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, Style};
39 use syntax::symbol::{sym, kw};
40 use syntax_pos::{DUMMY_SP, Span, ExpnKind, MultiSpan};
42 use rustc_error_codes::*;
44 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
45 pub fn report_fulfillment_errors(
47 errors: &[FulfillmentError<'tcx>],
48 body_id: Option<hir::BodyId>,
49 fallback_has_occurred: bool,
52 struct ErrorDescriptor<'tcx> {
53 predicate: ty::Predicate<'tcx>,
54 index: Option<usize>, // None if this is an old error
57 let mut error_map: FxHashMap<_, Vec<_>> =
58 self.reported_trait_errors.borrow().iter().map(|(&span, predicates)| {
59 (span, predicates.iter().map(|predicate| ErrorDescriptor {
60 predicate: predicate.clone(),
65 for (index, error) in errors.iter().enumerate() {
66 // We want to ignore desugarings here: spans are equivalent even
67 // if one is the result of a desugaring and the other is not.
68 let mut span = error.obligation.cause.span;
69 let expn_data = span.ctxt().outer_expn_data();
70 if let ExpnKind::Desugaring(_) = expn_data.kind {
71 span = expn_data.call_site;
74 error_map.entry(span).or_default().push(
76 predicate: error.obligation.predicate.clone(),
81 self.reported_trait_errors.borrow_mut()
82 .entry(span).or_default()
83 .push(error.obligation.predicate.clone());
86 // We do this in 2 passes because we want to display errors in order, though
87 // maybe it *is* better to sort errors by span or something.
88 let mut is_suppressed = vec![false; errors.len()];
89 for (_, error_set) in error_map.iter() {
90 // We want to suppress "duplicate" errors with the same span.
91 for error in error_set {
92 if let Some(index) = error.index {
93 // Suppress errors that are either:
94 // 1) strictly implied by another error.
95 // 2) implied by an error with a smaller index.
96 for error2 in error_set {
97 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
98 // Avoid errors being suppressed by already-suppressed
99 // errors, to prevent all errors from being suppressed
104 if self.error_implies(&error2.predicate, &error.predicate) &&
105 !(error2.index >= error.index &&
106 self.error_implies(&error.predicate, &error2.predicate))
108 info!("skipping {:?} (implied by {:?})", error, error2);
109 is_suppressed[index] = true;
117 for (error, suppressed) in errors.iter().zip(is_suppressed) {
119 self.report_fulfillment_error(error, body_id, fallback_has_occurred);
124 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
125 // `error` occurring implies that `cond` occurs.
128 cond: &ty::Predicate<'tcx>,
129 error: &ty::Predicate<'tcx>,
135 let (cond, error) = match (cond, error) {
136 (&ty::Predicate::Trait(..), &ty::Predicate::Trait(ref error))
139 // FIXME: make this work in other cases too.
144 for implication in super::elaborate_predicates(self.tcx, vec![cond.clone()]) {
145 if let ty::Predicate::Trait(implication) = implication {
146 let error = error.to_poly_trait_ref();
147 let implication = implication.to_poly_trait_ref();
148 // FIXME: I'm just not taking associated types at all here.
149 // Eventually I'll need to implement param-env-aware
150 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
151 let param_env = ty::ParamEnv::empty();
152 if self.can_sub(param_env, error, implication).is_ok() {
153 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
162 fn report_fulfillment_error(
164 error: &FulfillmentError<'tcx>,
165 body_id: Option<hir::BodyId>,
166 fallback_has_occurred: bool,
168 debug!("report_fulfillment_errors({:?})", error);
170 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
171 self.report_selection_error(
174 fallback_has_occurred,
175 error.points_at_arg_span,
178 FulfillmentErrorCode::CodeProjectionError(ref e) => {
179 self.report_projection_error(&error.obligation, e);
181 FulfillmentErrorCode::CodeAmbiguity => {
182 self.maybe_report_ambiguity(&error.obligation, body_id);
184 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
185 self.report_mismatched_types(
186 &error.obligation.cause,
187 expected_found.expected,
188 expected_found.found,
195 fn report_projection_error(
197 obligation: &PredicateObligation<'tcx>,
198 error: &MismatchedProjectionTypes<'tcx>,
200 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
202 if predicate.references_error() {
208 let mut err = &error.err;
209 let mut values = None;
211 // try to find the mismatched types to report the error with.
213 // this can fail if the problem was higher-ranked, in which
214 // cause I have no idea for a good error message.
215 if let ty::Predicate::Projection(ref data) = predicate {
216 let mut selcx = SelectionContext::new(self);
217 let (data, _) = self.replace_bound_vars_with_fresh_vars(
218 obligation.cause.span,
219 infer::LateBoundRegionConversionTime::HigherRankedType,
222 let mut obligations = vec![];
223 let normalized_ty = super::normalize_projection_type(
225 obligation.param_env,
227 obligation.cause.clone(),
232 debug!("report_projection_error obligation.cause={:?} obligation.param_env={:?}",
233 obligation.cause, obligation.param_env);
235 debug!("report_projection_error normalized_ty={:?} data.ty={:?}",
236 normalized_ty, data.ty);
238 let is_normalized_ty_expected = match &obligation.cause.code {
239 ObligationCauseCode::ItemObligation(_) |
240 ObligationCauseCode::BindingObligation(_, _) |
241 ObligationCauseCode::ObjectCastObligation(_) => false,
245 if let Err(error) = self.at(&obligation.cause, obligation.param_env)
246 .eq_exp(is_normalized_ty_expected, normalized_ty, data.ty)
248 values = Some(infer::ValuePairs::Types(
249 ExpectedFound::new(is_normalized_ty_expected, normalized_ty, data.ty)));
256 let msg = format!("type mismatch resolving `{}`", predicate);
258 DiagnosticMessageId::ErrorId(271),
259 Some(obligation.cause.span),
262 let fresh = self.tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
264 let mut diag = struct_span_err!(
266 obligation.cause.span,
268 "type mismatch resolving `{}`",
271 self.note_type_err(&mut diag, &obligation.cause, None, values, err);
272 self.note_obligation_cause(&mut diag, obligation);
278 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
279 /// returns the fuzzy category of a given type, or None
280 /// if the type can be equated to any type.
281 fn type_category(t: Ty<'_>) -> Option<u32> {
286 ty::Int(..) | ty::Uint(..) | ty::Infer(ty::IntVar(..)) => Some(3),
287 ty::Float(..) | ty::Infer(ty::FloatVar(..)) => Some(4),
288 ty::Ref(..) | ty::RawPtr(..) => Some(5),
289 ty::Array(..) | ty::Slice(..) => Some(6),
290 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
291 ty::Dynamic(..) => Some(8),
292 ty::Closure(..) => Some(9),
293 ty::Tuple(..) => Some(10),
294 ty::Projection(..) => Some(11),
295 ty::Param(..) => Some(12),
296 ty::Opaque(..) => Some(13),
297 ty::Never => Some(14),
298 ty::Adt(adt, ..) => match adt.adt_kind() {
299 AdtKind::Struct => Some(15),
300 AdtKind::Union => Some(16),
301 AdtKind::Enum => Some(17),
303 ty::Generator(..) => Some(18),
304 ty::Foreign(..) => Some(19),
305 ty::GeneratorWitness(..) => Some(20),
306 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error => None,
307 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
311 match (type_category(a), type_category(b)) {
312 (Some(cat_a), Some(cat_b)) => match (&a.kind, &b.kind) {
313 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => def_a == def_b,
316 // infer and error can be equated to all types
321 fn impl_similar_to(&self,
322 trait_ref: ty::PolyTraitRef<'tcx>,
323 obligation: &PredicateObligation<'tcx>)
327 let param_env = obligation.param_env;
328 let trait_ref = tcx.erase_late_bound_regions(&trait_ref);
329 let trait_self_ty = trait_ref.self_ty();
331 let mut self_match_impls = vec![];
332 let mut fuzzy_match_impls = vec![];
334 self.tcx.for_each_relevant_impl(
335 trait_ref.def_id, trait_self_ty, |def_id| {
336 let impl_substs = self.fresh_substs_for_item(obligation.cause.span, def_id);
337 let impl_trait_ref = tcx
338 .impl_trait_ref(def_id)
340 .subst(tcx, impl_substs);
342 let impl_self_ty = impl_trait_ref.self_ty();
344 if let Ok(..) = self.can_eq(param_env, trait_self_ty, impl_self_ty) {
345 self_match_impls.push(def_id);
347 if trait_ref.substs.types().skip(1)
348 .zip(impl_trait_ref.substs.types().skip(1))
349 .all(|(u,v)| self.fuzzy_match_tys(u, v))
351 fuzzy_match_impls.push(def_id);
356 let impl_def_id = if self_match_impls.len() == 1 {
358 } else if fuzzy_match_impls.len() == 1 {
364 if tcx.has_attr(impl_def_id, sym::rustc_on_unimplemented) {
371 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
372 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| {
374 hir::GeneratorKind::Gen => "a generator",
375 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
376 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
377 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
382 /// Used to set on_unimplemented's `ItemContext`
383 /// to be the enclosing (async) block/function/closure
384 fn describe_enclosure(&self, hir_id: hir::HirId) -> Option<&'static str> {
385 let hir = &self.tcx.hir();
386 let node = hir.find(hir_id)?;
387 if let hir::Node::Item(
388 hir::Item{kind: hir::ItemKind::Fn(sig, _, body_id), .. }) = &node {
389 self.describe_generator(*body_id).or_else(||
390 Some(if let hir::FnHeader{ asyncness: hir::IsAsync::Async, .. } = sig.header {
396 } else if let hir::Node::Expr(hir::Expr {
397 kind: hir::ExprKind::Closure(_is_move, _, body_id, _, gen_movability), .. }) = &node {
398 self.describe_generator(*body_id).or_else(||
399 Some(if gen_movability.is_some() {
405 } else if let hir::Node::Expr(hir::Expr { .. }) = &node {
406 let parent_hid = hir.get_parent_node(hir_id);
407 if parent_hid != hir_id {
408 return self.describe_enclosure(parent_hid);
417 fn on_unimplemented_note(
419 trait_ref: ty::PolyTraitRef<'tcx>,
420 obligation: &PredicateObligation<'tcx>,
421 ) -> OnUnimplementedNote {
422 let def_id = self.impl_similar_to(trait_ref, obligation)
423 .unwrap_or_else(|| trait_ref.def_id());
424 let trait_ref = *trait_ref.skip_binder();
426 let mut flags = vec![];
427 flags.push((sym::item_context,
428 self.describe_enclosure(obligation.cause.body_id).map(|s|s.to_owned())));
430 match obligation.cause.code {
431 ObligationCauseCode::BuiltinDerivedObligation(..) |
432 ObligationCauseCode::ImplDerivedObligation(..) => {}
434 // this is a "direct", user-specified, rather than derived,
436 flags.push((sym::direct, None));
440 if let ObligationCauseCode::ItemObligation(item) = obligation.cause.code {
441 // FIXME: maybe also have some way of handling methods
442 // from other traits? That would require name resolution,
443 // which we might want to be some sort of hygienic.
