1 // ignore-tidy-filelength
4 DefIdOrName, FindExprBySpan, Obligation, ObligationCause, ObligationCauseCode,
8 use crate::infer::InferCtxt;
9 use crate::traits::{NormalizeExt, ObligationCtxt};
12 use hir::{Expr, HirId};
13 use rustc_data_structures::fx::FxHashSet;
14 use rustc_data_structures::stack::ensure_sufficient_stack;
16 error_code, pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder,
17 ErrorGuaranteed, MultiSpan, Style,
20 use rustc_hir::def::DefKind;
21 use rustc_hir::def_id::DefId;
22 use rustc_hir::intravisit::Visitor;
23 use rustc_hir::lang_items::LangItem;
24 use rustc_hir::{AsyncGeneratorKind, GeneratorKind, Node};
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::symbol::{sym, Ident, Symbol};
38 use rustc_span::{BytePos, DesugaringKind, ExpnKind, MacroKind, Span, DUMMY_SP};
39 use rustc_target::spec::abi;
42 use super::method_chain::CollectAllMismatches;
43 use super::InferCtxtPrivExt;
44 use crate::infer::InferCtxtExt as _;
45 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
46 use rustc_middle::ty::print::{with_forced_trimmed_paths, with_no_trimmed_paths};
49 pub enum GeneratorInteriorOrUpvar {
50 // span of interior type
51 Interior(Span, Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>),
56 // This type provides a uniform interface to retrieve data on generators, whether it originated from
57 // the local crate being compiled or from a foreign crate.
59 pub enum GeneratorData<'tcx, 'a> {
60 Local(&'a TypeckResults<'tcx>),
61 Foreign(&'tcx GeneratorDiagnosticData<'tcx>),
64 impl<'tcx, 'a> GeneratorData<'tcx, 'a> {
65 // Try to get information about variables captured by the generator that matches a type we are
66 // looking for with `ty_matches` function. We uses it to find upvar which causes a failure to
68 fn try_get_upvar_span<F>(
70 infer_context: &InferCtxt<'tcx>,
73 ) -> Option<GeneratorInteriorOrUpvar>
75 F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool,
78 GeneratorData::Local(typeck_results) => {
79 infer_context.tcx.upvars_mentioned(generator_did).and_then(|upvars| {
80 upvars.iter().find_map(|(upvar_id, upvar)| {
81 let upvar_ty = typeck_results.node_type(*upvar_id);
82 let upvar_ty = infer_context.resolve_vars_if_possible(upvar_ty);
83 if ty_matches(ty::Binder::dummy(upvar_ty)) {
84 Some(GeneratorInteriorOrUpvar::Upvar(upvar.span))
91 GeneratorData::Foreign(_) => None,
95 // Try to get the span of a type being awaited on that matches the type we are looking with the
96 // `ty_matches` function. We uses it to find awaited type which causes a failure to meet an
98 fn get_from_await_ty<F>(
100 visitor: AwaitsVisitor,
105 F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool,
108 GeneratorData::Local(typeck_results) => visitor
111 .map(|id| hir.expect_expr(id))
113 ty_matches(ty::Binder::dummy(typeck_results.expr_ty_adjusted(&await_expr)))
115 .map(|expr| expr.span),
116 GeneratorData::Foreign(generator_diagnostic_data) => visitor
119 .map(|id| hir.expect_expr(id))
121 ty_matches(ty::Binder::dummy(
122 generator_diagnostic_data
124 .get(&await_expr.hir_id.local_id)
125 .map_or::<&[ty::adjustment::Adjustment<'tcx>], _>(&[], |a| &a[..])
127 .map_or_else::<Ty<'tcx>, _, _>(
129 generator_diagnostic_data
131 .get(&await_expr.hir_id.local_id)
135 "node_type: no type for node `{}`",
136 ty::tls::with(|tcx| tcx
138 .node_to_string(await_expr.hir_id))
146 .map(|expr| expr.span),
150 /// Get the type, expression, span and optional scope span of all types
151 /// that are live across the yield of this generator
152 fn get_generator_interior_types(
154 ) -> ty::Binder<'tcx, &[GeneratorInteriorTypeCause<'tcx>]> {
156 GeneratorData::Local(typeck_result) => {
157 typeck_result.generator_interior_types.as_deref()
159 GeneratorData::Foreign(generator_diagnostic_data) => {
160 generator_diagnostic_data.generator_interior_types.as_deref()
165 // Used to get the source of the data, note we don't have as much information for generators
166 // originated from foreign crates
167 fn is_foreign(&self) -> bool {
169 GeneratorData::Local(_) => false,
170 GeneratorData::Foreign(_) => true,
175 // This trait is public to expose the diagnostics methods to clippy.
176 pub trait TypeErrCtxtExt<'tcx> {
177 fn suggest_restricting_param_bound(
179 err: &mut Diagnostic,
180 trait_pred: ty::PolyTraitPredicate<'tcx>,
181 associated_item: Option<(&'static str, Ty<'tcx>)>,
185 fn suggest_dereferences(
187 obligation: &PredicateObligation<'tcx>,
188 err: &mut Diagnostic,
189 trait_pred: ty::PolyTraitPredicate<'tcx>,
192 fn get_closure_name(&self, def_id: DefId, err: &mut Diagnostic, msg: &str) -> Option<Symbol>;
196 obligation: &PredicateObligation<'tcx>,
197 err: &mut Diagnostic,
198 trait_pred: ty::PolyTraitPredicate<'tcx>,
201 fn check_for_binding_assigned_block_without_tail_expression(
203 obligation: &PredicateObligation<'tcx>,
204 err: &mut Diagnostic,
205 trait_pred: ty::PolyTraitPredicate<'tcx>,
208 fn suggest_add_clone_to_arg(
210 obligation: &PredicateObligation<'tcx>,
211 err: &mut Diagnostic,
212 trait_pred: ty::PolyTraitPredicate<'tcx>,
215 fn suggest_add_reference_to_arg(
217 obligation: &PredicateObligation<'tcx>,
218 err: &mut Diagnostic,
219 trait_pred: ty::PolyTraitPredicate<'tcx>,
220 has_custom_message: bool,
223 fn suggest_borrowing_for_object_cast(
225 err: &mut Diagnostic,
226 obligation: &PredicateObligation<'tcx>,
231 fn suggest_remove_reference(
233 obligation: &PredicateObligation<'tcx>,
234 err: &mut Diagnostic,
235 trait_pred: ty::PolyTraitPredicate<'tcx>,
238 fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic);
240 fn suggest_change_mut(
242 obligation: &PredicateObligation<'tcx>,
243 err: &mut Diagnostic,
244 trait_pred: ty::PolyTraitPredicate<'tcx>,
247 fn suggest_semicolon_removal(
249 obligation: &PredicateObligation<'tcx>,
250 err: &mut Diagnostic,
252 trait_pred: ty::PolyTraitPredicate<'tcx>,
255 fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span>;
257 fn suggest_impl_trait(
259 err: &mut Diagnostic,
261 obligation: &PredicateObligation<'tcx>,
262 trait_pred: ty::PolyTraitPredicate<'tcx>,
265 fn point_at_returns_when_relevant(
267 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
268 obligation: &PredicateObligation<'tcx>,
271 fn report_closure_arg_mismatch(
274 found_span: Option<Span>,
275 found: ty::PolyTraitRef<'tcx>,
276 expected: ty::PolyTraitRef<'tcx>,
277 cause: &ObligationCauseCode<'tcx>,
278 found_node: Option<Node<'_>>,
279 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
281 fn note_conflicting_closure_bounds(
283 cause: &ObligationCauseCode<'tcx>,
284 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
287 fn suggest_fully_qualified_path(
289 err: &mut Diagnostic,
295 fn maybe_note_obligation_cause_for_async_await(
297 err: &mut Diagnostic,
298 obligation: &PredicateObligation<'tcx>,
301 fn note_obligation_cause_for_async_await(
303 err: &mut Diagnostic,
304 interior_or_upvar_span: GeneratorInteriorOrUpvar,
306 outer_generator: Option<DefId>,
307 trait_pred: ty::TraitPredicate<'tcx>,
309 typeck_results: Option<&ty::TypeckResults<'tcx>>,
310 obligation: &PredicateObligation<'tcx>,
311 next_code: Option<&ObligationCauseCode<'tcx>>,
314 fn note_obligation_cause_code<T>(
316 err: &mut Diagnostic,
318 param_env: ty::ParamEnv<'tcx>,
319 cause_code: &ObligationCauseCode<'tcx>,
320 obligated_types: &mut Vec<Ty<'tcx>>,
321 seen_requirements: &mut FxHashSet<DefId>,
323 T: ToPredicate<'tcx>;
325 /// Suggest to await before try: future? => future.await?
326 fn suggest_await_before_try(
328 err: &mut Diagnostic,
329 obligation: &PredicateObligation<'tcx>,
330 trait_pred: ty::PolyTraitPredicate<'tcx>,
334 fn suggest_floating_point_literal(
336 obligation: &PredicateObligation<'tcx>,
337 err: &mut Diagnostic,
338 trait_ref: &ty::PolyTraitRef<'tcx>,
343 obligation: &PredicateObligation<'tcx>,
344 err: &mut Diagnostic,
345 trait_pred: ty::PolyTraitPredicate<'tcx>,
348 fn suggest_dereferencing_index(
350 obligation: &PredicateObligation<'tcx>,
351 err: &mut Diagnostic,
352 trait_pred: ty::PolyTraitPredicate<'tcx>,
354 fn note_function_argument_obligation(
357 err: &mut Diagnostic,
358 parent_code: &ObligationCauseCode<'tcx>,
359 param_env: ty::ParamEnv<'tcx>,
360 predicate: ty::Predicate<'tcx>,
365 expr: &hir::Expr<'_>,
366 typeck_results: &TypeckResults<'tcx>,
367 type_diffs: Vec<TypeError<'tcx>>,
368 param_env: ty::ParamEnv<'tcx>,
369 err: &mut Diagnostic,
371 fn probe_assoc_types_at_expr(
373 type_diffs: &[TypeError<'tcx>],
377 param_env: ty::ParamEnv<'tcx>,
378 ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>>;
381 fn predicate_constraint(generics: &hir::Generics<'_>, pred: ty::Predicate<'_>) -> (Span, String) {
383 generics.tail_span_for_predicate_suggestion(),
384 format!("{} {}", generics.add_where_or_trailing_comma(), pred),
388 /// Type parameter needs more bounds. The trivial case is `T` `where T: Bound`, but
389 /// it can also be an `impl Trait` param that needs to be decomposed to a type
390 /// param for cleaner code.
