1 // ignore-tidy-filelength
4 DefIdOrName, FindExprBySpan, Obligation, ObligationCause, ObligationCauseCode,
8 use crate::infer::InferCtxt;
9 use crate::traits::{NormalizeExt, ObligationCtxt};
12 use rustc_data_structures::fx::FxHashSet;
13 use rustc_data_structures::stack::ensure_sufficient_stack;
15 error_code, pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder,
16 ErrorGuaranteed, MultiSpan, Style,
19 use rustc_hir::def::DefKind;
20 use rustc_hir::def_id::DefId;
21 use rustc_hir::intravisit::Visitor;
22 use rustc_hir::lang_items::LangItem;
23 use rustc_hir::{AsyncGeneratorKind, GeneratorKind, Node};
24 use rustc_hir::{Expr, HirId};
25 use rustc_infer::infer::error_reporting::TypeErrCtxt;
26 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
27 use rustc_infer::infer::{InferOk, LateBoundRegionConversionTime};
28 use rustc_middle::hir::map;
29 use rustc_middle::ty::error::TypeError::{self, Sorts};
30 use rustc_middle::ty::relate::TypeRelation;
31 use rustc_middle::ty::{
32 self, suggest_arbitrary_trait_bound, suggest_constraining_type_param, AdtKind, DefIdTree,
33 GeneratorDiagnosticData, GeneratorInteriorTypeCause, Infer, InferTy, InternalSubsts,
34 IsSuggestable, ToPredicate, Ty, TyCtxt, TypeAndMut, TypeFoldable, TypeFolder,
35 TypeSuperFoldable, TypeVisitable, TypeckResults,
37 use rustc_span::def_id::LocalDefId;
38 use rustc_span::symbol::{sym, Ident, Symbol};
39 use rustc_span::{BytePos, DesugaringKind, ExpnKind, MacroKind, Span, DUMMY_SP};
40 use rustc_target::spec::abi;
43 use super::method_chain::CollectAllMismatches;
44 use super::InferCtxtPrivExt;
45 use crate::infer::InferCtxtExt as _;
46 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
47 use rustc_middle::ty::print::{with_forced_trimmed_paths, with_no_trimmed_paths};
50 pub enum GeneratorInteriorOrUpvar {
51 // span of interior type
52 Interior(Span, Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>),
57 // This type provides a uniform interface to retrieve data on generators, whether it originated from
58 // the local crate being compiled or from a foreign crate.
60 pub enum GeneratorData<'tcx, 'a> {
61 Local(&'a TypeckResults<'tcx>),
62 Foreign(&'tcx GeneratorDiagnosticData<'tcx>),
65 impl<'tcx, 'a> GeneratorData<'tcx, 'a> {
66 // Try to get information about variables captured by the generator that matches a type we are
67 // looking for with `ty_matches` function. We uses it to find upvar which causes a failure to
69 fn try_get_upvar_span<F>(
71 infer_context: &InferCtxt<'tcx>,
74 ) -> Option<GeneratorInteriorOrUpvar>
76 F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool,
79 GeneratorData::Local(typeck_results) => {
80 infer_context.tcx.upvars_mentioned(generator_did).and_then(|upvars| {
81 upvars.iter().find_map(|(upvar_id, upvar)| {
82 let upvar_ty = typeck_results.node_type(*upvar_id);
83 let upvar_ty = infer_context.resolve_vars_if_possible(upvar_ty);
84 if ty_matches(ty::Binder::dummy(upvar_ty)) {
85 Some(GeneratorInteriorOrUpvar::Upvar(upvar.span))
92 GeneratorData::Foreign(_) => None,
96 // Try to get the span of a type being awaited on that matches the type we are looking with the
97 // `ty_matches` function. We uses it to find awaited type which causes a failure to meet an
99 fn get_from_await_ty<F>(
101 visitor: AwaitsVisitor,
106 F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool,
109 GeneratorData::Local(typeck_results) => visitor
112 .map(|id| hir.expect_expr(id))
114 ty_matches(ty::Binder::dummy(typeck_results.expr_ty_adjusted(&await_expr)))
116 .map(|expr| expr.span),
117 GeneratorData::Foreign(generator_diagnostic_data) => visitor
120 .map(|id| hir.expect_expr(id))
122 ty_matches(ty::Binder::dummy(
123 generator_diagnostic_data
125 .get(&await_expr.hir_id.local_id)
126 .map_or::<&[ty::adjustment::Adjustment<'tcx>], _>(&[], |a| &a[..])
128 .map_or_else::<Ty<'tcx>, _, _>(
130 generator_diagnostic_data
132 .get(&await_expr.hir_id.local_id)
136 "node_type: no type for node {}",
137 ty::tls::with(|tcx| tcx
139 .node_to_string(await_expr.hir_id))
147 .map(|expr| expr.span),
151 /// Get the type, expression, span and optional scope span of all types
152 /// that are live across the yield of this generator
153 fn get_generator_interior_types(
155 ) -> ty::Binder<'tcx, &[GeneratorInteriorTypeCause<'tcx>]> {
157 GeneratorData::Local(typeck_result) => {
158 typeck_result.generator_interior_types.as_deref()
160 GeneratorData::Foreign(generator_diagnostic_data) => {
161 generator_diagnostic_data.generator_interior_types.as_deref()
166 // Used to get the source of the data, note we don't have as much information for generators
167 // originated from foreign crates
168 fn is_foreign(&self) -> bool {
170 GeneratorData::Local(_) => false,
171 GeneratorData::Foreign(_) => true,
176 // This trait is public to expose the diagnostics methods to clippy.
177 pub trait TypeErrCtxtExt<'tcx> {
178 fn suggest_restricting_param_bound(
180 err: &mut Diagnostic,
181 trait_pred: ty::PolyTraitPredicate<'tcx>,
182 associated_item: Option<(&'static str, Ty<'tcx>)>,
186 fn suggest_dereferences(
188 obligation: &PredicateObligation<'tcx>,
189 err: &mut Diagnostic,
190 trait_pred: ty::PolyTraitPredicate<'tcx>,
193 fn get_closure_name(&self, def_id: DefId, err: &mut Diagnostic, msg: &str) -> Option<Symbol>;
197 obligation: &PredicateObligation<'tcx>,
198 err: &mut Diagnostic,
199 trait_pred: ty::PolyTraitPredicate<'tcx>,
202 fn check_for_binding_assigned_block_without_tail_expression(
204 obligation: &PredicateObligation<'tcx>,
205 err: &mut Diagnostic,
206 trait_pred: ty::PolyTraitPredicate<'tcx>,
209 fn suggest_add_clone_to_arg(
211 obligation: &PredicateObligation<'tcx>,
212 err: &mut Diagnostic,
213 trait_pred: ty::PolyTraitPredicate<'tcx>,
216 fn extract_callable_info(
219 param_env: ty::ParamEnv<'tcx>,
221 ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)>;
223 fn suggest_add_reference_to_arg(
225 obligation: &PredicateObligation<'tcx>,
226 err: &mut Diagnostic,
227 trait_pred: ty::PolyTraitPredicate<'tcx>,
228 has_custom_message: bool,
231 fn suggest_borrowing_for_object_cast(
233 err: &mut Diagnostic,
234 obligation: &PredicateObligation<'tcx>,
239 fn suggest_remove_reference(
241 obligation: &PredicateObligation<'tcx>,
242 err: &mut Diagnostic,
243 trait_pred: ty::PolyTraitPredicate<'tcx>,
246 fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic);
248 fn suggest_change_mut(
250 obligation: &PredicateObligation<'tcx>,
251 err: &mut Diagnostic,
252 trait_pred: ty::PolyTraitPredicate<'tcx>,
255 fn suggest_semicolon_removal(
257 obligation: &PredicateObligation<'tcx>,
258 err: &mut Diagnostic,
260 trait_pred: ty::PolyTraitPredicate<'tcx>,
263 fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span>;
265 fn suggest_impl_trait(
267 err: &mut Diagnostic,
269 obligation: &PredicateObligation<'tcx>,
270 trait_pred: ty::PolyTraitPredicate<'tcx>,
273 fn point_at_returns_when_relevant(
275 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
276 obligation: &PredicateObligation<'tcx>,
279 fn report_closure_arg_mismatch(
282 found_span: Option<Span>,
283 found: ty::PolyTraitRef<'tcx>,
284 expected: ty::PolyTraitRef<'tcx>,
285 cause: &ObligationCauseCode<'tcx>,
286 found_node: Option<Node<'_>>,
287 param_env: ty::ParamEnv<'tcx>,
288 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
290 fn note_conflicting_closure_bounds(
292 cause: &ObligationCauseCode<'tcx>,
293 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
296 fn suggest_fully_qualified_path(
298 err: &mut Diagnostic,
304 fn maybe_note_obligation_cause_for_async_await(
306 err: &mut Diagnostic,
307 obligation: &PredicateObligation<'tcx>,
310 fn note_obligation_cause_for_async_await(
312 err: &mut Diagnostic,
313 interior_or_upvar_span: GeneratorInteriorOrUpvar,
315 outer_generator: Option<DefId>,
316 trait_pred: ty::TraitPredicate<'tcx>,
318 typeck_results: Option<&ty::TypeckResults<'tcx>>,
319 obligation: &PredicateObligation<'tcx>,
320 next_code: Option<&ObligationCauseCode<'tcx>>,
323 fn note_obligation_cause_code<T>(
325 err: &mut Diagnostic,
327 param_env: ty::ParamEnv<'tcx>,
328 cause_code: &ObligationCauseCode<'tcx>,
329 obligated_types: &mut Vec<Ty<'tcx>>,
330 seen_requirements: &mut FxHashSet<DefId>,
332 T: ToPredicate<'tcx>;
334 /// Suggest to await before try: future? => future.await?
335 fn suggest_await_before_try(
337 err: &mut Diagnostic,
338 obligation: &PredicateObligation<'tcx>,
339 trait_pred: ty::PolyTraitPredicate<'tcx>,
343 fn suggest_floating_point_literal(
345 obligation: &PredicateObligation<'tcx>,
346 err: &mut Diagnostic,
347 trait_ref: &ty::PolyTraitRef<'tcx>,
352 obligation: &PredicateObligation<'tcx>,
353 err: &mut Diagnostic,
354 trait_pred: ty::PolyTraitPredicate<'tcx>,
357 fn suggest_dereferencing_index(
359 obligation: &PredicateObligation<'tcx>,
360 err: &mut Diagnostic,
361 trait_pred: ty::PolyTraitPredicate<'tcx>,
363 fn note_function_argument_obligation(
366 err: &mut Diagnostic,
367 parent_code: &ObligationCauseCode<'tcx>,
368 param_env: ty::ParamEnv<'tcx>,
369 predicate: ty::Predicate<'tcx>,
374 expr: &hir::Expr<'_>,
375 typeck_results: &TypeckResults<'tcx>,
376 type_diffs: Vec<TypeError<'tcx>>,
377 param_env: ty::ParamEnv<'tcx>,
378 err: &mut Diagnostic,
380 fn probe_assoc_types_at_expr(
382 type_diffs: &[TypeError<'tcx>],
386 param_env: ty::ParamEnv<'tcx>,
387 ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>>;
390 fn predicate_constraint(generics: &hir::Generics<'_>, pred: ty::Predicate<'_>) -> (Span, String) {
392 generics.tail_span_for_predicate_suggestion(),
393 format!("{} {}", generics.add_where_or_trailing_comma(), pred),
397 /// Type parameter needs more bounds. The trivial case is `T` `where T: Bound`, but
398 /// it can also be an `impl Trait` param that needs to be decomposed to a type
399 /// param for cleaner code.
400 fn suggest_restriction<'tcx>(
403 hir_generics: &hir::Generics<'tcx>,
405 err: &mut Diagnostic,
406 fn_sig: Option<&hir::FnSig<'_>>,
407 projection: Option<&ty::AliasTy<'_>>,
408 trait_pred: ty::PolyTraitPredicate<'tcx>,
409 // When we are dealing with a trait, `super_traits` will be `Some`:
410 // Given `trait T: A + B + C {}`
411 // - ^^^^^^^^^ GenericBounds
414 super_traits: Option<(&Ident, &hir::GenericBounds<'_>)>,
416 if hir_generics.where_clause_span.from_expansion()
417 || hir_generics.where_clause_span.desugaring_kind().is_some()
421 let generics = tcx.generics_of(item_id);
422 // Given `fn foo(t: impl Trait)` where `Trait` requires assoc type `A`...
423 if let Some((param, bound_str, fn_sig)) =
424 fn_sig.zip(projection).and_then(|(sig, p)| match p.self_ty().kind() {
425 // Shenanigans to get the `Trait` from the `impl Trait`.
426 ty::Param(param) => {
427 let param_def = generics.type_param(param, tcx);
428 if param_def.kind.is_synthetic() {
430 param_def.name.as_str().strip_prefix("impl ")?.trim_start().to_string();
431 return Some((param_def, bound_str, sig));
438 let type_param_name = hir_generics.params.next_type_param_name(Some(&bound_str));
439 let trait_pred = trait_pred.fold_with(&mut ReplaceImplTraitFolder {
442 replace_ty: ty::ParamTy::new(generics.count() as u32, Symbol::intern(&type_param_name))
445 if !trait_pred.is_suggestable(tcx, false) {
448 // We know we have an `impl Trait` that doesn't satisfy a required projection.
450 // Find all of the occurrences of `impl Trait` for `Trait` in the function arguments'
451 // types. There should be at least one, but there might be *more* than one. In that
452 // case we could just ignore it and try to identify which one needs the restriction,
453 // but instead we choose to suggest replacing all instances of `impl Trait` with `T`
455 let mut ty_spans = vec![];
456 for input in fn_sig.decl.inputs {
457 ReplaceImplTraitVisitor { ty_spans: &mut ty_spans, param_did: param.def_id }
460 // The type param `T: Trait` we will suggest to introduce.
461 let type_param = format!("{}: {}", type_param_name, bound_str);
464 if let Some(span) = hir_generics.span_for_param_suggestion() {
465 (span, format!(", {}", type_param))
467 (hir_generics.span, format!("<{}>", type_param))
469 // `fn foo(t: impl Trait)`
470 // ^ suggest `where <T as Trait>::A: Bound`
471 predicate_constraint(hir_generics, trait_pred.to_predicate(tcx)),
473 sugg.extend(ty_spans.into_iter().map(|s| (s, type_param_name.to_string())));
475 // Suggest `fn foo<T: Trait>(t: T) where <T as Trait>::A: Bound`.
476 // FIXME: once `#![feature(associated_type_bounds)]` is stabilized, we should suggest
477 // `fn foo(t: impl Trait<A: Bound>)` instead.
478 err.multipart_suggestion(
479 "introduce a type parameter with a trait bound instead of using `impl Trait`",
481 Applicability::MaybeIncorrect,
484 if !trait_pred.is_suggestable(tcx, false) {
487 // Trivial case: `T` needs an extra bound: `T: Bound`.
488 let (sp, suggestion) = match (
492 .find(|p| !matches!(p.kind, hir::GenericParamKind::Type { synthetic: true, .. })),
495 (_, None) => predicate_constraint(hir_generics, trait_pred.to_predicate(tcx)),
496 (None, Some((ident, []))) => (
497 ident.span.shrink_to_hi(),
498 format!(": {}", trait_pred.print_modifiers_and_trait_path()),
500 (_, Some((_, [.., bounds]))) => (
501 bounds.span().shrink_to_hi(),
502 format!(" + {}", trait_pred.print_modifiers_and_trait_path()),
504 (Some(_), Some((_, []))) => (
505 hir_generics.span.shrink_to_hi(),
506 format!(": {}", trait_pred.print_modifiers_and_trait_path()),
510 err.span_suggestion_verbose(
512 &format!("consider further restricting {}", msg),
514 Applicability::MachineApplicable,
519 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
520 fn suggest_restricting_param_bound(
522 mut err: &mut Diagnostic,
523 trait_pred: ty::PolyTraitPredicate<'tcx>,
524 associated_ty: Option<(&'static str, Ty<'tcx>)>,
525 mut body_id: LocalDefId,
527 let trait_pred = self.resolve_numeric_literals_with_default(trait_pred);
529 let self_ty = trait_pred.skip_binder().self_ty();
530 let (param_ty, projection) = match self_ty.kind() {
531 ty::Param(_) => (true, None),
532 ty::Alias(ty::Projection, projection) => (false, Some(projection)),
536 // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
537 // don't suggest `T: Sized + ?Sized`.