445 // Currently I'm leaving it for what I need for `try`.
446 if self.tcx.trait_of_item(item) == Some(trait_ref.def_id) {
447 let method = self.tcx.item_name(item);
448 flags.push((sym::from_method, None));
449 flags.push((sym::from_method, Some(method.to_string())));
452 if let Some(t) = self.get_parent_trait_ref(&obligation.cause.code) {
453 flags.push((sym::parent_trait, Some(t)));
456 if let Some(k) = obligation.cause.span.desugaring_kind() {
457 flags.push((sym::from_desugaring, None));
458 flags.push((sym::from_desugaring, Some(format!("{:?}", k))));
460 let generics = self.tcx.generics_of(def_id);
461 let self_ty = trait_ref.self_ty();
462 // This is also included through the generics list as `Self`,
463 // but the parser won't allow you to use it
464 flags.push((sym::_Self, Some(self_ty.to_string())));
465 if let Some(def) = self_ty.ty_adt_def() {
466 // We also want to be able to select self's original
467 // signature with no type arguments resolved
468 flags.push((sym::_Self, Some(self.tcx.type_of(def.did).to_string())));
471 for param in generics.params.iter() {
472 let value = match param.kind {
473 GenericParamDefKind::Type { .. } |
474 GenericParamDefKind::Const => {
475 trait_ref.substs[param.index as usize].to_string()
477 GenericParamDefKind::Lifetime => continue,
479 let name = param.name;
480 flags.push((name, Some(value)));
483 if let Some(true) = self_ty.ty_adt_def().map(|def| def.did.is_local()) {
484 flags.push((sym::crate_local, None));
487 // Allow targeting all integers using `{integral}`, even if the exact type was resolved
488 if self_ty.is_integral() {
489 flags.push((sym::_Self, Some("{integral}".to_owned())));
492 if let ty::Array(aty, len) = self_ty.kind {
493 flags.push((sym::_Self, Some("[]".to_owned())));
494 flags.push((sym::_Self, Some(format!("[{}]", aty))));
495 if let Some(def) = aty.ty_adt_def() {
496 // We also want to be able to select the array's type's original
497 // signature with no type arguments resolved
500 Some(format!("[{}]", self.tcx.type_of(def.did).to_string())),
503 if let Some(len) = len.try_eval_usize(tcx, ty::ParamEnv::empty()) {
506 Some(format!("[{}; {}]", self.tcx.type_of(def.did).to_string(), len)),
511 Some(format!("[{}; _]", self.tcx.type_of(def.did).to_string())),
517 if let Ok(Some(command)) = OnUnimplementedDirective::of_item(
518 self.tcx, trait_ref.def_id, def_id
520 command.evaluate(self.tcx, trait_ref, &flags[..])
522 OnUnimplementedNote::empty()
526 fn find_similar_impl_candidates(
528 trait_ref: ty::PolyTraitRef<'tcx>,
529 ) -> Vec<ty::TraitRef<'tcx>> {
530 let simp = fast_reject::simplify_type(self.tcx, trait_ref.skip_binder().self_ty(), true);
531 let all_impls = self.tcx.all_impls(trait_ref.def_id());
534 Some(simp) => all_impls.iter().filter_map(|&def_id| {
535 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
536 let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
537 if let Some(imp_simp) = imp_simp {
538 if simp != imp_simp {
545 None => all_impls.iter().map(|&def_id|
546 self.tcx.impl_trait_ref(def_id).unwrap()
551 fn report_similar_impl_candidates(
553 impl_candidates: Vec<ty::TraitRef<'tcx>>,
554 err: &mut DiagnosticBuilder<'_>,
556 if impl_candidates.is_empty() {
560 let len = impl_candidates.len();
561 let end = if impl_candidates.len() <= 5 {
562 impl_candidates.len()
567 let normalize = |candidate| self.tcx.infer_ctxt().enter(|ref infcx| {
568 let normalized = infcx
569 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
570 .normalize(candidate)
573 Some(normalized) => format!("\n {:?}", normalized.value),
574 None => format!("\n {:?}", candidate),
578 // Sort impl candidates so that ordering is consistent for UI tests.
579 let mut normalized_impl_candidates = impl_candidates
582 .collect::<Vec<String>>();
584 // Sort before taking the `..end` range,
585 // because the ordering of `impl_candidates` may not be deterministic:
586 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
587 normalized_impl_candidates.sort();
589 err.help(&format!("the following implementations were found:{}{}",
590 normalized_impl_candidates[..end].join(""),
592 format!("\nand {} others", len - 4)
599 /// Reports that an overflow has occurred and halts compilation. We
600 /// halt compilation unconditionally because it is important that
601 /// overflows never be masked -- they basically represent computations
602 /// whose result could not be truly determined and thus we can't say
603 /// if the program type checks or not -- and they are unusual
604 /// occurrences in any case.