391 fn suggest_restriction<'tcx>(
394 hir_generics: &hir::Generics<'tcx>,
396 err: &mut Diagnostic,
397 fn_sig: Option<&hir::FnSig<'_>>,
398 projection: Option<&ty::AliasTy<'_>>,
399 trait_pred: ty::PolyTraitPredicate<'tcx>,
400 // When we are dealing with a trait, `super_traits` will be `Some`:
401 // Given `trait T: A + B + C {}`
402 // - ^^^^^^^^^ GenericBounds
405 super_traits: Option<(&Ident, &hir::GenericBounds<'_>)>,
407 if hir_generics.where_clause_span.from_expansion()
408 || hir_generics.where_clause_span.desugaring_kind().is_some()
412 let Some(item_id) = hir_id.as_owner() else { return; };
413 let generics = tcx.generics_of(item_id);
414 // Given `fn foo(t: impl Trait)` where `Trait` requires assoc type `A`...
415 if let Some((param, bound_str, fn_sig)) =
416 fn_sig.zip(projection).and_then(|(sig, p)| match p.self_ty().kind() {
417 // Shenanigans to get the `Trait` from the `impl Trait`.
418 ty::Param(param) => {
419 let param_def = generics.type_param(param, tcx);
420 if param_def.kind.is_synthetic() {
422 param_def.name.as_str().strip_prefix("impl ")?.trim_start().to_string();
423 return Some((param_def, bound_str, sig));
430 let type_param_name = hir_generics.params.next_type_param_name(Some(&bound_str));
431 let trait_pred = trait_pred.fold_with(&mut ReplaceImplTraitFolder {
434 replace_ty: ty::ParamTy::new(generics.count() as u32, Symbol::intern(&type_param_name))
437 if !trait_pred.is_suggestable(tcx, false) {
440 // We know we have an `impl Trait` that doesn't satisfy a required projection.
442 // Find all of the occurrences of `impl Trait` for `Trait` in the function arguments'
443 // types. There should be at least one, but there might be *more* than one. In that
444 // case we could just ignore it and try to identify which one needs the restriction,
445 // but instead we choose to suggest replacing all instances of `impl Trait` with `T`
447 let mut ty_spans = vec![];
448 for input in fn_sig.decl.inputs {
449 ReplaceImplTraitVisitor { ty_spans: &mut ty_spans, param_did: param.def_id }
452 // The type param `T: Trait` we will suggest to introduce.
453 let type_param = format!("{}: {}", type_param_name, bound_str);
456 if let Some(span) = hir_generics.span_for_param_suggestion() {
457 (span, format!(", {}", type_param))
459 (hir_generics.span, format!("<{}>", type_param))
461 // `fn foo(t: impl Trait)`
462 // ^ suggest `where <T as Trait>::A: Bound`
463 predicate_constraint(hir_generics, trait_pred.to_predicate(tcx)),
465 sugg.extend(ty_spans.into_iter().map(|s| (s, type_param_name.to_string())));
467 // Suggest `fn foo<T: Trait>(t: T) where <T as Trait>::A: Bound`.
468 // FIXME: once `#![feature(associated_type_bounds)]` is stabilized, we should suggest
469 // `fn foo(t: impl Trait<A: Bound>)` instead.
470 err.multipart_suggestion(
471 "introduce a type parameter with a trait bound instead of using `impl Trait`",
473 Applicability::MaybeIncorrect,
476 if !trait_pred.is_suggestable(tcx, false) {
479 // Trivial case: `T` needs an extra bound: `T: Bound`.
480 let (sp, suggestion) = match (
484 .find(|p| !matches!(p.kind, hir::GenericParamKind::Type { synthetic: true, .. })),
487 (_, None) => predicate_constraint(hir_generics, trait_pred.to_predicate(tcx)),
488 (None, Some((ident, []))) => (
489 ident.span.shrink_to_hi(),
490 format!(": {}", trait_pred.print_modifiers_and_trait_path()),
492 (_, Some((_, [.., bounds]))) => (
493 bounds.span().shrink_to_hi(),
494 format!(" + {}", trait_pred.print_modifiers_and_trait_path()),
496 (Some(_), Some((_, []))) => (
497 hir_generics.span.shrink_to_hi(),
498 format!(": {}", trait_pred.print_modifiers_and_trait_path()),
502 err.span_suggestion_verbose(
504 &format!("consider further restricting {}", msg),
506 Applicability::MachineApplicable,
511 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
512 fn suggest_restricting_param_bound(
514 mut err: &mut Diagnostic,
515 trait_pred: ty::PolyTraitPredicate<'tcx>,
516 associated_ty: Option<(&'static str, Ty<'tcx>)>,
519 let trait_pred = self.resolve_numeric_literals_with_default(trait_pred);
521 let self_ty = trait_pred.skip_binder().self_ty();
522 let (param_ty, projection) = match self_ty.kind() {
523 ty::Param(_) => (true, None),
524 ty::Alias(ty::Projection, projection) => (false, Some(projection)),
528 // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
529 // don't suggest `T: Sized + ?Sized`.
530 let mut hir_id = body_id;
531 while let Some(node) = self.tcx.hir().find(hir_id) {
533 hir::Node::Item(hir::Item {
535 kind: hir::ItemKind::Trait(_, _, generics, bounds, _),
537 }) if self_ty == self.tcx.types.self_param => {
539 // Restricting `Self` for a single method.
549 Some((ident, bounds)),
554 hir::Node::TraitItem(hir::TraitItem {
556 kind: hir::TraitItemKind::Fn(..),
558 }) if self_ty == self.tcx.types.self_param => {
560 // Restricting `Self` for a single method.
562 self.tcx, hir_id, &generics, "`Self`", err, None, projection, trait_pred,
568 hir::Node::TraitItem(hir::TraitItem {
570 kind: hir::TraitItemKind::Fn(fn_sig, ..),
573 | hir::Node::ImplItem(hir::ImplItem {
575 kind: hir::ImplItemKind::Fn(fn_sig, ..),
578 | hir::Node::Item(hir::Item {
579 kind: hir::ItemKind::Fn(fn_sig, generics, _), ..
580 }) if projection.is_some() => {
581 // Missing restriction on associated type of type parameter (unmet projection).
586 "the associated type",
595 hir::Node::Item(hir::Item {
597 hir::ItemKind::Trait(_, _, generics, ..)
598 | hir::ItemKind::Impl(hir::Impl { generics, .. }),
600 }) if projection.is_some() => {
601 // Missing restriction on associated type of type parameter (unmet projection).
606 "the associated type",
616 hir::Node::Item(hir::Item {
618 hir::ItemKind::Struct(_, generics)
619 | hir::ItemKind::Enum(_, generics)
620 | hir::ItemKind::Union(_, generics)
621 | hir::ItemKind::Trait(_, _, generics, ..)
622 | hir::ItemKind::Impl(hir::Impl { generics, .. })
623 | hir::ItemKind::Fn(_, generics, _)
624 | hir::ItemKind::TyAlias(_, generics)
625 | hir::ItemKind::TraitAlias(generics, _)
626 | hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }),
629 | hir::Node::TraitItem(hir::TraitItem { generics, .. })
630 | hir::Node::ImplItem(hir::ImplItem { generics, .. })
633 // We skip the 0'th subst (self) because we do not want
634 // to consider the predicate as not suggestible if the
635 // self type is an arg position `impl Trait` -- instead,
636 // we handle that by adding ` + Bound` below.
637 // FIXME(compiler-errors): It would be nice to do the same
638 // this that we do in `suggest_restriction` and pull the
639 // `impl Trait` into a new generic if it shows up somewhere
640 // else in the predicate.
641 if !trait_pred.skip_binder().trait_ref.substs[1..]
643 .all(|g| g.is_suggestable(self.tcx, false))
647 // Missing generic type parameter bound.
648 let param_name = self_ty.to_string();
649 let mut constraint = with_no_trimmed_paths!(
650 trait_pred.print_modifiers_and_trait_path().to_string()
653 if let Some((name, term)) = associated_ty {
654 // FIXME: this case overlaps with code in TyCtxt::note_and_explain_type_err.
655 // That should be extracted into a helper function.
656 if constraint.ends_with('>') {
657 constraint = format!(
659 &constraint[..constraint.len() - 1],
664 constraint.push_str(&format!("<{} = {}>", name, term));
668 if suggest_constraining_type_param(
674 Some(trait_pred.def_id()),
680 hir::Node::Item(hir::Item {
682 hir::ItemKind::Struct(_, generics)
683 | hir::ItemKind::Enum(_, generics)
684 | hir::ItemKind::Union(_, generics)
685 | hir::ItemKind::Trait(_, _, generics, ..)
686 | hir::ItemKind::Impl(hir::Impl { generics, .. })
687 | hir::ItemKind::Fn(_, generics, _)
688 | hir::ItemKind::TyAlias(_, generics)
689 | hir::ItemKind::TraitAlias(generics, _)
690 | hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }),
693 // Missing generic type parameter bound.
694 if suggest_arbitrary_trait_bound(
704 hir::Node::Crate(..) => return,
709 hir_id = self.tcx.hir().get_parent_item(hir_id).into();
713 /// When after several dereferencing, the reference satisfies the trait
714 /// binding. This function provides dereference suggestion for this
715 /// specific situation.