538 while let Some(node) = self.tcx.hir().find_by_def_id(body_id) {
540 hir::Node::Item(hir::Item {
542 kind: hir::ItemKind::Trait(_, _, generics, bounds, _),
544 }) if self_ty == self.tcx.types.self_param => {
546 // Restricting `Self` for a single method.
556 Some((ident, bounds)),
561 hir::Node::TraitItem(hir::TraitItem {
563 kind: hir::TraitItemKind::Fn(..),
565 }) if self_ty == self.tcx.types.self_param => {
567 // Restricting `Self` for a single method.
569 self.tcx, body_id, &generics, "`Self`", err, None, projection, trait_pred,
575 hir::Node::TraitItem(hir::TraitItem {
577 kind: hir::TraitItemKind::Fn(fn_sig, ..),
580 | hir::Node::ImplItem(hir::ImplItem {
582 kind: hir::ImplItemKind::Fn(fn_sig, ..),
585 | hir::Node::Item(hir::Item {
586 kind: hir::ItemKind::Fn(fn_sig, generics, _), ..
587 }) if projection.is_some() => {
588 // Missing restriction on associated type of type parameter (unmet projection).
593 "the associated type",
602 hir::Node::Item(hir::Item {
604 hir::ItemKind::Trait(_, _, generics, ..)
605 | hir::ItemKind::Impl(hir::Impl { generics, .. }),
607 }) if projection.is_some() => {
608 // Missing restriction on associated type of type parameter (unmet projection).
613 "the associated type",
623 hir::Node::Item(hir::Item {
625 hir::ItemKind::Struct(_, generics)
626 | hir::ItemKind::Enum(_, generics)
627 | hir::ItemKind::Union(_, generics)
628 | hir::ItemKind::Trait(_, _, generics, ..)
629 | hir::ItemKind::Impl(hir::Impl { generics, .. })
630 | hir::ItemKind::Fn(_, generics, _)
631 | hir::ItemKind::TyAlias(_, generics)
632 | hir::ItemKind::TraitAlias(generics, _)
633 | hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }),
636 | hir::Node::TraitItem(hir::TraitItem { generics, .. })
637 | hir::Node::ImplItem(hir::ImplItem { generics, .. })
640 // We skip the 0'th subst (self) because we do not want
641 // to consider the predicate as not suggestible if the
642 // self type is an arg position `impl Trait` -- instead,
643 // we handle that by adding ` + Bound` below.
644 // FIXME(compiler-errors): It would be nice to do the same
645 // this that we do in `suggest_restriction` and pull the
646 // `impl Trait` into a new generic if it shows up somewhere
647 // else in the predicate.
648 if !trait_pred.skip_binder().trait_ref.substs[1..]
650 .all(|g| g.is_suggestable(self.tcx, false))
654 // Missing generic type parameter bound.
655 let param_name = self_ty.to_string();
656 let mut constraint = with_no_trimmed_paths!(
657 trait_pred.print_modifiers_and_trait_path().to_string()
660 if let Some((name, term)) = associated_ty {
661 // FIXME: this case overlaps with code in TyCtxt::note_and_explain_type_err.
662 // That should be extracted into a helper function.
663 if constraint.ends_with('>') {
664 constraint = format!(
666 &constraint[..constraint.len() - 1],
671 constraint.push_str(&format!("<{} = {}>", name, term));
675 if suggest_constraining_type_param(
681 Some(trait_pred.def_id()),
688 hir::Node::Item(hir::Item {
690 hir::ItemKind::Struct(_, generics)
691 | hir::ItemKind::Enum(_, generics)
692 | hir::ItemKind::Union(_, generics)
693 | hir::ItemKind::Trait(_, _, generics, ..)
694 | hir::ItemKind::Impl(hir::Impl { generics, .. })
695 | hir::ItemKind::Fn(_, generics, _)
696 | hir::ItemKind::TyAlias(_, generics)
697 | hir::ItemKind::TraitAlias(generics, _)
698 | hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }),
701 // Missing generic type parameter bound.
702 if suggest_arbitrary_trait_bound(
712 hir::Node::Crate(..) => return,
716 body_id = self.tcx.local_parent(body_id);
720 /// When after several dereferencing, the reference satisfies the trait
721 /// binding. This function provides dereference suggestion for this
722 /// specific situation.
723 fn suggest_dereferences(
725 obligation: &PredicateObligation<'tcx>,
726 err: &mut Diagnostic,
727 trait_pred: ty::PolyTraitPredicate<'tcx>,
729 // It only make sense when suggesting dereferences for arguments
730 let ObligationCauseCode::FunctionArgumentObligation { arg_hir_id, call_hir_id, .. } = obligation.cause.code()
731 else { return false; };
732 let Some(typeck_results) = &self.typeck_results
733 else { return false; };
734 let hir::Node::Expr(expr) = self.tcx.hir().get(*arg_hir_id)
735 else { return false; };
736 let Some(arg_ty) = typeck_results.expr_ty_adjusted_opt(expr)
737 else { return false; };
739 let span = obligation.cause.span;
740 let mut real_trait_pred = trait_pred;
741 let mut code = obligation.cause.code();
742 while let Some((parent_code, parent_trait_pred)) = code.parent() {
744 if let Some(parent_trait_pred) = parent_trait_pred {
745 real_trait_pred = parent_trait_pred;
748 let real_ty = real_trait_pred.self_ty();
749 // We `erase_late_bound_regions` here because `make_subregion` does not handle
750 // `ReLateBound`, and we don't particularly care about the regions.
752 .can_eq(obligation.param_env, self.tcx.erase_late_bound_regions(real_ty), arg_ty)
758 if let ty::Ref(region, base_ty, mutbl) = *real_ty.skip_binder().kind() {
759 let autoderef = (self.autoderef_steps)(base_ty);
761 autoderef.into_iter().enumerate().find_map(|(steps, (ty, obligations))| {
763 let ty = self.tcx.mk_ref(region, TypeAndMut { ty, mutbl });
765 // Remapping bound vars here
766 let real_trait_pred_and_ty =
767 real_trait_pred.map_bound(|inner_trait_pred| (inner_trait_pred, ty));
768 let obligation = self.mk_trait_obligation_with_new_self_ty(
769 obligation.param_env,
770 real_trait_pred_and_ty,
774 .chain([&obligation])
775 .all(|obligation| self.predicate_may_hold(obligation))
784 // Don't care about `&mut` because `DerefMut` is used less
785 // often and user will not expect autoderef happens.
786 if let Some(hir::Node::Expr(hir::Expr {
788 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, expr),
790 })) = self.tcx.hir().find(*arg_hir_id)
792 let derefs = "*".repeat(steps);
793 err.span_suggestion_verbose(
794 expr.span.shrink_to_lo(),
795 "consider dereferencing here",
797 Applicability::MachineApplicable,
802 } else if real_trait_pred != trait_pred {
803 // This branch addresses #87437.
805 // Remapping bound vars here
806 let real_trait_pred_and_base_ty =
807 real_trait_pred.map_bound(|inner_trait_pred| (inner_trait_pred, base_ty));
808 let obligation = self.mk_trait_obligation_with_new_self_ty(
809 obligation.param_env,
810 real_trait_pred_and_base_ty,
812 if self.predicate_may_hold(&obligation) {
813 let call_node = self.tcx.hir().get(*call_hir_id);
814 let msg = "consider dereferencing here";
815 let is_receiver = matches!(
817 Node::Expr(hir::Expr {
818 kind: hir::ExprKind::MethodCall(_, receiver_expr, ..),
821 if receiver_expr.hir_id == *arg_hir_id
824 err.multipart_suggestion_verbose(
827 (span.shrink_to_lo(), "(*".to_string()),
828 (span.shrink_to_hi(), ")".to_string()),
830 Applicability::MachineApplicable,
833 err.span_suggestion_verbose(
837 Applicability::MachineApplicable,
848 /// Given a closure's `DefId`, return the given name of the closure.
850 /// This doesn't account for reassignments, but it's only used for suggestions.
851 fn get_closure_name(&self, def_id: DefId, err: &mut Diagnostic, msg: &str) -> Option<Symbol> {
852 let get_name = |err: &mut Diagnostic, kind: &hir::PatKind<'_>| -> Option<Symbol> {
853 // Get the local name of this closure. This can be inaccurate because
854 // of the possibility of reassignment, but this should be good enough.
856 hir::PatKind::Binding(hir::BindingAnnotation::NONE, _, ident, None) => {
866 let hir = self.tcx.hir();
867 let hir_id = hir.local_def_id_to_hir_id(def_id.as_local()?);
868 match hir.find_parent(hir_id) {
869 Some(hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(local), .. })) => {
870 get_name(err, &local.pat.kind)
872 // Different to previous arm because one is `&hir::Local` and the other
873 // is `P<hir::Local>`.
874 Some(hir::Node::Local(local)) => get_name(err, &local.pat.kind),
879 /// We tried to apply the bound to an `fn` or closure. Check whether calling it would
880 /// evaluate to a type that *would* satisfy the trait binding. If it would, suggest calling
881 /// it: `bar(foo)` → `bar(foo())`. This case is *very* likely to be hit if `foo` is `async`.
884 obligation: &PredicateObligation<'tcx>,
885 err: &mut Diagnostic,
886 trait_pred: ty::PolyTraitPredicate<'tcx>,
888 // It doesn't make sense to make this suggestion outside of typeck...
889 // (also autoderef will ICE...)
890 if self.typeck_results.is_none() {
894 if let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = obligation.predicate.kind().skip_binder()
895 && Some(trait_pred.def_id()) == self.tcx.lang_items().sized_trait()
897 // Don't suggest calling to turn an unsized type into a sized type
901 let self_ty = self.instantiate_binder_with_fresh_vars(
903 LateBoundRegionConversionTime::FnCall,
904 trait_pred.self_ty(),
907 let body_hir_id = self.tcx.hir().local_def_id_to_hir_id(obligation.cause.body_id);
908 let Some((def_id_or_name, output, inputs)) = self.extract_callable_info(
910 obligation.param_env,
912 ) else { return false; };
914 // Remapping bound vars here
915 let trait_pred_and_self = trait_pred.map_bound(|trait_pred| (trait_pred, output));
918 self.mk_trait_obligation_with_new_self_ty(obligation.param_env, trait_pred_and_self);
919 if !self.predicate_must_hold_modulo_regions(&new_obligation) {
923 // Get the name of the callable and the arguments to be used in the suggestion.
924 let hir = self.tcx.hir();
926 let msg = match def_id_or_name {
927 DefIdOrName::DefId(def_id) => match self.tcx.def_kind(def_id) {
928 DefKind::Ctor(CtorOf::Struct, _) => {
929 "use parentheses to construct this tuple struct".to_string()
931 DefKind::Ctor(CtorOf::Variant, _) => {
932 "use parentheses to construct this tuple variant".to_string()
934 kind => format!("use parentheses to call this {}", kind.descr(def_id)),
936 DefIdOrName::Name(name) => format!("use parentheses to call this {name}"),
942 if ty.is_suggestable(self.tcx, false) {
943 format!("/* {ty} */")
945 "/* value */".to_string()
951 if matches!(obligation.cause.code(), ObligationCauseCode::FunctionArgumentObligation { .. })
952 && obligation.cause.span.can_be_used_for_suggestions()
954 // When the obligation error has been ensured to have been caused by
955 // an argument, the `obligation.cause.span` points at the expression
956 // of the argument, so we can provide a suggestion. Otherwise, we give
957 // a more general note.
958 err.span_suggestion_verbose(
959 obligation.cause.span.shrink_to_hi(),
962 Applicability::HasPlaceholders,
964 } else if let DefIdOrName::DefId(def_id) = def_id_or_name {
965 let name = match hir.get_if_local(def_id) {
966 Some(hir::Node::Expr(hir::Expr {
967 kind: hir::ExprKind::Closure(hir::Closure { fn_decl_span, .. }),
970 err.span_label(*fn_decl_span, "consider calling this closure");
971 let Some(name) = self.get_closure_name(def_id, err, &msg) else {
976 Some(hir::Node::Item(hir::Item { ident, kind: hir::ItemKind::Fn(..), .. })) => {
977 err.span_label(ident.span, "consider calling this function");
980 Some(hir::Node::Ctor(..)) => {
981 let name = self.tcx.def_path_str(def_id);
983 self.tcx.def_span(def_id),
984 format!("consider calling the constructor for `{}`", name),
990 err.help(&format!("{msg}: `{name}({args})`"));
995 fn check_for_binding_assigned_block_without_tail_expression(
997 obligation: &PredicateObligation<'tcx>,
998 err: &mut Diagnostic,
999 trait_pred: ty::PolyTraitPredicate<'tcx>,
1001 let mut span = obligation.cause.span;
1002 while span.from_expansion() {
1003 // Remove all the desugaring and macro contexts.
1006 let mut expr_finder = FindExprBySpan::new(span);
1007 let Some(body_id) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) else { return; };
1008 let body = self.tcx.hir().body(body_id);
1009 expr_finder.visit_expr(body.value);
1010 let Some(expr) = expr_finder.result else { return; };
1011 let Some(typeck) = &self.typeck_results else { return; };
1012 let Some(ty) = typeck.expr_ty_adjusted_opt(expr) else { return; };
1016 let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind else { return; };
1017 let hir::def::Res::Local(hir_id) = path.res else { return; };
1018 let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(hir_id) else {
1021 let Some(hir::Node::Local(hir::Local {
1025 })) = self.tcx.hir().find_parent(pat.hir_id) else { return; };
1026 let hir::ExprKind::Block(block, None) = init.kind else { return; };
1027 if block.expr.is_some() {
1030 let [.., stmt] = block.stmts else {
1031 err.span_label(block.span, "this empty block is missing a tail expression");
1034 let hir::StmtKind::Semi(tail_expr) = stmt.kind else { return; };
1035 let Some(ty) = typeck.expr_ty_opt(tail_expr) else {
1036 err.span_label(block.span, "this block is missing a tail expression");
1039 let ty = self.resolve_numeric_literals_with_default(self.resolve_vars_if_possible(ty));
1040 let trait_pred_and_self = trait_pred.map_bound(|trait_pred| (trait_pred, ty));
1042 let new_obligation =
1043 self.mk_trait_obligation_with_new_self_ty(obligation.param_env, trait_pred_and_self);
1044 if self.predicate_must_hold_modulo_regions(&new_obligation) {
1045 err.span_suggestion_short(
1046 stmt.span.with_lo(tail_expr.span.hi()),
1047 "remove this semicolon",
1049 Applicability::MachineApplicable,
1052 err.span_label(block.span, "this block is missing a tail expression");
1056 fn suggest_add_clone_to_arg(
1058 obligation: &PredicateObligation<'tcx>,
1059 err: &mut Diagnostic,
1060 trait_pred: ty::PolyTraitPredicate<'tcx>,
1062 let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
1063 let ty = self.tcx.erase_late_bound_regions(self_ty);
1064 let Some(generics) = self.tcx.hir().get_generics(obligation.cause.body_id) else { return false };
1065 let ty::Ref(_, inner_ty, hir::Mutability::Not) = ty.kind() else { return false };
1066 let ty::Param(param) = inner_ty.kind() else { return false };
1067 let ObligationCauseCode::FunctionArgumentObligation { arg_hir_id, .. } = obligation.cause.code() else { return false };
1068 let arg_node = self.tcx.hir().get(*arg_hir_id);
1069 let Node::Expr(Expr { kind: hir::ExprKind::Path(_), ..}) = arg_node else { return false };
1071 let clone_trait = self.tcx.require_lang_item(LangItem::Clone, None);
1072 let has_clone = |ty| {
1073 self.type_implements_trait(clone_trait, [ty], obligation.param_env)
1074 .must_apply_modulo_regions()
1077 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
1078 obligation.param_env,
1079 trait_pred.map_bound(|trait_pred| (trait_pred, *inner_ty)),
1082 if self.predicate_may_hold(&new_obligation) && has_clone(ty) {
1083 if !has_clone(param.to_ty(self.tcx)) {
1084 suggest_constraining_type_param(
1088 param.name.as_str(),
1094 err.span_suggestion_verbose(
1095 obligation.cause.span.shrink_to_hi(),
1096 "consider using clone here",
1097 ".clone()".to_string(),
1098 Applicability::MaybeIncorrect,
1105 /// Extracts information about a callable type for diagnostics. This is a
1106 /// heuristic -- it doesn't necessarily mean that a type is always callable,
1107 /// because the callable type must also be well-formed to be called.
