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::ty::error::ExpectedFound;
15 use crate::ty::fast_reject;
16 use crate::ty::fold::TypeFolder;
17 use crate::ty::subst::Subst;
18 use crate::ty::GenericParamDefKind;
19 use crate::ty::SubtypePredicate;
20 use crate::ty::TypeckTables;
21 use crate::ty::{self, AdtKind, DefIdTree, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable};
22 use errors::{pluralize, Applicability, DiagnosticBuilder, Style};
23 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
25 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
27 use rustc_span::source_map::SourceMap;
28 use rustc_span::symbol::{kw, sym};
29 use rustc_span::{ExpnKind, MultiSpan, Span, DUMMY_SP};
33 use rustc_error_codes::*;
35 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
36 pub fn report_fulfillment_errors(
38 errors: &[FulfillmentError<'tcx>],
39 body_id: Option<hir::BodyId>,
40 fallback_has_occurred: bool,
43 struct ErrorDescriptor<'tcx> {
44 predicate: ty::Predicate<'tcx>,
45 index: Option<usize>, // None if this is an old error
48 let mut error_map: FxHashMap<_, Vec<_>> = self
49 .reported_trait_errors
52 .map(|(&span, predicates)| {
57 .map(|predicate| ErrorDescriptor {
58 predicate: predicate.clone(),
66 for (index, error) in errors.iter().enumerate() {
67 // We want to ignore desugarings here: spans are equivalent even
68 // if one is the result of a desugaring and the other is not.
69 let mut span = error.obligation.cause.span;
70 let expn_data = span.ctxt().outer_expn_data();
71 if let ExpnKind::Desugaring(_) = expn_data.kind {
72 span = expn_data.call_site;
75 error_map.entry(span).or_default().push(ErrorDescriptor {
76 predicate: error.obligation.predicate.clone(),
80 self.reported_trait_errors
84 .push(error.obligation.predicate.clone());
87 // We do this in 2 passes because we want to display errors in order, though
88 // maybe it *is* better to sort errors by span or something.
89 let mut is_suppressed = vec![false; errors.len()];
90 for (_, error_set) in error_map.iter() {
91 // We want to suppress "duplicate" errors with the same span.
92 for error in error_set {
93 if let Some(index) = error.index {
94 // Suppress errors that are either:
95 // 1) strictly implied by another error.
96 // 2) implied by an error with a smaller index.
97 for error2 in error_set {
98 if error2.index.map_or(false, |index2| is_suppressed[index2]) {
99 // Avoid errors being suppressed by already-suppressed
100 // errors, to prevent all errors from being suppressed
105 if self.error_implies(&error2.predicate, &error.predicate)
106 && !(error2.index >= error.index
107 && self.error_implies(&error.predicate, &error2.predicate))
109 info!("skipping {:?} (implied by {:?})", error, error2);
110 is_suppressed[index] = true;
118 for (error, suppressed) in errors.iter().zip(is_suppressed) {
120 self.report_fulfillment_error(error, body_id, fallback_has_occurred);
125 // returns if `cond` not occurring implies that `error` does not occur - i.e., that
126 // `error` occurring implies that `cond` occurs.
127 fn error_implies(&self, cond: &ty::Predicate<'tcx>, error: &ty::Predicate<'tcx>) -> bool {
132 let (cond, error) = match (cond, error) {
133 (&ty::Predicate::Trait(..), &ty::Predicate::Trait(ref error)) => (cond, error),
135 // FIXME: make this work in other cases too.
140 for implication in super::elaborate_predicates(self.tcx, vec![cond.clone()]) {
141 if let ty::Predicate::Trait(implication) = implication {
142 let error = error.to_poly_trait_ref();
143 let implication = implication.to_poly_trait_ref();
144 // FIXME: I'm just not taking associated types at all here.
145 // Eventually I'll need to implement param-env-aware
146 // `Γ₁ ⊦ φ₁ => Γ₂ ⊦ φ₂` logic.
147 let param_env = ty::ParamEnv::empty();
148 if self.can_sub(param_env, error, implication).is_ok() {
149 debug!("error_implies: {:?} -> {:?} -> {:?}", cond, error, implication);
158 fn report_fulfillment_error(
160 error: &FulfillmentError<'tcx>,
161 body_id: Option<hir::BodyId>,
162 fallback_has_occurred: bool,
164 debug!("report_fulfillment_error({:?})", error);
166 FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
167 self.report_selection_error(
170 fallback_has_occurred,
171 error.points_at_arg_span,
174 FulfillmentErrorCode::CodeProjectionError(ref e) => {
175 self.report_projection_error(&error.obligation, e);
177 FulfillmentErrorCode::CodeAmbiguity => {
178 self.maybe_report_ambiguity(&error.obligation, body_id);
180 FulfillmentErrorCode::CodeSubtypeError(ref expected_found, ref err) => {
181 self.report_mismatched_types(
182 &error.obligation.cause,
183 expected_found.expected,
184 expected_found.found,
192 fn report_projection_error(
194 obligation: &PredicateObligation<'tcx>,
195 error: &MismatchedProjectionTypes<'tcx>,
197 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
199 if predicate.references_error() {
205 let mut err = &error.err;
206 let mut values = None;
208 // try to find the mismatched types to report the error with.
210 // this can fail if the problem was higher-ranked, in which
211 // cause I have no idea for a good error message.
212 if let ty::Predicate::Projection(ref data) = predicate {
213 let mut selcx = SelectionContext::new(self);
214 let (data, _) = self.replace_bound_vars_with_fresh_vars(
215 obligation.cause.span,
216 infer::LateBoundRegionConversionTime::HigherRankedType,
219 let mut obligations = vec![];
220 let normalized_ty = super::normalize_projection_type(
222 obligation.param_env,
224 obligation.cause.clone(),
230 "report_projection_error obligation.cause={:?} obligation.param_env={:?}",
231 obligation.cause, obligation.param_env
235 "report_projection_error normalized_ty={:?} data.ty={:?}",
236 normalized_ty, data.ty
239 let is_normalized_ty_expected = match &obligation.cause.code {
240 ObligationCauseCode::ItemObligation(_)
241 | ObligationCauseCode::BindingObligation(_, _)
242 | ObligationCauseCode::ObjectCastObligation(_) => false,
246 if let Err(error) = self.at(&obligation.cause, obligation.param_env).eq_exp(
247 is_normalized_ty_expected,
251 values = Some(infer::ValuePairs::Types(ExpectedFound::new(
252 is_normalized_ty_expected,
262 let msg = format!("type mismatch resolving `{}`", predicate);
263 let error_id = (DiagnosticMessageId::ErrorId(271), Some(obligation.cause.span), msg);
264 let fresh = self.tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
266 let mut diag = struct_span_err!(
268 obligation.cause.span,
270 "type mismatch resolving `{}`",
273 self.note_type_err(&mut diag, &obligation.cause, None, values, err);
274 self.note_obligation_cause(&mut diag, obligation);
280 fn fuzzy_match_tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
281 /// returns the fuzzy category of a given type, or None
282 /// if the type can be equated to any type.
