but not for `{:?}`",
1420 trait_ref.skip_binder().self_ty(),
1428 fn suggest_semicolon_removal(
1430 obligation: &PredicateObligation<'tcx>,
1431 err: &mut DiagnosticBuilder<'tcx>,
1433 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1435 let hir = self.tcx.hir();
1436 let parent_node = hir.get_parent_node(obligation.cause.body_id);
1437 let node = hir.find(parent_node);
1438 if let Some(hir::Node::Item(hir::Item {
1439 kind: hir::ItemKind::Fn(sig, _, body_id),
1442 let body = hir.body(*body_id);
1443 if let hir::ExprKind::Block(blk, _) = &body.value.kind {
1444 if sig.decl.output.span().overlaps(span) && blk.expr.is_none() &&
1445 "()" == &trait_ref.self_ty().to_string()
1447 // FIXME(estebank): When encountering a method with a trait
1448 // bound not satisfied in the return type with a body that has
1449 // no return, suggest removal of semicolon on last statement.
1450 // Once that is added, close #54771.
1451 if let Some(ref stmt) = blk.stmts.last() {
1452 let sp = self.tcx.sess.source_map().end_point(stmt.span);
1453 err.span_label(sp, "consider removing this semicolon");
1460 /// Given some node representing a fn-like thing in the HIR map,
1461 /// returns a span and `ArgKind` information that describes the
1462 /// arguments it expects. This can be supplied to
1463 /// `report_arg_count_mismatch`.
1464 pub fn get_fn_like_arguments(&self, node: Node<'_>) -> (Span, Vec<ArgKind>) {
1466 Node::Expr(&hir::Expr {
1467 kind: hir::ExprKind::Closure(_, ref _decl, id, span, _),
1470 (self.tcx.sess.source_map().def_span(span),
1471 self.tcx.hir().body(id).params.iter()
1474 kind: hir::PatKind::Tuple(ref args, _),
1480 args.iter().map(|pat| {
1481 let snippet = self.tcx.sess.source_map()
1482 .span_to_snippet(pat.span).unwrap();
1483 (snippet, "_".to_owned())
1484 }).collect::<Vec<_>>(),
1487 let name = self.tcx.sess.source_map()
1488 .span_to_snippet(arg.pat.span).unwrap();
1489 ArgKind::Arg(name, "_".to_owned())
1492 .collect::<Vec<ArgKind>>())
1494 Node::Item(&hir::Item {
1496 kind: hir::ItemKind::Fn(ref sig, ..),
1499 Node::ImplItem(&hir::ImplItem {
1501 kind: hir::ImplItemKind::Method(ref sig, _),
1504 Node::TraitItem(&hir::TraitItem {
1506 kind: hir::TraitItemKind::Method(ref sig, _),
1509 (self.tcx.sess.source_map().def_span(span), sig.decl.inputs.iter()
1510 .map(|arg| match arg.clone().kind {
1511 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
1513 vec![("_".to_owned(), "_".to_owned()); tys.len()]
1515 _ => ArgKind::empty()
1516 }).collect::<Vec<ArgKind>>())
1518 Node::Ctor(ref variant_data) => {
1519 let span = variant_data.ctor_hir_id()
1520 .map(|hir_id| self.tcx.hir().span(hir_id))
1521 .unwrap_or(DUMMY_SP);
1522 let span = self.tcx.sess.source_map().def_span(span);
1524 (span, vec![ArgKind::empty(); variant_data.fields().len()])
1526 _ => panic!("non-FnLike node found: {:?}", node),
1530 /// Reports an error when the number of arguments needed by a
1531 /// trait match doesn't match the number that the expression
1533 pub fn report_arg_count_mismatch(
1536 found_span: Option<Span>,
1537 expected_args: Vec<ArgKind>,
1538 found_args: Vec<ArgKind>,
1540 ) -> DiagnosticBuilder<'tcx> {
1541 let kind = if is_closure { "closure" } else { "function" };
1543 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
1544 let arg_length = arguments.len();
1545 let distinct = match &other[..] {
1546 &[ArgKind::Tuple(..)] => true,
1549 match (arg_length, arguments.get(0)) {
1550 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
1551 format!("a single {}-tuple as argument", fields.len())
1553 _ => format!("{} {}argument{}",
1555 if distinct && arg_length > 1 { "distinct " } else { "" },
1556 pluralize!(arg_length))
1560 let expected_str = args_str(&expected_args, &found_args);
1561 let found_str = args_str(&found_args, &expected_args);
1563 let mut err = struct_span_err!(
1567 "{} is expected to take {}, but it takes {}",
1573 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
1575 if let Some(found_span) = found_span {
1576 err.span_label(found_span, format!("takes {}", found_str));
1579 // ^^^^^^^^-- def_span
1583 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
1586 let pipe_span = if let Some(span) = found_span.trim_start(prefix_span) {
1592 // Suggest to take and ignore the arguments with expected_args_length `_`s if
1593 // found arguments is empty (assume the user just wants to ignore args in this case).
