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, pluralise};
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>,
199 self.resolve_vars_if_possible(&obligation.predicate);
201 if predicate.references_error() {
207 let mut err = &error.err;
208 let mut values = None;
210 // try to find the mismatched types to report the error with.
212 // this can fail if the problem was higher-ranked, in which
213 // cause I have no idea for a good error message.
214 if let ty::Predicate::Projection(ref data) = predicate {
215 let mut selcx = SelectionContext::new(self);
216 let (data, _) = self.replace_bound_vars_with_fresh_vars(
217 obligation.cause.span,
218 infer::LateBoundRegionConversionTime::HigherRankedType,
221 let mut obligations = vec![];
222 let normalized_ty = super::normalize_projection_type(
224 obligation.param_env,
226 obligation.cause.clone(),
230 if let Err(error) = self.at(&obligation.cause, obligation.param_env)
231 .eq(normalized_ty, data.ty) {
232 values = Some(infer::ValuePairs::Types(ExpectedFound {
233 expected: normalized_ty,
241 let msg = format!("type mismatch resolving `{}`", predicate);
242 let error_id = (DiagnosticMessageId::ErrorId(271),
243 Some(obligation.cause.span), msg);
244 let fresh = self.tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
246 let mut diag = struct_span_err!(
247 self.tcx.sess, obligation.cause.span, E0271,
248 "type mismatch resolving `{}`", predicate
250 self.note_type_err(&mut diag, &obligation.cause, None, values, err);
251 self.note_obligation_cause(&mut diag, obligation);
257 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
258 /// returns the fuzzy category of a given type, or None
259 /// if the type can be equated to any type.
260 fn type_category(t: Ty<'_>) -> Option<u32> {
265 ty::Int(..) | ty::Uint(..) | ty::Infer(ty::IntVar(..)) => Some(3),
266 ty::Float(..) | ty::Infer(ty::FloatVar(..)) => Some(4),
267 ty::Ref(..) | ty::RawPtr(..) => Some(5),
268 ty::Array(..) | ty::Slice(..) => Some(6),
269 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
270 ty::Dynamic(..) => Some(8),
271 ty::Closure(..) => Some(9),
272 ty::Tuple(..) => Some(10),
273 ty::Projection(..) => Some(11),
274 ty::Param(..) => Some(12),
275 ty::Opaque(..) => Some(13),
276 ty::Never => Some(14),
277 ty::Adt(adt, ..) => match adt.adt_kind() {
278 AdtKind::Struct => Some(15),
279 AdtKind::Union => Some(16),
280 AdtKind::Enum => Some(17),
282 ty::Generator(..) => Some(18),
283 ty::Foreign(..) => Some(19),
284 ty::GeneratorWitness(..) => Some(20),
285 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error => None,
286 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
290 match (type_category(a), type_category(b)) {
291 (Some(cat_a), Some(cat_b)) => match (&a.kind, &b.kind) {
292 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => def_a == def_b,
295 // infer and error can be equated to all types
300 fn impl_similar_to(&self,
301 trait_ref: ty::PolyTraitRef<'tcx>,
302 obligation: &PredicateObligation<'tcx>)
306 let param_env = obligation.param_env;
307 let trait_ref = tcx.erase_late_bound_regions(&trait_ref);
308 let trait_self_ty = trait_ref.self_ty();
310 let mut self_match_impls = vec![];
311 let mut fuzzy_match_impls = vec![];
313 self.tcx.for_each_relevant_impl(
314 trait_ref.def_id, trait_self_ty, |def_id| {
315 let impl_substs = self.fresh_substs_for_item(obligation.cause.span, def_id);
316 let impl_trait_ref = tcx
317 .impl_trait_ref(def_id)
319 .subst(tcx, impl_substs);
321 let impl_self_ty = impl_trait_ref.self_ty();
323 if let Ok(..) = self.can_eq(param_env, trait_self_ty, impl_self_ty) {
324 self_match_impls.push(def_id);
326 if trait_ref.substs.types().skip(1)
327 .zip(impl_trait_ref.substs.types().skip(1))
328 .all(|(u,v)| self.fuzzy_match_tys(u, v))
330 fuzzy_match_impls.push(def_id);
335 let impl_def_id = if self_match_impls.len() == 1 {
337 } else if fuzzy_match_impls.len() == 1 {
343 if tcx.has_attr(impl_def_id, sym::rustc_on_unimplemented) {
350 fn on_unimplemented_note(
352 trait_ref: ty::PolyTraitRef<'tcx>,
353 obligation: &PredicateObligation<'tcx>,
354 ) -> OnUnimplementedNote {
355 let def_id = self.impl_similar_to(trait_ref, obligation)
356 .unwrap_or_else(|| trait_ref.def_id());
357 let trait_ref = *trait_ref.skip_binder();
359 let mut flags = vec![];
360 match obligation.cause.code {
361 ObligationCauseCode::BuiltinDerivedObligation(..) |
362 ObligationCauseCode::ImplDerivedObligation(..) => {}
364 // this is a "direct", user-specified, rather than derived,
366 flags.push((sym::direct, None));
370 if let ObligationCauseCode::ItemObligation(item) = obligation.cause.code {
371 // FIXME: maybe also have some way of handling methods
372 // from other traits? That would require name resolution,
373 // which we might want to be some sort of hygienic.
375 // Currently I'm leaving it for what I need for `try`.
376 if self.tcx.trait_of_item(item) == Some(trait_ref.def_id) {
377 let method = self.tcx.item_name(item);
378 flags.push((sym::from_method, None));
379 flags.push((sym::from_method, Some(method.to_string())));
382 if let Some(t) = self.get_parent_trait_ref(&obligation.cause.code) {
383 flags.push((sym::parent_trait, Some(t)));
386 if let Some(k) = obligation.cause.span.desugaring_kind() {
387 flags.push((sym::from_desugaring, None));
388 flags.push((sym::from_desugaring, Some(format!("{:?}", k))));
390 let generics = self.tcx.generics_of(def_id);
391 let self_ty = trait_ref.self_ty();
392 // This is also included through the generics list as `Self`,
393 // but the parser won't allow you to use it
394 flags.push((sym::_Self, Some(self_ty.to_string())));
395 if let Some(def) = self_ty.ty_adt_def() {
396 // We also want to be able to select self's original
397 // signature with no type arguments resolved
398 flags.push((sym::_Self, Some(self.tcx.type_of(def.did).to_string())));
401 for param in generics.params.iter() {
402 let value = match param.kind {
403 GenericParamDefKind::Type { .. } |
404 GenericParamDefKind::Const => {
405 trait_ref.substs[param.index as usize].to_string()
407 GenericParamDefKind::Lifetime => continue,
409 let name = param.name.as_symbol();
410 flags.push((name, Some(value)));
413 if let Some(true) = self_ty.ty_adt_def().map(|def| def.did.is_local()) {
414 flags.push((sym::crate_local, None));
417 // Allow targeting all integers using `{integral}`, even if the exact type was resolved
418 if self_ty.is_integral() {
419 flags.push((sym::_Self, Some("{integral}".to_owned())));
422 if let ty::Array(aty, len) = self_ty.kind {
423 flags.push((sym::_Self, Some("[]".to_owned())));
424 flags.push((sym::_Self, Some(format!("[{}]", aty))));
425 if let Some(def) = aty.ty_adt_def() {
426 // We also want to be able to select the array's type's original
427 // signature with no type arguments resolved
430 Some(format!("[{}]", self.tcx.type_of(def.did).to_string())),
433 if let Some(len) = len.try_eval_usize(tcx, ty::ParamEnv::empty()) {
436 Some(format!("[{}; {}]", self.tcx.type_of(def.did).to_string(), len)),
441 Some(format!("[{}; _]", self.tcx.type_of(def.did).to_string())),
447 if let Ok(Some(command)) = OnUnimplementedDirective::of_item(
448 self.tcx, trait_ref.def_id, def_id
450 command.evaluate(self.tcx, trait_ref, &flags[..])