605 pub fn report_overflow_error<T>(
607 obligation: &Obligation<'tcx, T>,
608 suggest_increasing_limit: bool,
610 where T: fmt::Display + TypeFoldable<'tcx>
613 self.resolve_vars_if_possible(&obligation.predicate);
614 let mut err = struct_span_err!(
616 obligation.cause.span,
618 "overflow evaluating the requirement `{}`",
622 if suggest_increasing_limit {
623 self.suggest_new_overflow_limit(&mut err);
626 self.note_obligation_cause_code(
628 &obligation.predicate,
629 &obligation.cause.code,
634 self.tcx.sess.abort_if_errors();
638 /// Reports that a cycle was detected which led to overflow and halts
639 /// compilation. This is equivalent to `report_overflow_error` except
640 /// that we can give a more helpful error message (and, in particular,
641 /// we do not suggest increasing the overflow limit, which is not
643 pub fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
644 let cycle = self.resolve_vars_if_possible(&cycle.to_owned());
645 assert!(cycle.len() > 0);
647 debug!("report_overflow_error_cycle: cycle={:?}", cycle);
649 self.report_overflow_error(&cycle[0], false);
652 pub fn report_extra_impl_obligation(&self,
654 item_name: ast::Name,
655 _impl_item_def_id: DefId,
656 trait_item_def_id: DefId,
657 requirement: &dyn fmt::Display)
658 -> DiagnosticBuilder<'tcx>
660 let msg = "impl has stricter requirements than trait";
661 let sp = self.tcx.sess.source_map().def_span(error_span);
663 let mut err = struct_span_err!(self.tcx.sess, sp, E0276, "{}", msg);
665 if let Some(trait_item_span) = self.tcx.hir().span_if_local(trait_item_def_id) {
666 let span = self.tcx.sess.source_map().def_span(trait_item_span);
667 err.span_label(span, format!("definition of `{}` from trait", item_name));
670 err.span_label(sp, format!("impl has extra requirement {}", requirement));
676 /// Gets the parent trait chain start
677 fn get_parent_trait_ref(&self, code: &ObligationCauseCode<'tcx>) -> Option<String> {
679 &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
680 let parent_trait_ref = self.resolve_vars_if_possible(
681 &data.parent_trait_ref);
682 match self.get_parent_trait_ref(&data.parent_code) {
684 None => Some(parent_trait_ref.skip_binder().self_ty().to_string()),
691 pub fn report_selection_error(
693 obligation: &PredicateObligation<'tcx>,
694 error: &SelectionError<'tcx>,
695 fallback_has_occurred: bool,
698 let span = obligation.cause.span;
700 let mut err = match *error {
701 SelectionError::Unimplemented => {
702 if let ObligationCauseCode::CompareImplMethodObligation {
703 item_name, impl_item_def_id, trait_item_def_id,
704 } = obligation.cause.code {
705 self.report_extra_impl_obligation(
710 &format!("`{}`", obligation.predicate))
714 match obligation.predicate {
715 ty::Predicate::Trait(ref trait_predicate) => {
716 let trait_predicate = self.resolve_vars_if_possible(trait_predicate);
718 if self.tcx.sess.has_errors() && trait_predicate.references_error() {
721 let trait_ref = trait_predicate.to_poly_trait_ref();
725 ) = self.get_parent_trait_ref(&obligation.cause.code)
726 .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
727 .unwrap_or_default();
729 let OnUnimplementedNote {
733 } = self.on_unimplemented_note(trait_ref, obligation);
734 let have_alt_message = message.is_some() || label.is_some();
735 let is_try = self.tcx.sess.source_map().span_to_snippet(span)
738 let is_from = format!("{}", trait_ref).starts_with("std::convert::From<");
739 let (message, note) = if is_try && is_from {
741 "`?` couldn't convert the error to `{}`",
744 "the question mark operation (`?`) implicitly performs a \
745 conversion on the error value using the `From` trait".to_owned()
751 let mut err = struct_span_err!(
756 message.unwrap_or_else(|| format!(
757 "the trait bound `{}` is not satisfied{}",
758 trait_ref.to_predicate(),
763 if obligation.cause.code == ObligationCauseCode::MainFunctionType {
764 "consider using `()`, or a `Result`".to_owned()
767 "{}the trait `{}` is not implemented for `{}`",
774 if self.suggest_add_reference_to_arg(
781 self.note_obligation_cause(&mut err, obligation);
785 if let Some(ref s) = label {
786 // If it has a custom `#[rustc_on_unimplemented]`
787 // error message, let's display it as the label!
788 err.span_label(span, s.as_str());
789 err.help(&explanation);
791 err.span_label(span, explanation);
793 if let Some(ref s) = note {
794 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
795 err.note(s.as_str());
798 self.suggest_borrow_on_unsized_slice(&obligation.cause.code, &mut err);
799 self.suggest_fn_call(&obligation, &mut err, &trait_ref, points_at_arg);
800 self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
801 self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
803 // Try to report a help message
804 if !trait_ref.has_infer_types() &&
805 self.predicate_can_apply(obligation.param_env, trait_ref) {
806 // If a where-clause may be useful, remind the
807 // user that they can add it.
809 // don't display an on-unimplemented note, as
810 // these notes will often be of the form
811 // "the type `T` can't be frobnicated"
812 // which is somewhat confusing.
813 self.suggest_restricting_param_bound(
816 obligation.cause.body_id,
819 if !have_alt_message {
820 // Can't show anything else useful, try to find similar impls.
821 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
822 self.report_similar_impl_candidates(impl_candidates, &mut err);
824 self.suggest_change_mut(
832 // If this error is due to `!: Trait` not implemented but `(): Trait` is
833 // implemented, and fallback has occurred, then it could be due to a
834 // variable that used to fallback to `()` now falling back to `!`. Issue a
835 // note informing about the change in behaviour.
836 if trait_predicate.skip_binder().self_ty().is_never()
837 && fallback_has_occurred
839 let predicate = trait_predicate.map_bound(|mut trait_pred| {
840 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
842 &trait_pred.trait_ref.substs[1..],
846 let unit_obligation = Obligation {
847 predicate: ty::Predicate::Trait(predicate),
848 .. obligation.clone()
850 if self.predicate_may_hold(&unit_obligation) {
851 err.note("the trait is implemented for `()`. \
852 Possibly this error has been caused by changes to \
853 Rust's type-inference algorithm \
854 (see: https://github.com/rust-lang/rust/issues/48950 \
855 for more info). Consider whether you meant to use the \
856 type `()` here instead.");
863 ty::Predicate::Subtype(ref predicate) => {
864 // Errors for Subtype predicates show up as
865 // `FulfillmentErrorCode::CodeSubtypeError`,
866 // not selection error.
867 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
870 ty::Predicate::RegionOutlives(ref predicate) => {
871 let predicate = self.resolve_vars_if_possible(predicate);
872 let err = self.region_outlives_predicate(&obligation.cause,
873 &predicate).err().unwrap();
875 self.tcx.sess, span, E0279,
876 "the requirement `{}` is not satisfied (`{}`)",
881 ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
883 self.resolve_vars_if_possible(&obligation.predicate);
884 struct_span_err!(self.tcx.sess, span, E0280,
885 "the requirement `{}` is not satisfied",
889 ty::Predicate::ObjectSafe(trait_def_id) => {
890 let violations = self.tcx.object_safety_violations(trait_def_id);
891 self.tcx.report_object_safety_error(
898 ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
899 let found_kind = self.closure_kind(closure_def_id, closure_substs).unwrap();
900 let closure_span = self.tcx.sess.source_map()
901 .def_span(self.tcx.hir().span_if_local(closure_def_id).unwrap());
902 let hir_id = self.tcx.hir().as_local_hir_id(closure_def_id).unwrap();
903 let mut err = struct_span_err!(
904 self.tcx.sess, closure_span, E0525,
905 "expected a closure that implements the `{}` trait, \
906 but this closure only implements `{}`",
912 format!("this closure implements `{}`, not `{}`", found_kind, kind));
914 obligation.cause.span,
915 format!("the requirement to implement `{}` derives from here", kind));
917 // Additional context information explaining why the closure only implements
918 // a particular trait.
919 if let Some(tables) = self.in_progress_tables {
920 let tables = tables.borrow();
921 match (found_kind, tables.closure_kind_origins().get(hir_id)) {
922 (ty::ClosureKind::FnOnce, Some((span, name))) => {
923 err.span_label(*span, format!(
924 "closure is `FnOnce` because it moves the \
925 variable `{}` out of its environment", name));
927 (ty::ClosureKind::FnMut, Some((span, name))) => {
928 err.span_label(*span, format!(
929 "closure is `FnMut` because it mutates the \
930 variable `{}` here", name));
940 ty::Predicate::WellFormed(ty) => {
941 if !self.tcx.sess.opts.debugging_opts.chalk {
942 // WF predicates cannot themselves make
943 // errors. They can only block due to
944 // ambiguity; otherwise, they always
945 // degenerate into other obligations
947 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
949 // FIXME: we'll need a better message which takes into account
950 // which bounds actually failed to hold.
951 self.tcx.sess.struct_span_err(
953 &format!("the type `{}` is not well-formed (chalk)", ty)
958 ty::Predicate::ConstEvaluatable(..) => {
959 // Errors for `ConstEvaluatable` predicates show up as
960 // `SelectionError::ConstEvalFailure`,
961 // not `Unimplemented`.
963 "const-evaluatable requirement gave wrong error: `{:?}`", obligation)
968 OutputTypeParameterMismatch(ref found_trait_ref, ref expected_trait_ref, _) => {
969 let found_trait_ref = self.resolve_vars_if_possible(&*found_trait_ref);
970 let expected_trait_ref = self.resolve_vars_if_possible(&*expected_trait_ref);
972 if expected_trait_ref.self_ty().references_error() {
976 let found_trait_ty = found_trait_ref.self_ty();
978 let found_did = match found_trait_ty.kind {
979 ty::Closure(did, _) | ty::Foreign(did) | ty::FnDef(did, _) => Some(did),
980 ty::Adt(def, _) => Some(def.did),
984 let found_span = found_did.and_then(|did|
985 self.tcx.hir().span_if_local(did)
986 ).map(|sp| self.tcx.sess.source_map().def_span(sp)); // the sp could be an fn def
988 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
989 // We check closures twice, with obligations flowing in different directions,
990 // but we want to complain about them only once.