283 fn type_category(t: Ty<'_>) -> Option<u32> {
288 ty::Int(..) | ty::Uint(..) | ty::Infer(ty::IntVar(..)) => Some(3),
289 ty::Float(..) | ty::Infer(ty::FloatVar(..)) => Some(4),
290 ty::Ref(..) | ty::RawPtr(..) => Some(5),
291 ty::Array(..) | ty::Slice(..) => Some(6),
292 ty::FnDef(..) | ty::FnPtr(..) => Some(7),
293 ty::Dynamic(..) => Some(8),
294 ty::Closure(..) => Some(9),
295 ty::Tuple(..) => Some(10),
296 ty::Projection(..) => Some(11),
297 ty::Param(..) => Some(12),
298 ty::Opaque(..) => Some(13),
299 ty::Never => Some(14),
300 ty::Adt(adt, ..) => match adt.adt_kind() {
301 AdtKind::Struct => Some(15),
302 AdtKind::Union => Some(16),
303 AdtKind::Enum => Some(17),
305 ty::Generator(..) => Some(18),
306 ty::Foreign(..) => Some(19),
307 ty::GeneratorWitness(..) => Some(20),
308 ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error => None,
309 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
313 match (type_category(a), type_category(b)) {
314 (Some(cat_a), Some(cat_b)) => match (&a.kind, &b.kind) {
315 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => def_a == def_b,
318 // infer and error can be equated to all types
325 trait_ref: ty::PolyTraitRef<'tcx>,
326 obligation: &PredicateObligation<'tcx>,
329 let param_env = obligation.param_env;
330 let trait_ref = tcx.erase_late_bound_regions(&trait_ref);
331 let trait_self_ty = trait_ref.self_ty();
333 let mut self_match_impls = vec![];
334 let mut fuzzy_match_impls = vec![];
336 self.tcx.for_each_relevant_impl(trait_ref.def_id, trait_self_ty, |def_id| {
337 let impl_substs = self.fresh_substs_for_item(obligation.cause.span, def_id);
338 let impl_trait_ref = tcx.impl_trait_ref(def_id).unwrap().subst(tcx, impl_substs);
340 let impl_self_ty = impl_trait_ref.self_ty();
342 if let Ok(..) = self.can_eq(param_env, trait_self_ty, impl_self_ty) {
343 self_match_impls.push(def_id);
349 .zip(impl_trait_ref.substs.types().skip(1))
350 .all(|(u, v)| self.fuzzy_match_tys(u, v))
352 fuzzy_match_impls.push(def_id);
357 let impl_def_id = if self_match_impls.len() == 1 {
359 } else if fuzzy_match_impls.len() == 1 {
365 tcx.has_attr(impl_def_id, sym::rustc_on_unimplemented).then_some(impl_def_id)
368 fn describe_generator(&self, body_id: hir::BodyId) -> Option<&'static str> {
369 self.tcx.hir().body(body_id).generator_kind.map(|gen_kind| match gen_kind {
370 hir::GeneratorKind::Gen => "a generator",
371 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Block) => "an async block",
372 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Fn) => "an async function",
373 hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure) => "an async closure",
377 /// Used to set on_unimplemented's `ItemContext`
378 /// to be the enclosing (async) block/function/closure
379 fn describe_enclosure(&self, hir_id: hir::HirId) -> Option<&'static str> {
380 let hir = &self.tcx.hir();
381 let node = hir.find(hir_id)?;
382 if let hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. }) = &node {
383 self.describe_generator(*body_id).or_else(|| {
384 Some(if let hir::FnHeader { asyncness: hir::IsAsync::Async, .. } = sig.header {
390 } else if let hir::Node::Expr(hir::Expr {
391 kind: hir::ExprKind::Closure(_is_move, _, body_id, _, gen_movability),
395 self.describe_generator(*body_id).or_else(|| {
396 Some(if gen_movability.is_some() { "an async closure" } else { "a closure" })
398 } else if let hir::Node::Expr(hir::Expr { .. }) = &node {
399 let parent_hid = hir.get_parent_node(hir_id);
400 if parent_hid != hir_id {
401 return self.describe_enclosure(parent_hid);
410 fn on_unimplemented_note(
412 trait_ref: ty::PolyTraitRef<'tcx>,
413 obligation: &PredicateObligation<'tcx>,
414 ) -> OnUnimplementedNote {
416 self.impl_similar_to(trait_ref, obligation).unwrap_or_else(|| trait_ref.def_id());
417 let trait_ref = *trait_ref.skip_binder();
419 let mut flags = vec![];
422 self.describe_enclosure(obligation.cause.body_id).map(|s| s.to_owned()),
425 match obligation.cause.code {
426 ObligationCauseCode::BuiltinDerivedObligation(..)
427 | ObligationCauseCode::ImplDerivedObligation(..) => {}
429 // this is a "direct", user-specified, rather than derived,
431 flags.push((sym::direct, None));
435 if let ObligationCauseCode::ItemObligation(item) = obligation.cause.code {
436 // FIXME: maybe also have some way of handling methods
437 // from other traits? That would require name resolution,
438 // which we might want to be some sort of hygienic.
440 // Currently I'm leaving it for what I need for `try`.
441 if self.tcx.trait_of_item(item) == Some(trait_ref.def_id) {
442 let method = self.tcx.item_name(item);
443 flags.push((sym::from_method, None));
444 flags.push((sym::from_method, Some(method.to_string())));
447 if let Some(t) = self.get_parent_trait_ref(&obligation.cause.code) {
448 flags.push((sym::parent_trait, Some(t)));
451 if let Some(k) = obligation.cause.span.desugaring_kind() {
452 flags.push((sym::from_desugaring, None));
453 flags.push((sym::from_desugaring, Some(format!("{:?}", k))));
455 let generics = self.tcx.generics_of(def_id);
456 let self_ty = trait_ref.self_ty();
457 // This is also included through the generics list as `Self`,
458 // but the parser won't allow you to use it
459 flags.push((sym::_Self, Some(self_ty.to_string())));
460 if let Some(def) = self_ty.ty_adt_def() {
461 // We also want to be able to select self's original
462 // signature with no type arguments resolved
463 flags.push((sym::_Self, Some(self.tcx.type_of(def.did).to_string())));
466 for param in generics.params.iter() {
467 let value = match param.kind {
468 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
469 trait_ref.substs[param.index as usize].to_string()
471 GenericParamDefKind::Lifetime => continue,
473 let name = param.name;
474 flags.push((name, Some(value)));
477 if let Some(true) = self_ty.ty_adt_def().map(|def| def.did.is_local()) {
478 flags.push((sym::crate_local, None));
481 // Allow targeting all integers using `{integral}`, even if the exact type was resolved
482 if self_ty.is_integral() {
483 flags.push((sym::_Self, Some("{integral}".to_owned())));
486 if let ty::Array(aty, len) = self_ty.kind {
487 flags.push((sym::_Self, Some("[]".to_owned())));
488 flags.push((sym::_Self, Some(format!("[{}]", aty))));
489 if let Some(def) = aty.ty_adt_def() {
490 // We also want to be able to select the array's type's original
491 // signature with no type arguments resolved
494 Some(format!("[{}]", self.tcx.type_of(def.did).to_string())),
497 if let Some(len) = len.try_eval_usize(tcx, ty::ParamEnv::empty()) {
500 Some(format!("[{}; {}]", self.tcx.type_of(def.did).to_string(), len)),
505 Some(format!("[{}; _]", self.tcx.type_of(def.did).to_string())),
511 if let Ok(Some(command)) =
512 OnUnimplementedDirective::of_item(self.tcx, trait_ref.def_id, def_id)
514 command.evaluate(self.tcx, trait_ref, &flags[..])