452 OnUnimplementedNote::empty()
456 fn find_similar_impl_candidates(
458 trait_ref: ty::PolyTraitRef<'tcx>,
459 ) -> Vec<ty::TraitRef<'tcx>> {
460 let simp = fast_reject::simplify_type(self.tcx, trait_ref.skip_binder().self_ty(), true);
461 let all_impls = self.tcx.all_impls(trait_ref.def_id());
464 Some(simp) => all_impls.iter().filter_map(|&def_id| {
465 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
466 let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
467 if let Some(imp_simp) = imp_simp {
468 if simp != imp_simp {
475 None => all_impls.iter().map(|&def_id|
476 self.tcx.impl_trait_ref(def_id).unwrap()
481 fn report_similar_impl_candidates(
483 impl_candidates: Vec<ty::TraitRef<'tcx>>,
484 err: &mut DiagnosticBuilder<'_>,
486 if impl_candidates.is_empty() {
490 let len = impl_candidates.len();
491 let end = if impl_candidates.len() <= 5 {
492 impl_candidates.len()
497 let normalize = |candidate| self.tcx.infer_ctxt().enter(|ref infcx| {
498 let normalized = infcx
499 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
500 .normalize(candidate)
503 Some(normalized) => format!("\n {:?}", normalized.value),
504 None => format!("\n {:?}", candidate),
508 // Sort impl candidates so that ordering is consistent for UI tests.
509 let mut normalized_impl_candidates = impl_candidates
512 .collect::<Vec<String>>();
514 // Sort before taking the `..end` range,
515 // because the ordering of `impl_candidates` may not be deterministic:
516 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
517 normalized_impl_candidates.sort();
519 err.help(&format!("the following implementations were found:{}{}",
520 normalized_impl_candidates[..end].join(""),
522 format!("\nand {} others", len - 4)
529 /// Reports that an overflow has occurred and halts compilation. We
530 /// halt compilation unconditionally because it is important that
531 /// overflows never be masked -- they basically represent computations
532 /// whose result could not be truly determined and thus we can't say
533 /// if the program type checks or not -- and they are unusual
534 /// occurrences in any case.
535 pub fn report_overflow_error<T>(&self,
536 obligation: &Obligation<'tcx, T>,
537 suggest_increasing_limit: bool) -> !
538 where T: fmt::Display + TypeFoldable<'tcx>
541 self.resolve_vars_if_possible(&obligation.predicate);
542 let mut err = struct_span_err!(self.tcx.sess, obligation.cause.span, E0275,
543 "overflow evaluating the requirement `{}`",
546 if suggest_increasing_limit {
547 self.suggest_new_overflow_limit(&mut err);
550 self.note_obligation_cause_code(&mut err, &obligation.predicate, &obligation.cause.code,
554 self.tcx.sess.abort_if_errors();
558 /// Reports that a cycle was detected which led to overflow and halts
559 /// compilation. This is equivalent to `report_overflow_error` except
560 /// that we can give a more helpful error message (and, in particular,
561 /// we do not suggest increasing the overflow limit, which is not
563 pub fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
564 let cycle = self.resolve_vars_if_possible(&cycle.to_owned());
565 assert!(cycle.len() > 0);
567 debug!("report_overflow_error_cycle: cycle={:?}", cycle);
569 self.report_overflow_error(&cycle[0], false);
572 pub fn report_extra_impl_obligation(&self,
574 item_name: ast::Name,
575 _impl_item_def_id: DefId,
576 trait_item_def_id: DefId,
577 requirement: &dyn fmt::Display)
578 -> DiagnosticBuilder<'tcx>
580 let msg = "impl has stricter requirements than trait";
581 let sp = self.tcx.sess.source_map().def_span(error_span);
583 let mut err = struct_span_err!(self.tcx.sess, sp, E0276, "{}", msg);
585 if let Some(trait_item_span) = self.tcx.hir().span_if_local(trait_item_def_id) {
586 let span = self.tcx.sess.source_map().def_span(trait_item_span);
587 err.span_label(span, format!("definition of `{}` from trait", item_name));
590 err.span_label(sp, format!("impl has extra requirement {}", requirement));
596 /// Gets the parent trait chain start
597 fn get_parent_trait_ref(&self, code: &ObligationCauseCode<'tcx>) -> Option<String> {
599 &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
600 let parent_trait_ref = self.resolve_vars_if_possible(
601 &data.parent_trait_ref);
602 match self.get_parent_trait_ref(&data.parent_code) {
604 None => Some(parent_trait_ref.skip_binder().self_ty().to_string()),
611 pub fn report_selection_error(
613 obligation: &PredicateObligation<'tcx>,
614 error: &SelectionError<'tcx>,
615 fallback_has_occurred: bool,
618 let span = obligation.cause.span;
620 let mut err = match *error {
621 SelectionError::Unimplemented => {
622 if let ObligationCauseCode::CompareImplMethodObligation {
623 item_name, impl_item_def_id, trait_item_def_id,
624 } = obligation.cause.code {
625 self.report_extra_impl_obligation(
630 &format!("`{}`", obligation.predicate))
634 match obligation.predicate {
635 ty::Predicate::Trait(ref trait_predicate) => {
636 let trait_predicate =
637 self.resolve_vars_if_possible(trait_predicate);
639 if self.tcx.sess.has_errors() && trait_predicate.references_error() {
642 let trait_ref = trait_predicate.to_poly_trait_ref();
643 let (post_message, pre_message) =
644 self.get_parent_trait_ref(&obligation.cause.code)
645 .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
646 .unwrap_or_default();
648 let OnUnimplementedNote { message, label, note }
649 = self.on_unimplemented_note(trait_ref, obligation);
650 let have_alt_message = message.is_some() || label.is_some();
651 let is_try = self.tcx.sess.source_map().span_to_snippet(span)
654 let is_from = format!("{}", trait_ref).starts_with("std::convert::From<");
655 let (message, note) = if is_try && is_from {
657 "`?` couldn't convert the error to `{}`",
660 "the question mark operation (`?`) implicitly performs a \
661 conversion on the error value using the `From` trait".to_owned()
667 let mut err = struct_span_err!(
672 message.unwrap_or_else(|| format!(
673 "the trait bound `{}` is not satisfied{}",
674 trait_ref.to_predicate(),
679 if obligation.cause.code == ObligationCauseCode::MainFunctionType {
680 "consider using `()`, or a `Result`".to_owned()
683 "{}the trait `{}` is not implemented for `{}`",
690 if let Some(ref s) = label {
691 // If it has a custom `#[rustc_on_unimplemented]`
692 // error message, let's display it as the label!
693 err.span_label(span, s.as_str());
694 err.help(&explanation);
696 err.span_label(span, explanation);
698 if let Some(ref s) = note {
699 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
700 err.note(s.as_str());
703 self.suggest_borrow_on_unsized_slice(&obligation.cause.code, &mut err);
704 self.suggest_fn_call(&obligation, &mut err, &trait_ref, points_at_arg);
705 self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
706 self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
708 // Try to report a help message
709 if !trait_ref.has_infer_types() &&
710 self.predicate_can_apply(obligation.param_env, trait_ref) {
711 // If a where-clause may be useful, remind the
712 // user that they can add it.
714 // don't display an on-unimplemented note, as
715 // these notes will often be of the form
716 // "the type `T` can't be frobnicated"
717 // which is somewhat confusing.
718 self.suggest_restricting_param_bound(
721 obligation.cause.body_id,
724 if !have_alt_message {
725 // Can't show anything else useful, try to find similar impls.