1594 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
1595 if found_args.is_empty() && is_closure {
1596 let underscores = vec!["_"; expected_args.len()].join(", ");
1597 err.span_suggestion(
1600 "consider changing the closure to take and ignore the expected argument{}",
1601 if expected_args.len() < 2 {
1607 format!("|{}|", underscores),
1608 Applicability::MachineApplicable,
1612 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
1613 if fields.len() == expected_args.len() {
1614 let sugg = fields.iter()
1615 .map(|(name, _)| name.to_owned())
1616 .collect::<Vec<String>>()
1618 err.span_suggestion(
1620 "change the closure to take multiple arguments instead of a single tuple",
1621 format!("|{}|", sugg),
1622 Applicability::MachineApplicable,
1626 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..] {
1627 if fields.len() == found_args.len() && is_closure {
1631 .map(|arg| match arg {
1632 ArgKind::Arg(name, _) => name.to_owned(),
1633 _ => "_".to_owned(),
1635 .collect::<Vec<String>>()
1637 // add type annotations if available
1638 if found_args.iter().any(|arg| match arg {
1639 ArgKind::Arg(_, ty) => ty != "_",
1644 .map(|(_, ty)| ty.to_owned())
1645 .collect::<Vec<String>>()
1651 err.span_suggestion(
1653 "change the closure to accept a tuple instead of individual arguments",
1655 Applicability::MachineApplicable,
1664 fn report_closure_arg_mismatch(
1667 found_span: Option<Span>,
1668 expected_ref: ty::PolyTraitRef<'tcx>,
1669 found: ty::PolyTraitRef<'tcx>,
1670 ) -> DiagnosticBuilder<'tcx> {
1671 fn build_fn_sig_string<'tcx>(tcx: TyCtxt<'tcx>, trait_ref: &ty::TraitRef<'tcx>) -> String {
1672 let inputs = trait_ref.substs.type_at(1);
1673 let sig = if let ty::Tuple(inputs) = inputs.kind {
1675 inputs.iter().map(|k| k.expect_ty()),
1676 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1678 hir::Unsafety::Normal,
1679 ::rustc_target::spec::abi::Abi::Rust
1683 ::std::iter::once(inputs),
1684 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1686 hir::Unsafety::Normal,
1687 ::rustc_target::spec::abi::Abi::Rust
1690 ty::Binder::bind(sig).to_string()
1693 let argument_is_closure = expected_ref.skip_binder().substs.type_at(0).is_closure();
1694 let mut err = struct_span_err!(self.tcx.sess, span, E0631,
1695 "type mismatch in {} arguments",
1696 if argument_is_closure { "closure" } else { "function" });
1698 let found_str = format!(
1699 "expected signature of `{}`",
1700 build_fn_sig_string(self.tcx, found.skip_binder())
1702 err.span_label(span, found_str);
1704 let found_span = found_span.unwrap_or(span);
1705 let expected_str = format!(
1706 "found signature of `{}`",
1707 build_fn_sig_string(self.tcx, expected_ref.skip_binder())
1709 err.span_label(found_span, expected_str);
1715 impl<'tcx> TyCtxt<'tcx> {
1716 pub fn recursive_type_with_infinite_size_error(self,
1718 -> DiagnosticBuilder<'tcx>
1720 assert!(type_def_id.is_local());
1721 let span = self.hir().span_if_local(type_def_id).unwrap();
1722 let span = self.sess.source_map().def_span(span);
1723 let mut err = struct_span_err!(self.sess, span, E0072,
1724 "recursive type `{}` has infinite size",
1725 self.def_path_str(type_def_id));
1726 err.span_label(span, "recursive type has infinite size");
1727 err.help(&format!("insert indirection (e.g., a `Box`, `Rc`, or `&`) \
1728 at some point to make `{}` representable",
1729 self.def_path_str(type_def_id)));
1733 pub fn report_object_safety_error(
1736 trait_def_id: DefId,
1737 violations: Vec<ObjectSafetyViolation>,
1738 ) -> DiagnosticBuilder<'tcx> {
1739 let trait_str = self.def_path_str(trait_def_id);