516 OnUnimplementedNote::default()
520 fn find_similar_impl_candidates(
522 trait_ref: ty::PolyTraitRef<'tcx>,
523 ) -> Vec<ty::TraitRef<'tcx>> {
524 let simp = fast_reject::simplify_type(self.tcx, trait_ref.skip_binder().self_ty(), true);
525 let all_impls = self.tcx.all_impls(trait_ref.def_id());
528 Some(simp) => all_impls
530 .filter_map(|&def_id| {
531 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
532 let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
533 if let Some(imp_simp) = imp_simp {
534 if simp != imp_simp {
543 all_impls.iter().map(|&def_id| self.tcx.impl_trait_ref(def_id).unwrap()).collect()
548 fn report_similar_impl_candidates(
550 impl_candidates: Vec<ty::TraitRef<'tcx>>,
551 err: &mut DiagnosticBuilder<'_>,
553 if impl_candidates.is_empty() {
557 let len = impl_candidates.len();
558 let end = if impl_candidates.len() <= 5 { impl_candidates.len() } else { 4 };
560 let normalize = |candidate| {
561 self.tcx.infer_ctxt().enter(|ref infcx| {
562 let normalized = infcx
563 .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
564 .normalize(candidate)
567 Some(normalized) => format!("\n {:?}", normalized.value),
568 None => format!("\n {:?}", candidate),
573 // Sort impl candidates so that ordering is consistent for UI tests.
574 let mut normalized_impl_candidates =
575 impl_candidates.iter().map(normalize).collect::<Vec<String>>();
577 // Sort before taking the `..end` range,
578 // because the ordering of `impl_candidates` may not be deterministic:
579 // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
580 normalized_impl_candidates.sort();
583 "the following implementations were found:{}{}",
584 normalized_impl_candidates[..end].join(""),
585 if len > 5 { format!("\nand {} others", len - 4) } else { String::new() }
589 /// Reports that an overflow has occurred and halts compilation. We
590 /// halt compilation unconditionally because it is important that
591 /// overflows never be masked -- they basically represent computations
592 /// whose result could not be truly determined and thus we can't say
593 /// if the program type checks or not -- and they are unusual
594 /// occurrences in any case.
595 pub fn report_overflow_error<T>(
597 obligation: &Obligation<'tcx, T>,
598 suggest_increasing_limit: bool,
601 T: fmt::Display + TypeFoldable<'tcx>,
603 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
604 let mut err = struct_span_err!(
606 obligation.cause.span,
608 "overflow evaluating the requirement `{}`",
612 if suggest_increasing_limit {
613 self.suggest_new_overflow_limit(&mut err);
616 self.note_obligation_cause_code(
618 &obligation.predicate,
619 &obligation.cause.code,
624 self.tcx.sess.abort_if_errors();
628 /// Reports that a cycle was detected which led to overflow and halts
629 /// compilation. This is equivalent to `report_overflow_error` except
630 /// that we can give a more helpful error message (and, in particular,
631 /// we do not suggest increasing the overflow limit, which is not
633 pub fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
634 let cycle = self.resolve_vars_if_possible(&cycle.to_owned());
635 assert!(cycle.len() > 0);
637 debug!("report_overflow_error_cycle: cycle={:?}", cycle);
639 self.report_overflow_error(&cycle[0], false);
642 pub fn report_extra_impl_obligation(
645 item_name: ast::Name,
646 _impl_item_def_id: DefId,
647 trait_item_def_id: DefId,
648 requirement: &dyn fmt::Display,
649 ) -> DiagnosticBuilder<'tcx> {
650 let msg = "impl has stricter requirements than trait";
651 let sp = self.tcx.sess.source_map().def_span(error_span);
653 let mut err = struct_span_err!(self.tcx.sess, sp, E0276, "{}", msg);
655 if let Some(trait_item_span) = self.tcx.hir().span_if_local(trait_item_def_id) {
656 let span = self.tcx.sess.source_map().def_span(trait_item_span);
657 err.span_label(span, format!("definition of `{}` from trait", item_name));
660 err.span_label(sp, format!("impl has extra requirement {}", requirement));
665 /// Gets the parent trait chain start
666 fn get_parent_trait_ref(&self, code: &ObligationCauseCode<'tcx>) -> Option<String> {
668 &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
669 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
670 match self.get_parent_trait_ref(&data.parent_code) {
672 None => Some(parent_trait_ref.skip_binder().self_ty().to_string()),
679 pub fn report_selection_error(
681 obligation: &PredicateObligation<'tcx>,
682 error: &SelectionError<'tcx>,
683 fallback_has_occurred: bool,
687 let span = obligation.cause.span;
689 let mut err = match *error {
690 SelectionError::Unimplemented => {
691 if let ObligationCauseCode::CompareImplMethodObligation {
696 | ObligationCauseCode::CompareImplTypeObligation {
700 } = obligation.cause.code
702 self.report_extra_impl_obligation(
707 &format!("`{}`", obligation.predicate),
712 match obligation.predicate {
713 ty::Predicate::Trait(ref trait_predicate) => {
714 let trait_predicate = self.resolve_vars_if_possible(trait_predicate);
716 if self.tcx.sess.has_errors() && trait_predicate.references_error() {
719 let trait_ref = trait_predicate.to_poly_trait_ref();
720 let (post_message, pre_message) = self
721 .get_parent_trait_ref(&obligation.cause.code)
722 .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
723 .unwrap_or_default();
725 let OnUnimplementedNote { message, label, note, enclosing_scope } =
726 self.on_unimplemented_note(trait_ref, obligation);
727 let have_alt_message = message.is_some() || label.is_some();
732 .span_to_snippet(span)
735 let is_from = format!("{}", trait_ref.print_only_trait_path())
736 .starts_with("std::convert::From<");
737 let (message, note) = if is_try && is_from {
740 "`?` couldn't convert the error to `{}`",
744 "the question mark operation (`?`) implicitly performs a \
745 conversion on the error value using the `From` trait"
753 let mut err = struct_span_err!(
758 message.unwrap_or_else(|| format!(
759 "the trait bound `{}` is not satisfied{}",
760 trait_ref.to_predicate(),
766 if obligation.cause.code == ObligationCauseCode::MainFunctionType {
767 "consider using `()`, or a `Result`".to_owned()
770 "{}the trait `{}` is not implemented for `{}`",
772 trait_ref.print_only_trait_path(),
777 if self.suggest_add_reference_to_arg(
784 self.note_obligation_cause(&mut err, obligation);
788 if let Some(ref s) = label {
789 // If it has a custom `#[rustc_on_unimplemented]`
790 // error message, let's display it as the label!