726 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
727 self.report_similar_impl_candidates(impl_candidates, &mut err);
729 self.suggest_change_mut(
737 // If this error is due to `!: Trait` not implemented but `(): Trait` is
738 // implemented, and fallback has occurred, then it could be due to a
739 // variable that used to fallback to `()` now falling back to `!`. Issue a
740 // note informing about the change in behaviour.
741 if trait_predicate.skip_binder().self_ty().is_never()
742 && fallback_has_occurred
744 let predicate = trait_predicate.map_bound(|mut trait_pred| {
745 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
747 &trait_pred.trait_ref.substs[1..],
751 let unit_obligation = Obligation {
752 predicate: ty::Predicate::Trait(predicate),
753 .. obligation.clone()
755 if self.predicate_may_hold(&unit_obligation) {
756 err.note("the trait is implemented for `()`. \
757 Possibly this error has been caused by changes to \
758 Rust's type-inference algorithm \
759 (see: https://github.com/rust-lang/rust/issues/48950 \
760 for more info). Consider whether you meant to use the \
761 type `()` here instead.");
768 ty::Predicate::Subtype(ref predicate) => {
769 // Errors for Subtype predicates show up as
770 // `FulfillmentErrorCode::CodeSubtypeError`,
771 // not selection error.
772 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
775 ty::Predicate::RegionOutlives(ref predicate) => {
776 let predicate = self.resolve_vars_if_possible(predicate);
777 let err = self.region_outlives_predicate(&obligation.cause,
778 &predicate).err().unwrap();
780 self.tcx.sess, span, E0279,
781 "the requirement `{}` is not satisfied (`{}`)",
786 ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
788 self.resolve_vars_if_possible(&obligation.predicate);
789 struct_span_err!(self.tcx.sess, span, E0280,
790 "the requirement `{}` is not satisfied",
794 ty::Predicate::ObjectSafe(trait_def_id) => {
795 let violations = self.tcx.object_safety_violations(trait_def_id);
796 self.tcx.report_object_safety_error(
803 ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
804 let found_kind = self.closure_kind(closure_def_id, closure_substs).unwrap();
805 let closure_span = self.tcx.sess.source_map()
806 .def_span(self.tcx.hir().span_if_local(closure_def_id).unwrap());
807 let hir_id = self.tcx.hir().as_local_hir_id(closure_def_id).unwrap();
808 let mut err = struct_span_err!(
809 self.tcx.sess, closure_span, E0525,
810 "expected a closure that implements the `{}` trait, \
811 but this closure only implements `{}`",
817 format!("this closure implements `{}`, not `{}`", found_kind, kind));
819 obligation.cause.span,
820 format!("the requirement to implement `{}` derives from here", kind));
822 // Additional context information explaining why the closure only implements
823 // a particular trait.
824 if let Some(tables) = self.in_progress_tables {
825 let tables = tables.borrow();
826 match (found_kind, tables.closure_kind_origins().get(hir_id)) {
827 (ty::ClosureKind::FnOnce, Some((span, name))) => {
828 err.span_label(*span, format!(
829 "closure is `FnOnce` because it moves the \
830 variable `{}` out of its environment", name));
832 (ty::ClosureKind::FnMut, Some((span, name))) => {
833 err.span_label(*span, format!(
834 "closure is `FnMut` because it mutates the \
835 variable `{}` here", name));
845 ty::Predicate::WellFormed(ty) => {
846 if !self.tcx.sess.opts.debugging_opts.chalk {
847 // WF predicates cannot themselves make
848 // errors. They can only block due to
849 // ambiguity; otherwise, they always
850 // degenerate into other obligations
852 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
854 // FIXME: we'll need a better message which takes into account
855 // which bounds actually failed to hold.
856 self.tcx.sess.struct_span_err(
858 &format!("the type `{}` is not well-formed (chalk)", ty)
863 ty::Predicate::ConstEvaluatable(..) => {
864 // Errors for `ConstEvaluatable` predicates show up as
865 // `SelectionError::ConstEvalFailure`,
866 // not `Unimplemented`.
868 "const-evaluatable requirement gave wrong error: `{:?}`", obligation)
873 OutputTypeParameterMismatch(ref found_trait_ref, ref expected_trait_ref, _) => {
874 let found_trait_ref = self.resolve_vars_if_possible(&*found_trait_ref);
875 let expected_trait_ref = self.resolve_vars_if_possible(&*expected_trait_ref);
877 if expected_trait_ref.self_ty().references_error() {
881 let found_trait_ty = found_trait_ref.self_ty();
883 let found_did = match found_trait_ty.kind {
884 ty::Closure(did, _) | ty::Foreign(did) | ty::FnDef(did, _) => Some(did),
885 ty::Adt(def, _) => Some(def.did),
889 let found_span = found_did.and_then(|did|
890 self.tcx.hir().span_if_local(did)
891 ).map(|sp| self.tcx.sess.source_map().def_span(sp)); // the sp could be an fn def
893 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
894 // We check closures twice, with obligations flowing in different directions,
895 // but we want to complain about them only once.
899 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
901 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind {
902 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
903 _ => vec![ArgKind::empty()],
906 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
907 let expected = match expected_ty.kind {
908 ty::Tuple(ref tys) => tys.iter()
909 .map(|t| ArgKind::from_expected_ty(t.expect_ty(), Some(span))).collect(),
910 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
913 if found.len() == expected.len() {
914 self.report_closure_arg_mismatch(span,
919 let (closure_span, found) = found_did
920 .and_then(|did| self.tcx.hir().get_if_local(did))
922 let (found_span, found) = self.get_fn_like_arguments(node);
923 (Some(found_span), found)
924 }).unwrap_or((found_span, found));
926 self.report_arg_count_mismatch(span,
930 found_trait_ty.is_closure())
934 TraitNotObjectSafe(did) => {
935 let violations = self.tcx.object_safety_violations(did);
936 self.tcx.report_object_safety_error(span, did, violations)
939 // already reported in the query
940 ConstEvalFailure(err) => {
941 self.tcx.sess.delay_span_bug(
943 &format!("constant in type had an ignored error: {:?}", err),
949 bug!("overflow should be handled before the `report_selection_error` path");
953 self.note_obligation_cause(&mut err, obligation);
958 fn suggest_restricting_param_bound(
960 err: &mut DiagnosticBuilder<'_>,
961 trait_ref: &ty::PolyTraitRef<'_>,
964 let self_ty = trait_ref.self_ty();
965 let (param_ty, projection) = match &self_ty.kind {
966 ty::Param(_) => (true, None),
967 ty::Projection(projection) => (false, Some(projection)),
971 let mut suggest_restriction = |generics: &hir::Generics, msg| {
972 let span = generics.where_clause.span_for_predicates_or_empty_place();
973 if !span.from_expansion() && span.desugaring_kind().is_none() {
975 generics.where_clause.span_for_predicates_or_empty_place().shrink_to_hi(),
976 &format!("consider further restricting {}", msg),
979 if !generics.where_clause.predicates.is_empty() {
984 trait_ref.to_predicate(),
986 Applicability::MachineApplicable,
991 // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
992 // don't suggest `T: Sized + ?Sized`.
993 let mut hir_id = body_id;
994 while let Some(node) = self.tcx.hir().find(hir_id) {
996 hir::Node::TraitItem(hir::TraitItem {
998 kind: hir::TraitItemKind::Method(..), ..
999 }) if param_ty && self_ty == self.tcx.types.self_param => {
1000 // Restricting `Self` for a single method.
1001 suggest_restriction(&generics, "`Self`");
1005 hir::Node::Item(hir::Item {
1006 kind: hir::ItemKind::Fn(_, _, generics, _), ..
1008 hir::Node::TraitItem(hir::TraitItem {
1010 kind: hir::TraitItemKind::Method(..), ..
1012 hir::Node::ImplItem(hir::ImplItem {
1014 kind: hir::ImplItemKind::Method(..), ..
1016 hir::Node::Item(hir::Item {
1017 kind: hir::ItemKind::Trait(_, _, generics, _, _), ..
