2 ConstEvalFailure, EvaluationResult, FulfillmentError, FulfillmentErrorCode,
3 MismatchedProjectionTypes, ObjectSafetyViolation, Obligation, ObligationCause,
4 ObligationCauseCode, OnUnimplementedDirective, OnUnimplementedNote,
5 OutputTypeParameterMismatch, Overflow, PredicateObligation, SelectionContext, SelectionError,
9 use crate::infer::error_reporting::TypeAnnotationNeeded as ErrorCode;
10 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
11 use crate::infer::{self, InferCtxt};
12 use crate::mir::interpret::ErrorHandled;
13 use crate::session::DiagnosticMessageId;
14 use crate::traits::object_safety_violations;
15 use crate::ty::error::ExpectedFound;
16 use crate::ty::fast_reject;
17 use crate::ty::fold::TypeFolder;
18 use crate::ty::subst::Subst;
19 use crate::ty::GenericParamDefKind;
20 use crate::ty::SubtypePredicate;
21 use crate::ty::TypeckTables;
22 use crate::ty::{self, AdtKind, DefIdTree, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable};
24 use errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, Style};
25 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
27 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
29 use rustc_span::source_map::SourceMap;
30 use rustc_span::symbol::{kw, sym};
31 use rustc_span::{ExpnKind, MultiSpan, Span, DUMMY_SP};
35 use rustc_error_codes::*;
37 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
38 pub fn report_fulfillment_errors(
40 errors: &[FulfillmentError<'tcx>],
41 body_id: Option<hir::BodyId>,
42 fallback_has_occurred: bool,
45 struct ErrorDescriptor<'tcx> {
46 predicate: ty::Predicate<'tcx>,
47 index: Option<usize>, // None if this is an old error
50 let mut error_map: FxHashMap<_, Vec<_>> = self
51 .reported_trait_errors
54 .map(|(&span, predicates)| {
59 .map(|predicate| ErrorDescriptor {
60 predicate: predicate.clone(),
68 for (index, error) in errors.iter().enumerate() {
69 // We want to ignore desugarings here: spans are equivalent even
70 // if one is the result of a desugaring and the other is not.
71 let mut span = error.obligation.cause.span;
72 let expn_data = span.ctxt().outer_expn_data();
73 if let ExpnKind::Desugaring(_) = expn_data.kind {
74 span = expn_data.call_site;
77 error_map.entry(span).or_default().push(ErrorDescriptor {
78 predicate: error.obligation.predicate.clone(),
82 self.reported_trait_errors
86 .push(error.obligation.predicate.clone());
89 // We do this in 2 passes because we want to display errors in order, though
90 // maybe it *is* better to sort errors by span or something.
91 let mut is_suppressed = vec![false; errors.len()];
92 for (_, error_set) in error_map.iter() {
93 // We want to suppress "duplicate" errors with the same span.
94 for error in error_set {
95 if let Some(index) = error.index {
96 // Suppress errors that are either:
97 // 1) strictly implied by another error.
98 // 2) implied by an error with a smaller index.
99 for error2 in error_set {
100 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
101 // Avoid errors being suppressed by already-suppressed
102 // errors, to prevent all errors from being suppressed
107 if self.error_implies(&error2.predicate, &error.predicate)
108 && !(error2.index >= error.index
109 && self.error_implies(&error.predicate, &error2.predicate))
111 info!("skipping {:?} (implied by {:?})", error, error2);
112 is_suppressed[index] = true;
120 for (error, suppressed) in errors.iter().zip(is_suppressed) {
122 self.report_fulfillment_error(error, body_id, fallback_has_occurred);
127 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
128 // `error` occurring implies that `cond` occurs.
129 fn error_implies(&self, cond: &ty::Predicate<'tcx>, error: &ty::Predicate<'tcx>) -> bool {
134 let (cond, error) = match (cond, error) {
135 (&ty::Predicate::Trait(..), &ty::Predicate::Trait(ref error)) => (cond, 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_error({:?})", 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,
194 fn report_projection_error(
196 obligation: &PredicateObligation<'tcx>,
197 error: &MismatchedProjectionTypes<'tcx>,
199 let predicate = 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(),
232 "report_projection_error obligation.cause={:?} obligation.param_env={:?}",
233 obligation.cause, obligation.param_env
237 "report_projection_error normalized_ty={:?} data.ty={:?}",
238 normalized_ty, data.ty
241 let is_normalized_ty_expected = match &obligation.cause.code {
242 ObligationCauseCode::ItemObligation(_)
243 | ObligationCauseCode::BindingObligation(_, _)
244 | ObligationCauseCode::ObjectCastObligation(_) => false,
248 if let Err(error) = self.at(&obligation.cause, obligation.param_env).eq_exp(
249 is_normalized_ty_expected,
253 values = Some(infer::ValuePairs::Types(ExpectedFound::new(
254 is_normalized_ty_expected,
264 let msg = format!("type mismatch resolving `{}`", predicate);
265 let error_id = (DiagnosticMessageId::ErrorId(271), Some(obligation.cause.span), msg);
266 let fresh = self.tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
268 let mut diag = struct_span_err!(
270 obligation.cause.span,
272 "type mismatch resolving `{}`",
275 self.note_type_err(&mut diag, &obligation.cause, None, values, err);
276 self.note_obligation_cause(&mut diag, obligation);
282 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
283 /// returns the fuzzy category of a given type, or None
284 /// if the type can be equated to any type.
285 fn type_category(t: Ty<'_>) -> Option<u32> {
290 ty::Int(..) | ty::Uint(..) | ty::Infer(ty::IntVar(..)) => Some(3),
291 ty::Float(..) | ty::Infer(ty::FloatVar(..)) => Some(4),
292 ty::Ref(..) | ty::RawPtr(..) => Some(5),
293 ty::Array(..) | ty::Slice(..) => Some(6),
294 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
295 ty::Dynamic(..) => Some(8),
296 ty::Closure(..) => Some(9),
297 ty::Tuple(..) => Some(10),
298 ty::Projection(..) => Some(11),
299 ty::Param(..) => Some(12),
300 ty::Opaque(..) => Some(13),
301 ty::Never => Some(14),
302 ty::Adt(adt, ..) => match adt.adt_kind() {
303 AdtKind::Struct => Some(15),
304 AdtKind::Union => Some(16),
305 AdtKind::Enum => Some(17),
307 ty::Generator(..) => Some(18),
308 ty::Foreign(..) => Some(19),
309 ty::GeneratorWitness(..) => Some(20),
310 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error => None,
311 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
315 match (type_category(a), type_category(b)) {
316 (Some(cat_a), Some(cat_b)) => match (&a.kind, &b.kind) {
317 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => def_a == def_b,
320 // infer and error can be equated to all types
327 trait_ref: ty::PolyTraitRef<'tcx>,
328 obligation: &PredicateObligation<'tcx>,
331 let param_env = obligation.param_env;
332 let trait_ref = tcx.erase_late_bound_regions(&trait_ref);
333 let trait_self_ty = trait_ref.self_ty();
335 let mut self_match_impls = vec![];
336 let mut fuzzy_match_impls = vec![];
338 self.tcx.for_each_relevant_impl(trait_ref.def_id, trait_self_ty, |def_id| {
339 let impl_substs = self.fresh_substs_for_item(obligation.cause.span, def_id);
340 let impl_trait_ref = tcx.impl_trait_ref(def_id).unwrap().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);
351 .zip(impl_trait_ref.substs.types().skip(1))
352 .all(|(u, v)| self.fuzzy_match_tys(u, v))
354 fuzzy_match_impls.push(def_id);
359 let impl_def_id = if self_match_impls.len() == 1 {
361 } else if fuzzy_match_impls.len() == 1 {
367 tcx.has_attr(impl_def_id, sym::rustc_on_unimplemented).then_some(impl_def_id)
370 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
371 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
372 hir::GeneratorKind::Gen => "a generator",
373 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
374 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
375 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
379 /// Used to set on_unimplemented's `ItemContext`
380 /// to be the enclosing (async) block/function/closure
381 fn describe_enclosure(&self, hir_id: hir::HirId) -> Option<&'static str> {
382 let hir = &self.tcx.hir();
383 let node = hir.find(hir_id)?;
384 if let hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. }) = &node {
385 self.describe_generator(*body_id).or_else(|| {
386 Some(if let hir::FnHeader { asyncness: hir::IsAsync::Async, .. } = sig.header {
392 } else if let hir::Node::Expr(hir::Expr {
393 kind: hir::ExprKind::Closure(_is_move, _, body_id, _, gen_movability),
397 self.describe_generator(*body_id).or_else(|| {
398 Some(if gen_movability.is_some() { "an async closure" } else { "a closure" })
400 } else if let hir::Node::Expr(hir::Expr { .. }) = &node {
401 let parent_hid = hir.get_parent_node(hir_id);
402 if parent_hid != hir_id {
403 return self.describe_enclosure(parent_hid);
412 fn on_unimplemented_note(
414 trait_ref: ty::PolyTraitRef<'tcx>,
415 obligation: &PredicateObligation<'tcx>,
416 ) -> OnUnimplementedNote {
418 self.impl_similar_to(trait_ref, obligation).unwrap_or_else(|| trait_ref.def_id());
419 let trait_ref = *trait_ref.skip_binder();
421 let mut flags = vec![];
424 self.describe_enclosure(obligation.cause.body_id).map(|s| s.to_owned()),
427 match obligation.cause.code {
428 ObligationCauseCode::BuiltinDerivedObligation(..)
429 | ObligationCauseCode::ImplDerivedObligation(..) => {}
431 // this is a "direct", user-specified, rather than derived,
433 flags.push((sym::direct, None));
437 if let ObligationCauseCode::ItemObligation(item) = obligation.cause.code {
438 // FIXME: maybe also have some way of handling methods
439 // from other traits? That would require name resolution,
440 // which we might want to be some sort of hygienic.
442 // Currently I'm leaving it for what I need for `try`.