1108 // FIXME(vincenzopalazzo): move the HirId to a LocalDefId
1109 fn extract_callable_info(
1112 param_env: ty::ParamEnv<'tcx>,
1114 ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)> {
1115 // Autoderef is useful here because sometimes we box callables, etc.
1116 let Some((def_id_or_name, output, inputs)) = (self.autoderef_steps)(found).into_iter().find_map(|(found, _)| {
1117 match *found.kind() {
1118 ty::FnPtr(fn_sig) =>
1119 Some((DefIdOrName::Name("function pointer"), fn_sig.output(), fn_sig.inputs())),
1120 ty::FnDef(def_id, _) => {
1121 let fn_sig = found.fn_sig(self.tcx);
1122 Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs()))
1124 ty::Closure(def_id, substs) => {
1125 let fn_sig = substs.as_closure().sig();
1126 Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs().map_bound(|inputs| &inputs[1..])))
1128 ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
1129 self.tcx.item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
1130 if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
1131 && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
1132 // args tuple will always be substs[1]
1133 && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
1136 DefIdOrName::DefId(def_id),
1137 pred.kind().rebind(proj.term.ty().unwrap()),
1138 pred.kind().rebind(args.as_slice()),
1145 ty::Dynamic(data, _, ty::Dyn) => {
1146 data.iter().find_map(|pred| {
1147 if let ty::ExistentialPredicate::Projection(proj) = pred.skip_binder()
1148 && Some(proj.def_id) == self.tcx.lang_items().fn_once_output()
1149 // for existential projection, substs are shifted over by 1
1150 && let ty::Tuple(args) = proj.substs.type_at(0).kind()
1153 DefIdOrName::Name("trait object"),
1154 pred.rebind(proj.term.ty().unwrap()),
1155 pred.rebind(args.as_slice()),
1162 ty::Param(param) => {
1163 let generics = self.tcx.generics_of(hir_id.owner.to_def_id());
1164 let name = if generics.count() > param.index as usize
1165 && let def = generics.param_at(param.index as usize, self.tcx)
1166 && matches!(def.kind, ty::GenericParamDefKind::Type { .. })
1167 && def.name == param.name
1169 DefIdOrName::DefId(def.def_id)
1171 DefIdOrName::Name("type parameter")
1173 param_env.caller_bounds().iter().find_map(|pred| {
1174 if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
1175 && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
1176 && proj.projection_ty.self_ty() == found
1177 // args tuple will always be substs[1]
1178 && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
1182 pred.kind().rebind(proj.term.ty().unwrap()),
1183 pred.kind().rebind(args.as_slice()),
1192 }) else { return None; };
1194 let output = self.instantiate_binder_with_fresh_vars(
1196 LateBoundRegionConversionTime::FnCall,
1203 self.instantiate_binder_with_fresh_vars(
1205 LateBoundRegionConversionTime::FnCall,
1211 // We don't want to register any extra obligations, which should be
1212 // implied by wf, but also because that would possibly result in
1213 // erroneous errors later on.
1214 let InferOk { value: output, obligations: _ } =
1215 self.at(&ObligationCause::dummy(), param_env).normalize(output);
1217 if output.is_ty_var() { None } else { Some((def_id_or_name, output, inputs)) }
1220 fn suggest_add_reference_to_arg(
1222 obligation: &PredicateObligation<'tcx>,
1223 err: &mut Diagnostic,
1224 poly_trait_pred: ty::PolyTraitPredicate<'tcx>,
1225 has_custom_message: bool,
1227 let span = obligation.cause.span;
1229 let code = if let ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } =
1230 obligation.cause.code()
1233 } else if let ObligationCauseCode::ItemObligation(_)
1234 | ObligationCauseCode::ExprItemObligation(..) = obligation.cause.code()
1236 obligation.cause.code()
1237 } else if let ExpnKind::Desugaring(DesugaringKind::ForLoop) =
1238 span.ctxt().outer_expn_data().kind
1240 obligation.cause.code()
1245 // List of traits for which it would be nonsensical to suggest borrowing.
1246 // For instance, immutable references are always Copy, so suggesting to
1247 // borrow would always succeed, but it's probably not what the user wanted.
1248 let mut never_suggest_borrow: Vec<_> =
1249 [LangItem::Copy, LangItem::Clone, LangItem::Unpin, LangItem::Sized]
1251 .filter_map(|lang_item| self.tcx.lang_items().get(*lang_item))
1254 if let Some(def_id) = self.tcx.get_diagnostic_item(sym::Send) {
1255 never_suggest_borrow.push(def_id);
1258 let param_env = obligation.param_env;
1260 // Try to apply the original trait binding obligation by borrowing.
1261 let mut try_borrowing = |old_pred: ty::PolyTraitPredicate<'tcx>,
1262 blacklist: &[DefId]|
1264 if blacklist.contains(&old_pred.def_id()) {
1267 // We map bounds to `&T` and `&mut T`
1268 let trait_pred_and_imm_ref = old_pred.map_bound(|trait_pred| {
1271 self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, trait_pred.self_ty()),
1274 let trait_pred_and_mut_ref = old_pred.map_bound(|trait_pred| {
1277 self.tcx.mk_mut_ref(self.tcx.lifetimes.re_static, trait_pred.self_ty()),
1281 let mk_result = |trait_pred_and_new_ty| {
1283 self.mk_trait_obligation_with_new_self_ty(param_env, trait_pred_and_new_ty);
1284 self.predicate_must_hold_modulo_regions(&obligation)
1286 let imm_ref_self_ty_satisfies_pred = mk_result(trait_pred_and_imm_ref);
1287 let mut_ref_self_ty_satisfies_pred = mk_result(trait_pred_and_mut_ref);
1289 let (ref_inner_ty_satisfies_pred, ref_inner_ty_mut) =
1290 if let ObligationCauseCode::ItemObligation(_) | ObligationCauseCode::ExprItemObligation(..) = obligation.cause.code()
1291 && let ty::Ref(_, ty, mutability) = old_pred.self_ty().skip_binder().kind()
1294 mk_result(old_pred.map_bound(|trait_pred| (trait_pred, *ty))),
1295 mutability.is_mut(),
1301 if imm_ref_self_ty_satisfies_pred
1302 || mut_ref_self_ty_satisfies_pred
1303 || ref_inner_ty_satisfies_pred
1305 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1306 // We don't want a borrowing suggestion on the fields in structs,
1309 // the_foos: Vec<Foo>
1313 span.ctxt().outer_expn_data().kind,
1314 ExpnKind::Root | ExpnKind::Desugaring(DesugaringKind::ForLoop)
1318 if snippet.starts_with('&') {
1319 // This is already a literal borrow and the obligation is failing
1320 // somewhere else in the obligation chain. Do not suggest non-sense.
1323 // We have a very specific type of error, where just borrowing this argument
1324 // might solve the problem. In cases like this, the important part is the
1325 // original type obligation, not the last one that failed, which is arbitrary.
1326 // Because of this, we modify the error to refer to the original obligation and
1327 // return early in the caller.
1329 let msg = format!("the trait bound `{}` is not satisfied", old_pred);
1330 if has_custom_message {
1334 vec![(rustc_errors::DiagnosticMessage::Str(msg), Style::NoStyle)];
1339 "the trait `{}` is not implemented for `{}`",
1340 old_pred.print_modifiers_and_trait_path(),
1341 old_pred.self_ty().skip_binder(),
1345 if imm_ref_self_ty_satisfies_pred && mut_ref_self_ty_satisfies_pred {
1346 err.span_suggestions(
1347 span.shrink_to_lo(),
1348 "consider borrowing here",
1349 ["&".to_string(), "&mut ".to_string()],
1350 Applicability::MaybeIncorrect,
1353 let is_mut = mut_ref_self_ty_satisfies_pred || ref_inner_ty_mut;
1354 err.span_suggestion_verbose(
1355 span.shrink_to_lo(),
1357 "consider{} borrowing here",
1358 if is_mut { " mutably" } else { "" }
1360 format!("&{}", if is_mut { "mut " } else { "" }),
1361 Applicability::MaybeIncorrect,
1370 if let ObligationCauseCode::ImplDerivedObligation(cause) = &*code {
1371 try_borrowing(cause.derived.parent_trait_pred, &[])
1372 } else if let ObligationCauseCode::BindingObligation(_, _)
1373 | ObligationCauseCode::ItemObligation(_)
1374 | ObligationCauseCode::ExprItemObligation(..)
1375 | ObligationCauseCode::ExprBindingObligation(..) = code
1377 try_borrowing(poly_trait_pred, &never_suggest_borrow)
1383 // Suggest borrowing the type
1384 fn suggest_borrowing_for_object_cast(
1386 err: &mut Diagnostic,
1387 obligation: &PredicateObligation<'tcx>,
1389 object_ty: Ty<'tcx>,
1391 let ty::Dynamic(predicates, _, ty::Dyn) = object_ty.kind() else { return; };
1392 let self_ref_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_erased, self_ty);
1394 for predicate in predicates.iter() {
1395 if !self.predicate_must_hold_modulo_regions(
1396 &obligation.with(self.tcx, predicate.with_self_ty(self.tcx, self_ref_ty)),
1402 err.span_suggestion(
1403 obligation.cause.span.shrink_to_lo(),
1405 "consider borrowing the value, since `&{self_ty}` can be coerced into `{object_ty}`"
1408 Applicability::MaybeIncorrect,
1412 /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
1413 /// suggest removing these references until we reach a type that implements the trait.
1414 fn suggest_remove_reference(
1416 obligation: &PredicateObligation<'tcx>,
1417 err: &mut Diagnostic,
1418 trait_pred: ty::PolyTraitPredicate<'tcx>,
1420 let mut span = obligation.cause.span;
1421 let mut trait_pred = trait_pred;
1422 let mut code = obligation.cause.code();
1423 while let Some((c, Some(parent_trait_pred))) = code.parent() {
1424 // We want the root obligation, in order to detect properly handle
1425 // `for _ in &mut &mut vec![] {}`.
1427 trait_pred = parent_trait_pred;
1429 while span.desugaring_kind().is_some() {
1430 // Remove all the hir desugaring contexts while maintaining the macro contexts.
1433 let mut expr_finder = super::FindExprBySpan::new(span);
1434 let Some(body_id) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) else {
1437 let body = self.tcx.hir().body(body_id);
1438 expr_finder.visit_expr(body.value);
1439 let mut maybe_suggest = |suggested_ty, count, suggestions| {
1440 // Remapping bound vars here
1441 let trait_pred_and_suggested_ty =
1442 trait_pred.map_bound(|trait_pred| (trait_pred, suggested_ty));
1444 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
1445 obligation.param_env,
1446 trait_pred_and_suggested_ty,
1449 if self.predicate_may_hold(&new_obligation) {
1450 let msg = if count == 1 {
1451 "consider removing the leading `&`-reference".to_string()
1453 format!("consider removing {count} leading `&`-references")
1456 err.multipart_suggestion_verbose(
1459 Applicability::MachineApplicable,
1467 // Maybe suggest removal of borrows from types in type parameters, like in
1468 // `src/test/ui/not-panic/not-panic-safe.rs`.
1470 let mut suggestions = vec![];
1471 // Skipping binder here, remapping below
1472 let mut suggested_ty = trait_pred.self_ty().skip_binder();
1473 if let Some(mut hir_ty) = expr_finder.ty_result {
1474 while let hir::TyKind::Ref(_, mut_ty) = &hir_ty.kind {
1476 let span = hir_ty.span.until(mut_ty.ty.span);
1477 suggestions.push((span, String::new()));
1479 let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else {
1482 suggested_ty = *inner_ty;
1486 if maybe_suggest(suggested_ty, count, suggestions.clone()) {
1492 // Maybe suggest removal of borrows from expressions, like in `for i in &&&foo {}`.
1493 let Some(mut expr) = expr_finder.result else { return false; };
1495 let mut suggestions = vec![];
1496 // Skipping binder here, remapping below
1497 let mut suggested_ty = trait_pred.self_ty().skip_binder();
1499 while let hir::ExprKind::AddrOf(_, _, borrowed) = expr.kind {
1501 let span = if expr.span.eq_ctxt(borrowed.span) {
1502 expr.span.until(borrowed.span)
1504 expr.span.with_hi(expr.span.lo() + BytePos(1))
1506 suggestions.push((span, String::new()));
1508 let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else {
1511 suggested_ty = *inner_ty;
1515 if maybe_suggest(suggested_ty, count, suggestions.clone()) {
1519 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
1520 && let hir::def::Res::Local(hir_id) = path.res
1521 && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(hir_id)
1522 && let Some(hir::Node::Local(local)) = self.tcx.hir().find_parent(binding.hir_id)
1523 && let None = local.ty
1524 && let Some(binding_expr) = local.init
1526 expr = binding_expr;
1534 fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic) {
1535 let span = obligation.cause.span;
1537 if let ObligationCauseCode::AwaitableExpr(hir_id) = obligation.cause.code().peel_derives() {
1538 let hir = self.tcx.hir();
1539 if let Some(hir::Node::Expr(expr)) = hir_id.and_then(|hir_id| hir.find(hir_id)) {
1540 // FIXME: use `obligation.predicate.kind()...trait_ref.self_ty()` to see if we have `()`
1541 // and if not maybe suggest doing something else? If we kept the expression around we
1542 // could also check if it is an fn call (very likely) and suggest changing *that*, if
1543 // it is from the local crate.
1544 err.span_suggestion(
1546 "remove the `.await`",
1548 Applicability::MachineApplicable,
1550 // FIXME: account for associated `async fn`s.
1551 if let hir::Expr { span, kind: hir::ExprKind::Call(base, _), .. } = expr {
1552 if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) =
1553 obligation.predicate.kind().skip_binder()
1555 err.span_label(*span, &format!("this call returns `{}`", pred.self_ty()));
1557 if let Some(typeck_results) = &self.typeck_results
1558 && let ty = typeck_results.expr_ty_adjusted(base)
1559 && let ty::FnDef(def_id, _substs) = ty.kind()
1560 && let Some(hir::Node::Item(hir::Item { ident, span, vis_span, .. })) =
1561 hir.get_if_local(*def_id)
1564 "alternatively, consider making `fn {}` asynchronous",
1567 if vis_span.is_empty() {
1568 err.span_suggestion_verbose(
1569 span.shrink_to_lo(),
1572 Applicability::MaybeIncorrect,
1575 err.span_suggestion_verbose(
1576 vis_span.shrink_to_hi(),
1579 Applicability::MaybeIncorrect,
1588 /// Check if the trait bound is implemented for a different mutability and note it in the
1590 fn suggest_change_mut(
1592 obligation: &PredicateObligation<'tcx>,
1593 err: &mut Diagnostic,
1594 trait_pred: ty::PolyTraitPredicate<'tcx>,
1596 let points_at_arg = matches!(
1597 obligation.cause.code(),
1598 ObligationCauseCode::FunctionArgumentObligation { .. },
1601 let span = obligation.cause.span;
1602 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1604 snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
1605 if let Some('\'') = snippet.chars().filter(|c| !c.is_whitespace()).nth(refs_number) {
1606 // Do not suggest removal of borrow from type arguments.
1609 let trait_pred = self.resolve_vars_if_possible(trait_pred);
1610 if trait_pred.has_non_region_infer() {
1611 // Do not ICE while trying to find if a reborrow would succeed on a trait with
1612 // unresolved bindings.