1019 hir::Node::Item(hir::Item {
1020 kind: hir::ItemKind::Impl(_, _, _, generics, ..), ..
1021 }) if projection.is_some() => {
1022 // Missing associated type bound.
1023 suggest_restriction(&generics, "the associated type");
1027 hir::Node::Item(hir::Item { kind: hir::ItemKind::Struct(_, generics), span, .. }) |
1028 hir::Node::Item(hir::Item { kind: hir::ItemKind::Enum(_, generics), span, .. }) |
1029 hir::Node::Item(hir::Item { kind: hir::ItemKind::Union(_, generics), span, .. }) |
1030 hir::Node::Item(hir::Item {
1031 kind: hir::ItemKind::Trait(_, _, generics, ..), span, ..
1033 hir::Node::Item(hir::Item {
1034 kind: hir::ItemKind::Impl(_, _, _, generics, ..), span, ..
1036 hir::Node::Item(hir::Item {
1037 kind: hir::ItemKind::Fn(_, _, generics, _), span, ..
1039 hir::Node::Item(hir::Item {
1040 kind: hir::ItemKind::TyAlias(_, generics), span, ..
1042 hir::Node::Item(hir::Item {
1043 kind: hir::ItemKind::TraitAlias(generics, _), span, ..
1045 hir::Node::Item(hir::Item {
1046 kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }), span, ..
1048 hir::Node::TraitItem(hir::TraitItem { generics, span, .. }) |
1049 hir::Node::ImplItem(hir::ImplItem { generics, span, .. })
1051 // Missing generic type parameter bound.
1052 let restrict_msg = "consider further restricting this bound";
1053 let param_name = self_ty.to_string();
1054 for param in generics.params.iter().filter(|p| {
1055 ¶m_name == std::convert::AsRef::<str>::as_ref(&p.name.ident().as_str())
1057 if param_name.starts_with("impl ") {
1058 // `impl Trait` in argument:
1059 // `fn foo(x: impl Trait) {}` → `fn foo(t: impl Trait + Trait2) {}`
1060 err.span_suggestion(
1063 // `impl CurrentTrait + MissingTrait`
1064 format!("{} + {}", param.name.ident(), trait_ref),
1065 Applicability::MachineApplicable,
1067 } else if generics.where_clause.predicates.is_empty() &&
1068 param.bounds.is_empty()
1070 // If there are no bounds whatsoever, suggest adding a constraint
1071 // to the type parameter:
1072 // `fn foo<T>(t: T) {}` → `fn foo<T: Trait>(t: T) {}`
1073 err.span_suggestion(
1075 "consider restricting this bound",
1076 format!("{}", trait_ref.to_predicate()),
1077 Applicability::MachineApplicable,
1079 } else if !generics.where_clause.predicates.is_empty() {
1080 // There is a `where` clause, so suggest expanding it:
1081 // `fn foo<T>(t: T) where T: Debug {}` →
1082 // `fn foo<T>(t: T) where T: Debug, T: Trait {}`
1083 err.span_suggestion(
1084 generics.where_clause.span().unwrap().shrink_to_hi(),
1086 "consider further restricting type parameter `{}`",
1089 format!(", {}", trait_ref.to_predicate()),
1090 Applicability::MachineApplicable,
1093 // If there is no `where` clause lean towards constraining to the
1095 // `fn foo<X: Bar, T>(t: T, x: X) {}` → `fn foo<T: Trait>(t: T) {}`
1096 // `fn foo<T: Bar>(t: T) {}` → `fn foo<T: Bar + Trait>(t: T) {}`
1097 let sp = param.span.with_hi(span.hi());
1098 let span = self.tcx.sess.source_map()
1099 .span_through_char(sp, ':');
1100 if sp != param.span && sp != span {
1101 // Only suggest if we have high certainty that the span
1102 // covers the colon in `foo<T: Trait>`.
1103 err.span_suggestion(span, restrict_msg, format!(
1105 trait_ref.to_predicate(),
1106 ), Applicability::MachineApplicable);
1108 err.span_label(param.span, &format!(
1109 "consider adding a `where {}` bound",
1110 trait_ref.to_predicate(),
1118 hir::Node::Crate => return,
1123 hir_id = self.tcx.hir().get_parent_item(hir_id);
1127 /// When encountering an assignment of an unsized trait, like `let x = ""[..];`, provide a
1128 /// suggestion to borrow the initializer in order to use have a slice instead.
1129 fn suggest_borrow_on_unsized_slice(
1131 code: &ObligationCauseCode<'tcx>,
1132 err: &mut DiagnosticBuilder<'tcx>,
1134 if let &ObligationCauseCode::VariableType(hir_id) = code {
1135 let parent_node = self.tcx.hir().get_parent_node(hir_id);
1136 if let Some(Node::Local(ref local)) = self.tcx.hir().find(parent_node) {
1137 if let Some(ref expr) = local.init {
1138 if let hir::ExprKind::Index(_, _) = expr.kind {
1139 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
1140 err.span_suggestion(
1142 "consider borrowing here",
1143 format!("&{}", snippet),
1144 Applicability::MachineApplicable
1155 obligation: &PredicateObligation<'tcx>,
1156 err: &mut DiagnosticBuilder<'tcx>,
1157 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1158 points_at_arg: bool,
1160 let self_ty = trait_ref.self_ty();
1161 match self_ty.kind {
1162 ty::FnDef(def_id, _) => {
1163 // We tried to apply the bound to an `fn`. Check whether calling it would evaluate
1164 // to a type that *would* satisfy the trait binding. If it would, suggest calling
1165 // it: `bar(foo)` -> `bar(foo)`. This case is *very* likely to be hit if `foo` is
1167 let output_ty = self_ty.fn_sig(self.tcx).output();
1168 let new_trait_ref = ty::TraitRef {
1169 def_id: trait_ref.def_id(),
1170 substs: self.tcx.mk_substs_trait(output_ty.skip_binder(), &[]),
1172 let obligation = Obligation::new(
1173 obligation.cause.clone(),
1174 obligation.param_env,
1175 new_trait_ref.to_predicate(),
1177 match self.evaluate_obligation(&obligation) {
1178 Ok(EvaluationResult::EvaluatedToOk) |
1179 Ok(EvaluationResult::EvaluatedToOkModuloRegions) |
1180 Ok(EvaluationResult::EvaluatedToAmbig) => {
1181 if let Some(hir::Node::Item(hir::Item {
1183 kind: hir::ItemKind::Fn(.., body_id),
1185 })) = self.tcx.hir().get_if_local(def_id) {
1186 let body = self.tcx.hir().body(*body_id);
1187 let msg = "use parentheses to call the function";
1188 let snippet = format!(
1192 .map(|arg| match &arg.pat.kind {
1193 hir::PatKind::Binding(_, _, ident, None)
1194 if ident.name != kw::SelfLower => ident.to_string(),
1195 _ => "_".to_string(),
1196 }).collect::<Vec<_>>().join(", "),
1198 // When the obligation error has been ensured to have been caused by
1199 // an argument, the `obligation.cause.span` points at the expression
1200 // of the argument, so we can provide a suggestion. This is signaled
1201 // by `points_at_arg`. Otherwise, we give a more general note.
1203 err.span_suggestion(
1204 obligation.cause.span,
1207 Applicability::HasPlaceholders,
1210 err.help(&format!("{}: `{}`", msg, snippet));
1221 /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
1222 /// suggest removing these references until we reach a type that implements the trait.
1223 fn suggest_remove_reference(
1225 obligation: &PredicateObligation<'tcx>,
1226 err: &mut DiagnosticBuilder<'tcx>,
1227 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1229 let trait_ref = trait_ref.skip_binder();
1230 let span = obligation.cause.span;
1232 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1233 let refs_number = snippet.chars()
1234 .filter(|c| !c.is_whitespace())
1235 .take_while(|c| *c == '&')
1237 if let Some('\'') = snippet.chars()
1238 .filter(|c| !c.is_whitespace())
1241 { // Do not suggest removal of borrow from type arguments.