791 err.span_label(span, s.as_str());
792 err.help(&explanation);
794 err.span_label(span, explanation);
796 if let Some(ref s) = note {
797 // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
798 err.note(s.as_str());
800 if let Some(ref s) = enclosing_scope {
801 let enclosing_scope_span = tcx.def_span(
803 .opt_local_def_id(obligation.cause.body_id)
805 tcx.hir().body_owner_def_id(hir::BodyId {
806 hir_id: obligation.cause.body_id,
811 err.span_label(enclosing_scope_span, s.as_str());
814 self.suggest_borrow_on_unsized_slice(&obligation.cause.code, &mut err);
815 self.suggest_fn_call(&obligation, &mut err, &trait_ref, points_at_arg);
816 self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
817 self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
818 self.note_version_mismatch(&mut err, &trait_ref);
820 // Try to report a help message
821 if !trait_ref.has_infer_types()
822 && self.predicate_can_apply(obligation.param_env, trait_ref)
824 // If a where-clause may be useful, remind the
825 // user that they can add it.
827 // don't display an on-unimplemented note, as
828 // these notes will often be of the form
829 // "the type `T` can't be frobnicated"
830 // which is somewhat confusing.
831 self.suggest_restricting_param_bound(
834 obligation.cause.body_id,
837 if !have_alt_message {
838 // Can't show anything else useful, try to find similar impls.
839 let impl_candidates = self.find_similar_impl_candidates(trait_ref);
840 self.report_similar_impl_candidates(impl_candidates, &mut err);
842 self.suggest_change_mut(
850 // If this error is due to `!: Trait` not implemented but `(): Trait` is
851 // implemented, and fallback has occurred, then it could be due to a
852 // variable that used to fallback to `()` now falling back to `!`. Issue a
853 // note informing about the change in behaviour.
854 if trait_predicate.skip_binder().self_ty().is_never()
855 && fallback_has_occurred
857 let predicate = trait_predicate.map_bound(|mut trait_pred| {
858 trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
860 &trait_pred.trait_ref.substs[1..],
864 let unit_obligation = Obligation {
865 predicate: ty::Predicate::Trait(predicate),
868 if self.predicate_may_hold(&unit_obligation) {
870 "the trait is implemented for `()`. \
871 Possibly this error has been caused by changes to \
872 Rust's type-inference algorithm \
873 (see: https://github.com/rust-lang/rust/issues/48950 \
874 for more info). Consider whether you meant to use the \
875 type `()` here instead.",
883 ty::Predicate::Subtype(ref predicate) => {
884 // Errors for Subtype predicates show up as
885 // `FulfillmentErrorCode::CodeSubtypeError`,
886 // not selection error.
887 span_bug!(span, "subtype requirement gave wrong error: `{:?}`", predicate)
890 ty::Predicate::RegionOutlives(ref predicate) => {
891 let predicate = self.resolve_vars_if_possible(predicate);
893 .region_outlives_predicate(&obligation.cause, &predicate)
900 "the requirement `{}` is not satisfied (`{}`)",
906 ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
907 let predicate = self.resolve_vars_if_possible(&obligation.predicate);
912 "the requirement `{}` is not satisfied",
917 ty::Predicate::ObjectSafe(trait_def_id) => {
918 let violations = self.tcx.object_safety_violations(trait_def_id);
919 self.tcx.report_object_safety_error(span, trait_def_id, violations)
922 ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) => {
923 let found_kind = self.closure_kind(closure_def_id, closure_substs).unwrap();
924 let closure_span = self
928 .def_span(self.tcx.hir().span_if_local(closure_def_id).unwrap());
929 let hir_id = self.tcx.hir().as_local_hir_id(closure_def_id).unwrap();
930 let mut err = struct_span_err!(
934 "expected a closure that implements the `{}` trait, \
935 but this closure only implements `{}`",
942 format!("this closure implements `{}`, not `{}`", found_kind, kind),
945 obligation.cause.span,
946 format!("the requirement to implement `{}` derives from here", kind),
949 // Additional context information explaining why the closure only implements
950 // a particular trait.
951 if let Some(tables) = self.in_progress_tables {
952 let tables = tables.borrow();
953 match (found_kind, tables.closure_kind_origins().get(hir_id)) {
954 (ty::ClosureKind::FnOnce, Some((span, name))) => {
958 "closure is `FnOnce` because it moves the \
959 variable `{}` out of its environment",
964 (ty::ClosureKind::FnMut, Some((span, name))) => {
968 "closure is `FnMut` because it mutates the \
982 ty::Predicate::WellFormed(ty) => {
983 if !self.tcx.sess.opts.debugging_opts.chalk {
984 // WF predicates cannot themselves make
985 // errors. They can only block due to
986 // ambiguity; otherwise, they always
987 // degenerate into other obligations
989 span_bug!(span, "WF predicate not satisfied for {:?}", ty);
991 // FIXME: we'll need a better message which takes into account
992 // which bounds actually failed to hold.
993 self.tcx.sess.struct_span_err(
995 &format!("the type `{}` is not well-formed (chalk)", ty),
1000 ty::Predicate::ConstEvaluatable(..) => {
1001 // Errors for `ConstEvaluatable` predicates show up as
1002 // `SelectionError::ConstEvalFailure`,
1003 // not `Unimplemented`.