1616 // Skipping binder here, remapping below
1617 if let ty::Ref(region, t_type, mutability) = *trait_pred.skip_binder().self_ty().kind()
1619 let suggested_ty = match mutability {
1620 hir::Mutability::Mut => self.tcx.mk_imm_ref(region, t_type),
1621 hir::Mutability::Not => self.tcx.mk_mut_ref(region, t_type),
1624 // Remapping bound vars here
1625 let trait_pred_and_suggested_ty =
1626 trait_pred.map_bound(|trait_pred| (trait_pred, suggested_ty));
1628 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
1629 obligation.param_env,
1630 trait_pred_and_suggested_ty,
1632 let suggested_ty_would_satisfy_obligation = self
1633 .evaluate_obligation_no_overflow(&new_obligation)
1634 .must_apply_modulo_regions();
1635 if suggested_ty_would_satisfy_obligation {
1640 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1641 if points_at_arg && mutability.is_not() && refs_number > 0 {
1642 // If we have a call like foo(&mut buf), then don't suggest foo(&mut mut buf)
1644 .trim_start_matches(|c: char| c.is_whitespace() || c == '&')
1649 err.span_suggestion_verbose(
1651 "consider changing this borrow's mutability",
1653 Applicability::MachineApplicable,
1657 "`{}` is implemented for `{:?}`, but not for `{:?}`",
1658 trait_pred.print_modifiers_and_trait_path(),
1660 trait_pred.skip_binder().self_ty(),
1668 fn suggest_semicolon_removal(
1670 obligation: &PredicateObligation<'tcx>,
1671 err: &mut Diagnostic,
1673 trait_pred: ty::PolyTraitPredicate<'tcx>,
1675 let hir = self.tcx.hir();
1676 let node = hir.find_by_def_id(obligation.cause.body_id);
1677 if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. })) = node
1678 && let hir::ExprKind::Block(blk, _) = &hir.body(*body_id).value.kind
1679 && sig.decl.output.span().overlaps(span)
1680 && blk.expr.is_none()
1681 && trait_pred.self_ty().skip_binder().is_unit()
1682 && let Some(stmt) = blk.stmts.last()
1683 && let hir::StmtKind::Semi(expr) = stmt.kind
1684 // Only suggest this if the expression behind the semicolon implements the predicate
1685 && let Some(typeck_results) = &self.typeck_results
1686 && let Some(ty) = typeck_results.expr_ty_opt(expr)
1687 && self.predicate_may_hold(&self.mk_trait_obligation_with_new_self_ty(
1688 obligation.param_env, trait_pred.map_bound(|trait_pred| (trait_pred, ty))
1694 "this expression has type `{}`, which implements `{}`",
1696 trait_pred.print_modifiers_and_trait_path()
1699 err.span_suggestion(
1700 self.tcx.sess.source_map().end_point(stmt.span),
1701 "remove this semicolon",
1703 Applicability::MachineApplicable
1710 fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span> {
1711 let hir = self.tcx.hir();
1712 let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. })) = hir.find_by_def_id(obligation.cause.body_id) else {
1716 if let hir::FnRetTy::Return(ret_ty) = sig.decl.output { Some(ret_ty.span) } else { None }
1719 /// If all conditions are met to identify a returned `dyn Trait`, suggest using `impl Trait` if
1720 /// applicable and signal that the error has been expanded appropriately and needs to be
1722 fn suggest_impl_trait(
1724 err: &mut Diagnostic,
1726 obligation: &PredicateObligation<'tcx>,
1727 trait_pred: ty::PolyTraitPredicate<'tcx>,
1729 match obligation.cause.code().peel_derives() {
1730 // Only suggest `impl Trait` if the return type is unsized because it is `dyn Trait`.
1731 ObligationCauseCode::SizedReturnType => {}
1735 let hir = self.tcx.hir();
1736 let fn_hir_id = hir.local_def_id_to_hir_id(obligation.cause.body_id);
1737 let node = hir.find_by_def_id(obligation.cause.body_id);
1738 let Some(hir::Node::Item(hir::Item {
1739 kind: hir::ItemKind::Fn(sig, _, body_id),
1745 let body = hir.body(*body_id);
1746 let trait_pred = self.resolve_vars_if_possible(trait_pred);
1747 let ty = trait_pred.skip_binder().self_ty();
1748 let is_object_safe = match ty.kind() {
1749 ty::Dynamic(predicates, _, ty::Dyn) => {
1750 // If the `dyn Trait` is not object safe, do not suggest `Box<dyn Trait>`.
1753 .map_or(true, |def_id| self.tcx.check_is_object_safe(def_id))
1755 // We only want to suggest `impl Trait` to `dyn Trait`s.
1756 // For example, `fn foo() -> str` needs to be filtered out.
1760 let hir::FnRetTy::Return(ret_ty) = sig.decl.output else {
1764 // Use `TypeVisitor` instead of the output type directly to find the span of `ty` for
1765 // cases like `fn foo() -> (dyn Trait, i32) {}`.
1766 // Recursively look for `TraitObject` types and if there's only one, use that span to
1767 // suggest `impl Trait`.
1769 // Visit to make sure there's a single `return` type to suggest `impl Trait`,
1770 // otherwise suggest using `Box<dyn Trait>` or an enum.
1771 let mut visitor = ReturnsVisitor::default();
1772 visitor.visit_body(&body);
1774 let typeck_results = self.typeck_results.as_ref().unwrap();
1775 let Some(liberated_sig) = typeck_results.liberated_fn_sigs().get(fn_hir_id).copied() else { return false; };
1777 let ret_types = visitor
1780 .filter_map(|expr| Some((expr.span, typeck_results.node_type_opt(expr.hir_id)?)))
1781 .map(|(expr_span, ty)| (expr_span, self.resolve_vars_if_possible(ty)));
1782 let (last_ty, all_returns_have_same_type, only_never_return) = ret_types.clone().fold(
1784 |(last_ty, mut same, only_never_return): (std::option::Option<Ty<'_>>, bool, bool),
1786 let ty = self.resolve_vars_if_possible(ty);
1788 !matches!(ty.kind(), ty::Error(_))
1789 && last_ty.map_or(true, |last_ty| {
1790 // FIXME: ideally we would use `can_coerce` here instead, but `typeck` comes
1791 // *after* in the dependency graph.
1792 match (ty.kind(), last_ty.kind()) {
1793 (Infer(InferTy::IntVar(_)), Infer(InferTy::IntVar(_)))
1794 | (Infer(InferTy::FloatVar(_)), Infer(InferTy::FloatVar(_)))
1795 | (Infer(InferTy::FreshIntTy(_)), Infer(InferTy::FreshIntTy(_)))
1797 Infer(InferTy::FreshFloatTy(_)),
1798 Infer(InferTy::FreshFloatTy(_)),
1803 (Some(ty), same, only_never_return && matches!(ty.kind(), ty::Never))
1806 let mut spans_and_needs_box = vec![];
1808 match liberated_sig.output().kind() {
1809 ty::Dynamic(predicates, _, ty::Dyn) => {
1810 let cause = ObligationCause::misc(ret_ty.span, obligation.cause.body_id);
1811 let param_env = ty::ParamEnv::empty();
1813 if !only_never_return {
1814 for (expr_span, return_ty) in ret_types {
1815 let self_ty_satisfies_dyn_predicates = |self_ty| {
1816 predicates.iter().all(|predicate| {
1817 let pred = predicate.with_self_ty(self.tcx, self_ty);
1818 let obl = Obligation::new(self.tcx, cause.clone(), param_env, pred);
1819 self.predicate_may_hold(&obl)
1823 if let ty::Adt(def, substs) = return_ty.kind()
1825 && self_ty_satisfies_dyn_predicates(substs.type_at(0))
1827 spans_and_needs_box.push((expr_span, false));
1828 } else if self_ty_satisfies_dyn_predicates(return_ty) {
1829 spans_and_needs_box.push((expr_span, true));
1839 let sm = self.tcx.sess.source_map();
1840 if !ret_ty.span.overlaps(span) {
1843 let snippet = if let hir::TyKind::TraitObject(..) = ret_ty.kind {
1844 if let Ok(snippet) = sm.span_to_snippet(ret_ty.span) {
1850 // Substitute the type, so we can print a fixup given `type Alias = dyn Trait`
1851 let name = liberated_sig.output().to_string();
1853 name.strip_prefix('(').and_then(|name| name.strip_suffix(')')).unwrap_or(&name);
1854 if !name.starts_with("dyn ") {
1860 err.code(error_code!(E0746));
1861 err.set_primary_message("return type cannot have an unboxed trait object");
1862 err.children.clear();
1863 let impl_trait_msg = "for information on `impl Trait`, see \
1864 <https://doc.rust-lang.org/book/ch10-02-traits.html\
1865 #returning-types-that-implement-traits>";
1866 let trait_obj_msg = "for information on trait objects, see \
1867 <https://doc.rust-lang.org/book/ch17-02-trait-objects.html\
1868 #using-trait-objects-that-allow-for-values-of-different-types>";
1870 let has_dyn = snippet.split_whitespace().next().map_or(false, |s| s == "dyn");
1871 let trait_obj = if has_dyn { &snippet[4..] } else { &snippet };
1872 if only_never_return {
1873 // No return paths, probably using `panic!()` or similar.
1874 // Suggest `-> impl Trait`, and if `Trait` is object safe, `-> Box<dyn Trait>`.
1875 suggest_trait_object_return_type_alternatives(
1881 } else if let (Some(last_ty), true) = (last_ty, all_returns_have_same_type) {
1882 // Suggest `-> impl Trait`.
1883 err.span_suggestion(
1886 "use `impl {1}` as the return type, as all return paths are of type `{}`, \
1887 which implements `{1}`",
1890 format!("impl {}", trait_obj),
1891 Applicability::MachineApplicable,
1893 err.note(impl_trait_msg);
1896 // Suggest `-> Box<dyn Trait>` and `Box::new(returned_value)`.
1897 err.multipart_suggestion(
1898 "return a boxed trait object instead",
1900 (ret_ty.span.shrink_to_lo(), "Box<".to_string()),
1901 (span.shrink_to_hi(), ">".to_string()),
1903 Applicability::MaybeIncorrect,
1905 for (span, needs_box) in spans_and_needs_box {
1907 err.multipart_suggestion(
1908 "... and box this value",
1910 (span.shrink_to_lo(), "Box::new(".to_string()),
1911 (span.shrink_to_hi(), ")".to_string()),
1913 Applicability::MaybeIncorrect,
1918 // This is currently not possible to trigger because E0038 takes precedence, but
1919 // leave it in for completeness in case anything changes in an earlier stage.
1921 "if trait `{}` were object-safe, you could return a trait object",
1925 err.note(trait_obj_msg);
1927 "if all the returned values were of the same type you could use `impl {}` as the \
1931 err.note(impl_trait_msg);
1932 err.note("you can create a new `enum` with a variant for each returned type");
1937 fn point_at_returns_when_relevant(
1939 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
1940 obligation: &PredicateObligation<'tcx>,
1942 match obligation.cause.code().peel_derives() {
1943 ObligationCauseCode::SizedReturnType => {}
1947 let hir = self.tcx.hir();
1948 let node = hir.find_by_def_id(obligation.cause.body_id);
1949 if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })) =
1952 let body = hir.body(*body_id);
1953 // Point at all the `return`s in the function as they have failed trait bounds.
1954 let mut visitor = ReturnsVisitor::default();
1955 visitor.visit_body(&body);
1956 let typeck_results = self.typeck_results.as_ref().unwrap();
1957 for expr in &visitor.returns {
1958 if let Some(returned_ty) = typeck_results.node_type_opt(expr.hir_id) {
1959 let ty = self.resolve_vars_if_possible(returned_ty);
1960 if ty.references_error() {
1961 // don't print out the [type error] here
1966 &format!("this returned value is of type `{}`", ty),
1974 fn report_closure_arg_mismatch(
1977 found_span: Option<Span>,
1978 found: ty::PolyTraitRef<'tcx>,
1979 expected: ty::PolyTraitRef<'tcx>,
1980 cause: &ObligationCauseCode<'tcx>,
1981 found_node: Option<Node<'_>>,
1982 param_env: ty::ParamEnv<'tcx>,
1983 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1984 pub(crate) fn build_fn_sig_ty<'tcx>(
1985 infcx: &InferCtxt<'tcx>,
1986 trait_ref: ty::PolyTraitRef<'tcx>,
1988 let inputs = trait_ref.skip_binder().substs.type_at(1);
1989 let sig = match inputs.kind() {
1990 ty::Tuple(inputs) if infcx.tcx.is_fn_trait(trait_ref.def_id()) => {
1991 infcx.tcx.mk_fn_sig(
1993 infcx.next_ty_var(TypeVariableOrigin {
1995 kind: TypeVariableOriginKind::MiscVariable,
1998 hir::Unsafety::Normal,
2002 _ => infcx.tcx.mk_fn_sig(
2003 std::iter::once(inputs),
2004 infcx.next_ty_var(TypeVariableOrigin {
2006 kind: TypeVariableOriginKind::MiscVariable,
2009 hir::Unsafety::Normal,
2014 infcx.tcx.mk_fn_ptr(trait_ref.rebind(sig))
2017 let argument_kind = match expected.skip_binder().self_ty().kind() {
2018 ty::Closure(..) => "closure",
2019 ty::Generator(..) => "generator",
2022 let mut err = struct_span_err!(
2026 "type mismatch in {argument_kind} arguments",
2029 err.span_label(span, "expected due to this");
2031 let found_span = found_span.unwrap_or(span);
2032 err.span_label(found_span, "found signature defined here");
2034 let expected = build_fn_sig_ty(self, expected);
2035 let found = build_fn_sig_ty(self, found);
2037 let (expected_str, found_str) = self.cmp(expected, found);
2039 let signature_kind = format!("{argument_kind} signature");
2040 err.note_expected_found(&signature_kind, expected_str, &signature_kind, found_str);
2042 self.note_conflicting_closure_bounds(cause, &mut err);
2044 if let Some(found_node) = found_node {
2045 hint_missing_borrow(self, param_env, span, found, expected, found_node, &mut err);
2051 // Add a note if there are two `Fn`-family bounds that have conflicting argument
2052 // requirements, which will always cause a closure to have a type error.
2053 fn note_conflicting_closure_bounds(
2055 cause: &ObligationCauseCode<'tcx>,
2056 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
2058 // First, look for an `ExprBindingObligation`, which means we can get
2059 // the unsubstituted predicate list of the called function. And check
2060 // that the predicate that we failed to satisfy is a `Fn`-like trait.
2061 if let ObligationCauseCode::ExprBindingObligation(def_id, _, _, idx) = cause
2062 && let predicates = self.tcx.predicates_of(def_id).instantiate_identity(self.tcx)
2063 && let Some(pred) = predicates.predicates.get(*idx)
2064 && let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = pred.kind().skip_binder()
2065 && self.tcx.is_fn_trait(trait_pred.def_id())
2068 self.tcx.anonymize_bound_vars(pred.kind().rebind(trait_pred.self_ty()));
2069 let expected_substs = self
2071 .anonymize_bound_vars(pred.kind().rebind(trait_pred.trait_ref.substs));
2073 // Find another predicate whose self-type is equal to the expected self type,
2074 // but whose substs don't match.
2075 let other_pred = predicates.into_iter()
2077 .find(|(other_idx, (pred, _))| match pred.kind().skip_binder() {
2078 ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred))
2079 if self.tcx.is_fn_trait(trait_pred.def_id())
2081 // Make sure that the self type matches
2082 // (i.e. constraining this closure)
2084 == self.tcx.anonymize_bound_vars(
2085 pred.kind().rebind(trait_pred.self_ty()),
2087 // But the substs don't match (i.e. incompatible args)
2089 != self.tcx.anonymize_bound_vars(
2090 pred.kind().rebind(trait_pred.trait_ref.substs),
2097 // If we found one, then it's very likely the cause of the error.