1245 let mut trait_type = trait_ref.self_ty();
1247 for refs_remaining in 0..refs_number {
1248 if let ty::Ref(_, t_type, _) = trait_type.kind {
1249 trait_type = t_type;
1251 let substs = self.tcx.mk_substs_trait(trait_type, &[]);
1252 let new_trait_ref = ty::TraitRef::new(trait_ref.def_id, substs);
1253 let new_obligation = Obligation::new(
1254 ObligationCause::dummy(),
1255 obligation.param_env,
1256 new_trait_ref.to_predicate(),
1259 if self.predicate_may_hold(&new_obligation) {
1260 let sp = self.tcx.sess.source_map()
1261 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1263 let remove_refs = refs_remaining + 1;
1264 let format_str = format!("consider removing {} leading `&`-references",
1267 err.span_suggestion_short(
1268 sp, &format_str, String::new(), Applicability::MachineApplicable
1279 /// Check if the trait bound is implemented for a different mutability and note it in the
1281 fn suggest_change_mut(
1283 obligation: &PredicateObligation<'tcx>,
1284 err: &mut DiagnosticBuilder<'tcx>,
1285 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1286 points_at_arg: bool,
1288 let span = obligation.cause.span;
1289 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1290 let refs_number = snippet.chars()
1291 .filter(|c| !c.is_whitespace())
1292 .take_while(|c| *c == '&')
1294 if let Some('\'') = snippet.chars()
1295 .filter(|c| !c.is_whitespace())
1298 { // Do not suggest removal of borrow from type arguments.
1301 let trait_ref = self.resolve_vars_if_possible(trait_ref);
1302 if trait_ref.has_infer_types() {
1303 // Do not ICE while trying to find if a reborrow would succeed on a trait with
1304 // unresolved bindings.
1308 if let ty::Ref(region, t_type, mutability) = trait_ref.skip_binder().self_ty().kind {
1309 let trait_type = match mutability {
1310 hir::Mutability::MutMutable => self.tcx.mk_imm_ref(region, t_type),
1311 hir::Mutability::MutImmutable => self.tcx.mk_mut_ref(region, t_type),
1314 let substs = self.tcx.mk_substs_trait(&trait_type, &[]);
1315 let new_trait_ref = ty::TraitRef::new(trait_ref.skip_binder().def_id, substs);
1316 let new_obligation = Obligation::new(
1317 ObligationCause::dummy(),
1318 obligation.param_env,
1319 new_trait_ref.to_predicate(),
1322 if self.evaluate_obligation_no_overflow(
1324 ).must_apply_modulo_regions() {
1325 let sp = self.tcx.sess.source_map()
1326 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1328 mutability == hir::Mutability::MutImmutable &&
1331 err.span_suggestion(
1333 "consider changing this borrow's mutability",
1334 "&mut ".to_string(),
1335 Applicability::MachineApplicable,
1339 "`{}` is implemented for `{:?}`, but not for `{:?}`",
1342 trait_ref.skip_binder().self_ty(),
1350 fn suggest_semicolon_removal(
1352 obligation: &PredicateObligation<'tcx>,
1353 err: &mut DiagnosticBuilder<'tcx>,
1355 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1357 let hir = self.tcx.hir();
1358 let parent_node = hir.get_parent_node(obligation.cause.body_id);
1359 let node = hir.find(parent_node);
1360 if let Some(hir::Node::Item(hir::Item {
1361 kind: hir::ItemKind::Fn(decl, _, _, body_id),
1364 let body = hir.body(*body_id);
1365 if let hir::ExprKind::Block(blk, _) = &body.value.kind {
1366 if decl.output.span().overlaps(span) && blk.expr.is_none() &&
1367 "()" == &trait_ref.self_ty().to_string()
1369 // FIXME(estebank): When encountering a method with a trait
1370 // bound not satisfied in the return type with a body that has
1371 // no return, suggest removal of semicolon on last statement.
1372 // Once that is added, close #54771.
1373 if let Some(ref stmt) = blk.stmts.last() {
1374 let sp = self.tcx.sess.source_map().end_point(stmt.span);
1375 err.span_label(sp, "consider removing this semicolon");
1382 /// Given some node representing a fn-like thing in the HIR map,
1383 /// returns a span and `ArgKind` information that describes the
1384 /// arguments it expects. This can be supplied to
1385 /// `report_arg_count_mismatch`.
1386 pub fn get_fn_like_arguments(&self, node: Node<'_>) -> (Span, Vec<ArgKind>) {
1388 Node::Expr(&hir::Expr {
1389 kind: hir::ExprKind::Closure(_, ref _decl, id, span, _),
1392 (self.tcx.sess.source_map().def_span(span),
1393 self.tcx.hir().body(id).params.iter()
1396 kind: hir::PatKind::Tuple(ref args, _),
1402 args.iter().map(|pat| {
1403 let snippet = self.tcx.sess.source_map()
1404 .span_to_snippet(pat.span).unwrap();
1405 (snippet, "_".to_owned())
1406 }).collect::<Vec<_>>(),
1409 let name = self.tcx.sess.source_map()
1410 .span_to_snippet(arg.pat.span).unwrap();
1411 ArgKind::Arg(name, "_".to_owned())
1414 .collect::<Vec<ArgKind>>())
1416 Node::Item(&hir::Item {
1418 kind: hir::ItemKind::Fn(ref decl, ..),
1421 Node::ImplItem(&hir::ImplItem {
1423 kind: hir::ImplItemKind::Method(hir::MethodSig { ref decl, .. }, _),
1426 Node::TraitItem(&hir::TraitItem {
1428 kind: hir::TraitItemKind::Method(hir::MethodSig { ref decl, .. }, _),
1431 (self.tcx.sess.source_map().def_span(span), decl.inputs.iter()
1432 .map(|arg| match arg.clone().kind {
1433 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
1435 vec![("_".to_owned(), "_".to_owned()); tys.len()]
1437 _ => ArgKind::empty()
1438 }).collect::<Vec<ArgKind>>())
1440 Node::Ctor(ref variant_data) => {
1441 let span = variant_data.ctor_hir_id()
1442 .map(|hir_id| self.tcx.hir().span(hir_id))
1443 .unwrap_or(DUMMY_SP);
1444 let span = self.tcx.sess.source_map().def_span(span);
1446 (span, vec![ArgKind::empty(); variant_data.fields().len()])
1448 _ => panic!("non-FnLike node found: {:?}", node),
1452 /// Reports an error when the number of arguments needed by a
1453 /// trait match doesn't match the number that the expression
1455 pub fn report_arg_count_mismatch(
1458 found_span: Option<Span>,
1459 expected_args: Vec<ArgKind>,
1460 found_args: Vec<ArgKind>,
1462 ) -> DiagnosticBuilder<'tcx> {
1463 let kind = if is_closure { "closure" } else { "function" };
1465 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
1466 let arg_length = arguments.len();
1467 let distinct = match &other[..] {
1468 &[ArgKind::Tuple(..)] => true,
1471 match (arg_length, arguments.get(0)) {
1472 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
1473 format!("a single {}-tuple as argument", fields.len())
1475 _ => format!("{} {}argument{}",
1477 if distinct && arg_length > 1 { "distinct " } else { "" },
1478 pluralise!(arg_length))
1482 let expected_str = args_str(&expected_args, &found_args);
1483 let found_str = args_str(&found_args, &expected_args);
1485 let mut err = struct_span_err!(
1489 "{} is expected to take {}, but it takes {}",
1495 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
1497 if let Some(found_span) = found_span {
1498 err.span_label(found_span, format!("takes {}", found_str));
1501 // ^^^^^^^^-- def_span
1505 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
1508 let pipe_span = if let Some(span) = found_span.trim_start(prefix_span) {
1514 // Suggest to take and ignore the arguments with expected_args_length `_`s if
1515 // found arguments is empty (assume the user just wants to ignore args in this case).