443 if self.tcx.trait_of_item(item) == Some(trait_ref.def_id) {
444 let method = self.tcx.item_name(item);
445 flags.push((sym::from_method, None));
446 flags.push((sym::from_method, Some(method.to_string())));
449 if let Some(t) = self.get_parent_trait_ref(&obligation.cause.code) {
450 flags.push((sym::parent_trait, Some(t)));
453 if let Some(k) = obligation.cause.span.desugaring_kind() {
454 flags.push((sym::from_desugaring, None));
455 flags.push((sym::from_desugaring, Some(format!("{:?}", k))));
457 let generics = self.tcx.generics_of(def_id);
458 let self_ty = trait_ref.self_ty();
459 // This is also included through the generics list as `Self`,
460 // but the parser won't allow you to use it
461 flags.push((sym::_Self, Some(self_ty.to_string())));
462 if let Some(def) = self_ty.ty_adt_def() {
463 // We also want to be able to select self's original
464 // signature with no type arguments resolved
465 flags.push((sym::_Self, Some(self.tcx.type_of(def.did).to_string())));
468 for param in generics.params.iter() {
469 let value = match param.kind {
470 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
471 trait_ref.substs[param.index as usize].to_string()
473 GenericParamDefKind::Lifetime => continue,
475 let name = param.name;
476 flags.push((name, Some(value)));
479 if let Some(true) = self_ty.ty_adt_def().map(|def| def.did.is_local()) {
480 flags.push((sym::crate_local, None));
483 // Allow targeting all integers using `{integral}`, even if the exact type was resolved
484 if self_ty.is_integral() {
485 flags.push((sym::_Self, Some("{integral}".to_owned())));
488 if let ty::Array(aty, len) = self_ty.kind {
489 flags.push((sym::_Self, Some("[]".to_owned())));
490 flags.push((sym::_Self, Some(format!("[{}]", aty))));
491 if let Some(def) = aty.ty_adt_def() {
492 // We also want to be able to select the array's type's original
493 // signature with no type arguments resolved
496 Some(format!("[{}]", self.tcx.type_of(def.did).to_string())),
499 if let Some(len) = len.try_eval_usize(tcx, ty::ParamEnv::empty()) {
502 Some(format!("[{}; {}]", self.tcx.type_of(def.did).to_string(), len)),
507 Some(format!("[{}; _]", self.tcx.type_of(def.did).to_string())),
513 if let Ok(Some(command)) =
514 OnUnimplementedDirective::of_item(self.tcx, trait_ref.def_id, def_id)
516 command.evaluate(self.tcx, trait_ref, &flags[..])
518 OnUnimplementedNote::default()
522 fn find_similar_impl_candidates(
524 trait_ref: ty::PolyTraitRef<'tcx>,
525 ) -> Vec<ty::TraitRef<'tcx>> {
526 let simp = fast_reject::simplify_type(self.tcx, trait_ref.skip_binder().self_ty(), true);
527 let all_impls = self.tcx.all_impls(trait_ref.def_id());
530 Some(simp) => all_impls
532 .filter_map(|&def_id| {
533 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
534 let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
535 if let Some(imp_simp) = imp_simp {
536 if simp != imp_simp {
545 all_impls.iter().map(|&def_id| self.tcx.impl_trait_ref(def_id).unwrap()).collect()
550 fn report_similar_impl_candidates(
552 impl_candidates: Vec<ty::TraitRef<'tcx>>,
553 err: &mut DiagnosticBuilder<'_>,
555 if impl_candidates.is_empty() {
559 let len = impl_candidates.len();
560 let end = if impl_candidates.len() <= 5 { impl_candidates.len() } else { 4 };
562 let normalize = |candidate| {
563 self.tcx.infer_ctxt().enter(|ref infcx| {
564 let normalized = infcx
565 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
566 .normalize(candidate)
569 Some(normalized) => format!("\n {:?}", normalized.value),
570 None => format!("\n {:?}", candidate),
575 // Sort impl candidates so that ordering is consistent for UI tests.
576 let mut normalized_impl_candidates =
577 impl_candidates.iter().map(normalize).collect::<Vec<String>>();
579 // Sort before taking the `..end` range,
580 // because the ordering of `impl_candidates` may not be deterministic:
581 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
582 normalized_impl_candidates.sort();
585 "the following implementations were found:{}{}",
586 normalized_impl_candidates[..end].join(""),
587 if len > 5 { format!("\nand {} others", len - 4) } else { String::new() }
591 /// Reports that an overflow has occurred and halts compilation. We
592 /// halt compilation unconditionally because it is important that
593 /// overflows never be masked -- they basically represent computations
594 /// whose result could not be truly determined and thus we can't say
595 /// if the program type checks or not -- and they are unusual
596 /// occurrences in any case.
597 pub fn report_overflow_error<T>(
599 obligation: &Obligation<'tcx, T>,
600 suggest_increasing_limit: bool,
603 T: fmt::Display + TypeFoldable<'tcx>,
605 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
606 let mut err = struct_span_err!(
608 obligation.cause.span,
610 "overflow evaluating the requirement `{}`",
614 if suggest_increasing_limit {
615 self.suggest_new_overflow_limit(&mut err);
618 self.note_obligation_cause_code(
620 &obligation.predicate,
621 &obligation.cause.code,
626 self.tcx.sess.abort_if_errors();
630 /// Reports that a cycle was detected which led to overflow and halts
631 /// compilation. This is equivalent to `report_overflow_error` except
632 /// that we can give a more helpful error message (and, in particular,
633 /// we do not suggest increasing the overflow limit, which is not
635 pub fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
636 let cycle = self.resolve_vars_if_possible(&cycle.to_owned());
637 assert!(cycle.len() > 0);
639 debug!("report_overflow_error_cycle: cycle={:?}", cycle);
641 self.report_overflow_error(&cycle[0], false);
644 pub fn report_extra_impl_obligation(
647 item_name: ast::Name,
648 _impl_item_def_id: DefId,
649 trait_item_def_id: DefId,
650 requirement: &dyn fmt::Display,
651 ) -> DiagnosticBuilder<'tcx> {
652 let msg = "impl has stricter requirements than trait";
653 let sp = self.tcx.sess.source_map().def_span(error_span);
655 let mut err = struct_span_err!(self.tcx.sess, sp, E0276, "{}", msg);
657 if let Some(trait_item_span) = self.tcx.hir().span_if_local(trait_item_def_id) {
658 let span = self.tcx.sess.source_map().def_span(trait_item_span);
659 err.span_label(span, format!("definition of `{}` from trait", item_name));
662 err.span_label(sp, format!("impl has extra requirement {}", requirement));
667 /// Gets the parent trait chain start
668 fn get_parent_trait_ref(&self, code: &ObligationCauseCode<'tcx>) -> Option<String> {
670 &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
671 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
672 match self.get_parent_trait_ref(&data.parent_code) {
674 None => Some(parent_trait_ref.skip_binder().self_ty().to_string()),
681 pub fn report_selection_error(
683 obligation: &PredicateObligation<'tcx>,
684 error: &SelectionError<'tcx>,
685 fallback_has_occurred: bool,
689 let span = obligation.cause.span;
691 let mut err = match *error {
692 SelectionError::Unimplemented => {
693 if let ObligationCauseCode::CompareImplMethodObligation {
698 | ObligationCauseCode::CompareImplTypeObligation {
702 } = obligation.cause.code
704 self.report_extra_impl_obligation(
709 &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();
722 let (post_message, pre_message) = self
723 .get_parent_trait_ref(&obligation.cause.code)
724 .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
725 .unwrap_or_default();
727 let OnUnimplementedNote { message, label, note, enclosing_scope } =
728 self.on_unimplemented_note(trait_ref, obligation);
729 let have_alt_message = message.is_some() || label.is_some();
734 .span_to_snippet(span)
737 let is_from = format!("{}", trait_ref.print_only_trait_path())
738 .starts_with("std::convert::From<");
739 let (message, note) = if is_try && is_from {
742 "`?` couldn't convert the error to `{}`",
746 "the question mark operation (`?`) implicitly performs a \
747 conversion on the error value using the `From` trait"
755 let mut err = struct_span_err!(
760 message.unwrap_or_else(|| format!(
761 "the trait bound `{}` is not satisfied{}",
762 trait_ref.to_predicate(),
768 if obligation.cause.code == ObligationCauseCode::MainFunctionType {
769 "consider using `()`, or a `Result`".to_owned()
772 "{}the trait `{}` is not implemented for `{}`",
774 trait_ref.print_only_trait_path(),
779 if self.suggest_add_reference_to_arg(
786 self.note_obligation_cause(&mut err, obligation);
790 if let Some(ref s) = label {
791 // If it has a custom `#[rustc_on_unimplemented]`
792 // error message, let's display it as the label!
793 err.span_label(span, s.as_str());
794 err.help(&explanation);
796 err.span_label(span, explanation);
798 if let Some(ref s) = note {
799 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
800 err.note(s.as_str());
802 if let Some(ref s) = enclosing_scope {
803 let enclosing_scope_span = tcx.def_span(
805 .opt_local_def_id(obligation.cause.body_id)
807 tcx.hir().body_owner_def_id(hir::BodyId {
808 hir_id: obligation.cause.body_id,
813 err.span_label(enclosing_scope_span, s.as_str());
816 self.suggest_borrow_on_unsized_slice(&obligation.cause.code, &mut err);
817 self.suggest_fn_call(&obligation, &mut err, &trait_ref, points_at_arg);
818 self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
819 self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
820 self.note_version_mismatch(&mut err, &trait_ref);
822 // Try to report a help message
823 if !trait_ref.has_infer_types()
824 && self.predicate_can_apply(obligation.param_env, trait_ref)
826 // If a where-clause may be useful, remind the
827 // user that they can add it.
829 // don't display an on-unimplemented note, as
830 // these notes will often be of the form
831 // "the type `T` can't be frobnicated"
832 // which is somewhat confusing.