1740 let span = self.sess.source_map().def_span(span);
1741 let mut err = struct_span_err!(
1742 self.sess, span, E0038,
1743 "the trait `{}` cannot be made into an object",
1745 err.span_label(span, format!("the trait `{}` cannot be made into an object", trait_str));
1747 let mut reported_violations = FxHashSet::default();
1748 for violation in violations {
1749 if reported_violations.insert(violation.clone()) {
1750 match violation.span() {
1751 Some(span) => err.span_label(span, violation.error_msg()),
1752 None => err.note(&violation.error_msg()),
1757 if self.sess.trait_methods_not_found.borrow().contains(&span) {
1758 // Avoid emitting error caused by non-existing method (#58734)
1766 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
1767 fn maybe_report_ambiguity(
1769 obligation: &PredicateObligation<'tcx>,
1770 body_id: Option<hir::BodyId>,
1772 // Unable to successfully determine, probably means
1773 // insufficient type information, but could mean
1774 // ambiguous impls. The latter *ought* to be a
1775 // coherence violation, so we don't report it here.
1777 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
1778 let span = obligation.cause.span;
1781 "maybe_report_ambiguity(predicate={:?}, obligation={:?} body_id={:?}, code={:?})",
1785 obligation.cause.code,
1788 // Ambiguity errors are often caused as fallout from earlier
1789 // errors. So just ignore them if this infcx is tainted.
1790 if self.is_tainted_by_errors() {
1795 ty::Predicate::Trait(ref data) => {
1796 let trait_ref = data.to_poly_trait_ref();
1797 let self_ty = trait_ref.self_ty();
1798 debug!("self_ty {:?} {:?} trait_ref {:?}", self_ty, self_ty.kind, trait_ref);
1800 if predicate.references_error() {
1803 // Typically, this ambiguity should only happen if
1804 // there are unresolved type inference variables
1805 // (otherwise it would suggest a coherence
1806 // failure). But given #21974 that is not necessarily
1807 // the case -- we can have multiple where clauses that
1808 // are only distinguished by a region, which results
1809 // in an ambiguity even when all types are fully
1810 // known, since we don't dispatch based on region
1813 // This is kind of a hack: it frequently happens that some earlier
1814 // error prevents types from being fully inferred, and then we get
1815 // a bunch of uninteresting errors saying something like "<generic
1816 // #0> doesn't implement Sized". It may even be true that we
1817 // could just skip over all checks where the self-ty is an
1818 // inference variable, but I was afraid that there might be an
1819 // inference variable created, registered as an obligation, and
1820 // then never forced by writeback, and hence by skipping here we'd
1821 // be ignoring the fact that we don't KNOW the type works
1822 // out. Though even that would probably be harmless, given that
1823 // we're only talking about builtin traits, which are known to be
1824 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
1825 // avoid inundating the user with unnecessary errors, but we now
1826 // check upstream for type errors and dont add the obligations to
1827 // begin with in those cases.
1829 self.tcx.lang_items().sized_trait()
1830 .map_or(false, |sized_id| sized_id == trait_ref.def_id())
1832 self.need_type_info_err(body_id, span, self_ty).emit();
1834 let mut err = struct_span_err!(
1838 "type annotations needed: cannot resolve `{}`",
1841 self.note_obligation_cause(&mut err, obligation);
1846 ty::Predicate::WellFormed(ty) => {
1847 // Same hacky approach as above to avoid deluging user
1848 // with error messages.