1006 "const-evaluatable requirement gave wrong error: `{:?}`",
1013 OutputTypeParameterMismatch(ref found_trait_ref, ref expected_trait_ref, _) => {
1014 let found_trait_ref = self.resolve_vars_if_possible(&*found_trait_ref);
1015 let expected_trait_ref = self.resolve_vars_if_possible(&*expected_trait_ref);
1017 if expected_trait_ref.self_ty().references_error() {
1021 let found_trait_ty = found_trait_ref.self_ty();
1023 let found_did = match found_trait_ty.kind {
1024 ty::Closure(did, _) | ty::Foreign(did) | ty::FnDef(did, _) => Some(did),
1025 ty::Adt(def, _) => Some(def.did),
1029 let found_span = found_did
1030 .and_then(|did| self.tcx.hir().span_if_local(did))
1031 .map(|sp| self.tcx.sess.source_map().def_span(sp)); // the sp could be an fn def
1033 if self.reported_closure_mismatch.borrow().contains(&(span, found_span)) {
1034 // We check closures twice, with obligations flowing in different directions,
1035 // but we want to complain about them only once.
1039 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
1041 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind {
1042 ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
1043 _ => vec![ArgKind::empty()],
1046 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
1047 let expected = match expected_ty.kind {
1048 ty::Tuple(ref tys) => tys
1050 .map(|t| ArgKind::from_expected_ty(t.expect_ty(), Some(span)))
1052 _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
1055 if found.len() == expected.len() {
1056 self.report_closure_arg_mismatch(
1063 let (closure_span, found) = found_did
1064 .and_then(|did| self.tcx.hir().get_if_local(did))
1066 let (found_span, found) = self.get_fn_like_arguments(node);
1067 (Some(found_span), found)
1069 .unwrap_or((found_span, found));
1071 self.report_arg_count_mismatch(
1076 found_trait_ty.is_closure(),
1081 TraitNotObjectSafe(did) => {
1082 let violations = self.tcx.object_safety_violations(did);
1083 self.tcx.report_object_safety_error(span, did, violations)
1086 // already reported in the query
1087 ConstEvalFailure(err) => {
1088 if let ErrorHandled::TooGeneric = err {
1089 // Silence this error, as it can be produced during intermediate steps
1090 // when a constant is not yet able to be evaluated (but will be later).
1093 self.tcx.sess.delay_span_bug(
1095 &format!("constant in type had an ignored error: {:?}", err),
1101 bug!("overflow should be handled before the `report_selection_error` path");
1105 self.note_obligation_cause(&mut err, obligation);
1110 /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
1111 /// with the same path as `trait_ref`, a help message about
1112 /// a probable version mismatch is added to `err`
1113 fn note_version_mismatch(
1115 err: &mut DiagnosticBuilder<'_>,
1116 trait_ref: &ty::PolyTraitRef<'tcx>,
1118 let get_trait_impl = |trait_def_id| {
1119 let mut trait_impl = None;
1120 self.tcx.for_each_relevant_impl(trait_def_id, trait_ref.self_ty(), |impl_def_id| {
1121 if trait_impl.is_none() {
1122 trait_impl = Some(impl_def_id);
1127 let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
1128 let all_traits = self.tcx.all_traits(LOCAL_CRATE);
1129 let traits_with_same_path: std::collections::BTreeSet<_> = all_traits
1131 .filter(|trait_def_id| **trait_def_id != trait_ref.def_id())
1132 .filter(|trait_def_id| self.tcx.def_path_str(**trait_def_id) == required_trait_path)
1134 for trait_with_same_path in traits_with_same_path {
1135 if let Some(impl_def_id) = get_trait_impl(*trait_with_same_path) {
1136 let impl_span = self.tcx.def_span(impl_def_id);
1137 err.span_help(impl_span, "trait impl with same name found");
1138 let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
1139 let crate_msg = format!(
1140 "Perhaps two different versions of crate `{}` are being used?",
1143 err.note(&crate_msg);
1147 fn suggest_restricting_param_bound(
1149 mut err: &mut DiagnosticBuilder<'_>,
1150 trait_ref: &ty::PolyTraitRef<'_>,
1151 body_id: hir::HirId,
1153 let self_ty = trait_ref.self_ty();
1154 let (param_ty, projection) = match &self_ty.kind {
1155 ty::Param(_) => (true, None),
1156 ty::Projection(projection) => (false, Some(projection)),
1160 let suggest_restriction =
1161 |generics: &hir::Generics<'_>, msg, err: &mut DiagnosticBuilder<'_>| {
1162 let span = generics.where_clause.span_for_predicates_or_empty_place();
1163 if !span.from_expansion() && span.desugaring_kind().is_none() {
1164 err.span_suggestion(
1165 generics.where_clause.span_for_predicates_or_empty_place().shrink_to_hi(),
1166 &format!("consider further restricting {}", msg),
1169 if !generics.where_clause.predicates.is_empty() {
1174 trait_ref.to_predicate(),
1176 Applicability::MachineApplicable,
1181 // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
1182 // don't suggest `T: Sized + ?Sized`.
1183 let mut hir_id = body_id;
1184 while let Some(node) = self.tcx.hir().find(hir_id) {
1186 hir::Node::TraitItem(hir::TraitItem {
1188 kind: hir::TraitItemKind::Method(..),
1190 }) if param_ty && self_ty == self.tcx.types.self_param => {
1191 // Restricting `Self` for a single method.
1192 suggest_restriction(&generics, "`Self`", err);
1196 hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, generics, _), .. })
1197 | hir::Node::TraitItem(hir::TraitItem {
1199 kind: hir::TraitItemKind::Method(..),
1202 | hir::Node::ImplItem(hir::ImplItem {
1204 kind: hir::ImplItemKind::Method(..),
1207 | hir::Node::Item(hir::Item {
1208 kind: hir::ItemKind::Trait(_, _, generics, _, _),
1211 | hir::Node::Item(hir::Item {
1212 kind: hir::ItemKind::Impl(_, _, _, generics, ..),
1214 }) if projection.is_some() => {
1215 // Missing associated type bound.
1216 suggest_restriction(&generics, "the associated type", err);
1220 hir::Node::Item(hir::Item {
1221 kind: hir::ItemKind::Struct(_, generics),
1225 | hir::Node::Item(hir::Item {
1226 kind: hir::ItemKind::Enum(_, generics), span, ..
1228 | hir::Node::Item(hir::Item {
1229 kind: hir::ItemKind::Union(_, generics),
1233 | hir::Node::Item(hir::Item {
1234 kind: hir::ItemKind::Trait(_, _, generics, ..),
1238 | hir::Node::Item(hir::Item {
1239 kind: hir::ItemKind::Impl(_, _, _, generics, ..),
1243 | hir::Node::Item(hir::Item {
1244 kind: hir::ItemKind::Fn(_, generics, _),
1248 | hir::Node::Item(hir::Item {
1249 kind: hir::ItemKind::TyAlias(_, generics),
1253 | hir::Node::Item(hir::Item {
1254 kind: hir::ItemKind::TraitAlias(generics, _),
1258 | hir::Node::Item(hir::Item {
1259 kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }),
1263 | hir::Node::TraitItem(hir::TraitItem { generics, span, .. })
1264 | hir::Node::ImplItem(hir::ImplItem { generics, span, .. })
1267 // Missing generic type parameter bound.