716 fn suggest_dereferences(
718 obligation: &PredicateObligation<'tcx>,
719 err: &mut Diagnostic,
720 trait_pred: ty::PolyTraitPredicate<'tcx>,
722 // It only make sense when suggesting dereferences for arguments
723 let ObligationCauseCode::FunctionArgumentObligation { arg_hir_id, call_hir_id, .. } = obligation.cause.code()
724 else { return false; };
725 let Some(typeck_results) = &self.typeck_results
726 else { return false; };
727 let hir::Node::Expr(expr) = self.tcx.hir().get(*arg_hir_id)
728 else { return false; };
729 let Some(arg_ty) = typeck_results.expr_ty_adjusted_opt(expr)
730 else { return false; };
732 let span = obligation.cause.span;
733 let mut real_trait_pred = trait_pred;
734 let mut code = obligation.cause.code();
735 while let Some((parent_code, parent_trait_pred)) = code.parent() {
737 if let Some(parent_trait_pred) = parent_trait_pred {
738 real_trait_pred = parent_trait_pred;
741 let real_ty = real_trait_pred.self_ty();
742 // We `erase_late_bound_regions` here because `make_subregion` does not handle
743 // `ReLateBound`, and we don't particularly care about the regions.
745 .can_eq(obligation.param_env, self.tcx.erase_late_bound_regions(real_ty), arg_ty)
751 if let ty::Ref(region, base_ty, mutbl) = *real_ty.skip_binder().kind() {
752 let autoderef = (self.autoderef_steps)(base_ty);
754 autoderef.into_iter().enumerate().find_map(|(steps, (ty, obligations))| {
756 let ty = self.tcx.mk_ref(region, TypeAndMut { ty, mutbl });
758 // Remapping bound vars here
759 let real_trait_pred_and_ty =
760 real_trait_pred.map_bound(|inner_trait_pred| (inner_trait_pred, ty));
761 let obligation = self.mk_trait_obligation_with_new_self_ty(
762 obligation.param_env,
763 real_trait_pred_and_ty,
767 .chain([&obligation])
768 .all(|obligation| self.predicate_may_hold(obligation))
777 // Don't care about `&mut` because `DerefMut` is used less
778 // often and user will not expect autoderef happens.
779 if let Some(hir::Node::Expr(hir::Expr {
781 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, expr),
783 })) = self.tcx.hir().find(*arg_hir_id)
785 let derefs = "*".repeat(steps);
786 err.span_suggestion_verbose(
787 expr.span.shrink_to_lo(),
788 "consider dereferencing here",
790 Applicability::MachineApplicable,
795 } else if real_trait_pred != trait_pred {
796 // This branch addresses #87437.
798 // Remapping bound vars here
799 let real_trait_pred_and_base_ty =
800 real_trait_pred.map_bound(|inner_trait_pred| (inner_trait_pred, base_ty));
801 let obligation = self.mk_trait_obligation_with_new_self_ty(
802 obligation.param_env,
803 real_trait_pred_and_base_ty,
805 if self.predicate_may_hold(&obligation) {
806 let call_node = self.tcx.hir().get(*call_hir_id);
807 let msg = "consider dereferencing here";
808 let is_receiver = matches!(
810 Node::Expr(hir::Expr {
811 kind: hir::ExprKind::MethodCall(_, receiver_expr, ..),
814 if receiver_expr.hir_id == *arg_hir_id
817 err.multipart_suggestion_verbose(
820 (span.shrink_to_lo(), "(*".to_string()),
821 (span.shrink_to_hi(), ")".to_string()),
823 Applicability::MachineApplicable,
826 err.span_suggestion_verbose(
830 Applicability::MachineApplicable,
841 /// Given a closure's `DefId`, return the given name of the closure.
843 /// This doesn't account for reassignments, but it's only used for suggestions.
844 fn get_closure_name(&self, def_id: DefId, err: &mut Diagnostic, msg: &str) -> Option<Symbol> {
845 let get_name = |err: &mut Diagnostic, kind: &hir::PatKind<'_>| -> Option<Symbol> {
846 // Get the local name of this closure. This can be inaccurate because
847 // of the possibility of reassignment, but this should be good enough.
849 hir::PatKind::Binding(hir::BindingAnnotation::NONE, _, ident, None) => {
859 let hir = self.tcx.hir();
860 let hir_id = hir.local_def_id_to_hir_id(def_id.as_local()?);
861 match hir.find_parent(hir_id) {
862 Some(hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(local), .. })) => {
863 get_name(err, &local.pat.kind)
865 // Different to previous arm because one is `&hir::Local` and the other
866 // is `P<hir::Local>`.
867 Some(hir::Node::Local(local)) => get_name(err, &local.pat.kind),
872 /// We tried to apply the bound to an `fn` or closure. Check whether calling it would
873 /// evaluate to a type that *would* satisfy the trait binding. If it would, suggest calling
874 /// it: `bar(foo)` → `bar(foo())`. This case is *very* likely to be hit if `foo` is `async`.
877 obligation: &PredicateObligation<'tcx>,
878 err: &mut Diagnostic,
879 trait_pred: ty::PolyTraitPredicate<'tcx>,
881 if let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = obligation.predicate.kind().skip_binder()
882 && Some(trait_pred.def_id()) == self.tcx.lang_items().sized_trait()
884 // Don't suggest calling to turn an unsized type into a sized type
888 // This is duplicated from `extract_callable_info` in typeck, which
889 // relies on autoderef, so we can't use it here.
890 let found = trait_pred.self_ty().skip_binder().peel_refs();
891 let Some((def_id_or_name, output, inputs)) = (match *found.kind()
893 ty::FnPtr(fn_sig) => {
894 Some((DefIdOrName::Name("function pointer"), fn_sig.output(), fn_sig.inputs()))
896 ty::FnDef(def_id, _) => {
897 let fn_sig = found.fn_sig(self.tcx);
898 Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs()))
900 ty::Closure(def_id, substs) => {
901 let fn_sig = substs.as_closure().sig();
903 DefIdOrName::DefId(def_id),
905 fn_sig.inputs().map_bound(|inputs| &inputs[1..]),
908 ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
909 self.tcx.bound_item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
910 if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
911 && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
912 // args tuple will always be substs[1]
913 && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
916 DefIdOrName::DefId(def_id),
917 pred.kind().rebind(proj.term.ty().unwrap()),
918 pred.kind().rebind(args.as_slice()),
925 ty::Dynamic(data, _, ty::Dyn) => {
926 data.iter().find_map(|pred| {
927 if let ty::ExistentialPredicate::Projection(proj) = pred.skip_binder()
928 && Some(proj.def_id) == self.tcx.lang_items().fn_once_output()
929 // for existential projection, substs are shifted over by 1
930 && let ty::Tuple(args) = proj.substs.type_at(0).kind()
933 DefIdOrName::Name("trait object"),
934 pred.rebind(proj.term.ty().unwrap()),
935 pred.rebind(args.as_slice()),
943 obligation.param_env.caller_bounds().iter().find_map(|pred| {
944 if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
945 && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
946 && proj.projection_ty.self_ty() == found
947 // args tuple will always be substs[1]
948 && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
951 DefIdOrName::Name("type parameter"),
952 pred.kind().rebind(proj.term.ty().unwrap()),
953 pred.kind().rebind(args.as_slice()),
961 }) else { return false; };
962 let output = self.replace_bound_vars_with_fresh_vars(
963 obligation.cause.span,
964 LateBoundRegionConversionTime::FnCall,
967 let inputs = inputs.skip_binder().iter().map(|ty| {
968 self.replace_bound_vars_with_fresh_vars(
969 obligation.cause.span,
970 LateBoundRegionConversionTime::FnCall,
975 // Remapping bound vars here
976 let trait_pred_and_self = trait_pred.map_bound(|trait_pred| (trait_pred, output));
979 self.mk_trait_obligation_with_new_self_ty(obligation.param_env, trait_pred_and_self);
980 if !self.predicate_must_hold_modulo_regions(&new_obligation) {
984 // Get the name of the callable and the arguments to be used in the suggestion.
985 let hir = self.tcx.hir();
987 let msg = match def_id_or_name {
988 DefIdOrName::DefId(def_id) => match self.tcx.def_kind(def_id) {
989 DefKind::Ctor(CtorOf::Struct, _) => {
990 "use parentheses to construct this tuple struct".to_string()
992 DefKind::Ctor(CtorOf::Variant, _) => {
993 "use parentheses to construct this tuple variant".to_string()
995 kind => format!("use parentheses to call this {}", kind.descr(def_id)),
997 DefIdOrName::Name(name) => format!("use parentheses to call this {name}"),
1002 if ty.is_suggestable(self.tcx, false) {
1003 format!("/* {ty} */")
1005 "/* value */".to_string()
1008 .collect::<Vec<_>>()
1011 if matches!(obligation.cause.code(), ObligationCauseCode::FunctionArgumentObligation { .. })
1012 && obligation.cause.span.can_be_used_for_suggestions()
1014 // When the obligation error has been ensured to have been caused by
1015 // an argument, the `obligation.cause.span` points at the expression
1016 // of the argument, so we can provide a suggestion. Otherwise, we give
1017 // a more general note.
1018 err.span_suggestion_verbose(
1019 obligation.cause.span.shrink_to_hi(),
1021 format!("({args})"),
1022 Applicability::HasPlaceholders,
1024 } else if let DefIdOrName::DefId(def_id) = def_id_or_name {
1025 let name = match hir.get_if_local(def_id) {
1026 Some(hir::Node::Expr(hir::Expr {
1027 kind: hir::ExprKind::Closure(hir::Closure { fn_decl_span, .. }),
1030 err.span_label(*fn_decl_span, "consider calling this closure");
1031 let Some(name) = self.get_closure_name(def_id, err, &msg) else {
1036 Some(hir::Node::Item(hir::Item { ident, kind: hir::ItemKind::Fn(..), .. })) => {
1037 err.span_label(ident.span, "consider calling this function");
1040 Some(hir::Node::Ctor(..)) => {
1041 let name = self.tcx.def_path_str(def_id);
1043 self.tcx.def_span(def_id),
1044 format!("consider calling the constructor for `{}`", name),
1050 err.help(&format!("{msg}: `{name}({args})`"));
1055 fn check_for_binding_assigned_block_without_tail_expression(
1057 obligation: &PredicateObligation<'tcx>,
1058 err: &mut Diagnostic,
1059 trait_pred: ty::PolyTraitPredicate<'tcx>,
1061 let mut span = obligation.cause.span;
1062 while span.from_expansion() {
1063 // Remove all the desugaring and macro contexts.