1849 if !ty.references_error() && !self.tcx.sess.has_errors() {
1850 self.need_type_info_err(body_id, span, ty).emit();
1854 ty::Predicate::Subtype(ref data) => {
1855 if data.references_error() || self.tcx.sess.has_errors() {
1856 // no need to overload user in such cases
1858 let &SubtypePredicate { a_is_expected: _, a, b } = data.skip_binder();
1859 // both must be type variables, or the other would've been instantiated
1860 assert!(a.is_ty_var() && b.is_ty_var());
1861 self.need_type_info_err(body_id,
1862 obligation.cause.span,
1868 if !self.tcx.sess.has_errors() {
1869 let mut err = struct_span_err!(
1871 obligation.cause.span,
1873 "type annotations needed: cannot resolve `{}`",
1876 self.note_obligation_cause(&mut err, obligation);
1883 /// Returns `true` if the trait predicate may apply for *some* assignment
1884 /// to the type parameters.
1885 fn predicate_can_apply(
1887 param_env: ty::ParamEnv<'tcx>,
1888 pred: ty::PolyTraitRef<'tcx>,
1890 struct ParamToVarFolder<'a, 'tcx> {
1891 infcx: &'a InferCtxt<'a, 'tcx>,
1892 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
1895 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
1896 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { self.infcx.tcx }
1898 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1899 if let ty::Param(ty::ParamTy {name, .. }) = ty.kind {
1900 let infcx = self.infcx;
1901 self.var_map.entry(ty).or_insert_with(||
1903 TypeVariableOrigin {
1904 kind: TypeVariableOriginKind::TypeParameterDefinition(name),
1910 ty.super_fold_with(self)
1916 let mut selcx = SelectionContext::new(self);
1918 let cleaned_pred = pred.fold_with(&mut ParamToVarFolder {
1920 var_map: Default::default()
1923 let cleaned_pred = super::project::normalize(
1926 ObligationCause::dummy(),
1930 let obligation = Obligation::new(
1931 ObligationCause::dummy(),
1933 cleaned_pred.to_predicate()
1936 self.predicate_may_hold(&obligation)
1940 fn note_obligation_cause(
1942 err: &mut DiagnosticBuilder<'_>,
1943 obligation: &PredicateObligation<'tcx>,
1945 // First, attempt to add note to this error with an async-await-specific
1946 // message, and fall back to regular note otherwise.
1947 if !self.note_obligation_cause_for_async_await(err, obligation) {
1948 self.note_obligation_cause_code(err, &obligation.predicate, &obligation.cause.code,
1953 /// Adds an async-await specific note to the diagnostic:
1955 /// ```ignore (diagnostic)
1956 /// note: future does not implement `std::marker::Send` because this value is used across an
1958 /// --> $DIR/issue-64130-non-send-future-diags.rs:15:5
1960 /// LL | let g = x.lock().unwrap();
1961 /// | - has type `std::sync::MutexGuard<'_, u32>`
1962 /// LL | baz().await;
1963 /// | ^^^^^^^^^^^ await occurs here, with `g` maybe used later
1965 /// | - `g` is later dropped here
1968 /// Returns `true` if an async-await specific note was added to the diagnostic.
1969 fn note_obligation_cause_for_async_await(
1971 err: &mut DiagnosticBuilder<'_>,
1972 obligation: &PredicateObligation<'tcx>,
1974 debug!("note_obligation_cause_for_async_await: obligation.predicate={:?} \
1975 obligation.cause.span={:?}", obligation.predicate, obligation.cause.span);
1976 let source_map = self.tcx.sess.source_map();
1978 // Look into the obligation predicate to determine the type in the generator which meant
1979 // that the predicate was not satisifed.
1980 let (trait_ref, target_ty) = match obligation.predicate {
1981 ty::Predicate::Trait(trait_predicate) =>
1982 (trait_predicate.skip_binder().trait_ref, trait_predicate.skip_binder().self_ty()),
1985 debug!("note_obligation_cause_for_async_await: target_ty={:?}", target_ty);
1987 // Attempt to detect an async-await error by looking at the obligation causes, looking
1988 // for only generators, generator witnesses, opaque types or `std::future::GenFuture` to
1991 // When a future does not implement a trait because of a captured type in one of the
1992 // generators somewhere in the call stack, then the result is a chain of obligations.