833 self.suggest_restricting_param_bound(
836 obligation.cause.body_id,
839 if !have_alt_message {
840 // Can't show anything else useful, try to find similar impls.
841 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
842 self.report_similar_impl_candidates(impl_candidates, &mut err);
844 self.suggest_change_mut(
852 // If this error is due to `!: Trait` not implemented but `(): Trait` is
853 // implemented, and fallback has occurred, then it could be due to a
854 // variable that used to fallback to `()` now falling back to `!`. Issue a
855 // note informing about the change in behaviour.
856 if trait_predicate.skip_binder().self_ty().is_never()
857 && fallback_has_occurred
859 let predicate = trait_predicate.map_bound(|mut trait_pred| {
860 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
862 &trait_pred.trait_ref.substs[1..],
866 let unit_obligation = Obligation {
867 predicate: ty::Predicate::Trait(predicate),
870 if self.predicate_may_hold(&unit_obligation) {
872 "the trait is implemented for `()`. \
873 Possibly this error has been caused by changes to \
874 Rust's type-inference algorithm \
875 (see: https://github.com/rust-lang/rust/issues/48950 \
876 for more info). Consider whether you meant to use the \
877 type `()` here instead.",
885 ty::Predicate::Subtype(ref predicate) => {
886 // Errors for Subtype predicates show up as
887 // `FulfillmentErrorCode::CodeSubtypeError`,
888 // not selection error.
889 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
892 ty::Predicate::RegionOutlives(ref predicate) => {
893 let predicate = self.resolve_vars_if_possible(predicate);
895 .region_outlives_predicate(&obligation.cause, &predicate)
902 "the requirement `{}` is not satisfied (`{}`)",
908 ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
909 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
914 "the requirement `{}` is not satisfied",
919 ty::Predicate::ObjectSafe(trait_def_id) => {
920 let violations = object_safety_violations(self.tcx, trait_def_id);
921 report_object_safety_error(self.tcx, span, trait_def_id, violations)
924 ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
925 let found_kind = self.closure_kind(closure_def_id, closure_substs).unwrap();
926 let closure_span = self
930 .def_span(self.tcx.hir().span_if_local(closure_def_id).unwrap());
931 let hir_id = self.tcx.hir().as_local_hir_id(closure_def_id).unwrap();
932 let mut err = struct_span_err!(
936 "expected a closure that implements the `{}` trait, \
937 but this closure only implements `{}`",
944 format!("this closure implements `{}`, not `{}`", found_kind, kind),
947 obligation.cause.span,
948 format!("the requirement to implement `{}` derives from here", kind),
951 // Additional context information explaining why the closure only implements
952 // a particular trait.
953 if let Some(tables) = self.in_progress_tables {
954 let tables = tables.borrow();
955 match (found_kind, tables.closure_kind_origins().get(hir_id)) {
956 (ty::ClosureKind::FnOnce, Some((span, name))) => {
960 "closure is `FnOnce` because it moves the \
961 variable `{}` out of its environment",
966 (ty::ClosureKind::FnMut, Some((span, name))) => {
970 "closure is `FnMut` because it mutates the \
984 ty::Predicate::WellFormed(ty) => {
985 if !self.tcx.sess.opts.debugging_opts.chalk {
986 // WF predicates cannot themselves make
987 // errors. They can only block due to
988 // ambiguity; otherwise, they always
989 // degenerate into other obligations
991 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
993 // FIXME: we'll need a better message which takes into account
994 // which bounds actually failed to hold.
995 self.tcx.sess.struct_span_err(
997 &format!("the type `{}` is not well-formed (chalk)", ty),
1002 ty::Predicate::ConstEvaluatable(..) => {
1003 // Errors for `ConstEvaluatable` predicates show up as
1004 // `SelectionError::ConstEvalFailure`,
1005 // not `Unimplemented`.
1008 "const-evaluatable requirement gave wrong error: `{:?}`",
1015 OutputTypeParameterMismatch(ref found_trait_ref, ref expected_trait_ref, _) => {
1016 let found_trait_ref = self.resolve_vars_if_possible(&*found_trait_ref);
1017 let expected_trait_ref = self.resolve_vars_if_possible(&*expected_trait_ref);
1019 if expected_trait_ref.self_ty().references_error() {
1023 let found_trait_ty = found_trait_ref.self_ty();
1025 let found_did = match found_trait_ty.kind {
1026 ty::Closure(did, _) | ty::Foreign(did) | ty::FnDef(did, _) => Some(did),
1027 ty::Adt(def, _) => Some(def.did),
1031 let found_span = found_did
1032 .and_then(|did| self.tcx.hir().span_if_local(did))
1033 .map(|sp| self.tcx.sess.source_map().def_span(sp)); // the sp could be an fn def
1035 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1036 // We check closures twice, with obligations flowing in different directions,
1037 // but we want to complain about them only once.
1041 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1043 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind {
1044 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1045 _ => vec![ArgKind::empty()],
1048 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1049 let expected = match expected_ty.kind {
1050 ty::Tuple(ref tys) => tys
1052 .map(|t| ArgKind::from_expected_ty(t.expect_ty(), Some(span)))
1054 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
1057 if found.len() == expected.len() {
1058 self.report_closure_arg_mismatch(
1065 let (closure_span, found) = found_did
1066 .and_then(|did| self.tcx.hir().get_if_local(did))
1068 let (found_span, found) = self.get_fn_like_arguments(node);
1069 (Some(found_span), found)
1071 .unwrap_or((found_span, found));
1073 self.report_arg_count_mismatch(
1078 found_trait_ty.is_closure(),
1083 TraitNotObjectSafe(did) => {
1084 let violations = object_safety_violations(self.tcx, did);
1085 report_object_safety_error(self.tcx, span, did, violations)
1088 // already reported in the query
1089 ConstEvalFailure(err) => {
1090 if let ErrorHandled::TooGeneric = err {
1091 // Silence this error, as it can be produced during intermediate steps
1092 // when a constant is not yet able to be evaluated (but will be later).
1095 self.tcx.sess.delay_span_bug(
1097 &format!("constant in type had an ignored error: {:?}", err),
1103 bug!("overflow should be handled before the `report_selection_error` path");
1107 self.note_obligation_cause(&mut err, obligation);
1112 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1113 /// with the same path as `trait_ref`, a help message about
1114 /// a probable version mismatch is added to `err`
1115 fn note_version_mismatch(
1117 err: &mut DiagnosticBuilder<'_>,
1118 trait_ref: &ty::PolyTraitRef<'tcx>,
1120 let get_trait_impl = |trait_def_id| {
1121 let mut trait_impl = None;
1122 self.tcx.for_each_relevant_impl(trait_def_id, trait_ref.self_ty(), |impl_def_id| {
1123 if trait_impl.is_none() {
1124 trait_impl = Some(impl_def_id);
1129 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
1130 let all_traits = self.tcx.all_traits(LOCAL_CRATE);
1131 let traits_with_same_path: std::collections::BTreeSet<_> = all_traits
1133 .filter(|trait_def_id| **trait_def_id != trait_ref.def_id())
1134 .filter(|trait_def_id| self.tcx.def_path_str(**trait_def_id) == required_trait_path)
1136 for trait_with_same_path in traits_with_same_path {
1137 if let Some(impl_def_id) = get_trait_impl(*trait_with_same_path) {
1138 let impl_span = self.tcx.def_span(impl_def_id);
1139 err.span_help(impl_span, "trait impl with same name found");
1140 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
1141 let crate_msg = format!(
1142 "Perhaps two different versions of crate `{}` are being used?",
1145 err.note(&crate_msg);
1149 fn suggest_restricting_param_bound(
1151 mut err: &mut DiagnosticBuilder<'_>,
1152 trait_ref: &ty::PolyTraitRef<'_>,
1153 body_id: hir::HirId,
1155 let self_ty = trait_ref.self_ty();
1156 let (param_ty, projection) = match &self_ty.kind {
1157 ty::Param(_) => (true, None),
1158 ty::Projection(projection) => (false, Some(projection)),
1162 let suggest_restriction =
1163 |generics: &hir::Generics<'_>, msg, err: &mut DiagnosticBuilder<'_>| {
1164 let span = generics.where_clause.span_for_predicates_or_empty_place();
1165 if !span.from_expansion() && span.desugaring_kind().is_none() {
1166 err.span_suggestion(
1167 generics.where_clause.span_for_predicates_or_empty_place().shrink_to_hi(),
1168 &format!("consider further restricting {}", msg),
1171 if !generics.where_clause.predicates.is_empty() {
1176 trait_ref.to_predicate(),
1178 Applicability::MachineApplicable,
1183 // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
1184 // don't suggest `T: Sized + ?Sized`.
1185 let mut hir_id = body_id;
1186 while let Some(node) = self.tcx.hir().find(hir_id) {
1188 hir::Node::TraitItem(hir::TraitItem {
1190 kind: hir::TraitItemKind::Method(..),
1192 }) if param_ty && self_ty == self.tcx.types.self_param => {
1193 // Restricting `Self` for a single method.
1194 suggest_restriction(&generics, "`Self`", err);
1198 hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, generics, _), .. })
1199 | hir::Node::TraitItem(hir::TraitItem {
1201 kind: hir::TraitItemKind::Method(..),
1204 | hir::Node::ImplItem(hir::ImplItem {
1206 kind: hir::ImplItemKind::Method(..),
1209 | hir::Node::Item(hir::Item {
1210 kind: hir::ItemKind::Trait(_, _, generics, _, _),
1213 | hir::Node::Item(hir::Item {
1214 kind: hir::ItemKind::Impl(_, _, _, generics, ..),
1216 }) if projection.is_some() => {
1217 // Missing associated type bound.
1218 suggest_restriction(&generics, "the associated type", err);
1222 hir::Node::Item(hir::Item {
1223 kind: hir::ItemKind::Struct(_, generics),
1227 | hir::Node::Item(hir::Item {
1228 kind: hir::ItemKind::Enum(_, generics), span, ..