994 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
996 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind {
997 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
998 _ => vec![ArgKind::empty()],
1001 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1002 let expected = match expected_ty.kind {
1003 ty::Tuple(ref tys) => tys.iter()
1004 .map(|t| ArgKind::from_expected_ty(t.expect_ty(), Some(span))).collect(),
1005 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
1008 if found.len() == expected.len() {
1009 self.report_closure_arg_mismatch(span,
1014 let (closure_span, found) = found_did
1015 .and_then(|did| self.tcx.hir().get_if_local(did))
1017 let (found_span, found) = self.get_fn_like_arguments(node);
1018 (Some(found_span), found)
1019 }).unwrap_or((found_span, found));
1021 self.report_arg_count_mismatch(span,
1025 found_trait_ty.is_closure())
1029 TraitNotObjectSafe(did) => {
1030 let violations = self.tcx.object_safety_violations(did);
1031 self.tcx.report_object_safety_error(span, did, violations)
1034 // already reported in the query
1035 ConstEvalFailure(err) => {
1036 self.tcx.sess.delay_span_bug(
1038 &format!("constant in type had an ignored error: {:?}", err),
1044 bug!("overflow should be handled before the `report_selection_error` path");
1048 self.note_obligation_cause(&mut err, obligation);
1053 fn suggest_restricting_param_bound(
1055 err: &mut DiagnosticBuilder<'_>,
1056 trait_ref: &ty::PolyTraitRef<'_>,
1057 body_id: hir::HirId,
1059 let self_ty = trait_ref.self_ty();
1060 let (param_ty, projection) = match &self_ty.kind {
1061 ty::Param(_) => (true, None),
1062 ty::Projection(projection) => (false, Some(projection)),
1066 let mut suggest_restriction = |generics: &hir::Generics, msg| {
1067 let span = generics.where_clause.span_for_predicates_or_empty_place();
1068 if !span.from_expansion() && span.desugaring_kind().is_none() {
1069 err.span_suggestion(
1070 generics.where_clause.span_for_predicates_or_empty_place().shrink_to_hi(),
1071 &format!("consider further restricting {}", msg),
1074 if !generics.where_clause.predicates.is_empty() {
1079 trait_ref.to_predicate(),
1081 Applicability::MachineApplicable,
1086 // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
1087 // don't suggest `T: Sized + ?Sized`.
1088 let mut hir_id = body_id;
1089 while let Some(node) = self.tcx.hir().find(hir_id) {
1091 hir::Node::TraitItem(hir::TraitItem {
1093 kind: hir::TraitItemKind::Method(..), ..
1094 }) if param_ty && self_ty == self.tcx.types.self_param => {
1095 // Restricting `Self` for a single method.
1096 suggest_restriction(&generics, "`Self`");
1100 hir::Node::Item(hir::Item {
1101 kind: hir::ItemKind::Fn(_, generics, _), ..
1103 hir::Node::TraitItem(hir::TraitItem {
1105 kind: hir::TraitItemKind::Method(..), ..
1107 hir::Node::ImplItem(hir::ImplItem {
1109 kind: hir::ImplItemKind::Method(..), ..
1111 hir::Node::Item(hir::Item {
1112 kind: hir::ItemKind::Trait(_, _, generics, _, _), ..
1114 hir::Node::Item(hir::Item {
1115 kind: hir::ItemKind::Impl(_, _, _, generics, ..), ..
1116 }) if projection.is_some() => {
1117 // Missing associated type bound.
1118 suggest_restriction(&generics, "the associated type");
1122 hir::Node::Item(hir::Item { kind: hir::ItemKind::Struct(_, generics), span, .. }) |
1123 hir::Node::Item(hir::Item { kind: hir::ItemKind::Enum(_, generics), span, .. }) |
1124 hir::Node::Item(hir::Item { kind: hir::ItemKind::Union(_, generics), span, .. }) |
1125 hir::Node::Item(hir::Item {
1126 kind: hir::ItemKind::Trait(_, _, generics, ..), span, ..
1128 hir::Node::Item(hir::Item {
1129 kind: hir::ItemKind::Impl(_, _, _, generics, ..), span, ..
1131 hir::Node::Item(hir::Item {
1132 kind: hir::ItemKind::Fn(_, generics, _), span, ..
1134 hir::Node::Item(hir::Item {
1135 kind: hir::ItemKind::TyAlias(_, generics), span, ..
1137 hir::Node::Item(hir::Item {
1138 kind: hir::ItemKind::TraitAlias(generics, _), span, ..
1140 hir::Node::Item(hir::Item {
1141 kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }), span, ..
1143 hir::Node::TraitItem(hir::TraitItem { generics, span, .. }) |
1144 hir::Node::ImplItem(hir::ImplItem { generics, span, .. })
1146 // Missing generic type parameter bound.
1147 let restrict_msg = "consider further restricting this bound";
1148 let param_name = self_ty.to_string();
1149 for param in generics.params.iter().filter(|p| {
1150 p.name.ident().as_str() == param_name
1152 if param_name.starts_with("impl ") {
1153 // `impl Trait` in argument:
1154 // `fn foo(x: impl Trait) {}` → `fn foo(t: impl Trait + Trait2) {}`
1155 err.span_suggestion(
1158 // `impl CurrentTrait + MissingTrait`
1159 format!("{} + {}", param.name.ident(), trait_ref),
1160 Applicability::MachineApplicable,
1162 } else if generics.where_clause.predicates.is_empty() &&
1163 param.bounds.is_empty()
1165 // If there are no bounds whatsoever, suggest adding a constraint
1166 // to the type parameter:
1167 // `fn foo<T>(t: T) {}` → `fn foo<T: Trait>(t: T) {}`
1168 err.span_suggestion(
1170 "consider restricting this bound",
1171 format!("{}", trait_ref.to_predicate()),
1172 Applicability::MachineApplicable,
1174 } else if !generics.where_clause.predicates.is_empty() {
1175 // There is a `where` clause, so suggest expanding it:
1176 // `fn foo<T>(t: T) where T: Debug {}` →
1177 // `fn foo<T>(t: T) where T: Debug, T: Trait {}`
1178 err.span_suggestion(
1179 generics.where_clause.span().unwrap().shrink_to_hi(),
1181 "consider further restricting type parameter `{}`",
1184 format!(", {}", trait_ref.to_predicate()),
1185 Applicability::MachineApplicable,
1188 // If there is no `where` clause lean towards constraining to the
1190 // `fn foo<X: Bar, T>(t: T, x: X) {}` → `fn foo<T: Trait>(t: T) {}`
1191 // `fn foo<T: Bar>(t: T) {}` → `fn foo<T: Bar + Trait>(t: T) {}`
1192 let sp = param.span.with_hi(span.hi());
1193 let span = self.tcx.sess.source_map()
1194 .span_through_char(sp, ':');
1195 if sp != param.span && sp != span {
1196 // Only suggest if we have high certainty that the span
1197 // covers the colon in `foo<T: Trait>`.
1198 err.span_suggestion(span, restrict_msg, format!(
1200 trait_ref.to_predicate(),
1201 ), Applicability::MachineApplicable);
1203 err.span_label(param.span, &format!(
1204 "consider adding a `where {}` bound",
1205 trait_ref.to_predicate(),
1213 hir::Node::Crate => return,
1218 hir_id = self.tcx.hir().get_parent_item(hir_id);
1222 /// When encountering an assignment of an unsized trait, like `let x = ""[..];`, provide a
1223 /// suggestion to borrow the initializer in order to use have a slice instead.
1224 fn suggest_borrow_on_unsized_slice(
1226 code: &ObligationCauseCode<'tcx>,
1227 err: &mut DiagnosticBuilder<'tcx>,
1229 if let &ObligationCauseCode::VariableType(hir_id) = code {
1230 let parent_node = self.tcx.hir().get_parent_node(hir_id);
1231 if let Some(Node::Local(ref local)) = self.tcx.hir().find(parent_node) {
1232 if let Some(ref expr) = local.init {
1233 if let hir::ExprKind::Index(_, _) = expr.kind {
1234 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
1235 err.span_suggestion(
1237 "consider borrowing here",
1238 format!("&{}", snippet),
1239 Applicability::MachineApplicable
1250 obligation: &PredicateObligation<'tcx>,
1251 err: &mut DiagnosticBuilder<'_>,
1252 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1253 points_at_arg: bool,
1255 let self_ty = trait_ref.self_ty();
1256 match self_ty.kind {
1257 ty::FnDef(def_id, _) => {
1258 // We tried to apply the bound to an `fn`. Check whether calling it would evaluate
1259 // to a type that *would* satisfy the trait binding. If it would, suggest calling
1260 // it: `bar(foo)` -> `bar(foo)`. This case is *very* likely to be hit if `foo` is
1262 let output_ty = self_ty.fn_sig(self.tcx).output();
1263 let new_trait_ref = ty::TraitRef {
1264 def_id: trait_ref.def_id(),
1265 substs: self.tcx.mk_substs_trait(output_ty.skip_binder(), &[]),
1267 let obligation = Obligation::new(
1268 obligation.cause.clone(),
1269 obligation.param_env,
1270 new_trait_ref.to_predicate(),
1272 match self.evaluate_obligation(&obligation) {
1273 Ok(EvaluationResult::EvaluatedToOk) |
1274 Ok(EvaluationResult::EvaluatedToOkModuloRegions) |
1275 Ok(EvaluationResult::EvaluatedToAmbig) => {
1276 if let Some(hir::Node::Item(hir::Item {
1278 kind: hir::ItemKind::Fn(.., body_id),
1280 })) = self.tcx.hir().get_if_local(def_id) {
1281 let body = self.tcx.hir().body(*body_id);
1282 let msg = "use parentheses to call the function";
1283 let snippet = format!(
1287 .map(|arg| match &arg.pat.kind {
1288 hir::PatKind::Binding(_, _, ident, None)
1289 if ident.name != kw::SelfLower => ident.to_string(),
1290 _ => "_".to_string(),
1291 }).collect::<Vec<_>>().join(", "),
1293 // When the obligation error has been ensured to have been caused by
1294 // an argument, the `obligation.cause.span` points at the expression
1295 // of the argument, so we can provide a suggestion. This is signaled
1296 // by `points_at_arg`. Otherwise, we give a more general note.