1993 // Given a `async fn` A that calls a `async fn` B which captures a non-send type and that
1994 // future is passed as an argument to a function C which requires a `Send` type, then the
1995 // chain looks something like this:
1997 // - `BuiltinDerivedObligation` with a generator witness (B)
1998 // - `BuiltinDerivedObligation` with a generator (B)
1999 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (B)
2000 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
2001 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
2002 // - `BuiltinDerivedObligation` with a generator witness (A)
2003 // - `BuiltinDerivedObligation` with a generator (A)
2004 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (A)
2005 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
2006 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
2007 // - `BindingObligation` with `impl_send (Send requirement)
2009 // The first obligations in the chain can be used to get the details of the type that is
2010 // captured but the entire chain must be inspected to detect this case.
2011 let mut generator = None;
2012 let mut next_code = Some(&obligation.cause.code);
2013 while let Some(code) = next_code {
2014 debug!("note_obligation_cause_for_async_await: code={:?}", code);
2016 ObligationCauseCode::BuiltinDerivedObligation(derived_obligation) |
2017 ObligationCauseCode::ImplDerivedObligation(derived_obligation) => {
2018 debug!("note_obligation_cause_for_async_await: self_ty.kind={:?}",
2019 derived_obligation.parent_trait_ref.self_ty().kind);
2020 match derived_obligation.parent_trait_ref.self_ty().kind {
2021 ty::Adt(ty::AdtDef { did, .. }, ..) if
2022 self.tcx.is_diagnostic_item(sym::gen_future, *did) => {},
2023 ty::Generator(did, ..) => generator = generator.or(Some(did)),
2024 ty::GeneratorWitness(_) | ty::Opaque(..) => {},
2028 next_code = Some(derived_obligation.parent_code.as_ref());
2030 ObligationCauseCode::ItemObligation(_) | ObligationCauseCode::BindingObligation(..)
2031 if generator.is_some() => break,
2036 let generator_did = generator.expect("can only reach this if there was a generator");
2038 // Only continue to add a note if the generator is from an `async` function.
2039 let parent_node = self.tcx.parent(generator_did)
2040 .and_then(|parent_did| self.tcx.hir().get_if_local(parent_did));
2041 debug!("note_obligation_cause_for_async_await: parent_node={:?}", parent_node);
2042 if let Some(hir::Node::Item(hir::Item {
2043 kind: hir::ItemKind::Fn(sig, _, _),
2046 debug!("note_obligation_cause_for_async_await: header={:?}", sig.header);
2047 if sig.header.asyncness != hir::IsAsync::Async {
2052 let span = self.tcx.def_span(generator_did);
2053 let tables = self.tcx.typeck_tables_of(generator_did);
2054 debug!("note_obligation_cause_for_async_await: generator_did={:?} span={:?} ",
2055 generator_did, span);
2057 // Look for a type inside the generator interior that matches the target type to get
2059 let target_span = tables.generator_interior_types.iter()
2060 .find(|ty::GeneratorInteriorTypeCause { ty, .. }| ty::TyS::same_type(*ty, target_ty))
2061 .map(|ty::GeneratorInteriorTypeCause { span, scope_span, .. }|
2062 (span, source_map.span_to_snippet(*span), scope_span));
2063 if let Some((target_span, Ok(snippet), scope_span)) = target_span {
2064 // Look at the last interior type to get a span for the `.await`.
2065 let await_span = tables.generator_interior_types.iter().map(|i| i.span).last().unwrap();
2066 let mut span = MultiSpan::from_span(await_span);
2067 span.push_span_label(
2068 await_span, format!("await occurs here, with `{}` maybe used later", snippet));
2070 span.push_span_label(*target_span, format!("has type `{}`", target_ty));
2072 // If available, use the scope span to annotate the drop location.
2073 if let Some(scope_span) = scope_span {
2074 span.push_span_label(
2075 source_map.end_point(*scope_span),
2076 format!("`{}` is later dropped here", snippet),
2080 err.span_note(span, &format!(
2081 "future does not implement `{}` as this value is used across an await",
2085 // Add a note for the item obligation that remains - normally a note pointing to the
2086 // bound that introduced the obligation (e.g. `T: Send`).