1230 | hir::Node::Item(hir::Item {
1231 kind: hir::ItemKind::Union(_, generics),
1235 | hir::Node::Item(hir::Item {
1236 kind: hir::ItemKind::Trait(_, _, generics, ..),
1240 | hir::Node::Item(hir::Item {
1241 kind: hir::ItemKind::Impl(_, _, _, generics, ..),
1245 | hir::Node::Item(hir::Item {
1246 kind: hir::ItemKind::Fn(_, generics, _),
1250 | hir::Node::Item(hir::Item {
1251 kind: hir::ItemKind::TyAlias(_, generics),
1255 | hir::Node::Item(hir::Item {
1256 kind: hir::ItemKind::TraitAlias(generics, _),
1260 | hir::Node::Item(hir::Item {
1261 kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }),
1265 | hir::Node::TraitItem(hir::TraitItem { generics, span, .. })
1266 | hir::Node::ImplItem(hir::ImplItem { generics, span, .. })
1269 // Missing generic type parameter bound.
1270 let param_name = self_ty.to_string();
1271 let constraint = trait_ref.print_only_trait_path().to_string();
1272 if suggest_constraining_type_param(
1277 self.tcx.sess.source_map(),
1284 hir::Node::Crate => return,
1289 hir_id = self.tcx.hir().get_parent_item(hir_id);
1293 /// When encountering an assignment of an unsized trait, like `let x = ""[..];`, provide a
1294 /// suggestion to borrow the initializer in order to use have a slice instead.
1295 fn suggest_borrow_on_unsized_slice(
1297 code: &ObligationCauseCode<'tcx>,
1298 err: &mut DiagnosticBuilder<'tcx>,
1300 if let &ObligationCauseCode::VariableType(hir_id) = code {
1301 let parent_node = self.tcx.hir().get_parent_node(hir_id);
1302 if let Some(Node::Local(ref local)) = self.tcx.hir().find(parent_node) {
1303 if let Some(ref expr) = local.init {
1304 if let hir::ExprKind::Index(_, _) = expr.kind {
1305 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
1306 err.span_suggestion(
1308 "consider borrowing here",
1309 format!("&{}", snippet),
1310 Applicability::MachineApplicable,
1319 fn mk_obligation_for_def_id(
1322 output_ty: Ty<'tcx>,
1323 cause: ObligationCause<'tcx>,
1324 param_env: ty::ParamEnv<'tcx>,
1325 ) -> PredicateObligation<'tcx> {
1327 ty::TraitRef { def_id, substs: self.tcx.mk_substs_trait(output_ty, &[]) };
1328 Obligation::new(cause, param_env, new_trait_ref.to_predicate())
1331 /// Given a closure's `DefId`, return the given name of the closure.
1333 /// This doesn't account for reassignments, but it's only used for suggestions.
1334 fn get_closure_name(
1337 err: &mut DiagnosticBuilder<'_>,
1339 ) -> Option<String> {
1341 |err: &mut DiagnosticBuilder<'_>, kind: &hir::PatKind<'_>| -> Option<String> {
1342 // Get the local name of this closure. This can be inaccurate because
1343 // of the possibility of reassignment, but this should be good enough.
1345 hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, name, None) => {
1346 Some(format!("{}", name))
1355 let hir = self.tcx.hir();
1356 let hir_id = hir.as_local_hir_id(def_id)?;
1357 let parent_node = hir.get_parent_node(hir_id);
1358 match hir.find(parent_node) {
1359 Some(hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(local), .. })) => {
1360 get_name(err, &local.pat.kind)
1362 // Different to previous arm because one is `&hir::Local` and the other
1363 // is `P<hir::Local>`.
1364 Some(hir::Node::Local(local)) => get_name(err, &local.pat.kind),
1369 /// We tried to apply the bound to an `fn` or closure. Check whether calling it would
1370 /// evaluate to a type that *would* satisfy the trait binding. If it would, suggest calling
1371 /// it: `bar(foo)` → `bar(foo())`. This case is *very* likely to be hit if `foo` is `async`.
1374 obligation: &PredicateObligation<'tcx>,
1375 err: &mut DiagnosticBuilder<'_>,
1376 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1377 points_at_arg: bool,
1379 let self_ty = trait_ref.self_ty();
1380 let (def_id, output_ty, callable) = match self_ty.kind {
1381 ty::Closure(def_id, substs) => {
1382 (def_id, self.closure_sig(def_id, substs).output(), "closure")
1384 ty::FnDef(def_id, _) => (def_id, self_ty.fn_sig(self.tcx).output(), "function"),
1387 let msg = format!("use parentheses to call the {}", callable);
1389 let obligation = self.mk_obligation_for_def_id(
1391 output_ty.skip_binder(),
1392 obligation.cause.clone(),
1393 obligation.param_env,
1396 match self.evaluate_obligation(&obligation) {
1397 Ok(EvaluationResult::EvaluatedToOk)
1398 | Ok(EvaluationResult::EvaluatedToOkModuloRegions)
1399 | Ok(EvaluationResult::EvaluatedToAmbig) => {}
1402 let hir = self.tcx.hir();
1403 // Get the name of the callable and the arguments to be used in the suggestion.
1404 let snippet = match hir.get_if_local(def_id) {
1405 Some(hir::Node::Expr(hir::Expr {
1406 kind: hir::ExprKind::Closure(_, decl, _, span, ..),
1409 err.span_label(*span, "consider calling this closure");
1410 let name = match self.get_closure_name(def_id, err, &msg) {
1414 let args = decl.inputs.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
1415 format!("{}({})", name, args)
1417 Some(hir::Node::Item(hir::Item {
1419 kind: hir::ItemKind::Fn(.., body_id),
1422 err.span_label(ident.span, "consider calling this function");
1423 let body = hir.body(*body_id);
1427 .map(|arg| match &arg.pat.kind {
1428 hir::PatKind::Binding(_, _, ident, None)
1429 // FIXME: provide a better suggestion when encountering `SelfLower`, it
1430 // should suggest a method call.
1431 if ident.name != kw::SelfLower => ident.to_string(),
1432 _ => "_".to_string(),
1434 .collect::<Vec<_>>()
1436 format!("{}({})", ident, args)
1441 // When the obligation error has been ensured to have been caused by
1442 // an argument, the `obligation.cause.span` points at the expression
1443 // of the argument, so we can provide a suggestion. This is signaled
1444 // by `points_at_arg`. Otherwise, we give a more general note.
1445 err.span_suggestion(
1446 obligation.cause.span,
1449 Applicability::HasPlaceholders,
1452 err.help(&format!("{}: `{}`", msg, snippet));
1456 fn suggest_add_reference_to_arg(
1458 obligation: &PredicateObligation<'tcx>,
1459 err: &mut DiagnosticBuilder<'tcx>,
1460 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1461 points_at_arg: bool,
1462 has_custom_message: bool,
1468 let span = obligation.cause.span;
1469 let param_env = obligation.param_env;
1470 let trait_ref = trait_ref.skip_binder();
1472 if let ObligationCauseCode::ImplDerivedObligation(obligation) = &obligation.cause.code {
1473 // Try to apply the original trait binding obligation by borrowing.
1474 let self_ty = trait_ref.self_ty();
1475 let found = self_ty.to_string();
1476 let new_self_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, self_ty);
1477 let substs = self.tcx.mk_substs_trait(new_self_ty, &[]);
1478 let new_trait_ref = ty::TraitRef::new(obligation.parent_trait_ref.def_id(), substs);
1479 let new_obligation =
1480 Obligation::new(ObligationCause::dummy(), param_env, new_trait_ref.to_predicate());
1481 if self.predicate_must_hold_modulo_regions(&new_obligation) {
1482 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1483 // We have a very specific type of error, where just borrowing this argument
1484 // might solve the problem. In cases like this, the important part is the
1485 // original type obligation, not the last one that failed, which is arbitrary.
1486 // Because of this, we modify the error to refer to the original obligation and
1487 // return early in the caller.
1489 "the trait bound `{}: {}` is not satisfied",
1491 obligation.parent_trait_ref.skip_binder().print_only_trait_path(),
1493 if has_custom_message {
1496 err.message = vec![(msg, Style::NoStyle)];
1498 if snippet.starts_with('&') {
1499 // This is already a literal borrow and the obligation is failing
1500 // somewhere else in the obligation chain. Do not suggest non-sense.
1506 "expected an implementor of trait `{}`",
1507 obligation.parent_trait_ref.skip_binder().print_only_trait_path(),
1510 err.span_suggestion(
1512 "consider borrowing here",
1513 format!("&{}", snippet),
1514 Applicability::MaybeIncorrect,
1523 /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
1524 /// suggest removing these references until we reach a type that implements the trait.
1525 fn suggest_remove_reference(
1527 obligation: &PredicateObligation<'tcx>,
1528 err: &mut DiagnosticBuilder<'tcx>,
1529 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1531 let trait_ref = trait_ref.skip_binder();
1532 let span = obligation.cause.span;
1534 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1536 snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
1538 snippet.chars().filter(|c| !c.is_whitespace()).skip(refs_number).next()
1540 // Do not suggest removal of borrow from type arguments.
1544 let mut trait_type = trait_ref.self_ty();
1546 for refs_remaining in 0..refs_number {
1547 if let ty::Ref(_, t_type, _) = trait_type.kind {
1548 trait_type = t_type;
1550 let new_obligation = self.mk_obligation_for_def_id(
1553 ObligationCause::dummy(),
1554 obligation.param_env,
1557 if self.predicate_may_hold(&new_obligation) {
1562 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1564 let remove_refs = refs_remaining + 1;
1566 format!("consider removing {} leading `&`-references", remove_refs);
1568 err.span_suggestion_short(
1572 Applicability::MachineApplicable,
1583 /// Check if the trait bound is implemented for a different mutability and note it in the
1585 fn suggest_change_mut(
1587 obligation: &PredicateObligation<'tcx>,
1588 err: &mut DiagnosticBuilder<'tcx>,
1589 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1590 points_at_arg: bool,
1592 let span = obligation.cause.span;
1593 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1595 snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
1597 snippet.chars().filter(|c| !c.is_whitespace()).skip(refs_number).next()
1599 // Do not suggest removal of borrow from type arguments.