2098 if let Some((_, (_, other_pred_span))) = other_pred {
2101 "closure inferred to have a different signature due to this bound",
2107 fn suggest_fully_qualified_path(
2109 err: &mut Diagnostic,
2114 if let Some(assoc_item) = self.tcx.opt_associated_item(item_def_id) {
2115 if let ty::AssocKind::Const | ty::AssocKind::Type = assoc_item.kind {
2117 "{}s cannot be accessed directly on a `trait`, they can only be \
2118 accessed through a specific `impl`",
2119 assoc_item.kind.as_def_kind().descr(item_def_id)
2121 err.span_suggestion(
2123 "use the fully qualified path to an implementation",
2124 format!("<Type as {}>::{}", self.tcx.def_path_str(trait_ref), assoc_item.name),
2125 Applicability::HasPlaceholders,
2131 /// Adds an async-await specific note to the diagnostic when the future does not implement
2132 /// an auto trait because of a captured type.
2135 /// note: future does not implement `Qux` as this value is used across an await
2136 /// --> $DIR/issue-64130-3-other.rs:17:5
2138 /// LL | let x = Foo;
2139 /// | - has type `Foo`
2140 /// LL | baz().await;
2141 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
2143 /// | - `x` is later dropped here
2146 /// When the diagnostic does not implement `Send` or `Sync` specifically, then the diagnostic
2147 /// is "replaced" with a different message and a more specific error.
2150 /// error: future cannot be sent between threads safely
2151 /// --> $DIR/issue-64130-2-send.rs:21:5
2153 /// LL | fn is_send<T: Send>(t: T) { }
2154 /// | ---- required by this bound in `is_send`
2156 /// LL | is_send(bar());
2157 /// | ^^^^^^^ future returned by `bar` is not send
2159 /// = help: within `impl std::future::Future`, the trait `std::marker::Send` is not
2160 /// implemented for `Foo`
2161 /// note: future is not send as this value is used across an await
2162 /// --> $DIR/issue-64130-2-send.rs:15:5
2164 /// LL | let x = Foo;
2165 /// | - has type `Foo`
2166 /// LL | baz().await;
2167 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
2169 /// | - `x` is later dropped here
2172 /// Returns `true` if an async-await specific note was added to the diagnostic.
2173 #[instrument(level = "debug", skip_all, fields(?obligation.predicate, ?obligation.cause.span))]
2174 fn maybe_note_obligation_cause_for_async_await(
2176 err: &mut Diagnostic,
2177 obligation: &PredicateObligation<'tcx>,
2179 let hir = self.tcx.hir();
2181 // Attempt to detect an async-await error by looking at the obligation causes, looking
2182 // for a generator to be present.
2184 // When a future does not implement a trait because of a captured type in one of the
2185 // generators somewhere in the call stack, then the result is a chain of obligations.
2187 // Given an `async fn` A that calls an `async fn` B which captures a non-send type and that
2188 // future is passed as an argument to a function C which requires a `Send` type, then the
2189 // chain looks something like this:
2191 // - `BuiltinDerivedObligation` with a generator witness (B)
2192 // - `BuiltinDerivedObligation` with a generator (B)
2193 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
2194 // - `BuiltinDerivedObligation` with a generator witness (A)
2195 // - `BuiltinDerivedObligation` with a generator (A)
2196 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
2197 // - `BindingObligation` with `impl_send (Send requirement)
2199 // The first obligation in the chain is the most useful and has the generator that captured
2200 // the type. The last generator (`outer_generator` below) has information about where the
2201 // bound was introduced. At least one generator should be present for this diagnostic to be
2203 let (mut trait_ref, mut target_ty) = match obligation.predicate.kind().skip_binder() {
2204 ty::PredicateKind::Clause(ty::Clause::Trait(p)) => (Some(p), Some(p.self_ty())),
2207 let mut generator = None;
2208 let mut outer_generator = None;
2209 let mut next_code = Some(obligation.cause.code());
2211 let mut seen_upvar_tys_infer_tuple = false;
2213 while let Some(code) = next_code {
2216 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
2217 next_code = Some(parent_code);
2219 ObligationCauseCode::ImplDerivedObligation(cause) => {
2220 let ty = cause.derived.parent_trait_pred.skip_binder().self_ty();
2222 parent_trait_ref = ?cause.derived.parent_trait_pred,
2223 self_ty.kind = ?ty.kind(),
2228 ty::Generator(did, ..) | ty::GeneratorWitnessMIR(did, _) => {
2229 generator = generator.or(Some(did));
2230 outer_generator = Some(did);
2232 ty::GeneratorWitness(..) => {}
2233 ty::Tuple(_) if !seen_upvar_tys_infer_tuple => {
2234 // By introducing a tuple of upvar types into the chain of obligations
2235 // of a generator, the first non-generator item is now the tuple itself,
2236 // we shall ignore this.
2238 seen_upvar_tys_infer_tuple = true;
2240 _ if generator.is_none() => {
2241 trait_ref = Some(cause.derived.parent_trait_pred.skip_binder());
2242 target_ty = Some(ty);
2247 next_code = Some(&cause.derived.parent_code);
2249 ObligationCauseCode::DerivedObligation(derived_obligation)
2250 | ObligationCauseCode::BuiltinDerivedObligation(derived_obligation) => {
2251 let ty = derived_obligation.parent_trait_pred.skip_binder().self_ty();
2253 parent_trait_ref = ?derived_obligation.parent_trait_pred,
2254 self_ty.kind = ?ty.kind(),
2258 ty::Generator(did, ..) | ty::GeneratorWitnessMIR(did, ..) => {
2259 generator = generator.or(Some(did));
2260 outer_generator = Some(did);
2262 ty::GeneratorWitness(..) => {}
2263 ty::Tuple(_) if !seen_upvar_tys_infer_tuple => {
2264 // By introducing a tuple of upvar types into the chain of obligations
2265 // of a generator, the first non-generator item is now the tuple itself,
2266 // we shall ignore this.
2268 seen_upvar_tys_infer_tuple = true;
2270 _ if generator.is_none() => {
2271 trait_ref = Some(derived_obligation.parent_trait_pred.skip_binder());
2272 target_ty = Some(ty);
2277 next_code = Some(&derived_obligation.parent_code);
2283 // Only continue if a generator was found.
2284 debug!(?generator, ?trait_ref, ?target_ty);
2285 let (Some(generator_did), Some(trait_ref), Some(target_ty)) = (generator, trait_ref, target_ty) else {
2289 let span = self.tcx.def_span(generator_did);
2291 let generator_did_root = self.tcx.typeck_root_def_id(generator_did);
2294 ?generator_did_root,
2295 typeck_results.hir_owner = ?self.typeck_results.as_ref().map(|t| t.hir_owner),
2299 let generator_body = generator_did
2301 .and_then(|def_id| hir.maybe_body_owned_by(def_id))
2302 .map(|body_id| hir.body(body_id));
2303 let mut visitor = AwaitsVisitor::default();
2304 if let Some(body) = generator_body {
2305 visitor.visit_body(body);
2307 debug!(awaits = ?visitor.awaits);
2309 // Look for a type inside the generator interior that matches the target type to get
2311 let target_ty_erased = self.tcx.erase_regions(target_ty);
2312 let ty_matches = |ty| -> bool {
2313 // Careful: the regions for types that appear in the
2314 // generator interior are not generally known, so we
2315 // want to erase them when comparing (and anyway,
2316 // `Send` and other bounds are generally unaffected by
2317 // the choice of region). When erasing regions, we
2318 // also have to erase late-bound regions. This is
2319 // because the types that appear in the generator
2320 // interior generally contain "bound regions" to
2321 // represent regions that are part of the suspended
2322 // generator frame. Bound regions are preserved by
2323 // `erase_regions` and so we must also call
2324 // `erase_late_bound_regions`.
2325 let ty_erased = self.tcx.erase_late_bound_regions(ty);
2326 let ty_erased = self.tcx.erase_regions(ty_erased);
2327 let eq = ty_erased == target_ty_erased;
2328 debug!(?ty_erased, ?target_ty_erased, ?eq);
2332 // Get the typeck results from the infcx if the generator is the function we are currently
2333 // type-checking; otherwise, get them by performing a query. This is needed to avoid
2334 // cycles. If we can't use resolved types because the generator comes from another crate,
2335 // we still provide a targeted error but without all the relevant spans.
2336 let generator_data = match &self.typeck_results {
2337 Some(t) if t.hir_owner.to_def_id() == generator_did_root => GeneratorData::Local(&t),
2338 _ if generator_did.is_local() => {
2339 GeneratorData::Local(self.tcx.typeck(generator_did.expect_local()))
2341 _ if let Some(generator_diag_data) = self.tcx.generator_diagnostic_data(generator_did) => {
2342 GeneratorData::Foreign(generator_diag_data)
2347 let generator_within_in_progress_typeck = match &self.typeck_results {
2348 Some(t) => t.hir_owner.to_def_id() == generator_did_root,
2352 let mut interior_or_upvar_span = None;
2354 let from_awaited_ty = generator_data.get_from_await_ty(visitor, hir, ty_matches);
2355 debug!(?from_awaited_ty);
2357 // The generator interior types share the same binders
2358 if let Some(cause) =
2359 generator_data.get_generator_interior_types().skip_binder().iter().find(
2360 |ty::GeneratorInteriorTypeCause { ty, .. }| {
2361 ty_matches(generator_data.get_generator_interior_types().rebind(*ty))
2365 let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } = cause;
2367 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(
2369 Some((*scope_span, *yield_span, *expr, from_awaited_ty)),
2372 if interior_or_upvar_span.is_none() && generator_data.is_foreign() {
2373 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(*span, None));
2375 } else if self.tcx.sess.opts.unstable_opts.drop_tracking_mir
2376 // Avoid disclosing internal information to downstream crates.
2377 && generator_did.is_local()
2378 // Try to avoid cycles.
2379 && !generator_within_in_progress_typeck
2381 let generator_info = &self.tcx.mir_generator_witnesses(generator_did);
2382 debug!(?generator_info);
2384 'find_source: for (variant, source_info) in
2385 generator_info.variant_fields.iter().zip(&generator_info.variant_source_info)
2388 for &local in variant {
2389 let decl = &generator_info.field_tys[local];
2391 if ty_matches(ty::Binder::dummy(decl.ty)) && !decl.ignore_for_traits {
2392 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(
2393 decl.source_info.span,
2394 Some((None, source_info.span, None, from_awaited_ty)),
2402 if interior_or_upvar_span.is_none() {
2403 interior_or_upvar_span =
2404 generator_data.try_get_upvar_span(&self, generator_did, ty_matches);
2407 if interior_or_upvar_span.is_none() && generator_data.is_foreign() {
2408 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(span, None));
2411 debug!(?interior_or_upvar_span);
2412 if let Some(interior_or_upvar_span) = interior_or_upvar_span {
2413 let is_async = self.tcx.generator_is_async(generator_did);
2414 let typeck_results = match generator_data {
2415 GeneratorData::Local(typeck_results) => Some(typeck_results),
2416 GeneratorData::Foreign(_) => None,
2418 self.note_obligation_cause_for_async_await(
2420 interior_or_upvar_span,
2435 /// Unconditionally adds the diagnostic note described in
2436 /// `maybe_note_obligation_cause_for_async_await`'s documentation comment.
2437 #[instrument(level = "debug", skip_all)]
2438 fn note_obligation_cause_for_async_await(
2440 err: &mut Diagnostic,
2441 interior_or_upvar_span: GeneratorInteriorOrUpvar,
2443 outer_generator: Option<DefId>,
2444 trait_pred: ty::TraitPredicate<'tcx>,
2445 target_ty: Ty<'tcx>,
2446 typeck_results: Option<&ty::TypeckResults<'tcx>>,
2447 obligation: &PredicateObligation<'tcx>,
2448 next_code: Option<&ObligationCauseCode<'tcx>>,
2450 let source_map = self.tcx.sess.source_map();
2452 let (await_or_yield, an_await_or_yield) =
2453 if is_async { ("await", "an await") } else { ("yield", "a yield") };
2454 let future_or_generator = if is_async { "future" } else { "generator" };
2456 // Special case the primary error message when send or sync is the trait that was
2458 let hir = self.tcx.hir();
2459 let trait_explanation = if let Some(name @ (sym::Send | sym::Sync)) =
2460 self.tcx.get_diagnostic_name(trait_pred.def_id())
2462 let (trait_name, trait_verb) =
2463 if name == sym::Send { ("`Send`", "sent") } else { ("`Sync`", "shared") };
2466 err.set_primary_message(format!(
2467 "{} cannot be {} between threads safely",
2468 future_or_generator, trait_verb
2471 let original_span = err.span.primary_span().unwrap();
2472 let mut span = MultiSpan::from_span(original_span);
2474 let message = outer_generator
2475 .and_then(|generator_did| {
2476 Some(match self.tcx.generator_kind(generator_did).unwrap() {
2477 GeneratorKind::Gen => format!("generator is not {}", trait_name),
2478 GeneratorKind::Async(AsyncGeneratorKind::Fn) => self
2480 .parent(generator_did)
2482 .map(|parent_did| hir.local_def_id_to_hir_id(parent_did))
2483 .and_then(|parent_hir_id| hir.opt_name(parent_hir_id))
2485 format!("future returned by `{}` is not {}", name, trait_name)
2487 GeneratorKind::Async(AsyncGeneratorKind::Block) => {
2488 format!("future created by async block is not {}", trait_name)
2490 GeneratorKind::Async(AsyncGeneratorKind::Closure) => {
2491 format!("future created by async closure is not {}", trait_name)
2495 .unwrap_or_else(|| format!("{} is not {}", future_or_generator, trait_name));
2497 span.push_span_label(original_span, message);
2500 format!("is not {}", trait_name)
2502 format!("does not implement `{}`", trait_pred.print_modifiers_and_trait_path())
2505 let mut explain_yield =
2506 |interior_span: Span, yield_span: Span, scope_span: Option<Span>| {
2507 let mut span = MultiSpan::from_span(yield_span);
2508 let snippet = match source_map.span_to_snippet(interior_span) {
2509 // #70935: If snippet contains newlines, display "the value" instead
2510 // so that we do not emit complex diagnostics.
2511 Ok(snippet) if !snippet.contains('\n') => format!("`{}`", snippet),
2512 _ => "the value".to_string(),
2514 // note: future is not `Send` as this value is used across an await
2515 // --> $DIR/issue-70935-complex-spans.rs:13:9
2517 // LL | baz(|| async {
2518 // | ______________-
2521 // LL | | foo(tx.clone());
2523 // | | - ^^^^^^ await occurs here, with value maybe used later
2525 // | has type `closure` which is not `Send`
2526 // note: value is later dropped here
2530 span.push_span_label(
2532 format!("{} occurs here, with {} maybe used later", await_or_yield, snippet),
2534 span.push_span_label(
2536 format!("has type `{}` which {}", target_ty, trait_explanation),
2538 if let Some(scope_span) = scope_span {
2539 let scope_span = source_map.end_point(scope_span);
2541 let msg = format!("{} is later dropped here", snippet);
2542 span.push_span_label(scope_span, msg);
2547 "{} {} as this value is used across {}",
2548 future_or_generator, trait_explanation, an_await_or_yield
2552 match interior_or_upvar_span {
2553 GeneratorInteriorOrUpvar::Interior(interior_span, interior_extra_info) => {
2554 if let Some((scope_span, yield_span, expr, from_awaited_ty)) = interior_extra_info {
2555 if let Some(await_span) = from_awaited_ty {
2556 // The type causing this obligation is one being awaited at await_span.
2557 let mut span = MultiSpan::from_span(await_span);
2558 span.push_span_label(
2561 "await occurs here on type `{}`, which {}",
2562 target_ty, trait_explanation
2568 "future {not_trait} as it awaits another future which {not_trait}",
2569 not_trait = trait_explanation
2573 // Look at the last interior type to get a span for the `.await`.