1516 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
1517 if found_args.is_empty() && is_closure {
1518 let underscores = vec!["_"; expected_args.len()].join(", ");
1519 err.span_suggestion(
1522 "consider changing the closure to take and ignore the expected argument{}",
1523 if expected_args.len() < 2 {
1529 format!("|{}|", underscores),
1530 Applicability::MachineApplicable,
1534 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
1535 if fields.len() == expected_args.len() {
1536 let sugg = fields.iter()
1537 .map(|(name, _)| name.to_owned())
1538 .collect::<Vec<String>>()
1540 err.span_suggestion(
1542 "change the closure to take multiple arguments instead of a single tuple",
1543 format!("|{}|", sugg),
1544 Applicability::MachineApplicable,
1548 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..] {
1549 if fields.len() == found_args.len() && is_closure {
1553 .map(|arg| match arg {
1554 ArgKind::Arg(name, _) => name.to_owned(),
1555 _ => "_".to_owned(),
1557 .collect::<Vec<String>>()
1559 // add type annotations if available
1560 if found_args.iter().any(|arg| match arg {
1561 ArgKind::Arg(_, ty) => ty != "_",
1566 .map(|(_, ty)| ty.to_owned())
1567 .collect::<Vec<String>>()
1573 err.span_suggestion(
1575 "change the closure to accept a tuple instead of individual arguments",
1577 Applicability::MachineApplicable,
1586 fn report_closure_arg_mismatch(
1589 found_span: Option<Span>,
1590 expected_ref: ty::PolyTraitRef<'tcx>,
1591 found: ty::PolyTraitRef<'tcx>,
1592 ) -> DiagnosticBuilder<'tcx> {
1593 fn build_fn_sig_string<'tcx>(tcx: TyCtxt<'tcx>, trait_ref: &ty::TraitRef<'tcx>) -> String {
1594 let inputs = trait_ref.substs.type_at(1);
1595 let sig = if let ty::Tuple(inputs) = inputs.kind {
1597 inputs.iter().map(|k| k.expect_ty()),
1598 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1600 hir::Unsafety::Normal,
1601 ::rustc_target::spec::abi::Abi::Rust
1605 ::std::iter::once(inputs),
1606 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1608 hir::Unsafety::Normal,
1609 ::rustc_target::spec::abi::Abi::Rust
1612 ty::Binder::bind(sig).to_string()
1615 let argument_is_closure = expected_ref.skip_binder().substs.type_at(0).is_closure();
1616 let mut err = struct_span_err!(self.tcx.sess, span, E0631,
1617 "type mismatch in {} arguments",
1618 if argument_is_closure { "closure" } else { "function" });
1620 let found_str = format!(
1621 "expected signature of `{}`",
1622 build_fn_sig_string(self.tcx, found.skip_binder())
1624 err.span_label(span, found_str);
1626 let found_span = found_span.unwrap_or(span);
1627 let expected_str = format!(
1628 "found signature of `{}`",
1629 build_fn_sig_string(self.tcx, expected_ref.skip_binder())
1631 err.span_label(found_span, expected_str);
1637 impl<'tcx> TyCtxt<'tcx> {
1638 pub fn recursive_type_with_infinite_size_error(self,
1640 -> DiagnosticBuilder<'tcx>
1642 assert!(type_def_id.is_local());
1643 let span = self.hir().span_if_local(type_def_id).unwrap();
1644 let span = self.sess.source_map().def_span(span);
1645 let mut err = struct_span_err!(self.sess, span, E0072,
1646 "recursive type `{}` has infinite size",
1647 self.def_path_str(type_def_id));
1648 err.span_label(span, "recursive type has infinite size");
1649 err.help(&format!("insert indirection (e.g., a `Box`, `Rc`, or `&`) \
1650 at some point to make `{}` representable",
1651 self.def_path_str(type_def_id)));
1655 pub fn report_object_safety_error(
1658 trait_def_id: DefId,
1659 violations: Vec<ObjectSafetyViolation>,
1660 ) -> DiagnosticBuilder<'tcx> {
1661 let trait_str = self.def_path_str(trait_def_id);
1662 let span = self.sess.source_map().def_span(span);
1663 let mut err = struct_span_err!(
1664 self.sess, span, E0038,
1665 "the trait `{}` cannot be made into an object",
1667 err.span_label(span, format!("the trait `{}` cannot be made into an object", trait_str));
1669 let mut reported_violations = FxHashSet::default();
1670 for violation in violations {
1671 if reported_violations.insert(violation.clone()) {
1672 match violation.span() {
1673 Some(span) => err.span_label(span, violation.error_msg()),
1674 None => err.note(&violation.error_msg()),
1679 if self.sess.trait_methods_not_found.borrow().contains(&span) {
1680 // Avoid emitting error caused by non-existing method (#58734)
1688 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
1689 fn maybe_report_ambiguity(
1691 obligation: &PredicateObligation<'tcx>,
1692 body_id: Option<hir::BodyId>,
1694 // Unable to successfully determine, probably means
1695 // insufficient type information, but could mean
1696 // ambiguous impls. The latter *ought* to be a
1697 // coherence violation, so we don't report it here.
1699 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
1700 let span = obligation.cause.span;
1703 "maybe_report_ambiguity(predicate={:?}, obligation={:?} body_id={:?}, code={:?})",
1707 obligation.cause.code,
1710 // Ambiguity errors are often caused as fallout from earlier
1711 // errors. So just ignore them if this infcx is tainted.
1712 if self.is_tainted_by_errors() {
1717 ty::Predicate::Trait(ref data) => {
1718 let trait_ref = data.to_poly_trait_ref();
1719 let self_ty = trait_ref.self_ty();
1720 debug!("self_ty {:?} {:?} trait_ref {:?}", self_ty, self_ty.kind, trait_ref);
1722 if predicate.references_error() {
1725 // Typically, this ambiguity should only happen if
1726 // there are unresolved type inference variables
1727 // (otherwise it would suggest a coherence
1728 // failure). But given #21974 that is not necessarily
1729 // the case -- we can have multiple where clauses that
1730 // are only distinguished by a region, which results
1731 // in an ambiguity even when all types are fully
1732 // known, since we don't dispatch based on region
1735 // This is kind of a hack: it frequently happens that some earlier
1736 // error prevents types from being fully inferred, and then we get
1737 // a bunch of uninteresting errors saying something like "<generic
1738 // #0> doesn't implement Sized". It may even be true that we
1739 // could just skip over all checks where the self-ty is an
1740 // inference variable, but I was afraid that there might be an
1741 // inference variable created, registered as an obligation, and
1742 // then never forced by writeback, and hence by skipping here we'd
1743 // be ignoring the fact that we don't KNOW the type works
1744 // out. Though even that would probably be harmless, given that
1745 // we're only talking about builtin traits, which are known to be
1746 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
1747 // avoid inundating the user with unnecessary errors, but we now
1748 // check upstream for type errors and dont add the obligations to
1749 // begin with in those cases.
1751 self.tcx.lang_items().sized_trait()
1752 .map_or(false, |sized_id| sized_id == trait_ref.def_id())
1754 self.need_type_info_err(body_id, span, self_ty).emit();
1756 let mut err = struct_span_err!(
1760 "type annotations needed: cannot resolve `{}`",
1763 self.note_obligation_cause(&mut err, obligation);
1768 ty::Predicate::WellFormed(ty) => {
1769 // Same hacky approach as above to avoid deluging user
1770 // with error messages.