1602 let trait_ref = self.resolve_vars_if_possible(trait_ref);
1603 if trait_ref.has_infer_types() {
1604 // Do not ICE while trying to find if a reborrow would succeed on a trait with
1605 // unresolved bindings.
1609 if let ty::Ref(region, t_type, mutability) = trait_ref.skip_binder().self_ty().kind {
1610 let trait_type = match mutability {
1611 hir::Mutability::Mut => self.tcx.mk_imm_ref(region, t_type),
1612 hir::Mutability::Not => self.tcx.mk_mut_ref(region, t_type),
1615 let new_obligation = self.mk_obligation_for_def_id(
1616 trait_ref.skip_binder().def_id,
1618 ObligationCause::dummy(),
1619 obligation.param_env,
1622 if self.evaluate_obligation_no_overflow(&new_obligation).must_apply_modulo_regions()
1628 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1629 if points_at_arg && mutability == hir::Mutability::Not && refs_number > 0 {
1630 err.span_suggestion(
1632 "consider changing this borrow's mutability",
1633 "&mut ".to_string(),
1634 Applicability::MachineApplicable,
1638 "`{}` is implemented for `{:?}`, but not for `{:?}`",
1639 trait_ref.print_only_trait_path(),
1641 trait_ref.skip_binder().self_ty(),
1649 fn suggest_semicolon_removal(
1651 obligation: &PredicateObligation<'tcx>,
1652 err: &mut DiagnosticBuilder<'tcx>,
1654 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1656 let hir = self.tcx.hir();
1657 let parent_node = hir.get_parent_node(obligation.cause.body_id);
1658 let node = hir.find(parent_node);
1659 if let Some(hir::Node::Item(hir::Item {
1660 kind: hir::ItemKind::Fn(sig, _, body_id), ..
1663 let body = hir.body(*body_id);
1664 if let hir::ExprKind::Block(blk, _) = &body.value.kind {
1665 if sig.decl.output.span().overlaps(span)
1666 && blk.expr.is_none()
1667 && "()" == &trait_ref.self_ty().to_string()
1669 // FIXME(estebank): When encountering a method with a trait
1670 // bound not satisfied in the return type with a body that has
1671 // no return, suggest removal of semicolon on last statement.
1672 // Once that is added, close #54771.
1673 if let Some(ref stmt) = blk.stmts.last() {
1674 let sp = self.tcx.sess.source_map().end_point(stmt.span);
1675 err.span_label(sp, "consider removing this semicolon");
1682 /// Given some node representing a fn-like thing in the HIR map,
1683 /// returns a span and `ArgKind` information that describes the
1684 /// arguments it expects. This can be supplied to
1685 /// `report_arg_count_mismatch`.
1686 pub fn get_fn_like_arguments(&self, node: Node<'_>) -> (Span, Vec<ArgKind>) {
1688 Node::Expr(&hir::Expr {
1689 kind: hir::ExprKind::Closure(_, ref _decl, id, span, _),
1692 self.tcx.sess.source_map().def_span(span),
1699 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
1710 .span_to_snippet(pat.span)
1712 (snippet, "_".to_owned())
1714 .collect::<Vec<_>>(),
1718 self.tcx.sess.source_map().span_to_snippet(arg.pat.span).unwrap();
1719 ArgKind::Arg(name, "_".to_owned())
1722 .collect::<Vec<ArgKind>>(),
1724 Node::Item(&hir::Item { span, kind: hir::ItemKind::Fn(ref sig, ..), .. })
1725 | Node::ImplItem(&hir::ImplItem {
1727 kind: hir::ImplItemKind::Method(ref sig, _),
1730 | Node::TraitItem(&hir::TraitItem {
1732 kind: hir::TraitItemKind::Method(ref sig, _),
1735 self.tcx.sess.source_map().def_span(span),
1739 .map(|arg| match arg.clone().kind {
1740 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
1742 vec![("_".to_owned(), "_".to_owned()); tys.len()],
1744 _ => ArgKind::empty(),
1746 .collect::<Vec<ArgKind>>(),
1748 Node::Ctor(ref variant_data) => {
1749 let span = variant_data
1751 .map(|hir_id| self.tcx.hir().span(hir_id))
1752 .unwrap_or(DUMMY_SP);
1753 let span = self.tcx.sess.source_map().def_span(span);
1755 (span, vec![ArgKind::empty(); variant_data.fields().len()])
1757 _ => panic!("non-FnLike node found: {:?}", node),
1761 /// Reports an error when the number of arguments needed by a
1762 /// trait match doesn't match the number that the expression
1764 pub fn report_arg_count_mismatch(
1767 found_span: Option<Span>,
1768 expected_args: Vec<ArgKind>,
1769 found_args: Vec<ArgKind>,
1771 ) -> DiagnosticBuilder<'tcx> {
1772 let kind = if is_closure { "closure" } else { "function" };
1774 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
1775 let arg_length = arguments.len();
1776 let distinct = match &other[..] {
1777 &[ArgKind::Tuple(..)] => true,
1780 match (arg_length, arguments.get(0)) {
1781 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
1782 format!("a single {}-tuple as argument", fields.len())
1787 if distinct && arg_length > 1 { "distinct " } else { "" },
1788 pluralize!(arg_length)
1793 let expected_str = args_str(&expected_args, &found_args);
1794 let found_str = args_str(&found_args, &expected_args);
1796 let mut err = struct_span_err!(
1800 "{} is expected to take {}, but it takes {}",
1806 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
1808 if let Some(found_span) = found_span {
1809 err.span_label(found_span, format!("takes {}", found_str));
1812 // ^^^^^^^^-- def_span
1816 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
1820 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
1822 // Suggest to take and ignore the arguments with expected_args_length `_`s if
1823 // found arguments is empty (assume the user just wants to ignore args in this case).
1824 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
1825 if found_args.is_empty() && is_closure {
1826 let underscores = vec!["_"; expected_args.len()].join(", ");
1827 err.span_suggestion(
1830 "consider changing the closure to take and ignore the expected argument{}",
1831 if expected_args.len() < 2 { "" } else { "s" }
1833 format!("|{}|", underscores),
1834 Applicability::MachineApplicable,
1838 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
1839 if fields.len() == expected_args.len() {
1842 .map(|(name, _)| name.to_owned())
1843 .collect::<Vec<String>>()
1845 err.span_suggestion(
1847 "change the closure to take multiple arguments instead of a single tuple",
1848 format!("|{}|", sugg),
1849 Applicability::MachineApplicable,
1853 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..] {
1854 if fields.len() == found_args.len() && is_closure {
1859 .map(|arg| match arg {
1860 ArgKind::Arg(name, _) => name.to_owned(),
1861 _ => "_".to_owned(),
1863 .collect::<Vec<String>>()
1865 // add type annotations if available
1866 if found_args.iter().any(|arg| match arg {
1867 ArgKind::Arg(_, ty) => ty != "_",
1874 .map(|(_, ty)| ty.to_owned())
1875 .collect::<Vec<String>>()
1882 err.span_suggestion(
1884 "change the closure to accept a tuple instead of individual arguments",
1886 Applicability::MachineApplicable,
1895 fn report_closure_arg_mismatch(
1898 found_span: Option<Span>,
1899 expected_ref: ty::PolyTraitRef<'tcx>,
1900 found: ty::PolyTraitRef<'tcx>,
1901 ) -> DiagnosticBuilder<'tcx> {
1902 fn build_fn_sig_string<'tcx>(tcx: TyCtxt<'tcx>, trait_ref: &ty::TraitRef<'tcx>) -> String {
1903 let inputs = trait_ref.substs.type_at(1);
1904 let sig = if let ty::Tuple(inputs) = inputs.kind {
1906 inputs.iter().map(|k| k.expect_ty()),
1907 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1909 hir::Unsafety::Normal,
1910 ::rustc_target::spec::abi::Abi::Rust,
1914 ::std::iter::once(inputs),
1915 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1917 hir::Unsafety::Normal,
1918 ::rustc_target::spec::abi::Abi::Rust,
1921 ty::Binder::bind(sig).to_string()
1924 let argument_is_closure = expected_ref.skip_binder().substs.type_at(0).is_closure();
1925 let mut err = struct_span_err!(
1929 "type mismatch in {} arguments",
1930 if argument_is_closure { "closure" } else { "function" }
1933 let found_str = format!(
1934 "expected signature of `{}`",
1935 build_fn_sig_string(self.tcx, found.skip_binder())
1937 err.span_label(span, found_str);
1939 let found_span = found_span.unwrap_or(span);
1940 let expected_str = format!(
1941 "found signature of `{}`",
1942 build_fn_sig_string(self.tcx, expected_ref.skip_binder())
1944 err.span_label(found_span, expected_str);
1950 pub fn recursive_type_with_infinite_size_error(
1953 ) -> DiagnosticBuilder<'tcx> {
1954 assert!(type_def_id.is_local());
1955 let span = tcx.hir().span_if_local(type_def_id).unwrap();
1956 let span = tcx.sess.source_map().def_span(span);
1957 let mut err = struct_span_err!(
1961 "recursive type `{}` has infinite size",
1962 tcx.def_path_str(type_def_id)
1964 err.span_label(span, "recursive type has infinite size");
1966 "insert indirection (e.g., a `Box`, `Rc`, or `&`) \
1967 at some point to make `{}` representable",
1968 tcx.def_path_str(type_def_id)
1973 pub fn report_object_safety_error(
1976 trait_def_id: DefId,
1977 violations: Vec<ObjectSafetyViolation>,
1978 ) -> DiagnosticBuilder<'tcx> {
1979 let trait_str = tcx.def_path_str(trait_def_id);
1980 let span = tcx.sess.source_map().def_span(span);
1981 let mut err = struct_span_err!(
1985 "the trait `{}` cannot be made into an object",
1988 err.span_label(span, format!("the trait `{}` cannot be made into an object", trait_str));
1990 let mut reported_violations = FxHashSet::default();
1991 for violation in violations {
1992 if reported_violations.insert(violation.clone()) {
1993 match violation.span() {
1994 Some(span) => err.span_label(span, violation.error_msg()),
1995 None => err.note(&violation.error_msg()),
2000 if tcx.sess.trait_methods_not_found.borrow().contains(&span) {
2001 // Avoid emitting error caused by non-existing method (#58734)
2008 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
2009 fn maybe_report_ambiguity(
2011 obligation: &PredicateObligation<'tcx>,
2012 body_id: Option<hir::BodyId>,
2014 // Unable to successfully determine, probably means
2015 // insufficient type information, but could mean
2016 // ambiguous impls. The latter *ought* to be a
2017 // coherence violation, so we don't report it here.