2575 generator_interior_types = ?format_args!(
2576 "{:#?}", typeck_results.as_ref().map(|t| &t.generator_interior_types)
2579 explain_yield(interior_span, yield_span, scope_span);
2582 if let Some(expr_id) = expr {
2583 let expr = hir.expect_expr(expr_id);
2584 debug!("target_ty evaluated from {:?}", expr);
2586 let parent = hir.parent_id(expr_id);
2587 if let Some(hir::Node::Expr(e)) = hir.find(parent) {
2588 let parent_span = hir.span(parent);
2589 let parent_did = parent.owner.to_def_id();
2592 // fn foo(&self) -> i32 {}
2595 // ^^^^^^^ a temporary `&T` created inside this method call due to `&self`
2598 let is_region_borrow = if let Some(typeck_results) = typeck_results {
2600 .expr_adjustments(expr)
2602 .any(|adj| adj.is_region_borrow())
2608 // struct Foo(*const u8);
2609 // bar(Foo(std::ptr::null())).await;
2610 // ^^^^^^^^^^^^^^^^^^^^^ raw-ptr `*T` created inside this struct ctor.
2612 debug!(parent_def_kind = ?self.tcx.def_kind(parent_did));
2613 let is_raw_borrow_inside_fn_like_call =
2614 match self.tcx.def_kind(parent_did) {
2615 DefKind::Fn | DefKind::Ctor(..) => target_ty.is_unsafe_ptr(),
2618 if let Some(typeck_results) = typeck_results {
2619 if (typeck_results.is_method_call(e) && is_region_borrow)
2620 || is_raw_borrow_inside_fn_like_call
2624 "consider moving this into a `let` \
2625 binding to create a shorter lived borrow",
2633 GeneratorInteriorOrUpvar::Upvar(upvar_span) => {
2634 // `Some((ref_ty, is_mut))` if `target_ty` is `&T` or `&mut T` and fails to impl `Send`
2635 let non_send = match target_ty.kind() {
2636 ty::Ref(_, ref_ty, mutability) => match self.evaluate_obligation(&obligation) {
2637 Ok(eval) if !eval.may_apply() => Some((ref_ty, mutability.is_mut())),
2643 let (span_label, span_note) = match non_send {
2644 // if `target_ty` is `&T` or `&mut T` and fails to impl `Send`,
2645 // include suggestions to make `T: Sync` so that `&T: Send`,
2646 // or to make `T: Send` so that `&mut T: Send`
2647 Some((ref_ty, is_mut)) => {
2648 let ref_ty_trait = if is_mut { "Send" } else { "Sync" };
2649 let ref_kind = if is_mut { "&mut" } else { "&" };
2652 "has type `{}` which {}, because `{}` is not `{}`",
2653 target_ty, trait_explanation, ref_ty, ref_ty_trait
2656 "captured value {} because `{}` references cannot be sent unless their referent is `{}`",
2657 trait_explanation, ref_kind, ref_ty_trait
2662 format!("has type `{}` which {}", target_ty, trait_explanation),
2663 format!("captured value {}", trait_explanation),
2667 let mut span = MultiSpan::from_span(upvar_span);
2668 span.push_span_label(upvar_span, span_label);
2669 err.span_note(span, &span_note);
2673 // Add a note for the item obligation that remains - normally a note pointing to the
2674 // bound that introduced the obligation (e.g. `T: Send`).
2676 self.note_obligation_cause_code(
2678 obligation.predicate,
2679 obligation.param_env,
2682 &mut Default::default(),
2686 fn note_obligation_cause_code<T>(
2688 err: &mut Diagnostic,
2690 param_env: ty::ParamEnv<'tcx>,
2691 cause_code: &ObligationCauseCode<'tcx>,
2692 obligated_types: &mut Vec<Ty<'tcx>>,
2693 seen_requirements: &mut FxHashSet<DefId>,
2695 T: ToPredicate<'tcx>,
2698 let predicate = predicate.to_predicate(tcx);
2700 ObligationCauseCode::ExprAssignable
2701 | ObligationCauseCode::MatchExpressionArm { .. }
2702 | ObligationCauseCode::Pattern { .. }
2703 | ObligationCauseCode::IfExpression { .. }
2704 | ObligationCauseCode::IfExpressionWithNoElse
2705 | ObligationCauseCode::MainFunctionType
2706 | ObligationCauseCode::StartFunctionType
2707 | ObligationCauseCode::IntrinsicType
2708 | ObligationCauseCode::MethodReceiver
2709 | ObligationCauseCode::ReturnNoExpression
2710 | ObligationCauseCode::UnifyReceiver(..)
2711 | ObligationCauseCode::OpaqueType
2712 | ObligationCauseCode::MiscObligation
2713 | ObligationCauseCode::WellFormed(..)
2714 | ObligationCauseCode::MatchImpl(..)
2715 | ObligationCauseCode::ReturnType
2716 | ObligationCauseCode::ReturnValue(_)
2717 | ObligationCauseCode::BlockTailExpression(_)
2718 | ObligationCauseCode::AwaitableExpr(_)
2719 | ObligationCauseCode::ForLoopIterator
2720 | ObligationCauseCode::QuestionMark
2721 | ObligationCauseCode::CheckAssociatedTypeBounds { .. }
2722 | ObligationCauseCode::LetElse
2723 | ObligationCauseCode::BinOp { .. }
2724 | ObligationCauseCode::AscribeUserTypeProvePredicate(..)
2725 | ObligationCauseCode::RustCall => {}
2726 ObligationCauseCode::SliceOrArrayElem => {
2727 err.note("slice and array elements must have `Sized` type");
2729 ObligationCauseCode::TupleElem => {
2730 err.note("only the last element of a tuple may have a dynamically sized type");
2732 ObligationCauseCode::ProjectionWf(data) => {
2733 err.note(&format!("required so that the projection `{data}` is well-formed"));
2735 ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
2737 "required so that reference `{ref_ty}` does not outlive its referent"
2740 ObligationCauseCode::ObjectTypeBound(object_ty, region) => {
2742 "required so that the lifetime bound of `{}` for `{}` is satisfied",
2746 ObligationCauseCode::ItemObligation(_)
2747 | ObligationCauseCode::ExprItemObligation(..) => {
2748 // We hold the `DefId` of the item introducing the obligation, but displaying it
2749 // doesn't add user usable information. It always point at an associated item.
2751 ObligationCauseCode::BindingObligation(item_def_id, span)
2752 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..) => {
2753 let item_name = tcx.def_path_str(item_def_id);
2754 let short_item_name = with_forced_trimmed_paths!(tcx.def_path_str(item_def_id));
2755 let mut multispan = MultiSpan::from(span);
2756 let sm = tcx.sess.source_map();
2757 if let Some(ident) = tcx.opt_item_ident(item_def_id) {
2759 match (sm.lookup_line(ident.span.hi()), sm.lookup_line(span.lo())) {
2760 (Ok(l), Ok(r)) => l.line == r.line,
2763 if ident.span.is_visible(sm) && !ident.span.overlaps(span) && !same_line {
2764 multispan.push_span_label(ident.span, "required by a bound in this");
2767 let descr = format!("required by a bound in `{item_name}`");
2768 if span.is_visible(sm) {
2769 let msg = format!("required by this bound in `{short_item_name}`");
2770 multispan.push_span_label(span, msg);
2771 err.span_note(multispan, &descr);
2773 err.span_note(tcx.def_span(item_def_id), &descr);
2776 ObligationCauseCode::ObjectCastObligation(concrete_ty, object_ty) => {
2777 let (concrete_ty, concrete_file) =
2778 self.tcx.short_ty_string(self.resolve_vars_if_possible(concrete_ty));
2779 let (object_ty, object_file) =
2780 self.tcx.short_ty_string(self.resolve_vars_if_possible(object_ty));
2781 err.note(&with_forced_trimmed_paths!(format!(
2782 "required for the cast from `{concrete_ty}` to the object type `{object_ty}`",
2784 if let Some(file) = concrete_file {
2786 "the full name for the casted type has been written to '{}'",
2790 if let Some(file) = object_file {
2792 "the full name for the object type has been written to '{}'",
2797 ObligationCauseCode::Coercion { source: _, target } => {
2798 err.note(&format!("required by cast to type `{}`", self.ty_to_string(target)));
2800 ObligationCauseCode::RepeatElementCopy { is_const_fn } => {
2802 "the `Copy` trait is required because this value will be copied for each element of the array",
2807 "consider creating a new `const` item and initializing it with the result \
2808 of the function call to be used in the repeat position, like \
2809 `const VAL: Type = const_fn();` and `let x = [VAL; 42];`",
2813 if self.tcx.sess.is_nightly_build() && is_const_fn {
2815 "create an inline `const` block, see RFC #2920 \
2816 <https://github.com/rust-lang/rfcs/pull/2920> for more information",
2820 ObligationCauseCode::VariableType(hir_id) => {
2821 let parent_node = self.tcx.hir().parent_id(hir_id);
2822 match self.tcx.hir().find(parent_node) {
2823 Some(Node::Local(hir::Local { ty: Some(ty), .. })) => {
2824 err.span_suggestion_verbose(
2825 ty.span.shrink_to_lo(),
2826 "consider borrowing here",
2828 Applicability::MachineApplicable,
2830 err.note("all local variables must have a statically known size");
2832 Some(Node::Local(hir::Local {
2833 init: Some(hir::Expr { kind: hir::ExprKind::Index(_, _), span, .. }),
2836 // When encountering an assignment of an unsized trait, like
2837 // `let x = ""[..];`, provide a suggestion to borrow the initializer in
2838 // order to use have a slice instead.
2839 err.span_suggestion_verbose(
2840 span.shrink_to_lo(),
2841 "consider borrowing here",
2843 Applicability::MachineApplicable,
2845 err.note("all local variables must have a statically known size");
2847 Some(Node::Param(param)) => {
2848 err.span_suggestion_verbose(
2849 param.ty_span.shrink_to_lo(),
2850 "function arguments must have a statically known size, borrowed types \
2851 always have a known size",
2853 Applicability::MachineApplicable,
2857 err.note("all local variables must have a statically known size");
2860 if !self.tcx.features().unsized_locals {
2861 err.help("unsized locals are gated as an unstable feature");
2864 ObligationCauseCode::SizedArgumentType(sp) => {
2865 if let Some(span) = sp {
2866 if let ty::PredicateKind::Clause(clause) = predicate.kind().skip_binder()
2867 && let ty::Clause::Trait(trait_pred) = clause
2868 && let ty::Dynamic(..) = trait_pred.self_ty().kind()
2870 let span = if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
2871 && snippet.starts_with("dyn ")
2873 let pos = snippet.len() - snippet[3..].trim_start().len();
2874 span.with_hi(span.lo() + BytePos(pos as u32))
2878 err.span_suggestion_verbose(
2880 "you can use `impl Trait` as the argument type",
2881 "impl ".to_string(),
2882 Applicability::MaybeIncorrect,
2885 err.span_suggestion_verbose(
2886 span.shrink_to_lo(),
2887 "function arguments must have a statically known size, borrowed types \
2888 always have a known size",
2890 Applicability::MachineApplicable,
2893 err.note("all function arguments must have a statically known size");
2895 if tcx.sess.opts.unstable_features.is_nightly_build()
2896 && !self.tcx.features().unsized_fn_params
2898 err.help("unsized fn params are gated as an unstable feature");
2901 ObligationCauseCode::SizedReturnType => {
2902 err.note("the return type of a function must have a statically known size");
2904 ObligationCauseCode::SizedYieldType => {
2905 err.note("the yield type of a generator must have a statically known size");
2907 ObligationCauseCode::SizedBoxType => {
2908 err.note("the type of a box expression must have a statically known size");
2910 ObligationCauseCode::AssignmentLhsSized => {
2911 err.note("the left-hand-side of an assignment must have a statically known size");
2913 ObligationCauseCode::TupleInitializerSized => {
2914 err.note("tuples must have a statically known size to be initialized");
2916 ObligationCauseCode::StructInitializerSized => {
2917 err.note("structs must have a statically known size to be initialized");
2919 ObligationCauseCode::FieldSized { adt_kind: ref item, last, span } => {
2921 AdtKind::Struct => {
2924 "the last field of a packed struct may only have a \
2925 dynamically sized type if it does not need drop to be run",
2929 "only the last field of a struct may have a dynamically sized type",
2934 err.note("no field of a union may have a dynamically sized type");
2937 err.note("no field of an enum variant may have a dynamically sized type");
2940 err.help("change the field's type to have a statically known size");
2941 err.span_suggestion(
2942 span.shrink_to_lo(),
2943 "borrowed types always have a statically known size",
2945 Applicability::MachineApplicable,
2947 err.multipart_suggestion(
2948 "the `Box` type always has a statically known size and allocates its contents \
2951 (span.shrink_to_lo(), "Box<".to_string()),
2952 (span.shrink_to_hi(), ">".to_string()),
2954 Applicability::MachineApplicable,
2957 ObligationCauseCode::ConstSized => {
2958 err.note("constant expressions must have a statically known size");
2960 ObligationCauseCode::InlineAsmSized => {
2961 err.note("all inline asm arguments must have a statically known size");
2963 ObligationCauseCode::ConstPatternStructural => {
2964 err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`");
2966 ObligationCauseCode::SharedStatic => {
2967 err.note("shared static variables must have a type that implements `Sync`");
2969 ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
2970 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2971 let ty = parent_trait_ref.skip_binder().self_ty();
2972 if parent_trait_ref.references_error() {
2973 // NOTE(eddyb) this was `.cancel()`, but `err`
2974 // is borrowed, so we can't fully defuse it.
2975 err.downgrade_to_delayed_bug();
2979 // If the obligation for a tuple is set directly by a Generator or Closure,
2980 // then the tuple must be the one containing capture types.
2981 let is_upvar_tys_infer_tuple = if !matches!(ty.kind(), ty::Tuple(..)) {
2984 if let ObligationCauseCode::BuiltinDerivedObligation(data) = &*data.parent_code
2986 let parent_trait_ref =
2987 self.resolve_vars_if_possible(data.parent_trait_pred);
2988 let nested_ty = parent_trait_ref.skip_binder().self_ty();
2989 matches!(nested_ty.kind(), ty::Generator(..))
2990 || matches!(nested_ty.kind(), ty::Closure(..))
2996 let identity_future = tcx.require_lang_item(LangItem::IdentityFuture, None);
2998 // Don't print the tuple of capture types
3000 if !is_upvar_tys_infer_tuple {
3001 let msg = with_forced_trimmed_paths!(format!(
3002 "required because it appears within the type `{ty}`",
3005 ty::Adt(def, _) => match self.tcx.opt_item_ident(def.did()) {
3006 Some(ident) => err.span_note(ident.span, &msg),
3007 None => err.note(&msg),
3009 ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) => {
3010 // Avoid printing the future from `core::future::identity_future`, it's not helpful
3011 if tcx.parent(*def_id) == identity_future {
3015 // If the previous type is `identity_future`, this is the future generated by the body of an async function.
3016 // Avoid printing it twice (it was already printed in the `ty::Generator` arm below).
3017 let is_future = tcx.ty_is_opaque_future(ty);
3021 "note_obligation_cause_code: check for async fn"
3024 && obligated_types.last().map_or(false, |ty| match ty.kind() {
3025 ty::Generator(last_def_id, ..) => {
3026 tcx.generator_is_async(*last_def_id)
3033 err.span_note(self.tcx.def_span(def_id), &msg)
3035 ty::GeneratorWitness(bound_tys) => {
3036 use std::fmt::Write;
3038 // FIXME: this is kind of an unusual format for rustc, can we make it more clear?
3039 // Maybe we should just remove this note altogether?
3040 // FIXME: only print types which don't meet the trait requirement
3042 "required because it captures the following types: ".to_owned();
3043 for ty in bound_tys.skip_binder() {
3044 with_forced_trimmed_paths!(write!(msg, "`{}`, ", ty).unwrap());
3046 err.note(msg.trim_end_matches(", "))
3048 ty::GeneratorWitnessMIR(def_id, substs) => {
3049 use std::fmt::Write;
3051 // FIXME: this is kind of an unusual format for rustc, can we make it more clear?
3052 // Maybe we should just remove this note altogether?
3053 // FIXME: only print types which don't meet the trait requirement
3055 "required because it captures the following types: ".to_owned();
3056 for bty in tcx.generator_hidden_types(*def_id) {
3057 let ty = bty.subst(tcx, substs);
3058 write!(msg, "`{}`, ", ty).unwrap();
3060 err.note(msg.trim_end_matches(", "))
3062 ty::Generator(def_id, _, _) => {
3063 let sp = self.tcx.def_span(def_id);
3065 // Special-case this to say "async block" instead of `[static generator]`.