1066 let mut expr_finder = FindExprBySpan::new(span);
1067 let Some(hir::Node::Expr(body)) = self.tcx.hir().find(obligation.cause.body_id) else { return; };
1068 expr_finder.visit_expr(&body);
1069 let Some(expr) = expr_finder.result else { return; };
1070 let Some(typeck) = &self.typeck_results else { return; };
1071 let Some(ty) = typeck.expr_ty_adjusted_opt(expr) else { return; };
1075 let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind else { return; };
1076 let hir::def::Res::Local(hir_id) = path.res else { return; };
1077 let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(hir_id) else {
1080 let Some(hir::Node::Local(hir::Local {
1084 })) = self.tcx.hir().find_parent(pat.hir_id) else { return; };
1085 let hir::ExprKind::Block(block, None) = init.kind else { return; };
1086 if block.expr.is_some() {
1089 let [.., stmt] = block.stmts else {
1090 err.span_label(block.span, "this empty block is missing a tail expression");
1093 let hir::StmtKind::Semi(tail_expr) = stmt.kind else { return; };
1094 let Some(ty) = typeck.expr_ty_opt(tail_expr) else {
1095 err.span_label(block.span, "this block is missing a tail expression");
1098 let ty = self.resolve_numeric_literals_with_default(self.resolve_vars_if_possible(ty));
1099 let trait_pred_and_self = trait_pred.map_bound(|trait_pred| (trait_pred, ty));
1101 let new_obligation =
1102 self.mk_trait_obligation_with_new_self_ty(obligation.param_env, trait_pred_and_self);
1103 if self.predicate_must_hold_modulo_regions(&new_obligation) {
1104 err.span_suggestion_short(
1105 stmt.span.with_lo(tail_expr.span.hi()),
1106 "remove this semicolon",
1108 Applicability::MachineApplicable,
1111 err.span_label(block.span, "this block is missing a tail expression");
1115 fn suggest_add_clone_to_arg(
1117 obligation: &PredicateObligation<'tcx>,
1118 err: &mut Diagnostic,
1119 trait_pred: ty::PolyTraitPredicate<'tcx>,
1121 let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
1122 let ty = self.tcx.erase_late_bound_regions(self_ty);
1123 let owner = self.tcx.hir().get_parent_item(obligation.cause.body_id);
1124 let Some(generics) = self.tcx.hir().get_generics(owner.def_id) else { return false };
1125 let ty::Ref(_, inner_ty, hir::Mutability::Not) = ty.kind() else { return false };
1126 let ty::Param(param) = inner_ty.kind() else { return false };
1127 let ObligationCauseCode::FunctionArgumentObligation { arg_hir_id, .. } = obligation.cause.code() else { return false };
1128 let arg_node = self.tcx.hir().get(*arg_hir_id);
1129 let Node::Expr(Expr { kind: hir::ExprKind::Path(_), ..}) = arg_node else { return false };
1131 let clone_trait = self.tcx.require_lang_item(LangItem::Clone, None);
1132 let has_clone = |ty| {
1133 self.type_implements_trait(clone_trait, [ty], obligation.param_env)
1134 .must_apply_modulo_regions()
1137 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
1138 obligation.param_env,
1139 trait_pred.map_bound(|trait_pred| (trait_pred, *inner_ty)),
1142 if self.predicate_may_hold(&new_obligation) && has_clone(ty) {
1143 if !has_clone(param.to_ty(self.tcx)) {
1144 suggest_constraining_type_param(
1148 param.name.as_str(),
1153 err.span_suggestion_verbose(
1154 obligation.cause.span.shrink_to_hi(),
1155 "consider using clone here",
1156 ".clone()".to_string(),
1157 Applicability::MaybeIncorrect,
1164 fn suggest_add_reference_to_arg(
1166 obligation: &PredicateObligation<'tcx>,
1167 err: &mut Diagnostic,
1168 poly_trait_pred: ty::PolyTraitPredicate<'tcx>,
1169 has_custom_message: bool,
1171 let span = obligation.cause.span;
1173 let code = if let ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } =
1174 obligation.cause.code()
1177 } else if let ObligationCauseCode::ItemObligation(_)
1178 | ObligationCauseCode::ExprItemObligation(..) = obligation.cause.code()
1180 obligation.cause.code()
1181 } else if let ExpnKind::Desugaring(DesugaringKind::ForLoop) =
1182 span.ctxt().outer_expn_data().kind
1184 obligation.cause.code()
1189 // List of traits for which it would be nonsensical to suggest borrowing.
1190 // For instance, immutable references are always Copy, so suggesting to
1191 // borrow would always succeed, but it's probably not what the user wanted.
1192 let mut never_suggest_borrow: Vec<_> =
1193 [LangItem::Copy, LangItem::Clone, LangItem::Unpin, LangItem::Sized]
1195 .filter_map(|lang_item| self.tcx.lang_items().get(*lang_item))
1198 if let Some(def_id) = self.tcx.get_diagnostic_item(sym::Send) {
1199 never_suggest_borrow.push(def_id);
1202 let param_env = obligation.param_env;
1204 // Try to apply the original trait binding obligation by borrowing.
1205 let mut try_borrowing = |old_pred: ty::PolyTraitPredicate<'tcx>,
1206 blacklist: &[DefId]|
1208 if blacklist.contains(&old_pred.def_id()) {
1211 // We map bounds to `&T` and `&mut T`
1212 let trait_pred_and_imm_ref = old_pred.map_bound(|trait_pred| {
1215 self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, trait_pred.self_ty()),
1218 let trait_pred_and_mut_ref = old_pred.map_bound(|trait_pred| {
1221 self.tcx.mk_mut_ref(self.tcx.lifetimes.re_static, trait_pred.self_ty()),
1225 let mk_result = |trait_pred_and_new_ty| {
1227 self.mk_trait_obligation_with_new_self_ty(param_env, trait_pred_and_new_ty);
1228 self.predicate_must_hold_modulo_regions(&obligation)
1230 let imm_ref_self_ty_satisfies_pred = mk_result(trait_pred_and_imm_ref);
1231 let mut_ref_self_ty_satisfies_pred = mk_result(trait_pred_and_mut_ref);
1233 let (ref_inner_ty_satisfies_pred, ref_inner_ty_mut) =
1234 if let ObligationCauseCode::ItemObligation(_) | ObligationCauseCode::ExprItemObligation(..) = obligation.cause.code()
1235 && let ty::Ref(_, ty, mutability) = old_pred.self_ty().skip_binder().kind()
1238 mk_result(old_pred.map_bound(|trait_pred| (trait_pred, *ty))),
1239 mutability.is_mut(),
1245 if imm_ref_self_ty_satisfies_pred
1246 || mut_ref_self_ty_satisfies_pred
1247 || ref_inner_ty_satisfies_pred
1249 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1250 // We don't want a borrowing suggestion on the fields in structs,
1253 // the_foos: Vec<Foo>
1257 span.ctxt().outer_expn_data().kind,
1258 ExpnKind::Root | ExpnKind::Desugaring(DesugaringKind::ForLoop)
1262 if snippet.starts_with('&') {
1263 // This is already a literal borrow and the obligation is failing
1264 // somewhere else in the obligation chain. Do not suggest non-sense.
1267 // We have a very specific type of error, where just borrowing this argument
1268 // might solve the problem. In cases like this, the important part is the
1269 // original type obligation, not the last one that failed, which is arbitrary.
1270 // Because of this, we modify the error to refer to the original obligation and
1271 // return early in the caller.
1273 let msg = format!("the trait bound `{}` is not satisfied", old_pred);
1274 if has_custom_message {
1278 vec![(rustc_errors::DiagnosticMessage::Str(msg), Style::NoStyle)];
1283 "the trait `{}` is not implemented for `{}`",
1284 old_pred.print_modifiers_and_trait_path(),
1285 old_pred.self_ty().skip_binder(),
1289 if imm_ref_self_ty_satisfies_pred && mut_ref_self_ty_satisfies_pred {
1290 err.span_suggestions(
1291 span.shrink_to_lo(),
1292 "consider borrowing here",
1293 ["&".to_string(), "&mut ".to_string()],
1294 Applicability::MaybeIncorrect,
1297 let is_mut = mut_ref_self_ty_satisfies_pred || ref_inner_ty_mut;
1298 err.span_suggestion_verbose(
1299 span.shrink_to_lo(),
1301 "consider{} borrowing here",
1302 if is_mut { " mutably" } else { "" }
1304 format!("&{}", if is_mut { "mut " } else { "" }),
1305 Applicability::MaybeIncorrect,
1314 if let ObligationCauseCode::ImplDerivedObligation(cause) = &*code {
1315 try_borrowing(cause.derived.parent_trait_pred, &[])
1316 } else if let ObligationCauseCode::BindingObligation(_, _)
1317 | ObligationCauseCode::ItemObligation(_)
1318 | ObligationCauseCode::ExprItemObligation(..)
1319 | ObligationCauseCode::ExprBindingObligation(..) = code
1321 try_borrowing(poly_trait_pred, &never_suggest_borrow)
1327 // Suggest borrowing the type
1328 fn suggest_borrowing_for_object_cast(
1330 err: &mut Diagnostic,
1331 obligation: &PredicateObligation<'tcx>,
1333 object_ty: Ty<'tcx>,
1335 let ty::Dynamic(predicates, _, ty::Dyn) = object_ty.kind() else { return; };
1336 let self_ref_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_erased, self_ty);
1338 for predicate in predicates.iter() {
1339 if !self.predicate_must_hold_modulo_regions(
1340 &obligation.with(self.tcx, predicate.with_self_ty(self.tcx, self_ref_ty)),
1346 err.span_suggestion(
1347 obligation.cause.span.shrink_to_lo(),
1349 "consider borrowing the value, since `&{self_ty}` can be coerced into `{object_ty}`"
1352 Applicability::MaybeIncorrect,
1356 /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
1357 /// suggest removing these references until we reach a type that implements the trait.