2087 debug!("note_obligation_cause_for_async_await: next_code={:?}", next_code);
2088 self.note_obligation_cause_code(
2090 &obligation.predicate,
2101 fn note_obligation_cause_code<T>(&self,
2102 err: &mut DiagnosticBuilder<'_>,
2104 cause_code: &ObligationCauseCode<'tcx>,
2105 obligated_types: &mut Vec<&ty::TyS<'tcx>>)
2106 where T: fmt::Display
2110 ObligationCauseCode::ExprAssignable |
2111 ObligationCauseCode::MatchExpressionArm { .. } |
2112 ObligationCauseCode::MatchExpressionArmPattern { .. } |
2113 ObligationCauseCode::IfExpression { .. } |
2114 ObligationCauseCode::IfExpressionWithNoElse |
2115 ObligationCauseCode::MainFunctionType |
2116 ObligationCauseCode::StartFunctionType |
2117 ObligationCauseCode::IntrinsicType |
2118 ObligationCauseCode::MethodReceiver |
2119 ObligationCauseCode::ReturnNoExpression |
2120 ObligationCauseCode::MiscObligation => {}
2121 ObligationCauseCode::SliceOrArrayElem => {
2122 err.note("slice and array elements must have `Sized` type");
2124 ObligationCauseCode::TupleElem => {
2125 err.note("only the last element of a tuple may have a dynamically sized type");
2127 ObligationCauseCode::ProjectionWf(data) => {
2129 "required so that the projection `{}` is well-formed",
2133 ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
2135 "required so that reference `{}` does not outlive its referent",
2139 ObligationCauseCode::ObjectTypeBound(object_ty, region) => {
2141 "required so that the lifetime bound of `{}` for `{}` is satisfied",
2146 ObligationCauseCode::ItemObligation(item_def_id) => {
2147 let item_name = tcx.def_path_str(item_def_id);
2148 let msg = format!("required by `{}`", item_name);
2150 if let Some(sp) = tcx.hir().span_if_local(item_def_id) {
2151 let sp = tcx.sess.source_map().def_span(sp);
2152 err.span_label(sp, &msg);
2157 ObligationCauseCode::BindingObligation(item_def_id, span) => {
2158 let item_name = tcx.def_path_str(item_def_id);
2159 let msg = format!("required by this bound in `{}`", item_name);
2160 if let Some(ident) = tcx.opt_item_name(item_def_id) {
2161 err.span_label(ident.span, "");
2163 if span != DUMMY_SP {
2164 err.span_label(span, &msg);
2169 ObligationCauseCode::ObjectCastObligation(object_ty) => {
2170 err.note(&format!("required for the cast to the object type `{}`",
2171 self.ty_to_string(object_ty)));
2173 ObligationCauseCode::Coercion { source: _, target } => {
2174 err.note(&format!("required by cast to type `{}`",
2175 self.ty_to_string(target)));
2177 ObligationCauseCode::RepeatVec(suggest_const_in_array_repeat_expression) => {
2178 err.note("the `Copy` trait is required because the \
2179 repeated element will be copied");
2180 if suggest_const_in_array_repeat_expression {
2181 err.note("this array initializer can be evaluated at compile-time, for more \
2182 information, see issue \
2183 https://github.com/rust-lang/rust/issues/49147");
2184 if tcx.sess.opts.unstable_features.is_nightly_build() {
2185 err.help("add `#![feature(const_in_array_repeat_expression)]` to the \
2186 crate attributes to enable");
2190 ObligationCauseCode::VariableType(_) => {
2191 err.note("all local variables must have a statically known size");
2192 if !self.tcx.features().unsized_locals {
2193 err.help("unsized locals are gated as an unstable feature");
2196 ObligationCauseCode::SizedArgumentType => {
2197 err.note("all function arguments must have a statically known size");
2198 if !self.tcx.features().unsized_locals {
2199 err.help("unsized locals are gated as an unstable feature");
2202 ObligationCauseCode::SizedReturnType => {
2203 err.note("the return type of a function must have a \
2204 statically known size");
2206 ObligationCauseCode::SizedYieldType => {
2207 err.note("the yield type of a generator must have a \
2208 statically known size");
2210 ObligationCauseCode::AssignmentLhsSized => {
2211 err.note("the left-hand-side of an assignment must have a statically known size");
2213 ObligationCauseCode::TupleInitializerSized => {
2214 err.note("tuples must have a statically known size to be initialized");