2019 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
2020 let span = obligation.cause.span;
2023 "maybe_report_ambiguity(predicate={:?}, obligation={:?} body_id={:?}, code={:?})",
2024 predicate, obligation, body_id, obligation.cause.code,
2027 // Ambiguity errors are often caused as fallout from earlier
2028 // errors. So just ignore them if this infcx is tainted.
2029 if self.is_tainted_by_errors() {
2033 let mut err = match predicate {
2034 ty::Predicate::Trait(ref data) => {
2035 let trait_ref = data.to_poly_trait_ref();
2036 let self_ty = trait_ref.self_ty();
2037 debug!("self_ty {:?} {:?} trait_ref {:?}", self_ty, self_ty.kind, trait_ref);
2039 if predicate.references_error() {
2042 // Typically, this ambiguity should only happen if
2043 // there are unresolved type inference variables
2044 // (otherwise it would suggest a coherence
2045 // failure). But given #21974 that is not necessarily
2046 // the case -- we can have multiple where clauses that
2047 // are only distinguished by a region, which results
2048 // in an ambiguity even when all types are fully
2049 // known, since we don't dispatch based on region
2052 // This is kind of a hack: it frequently happens that some earlier
2053 // error prevents types from being fully inferred, and then we get
2054 // a bunch of uninteresting errors saying something like "<generic
2055 // #0> doesn't implement Sized". It may even be true that we
2056 // could just skip over all checks where the self-ty is an
2057 // inference variable, but I was afraid that there might be an
2058 // inference variable created, registered as an obligation, and
2059 // then never forced by writeback, and hence by skipping here we'd
2060 // be ignoring the fact that we don't KNOW the type works
2061 // out. Though even that would probably be harmless, given that
2062 // we're only talking about builtin traits, which are known to be
2063 // inhabited. We used to check for `self.tcx.sess.has_errors()` to
2064 // avoid inundating the user with unnecessary errors, but we now
2065 // check upstream for type errors and dont add the obligations to
2066 // begin with in those cases.
2071 .map_or(false, |sized_id| sized_id == trait_ref.def_id())
2073 self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0282).emit();
2076 let mut err = self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0283);
2077 err.note(&format!("cannot resolve `{}`", predicate));
2078 if let (Ok(ref snippet), ObligationCauseCode::BindingObligation(ref def_id, _)) =
2079 (self.tcx.sess.source_map().span_to_snippet(span), &obligation.cause.code)
2081 let generics = self.tcx.generics_of(*def_id);
2082 if !generics.params.is_empty() && !snippet.ends_with('>') {
2083 // FIXME: To avoid spurious suggestions in functions where type arguments
2084 // where already supplied, we check the snippet to make sure it doesn't
2085 // end with a turbofish. Ideally we would have access to a `PathSegment`
2086 // instead. Otherwise we would produce the following output:
2088 // error[E0283]: type annotations needed
2089 // --> $DIR/issue-54954.rs:3:24
2091 // LL | const ARR_LEN: usize = Tt::const_val::<[i8; 123]>();
2092 // | ^^^^^^^^^^^^^^^^^^^^^^^^^^
2094 // | cannot infer type
2095 // | help: consider specifying the type argument
2096 // | in the function call:
2097 // | `Tt::const_val::<[i8; 123]>::<T>`
2099 // LL | const fn const_val<T: Sized>() -> usize {
2100 // | --------- - required by this bound in `Tt::const_val`
2102 // = note: cannot resolve `_: Tt`
2104 err.span_suggestion(
2107 "consider specifying the type argument{} in the function call",
2108 if generics.params.len() > 1 { "s" } else { "" },
2116 .map(|p| p.name.to_string())
2117 .collect::<Vec<String>>()
2120 Applicability::HasPlaceholders,
2127 ty::Predicate::WellFormed(ty) => {
2128 // Same hacky approach as above to avoid deluging user
2129 // with error messages.
2130 if ty.references_error() || self.tcx.sess.has_errors() {
2133 self.need_type_info_err(body_id, span, ty, ErrorCode::E0282)
2136 ty::Predicate::Subtype(ref data) => {
2137 if data.references_error() || self.tcx.sess.has_errors() {
2138 // no need to overload user in such cases
2141 let &SubtypePredicate { a_is_expected: _, a, b } = data.skip_binder();
2142 // both must be type variables, or the other would've been instantiated
2143 assert!(a.is_ty_var() && b.is_ty_var());
2144 self.need_type_info_err(body_id, span, a, ErrorCode::E0282)
2146 ty::Predicate::Projection(ref data) => {
2147 let trait_ref = data.to_poly_trait_ref(self.tcx);
2148 let self_ty = trait_ref.self_ty();
2149 if predicate.references_error() {
2152 let mut err = self.need_type_info_err(body_id, span, self_ty, ErrorCode::E0284);
2153 err.note(&format!("cannot resolve `{}`", predicate));
2158 if self.tcx.sess.has_errors() {
2161 let mut err = struct_span_err!(
2165 "type annotations needed: cannot resolve `{}`",
2168 err.span_label(span, &format!("cannot resolve `{}`", predicate));
2172 self.note_obligation_cause(&mut err, obligation);
2176 /// Returns `true` if the trait predicate may apply for *some* assignment
2177 /// to the type parameters.
2178 fn predicate_can_apply(
2180 param_env: ty::ParamEnv<'tcx>,
2181 pred: ty::PolyTraitRef<'tcx>,
2183 struct ParamToVarFolder<'a, 'tcx> {
2184 infcx: &'a InferCtxt<'a, 'tcx>,
2185 var_map: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
2188 impl<'a, 'tcx> TypeFolder<'tcx> for ParamToVarFolder<'a, 'tcx> {
2189 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
2193 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
2194 if let ty::Param(ty::ParamTy { name, .. }) = ty.kind {
2195 let infcx = self.infcx;
2196 self.var_map.entry(ty).or_insert_with(|| {
2197 infcx.next_ty_var(TypeVariableOrigin {
2198 kind: TypeVariableOriginKind::TypeParameterDefinition(name, None),
2203 ty.super_fold_with(self)
2209 let mut selcx = SelectionContext::new(self);
2212 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
2214 let cleaned_pred = super::project::normalize(
2217 ObligationCause::dummy(),
2223 Obligation::new(ObligationCause::dummy(), param_env, cleaned_pred.to_predicate());
2225 self.predicate_may_hold(&obligation)
2229 fn note_obligation_cause(
2231 err: &mut DiagnosticBuilder<'_>,
2232 obligation: &PredicateObligation<'tcx>,
2234 // First, attempt to add note to this error with an async-await-specific
2235 // message, and fall back to regular note otherwise.
2236 if !self.maybe_note_obligation_cause_for_async_await(err, obligation) {
2237 self.note_obligation_cause_code(
2239 &obligation.predicate,
2240 &obligation.cause.code,
2246 /// Adds an async-await specific note to the diagnostic when the future does not implement
2247 /// an auto trait because of a captured type.
2249 /// ```ignore (diagnostic)
2250 /// note: future does not implement `Qux` as this value is used across an await
2251 /// --> $DIR/issue-64130-3-other.rs:17:5
2253 /// LL | let x = Foo;
2254 /// | - has type `Foo`
2255 /// LL | baz().await;
2256 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
2258 /// | - `x` is later dropped here
2261 /// When the diagnostic does not implement `Send` or `Sync` specifically, then the diagnostic
2262 /// is "replaced" with a different message and a more specific error.
2264 /// ```ignore (diagnostic)
2265 /// error: future cannot be sent between threads safely
2266 /// --> $DIR/issue-64130-2-send.rs:21:5
2268 /// LL | fn is_send<T: Send>(t: T) { }
2269 /// | ------- ---- required by this bound in `is_send`
2271 /// LL | is_send(bar());
2272 /// | ^^^^^^^ future returned by `bar` is not send
2274 /// = help: within `impl std::future::Future`, the trait `std::marker::Send` is not
2275 /// implemented for `Foo`
2276 /// note: future is not send as this value is used across an await
2277 /// --> $DIR/issue-64130-2-send.rs:15:5
2279 /// LL | let x = Foo;
2280 /// | - has type `Foo`
2281 /// LL | baz().await;
2282 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
2284 /// | - `x` is later dropped here
2287 /// Returns `true` if an async-await specific note was added to the diagnostic.
2288 fn maybe_note_obligation_cause_for_async_await(
2290 err: &mut DiagnosticBuilder<'_>,
2291 obligation: &PredicateObligation<'tcx>,
2294 "maybe_note_obligation_cause_for_async_await: obligation.predicate={:?} \
2295 obligation.cause.span={:?}",
2296 obligation.predicate, obligation.cause.span
2298 let source_map = self.tcx.sess.source_map();
2300 // Attempt to detect an async-await error by looking at the obligation causes, looking
2301 // for a generator to be present.