1771 if !ty.references_error() && !self.tcx.sess.has_errors() {
1772 self.need_type_info_err(body_id, span, ty).emit();
1776 ty::Predicate::Subtype(ref data) => {
1777 if data.references_error() || self.tcx.sess.has_errors() {
1778 // no need to overload user in such cases
1780 let &SubtypePredicate { a_is_expected: _, a, b } = data.skip_binder();
1781 // both must be type variables, or the other would've been instantiated
1782 assert!(a.is_ty_var() && b.is_ty_var());
1783 self.need_type_info_err(body_id,
1784 obligation.cause.span,
1790 if !self.tcx.sess.has_errors() {
1791 let mut err = struct_span_err!(
1793 obligation.cause.span,
1795 "type annotations needed: cannot resolve `{}`",
1798 self.note_obligation_cause(&mut err, obligation);
1805 /// Returns `true` if the trait predicate may apply for *some* assignment
1806 /// to the type parameters.
1807 fn predicate_can_apply(
1809 param_env: ty::ParamEnv<'tcx>,
1810 pred: ty::PolyTraitRef<'tcx>,
1812 struct ParamToVarFolder<'a, 'tcx> {
1813 infcx: &'a InferCtxt<'a, 'tcx>,
1814 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
1817 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
1818 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { self.infcx.tcx }
1820 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1821 if let ty::Param(ty::ParamTy {name, .. }) = ty.kind {
1822 let infcx = self.infcx;
1823 self.var_map.entry(ty).or_insert_with(||
1825 TypeVariableOrigin {
1826 kind: TypeVariableOriginKind::TypeParameterDefinition(name),
1832 ty.super_fold_with(self)
1838 let mut selcx = SelectionContext::new(self);
1840 let cleaned_pred = pred.fold_with(&mut ParamToVarFolder {
1842 var_map: Default::default()
1845 let cleaned_pred = super::project::normalize(
1848 ObligationCause::dummy(),
1852 let obligation = Obligation::new(
1853 ObligationCause::dummy(),
1855 cleaned_pred.to_predicate()
1858 self.predicate_may_hold(&obligation)
1862 fn note_obligation_cause(
1864 err: &mut DiagnosticBuilder<'_>,
1865 obligation: &PredicateObligation<'tcx>,
1867 // First, attempt to add note to this error with an async-await-specific
1868 // message, and fall back to regular note otherwise.
1869 if !self.note_obligation_cause_for_async_await(err, obligation) {
1870 self.note_obligation_cause_code(err, &obligation.predicate, &obligation.cause.code,
1875 /// Adds an async-await specific note to the diagnostic:
1877 /// ```ignore (diagnostic)
1878 /// note: future does not implement `std::marker::Send` because this value is used across an
1880 /// --> $DIR/issue-64130-non-send-future-diags.rs:15:5
1882 /// LL | let g = x.lock().unwrap();
1883 /// | - has type `std::sync::MutexGuard<'_, u32>`
1884 /// LL | baz().await;
1885 /// | ^^^^^^^^^^^ await occurs here, with `g` maybe used later
1887 /// | - `g` is later dropped here
1890 /// Returns `true` if an async-await specific note was added to the diagnostic.
1891 fn note_obligation_cause_for_async_await(
1893 err: &mut DiagnosticBuilder<'_>,
1894 obligation: &PredicateObligation<'tcx>,
1896 debug!("note_obligation_cause_for_async_await: obligation.predicate={:?} \
1897 obligation.cause.span={:?}", obligation.predicate, obligation.cause.span);
1898 let source_map = self.tcx.sess.source_map();
1900 // Look into the obligation predicate to determine the type in the generator which meant
1901 // that the predicate was not satisifed.
1902 let (trait_ref, target_ty) = match obligation.predicate {
1903 ty::Predicate::Trait(trait_predicate) =>
1904 (trait_predicate.skip_binder().trait_ref, trait_predicate.skip_binder().self_ty()),
1907 debug!("note_obligation_cause_for_async_await: target_ty={:?}", target_ty);
1909 // Attempt to detect an async-await error by looking at the obligation causes, looking
1910 // for only generators, generator witnesses, opaque types or `std::future::GenFuture` to
1913 // When a future does not implement a trait because of a captured type in one of the
1914 // generators somewhere in the call stack, then the result is a chain of obligations.
1915 // Given a `async fn` A that calls a `async fn` B which captures a non-send type and that
1916 // future is passed as an argument to a function C which requires a `Send` type, then the
1917 // chain looks something like this:
1919 // - `BuiltinDerivedObligation` with a generator witness (B)
1920 // - `BuiltinDerivedObligation` with a generator (B)
1921 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (B)
1922 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
1923 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
1924 // - `BuiltinDerivedObligation` with a generator witness (A)
1925 // - `BuiltinDerivedObligation` with a generator (A)
1926 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (A)
1927 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
1928 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
1929 // - `BindingObligation` with `impl_send (Send requirement)
1931 // The first obligations in the chain can be used to get the details of the type that is
1932 // captured but the entire chain must be inspected to detect this case.
1933 let mut generator = None;
1934 let mut next_code = Some(&obligation.cause.code);
1935 while let Some(code) = next_code {
1936 debug!("note_obligation_cause_for_async_await: code={:?}", code);
1938 ObligationCauseCode::BuiltinDerivedObligation(derived_obligation) |
1939 ObligationCauseCode::ImplDerivedObligation(derived_obligation) => {
1940 debug!("note_obligation_cause_for_async_await: self_ty.kind={:?}",
1941 derived_obligation.parent_trait_ref.self_ty().kind);
1942 match derived_obligation.parent_trait_ref.self_ty().kind {
1943 ty::Adt(ty::AdtDef { did, .. }, ..) if
1944 self.tcx.is_diagnostic_item(sym::gen_future, *did) => {},
1945 ty::Generator(did, ..) => generator = generator.or(Some(did)),
1946 ty::GeneratorWitness(_) | ty::Opaque(..) => {},
1950 next_code = Some(derived_obligation.parent_code.as_ref());
1952 ObligationCauseCode::ItemObligation(_) | ObligationCauseCode::BindingObligation(..)
1953 if generator.is_some() => break,
1958 let generator_did = generator.expect("can only reach this if there was a generator");
1960 // Only continue to add a note if the generator is from an `async` function.
1961 let parent_node = self.tcx.parent(generator_did)
1962 .and_then(|parent_did| self.tcx.hir().get_if_local(parent_did));
1963 debug!("note_obligation_cause_for_async_await: parent_node={:?}", parent_node);
1964 if let Some(hir::Node::Item(hir::Item {
1965 kind: hir::ItemKind::Fn(_, header, _, _),
1968 debug!("note_obligation_cause_for_async_await: header={:?}", header);
1969 if header.asyncness != hir::IsAsync::Async {
1974 let span = self.tcx.def_span(generator_did);
1975 let tables = self.tcx.typeck_tables_of(generator_did);
1976 debug!("note_obligation_cause_for_async_await: generator_did={:?} span={:?} ",
1977 generator_did, span);
1979 // Look for a type inside the generator interior that matches the target type to get
1981 let target_span = tables.generator_interior_types.iter()
1982 .find(|ty::GeneratorInteriorTypeCause { ty, .. }| ty::TyS::same_type(*ty, target_ty))
1983 .map(|ty::GeneratorInteriorTypeCause { span, scope_span, .. }|
1984 (span, source_map.span_to_snippet(*span), scope_span));
1985 if let Some((target_span, Ok(snippet), scope_span)) = target_span {
1986 // Look at the last interior type to get a span for the `.await`.
1987 let await_span = tables.generator_interior_types.iter().map(|i| i.span).last().unwrap();
1988 let mut span = MultiSpan::from_span(await_span);
1989 span.push_span_label(
1990 await_span, format!("await occurs here, with `{}` maybe used later", snippet));
1992 span.push_span_label(*target_span, format!("has type `{}`", target_ty));
1994 // If available, use the scope span to annotate the drop location.