2216 ObligationCauseCode::StructInitializerSized => {
2217 err.note("structs must have a statically known size to be initialized");
2219 ObligationCauseCode::FieldSized { adt_kind: ref item, last } => {
2221 AdtKind::Struct => {
2223 err.note("the last field of a packed struct may only have a \
2224 dynamically sized type if it does not need drop to be run");
2226 err.note("only the last field of a struct may have a dynamically \
2231 err.note("no field of a union may have a dynamically sized type");
2234 err.note("no field of an enum variant may have a dynamically sized type");
2238 ObligationCauseCode::ConstSized => {
2239 err.note("constant expressions must have a statically known size");
2241 ObligationCauseCode::ConstPatternStructural => {
2242 err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`");
2244 ObligationCauseCode::SharedStatic => {
2245 err.note("shared static variables must have a type that implements `Sync`");
2247 ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
2248 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2249 let ty = parent_trait_ref.skip_binder().self_ty();
2250 err.note(&format!("required because it appears within the type `{}`", ty));
2251 obligated_types.push(ty);
2253 let parent_predicate = parent_trait_ref.to_predicate();
2254 if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
2255 self.note_obligation_cause_code(err,
2261 ObligationCauseCode::ImplDerivedObligation(ref data) => {
2262 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2264 &format!("required because of the requirements on the impl of `{}` for `{}`",
2266 parent_trait_ref.skip_binder().self_ty()));
2267 let parent_predicate = parent_trait_ref.to_predicate();
2268 self.note_obligation_cause_code(err,
2273 ObligationCauseCode::CompareImplMethodObligation { .. } => {
2275 &format!("the requirement `{}` appears on the impl method \
2276 but not on the corresponding trait method",
2279 ObligationCauseCode::ReturnType |
2280 ObligationCauseCode::ReturnValue(_) |
2281 ObligationCauseCode::BlockTailExpression(_) => (),
2282 ObligationCauseCode::TrivialBound => {
2283 err.help("see issue #48214");
2284 if tcx.sess.opts.unstable_features.is_nightly_build() {
2285 err.help("add `#![feature(trivial_bounds)]` to the \
2286 crate attributes to enable",
2290 ObligationCauseCode::AssocTypeBound(ref data) => {
2291 err.span_label(data.original, "associated type defined here");
2292 if let Some(sp) = data.impl_span {
2293 err.span_label(sp, "in this `impl` item");
2295 for sp in &data.bounds {
2296 err.span_label(*sp, "restricted in this bound");
2302 fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder<'_>) {
2303 let current_limit = self.tcx.sess.recursion_limit.get();
2304 let suggested_limit = current_limit * 2;
2305 err.help(&format!("consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
2309 fn is_recursive_obligation(&self,
2310 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
2311 cause_code: &ObligationCauseCode<'tcx>) -> bool {
2312 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2313 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2315 if obligated_types.iter().any(|ot| ot == &parent_trait_ref.skip_binder().self_ty()) {
2323 /// Summarizes information
2326 /// An argument of non-tuple type. Parameters are (name, ty)
2327 Arg(String, String),
2329 /// An argument of tuple type. For a "found" argument, the span is
2330 /// the locationo in the source of the pattern. For a "expected"
2331 /// argument, it will be None. The vector is a list of (name, ty)
2332 /// strings for the components of the tuple.
2333 Tuple(Option<Span>, Vec<(String, String)>),
2337 fn empty() -> ArgKind {
2338 ArgKind::Arg("_".to_owned(), "_".to_owned())
2341 /// Creates an `ArgKind` from the expected type of an
2342 /// argument. It has no name (`_`) and an optional source span.
2343 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2345 ty::Tuple(ref tys) => ArgKind::Tuple(
2348 .map(|ty| ("_".to_owned(), ty.to_string()))
2349 .collect::<Vec<_>>()
2351 _ => ArgKind::Arg("_".to_owned(), t.to_string()),