3066 let kind = tcx.generator_kind(def_id).unwrap().descr();
3069 with_forced_trimmed_paths!(&format!(
3070 "required because it's used within this {kind}",
3074 ty::Closure(def_id, _) => err.span_note(
3075 self.tcx.def_span(def_id),
3076 "required because it's used within this closure",
3078 _ => err.note(&msg),
3083 obligated_types.push(ty);
3085 let parent_predicate = parent_trait_ref;
3086 if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
3087 // #74711: avoid a stack overflow
3088 ensure_sufficient_stack(|| {
3089 self.note_obligation_cause_code(
3099 ensure_sufficient_stack(|| {
3100 self.note_obligation_cause_code(
3104 cause_code.peel_derives(),
3111 ObligationCauseCode::ImplDerivedObligation(ref data) => {
3112 let mut parent_trait_pred =
3113 self.resolve_vars_if_possible(data.derived.parent_trait_pred);
3114 parent_trait_pred.remap_constness_diag(param_env);
3115 let parent_def_id = parent_trait_pred.def_id();
3116 let (self_ty, file) =
3117 self.tcx.short_ty_string(parent_trait_pred.skip_binder().self_ty());
3119 "required for `{self_ty}` to implement `{}`",
3120 parent_trait_pred.print_modifiers_and_trait_path()
3122 let mut is_auto_trait = false;
3123 match self.tcx.hir().get_if_local(data.impl_def_id) {
3124 Some(Node::Item(hir::Item {
3125 kind: hir::ItemKind::Trait(is_auto, ..),
3129 // FIXME: we should do something else so that it works even on crate foreign
3131 is_auto_trait = matches!(is_auto, hir::IsAuto::Yes);
3132 err.span_note(ident.span, &msg);
3134 Some(Node::Item(hir::Item {
3135 kind: hir::ItemKind::Impl(hir::Impl { of_trait, self_ty, .. }),
3138 let mut spans = Vec::with_capacity(2);
3139 if let Some(trait_ref) = of_trait {
3140 spans.push(trait_ref.path.span);
3142 spans.push(self_ty.span);
3143 let mut spans: MultiSpan = spans.into();
3145 self_ty.span.ctxt().outer_expn_data().kind,
3146 ExpnKind::Macro(MacroKind::Derive, _)
3148 of_trait.as_ref().map(|t| t.path.span.ctxt().outer_expn_data().kind),
3149 Some(ExpnKind::Macro(MacroKind::Derive, _))
3151 spans.push_span_label(
3153 "unsatisfied trait bound introduced in this `derive` macro",
3155 } else if !data.span.is_dummy() && !data.span.overlaps(self_ty.span) {
3156 spans.push_span_label(
3158 "unsatisfied trait bound introduced here",
3161 err.span_note(spans, &msg);
3168 if let Some(file) = file {
3170 "the full type name has been written to '{}'",
3174 let mut parent_predicate = parent_trait_pred;
3175 let mut data = &data.derived;
3177 seen_requirements.insert(parent_def_id);
3179 // We don't want to point at the ADT saying "required because it appears within
3180 // the type `X`", like we would otherwise do in test `supertrait-auto-trait.rs`.
3181 while let ObligationCauseCode::BuiltinDerivedObligation(derived) =
3184 let child_trait_ref =
3185 self.resolve_vars_if_possible(derived.parent_trait_pred);
3186 let child_def_id = child_trait_ref.def_id();
3187 if seen_requirements.insert(child_def_id) {
3191 parent_predicate = child_trait_ref.to_predicate(tcx);
3192 parent_trait_pred = child_trait_ref;
3195 while let ObligationCauseCode::ImplDerivedObligation(child) = &*data.parent_code {
3196 // Skip redundant recursive obligation notes. See `ui/issue-20413.rs`.
3197 let child_trait_pred =
3198 self.resolve_vars_if_possible(child.derived.parent_trait_pred);
3199 let child_def_id = child_trait_pred.def_id();
3200 if seen_requirements.insert(child_def_id) {
3204 data = &child.derived;
3205 parent_predicate = child_trait_pred.to_predicate(tcx);
3206 parent_trait_pred = child_trait_pred;
3210 "{} redundant requirement{} hidden",
3214 let (self_ty, file) =
3215 self.tcx.short_ty_string(parent_trait_pred.skip_binder().self_ty());
3217 "required for `{self_ty}` to implement `{}`",
3218 parent_trait_pred.print_modifiers_and_trait_path()
3220 if let Some(file) = file {
3222 "the full type name has been written to '{}'",
3227 // #74711: avoid a stack overflow
3228 ensure_sufficient_stack(|| {
3229 self.note_obligation_cause_code(
3239 ObligationCauseCode::DerivedObligation(ref data) => {
3240 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
3241 let parent_predicate = parent_trait_ref;
3242 // #74711: avoid a stack overflow
3243 ensure_sufficient_stack(|| {
3244 self.note_obligation_cause_code(
3254 ObligationCauseCode::FunctionArgumentObligation {
3260 self.note_function_argument_obligation(
3268 ensure_sufficient_stack(|| {
3269 self.note_obligation_cause_code(
3279 ObligationCauseCode::CompareImplItemObligation { trait_item_def_id, kind, .. } => {
3280 let item_name = self.tcx.item_name(trait_item_def_id);
3282 "the requirement `{predicate}` appears on the `impl`'s {kind} \
3283 `{item_name}` but not on the corresponding trait's {kind}",
3287 .opt_item_ident(trait_item_def_id)
3289 .unwrap_or_else(|| self.tcx.def_span(trait_item_def_id));
3290 let mut assoc_span: MultiSpan = sp.into();
3291 assoc_span.push_span_label(
3293 format!("this trait's {kind} doesn't have the requirement `{predicate}`"),
3295 if let Some(ident) = self
3297 .opt_associated_item(trait_item_def_id)
3298 .and_then(|i| self.tcx.opt_item_ident(i.container_id(self.tcx)))
3300 assoc_span.push_span_label(ident.span, "in this trait");
3302 err.span_note(assoc_span, &msg);
3304 ObligationCauseCode::TrivialBound => {
3305 err.help("see issue #48214");
3306 if tcx.sess.opts.unstable_features.is_nightly_build() {
3307 err.help("add `#![feature(trivial_bounds)]` to the crate attributes to enable");
3310 ObligationCauseCode::OpaqueReturnType(expr_info) => {
3311 if let Some((expr_ty, expr_span)) = expr_info {
3312 let expr_ty = with_forced_trimmed_paths!(self.ty_to_string(expr_ty));
3315 with_forced_trimmed_paths!(format!(
3316 "return type was inferred to be `{expr_ty}` here",
3325 level = "debug", skip(self, err), fields(trait_pred.self_ty = ?trait_pred.self_ty())
3327 fn suggest_await_before_try(
3329 err: &mut Diagnostic,
3330 obligation: &PredicateObligation<'tcx>,
3331 trait_pred: ty::PolyTraitPredicate<'tcx>,
3334 if let Some(body_id) = self.tcx.hir().maybe_body_owned_by(obligation.cause.body_id) {
3335 let body = self.tcx.hir().body(body_id);
3336 if let Some(hir::GeneratorKind::Async(_)) = body.generator_kind {
3337 let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
3339 let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
3340 let impls_future = self.type_implements_trait(
3342 [self.tcx.erase_late_bound_regions(self_ty)],
3343 obligation.param_env,
3345 if !impls_future.must_apply_modulo_regions() {
3349 let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0];
3350 // `<T as Future>::Output`
3351 let projection_ty = trait_pred.map_bound(|trait_pred| {
3352 self.tcx.mk_projection(
3354 // Future::Output has no substs
3355 [trait_pred.self_ty()],
3358 let InferOk { value: projection_ty, .. } =
3359 self.at(&obligation.cause, obligation.param_env).normalize(projection_ty);
3362 normalized_projection_type = ?self.resolve_vars_if_possible(projection_ty)
3364 let try_obligation = self.mk_trait_obligation_with_new_self_ty(
3365 obligation.param_env,
3366 trait_pred.map_bound(|trait_pred| (trait_pred, projection_ty.skip_binder())),
3368 debug!(try_trait_obligation = ?try_obligation);
3369 if self.predicate_may_hold(&try_obligation)
3370 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
3371 && snippet.ends_with('?')
3373 err.span_suggestion_verbose(
3374 span.with_hi(span.hi() - BytePos(1)).shrink_to_hi(),
3375 "consider `await`ing on the `Future`",
3377 Applicability::MaybeIncorrect,
3384 fn suggest_floating_point_literal(
3386 obligation: &PredicateObligation<'tcx>,
3387 err: &mut Diagnostic,
3388 trait_ref: &ty::PolyTraitRef<'tcx>,
3390 let rhs_span = match obligation.cause.code() {
3391 ObligationCauseCode::BinOp { rhs_span: Some(span), is_lit, .. } if *is_lit => span,
3394 if let ty::Float(_) = trait_ref.skip_binder().self_ty().kind()
3395 && let ty::Infer(InferTy::IntVar(_)) = trait_ref.skip_binder().substs.type_at(1).kind()
3397 err.span_suggestion_verbose(
3398 rhs_span.shrink_to_hi(),
3399 "consider using a floating-point literal by writing it with `.0`",
3401 Applicability::MaybeIncorrect,
3408 obligation: &PredicateObligation<'tcx>,
3409 err: &mut Diagnostic,
3410 trait_pred: ty::PolyTraitPredicate<'tcx>,
3412 let Some(diagnostic_name) = self.tcx.get_diagnostic_name(trait_pred.def_id()) else {
3415 let (adt, substs) = match trait_pred.skip_binder().self_ty().kind() {
3416 ty::Adt(adt, substs) if adt.did().is_local() => (adt, substs),
3420 let is_derivable_trait = match diagnostic_name {
3421 sym::Default => !adt.is_enum(),
3422 sym::PartialEq | sym::PartialOrd => {
3423 let rhs_ty = trait_pred.skip_binder().trait_ref.substs.type_at(1);
3424 trait_pred.skip_binder().self_ty() == rhs_ty
3426 sym::Eq | sym::Ord | sym::Clone | sym::Copy | sym::Hash | sym::Debug => true,
3429 is_derivable_trait &&
3430 // Ensure all fields impl the trait.
3431 adt.all_fields().all(|field| {
3432 let field_ty = field.ty(self.tcx, substs);
3433 let trait_substs = match diagnostic_name {
3434 sym::PartialEq | sym::PartialOrd => {
3439 let trait_pred = trait_pred.map_bound_ref(|tr| ty::TraitPredicate {
3440 trait_ref: self.tcx.mk_trait_ref(
3441 trait_pred.def_id(),
3442 [field_ty].into_iter().chain(trait_substs),
3446 let field_obl = Obligation::new(
3448 obligation.cause.clone(),
3449 obligation.param_env,
3452 self.predicate_must_hold_modulo_regions(&field_obl)
3456 err.span_suggestion_verbose(
3457 self.tcx.def_span(adt.did()).shrink_to_lo(),
3459 "consider annotating `{}` with `#[derive({})]`",
3460 trait_pred.skip_binder().self_ty(),
3463 format!("#[derive({})]\n", diagnostic_name),
3464 Applicability::MaybeIncorrect,
3469 fn suggest_dereferencing_index(
3471 obligation: &PredicateObligation<'tcx>,
3472 err: &mut Diagnostic,
3473 trait_pred: ty::PolyTraitPredicate<'tcx>,
3475 if let ObligationCauseCode::ImplDerivedObligation(_) = obligation.cause.code()
3476 && self.tcx.is_diagnostic_item(sym::SliceIndex, trait_pred.skip_binder().trait_ref.def_id)
3477 && let ty::Slice(_) = trait_pred.skip_binder().trait_ref.substs.type_at(1).kind()
3478 && let ty::Ref(_, inner_ty, _) = trait_pred.skip_binder().self_ty().kind()
3479 && let ty::Uint(ty::UintTy::Usize) = inner_ty.kind()
3481 err.span_suggestion_verbose(
3482 obligation.cause.span.shrink_to_lo(),
3483 "dereference this index",
3485 Applicability::MachineApplicable,
3489 fn note_function_argument_obligation(
3492 err: &mut Diagnostic,
3493 parent_code: &ObligationCauseCode<'tcx>,
3494 param_env: ty::ParamEnv<'tcx>,
3495 failed_pred: ty::Predicate<'tcx>,
3499 let hir = tcx.hir();
3500 if let Some(Node::Expr(expr)) = hir.find(arg_hir_id)
3501 && let Some(typeck_results) = &self.typeck_results
3503 if let hir::Expr { kind: hir::ExprKind::Block(..), .. } = expr {
3504 let expr = expr.peel_blocks();
3505 let ty = typeck_results.expr_ty_adjusted_opt(expr).unwrap_or(tcx.ty_error());
3506 let span = expr.span;
3507 if Some(span) != err.span.primary_span() {
3510 if ty.references_error() {
3513 let ty = with_forced_trimmed_paths!(self.ty_to_string(ty));
3514 format!("this tail expression is of type `{ty}`")
3520 // FIXME: visit the ty to see if there's any closure involved, and if there is,
3521 // check whether its evaluated return type is the same as the one corresponding
3522 // to an associated type (as seen from `trait_pred`) in the predicate. Like in
3523 // trait_pred `S: Sum<<Self as Iterator>::Item>` and predicate `i32: Sum<&()>`
3524 let mut type_diffs = vec![];
3526 if let ObligationCauseCode::ExprBindingObligation(def_id, _, _, idx) = parent_code.deref()
3527 && let Some(node_substs) = typeck_results.node_substs_opt(call_hir_id)
3528 && let where_clauses = self.tcx.predicates_of(def_id).instantiate(self.tcx, node_substs)
3529 && let Some(where_pred) = where_clauses.predicates.get(*idx)
3531 if let Some(where_pred) = where_pred.to_opt_poly_trait_pred()
3532 && let Some(failed_pred) = failed_pred.to_opt_poly_trait_pred()
3534 let mut c = CollectAllMismatches {
3539 if let Ok(_) = c.relate(where_pred, failed_pred) {
3540 type_diffs = c.errors;
3542 } else if let Some(where_pred) = where_pred.to_opt_poly_projection_pred()
3543 && let Some(failed_pred) = failed_pred.to_opt_poly_projection_pred()
3544 && let Some(found) = failed_pred.skip_binder().term.ty()
3547 Sorts(ty::error::ExpectedFound {
3548 expected: self.tcx.mk_ty(ty::Alias(ty::Projection, where_pred.skip_binder().projection_ty)),
3554 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
3555 && let hir::Path { res: hir::def::Res::Local(hir_id), .. } = path
3556 && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(*hir_id)
3557 && let parent_hir_id = self.tcx.hir().parent_id(binding.hir_id)
3558 && let Some(hir::Node::Local(local)) = self.tcx.hir().find(parent_hir_id)
3559 && let Some(binding_expr) = local.init
3561 // If the expression we're calling on is a binding, we want to point at the
3562 // `let` when talking about the type. Otherwise we'll point at every part
3563 // of the method chain with the type.
3564 self.point_at_chain(binding_expr, &typeck_results, type_diffs, param_env, err);
3566 self.point_at_chain(expr, &typeck_results, type_diffs, param_env, err);
3569 let call_node = hir.find(call_hir_id);
3570 if let Some(Node::Expr(hir::Expr {
3571 kind: hir::ExprKind::MethodCall(path, rcvr, ..), ..