2303 // When a future does not implement a trait because of a captured type in one of the
2304 // generators somewhere in the call stack, then the result is a chain of obligations.
2306 // Given a `async fn` A that calls a `async fn` B which captures a non-send type and that
2307 // future is passed as an argument to a function C which requires a `Send` type, then the
2308 // chain looks something like this:
2310 // - `BuiltinDerivedObligation` with a generator witness (B)
2311 // - `BuiltinDerivedObligation` with a generator (B)
2312 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (B)
2313 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
2314 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
2315 // - `BuiltinDerivedObligation` with a generator witness (A)
2316 // - `BuiltinDerivedObligation` with a generator (A)
2317 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (A)
2318 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
2319 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
2320 // - `BindingObligation` with `impl_send (Send requirement)
2322 // The first obligation in the chain is the most useful and has the generator that captured
2323 // the type. The last generator has information about where the bound was introduced. At
2324 // least one generator should be present for this diagnostic to be modified.
2325 let (mut trait_ref, mut target_ty) = match obligation.predicate {
2326 ty::Predicate::Trait(p) => {
2327 (Some(p.skip_binder().trait_ref), Some(p.skip_binder().self_ty()))
2331 let mut generator = None;
2332 let mut last_generator = None;
2333 let mut next_code = Some(&obligation.cause.code);
2334 while let Some(code) = next_code {
2335 debug!("maybe_note_obligation_cause_for_async_await: code={:?}", code);
2337 ObligationCauseCode::BuiltinDerivedObligation(derived_obligation)
2338 | ObligationCauseCode::ImplDerivedObligation(derived_obligation) => {
2339 let ty = derived_obligation.parent_trait_ref.self_ty();
2341 "maybe_note_obligation_cause_for_async_await: \
2342 parent_trait_ref={:?} self_ty.kind={:?}",
2343 derived_obligation.parent_trait_ref, ty.kind
2347 ty::Generator(did, ..) => {
2348 generator = generator.or(Some(did));
2349 last_generator = Some(did);
2351 ty::GeneratorWitness(..) => {}
2352 _ if generator.is_none() => {
2353 trait_ref = Some(*derived_obligation.parent_trait_ref.skip_binder());
2354 target_ty = Some(ty);
2359 next_code = Some(derived_obligation.parent_code.as_ref());
2365 // Only continue if a generator was found.
2367 "maybe_note_obligation_cause_for_async_await: generator={:?} trait_ref={:?} \
2369 generator, trait_ref, target_ty
2371 let (generator_did, trait_ref, target_ty) = match (generator, trait_ref, target_ty) {
2372 (Some(generator_did), Some(trait_ref), Some(target_ty)) => {
2373 (generator_did, trait_ref, target_ty)
2378 let span = self.tcx.def_span(generator_did);
2380 // Do not ICE on closure typeck (#66868).
2381 if self.tcx.hir().as_local_hir_id(generator_did).is_none() {
2385 // Get the tables from the infcx if the generator is the function we are
2386 // currently type-checking; otherwise, get them by performing a query.
2387 // This is needed to avoid cycles.
2388 let in_progress_tables = self.in_progress_tables.map(|t| t.borrow());
2389 let generator_did_root = self.tcx.closure_base_def_id(generator_did);
2391 "maybe_note_obligation_cause_for_async_await: generator_did={:?} \
2392 generator_did_root={:?} in_progress_tables.local_id_root={:?} span={:?}",
2395 in_progress_tables.as_ref().map(|t| t.local_id_root),
2399 let tables: &TypeckTables<'tcx> = match &in_progress_tables {
2400 Some(t) if t.local_id_root == Some(generator_did_root) => t,
2402 query_tables = self.tcx.typeck_tables_of(generator_did);
2407 // Look for a type inside the generator interior that matches the target type to get
2409 let target_ty_erased = self.tcx.erase_regions(&target_ty);
2410 let target_span = tables
2411 .generator_interior_types
2413 .find(|ty::GeneratorInteriorTypeCause { ty, .. }| {
2414 // Careful: the regions for types that appear in the
2415 // generator interior are not generally known, so we
2416 // want to erase them when comparing (and anyway,
2417 // `Send` and other bounds are generally unaffected by
2418 // the choice of region). When erasing regions, we
2419 // also have to erase late-bound regions. This is
2420 // because the types that appear in the generator
2421 // interior generally contain "bound regions" to
2422 // represent regions that are part of the suspended
2423 // generator frame. Bound regions are preserved by
2424 // `erase_regions` and so we must also call
2425 // `erase_late_bound_regions`.
2426 let ty_erased = self.tcx.erase_late_bound_regions(&ty::Binder::bind(*ty));
2427 let ty_erased = self.tcx.erase_regions(&ty_erased);
2428 let eq = ty::TyS::same_type(ty_erased, target_ty_erased);
2430 "maybe_note_obligation_cause_for_async_await: ty_erased={:?} \
2431 target_ty_erased={:?} eq={:?}",
2432 ty_erased, target_ty_erased, eq
2436 .map(|ty::GeneratorInteriorTypeCause { span, scope_span, .. }| {
2437 (span, source_map.span_to_snippet(*span), scope_span)
2440 "maybe_note_obligation_cause_for_async_await: target_ty={:?} \
2441 generator_interior_types={:?} target_span={:?}",
2442 target_ty, tables.generator_interior_types, target_span
2444 if let Some((target_span, Ok(snippet), scope_span)) = target_span {
2445 self.note_obligation_cause_for_async_await(
2464 /// Unconditionally adds the diagnostic note described in
2465 /// `maybe_note_obligation_cause_for_async_await`'s documentation comment.
2466 fn note_obligation_cause_for_async_await(
2468 err: &mut DiagnosticBuilder<'_>,
2470 scope_span: &Option<Span>,
2472 first_generator: DefId,
2473 last_generator: Option<DefId>,
2474 trait_ref: ty::TraitRef<'_>,
2475 target_ty: Ty<'tcx>,
2476 tables: &ty::TypeckTables<'_>,
2477 obligation: &PredicateObligation<'tcx>,
2478 next_code: Option<&ObligationCauseCode<'tcx>>,
2480 let source_map = self.tcx.sess.source_map();
2482 let is_async_fn = self
2484 .parent(first_generator)
2485 .map(|parent_did| self.tcx.asyncness(parent_did))
2486 .map(|parent_asyncness| parent_asyncness == hir::IsAsync::Async)
2488 let is_async_move = self
2491 .as_local_hir_id(first_generator)
2492 .and_then(|hir_id| self.tcx.hir().maybe_body_owned_by(hir_id))
2493 .map(|body_id| self.tcx.hir().body(body_id))
2494 .and_then(|body| body.generator_kind())
2495 .map(|generator_kind| match generator_kind {
2496 hir::GeneratorKind::Async(..) => true,
2500 let await_or_yield = if is_async_fn || is_async_move { "await" } else { "yield" };
2502 // Special case the primary error message when send or sync is the trait that was
2504 let is_send = self.tcx.is_diagnostic_item(sym::send_trait, trait_ref.def_id);
2505 let is_sync = self.tcx.is_diagnostic_item(sym::sync_trait, trait_ref.def_id);
2506 let trait_explanation = if is_send || is_sync {
2507 let (trait_name, trait_verb) =
2508 if is_send { ("`Send`", "sent") } else { ("`Sync`", "shared") };
2511 err.set_primary_message(format!(
2512 "future cannot be {} between threads safely",
2516 let original_span = err.span.primary_span().unwrap();
2517 let mut span = MultiSpan::from_span(original_span);
2519 let message = if let Some(name) = last_generator
2520 .and_then(|generator_did| self.tcx.parent(generator_did))
2521 .and_then(|parent_did| self.tcx.hir().as_local_hir_id(parent_did))
2522 .and_then(|parent_hir_id| self.tcx.hir().opt_name(parent_hir_id))
2524 format!("future returned by `{}` is not {}", name, trait_name)
2526 format!("future is not {}", trait_name)
2529 span.push_span_label(original_span, message);
2532 format!("is not {}", trait_name)
2534 format!("does not implement `{}`", trait_ref.print_only_trait_path())
2537 // Look at the last interior type to get a span for the `.await`.
2538 let await_span = tables.generator_interior_types.iter().map(|i| i.span).last().unwrap();
2539 let mut span = MultiSpan::from_span(await_span);
2540 span.push_span_label(
2542 format!("{} occurs here, with `{}` maybe used later", await_or_yield, snippet),
2545 span.push_span_label(target_span, format!("has type `{}`", target_ty));
2547 // If available, use the scope span to annotate the drop location.
2548 if let Some(scope_span) = scope_span {
2549 span.push_span_label(
2550 source_map.end_point(*scope_span),
2551 format!("`{}` is later dropped here", snippet),
2558 "future {} as this value is used across an {}",
2559 trait_explanation, await_or_yield,
2563 // Add a note for the item obligation that remains - normally a note pointing to the
2564 // bound that introduced the obligation (e.g. `T: Send`).