1298 err.span_suggestion(
1299 obligation.cause.span,
1302 Applicability::HasPlaceholders,
1305 err.help(&format!("{}: `{}`", msg, snippet));
1316 fn suggest_add_reference_to_arg(
1318 obligation: &PredicateObligation<'tcx>,
1319 err: &mut DiagnosticBuilder<'tcx>,
1320 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1321 points_at_arg: bool,
1322 has_custom_message: bool,
1328 let span = obligation.cause.span;
1329 let param_env = obligation.param_env;
1330 let trait_ref = trait_ref.skip_binder();
1332 if let ObligationCauseCode::ImplDerivedObligation(obligation) = &obligation.cause.code {
1333 // Try to apply the original trait binding obligation by borrowing.
1334 let self_ty = trait_ref.self_ty();
1335 let found = self_ty.to_string();
1336 let new_self_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, self_ty);
1337 let substs = self.tcx.mk_substs_trait(new_self_ty, &[]);
1338 let new_trait_ref = ty::TraitRef::new(obligation.parent_trait_ref.def_id(), substs);
1339 let new_obligation = Obligation::new(
1340 ObligationCause::dummy(),
1342 new_trait_ref.to_predicate(),
1344 if self.predicate_must_hold_modulo_regions(&new_obligation) {
1345 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1346 // We have a very specific type of error, where just borrowing this argument
1347 // might solve the problem. In cases like this, the important part is the
1348 // original type obligation, not the last one that failed, which is arbitrary.
1349 // Because of this, we modify the error to refer to the original obligation and
1350 // return early in the caller.
1352 "the trait bound `{}: {}` is not satisfied",
1354 obligation.parent_trait_ref.skip_binder(),
1356 if has_custom_message {
1359 err.message = vec![(msg, Style::NoStyle)];
1361 if snippet.starts_with('&') {
1362 // This is already a literal borrow and the obligation is failing
1363 // somewhere else in the obligation chain. Do not suggest non-sense.
1366 err.span_label(span, &format!(
1367 "expected an implementor of trait `{}`",
1368 obligation.parent_trait_ref.skip_binder(),
1370 err.span_suggestion(
1372 "consider borrowing here",
1373 format!("&{}", snippet),
1374 Applicability::MaybeIncorrect,
1383 /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
1384 /// suggest removing these references until we reach a type that implements the trait.
1385 fn suggest_remove_reference(
1387 obligation: &PredicateObligation<'tcx>,
1388 err: &mut DiagnosticBuilder<'tcx>,
1389 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1391 let trait_ref = trait_ref.skip_binder();
1392 let span = obligation.cause.span;
1394 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1395 let refs_number = snippet.chars()
1396 .filter(|c| !c.is_whitespace())
1397 .take_while(|c| *c == '&')
1399 if let Some('\'') = snippet.chars()
1400 .filter(|c| !c.is_whitespace())
1403 { // Do not suggest removal of borrow from type arguments.
1407 let mut trait_type = trait_ref.self_ty();
1409 for refs_remaining in 0..refs_number {
1410 if let ty::Ref(_, t_type, _) = trait_type.kind {
1411 trait_type = t_type;
1413 let substs = self.tcx.mk_substs_trait(trait_type, &[]);
1414 let new_trait_ref = ty::TraitRef::new(trait_ref.def_id, substs);
1415 let new_obligation = Obligation::new(
1416 ObligationCause::dummy(),
1417 obligation.param_env,
1418 new_trait_ref.to_predicate(),
1421 if self.predicate_may_hold(&new_obligation) {
1422 let sp = self.tcx.sess.source_map()
1423 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1425 let remove_refs = refs_remaining + 1;
1426 let format_str = format!("consider removing {} leading `&`-references",
1429 err.span_suggestion_short(
1430 sp, &format_str, String::new(), Applicability::MachineApplicable
1441 /// Check if the trait bound is implemented for a different mutability and note it in the
1443 fn suggest_change_mut(
1445 obligation: &PredicateObligation<'tcx>,
1446 err: &mut DiagnosticBuilder<'tcx>,
1447 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1448 points_at_arg: bool,
1450 let span = obligation.cause.span;
1451 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1452 let refs_number = snippet.chars()
1453 .filter(|c| !c.is_whitespace())
1454 .take_while(|c| *c == '&')
1456 if let Some('\'') = snippet.chars()
1457 .filter(|c| !c.is_whitespace())
1460 { // Do not suggest removal of borrow from type arguments.
1463 let trait_ref = self.resolve_vars_if_possible(trait_ref);
1464 if trait_ref.has_infer_types() {
1465 // Do not ICE while trying to find if a reborrow would succeed on a trait with
1466 // unresolved bindings.
1470 if let ty::Ref(region, t_type, mutability) = trait_ref.skip_binder().self_ty().kind {
1471 let trait_type = match mutability {
1472 hir::Mutability::Mutable => self.tcx.mk_imm_ref(region, t_type),
1473 hir::Mutability::Immutable => self.tcx.mk_mut_ref(region, t_type),
1476 let substs = self.tcx.mk_substs_trait(&trait_type, &[]);
1477 let new_trait_ref = ty::TraitRef::new(trait_ref.skip_binder().def_id, substs);
1478 let new_obligation = Obligation::new(
1479 ObligationCause::dummy(),
1480 obligation.param_env,
1481 new_trait_ref.to_predicate(),
1484 if self.evaluate_obligation_no_overflow(
1486 ).must_apply_modulo_regions() {
1487 let sp = self.tcx.sess.source_map()
1488 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1490 mutability == hir::Mutability::Immutable &&
1493 err.span_suggestion(
1495 "consider changing this borrow's mutability",
1496 "&mut ".to_string(),
1497 Applicability::MachineApplicable,
1501 "`{}` is implemented for `{:?}`, but not for `{:?}`",
1504 trait_ref.skip_binder().self_ty(),
1512 fn suggest_semicolon_removal(
1514 obligation: &PredicateObligation<'tcx>,
1515 err: &mut DiagnosticBuilder<'tcx>,
1517 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1519 let hir = self.tcx.hir();
1520 let parent_node = hir.get_parent_node(obligation.cause.body_id);
1521 let node = hir.find(parent_node);
1522 if let Some(hir::Node::Item(hir::Item {
1523 kind: hir::ItemKind::Fn(sig, _, body_id),
1526 let body = hir.body(*body_id);
1527 if let hir::ExprKind::Block(blk, _) = &body.value.kind {
1528 if sig.decl.output.span().overlaps(span) && blk.expr.is_none() &&
1529 "()" == &trait_ref.self_ty().to_string()
1531 // FIXME(estebank): When encountering a method with a trait
1532 // bound not satisfied in the return type with a body that has
1533 // no return, suggest removal of semicolon on last statement.
1534 // Once that is added, close #54771.
1535 if let Some(ref stmt) = blk.stmts.last() {
1536 let sp = self.tcx.sess.source_map().end_point(stmt.span);
1537 err.span_label(sp, "consider removing this semicolon");
1544 /// Given some node representing a fn-like thing in the HIR map,
1545 /// returns a span and `ArgKind` information that describes the
1546 /// arguments it expects. This can be supplied to
1547 /// `report_arg_count_mismatch`.