1358 fn suggest_remove_reference(
1360 obligation: &PredicateObligation<'tcx>,
1361 err: &mut Diagnostic,
1362 trait_pred: ty::PolyTraitPredicate<'tcx>,
1364 let mut span = obligation.cause.span;
1365 let mut trait_pred = trait_pred;
1366 let mut code = obligation.cause.code();
1367 while let Some((c, Some(parent_trait_pred))) = code.parent() {
1368 // We want the root obligation, in order to detect properly handle
1369 // `for _ in &mut &mut vec![] {}`.
1371 trait_pred = parent_trait_pred;
1373 while span.desugaring_kind().is_some() {
1374 // Remove all the hir desugaring contexts while maintaining the macro contexts.
1377 let mut expr_finder = super::FindExprBySpan::new(span);
1378 let Some(hir::Node::Expr(body)) = self.tcx.hir().find(obligation.cause.body_id) else {
1381 expr_finder.visit_expr(&body);
1382 let mut maybe_suggest = |suggested_ty, count, suggestions| {
1383 // Remapping bound vars here
1384 let trait_pred_and_suggested_ty =
1385 trait_pred.map_bound(|trait_pred| (trait_pred, suggested_ty));
1387 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
1388 obligation.param_env,
1389 trait_pred_and_suggested_ty,
1392 if self.predicate_may_hold(&new_obligation) {
1393 let msg = if count == 1 {
1394 "consider removing the leading `&`-reference".to_string()
1396 format!("consider removing {count} leading `&`-references")
1399 err.multipart_suggestion_verbose(
1402 Applicability::MachineApplicable,
1410 // Maybe suggest removal of borrows from types in type parameters, like in
1411 // `src/test/ui/not-panic/not-panic-safe.rs`.
1413 let mut suggestions = vec![];
1414 // Skipping binder here, remapping below
1415 let mut suggested_ty = trait_pred.self_ty().skip_binder();
1416 if let Some(mut hir_ty) = expr_finder.ty_result {
1417 while let hir::TyKind::Ref(_, mut_ty) = &hir_ty.kind {
1419 let span = hir_ty.span.until(mut_ty.ty.span);
1420 suggestions.push((span, String::new()));
1422 let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else {
1425 suggested_ty = *inner_ty;
1429 if maybe_suggest(suggested_ty, count, suggestions.clone()) {
1435 // Maybe suggest removal of borrows from expressions, like in `for i in &&&foo {}`.
1436 let Some(mut expr) = expr_finder.result else { return false; };
1438 let mut suggestions = vec![];
1439 // Skipping binder here, remapping below
1440 let mut suggested_ty = trait_pred.self_ty().skip_binder();
1442 while let hir::ExprKind::AddrOf(_, _, borrowed) = expr.kind {
1444 let span = if expr.span.eq_ctxt(borrowed.span) {
1445 expr.span.until(borrowed.span)
1447 expr.span.with_hi(expr.span.lo() + BytePos(1))
1449 suggestions.push((span, String::new()));
1451 let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else {
1454 suggested_ty = *inner_ty;
1458 if maybe_suggest(suggested_ty, count, suggestions.clone()) {
1462 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
1463 && let hir::def::Res::Local(hir_id) = path.res
1464 && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(hir_id)
1465 && let Some(hir::Node::Local(local)) = self.tcx.hir().find_parent(binding.hir_id)
1466 && let None = local.ty
1467 && let Some(binding_expr) = local.init
1469 expr = binding_expr;
1477 fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic) {
1478 let span = obligation.cause.span;
1480 if let ObligationCauseCode::AwaitableExpr(hir_id) = obligation.cause.code().peel_derives() {
1481 let hir = self.tcx.hir();
1482 if let Some(hir::Node::Expr(expr)) = hir_id.and_then(|hir_id| hir.find(hir_id)) {
1483 // FIXME: use `obligation.predicate.kind()...trait_ref.self_ty()` to see if we have `()`
1484 // and if not maybe suggest doing something else? If we kept the expression around we
1485 // could also check if it is an fn call (very likely) and suggest changing *that*, if
1486 // it is from the local crate.
1487 err.span_suggestion(
1489 "remove the `.await`",
1491 Applicability::MachineApplicable,
1493 // FIXME: account for associated `async fn`s.
1494 if let hir::Expr { span, kind: hir::ExprKind::Call(base, _), .. } = expr {
1495 if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) =
1496 obligation.predicate.kind().skip_binder()
1498 err.span_label(*span, &format!("this call returns `{}`", pred.self_ty()));
1500 if let Some(typeck_results) = &self.typeck_results
1501 && let ty = typeck_results.expr_ty_adjusted(base)
1502 && let ty::FnDef(def_id, _substs) = ty.kind()
1503 && let Some(hir::Node::Item(hir::Item { ident, span, vis_span, .. })) =
1504 hir.get_if_local(*def_id)
1507 "alternatively, consider making `fn {}` asynchronous",
1510 if vis_span.is_empty() {
1511 err.span_suggestion_verbose(
1512 span.shrink_to_lo(),
1515 Applicability::MaybeIncorrect,
1518 err.span_suggestion_verbose(
1519 vis_span.shrink_to_hi(),
1522 Applicability::MaybeIncorrect,
1531 /// Check if the trait bound is implemented for a different mutability and note it in the
1533 fn suggest_change_mut(
1535 obligation: &PredicateObligation<'tcx>,
1536 err: &mut Diagnostic,
1537 trait_pred: ty::PolyTraitPredicate<'tcx>,
1539 let points_at_arg = matches!(
1540 obligation.cause.code(),
1541 ObligationCauseCode::FunctionArgumentObligation { .. },
1544 let span = obligation.cause.span;
1545 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
1547 snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
1548 if let Some('\'') = snippet.chars().filter(|c| !c.is_whitespace()).nth(refs_number) {
1549 // Do not suggest removal of borrow from type arguments.
1552 let trait_pred = self.resolve_vars_if_possible(trait_pred);
1553 if trait_pred.has_non_region_infer() {
1554 // Do not ICE while trying to find if a reborrow would succeed on a trait with
1555 // unresolved bindings.
1559 // Skipping binder here, remapping below
1560 if let ty::Ref(region, t_type, mutability) = *trait_pred.skip_binder().self_ty().kind()
1562 let suggested_ty = match mutability {
1563 hir::Mutability::Mut => self.tcx.mk_imm_ref(region, t_type),
1564 hir::Mutability::Not => self.tcx.mk_mut_ref(region, t_type),
1567 // Remapping bound vars here
1568 let trait_pred_and_suggested_ty =
1569 trait_pred.map_bound(|trait_pred| (trait_pred, suggested_ty));
1571 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
1572 obligation.param_env,
1573 trait_pred_and_suggested_ty,
1575 let suggested_ty_would_satisfy_obligation = self
1576 .evaluate_obligation_no_overflow(&new_obligation)
1577 .must_apply_modulo_regions();
1578 if suggested_ty_would_satisfy_obligation {
1583 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
1584 if points_at_arg && mutability.is_not() && refs_number > 0 {
1585 // If we have a call like foo(&mut buf), then don't suggest foo(&mut mut buf)
1587 .trim_start_matches(|c: char| c.is_whitespace() || c == '&')
1592 err.span_suggestion_verbose(
1594 "consider changing this borrow's mutability",
1596 Applicability::MachineApplicable,
1600 "`{}` is implemented for `{:?}`, but not for `{:?}`",
1601 trait_pred.print_modifiers_and_trait_path(),
1603 trait_pred.skip_binder().self_ty(),
1611 fn suggest_semicolon_removal(
1613 obligation: &PredicateObligation<'tcx>,
1614 err: &mut Diagnostic,
1616 trait_pred: ty::PolyTraitPredicate<'tcx>,
1618 let hir = self.tcx.hir();
1619 let parent_node = hir.parent_id(obligation.cause.body_id);
1620 let node = hir.find(parent_node);
1621 if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. })) = node
1622 && let hir::ExprKind::Block(blk, _) = &hir.body(*body_id).value.kind
1623 && sig.decl.output.span().overlaps(span)
1624 && blk.expr.is_none()
1625 && trait_pred.self_ty().skip_binder().is_unit()
1626 && let Some(stmt) = blk.stmts.last()
1627 && let hir::StmtKind::Semi(expr) = stmt.kind
1628 // Only suggest this if the expression behind the semicolon implements the predicate
1629 && let Some(typeck_results) = &self.typeck_results
1630 && let Some(ty) = typeck_results.expr_ty_opt(expr)
1631 && self.predicate_may_hold(&self.mk_trait_obligation_with_new_self_ty(
1632 obligation.param_env, trait_pred.map_bound(|trait_pred| (trait_pred, ty))
1638 "this expression has type `{}`, which implements `{}`",
1640 trait_pred.print_modifiers_and_trait_path()
1643 err.span_suggestion(
1644 self.tcx.sess.source_map().end_point(stmt.span),
1645 "remove this semicolon",
1647 Applicability::MachineApplicable
1654 fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span> {
1655 let hir = self.tcx.hir();
1656 let parent_node = hir.parent_id(obligation.cause.body_id);
1657 let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. })) = hir.find(parent_node) else {
1661 if let hir::FnRetTy::Return(ret_ty) = sig.decl.output { Some(ret_ty.span) } else { None }
1664 /// If all conditions are met to identify a returned `dyn Trait`, suggest using `impl Trait` if
1665 /// applicable and signal that the error has been expanded appropriately and needs to be
1667 fn suggest_impl_trait(
1669 err: &mut Diagnostic,
1671 obligation: &PredicateObligation<'tcx>,
1672 trait_pred: ty::PolyTraitPredicate<'tcx>,
1674 match obligation.cause.code().peel_derives() {
1675 // Only suggest `impl Trait` if the return type is unsized because it is `dyn Trait`.