1268 let param_name = self_ty.to_string();
1269 let constraint = trait_ref.print_only_trait_path().to_string();
1270 if suggest_constraining_type_param(
1275 self.tcx.sess.source_map(),
1282 hir::Node::Crate => return,
1287 hir_id = self.tcx.hir().get_parent_item(hir_id);
1291 /// When encountering an assignment of an unsized trait, like `let x = ""[..];`, provide a
1292 /// suggestion to borrow the initializer in order to use have a slice instead.
1293 fn suggest_borrow_on_unsized_slice(
1295 code: &ObligationCauseCode<'tcx>,
1296 err: &mut DiagnosticBuilder<'tcx>,
1298 if let &ObligationCauseCode::VariableType(hir_id) = code {
1299 let parent_node = self.tcx.hir().get_parent_node(hir_id);
1300 if let Some(Node::Local(ref local)) = self.tcx.hir().find(parent_node) {
1301 if let Some(ref expr) = local.init {
1302 if let hir::ExprKind::Index(_, _) = expr.kind {
1303 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
1304 err.span_suggestion(
1306 "consider borrowing here",
1307 format!("&{}", snippet),
1308 Applicability::MachineApplicable,
1317 fn mk_obligation_for_def_id(
1320 output_ty: Ty<'tcx>,
1321 cause: ObligationCause<'tcx>,
1322 param_env: ty::ParamEnv<'tcx>,
1323 ) -> PredicateObligation<'tcx> {
1325 ty::TraitRef { def_id, substs: self.tcx.mk_substs_trait(output_ty, &[]) };
1326 Obligation::new(cause, param_env, new_trait_ref.to_predicate())
1329 /// Given a closure's `DefId`, return the given name of the closure.
1331 /// This doesn't account for reassignments, but it's only used for suggestions.
1332 fn get_closure_name(
1335 err: &mut DiagnosticBuilder<'_>,
1337 ) -> Option<String> {
1339 |err: &mut DiagnosticBuilder<'_>, kind: &hir::PatKind<'_>| -> Option<String> {
1340 // Get the local name of this closure. This can be inaccurate because
1341 // of the possibility of reassignment, but this should be good enough.
1343 hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, name, None) => {
1344 Some(format!("{}", name))
1353 let hir = self.tcx.hir();
1354 let hir_id = hir.as_local_hir_id(def_id)?;
1355 let parent_node = hir.get_parent_node(hir_id);
1356 match hir.find(parent_node) {
1357 Some(hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(local), .. })) => {
1358 get_name(err, &local.pat.kind)
1360 // Different to previous arm because one is `&hir::Local` and the other
1361 // is `P<hir::Local>`.
1362 Some(hir::Node::Local(local)) => get_name(err, &local.pat.kind),
1367 /// We tried to apply the bound to an `fn` or closure. Check whether calling it would
1368 /// evaluate to a type that *would* satisfy the trait binding. If it would, suggest calling
1369 /// it: `bar(foo)` → `bar(foo())`. This case is *very* likely to be hit if `foo` is `async`.
1372 obligation: &PredicateObligation<'tcx>,
1373 err: &mut DiagnosticBuilder<'_>,
1374 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1375 points_at_arg: bool,
1377 let self_ty = trait_ref.self_ty();
1378 let (def_id, output_ty, callable) = match self_ty.kind {
1379 ty::Closure(def_id, substs) => {
1380 (def_id, self.closure_sig(def_id, substs).output(), "closure")
1382 ty::FnDef(def_id, _) => (def_id, self_ty.fn_sig(self.tcx).output(), "function"),
1385 let msg = format!("use parentheses to call the {}", callable);
1387 let obligation = self.mk_obligation_for_def_id(
1389 output_ty.skip_binder(),
1390 obligation.cause.clone(),
1391 obligation.param_env,
1394 match self.evaluate_obligation(&obligation) {
1395 Ok(EvaluationResult::EvaluatedToOk)
1396 | Ok(EvaluationResult::EvaluatedToOkModuloRegions)
1397 | Ok(EvaluationResult::EvaluatedToAmbig) => {}
1400 let hir = self.tcx.hir();
1401 // Get the name of the callable and the arguments to be used in the suggestion.
1402 let snippet = match hir.get_if_local(def_id) {
1403 Some(hir::Node::Expr(hir::Expr {
1404 kind: hir::ExprKind::Closure(_, decl, _, span, ..),
1407 err.span_label(*span, "consider calling this closure");
1408 let name = match self.get_closure_name(def_id, err, &msg) {
1412 let args = decl.inputs.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
1413 format!("{}({})", name, args)
1415 Some(hir::Node::Item(hir::Item {
1417 kind: hir::ItemKind::Fn(.., body_id),
1420 err.span_label(ident.span, "consider calling this function");
1421 let body = hir.body(*body_id);
1425 .map(|arg| match &arg.pat.kind {
1426 hir::PatKind::Binding(_, _, ident, None)
1427 // FIXME: provide a better suggestion when encountering `SelfLower`, it
1428 // should suggest a method call.
1429 if ident.name != kw::SelfLower => ident.to_string(),
1430 _ => "_".to_string(),
1432 .collect::<Vec<_>>()
1434 format!("{}({})", ident, args)
1439 // When the obligation error has been ensured to have been caused by
1440 // an argument, the `obligation.cause.span` points at the expression
1441 // of the argument, so we can provide a suggestion. This is signaled
1442 // by `points_at_arg`. Otherwise, we give a more general note.
1443 err.span_suggestion(
1444 obligation.cause.span,
1447 Applicability::HasPlaceholders,
1450 err.help(&format!("{}: `{}`", msg, snippet));
1454 fn suggest_add_reference_to_arg(
1456 obligation: &PredicateObligation<'tcx>,
1457 err: &mut DiagnosticBuilder<'tcx>,
1458 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1459 points_at_arg: bool,
1460 has_custom_message: bool,
1466 let span = obligation.cause.span;
1467 let param_env = obligation.param_env;
1468 let trait_ref = trait_ref.skip_binder();
1470 if let ObligationCauseCode::ImplDerivedObligation(obligation) = &obligation.cause.code {
1471 // Try to apply the original trait binding obligation by borrowing.