1548 pub fn get_fn_like_arguments(&self, node: Node<'_>) -> (Span, Vec<ArgKind>) {
1550 Node::Expr(&hir::Expr {
1551 kind: hir::ExprKind::Closure(_, ref _decl, id, span, _),
1554 (self.tcx.sess.source_map().def_span(span),
1555 self.tcx.hir().body(id).params.iter()
1558 kind: hir::PatKind::Tuple(ref args, _),
1564 args.iter().map(|pat| {
1565 let snippet = self.tcx.sess.source_map()
1566 .span_to_snippet(pat.span).unwrap();
1567 (snippet, "_".to_owned())
1568 }).collect::<Vec<_>>(),
1571 let name = self.tcx.sess.source_map()
1572 .span_to_snippet(arg.pat.span).unwrap();
1573 ArgKind::Arg(name, "_".to_owned())
1576 .collect::<Vec<ArgKind>>())
1578 Node::Item(&hir::Item {
1580 kind: hir::ItemKind::Fn(ref sig, ..),
1583 Node::ImplItem(&hir::ImplItem {
1585 kind: hir::ImplItemKind::Method(ref sig, _),
1588 Node::TraitItem(&hir::TraitItem {
1590 kind: hir::TraitItemKind::Method(ref sig, _),
1593 (self.tcx.sess.source_map().def_span(span), sig.decl.inputs.iter()
1594 .map(|arg| match arg.clone().kind {
1595 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
1597 vec![("_".to_owned(), "_".to_owned()); tys.len()]
1599 _ => ArgKind::empty()
1600 }).collect::<Vec<ArgKind>>())
1602 Node::Ctor(ref variant_data) => {
1603 let span = variant_data.ctor_hir_id()
1604 .map(|hir_id| self.tcx.hir().span(hir_id))
1605 .unwrap_or(DUMMY_SP);
1606 let span = self.tcx.sess.source_map().def_span(span);
1608 (span, vec![ArgKind::empty(); variant_data.fields().len()])
1610 _ => panic!("non-FnLike node found: {:?}", node),
1614 /// Reports an error when the number of arguments needed by a
1615 /// trait match doesn't match the number that the expression
1617 pub fn report_arg_count_mismatch(
1620 found_span: Option<Span>,
1621 expected_args: Vec<ArgKind>,
1622 found_args: Vec<ArgKind>,
1624 ) -> DiagnosticBuilder<'tcx> {
1625 let kind = if is_closure { "closure" } else { "function" };
1627 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
1628 let arg_length = arguments.len();
1629 let distinct = match &other[..] {
1630 &[ArgKind::Tuple(..)] => true,
1633 match (arg_length, arguments.get(0)) {
1634 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
1635 format!("a single {}-tuple as argument", fields.len())
1637 _ => format!("{} {}argument{}",
1639 if distinct && arg_length > 1 { "distinct " } else { "" },
1640 pluralize!(arg_length))
1644 let expected_str = args_str(&expected_args, &found_args);
1645 let found_str = args_str(&found_args, &expected_args);
1647 let mut err = struct_span_err!(
1651 "{} is expected to take {}, but it takes {}",
1657 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
1659 if let Some(found_span) = found_span {
1660 err.span_label(found_span, format!("takes {}", found_str));
1663 // ^^^^^^^^-- def_span
1667 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
1670 let pipe_span = if let Some(span) = found_span.trim_start(prefix_span) {
1676 // Suggest to take and ignore the arguments with expected_args_length `_`s if
1677 // found arguments is empty (assume the user just wants to ignore args in this case).
1678 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
1679 if found_args.is_empty() && is_closure {
1680 let underscores = vec!["_"; expected_args.len()].join(", ");
1681 err.span_suggestion(
1684 "consider changing the closure to take and ignore the expected argument{}",
1685 if expected_args.len() < 2 {
1691 format!("|{}|", underscores),
1692 Applicability::MachineApplicable,
1696 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
1697 if fields.len() == expected_args.len() {
1698 let sugg = fields.iter()
1699 .map(|(name, _)| name.to_owned())
1700 .collect::<Vec<String>>()
1702 err.span_suggestion(
1704 "change the closure to take multiple arguments instead of a single tuple",
1705 format!("|{}|", sugg),
1706 Applicability::MachineApplicable,
1710 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..] {
1711 if fields.len() == found_args.len() && is_closure {
1715 .map(|arg| match arg {
1716 ArgKind::Arg(name, _) => name.to_owned(),
1717 _ => "_".to_owned(),
1719 .collect::<Vec<String>>()
1721 // add type annotations if available
1722 if found_args.iter().any(|arg| match arg {
1723 ArgKind::Arg(_, ty) => ty != "_",
1728 .map(|(_, ty)| ty.to_owned())
1729 .collect::<Vec<String>>()
1735 err.span_suggestion(
1737 "change the closure to accept a tuple instead of individual arguments",
1739 Applicability::MachineApplicable,
1748 fn report_closure_arg_mismatch(
1751 found_span: Option<Span>,
1752 expected_ref: ty::PolyTraitRef<'tcx>,
1753 found: ty::PolyTraitRef<'tcx>,
1754 ) -> DiagnosticBuilder<'tcx> {
1755 fn build_fn_sig_string<'tcx>(tcx: TyCtxt<'tcx>, trait_ref: &ty::TraitRef<'tcx>) -> String {
1756 let inputs = trait_ref.substs.type_at(1);
1757 let sig = if let ty::Tuple(inputs) = inputs.kind {
1759 inputs.iter().map(|k| k.expect_ty()),
1760 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1762 hir::Unsafety::Normal,
1763 ::rustc_target::spec::abi::Abi::Rust
1767 ::std::iter::once(inputs),
1768 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1770 hir::Unsafety::Normal,
1771 ::rustc_target::spec::abi::Abi::Rust
1774 ty::Binder::bind(sig).to_string()
1777 let argument_is_closure = expected_ref.skip_binder().substs.type_at(0).is_closure();
1778 let mut err = struct_span_err!(self.tcx.sess, span, E0631,
1779 "type mismatch in {} arguments",
1780 if argument_is_closure { "closure" } else { "function" });
1782 let found_str = format!(
1783 "expected signature of `{}`",
1784 build_fn_sig_string(self.tcx, found.skip_binder())
1786 err.span_label(span, found_str);
1788 let found_span = found_span.unwrap_or(span);
1789 let expected_str = format!(
1790 "found signature of `{}`",
1791 build_fn_sig_string(self.tcx, expected_ref.skip_binder())
1793 err.span_label(found_span, expected_str);
1799 impl<'tcx> TyCtxt<'tcx> {
1800 pub fn recursive_type_with_infinite_size_error(self,
1802 -> DiagnosticBuilder<'tcx>
1804 assert!(type_def_id.is_local());
1805 let span = self.hir().span_if_local(type_def_id).unwrap();
1806 let span = self.sess.source_map().def_span(span);
1807 let mut err = struct_span_err!(self.sess, span, E0072,
1808 "recursive type `{}` has infinite size",
1809 self.def_path_str(type_def_id));
1810 err.span_label(span, "recursive type has infinite size");
1811 err.help(&format!("insert indirection (e.g., a `Box`, `Rc`, or `&`) \
1812 at some point to make `{}` representable",
1813 self.def_path_str(type_def_id)));
1817 pub fn report_object_safety_error(
1820 trait_def_id: DefId,
1821 violations: Vec<ObjectSafetyViolation>,
1822 ) -> DiagnosticBuilder<'tcx> {
1823 let trait_str = self.def_path_str(trait_def_id);
1824 let span = self.sess.source_map().def_span(span);
1825 let mut err = struct_span_err!(
1826 self.sess, span, E0038,
1827 "the trait `{}` cannot be made into an object",
1829 err.span_label(span, format!("the trait `{}` cannot be made into an object", trait_str));
1831 let mut reported_violations = FxHashSet::default();
1832 for violation in violations {
1833 if reported_violations.insert(violation.clone()) {
1834 match violation.span() {
1835 Some(span) => err.span_label(span, violation.error_msg()),
1836 None => err.note(&violation.error_msg()),
1841 if self.sess.trait_methods_not_found.borrow().contains(&span) {
1842 // Avoid emitting error caused by non-existing method (#58734)
1850 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
1851 fn maybe_report_ambiguity(
1853 obligation: &PredicateObligation<'tcx>,
1854 body_id: Option<hir::BodyId>,
1856 // Unable to successfully determine, probably means
1857 // insufficient type information, but could mean
1858 // ambiguous impls. The latter *ought* to be a
1859 // coherence violation, so we don't report it here.
1861 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
1862 let span = obligation.cause.span;
1865 "maybe_report_ambiguity(predicate={:?}, obligation={:?} body_id={:?}, code={:?})",
1869 obligation.cause.code,
1872 // Ambiguity errors are often caused as fallout from earlier
1873 // errors. So just ignore them if this infcx is tainted.
1874 if self.is_tainted_by_errors() {
1879 ty::Predicate::Trait(ref data) => {
1880 let trait_ref = data.to_poly_trait_ref();
1881 let self_ty = trait_ref.self_ty();
1882 debug!("self_ty {:?} {:?} trait_ref {:?}", self_ty, self_ty.kind, trait_ref);
1884 if predicate.references_error() {
1887 // Typically, this ambiguity should only happen if
1888 // there are unresolved type inference variables
1889 // (otherwise it would suggest a coherence
1890 // failure). But given #21974 that is not necessarily
1891 // the case -- we can have multiple where clauses that
1892 // are only distinguished by a region, which results
1893 // in an ambiguity even when all types are fully
1894 // known, since we don't dispatch based on region
1897 // This is kind of a hack: it frequently happens that some earlier
1898 // error prevents types from being fully inferred, and then we get
1899 // a bunch of uninteresting errors saying something like "<generic
1900 // #0> doesn't implement Sized". It may even be true that we
1901 // could just skip over all checks where the self-ty is an
1902 // inference variable, but I was afraid that there might be an
1903 // inference variable created, registered as an obligation, and
1904 // then never forced by writeback, and hence by skipping here we'd
1905 // be ignoring the fact that we don't KNOW the type works
1906 // out. Though even that would probably be harmless, given that
1907 // we're only talking about builtin traits, which are known to be
1908 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
1909 // avoid inundating the user with unnecessary errors, but we now
1910 // check upstream for type errors and dont add the obligations to
1911 // begin with in those cases.