1676 ObligationCauseCode::SizedReturnType => {}
1680 let hir = self.tcx.hir();
1681 let fn_hir_id = hir.parent_id(obligation.cause.body_id);
1682 let node = hir.find(fn_hir_id);
1683 let Some(hir::Node::Item(hir::Item {
1684 kind: hir::ItemKind::Fn(sig, _, body_id),
1690 let body = hir.body(*body_id);
1691 let trait_pred = self.resolve_vars_if_possible(trait_pred);
1692 let ty = trait_pred.skip_binder().self_ty();
1693 let is_object_safe = match ty.kind() {
1694 ty::Dynamic(predicates, _, ty::Dyn) => {
1695 // If the `dyn Trait` is not object safe, do not suggest `Box<dyn Trait>`.
1698 .map_or(true, |def_id| self.tcx.object_safety_violations(def_id).is_empty())
1700 // We only want to suggest `impl Trait` to `dyn Trait`s.
1701 // For example, `fn foo() -> str` needs to be filtered out.
1705 let hir::FnRetTy::Return(ret_ty) = sig.decl.output else {
1709 // Use `TypeVisitor` instead of the output type directly to find the span of `ty` for
1710 // cases like `fn foo() -> (dyn Trait, i32) {}`.
1711 // Recursively look for `TraitObject` types and if there's only one, use that span to
1712 // suggest `impl Trait`.
1714 // Visit to make sure there's a single `return` type to suggest `impl Trait`,
1715 // otherwise suggest using `Box<dyn Trait>` or an enum.
1716 let mut visitor = ReturnsVisitor::default();
1717 visitor.visit_body(&body);
1719 let typeck_results = self.typeck_results.as_ref().unwrap();
1720 let Some(liberated_sig) = typeck_results.liberated_fn_sigs().get(fn_hir_id).copied() else { return false; };
1722 let ret_types = visitor
1725 .filter_map(|expr| Some((expr.span, typeck_results.node_type_opt(expr.hir_id)?)))
1726 .map(|(expr_span, ty)| (expr_span, self.resolve_vars_if_possible(ty)));
1727 let (last_ty, all_returns_have_same_type, only_never_return) = ret_types.clone().fold(
1729 |(last_ty, mut same, only_never_return): (std::option::Option<Ty<'_>>, bool, bool),
1731 let ty = self.resolve_vars_if_possible(ty);
1733 !matches!(ty.kind(), ty::Error(_))
1734 && last_ty.map_or(true, |last_ty| {
1735 // FIXME: ideally we would use `can_coerce` here instead, but `typeck` comes
1736 // *after* in the dependency graph.
1737 match (ty.kind(), last_ty.kind()) {
1738 (Infer(InferTy::IntVar(_)), Infer(InferTy::IntVar(_)))
1739 | (Infer(InferTy::FloatVar(_)), Infer(InferTy::FloatVar(_)))
1740 | (Infer(InferTy::FreshIntTy(_)), Infer(InferTy::FreshIntTy(_)))
1742 Infer(InferTy::FreshFloatTy(_)),
1743 Infer(InferTy::FreshFloatTy(_)),
1748 (Some(ty), same, only_never_return && matches!(ty.kind(), ty::Never))
1751 let mut spans_and_needs_box = vec![];
1753 match liberated_sig.output().kind() {
1754 ty::Dynamic(predicates, _, ty::Dyn) => {
1755 let cause = ObligationCause::misc(ret_ty.span, fn_hir_id);
1756 let param_env = ty::ParamEnv::empty();
1758 if !only_never_return {
1759 for (expr_span, return_ty) in ret_types {
1760 let self_ty_satisfies_dyn_predicates = |self_ty| {
1761 predicates.iter().all(|predicate| {
1762 let pred = predicate.with_self_ty(self.tcx, self_ty);
1763 let obl = Obligation::new(self.tcx, cause.clone(), param_env, pred);
1764 self.predicate_may_hold(&obl)
1768 if let ty::Adt(def, substs) = return_ty.kind()
1770 && self_ty_satisfies_dyn_predicates(substs.type_at(0))
1772 spans_and_needs_box.push((expr_span, false));
1773 } else if self_ty_satisfies_dyn_predicates(return_ty) {
1774 spans_and_needs_box.push((expr_span, true));
1784 let sm = self.tcx.sess.source_map();
1785 if !ret_ty.span.overlaps(span) {
1788 let snippet = if let hir::TyKind::TraitObject(..) = ret_ty.kind {
1789 if let Ok(snippet) = sm.span_to_snippet(ret_ty.span) {
1795 // Substitute the type, so we can print a fixup given `type Alias = dyn Trait`
1796 let name = liberated_sig.output().to_string();
1798 name.strip_prefix('(').and_then(|name| name.strip_suffix(')')).unwrap_or(&name);
1799 if !name.starts_with("dyn ") {
1805 err.code(error_code!(E0746));
1806 err.set_primary_message("return type cannot have an unboxed trait object");
1807 err.children.clear();
1808 let impl_trait_msg = "for information on `impl Trait`, see \
1809 <https://doc.rust-lang.org/book/ch10-02-traits.html\
1810 #returning-types-that-implement-traits>";
1811 let trait_obj_msg = "for information on trait objects, see \
1812 <https://doc.rust-lang.org/book/ch17-02-trait-objects.html\
1813 #using-trait-objects-that-allow-for-values-of-different-types>";
1815 let has_dyn = snippet.split_whitespace().next().map_or(false, |s| s == "dyn");
1816 let trait_obj = if has_dyn { &snippet[4..] } else { &snippet };
1817 if only_never_return {
1818 // No return paths, probably using `panic!()` or similar.
1819 // Suggest `-> impl Trait`, and if `Trait` is object safe, `-> Box<dyn Trait>`.
1820 suggest_trait_object_return_type_alternatives(
1826 } else if let (Some(last_ty), true) = (last_ty, all_returns_have_same_type) {
1827 // Suggest `-> impl Trait`.
1828 err.span_suggestion(
1831 "use `impl {1}` as the return type, as all return paths are of type `{}`, \
1832 which implements `{1}`",
1835 format!("impl {}", trait_obj),
1836 Applicability::MachineApplicable,
1838 err.note(impl_trait_msg);
1841 // Suggest `-> Box<dyn Trait>` and `Box::new(returned_value)`.
1842 err.multipart_suggestion(
1843 "return a boxed trait object instead",
1845 (ret_ty.span.shrink_to_lo(), "Box<".to_string()),
1846 (span.shrink_to_hi(), ">".to_string()),
1848 Applicability::MaybeIncorrect,
1850 for (span, needs_box) in spans_and_needs_box {
1852 err.multipart_suggestion(
1853 "... and box this value",
1855 (span.shrink_to_lo(), "Box::new(".to_string()),
1856 (span.shrink_to_hi(), ")".to_string()),
1858 Applicability::MaybeIncorrect,
1863 // This is currently not possible to trigger because E0038 takes precedence, but
1864 // leave it in for completeness in case anything changes in an earlier stage.
1866 "if trait `{}` were object-safe, you could return a trait object",
1870 err.note(trait_obj_msg);
1872 "if all the returned values were of the same type you could use `impl {}` as the \
1876 err.note(impl_trait_msg);
1877 err.note("you can create a new `enum` with a variant for each returned type");
1882 fn point_at_returns_when_relevant(
1884 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
1885 obligation: &PredicateObligation<'tcx>,
1887 match obligation.cause.code().peel_derives() {
1888 ObligationCauseCode::SizedReturnType => {}
1892 let hir = self.tcx.hir();
1893 let parent_node = hir.parent_id(obligation.cause.body_id);
1894 let node = hir.find(parent_node);
1895 if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })) =
1898 let body = hir.body(*body_id);
1899 // Point at all the `return`s in the function as they have failed trait bounds.
1900 let mut visitor = ReturnsVisitor::default();
1901 visitor.visit_body(&body);
1902 let typeck_results = self.typeck_results.as_ref().unwrap();
1903 for expr in &visitor.returns {
1904 if let Some(returned_ty) = typeck_results.node_type_opt(expr.hir_id) {
1905 let ty = self.resolve_vars_if_possible(returned_ty);
1906 if ty.references_error() {
1907 // don't print out the [type error] here
1912 &format!("this returned value is of type `{}`", ty),
1920 fn report_closure_arg_mismatch(
1923 found_span: Option<Span>,
1924 found: ty::PolyTraitRef<'tcx>,
1925 expected: ty::PolyTraitRef<'tcx>,
1926 cause: &ObligationCauseCode<'tcx>,
1927 found_node: Option<Node<'_>>,
1928 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1929 pub(crate) fn build_fn_sig_ty<'tcx>(
1930 infcx: &InferCtxt<'tcx>,
1931 trait_ref: ty::PolyTraitRef<'tcx>,
1933 let inputs = trait_ref.skip_binder().substs.type_at(1);
1934 let sig = match inputs.kind() {
1935 ty::Tuple(inputs) if infcx.tcx.is_fn_trait(trait_ref.def_id()) => {
1936 infcx.tcx.mk_fn_sig(
1938 infcx.next_ty_var(TypeVariableOrigin {
1940 kind: TypeVariableOriginKind::MiscVariable,
1943 hir::Unsafety::Normal,
1947 _ => infcx.tcx.mk_fn_sig(
1948 std::iter::once(inputs),
1949 infcx.next_ty_var(TypeVariableOrigin {
1951 kind: TypeVariableOriginKind::MiscVariable,
1954 hir::Unsafety::Normal,
1959 infcx.tcx.mk_fn_ptr(trait_ref.rebind(sig))
1962 let argument_kind = match expected.skip_binder().self_ty().kind() {
1963 ty::Closure(..) => "closure",
1964 ty::Generator(..) => "generator",
1967 let mut err = struct_span_err!(
1971 "type mismatch in {argument_kind} arguments",
1974 err.span_label(span, "expected due to this");
1976 let found_span = found_span.unwrap_or(span);
1977 err.span_label(found_span, "found signature defined here");
1979 let expected = build_fn_sig_ty(self, expected);
1980 let found = build_fn_sig_ty(self, found);
1982 let (expected_str, found_str) = self.cmp(expected, found);
1984 let signature_kind = format!("{argument_kind} signature");
1985 err.note_expected_found(&signature_kind, expected_str, &signature_kind, found_str);
1987 self.note_conflicting_closure_bounds(cause, &mut err);
1989 if let Some(found_node) = found_node {
1990 hint_missing_borrow(span, found, expected, found_node, &mut err);
1996 // Add a note if there are two `Fn`-family bounds that have conflicting argument
1997 // requirements, which will always cause a closure to have a type error.