3574 if Some(rcvr.span) == err.span.primary_span() {
3575 err.replace_span_with(path.ident.span, true);
3578 if let Some(Node::Expr(hir::Expr {
3580 hir::ExprKind::Call(hir::Expr { span, .. }, _)
3581 | hir::ExprKind::MethodCall(hir::PathSegment { ident: Ident { span, .. }, .. }, ..),
3583 })) = hir.find(call_hir_id)
3585 if Some(*span) != err.span.primary_span() {
3586 err.span_label(*span, "required by a bound introduced by this call");
3593 expr: &hir::Expr<'_>,
3594 typeck_results: &TypeckResults<'tcx>,
3595 type_diffs: Vec<TypeError<'tcx>>,
3596 param_env: ty::ParamEnv<'tcx>,
3597 err: &mut Diagnostic,
3599 let mut primary_spans = vec![];
3600 let mut span_labels = vec![];
3604 let mut print_root_expr = true;
3605 let mut assocs = vec![];
3606 let mut expr = expr;
3607 let mut prev_ty = self.resolve_vars_if_possible(
3608 typeck_results.expr_ty_adjusted_opt(expr).unwrap_or(tcx.ty_error()),
3610 while let hir::ExprKind::MethodCall(_path_segment, rcvr_expr, _args, span) = expr.kind {
3611 // Point at every method call in the chain with the resulting type.
3612 // vec![1, 2, 3].iter().map(mapper).sum<i32>()
3613 // ^^^^^^ ^^^^^^^^^^^
3615 let assocs_in_this_method =
3616 self.probe_assoc_types_at_expr(&type_diffs, span, prev_ty, expr.hir_id, param_env);
3617 assocs.push(assocs_in_this_method);
3618 prev_ty = self.resolve_vars_if_possible(
3619 typeck_results.expr_ty_adjusted_opt(expr).unwrap_or(tcx.ty_error()),
3622 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
3623 && let hir::Path { res: hir::def::Res::Local(hir_id), .. } = path
3624 && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(*hir_id)
3625 && let Some(parent) = self.tcx.hir().find_parent(binding.hir_id)
3627 // We've reached the root of the method call chain...
3628 if let hir::Node::Local(local) = parent
3629 && let Some(binding_expr) = local.init
3631 // ...and it is a binding. Get the binding creation and continue the chain.
3632 expr = binding_expr;
3634 if let hir::Node::Param(param) = parent {
3635 // ...and it is a an fn argument.
3636 let prev_ty = self.resolve_vars_if_possible(
3637 typeck_results.node_type_opt(param.hir_id).unwrap_or(tcx.ty_error()),
3639 let assocs_in_this_method = self.probe_assoc_types_at_expr(&type_diffs, param.ty_span, prev_ty, param.hir_id, param_env);
3640 if assocs_in_this_method.iter().any(|a| a.is_some()) {
3641 assocs.push(assocs_in_this_method);
3642 print_root_expr = false;
3648 // We want the type before deref coercions, otherwise we talk about `&[_]`
3649 // instead of `Vec<_>`.
3650 if let Some(ty) = typeck_results.expr_ty_opt(expr) && print_root_expr {
3651 let ty = with_forced_trimmed_paths!(self.ty_to_string(ty));
3652 // Point at the root expression
3653 // vec![1, 2, 3].iter().map(mapper).sum<i32>()
3655 span_labels.push((expr.span, format!("this expression has type `{ty}`")));
3657 // Only show this if it is not a "trivial" expression (not a method
3658 // chain) and there are associated types to talk about.
3659 let mut assocs = assocs.into_iter().peekable();
3660 while let Some(assocs_in_method) = assocs.next() {
3661 let Some(prev_assoc_in_method) = assocs.peek() else {
3662 for entry in assocs_in_method {
3663 let Some((span, (assoc, ty))) = entry else { continue; };
3664 if primary_spans.is_empty() || type_diffs.iter().any(|diff| {
3665 let Sorts(expected_found) = diff else { return false; };
3666 self.can_eq(param_env, expected_found.found, ty).is_ok()
3668 // FIXME: this doesn't quite work for `Iterator::collect`
3669 // because we have `Vec<i32>` and `()`, but we'd want `i32`
3670 // to point at the `.into_iter()` call, but as long as we
3671 // still point at the other method calls that might have
3672 // introduced the issue, this is fine for now.
3673 primary_spans.push(span);
3677 with_forced_trimmed_paths!(format!(
3678 "`{}` is `{ty}` here",
3679 self.tcx.def_path_str(assoc),
3685 for (entry, prev_entry) in
3686 assocs_in_method.into_iter().zip(prev_assoc_in_method.into_iter())
3688 match (entry, prev_entry) {
3689 (Some((span, (assoc, ty))), Some((_, (_, prev_ty)))) => {
3690 let ty_str = with_forced_trimmed_paths!(self.ty_to_string(ty));
3692 let assoc = with_forced_trimmed_paths!(self.tcx.def_path_str(assoc));
3693 if self.can_eq(param_env, ty, *prev_ty).is_err() {
3694 if type_diffs.iter().any(|diff| {
3695 let Sorts(expected_found) = diff else { return false; };
3696 self.can_eq(param_env, expected_found.found, ty).is_ok()
3698 primary_spans.push(span);
3701 .push((span, format!("`{assoc}` changed to `{ty_str}` here")));
3703 span_labels.push((span, format!("`{assoc}` remains `{ty_str}` here")));
3706 (Some((span, (assoc, ty))), None) => {
3709 with_forced_trimmed_paths!(format!(
3710 "`{}` is `{}` here",
3711 self.tcx.def_path_str(assoc),
3712 self.ty_to_string(ty),
3716 (None, Some(_)) | (None, None) => {}
3720 if !primary_spans.is_empty() {
3721 let mut multi_span: MultiSpan = primary_spans.into();
3722 for (span, label) in span_labels {
3723 multi_span.push_span_label(span, label);
3727 "the method call chain might not have had the expected associated types",
3732 fn probe_assoc_types_at_expr(
3734 type_diffs: &[TypeError<'tcx>],
3737 body_id: hir::HirId,
3738 param_env: ty::ParamEnv<'tcx>,
3739 ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>> {
3740 let ocx = ObligationCtxt::new_in_snapshot(self.infcx);
3741 let mut assocs_in_this_method = Vec::with_capacity(type_diffs.len());
3742 for diff in type_diffs {
3743 let Sorts(expected_found) = diff else { continue; };
3744 let ty::Alias(ty::Projection, proj) = expected_found.expected.kind() else { continue; };
3746 let origin = TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span };
3747 let trait_def_id = proj.trait_def_id(self.tcx);
3748 // Make `Self` be equivalent to the type of the call chain
3749 // expression we're looking at now, so that we can tell what
3750 // for example `Iterator::Item` is at this point in the chain.
3751 let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
3753 ty::GenericParamDefKind::Type { .. } => {
3754 if param.index == 0 {
3755 return prev_ty.into();
3758 ty::GenericParamDefKind::Lifetime | ty::GenericParamDefKind::Const { .. } => {}
3760 self.var_for_def(span, param)
3762 // This will hold the resolved type of the associated type, if the
3763 // current expression implements the trait that associated type is
3764 // in. For example, this would be what `Iterator::Item` is here.
3765 let ty_var = self.infcx.next_ty_var(origin);
3766 // This corresponds to `<ExprTy as Iterator>::Item = _`.
3767 let projection = ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::Projection(
3768 ty::ProjectionPredicate {
3769 projection_ty: self.tcx.mk_alias_ty(proj.def_id, substs),
3770 term: ty_var.into(),
3773 let body_def_id = self.tcx.hir().enclosing_body_owner(body_id);
3774 // Add `<ExprTy as Iterator>::Item = _` obligation.
3775 ocx.register_obligation(Obligation::misc(
3782 if ocx.select_where_possible().is_empty() {
3783 // `ty_var` now holds the type that `Item` is for `ExprTy`.
3784 let ty_var = self.resolve_vars_if_possible(ty_var);
3785 assocs_in_this_method.push(Some((span, (proj.def_id, ty_var))));
3787 // `<ExprTy as Iterator>` didn't select, so likely we've
3788 // reached the end of the iterator chain, like the originating
3790 // Keep the space consistent for later zipping.
3791 assocs_in_this_method.push(None);
3794 assocs_in_this_method
3798 /// Add a hint to add a missing borrow or remove an unnecessary one.
3799 fn hint_missing_borrow<'tcx>(
3800 infcx: &InferCtxt<'tcx>,
3801 param_env: ty::ParamEnv<'tcx>,
3805 found_node: Node<'_>,
3806 err: &mut Diagnostic,
3808 let found_args = match found.kind() {
3809 ty::FnPtr(f) => infcx.instantiate_binder_with_placeholders(*f).inputs().iter(),
3811 span_bug!(span, "found was converted to a FnPtr above but is now {:?}", kind)
3814 let expected_args = match expected.kind() {
3815 ty::FnPtr(f) => infcx.instantiate_binder_with_placeholders(*f).inputs().iter(),
3817 span_bug!(span, "expected was converted to a FnPtr above but is now {:?}", kind)
3821 // This could be a variant constructor, for example.
3822 let Some(fn_decl) = found_node.fn_decl() else { return; };
3824 let args = fn_decl.inputs.iter().map(|ty| ty);
3826 fn get_deref_type_and_refs(mut ty: Ty<'_>) -> (Ty<'_>, Vec<hir::Mutability>) {
3827 let mut refs = vec![];
3829 while let ty::Ref(_, new_ty, mutbl) = ty.kind() {
3837 let mut to_borrow = Vec::new();
3838 let mut remove_borrow = Vec::new();
3840 for ((found_arg, expected_arg), arg) in found_args.zip(expected_args).zip(args) {
3841 let (found_ty, found_refs) = get_deref_type_and_refs(*found_arg);
3842 let (expected_ty, expected_refs) = get_deref_type_and_refs(*expected_arg);
3844 if infcx.can_eq(param_env, found_ty, expected_ty).is_ok() {
3845 // FIXME: This could handle more exotic cases like mutability mismatches too!
3846 if found_refs.len() < expected_refs.len()
3847 && found_refs[..] == expected_refs[expected_refs.len() - found_refs.len()..]
3850 arg.span.shrink_to_lo(),
3851 expected_refs[..expected_refs.len() - found_refs.len()]
3853 .map(|mutbl| format!("&{}", mutbl.prefix_str()))
3854 .collect::<Vec<_>>()
3857 } else if found_refs.len() > expected_refs.len() {
3858 let mut span = arg.span.shrink_to_lo();
3859 let mut left = found_refs.len() - expected_refs.len();
3861 while let hir::TyKind::Ref(_, mut_ty) = &ty.kind && left > 0 {
3862 span = span.with_hi(mut_ty.ty.span.lo());
3866 let sugg = if left == 0 {
3867 (span, String::new())
3869 (arg.span, expected_arg.to_string())
3871 remove_borrow.push(sugg);
3876 if !to_borrow.is_empty() {
3877 err.multipart_suggestion_verbose(
3878 "consider borrowing the argument",
3880 Applicability::MaybeIncorrect,
3884 if !remove_borrow.is_empty() {
3885 err.multipart_suggestion_verbose(
3886 "do not borrow the argument",
3888 Applicability::MaybeIncorrect,
3893 /// Collect all the returned expressions within the input expression.
3894 /// Used to point at the return spans when we want to suggest some change to them.
3896 pub struct ReturnsVisitor<'v> {
3897 pub returns: Vec<&'v hir::Expr<'v>>,
3898 in_block_tail: bool,
3901 impl<'v> Visitor<'v> for ReturnsVisitor<'v> {
3902 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
3903 // Visit every expression to detect `return` paths, either through the function's tail
3904 // expression or `return` statements. We walk all nodes to find `return` statements, but
3905 // we only care about tail expressions when `in_block_tail` is `true`, which means that
3906 // they're in the return path of the function body.
3908 hir::ExprKind::Ret(Some(ex)) => {
3909 self.returns.push(ex);
3911 hir::ExprKind::Block(block, _) if self.in_block_tail => {
3912 self.in_block_tail = false;
3913 for stmt in block.stmts {
3914 hir::intravisit::walk_stmt(self, stmt);
3916 self.in_block_tail = true;
3917 if let Some(expr) = block.expr {
3918 self.visit_expr(expr);
3921 hir::ExprKind::If(_, then, else_opt) if self.in_block_tail => {
3922 self.visit_expr(then);
3923 if let Some(el) = else_opt {
3924 self.visit_expr(el);
3927 hir::ExprKind::Match(_, arms, _) if self.in_block_tail => {
3929 self.visit_expr(arm.body);
3932 // We need to walk to find `return`s in the entire body.
3933 _ if !self.in_block_tail => hir::intravisit::walk_expr(self, ex),
3934 _ => self.returns.push(ex),
3938 fn visit_body(&mut self, body: &'v hir::Body<'v>) {
3939 assert!(!self.in_block_tail);
3940 if body.generator_kind().is_none() {
3941 if let hir::ExprKind::Block(block, None) = body.value.kind {
3942 if block.expr.is_some() {
3943 self.in_block_tail = true;
3947 hir::intravisit::walk_body(self, body);
3951 /// Collect all the awaited expressions within the input expression.
3953 struct AwaitsVisitor {
3954 awaits: Vec<hir::HirId>,
3957 impl<'v> Visitor<'v> for AwaitsVisitor {
3958 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
3959 if let hir::ExprKind::Yield(_, hir::YieldSource::Await { expr: Some(id) }) = ex.kind {
3960 self.awaits.push(id)
3962 hir::intravisit::walk_expr(self, ex)
3966 pub trait NextTypeParamName {
3967 fn next_type_param_name(&self, name: Option<&str>) -> String;
3970 impl NextTypeParamName for &[hir::GenericParam<'_>] {
3971 fn next_type_param_name(&self, name: Option<&str>) -> String {
3972 // This is the list of possible parameter names that we might suggest.
3973 let name = name.and_then(|n| n.chars().next()).map(|c| c.to_string().to_uppercase());
3974 let name = name.as_deref();
3975 let possible_names = [name.unwrap_or("T"), "T", "U", "V", "X", "Y", "Z", "A", "B", "C"];
3976 let used_names = self
3978 .filter_map(|p| match p.name {
3979 hir::ParamName::Plain(ident) => Some(ident.name),
3982 .collect::<Vec<_>>();
3986 .find(|n| !used_names.contains(&Symbol::intern(n)))
3987 .unwrap_or(&"ParamName")
3992 fn suggest_trait_object_return_type_alternatives(
3993 err: &mut Diagnostic,
3996 is_object_safe: bool,
3998 err.span_suggestion(
4001 "use `impl {}` as the return type if all return paths have the same type but you \
4002 want to expose only the trait in the signature",
4005 format!("impl {}", trait_obj),
4006 Applicability::MaybeIncorrect,
4009 err.multipart_suggestion(
4011 "use a boxed trait object if all return paths implement trait `{}`",
4015 (ret_ty.shrink_to_lo(), "Box<".to_string()),
4016 (ret_ty.shrink_to_hi(), ">".to_string()),
4018 Applicability::MaybeIncorrect,
4023 /// Collect the spans that we see the generic param `param_did`
4024 struct ReplaceImplTraitVisitor<'a> {
4025 ty_spans: &'a mut Vec<Span>,
4029 impl<'a, 'hir> hir::intravisit::Visitor<'hir> for ReplaceImplTraitVisitor<'a> {
4030 fn visit_ty(&mut self, t: &'hir hir::Ty<'hir>) {
4031 if let hir::TyKind::Path(hir::QPath::Resolved(
4033 hir::Path { res: hir::def::Res::Def(_, segment_did), .. },
4036 if self.param_did == *segment_did {
4037 // `fn foo(t: impl Trait)`
4038 // ^^^^^^^^^^ get this to suggest `T` instead
4040 // There might be more than one `impl Trait`.
4041 self.ty_spans.push(t.span);
4046 hir::intravisit::walk_ty(self, t);
4050 // Replace `param` with `replace_ty`
4051 struct ReplaceImplTraitFolder<'tcx> {
4053 param: &'tcx ty::GenericParamDef,
4054 replace_ty: Ty<'tcx>,
4057 impl<'tcx> TypeFolder<'tcx> for ReplaceImplTraitFolder<'tcx> {
4058 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
4059 if let ty::Param(ty::ParamTy { index, .. }) = t.kind() {
4060 if self.param.index == *index {
4061 return self.replace_ty;
4064 t.super_fold_with(self)
4067 fn tcx(&self) -> TyCtxt<'tcx> {