1913 self.tcx.lang_items().sized_trait()
1914 .map_or(false, |sized_id| sized_id == trait_ref.def_id())
1916 self.need_type_info_err(body_id, span, self_ty).emit();
1918 let mut err = struct_span_err!(
1922 "type annotations needed: cannot resolve `{}`",
1925 self.note_obligation_cause(&mut err, obligation);
1930 ty::Predicate::WellFormed(ty) => {
1931 // Same hacky approach as above to avoid deluging user
1932 // with error messages.
1933 if !ty.references_error() && !self.tcx.sess.has_errors() {
1934 self.need_type_info_err(body_id, span, ty).emit();
1938 ty::Predicate::Subtype(ref data) => {
1939 if data.references_error() || self.tcx.sess.has_errors() {
1940 // no need to overload user in such cases
1942 let &SubtypePredicate { a_is_expected: _, a, b } = data.skip_binder();
1943 // both must be type variables, or the other would've been instantiated
1944 assert!(a.is_ty_var() && b.is_ty_var());
1945 self.need_type_info_err(body_id,
1946 obligation.cause.span,
1952 if !self.tcx.sess.has_errors() {
1953 let mut err = struct_span_err!(
1955 obligation.cause.span,
1957 "type annotations needed: cannot resolve `{}`",
1960 self.note_obligation_cause(&mut err, obligation);
1967 /// Returns `true` if the trait predicate may apply for *some* assignment
1968 /// to the type parameters.
1969 fn predicate_can_apply(
1971 param_env: ty::ParamEnv<'tcx>,
1972 pred: ty::PolyTraitRef<'tcx>,
1974 struct ParamToVarFolder<'a, 'tcx> {
1975 infcx: &'a InferCtxt<'a, 'tcx>,
1976 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
1979 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
1980 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { self.infcx.tcx }
1982 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1983 if let ty::Param(ty::ParamTy {name, .. }) = ty.kind {
1984 let infcx = self.infcx;
1985 self.var_map.entry(ty).or_insert_with(||
1987 TypeVariableOrigin {
1988 kind: TypeVariableOriginKind::TypeParameterDefinition(name),
1994 ty.super_fold_with(self)
2000 let mut selcx = SelectionContext::new(self);
2002 let cleaned_pred = pred.fold_with(&mut ParamToVarFolder {
2004 var_map: Default::default()
2007 let cleaned_pred = super::project::normalize(
2010 ObligationCause::dummy(),
2014 let obligation = Obligation::new(
2015 ObligationCause::dummy(),
2017 cleaned_pred.to_predicate()
2020 self.predicate_may_hold(&obligation)
2024 fn note_obligation_cause(
2026 err: &mut DiagnosticBuilder<'_>,
2027 obligation: &PredicateObligation<'tcx>,
2029 // First, attempt to add note to this error with an async-await-specific
2030 // message, and fall back to regular note otherwise.
2031 if !self.note_obligation_cause_for_async_await(err, obligation) {
2032 self.note_obligation_cause_code(err, &obligation.predicate, &obligation.cause.code,
2037 /// Adds an async-await specific note to the diagnostic:
2039 /// ```ignore (diagnostic)
2040 /// note: future does not implement `std::marker::Send` because this value is used across an
2042 /// --> $DIR/issue-64130-non-send-future-diags.rs:15:5
2044 /// LL | let g = x.lock().unwrap();
2045 /// | - has type `std::sync::MutexGuard<'_, u32>`
2046 /// LL | baz().await;
2047 /// | ^^^^^^^^^^^ await occurs here, with `g` maybe used later
2049 /// | - `g` is later dropped here
2052 /// Returns `true` if an async-await specific note was added to the diagnostic.
2053 fn note_obligation_cause_for_async_await(
2055 err: &mut DiagnosticBuilder<'_>,
2056 obligation: &PredicateObligation<'tcx>,
2058 debug!("note_obligation_cause_for_async_await: obligation.predicate={:?} \
2059 obligation.cause.span={:?}", obligation.predicate, obligation.cause.span);
2060 let source_map = self.tcx.sess.source_map();
2062 // Look into the obligation predicate to determine the type in the generator which meant
2063 // that the predicate was not satisifed.
2064 let (trait_ref, target_ty) = match obligation.predicate {
2065 ty::Predicate::Trait(trait_predicate) =>
2066 (trait_predicate.skip_binder().trait_ref, trait_predicate.skip_binder().self_ty()),
2069 debug!("note_obligation_cause_for_async_await: target_ty={:?}", target_ty);
2071 // Attempt to detect an async-await error by looking at the obligation causes, looking
2072 // for only generators, generator witnesses, opaque types or `std::future::GenFuture` to
2075 // When a future does not implement a trait because of a captured type in one of the
2076 // generators somewhere in the call stack, then the result is a chain of obligations.
2077 // Given a `async fn` A that calls a `async fn` B which captures a non-send type and that
2078 // future is passed as an argument to a function C which requires a `Send` type, then the
2079 // chain looks something like this:
2081 // - `BuiltinDerivedObligation` with a generator witness (B)
2082 // - `BuiltinDerivedObligation` with a generator (B)
2083 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (B)
2084 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
2085 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
2086 // - `BuiltinDerivedObligation` with a generator witness (A)
2087 // - `BuiltinDerivedObligation` with a generator (A)
2088 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (A)
2089 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
2090 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
2091 // - `BindingObligation` with `impl_send (Send requirement)
2093 // The first obligations in the chain can be used to get the details of the type that is
2094 // captured but the entire chain must be inspected to detect this case.
2095 let mut generator = None;
2096 let mut next_code = Some(&obligation.cause.code);
2097 while let Some(code) = next_code {
2098 debug!("note_obligation_cause_for_async_await: code={:?}", code);
2100 ObligationCauseCode::BuiltinDerivedObligation(derived_obligation) |
2101 ObligationCauseCode::ImplDerivedObligation(derived_obligation) => {
2102 debug!("note_obligation_cause_for_async_await: self_ty.kind={:?}",
2103 derived_obligation.parent_trait_ref.self_ty().kind);
2104 match derived_obligation.parent_trait_ref.self_ty().kind {
2105 ty::Adt(ty::AdtDef { did, .. }, ..) if
2106 self.tcx.is_diagnostic_item(sym::gen_future, *did) => {},
2107 ty::Generator(did, ..) => generator = generator.or(Some(did)),
2108 ty::GeneratorWitness(_) | ty::Opaque(..) => {},
2112 next_code = Some(derived_obligation.parent_code.as_ref());
2114 ObligationCauseCode::ItemObligation(_) | ObligationCauseCode::BindingObligation(..)
2115 if generator.is_some() => break,
2120 let generator_did = generator.expect("can only reach this if there was a generator");
2122 // Only continue to add a note if the generator is from an `async` function.
2123 let parent_node = self.tcx.parent(generator_did)
2124 .and_then(|parent_did| self.tcx.hir().get_if_local(parent_did));
2125 debug!("note_obligation_cause_for_async_await: parent_node={:?}", parent_node);
2126 if let Some(hir::Node::Item(hir::Item {
2127 kind: hir::ItemKind::Fn(sig, _, _),
2130 debug!("note_obligation_cause_for_async_await: header={:?}", sig.header);
2131 if sig.header.asyncness != hir::IsAsync::Async {
2136 let span = self.tcx.def_span(generator_did);
2137 let tables = self.tcx.typeck_tables_of(generator_did);
2138 debug!("note_obligation_cause_for_async_await: generator_did={:?} span={:?} ",
2139 generator_did, span);
2141 // Look for a type inside the generator interior that matches the target type to get
2143 let target_span = tables.generator_interior_types.iter()
2144 .find(|ty::GeneratorInteriorTypeCause { ty, .. }| ty::TyS::same_type(*ty, target_ty))
2145 .map(|ty::GeneratorInteriorTypeCause { span, scope_span, .. }|
2146 (span, source_map.span_to_snippet(*span), scope_span));
2147 if let Some((target_span, Ok(snippet), scope_span)) = target_span {
2148 // Look at the last interior type to get a span for the `.await`.