1995 if let Some(scope_span) = scope_span {
1996 span.push_span_label(
1997 source_map.end_point(*scope_span),
1998 format!("`{}` is later dropped here", snippet),
2002 err.span_note(span, &format!(
2003 "future does not implement `{}` as this value is used across an await",
2007 // Add a note for the item obligation that remains - normally a note pointing to the
2008 // bound that introduced the obligation (e.g. `T: Send`).
2009 debug!("note_obligation_cause_for_async_await: next_code={:?}", next_code);
2010 self.note_obligation_cause_code(
2012 &obligation.predicate,
2023 fn note_obligation_cause_code<T>(&self,
2024 err: &mut DiagnosticBuilder<'_>,
2026 cause_code: &ObligationCauseCode<'tcx>,
2027 obligated_types: &mut Vec<&ty::TyS<'tcx>>)
2028 where T: fmt::Display
2032 ObligationCauseCode::ExprAssignable |
2033 ObligationCauseCode::MatchExpressionArm { .. } |
2034 ObligationCauseCode::MatchExpressionArmPattern { .. } |
2035 ObligationCauseCode::IfExpression { .. } |
2036 ObligationCauseCode::IfExpressionWithNoElse |
2037 ObligationCauseCode::MainFunctionType |
2038 ObligationCauseCode::StartFunctionType |
2039 ObligationCauseCode::IntrinsicType |
2040 ObligationCauseCode::MethodReceiver |
2041 ObligationCauseCode::ReturnNoExpression |
2042 ObligationCauseCode::MiscObligation => {}
2043 ObligationCauseCode::SliceOrArrayElem => {
2044 err.note("slice and array elements must have `Sized` type");
2046 ObligationCauseCode::TupleElem => {
2047 err.note("only the last element of a tuple may have a dynamically sized type");
2049 ObligationCauseCode::ProjectionWf(data) => {
2051 "required so that the projection `{}` is well-formed",
2055 ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
2057 "required so that reference `{}` does not outlive its referent",
2061 ObligationCauseCode::ObjectTypeBound(object_ty, region) => {
2063 "required so that the lifetime bound of `{}` for `{}` is satisfied",
2068 ObligationCauseCode::ItemObligation(item_def_id) => {
2069 let item_name = tcx.def_path_str(item_def_id);
2070 let msg = format!("required by `{}`", item_name);
2072 if let Some(sp) = tcx.hir().span_if_local(item_def_id) {
2073 let sp = tcx.sess.source_map().def_span(sp);
2074 err.span_label(sp, &msg);
2079 ObligationCauseCode::BindingObligation(item_def_id, span) => {
2080 let item_name = tcx.def_path_str(item_def_id);
2081 let msg = format!("required by this bound in `{}`", item_name);
2082 if let Some(ident) = tcx.opt_item_name(item_def_id) {
2083 err.span_label(ident.span, "");
2085 if span != DUMMY_SP {
2086 err.span_label(span, &msg);
2091 ObligationCauseCode::ObjectCastObligation(object_ty) => {
2092 err.note(&format!("required for the cast to the object type `{}`",
2093 self.ty_to_string(object_ty)));
2095 ObligationCauseCode::Coercion { source: _, target } => {
2096 err.note(&format!("required by cast to type `{}`",
2097 self.ty_to_string(target)));
2099 ObligationCauseCode::RepeatVec => {
2100 err.note("the `Copy` trait is required because the \
2101 repeated element will be copied");
2103 ObligationCauseCode::VariableType(_) => {
2104 err.note("all local variables must have a statically known size");
2105 if !self.tcx.features().unsized_locals {
2106 err.help("unsized locals are gated as an unstable feature");
2109 ObligationCauseCode::SizedArgumentType => {
2110 err.note("all function arguments must have a statically known size");
2111 if !self.tcx.features().unsized_locals {
2112 err.help("unsized locals are gated as an unstable feature");
2115 ObligationCauseCode::SizedReturnType => {
2116 err.note("the return type of a function must have a \
2117 statically known size");
2119 ObligationCauseCode::SizedYieldType => {
2120 err.note("the yield type of a generator must have a \
2121 statically known size");
2123 ObligationCauseCode::AssignmentLhsSized => {
2124 err.note("the left-hand-side of an assignment must have a statically known size");
2126 ObligationCauseCode::TupleInitializerSized => {
2127 err.note("tuples must have a statically known size to be initialized");
2129 ObligationCauseCode::StructInitializerSized => {
2130 err.note("structs must have a statically known size to be initialized");
2132 ObligationCauseCode::FieldSized { adt_kind: ref item, last } => {
2134 AdtKind::Struct => {
2136 err.note("the last field of a packed struct may only have a \
2137 dynamically sized type if it does not need drop to be run");
2139 err.note("only the last field of a struct may have a dynamically \
2144 err.note("no field of a union may have a dynamically sized type");
2147 err.note("no field of an enum variant may have a dynamically sized type");
2151 ObligationCauseCode::ConstSized => {
2152 err.note("constant expressions must have a statically known size");
2154 ObligationCauseCode::SharedStatic => {
2155 err.note("shared static variables must have a type that implements `Sync`");
2157 ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
2158 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2159 let ty = parent_trait_ref.skip_binder().self_ty();
2160 err.note(&format!("required because it appears within the type `{}`", ty));
2161 obligated_types.push(ty);
2163 let parent_predicate = parent_trait_ref.to_predicate();
2164 if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
2165 self.note_obligation_cause_code(err,
2171 ObligationCauseCode::ImplDerivedObligation(ref data) => {
2172 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2174 &format!("required because of the requirements on the impl of `{}` for `{}`",
2176 parent_trait_ref.skip_binder().self_ty()));
2177 let parent_predicate = parent_trait_ref.to_predicate();
2178 self.note_obligation_cause_code(err,
2183 ObligationCauseCode::CompareImplMethodObligation { .. } => {
2185 &format!("the requirement `{}` appears on the impl method \
2186 but not on the corresponding trait method",
2189 ObligationCauseCode::ReturnType |
2190 ObligationCauseCode::ReturnValue(_) |
2191 ObligationCauseCode::BlockTailExpression(_) => (),
2192 ObligationCauseCode::TrivialBound => {
2193 err.help("see issue #48214");
2194 if tcx.sess.opts.unstable_features.is_nightly_build() {
2195 err.help("add `#![feature(trivial_bounds)]` to the \
2196 crate attributes to enable",
2203 fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder<'_>) {
2204 let current_limit = self.tcx.sess.recursion_limit.get();
2205 let suggested_limit = current_limit * 2;
2206 err.help(&format!("consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
2210 fn is_recursive_obligation(&self,
2211 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
2212 cause_code: &ObligationCauseCode<'tcx>) -> bool {
2213 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2214 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2216 if obligated_types.iter().any(|ot| ot == &parent_trait_ref.skip_binder().self_ty()) {
2224 /// Summarizes information
2227 /// An argument of non-tuple type. Parameters are (name, ty)
2228 Arg(String, String),
2230 /// An argument of tuple type. For a "found" argument, the span is
2231 /// the locationo in the source of the pattern. For a "expected"
2232 /// argument, it will be None. The vector is a list of (name, ty)
2233 /// strings for the components of the tuple.
2234 Tuple(Option<Span>, Vec<(String, String)>),
2238 fn empty() -> ArgKind {
2239 ArgKind::Arg("_".to_owned(), "_".to_owned())
2242 /// Creates an `ArgKind` from the expected type of an
2243 /// argument. It has no name (`_`) and an optional source span.
2244 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2246 ty::Tuple(ref tys) => ArgKind::Tuple(
2249 .map(|ty| ("_".to_owned(), ty.to_string()))
2250 .collect::<Vec<_>>()
2252 _ => ArgKind::Arg("_".to_owned(), t.to_string()),