1998 fn note_conflicting_closure_bounds(
2000 cause: &ObligationCauseCode<'tcx>,
2001 err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
2003 // First, look for an `ExprBindingObligation`, which means we can get
2004 // the unsubstituted predicate list of the called function. And check
2005 // that the predicate that we failed to satisfy is a `Fn`-like trait.
2006 if let ObligationCauseCode::ExprBindingObligation(def_id, _, _, idx) = cause
2007 && let predicates = self.tcx.predicates_of(def_id).instantiate_identity(self.tcx)
2008 && let Some(pred) = predicates.predicates.get(*idx)
2009 && let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = pred.kind().skip_binder()
2010 && self.tcx.is_fn_trait(trait_pred.def_id())
2013 self.tcx.anonymize_bound_vars(pred.kind().rebind(trait_pred.self_ty()));
2014 let expected_substs = self
2016 .anonymize_bound_vars(pred.kind().rebind(trait_pred.trait_ref.substs));
2018 // Find another predicate whose self-type is equal to the expected self type,
2019 // but whose substs don't match.
2020 let other_pred = std::iter::zip(&predicates.predicates, &predicates.spans)
2022 .find(|(other_idx, (pred, _))| match pred.kind().skip_binder() {
2023 ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred))
2024 if self.tcx.is_fn_trait(trait_pred.def_id())
2026 // Make sure that the self type matches
2027 // (i.e. constraining this closure)
2029 == self.tcx.anonymize_bound_vars(
2030 pred.kind().rebind(trait_pred.self_ty()),
2032 // But the substs don't match (i.e. incompatible args)
2034 != self.tcx.anonymize_bound_vars(
2035 pred.kind().rebind(trait_pred.trait_ref.substs),
2042 // If we found one, then it's very likely the cause of the error.
2043 if let Some((_, (_, other_pred_span))) = other_pred {
2046 "closure inferred to have a different signature due to this bound",
2052 fn suggest_fully_qualified_path(
2054 err: &mut Diagnostic,
2059 if let Some(assoc_item) = self.tcx.opt_associated_item(item_def_id) {
2060 if let ty::AssocKind::Const | ty::AssocKind::Type = assoc_item.kind {
2062 "{}s cannot be accessed directly on a `trait`, they can only be \
2063 accessed through a specific `impl`",
2064 assoc_item.kind.as_def_kind().descr(item_def_id)
2066 err.span_suggestion(
2068 "use the fully qualified path to an implementation",
2069 format!("<Type as {}>::{}", self.tcx.def_path_str(trait_ref), assoc_item.name),
2070 Applicability::HasPlaceholders,
2076 /// Adds an async-await specific note to the diagnostic when the future does not implement
2077 /// an auto trait because of a captured type.
2080 /// note: future does not implement `Qux` as this value is used across an await
2081 /// --> $DIR/issue-64130-3-other.rs:17:5
2083 /// LL | let x = Foo;
2084 /// | - has type `Foo`
2085 /// LL | baz().await;
2086 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
2088 /// | - `x` is later dropped here
2091 /// When the diagnostic does not implement `Send` or `Sync` specifically, then the diagnostic
2092 /// is "replaced" with a different message and a more specific error.
2095 /// error: future cannot be sent between threads safely
2096 /// --> $DIR/issue-64130-2-send.rs:21:5
2098 /// LL | fn is_send<T: Send>(t: T) { }
2099 /// | ---- required by this bound in `is_send`
2101 /// LL | is_send(bar());
2102 /// | ^^^^^^^ future returned by `bar` is not send
2104 /// = help: within `impl std::future::Future`, the trait `std::marker::Send` is not
2105 /// implemented for `Foo`
2106 /// note: future is not send as this value is used across an await
2107 /// --> $DIR/issue-64130-2-send.rs:15:5
2109 /// LL | let x = Foo;
2110 /// | - has type `Foo`
2111 /// LL | baz().await;
2112 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
2114 /// | - `x` is later dropped here
2117 /// Returns `true` if an async-await specific note was added to the diagnostic.
2118 #[instrument(level = "debug", skip_all, fields(?obligation.predicate, ?obligation.cause.span))]
2119 fn maybe_note_obligation_cause_for_async_await(
2121 err: &mut Diagnostic,
2122 obligation: &PredicateObligation<'tcx>,
2124 let hir = self.tcx.hir();
2126 // Attempt to detect an async-await error by looking at the obligation causes, looking
2127 // for a generator to be present.
2129 // When a future does not implement a trait because of a captured type in one of the
2130 // generators somewhere in the call stack, then the result is a chain of obligations.
2132 // Given an `async fn` A that calls an `async fn` B which captures a non-send type and that
2133 // future is passed as an argument to a function C which requires a `Send` type, then the
2134 // chain looks something like this:
2136 // - `BuiltinDerivedObligation` with a generator witness (B)
2137 // - `BuiltinDerivedObligation` with a generator (B)
2138 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
2139 // - `BuiltinDerivedObligation` with a generator witness (A)
2140 // - `BuiltinDerivedObligation` with a generator (A)
2141 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
2142 // - `BindingObligation` with `impl_send (Send requirement)
2144 // The first obligation in the chain is the most useful and has the generator that captured
2145 // the type. The last generator (`outer_generator` below) has information about where the
2146 // bound was introduced. At least one generator should be present for this diagnostic to be
2148 let (mut trait_ref, mut target_ty) = match obligation.predicate.kind().skip_binder() {
2149 ty::PredicateKind::Clause(ty::Clause::Trait(p)) => (Some(p), Some(p.self_ty())),
2152 let mut generator = None;
2153 let mut outer_generator = None;
2154 let mut next_code = Some(obligation.cause.code());
2156 let mut seen_upvar_tys_infer_tuple = false;
2158 while let Some(code) = next_code {
2161 ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => {
2162 next_code = Some(parent_code);
2164 ObligationCauseCode::ImplDerivedObligation(cause) => {
2165 let ty = cause.derived.parent_trait_pred.skip_binder().self_ty();
2167 parent_trait_ref = ?cause.derived.parent_trait_pred,
2168 self_ty.kind = ?ty.kind(),
2173 ty::Generator(did, ..) => {
2174 generator = generator.or(Some(did));
2175 outer_generator = Some(did);
2177 ty::GeneratorWitness(..) => {}
2178 ty::Tuple(_) if !seen_upvar_tys_infer_tuple => {
2179 // By introducing a tuple of upvar types into the chain of obligations
2180 // of a generator, the first non-generator item is now the tuple itself,
2181 // we shall ignore this.
2183 seen_upvar_tys_infer_tuple = true;
2185 _ if generator.is_none() => {
2186 trait_ref = Some(cause.derived.parent_trait_pred.skip_binder());
2187 target_ty = Some(ty);
2192 next_code = Some(&cause.derived.parent_code);
2194 ObligationCauseCode::DerivedObligation(derived_obligation)
2195 | ObligationCauseCode::BuiltinDerivedObligation(derived_obligation) => {
2196 let ty = derived_obligation.parent_trait_pred.skip_binder().self_ty();
2198 parent_trait_ref = ?derived_obligation.parent_trait_pred,
2199 self_ty.kind = ?ty.kind(),
2203 ty::Generator(did, ..) => {
2204 generator = generator.or(Some(did));
2205 outer_generator = Some(did);
2207 ty::GeneratorWitness(..) => {}
2208 ty::Tuple(_) if !seen_upvar_tys_infer_tuple => {
2209 // By introducing a tuple of upvar types into the chain of obligations
2210 // of a generator, the first non-generator item is now the tuple itself,
2211 // we shall ignore this.
2213 seen_upvar_tys_infer_tuple = true;
2215 _ if generator.is_none() => {
2216 trait_ref = Some(derived_obligation.parent_trait_pred.skip_binder());
2217 target_ty = Some(ty);
2222 next_code = Some(&derived_obligation.parent_code);
2228 // Only continue if a generator was found.
2229 debug!(?generator, ?trait_ref, ?target_ty);
2230 let (Some(generator_did), Some(trait_ref), Some(target_ty)) = (generator, trait_ref, target_ty) else {
2234 let span = self.tcx.def_span(generator_did);
2236 let generator_did_root = self.tcx.typeck_root_def_id(generator_did);
2239 ?generator_did_root,
2240 typeck_results.hir_owner = ?self.typeck_results.as_ref().map(|t| t.hir_owner),
2244 let generator_body = generator_did
2246 .and_then(|def_id| hir.maybe_body_owned_by(def_id))
2247 .map(|body_id| hir.body(body_id));
2248 let mut visitor = AwaitsVisitor::default();
2249 if let Some(body) = generator_body {
2250 visitor.visit_body(body);
2252 debug!(awaits = ?visitor.awaits);
2254 // Look for a type inside the generator interior that matches the target type to get
2256 let target_ty_erased = self.tcx.erase_regions(target_ty);
2257 let ty_matches = |ty| -> bool {
2258 // Careful: the regions for types that appear in the
2259 // generator interior are not generally known, so we
2260 // want to erase them when comparing (and anyway,
2261 // `Send` and other bounds are generally unaffected by
2262 // the choice of region). When erasing regions, we
2263 // also have to erase late-bound regions. This is
2264 // because the types that appear in the generator
2265 // interior generally contain "bound regions" to
2266 // represent regions that are part of the suspended
2267 // generator frame. Bound regions are preserved by
2268 // `erase_regions` and so we must also call
2269 // `erase_late_bound_regions`.