1472 let self_ty = trait_ref.self_ty();
1473 let found = self_ty.to_string();
1474 let new_self_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, self_ty);
1475 let substs = self.tcx.mk_substs_trait(new_self_ty, &[]);
1476 let new_trait_ref = ty::TraitRef::new(obligation.parent_trait_ref.def_id(), substs);
1477 let new_obligation =
1478 Obligation::new(ObligationCause::dummy(), param_env, new_trait_ref.to_predicate());
1479 if self.predicate_must_hold_modulo_regions(&new_obligation) {
1480 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1481 // We have a very specific type of error, where just borrowing this argument
1482 // might solve the problem. In cases like this, the important part is the
1483 // original type obligation, not the last one that failed, which is arbitrary.
1484 // Because of this, we modify the error to refer to the original obligation and
1485 // return early in the caller.
1487 "the trait bound `{}: {}` is not satisfied",
1489 obligation.parent_trait_ref.skip_binder().print_only_trait_path(),
1491 if has_custom_message {
1494 err.message = vec![(msg, Style::NoStyle)];
1496 if snippet.starts_with('&') {
1497 // This is already a literal borrow and the obligation is failing
1498 // somewhere else in the obligation chain. Do not suggest non-sense.
1504 "expected an implementor of trait `{}`",
1505 obligation.parent_trait_ref.skip_binder().print_only_trait_path(),
1508 err.span_suggestion(
1510 "consider borrowing here",
1511 format!("&{}", snippet),
1512 Applicability::MaybeIncorrect,
1521 /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
1522 /// suggest removing these references until we reach a type that implements the trait.
1523 fn suggest_remove_reference(
1525 obligation: &PredicateObligation<'tcx>,
1526 err: &mut DiagnosticBuilder<'tcx>,
1527 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1529 let trait_ref = trait_ref.skip_binder();
1530 let span = obligation.cause.span;
1532 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1534 snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
1536 snippet.chars().filter(|c| !c.is_whitespace()).skip(refs_number).next()
1538 // Do not suggest removal of borrow from type arguments.
1542 let mut trait_type = trait_ref.self_ty();
1544 for refs_remaining in 0..refs_number {
1545 if let ty::Ref(_, t_type, _) = trait_type.kind {
1546 trait_type = t_type;
1548 let new_obligation = self.mk_obligation_for_def_id(
1551 ObligationCause::dummy(),
1552 obligation.param_env,
1555 if self.predicate_may_hold(&new_obligation) {
1560 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1562 let remove_refs = refs_remaining + 1;
1564 format!("consider removing {} leading `&`-references", remove_refs);
1566 err.span_suggestion_short(
1570 Applicability::MachineApplicable,
1581 /// Check if the trait bound is implemented for a different mutability and note it in the
1583 fn suggest_change_mut(
1585 obligation: &PredicateObligation<'tcx>,
1586 err: &mut DiagnosticBuilder<'tcx>,
1587 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1588 points_at_arg: bool,
1590 let span = obligation.cause.span;
1591 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1593 snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
1595 snippet.chars().filter(|c| !c.is_whitespace()).skip(refs_number).next()
1597 // Do not suggest removal of borrow from type arguments.
1600 let trait_ref = self.resolve_vars_if_possible(trait_ref);
1601 if trait_ref.has_infer_types() {
1602 // Do not ICE while trying to find if a reborrow would succeed on a trait with
1603 // unresolved bindings.
1607 if let ty::Ref(region, t_type, mutability) = trait_ref.skip_binder().self_ty().kind {
1608 let trait_type = match mutability {
1609 hir::Mutability::Mut => self.tcx.mk_imm_ref(region, t_type),
1610 hir::Mutability::Not => self.tcx.mk_mut_ref(region, t_type),
1613 let new_obligation = self.mk_obligation_for_def_id(
1614 trait_ref.skip_binder().def_id,
1616 ObligationCause::dummy(),
1617 obligation.param_env,
1620 if self.evaluate_obligation_no_overflow(&new_obligation).must_apply_modulo_regions()
1626 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1627 if points_at_arg && mutability == hir::Mutability::Not && refs_number > 0 {
1628 err.span_suggestion(
1630 "consider changing this borrow's mutability",
1631 "&mut ".to_string(),
1632 Applicability::MachineApplicable,
1636 "`{}` is implemented for `{:?}`, but not for `{:?}`",
1637 trait_ref.print_only_trait_path(),
1639 trait_ref.skip_binder().self_ty(),
1647 fn suggest_semicolon_removal(
1649 obligation: &PredicateObligation<'tcx>,
1650 err: &mut DiagnosticBuilder<'tcx>,
1652 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1654 let hir = self.tcx.hir();
1655 let parent_node = hir.get_parent_node(obligation.cause.body_id);
1656 let node = hir.find(parent_node);
1657 if let Some(hir::Node::Item(hir::Item {
1658 kind: hir::ItemKind::Fn(sig, _, body_id), ..
1661 let body = hir.body(*body_id);
1662 if let hir::ExprKind::Block(blk, _) = &body.value.kind {
1663 if sig.decl.output.span().overlaps(span)
1664 && blk.expr.is_none()
1665 && "()" == &trait_ref.self_ty().to_string()
1667 // FIXME(estebank): When encountering a method with a trait
1668 // bound not satisfied in the return type with a body that has
1669 // no return, suggest removal of semicolon on last statement.
1670 // Once that is added, close #54771.
1671 if let Some(ref stmt) = blk.stmts.last() {
1672 let sp = self.tcx.sess.source_map().end_point(stmt.span);
1673 err.span_label(sp, "consider removing this semicolon");
1680 /// Given some node representing a fn-like thing in the HIR map,
1681 /// returns a span and `ArgKind` information that describes the
1682 /// arguments it expects. This can be supplied to
1683 /// `report_arg_count_mismatch`.