2565 debug!("note_obligation_cause_for_async_await: next_code={:?}", next_code);
2566 self.note_obligation_cause_code(
2568 &obligation.predicate,
2574 fn note_obligation_cause_code<T>(
2576 err: &mut DiagnosticBuilder<'_>,
2578 cause_code: &ObligationCauseCode<'tcx>,
2579 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
2585 ObligationCauseCode::ExprAssignable
2586 | ObligationCauseCode::MatchExpressionArm { .. }
2587 | ObligationCauseCode::Pattern { .. }
2588 | ObligationCauseCode::IfExpression { .. }
2589 | ObligationCauseCode::IfExpressionWithNoElse
2590 | ObligationCauseCode::MainFunctionType
2591 | ObligationCauseCode::StartFunctionType
2592 | ObligationCauseCode::IntrinsicType
2593 | ObligationCauseCode::MethodReceiver
2594 | ObligationCauseCode::ReturnNoExpression
2595 | ObligationCauseCode::MiscObligation => {}
2596 ObligationCauseCode::SliceOrArrayElem => {
2597 err.note("slice and array elements must have `Sized` type");
2599 ObligationCauseCode::TupleElem => {
2600 err.note("only the last element of a tuple may have a dynamically sized type");
2602 ObligationCauseCode::ProjectionWf(data) => {
2603 err.note(&format!("required so that the projection `{}` is well-formed", data,));
2605 ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
2607 "required so that reference `{}` does not outlive its referent",
2611 ObligationCauseCode::ObjectTypeBound(object_ty, region) => {
2613 "required so that the lifetime bound of `{}` for `{}` is satisfied",
2617 ObligationCauseCode::ItemObligation(item_def_id) => {
2618 let item_name = tcx.def_path_str(item_def_id);
2619 let msg = format!("required by `{}`", item_name);
2621 if let Some(sp) = tcx.hir().span_if_local(item_def_id) {
2622 let sp = tcx.sess.source_map().def_span(sp);
2623 err.span_label(sp, &msg);
2628 ObligationCauseCode::BindingObligation(item_def_id, span) => {
2629 let item_name = tcx.def_path_str(item_def_id);
2630 let msg = format!("required by this bound in `{}`", item_name);
2631 if let Some(ident) = tcx.opt_item_name(item_def_id) {
2632 err.span_label(ident.span, "");
2634 if span != DUMMY_SP {
2635 err.span_label(span, &msg);
2640 ObligationCauseCode::ObjectCastObligation(object_ty) => {
2642 "required for the cast to the object type `{}`",
2643 self.ty_to_string(object_ty)
2646 ObligationCauseCode::Coercion { source: _, target } => {
2647 err.note(&format!("required by cast to type `{}`", self.ty_to_string(target)));
2649 ObligationCauseCode::RepeatVec(suggest_const_in_array_repeat_expressions) => {
2651 "the `Copy` trait is required because the \
2652 repeated element will be copied",
2654 if suggest_const_in_array_repeat_expressions {
2656 "this array initializer can be evaluated at compile-time, for more \
2657 information, see issue \
2658 https://github.com/rust-lang/rust/issues/49147",
2660 if tcx.sess.opts.unstable_features.is_nightly_build() {
2662 "add `#![feature(const_in_array_repeat_expressions)]` to the \
2663 crate attributes to enable",
2668 ObligationCauseCode::VariableType(_) => {
2669 err.note("all local variables must have a statically known size");
2670 if !self.tcx.features().unsized_locals {
2671 err.help("unsized locals are gated as an unstable feature");
2674 ObligationCauseCode::SizedArgumentType => {
2675 err.note("all function arguments must have a statically known size");
2676 if !self.tcx.features().unsized_locals {
2677 err.help("unsized locals are gated as an unstable feature");
2680 ObligationCauseCode::SizedReturnType => {
2682 "the return type of a function must have a \
2683 statically known size",
2686 ObligationCauseCode::SizedYieldType => {
2688 "the yield type of a generator must have a \
2689 statically known size",
2692 ObligationCauseCode::AssignmentLhsSized => {
2693 err.note("the left-hand-side of an assignment must have a statically known size");
2695 ObligationCauseCode::TupleInitializerSized => {
2696 err.note("tuples must have a statically known size to be initialized");
2698 ObligationCauseCode::StructInitializerSized => {
2699 err.note("structs must have a statically known size to be initialized");
2701 ObligationCauseCode::FieldSized { adt_kind: ref item, last } => match *item {
2702 AdtKind::Struct => {
2705 "the last field of a packed struct may only have a \
2706 dynamically sized type if it does not need drop to be run",
2710 "only the last field of a struct may have a dynamically \
2716 err.note("no field of a union may have a dynamically sized type");
2719 err.note("no field of an enum variant may have a dynamically sized type");
2722 ObligationCauseCode::ConstSized => {
2723 err.note("constant expressions must have a statically known size");
2725 ObligationCauseCode::ConstPatternStructural => {
2726 err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`");
2728 ObligationCauseCode::SharedStatic => {
2729 err.note("shared static variables must have a type that implements `Sync`");
2731 ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
2732 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2733 let ty = parent_trait_ref.skip_binder().self_ty();
2734 err.note(&format!("required because it appears within the type `{}`", ty));
2735 obligated_types.push(ty);
2737 let parent_predicate = parent_trait_ref.to_predicate();
2738 if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
2739 self.note_obligation_cause_code(
2747 ObligationCauseCode::ImplDerivedObligation(ref data) => {
2748 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2750 "required because of the requirements on the impl of `{}` for `{}`",
2751 parent_trait_ref.print_only_trait_path(),
2752 parent_trait_ref.skip_binder().self_ty()
2754 let parent_predicate = parent_trait_ref.to_predicate();
2755 self.note_obligation_cause_code(
2762 ObligationCauseCode::CompareImplMethodObligation { .. } => {
2764 "the requirement `{}` appears on the impl method \
2765 but not on the corresponding trait method",
2769 ObligationCauseCode::CompareImplTypeObligation { .. } => {
2771 "the requirement `{}` appears on the associated impl type\
2772 but not on the corresponding associated trait type",
2776 ObligationCauseCode::ReturnType
2777 | ObligationCauseCode::ReturnValue(_)
2778 | ObligationCauseCode::BlockTailExpression(_) => (),
2779 ObligationCauseCode::TrivialBound => {
2780 err.help("see issue #48214");
2781 if tcx.sess.opts.unstable_features.is_nightly_build() {
2783 "add `#![feature(trivial_bounds)]` to the \
2784 crate attributes to enable",
2788 ObligationCauseCode::AssocTypeBound(ref data) => {
2789 err.span_label(data.original, "associated type defined here");
2790 if let Some(sp) = data.impl_span {
2791 err.span_label(sp, "in this `impl` item");
2793 for sp in &data.bounds {
2794 err.span_label(*sp, "restricted in this bound");
2800 fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder<'_>) {
2801 let current_limit = self.tcx.sess.recursion_limit.get();
2802 let suggested_limit = current_limit * 2;
2804 "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
2809 fn is_recursive_obligation(
2811 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
2812 cause_code: &ObligationCauseCode<'tcx>,
2814 if let ObligationCauseCode::BuiltinDerivedObligation(ref data) = cause_code {
2815 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
2817 if obligated_types.iter().any(|ot| ot == &parent_trait_ref.skip_binder().self_ty()) {
2825 /// Summarizes information
2828 /// An argument of non-tuple type. Parameters are (name, ty)
2829 Arg(String, String),
2831 /// An argument of tuple type. For a "found" argument, the span is
2832 /// the locationo in the source of the pattern. For a "expected"
2833 /// argument, it will be None. The vector is a list of (name, ty)
2834 /// strings for the components of the tuple.
2835 Tuple(Option<Span>, Vec<(String, String)>),
2839 fn empty() -> ArgKind {
2840 ArgKind::Arg("_".to_owned(), "_".to_owned())
2843 /// Creates an `ArgKind` from the expected type of an
2844 /// argument. It has no name (`_`) and an optional source span.
2845 pub fn from_expected_ty(t: Ty<'_>, span: Option<Span>) -> ArgKind {
2847 ty::Tuple(ref tys) => ArgKind::Tuple(
2849 tys.iter().map(|ty| ("_".to_owned(), ty.to_string())).collect::<Vec<_>>(),
2851 _ => ArgKind::Arg("_".to_owned(), t.to_string()),
2856 /// Suggest restricting a type param with a new bound.
2857 pub fn suggest_constraining_type_param(
2858 generics: &hir::Generics<'_>,
2859 err: &mut DiagnosticBuilder<'_>,
2862 source_map: &SourceMap,
2865 let restrict_msg = "consider further restricting this bound";
2866 if let Some(param) =
2867 generics.params.iter().filter(|p| p.name.ident().as_str() == param_name).next()
2869 if param_name.starts_with("impl ") {
2870 // `impl Trait` in argument:
2871 // `fn foo(x: impl Trait) {}` → `fn foo(t: impl Trait + Trait2) {}`
2872 err.span_suggestion(
2875 // `impl CurrentTrait + MissingTrait`
2876 format!("{} + {}", param_name, constraint),
2877 Applicability::MachineApplicable,
2879 } else if generics.where_clause.predicates.is_empty() && param.bounds.is_empty() {
2880 // If there are no bounds whatsoever, suggest adding a constraint
2881 // to the type parameter:
2882 // `fn foo<T>(t: T) {}` → `fn foo<T: Trait>(t: T) {}`
2883 err.span_suggestion(
2885 "consider restricting this bound",
2886 format!("{}: {}", param_name, constraint),
2887 Applicability::MachineApplicable,
2889 } else if !generics.where_clause.predicates.is_empty() {
2890 // There is a `where` clause, so suggest expanding it:
2891 // `fn foo<T>(t: T) where T: Debug {}` →
2892 // `fn foo<T>(t: T) where T: Debug, T: Trait {}`
2893 err.span_suggestion(
2894 generics.where_clause.span().unwrap().shrink_to_hi(),
2895 &format!("consider further restricting type parameter `{}`", param_name),
2896 format!(", {}: {}", param_name, constraint),
2897 Applicability::MachineApplicable,
2900 // If there is no `where` clause lean towards constraining to the
2902 // `fn foo<X: Bar, T>(t: T, x: X) {}` → `fn foo<T: Trait>(t: T) {}`
2903 // `fn foo<T: Bar>(t: T) {}` → `fn foo<T: Bar + Trait>(t: T) {}`
2904 let sp = param.span.with_hi(span.hi());
2905 let span = source_map.span_through_char(sp, ':');
2906 if sp != param.span && sp != span {
2907 // Only suggest if we have high certainty that the span
2908 // covers the colon in `foo<T: Trait>`.
2909 err.span_suggestion(
2912 format!("{}: {} + ", param_name, constraint),
2913 Applicability::MachineApplicable,
2918 &format!("consider adding a `where {}: {}` bound", param_name, constraint),