2149 let await_span = tables.generator_interior_types.iter().map(|i| i.span).last().unwrap();
2150 let mut span = MultiSpan::from_span(await_span);
2151 span.push_span_label(
2152 await_span, format!("await occurs here, with `{}` maybe used later", snippet));
2154 span.push_span_label(*target_span, format!("has type `{}`", target_ty));
2156 // If available, use the scope span to annotate the drop location.
2157 if let Some(scope_span) = scope_span {
2158 span.push_span_label(
2159 source_map.end_point(*scope_span),
2160 format!("`{}` is later dropped here", snippet),
2164 err.span_note(span, &format!(
2165 "future does not implement `{}` as this value is used across an await",
2169 // Add a note for the item obligation that remains - normally a note pointing to the
2170 // bound that introduced the obligation (e.g. `T: Send`).
2171 debug!("note_obligation_cause_for_async_await: next_code={:?}", next_code);
2172 self.note_obligation_cause_code(
2174 &obligation.predicate,
2185 fn note_obligation_cause_code<T>(&self,
2186 err: &mut DiagnosticBuilder<'_>,
2188 cause_code: &ObligationCauseCode<'tcx>,
2189 obligated_types: &mut Vec<&ty::TyS<'tcx>>)
2190 where T: fmt::Display
2194 ObligationCauseCode::ExprAssignable |
2195 ObligationCauseCode::MatchExpressionArm { .. } |
2196 ObligationCauseCode::MatchExpressionArmPattern { .. } |
2197 ObligationCauseCode::IfExpression { .. } |
2198 ObligationCauseCode::IfExpressionWithNoElse |
2199 ObligationCauseCode::MainFunctionType |
2200 ObligationCauseCode::StartFunctionType |
2201 ObligationCauseCode::IntrinsicType |
2202 ObligationCauseCode::MethodReceiver |
2203 ObligationCauseCode::ReturnNoExpression |
2204 ObligationCauseCode::MiscObligation => {}
2205 ObligationCauseCode::SliceOrArrayElem => {
2206 err.note("slice and array elements must have `Sized` type");
2208 ObligationCauseCode::TupleElem => {
2209 err.note("only the last element of a tuple may have a dynamically sized type");
2211 ObligationCauseCode::ProjectionWf(data) => {
2213 "required so that the projection `{}` is well-formed",
2217 ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
2219 "required so that reference `{}` does not outlive its referent",
2223 ObligationCauseCode::ObjectTypeBound(object_ty, region) => {
2225 "required so that the lifetime bound of `{}` for `{}` is satisfied",
2230 ObligationCauseCode::ItemObligation(item_def_id) => {
2231 let item_name = tcx.def_path_str(item_def_id);
2232 let msg = format!("required by `{}`", item_name);
2234 if let Some(sp) = tcx.hir().span_if_local(item_def_id) {
2235 let sp = tcx.sess.source_map().def_span(sp);
2236 err.span_label(sp, &msg);
2241 ObligationCauseCode::BindingObligation(item_def_id, span) => {
2242 let item_name = tcx.def_path_str(item_def_id);
2243 let msg = format!("required by this bound in `{}`", item_name);
2244 if let Some(ident) = tcx.opt_item_name(item_def_id) {
2245 err.span_label(ident.span, "");
2247 if span != DUMMY_SP {
2248 err.span_label(span, &msg);
2253 ObligationCauseCode::ObjectCastObligation(object_ty) => {
2254 err.note(&format!("required for the cast to the object type `{}`",
2255 self.ty_to_string(object_ty)));
2257 ObligationCauseCode::Coercion { source: _, target } => {
2258 err.note(&format!("required by cast to type `{}`",
2259 self.ty_to_string(target)));
2261 ObligationCauseCode::RepeatVec(suggest_const_in_array_repeat_expressions) => {
2262 err.note("the `Copy` trait is required because the \
2263 repeated element will be copied");
2264 if suggest_const_in_array_repeat_expressions {
2265 err.note("this array initializer can be evaluated at compile-time, for more \
2266 information, see issue \
2267 https://github.com/rust-lang/rust/issues/49147");
2268 if tcx.sess.opts.unstable_features.is_nightly_build() {
2269 err.help("add `#![feature(const_in_array_repeat_expressions)]` to the \
2270 crate attributes to enable");
2274 ObligationCauseCode::VariableType(_) => {
2275 err.note("all local variables must have a statically known size");
2276 if !self.tcx.features().unsized_locals {
2277 err.help("unsized locals are gated as an unstable feature");
2280 ObligationCauseCode::SizedArgumentType => {
2281 err.note("all function arguments must have a statically known size");
2282 if !self.tcx.features().unsized_locals {
2283 err.help("unsized locals are gated as an unstable feature");
2286 ObligationCauseCode::SizedReturnType => {
2287 err.note("the return type of a function must have a \
2288 statically known size");
2290 ObligationCauseCode::SizedYieldType => {
2291 err.note("the yield type of a generator must have a \
2292 statically known size");
2294 ObligationCauseCode::AssignmentLhsSized => {
2295 err.note("the left-hand-side of an assignment must have a statically known size");
2297 ObligationCauseCode::TupleInitializerSized => {
2298 err.note("tuples must have a statically known size to be initialized");
2300 ObligationCauseCode::StructInitializerSized => {
2301 err.note("structs must have a statically known size to be initialized");
2303 ObligationCauseCode::FieldSized { adt_kind: ref item, last } => {
2305 AdtKind::Struct => {
2307 err.note("the last field of a packed struct may only have a \
2308 dynamically sized type if it does not need drop to be run");
2310 err.note("only the last field of a struct may have a dynamically \
2315 err.note("no field of a union may have a dynamically sized type");
2318 err.note("no field of an enum variant may have a dynamically sized type");
2322 ObligationCauseCode::ConstSized => {
2323 err.note("constant expressions must have a statically known size");
2325 ObligationCauseCode::ConstPatternStructural => {
2326 err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`");
2328 ObligationCauseCode::SharedStatic => {
2329 err.note("shared static variables must have a type that implements `Sync`");
2331 ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
2332 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2333 let ty = parent_trait_ref.skip_binder().self_ty();
2334 err.note(&format!("required because it appears within the type `{}`", ty));
2335 obligated_types.push(ty);
2337 let parent_predicate = parent_trait_ref.to_predicate();
2338 if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
2339 self.note_obligation_cause_code(err,
2345 ObligationCauseCode::ImplDerivedObligation(ref data) => {
2346 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2348 &format!("required because of the requirements on the impl of `{}` for `{}`",
2350 parent_trait_ref.skip_binder().self_ty()));
2351 let parent_predicate = parent_trait_ref.to_predicate();
2352 self.note_obligation_cause_code(err,
2357 ObligationCauseCode::CompareImplMethodObligation { .. } => {
2359 &format!("the requirement `{}` appears on the impl method \
2360 but not on the corresponding trait method",
2363 ObligationCauseCode::ReturnType |
2364 ObligationCauseCode::ReturnValue(_) |
2365 ObligationCauseCode::BlockTailExpression(_) => (),
2366 ObligationCauseCode::TrivialBound => {
2367 err.help("see issue #48214");
2368 if tcx.sess.opts.unstable_features.is_nightly_build() {
2369 err.help("add `#![feature(trivial_bounds)]` to the \
2370 crate attributes to enable",
2374 ObligationCauseCode::AssocTypeBound(ref data) => {
2375 err.span_label(data.original, "associated type defined here");
2376 if let Some(sp) = data.impl_span {
2377 err.span_label(sp, "in this `impl` item");
2379 for sp in &data.bounds {
2380 err.span_label(*sp, "restricted in this bound");
2386 fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder<'_>) {
2387 let current_limit = self.tcx.sess.recursion_limit.get();
2388 let suggested_limit = current_limit * 2;
2389 err.help(&format!("consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
2393 fn is_recursive_obligation(&self,
2394 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
2395 cause_code: &ObligationCauseCode<'tcx>) -> bool {
2396 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2397 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2399 if obligated_types.iter().any(|ot| ot == &parent_trait_ref.skip_binder().self_ty()) {
2407 /// Summarizes information
2410 /// An argument of non-tuple type. Parameters are (name, ty)
2411 Arg(String, String),
2413 /// An argument of tuple type. For a "found" argument, the span is
2414 /// the locationo in the source of the pattern. For a "expected"
2415 /// argument, it will be None. The vector is a list of (name, ty)
2416 /// strings for the components of the tuple.
2417 Tuple(Option<Span>, Vec<(String, String)>),
2421 fn empty() -> ArgKind {
2422 ArgKind::Arg("_".to_owned(), "_".to_owned())
2425 /// Creates an `ArgKind` from the expected type of an
2426 /// argument. It has no name (`_`) and an optional source span.
2427 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2429 ty::Tuple(ref tys) => ArgKind::Tuple(
2432 .map(|ty| ("_".to_owned(), ty.to_string()))
2433 .collect::<Vec<_>>()
2435 _ => ArgKind::Arg("_".to_owned(), t.to_string()),