1684 pub fn get_fn_like_arguments(&self, node: Node<'_>) -> (Span, Vec<ArgKind>) {
1686 Node::Expr(&hir::Expr {
1687 kind: hir::ExprKind::Closure(_, ref _decl, id, span, _),
1690 self.tcx.sess.source_map().def_span(span),
1697 if let hir::Pat { kind: hir::PatKind::Tuple(ref args, _), span, .. } =
1708 .span_to_snippet(pat.span)
1710 (snippet, "_".to_owned())
1712 .collect::<Vec<_>>(),
1716 self.tcx.sess.source_map().span_to_snippet(arg.pat.span).unwrap();
1717 ArgKind::Arg(name, "_".to_owned())
1720 .collect::<Vec<ArgKind>>(),
1722 Node::Item(&hir::Item { span, kind: hir::ItemKind::Fn(ref sig, ..), .. })
1723 | Node::ImplItem(&hir::ImplItem {
1725 kind: hir::ImplItemKind::Method(ref sig, _),
1728 | Node::TraitItem(&hir::TraitItem {
1730 kind: hir::TraitItemKind::Method(ref sig, _),
1733 self.tcx.sess.source_map().def_span(span),
1737 .map(|arg| match arg.clone().kind {
1738 hir::TyKind::Tup(ref tys) => ArgKind::Tuple(
1740 vec![("_".to_owned(), "_".to_owned()); tys.len()],
1742 _ => ArgKind::empty(),
1744 .collect::<Vec<ArgKind>>(),
1746 Node::Ctor(ref variant_data) => {
1747 let span = variant_data
1749 .map(|hir_id| self.tcx.hir().span(hir_id))
1750 .unwrap_or(DUMMY_SP);
1751 let span = self.tcx.sess.source_map().def_span(span);
1753 (span, vec![ArgKind::empty(); variant_data.fields().len()])
1755 _ => panic!("non-FnLike node found: {:?}", node),
1759 /// Reports an error when the number of arguments needed by a
1760 /// trait match doesn't match the number that the expression
1762 pub fn report_arg_count_mismatch(
1765 found_span: Option<Span>,
1766 expected_args: Vec<ArgKind>,
1767 found_args: Vec<ArgKind>,
1769 ) -> DiagnosticBuilder<'tcx> {
1770 let kind = if is_closure { "closure" } else { "function" };
1772 let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
1773 let arg_length = arguments.len();
1774 let distinct = match &other[..] {
1775 &[ArgKind::Tuple(..)] => true,
1778 match (arg_length, arguments.get(0)) {
1779 (1, Some(&ArgKind::Tuple(_, ref fields))) => {
1780 format!("a single {}-tuple as argument", fields.len())
1785 if distinct && arg_length > 1 { "distinct " } else { "" },
1786 pluralize!(arg_length)
1791 let expected_str = args_str(&expected_args, &found_args);
1792 let found_str = args_str(&found_args, &expected_args);
1794 let mut err = struct_span_err!(
1798 "{} is expected to take {}, but it takes {}",
1804 err.span_label(span, format!("expected {} that takes {}", kind, expected_str));
1806 if let Some(found_span) = found_span {
1807 err.span_label(found_span, format!("takes {}", found_str));
1810 // ^^^^^^^^-- def_span
1814 let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
1818 if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
1820 // Suggest to take and ignore the arguments with expected_args_length `_`s if
1821 // found arguments is empty (assume the user just wants to ignore args in this case).
1822 // For example, if `expected_args_length` is 2, suggest `|_, _|`.
1823 if found_args.is_empty() && is_closure {
1824 let underscores = vec!["_"; expected_args.len()].join(", ");
1825 err.span_suggestion(
1828 "consider changing the closure to take and ignore the expected argument{}",
1829 if expected_args.len() < 2 { "" } else { "s" }
1831 format!("|{}|", underscores),
1832 Applicability::MachineApplicable,
1836 if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
1837 if fields.len() == expected_args.len() {
1840 .map(|(name, _)| name.to_owned())
1841 .collect::<Vec<String>>()
1843 err.span_suggestion(
1845 "change the closure to take multiple arguments instead of a single tuple",
1846 format!("|{}|", sugg),
1847 Applicability::MachineApplicable,
1851 if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..] {
1852 if fields.len() == found_args.len() && is_closure {
1857 .map(|arg| match arg {
1858 ArgKind::Arg(name, _) => name.to_owned(),
1859 _ => "_".to_owned(),
1861 .collect::<Vec<String>>()
1863 // add type annotations if available
1864 if found_args.iter().any(|arg| match arg {
1865 ArgKind::Arg(_, ty) => ty != "_",
1872 .map(|(_, ty)| ty.to_owned())
1873 .collect::<Vec<String>>()
1880 err.span_suggestion(
1882 "change the closure to accept a tuple instead of individual arguments",
1884 Applicability::MachineApplicable,
1893 fn report_closure_arg_mismatch(
1896 found_span: Option<Span>,
1897 expected_ref: ty::PolyTraitRef<'tcx>,
1898 found: ty::PolyTraitRef<'tcx>,
1899 ) -> DiagnosticBuilder<'tcx> {
1900 fn build_fn_sig_string<'tcx>(tcx: TyCtxt<'tcx>, trait_ref: &ty::TraitRef<'tcx>) -> String {
1901 let inputs = trait_ref.substs.type_at(1);
1902 let sig = if let ty::Tuple(inputs) = inputs.kind {
1904 inputs.iter().map(|k| k.expect_ty()),
1905 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1907 hir::Unsafety::Normal,
1908 ::rustc_target::spec::abi::Abi::Rust,
1912 ::std::iter::once(inputs),
1913 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1915 hir::Unsafety::Normal,
1916 ::rustc_target::spec::abi::Abi::Rust,
1919 ty::Binder::bind(sig).to_string()
1922 let argument_is_closure = expected_ref.skip_binder().substs.type_at(0).is_closure();
1923 let mut err = struct_span_err!(
1927 "type mismatch in {} arguments",
1928 if argument_is_closure { "closure" } else { "function" }
1931 let found_str = format!(
1932 "expected signature of `{}`",
1933 build_fn_sig_string(self.tcx, found.skip_binder())
1935 err.span_label(span, found_str);
1937 let found_span = found_span.unwrap_or(span);
1938 let expected_str = format!(
1939 "found signature of `{}`",
1940 build_fn_sig_string(self.tcx, expected_ref.skip_binder())
1942 err.span_label(found_span, expected_str);
1948 impl<'tcx> TyCtxt<'tcx> {
1949 pub fn recursive_type_with_infinite_size_error(
1952 ) -> DiagnosticBuilder<'tcx> {
1953 assert!(type_def_id.is_local());
1954 let span = self.hir().span_if_local(type_def_id).unwrap();
1955 let span = self.sess.source_map().def_span(span);
1956 let mut err = struct_span_err!(
1960 "recursive type `{}` has infinite size",
1961 self.def_path_str(type_def_id)
1963 err.span_label(span, "recursive type has infinite size");
1965 "insert indirection (e.g., a `Box`, `Rc`, or `&`) \
1966 at some point to make `{}` representable",
1967 self.def_path_str(type_def_id)
1972 pub fn report_object_safety_error(
1975 trait_def_id: DefId,
1976 violations: Vec<ObjectSafetyViolation>,
1977 ) -> DiagnosticBuilder<'tcx> {
1978 let trait_str = self.def_path_str(trait_def_id);
1979 let span = self.sess.source_map().def_span(span);
1980 let mut err = struct_span_err!(
1984 "the trait `{}` cannot be made into an object",
1987 err.span_label(span, format!("the trait `{}` cannot be made into an object", trait_str));
1989 let mut reported_violations = FxHashSet::default();
1990 for violation in violations {
1991 if reported_violations.insert(violation.clone()) {
1992 match violation.span() {
1993 Some(span) => err.span_label(span, violation.error_msg()),
1994 None => err.note(&violation.error_msg()),
1999 if self.sess.trait_methods_not_found.borrow().contains(&span) {
2000 // 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),