2270 let ty_erased = self.tcx.erase_late_bound_regions(ty);
2271 let ty_erased = self.tcx.erase_regions(ty_erased);
2272 let eq = ty_erased == target_ty_erased;
2273 debug!(?ty_erased, ?target_ty_erased, ?eq);
2277 // Get the typeck results from the infcx if the generator is the function we are currently
2278 // type-checking; otherwise, get them by performing a query. This is needed to avoid
2279 // cycles. If we can't use resolved types because the generator comes from another crate,
2280 // we still provide a targeted error but without all the relevant spans.
2281 let generator_data = match &self.typeck_results {
2282 Some(t) if t.hir_owner.to_def_id() == generator_did_root => GeneratorData::Local(&t),
2283 _ if generator_did.is_local() => {
2284 GeneratorData::Local(self.tcx.typeck(generator_did.expect_local()))
2286 _ if let Some(generator_diag_data) = self.tcx.generator_diagnostic_data(generator_did) => {
2287 GeneratorData::Foreign(generator_diag_data)
2292 let mut interior_or_upvar_span = None;
2294 let from_awaited_ty = generator_data.get_from_await_ty(visitor, hir, ty_matches);
2295 debug!(?from_awaited_ty);
2297 // The generator interior types share the same binders
2298 if let Some(cause) =
2299 generator_data.get_generator_interior_types().skip_binder().iter().find(
2300 |ty::GeneratorInteriorTypeCause { ty, .. }| {
2301 ty_matches(generator_data.get_generator_interior_types().rebind(*ty))
2305 let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } = cause;
2307 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(
2309 Some((*scope_span, *yield_span, *expr, from_awaited_ty)),
2313 if interior_or_upvar_span.is_none() {
2314 interior_or_upvar_span =
2315 generator_data.try_get_upvar_span(&self, generator_did, ty_matches);
2318 if interior_or_upvar_span.is_none() && generator_data.is_foreign() {
2319 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(span, None));
2322 debug!(?interior_or_upvar_span);
2323 if let Some(interior_or_upvar_span) = interior_or_upvar_span {
2324 let is_async = self.tcx.generator_is_async(generator_did);
2325 let typeck_results = match generator_data {
2326 GeneratorData::Local(typeck_results) => Some(typeck_results),
2327 GeneratorData::Foreign(_) => None,
2329 self.note_obligation_cause_for_async_await(
2331 interior_or_upvar_span,
2346 /// Unconditionally adds the diagnostic note described in
2347 /// `maybe_note_obligation_cause_for_async_await`'s documentation comment.
2348 #[instrument(level = "debug", skip_all)]
2349 fn note_obligation_cause_for_async_await(
2351 err: &mut Diagnostic,
2352 interior_or_upvar_span: GeneratorInteriorOrUpvar,
2354 outer_generator: Option<DefId>,
2355 trait_pred: ty::TraitPredicate<'tcx>,
2356 target_ty: Ty<'tcx>,
2357 typeck_results: Option<&ty::TypeckResults<'tcx>>,
2358 obligation: &PredicateObligation<'tcx>,
2359 next_code: Option<&ObligationCauseCode<'tcx>>,
2361 let source_map = self.tcx.sess.source_map();
2363 let (await_or_yield, an_await_or_yield) =
2364 if is_async { ("await", "an await") } else { ("yield", "a yield") };
2365 let future_or_generator = if is_async { "future" } else { "generator" };
2367 // Special case the primary error message when send or sync is the trait that was
2369 let hir = self.tcx.hir();
2370 let trait_explanation = if let Some(name @ (sym::Send | sym::Sync)) =
2371 self.tcx.get_diagnostic_name(trait_pred.def_id())
2373 let (trait_name, trait_verb) =
2374 if name == sym::Send { ("`Send`", "sent") } else { ("`Sync`", "shared") };
2377 err.set_primary_message(format!(
2378 "{} cannot be {} between threads safely",
2379 future_or_generator, trait_verb
2382 let original_span = err.span.primary_span().unwrap();
2383 let mut span = MultiSpan::from_span(original_span);
2385 let message = outer_generator
2386 .and_then(|generator_did| {
2387 Some(match self.tcx.generator_kind(generator_did).unwrap() {
2388 GeneratorKind::Gen => format!("generator is not {}", trait_name),
2389 GeneratorKind::Async(AsyncGeneratorKind::Fn) => self
2391 .parent(generator_did)
2393 .map(|parent_did| hir.local_def_id_to_hir_id(parent_did))
2394 .and_then(|parent_hir_id| hir.opt_name(parent_hir_id))
2396 format!("future returned by `{}` is not {}", name, trait_name)
2398 GeneratorKind::Async(AsyncGeneratorKind::Block) => {
2399 format!("future created by async block is not {}", trait_name)
2401 GeneratorKind::Async(AsyncGeneratorKind::Closure) => {
2402 format!("future created by async closure is not {}", trait_name)
2406 .unwrap_or_else(|| format!("{} is not {}", future_or_generator, trait_name));
2408 span.push_span_label(original_span, message);
2411 format!("is not {}", trait_name)
2413 format!("does not implement `{}`", trait_pred.print_modifiers_and_trait_path())
2416 let mut explain_yield =
2417 |interior_span: Span, yield_span: Span, scope_span: Option<Span>| {
2418 let mut span = MultiSpan::from_span(yield_span);
2419 let snippet = match source_map.span_to_snippet(interior_span) {
2420 // #70935: If snippet contains newlines, display "the value" instead
2421 // so that we do not emit complex diagnostics.
2422 Ok(snippet) if !snippet.contains('\n') => format!("`{}`", snippet),
2423 _ => "the value".to_string(),
2425 // note: future is not `Send` as this value is used across an await
2426 // --> $DIR/issue-70935-complex-spans.rs:13:9
2428 // LL | baz(|| async {
2429 // | ______________-
2432 // LL | | foo(tx.clone());
2434 // | | - ^^^^^^ await occurs here, with value maybe used later
2436 // | has type `closure` which is not `Send`
2437 // note: value is later dropped here
2441 span.push_span_label(
2443 format!("{} occurs here, with {} maybe used later", await_or_yield, snippet),
2445 span.push_span_label(
2447 format!("has type `{}` which {}", target_ty, trait_explanation),
2449 if let Some(scope_span) = scope_span {
2450 let scope_span = source_map.end_point(scope_span);
2452 let msg = format!("{} is later dropped here", snippet);
2453 span.push_span_label(scope_span, msg);
2458 "{} {} as this value is used across {}",
2459 future_or_generator, trait_explanation, an_await_or_yield
2463 match interior_or_upvar_span {
2464 GeneratorInteriorOrUpvar::Interior(interior_span, interior_extra_info) => {
2465 if let Some((scope_span, yield_span, expr, from_awaited_ty)) = interior_extra_info {
2466 if let Some(await_span) = from_awaited_ty {
2467 // The type causing this obligation is one being awaited at await_span.
2468 let mut span = MultiSpan::from_span(await_span);
2469 span.push_span_label(
2472 "await occurs here on type `{}`, which {}",
2473 target_ty, trait_explanation
2479 "future {not_trait} as it awaits another future which {not_trait}",
2480 not_trait = trait_explanation
2484 // Look at the last interior type to get a span for the `.await`.
2486 generator_interior_types = ?format_args!(
2487 "{:#?}", typeck_results.as_ref().map(|t| &t.generator_interior_types)
2490 explain_yield(interior_span, yield_span, scope_span);
2493 if let Some(expr_id) = expr {
2494 let expr = hir.expect_expr(expr_id);
2495 debug!("target_ty evaluated from {:?}", expr);
2497 let parent = hir.parent_id(expr_id);
2498 if let Some(hir::Node::Expr(e)) = hir.find(parent) {
2499 let parent_span = hir.span(parent);
2500 let parent_did = parent.owner.to_def_id();
2503 // fn foo(&self) -> i32 {}
2506 // ^^^^^^^ a temporary `&T` created inside this method call due to `&self`
2509 let is_region_borrow = if let Some(typeck_results) = typeck_results {
2511 .expr_adjustments(expr)
2513 .any(|adj| adj.is_region_borrow())
2519 // struct Foo(*const u8);
2520 // bar(Foo(std::ptr::null())).await;
2521 // ^^^^^^^^^^^^^^^^^^^^^ raw-ptr `*T` created inside this struct ctor.
2523 debug!(parent_def_kind = ?self.tcx.def_kind(parent_did));
2524 let is_raw_borrow_inside_fn_like_call =
2525 match self.tcx.def_kind(parent_did) {
2526 DefKind::Fn | DefKind::Ctor(..) => target_ty.is_unsafe_ptr(),
2529 if let Some(typeck_results) = typeck_results {
2530 if (typeck_results.is_method_call(e) && is_region_borrow)
2531 || is_raw_borrow_inside_fn_like_call
2535 "consider moving this into a `let` \
2536 binding to create a shorter lived borrow",
2544 GeneratorInteriorOrUpvar::Upvar(upvar_span) => {
2545 // `Some((ref_ty, is_mut))` if `target_ty` is `&T` or `&mut T` and fails to impl `Send`
2546 let non_send = match target_ty.kind() {
2547 ty::Ref(_, ref_ty, mutability) => match self.evaluate_obligation(&obligation) {
2548 Ok(eval) if !eval.may_apply() => Some((ref_ty, mutability.is_mut())),
2554 let (span_label, span_note) = match non_send {
2555 // if `target_ty` is `&T` or `&mut T` and fails to impl `Send`,
2556 // include suggestions to make `T: Sync` so that `&T: Send`,
2557 // or to make `T: Send` so that `&mut T: Send`
2558 Some((ref_ty, is_mut)) => {
2559 let ref_ty_trait = if is_mut { "Send" } else { "Sync" };
2560 let ref_kind = if is_mut { "&mut" } else { "&" };
2563 "has type `{}` which {}, because `{}` is not `{}`",
2564 target_ty, trait_explanation, ref_ty, ref_ty_trait
2567 "captured value {} because `{}` references cannot be sent unless their referent is `{}`",
2568 trait_explanation, ref_kind, ref_ty_trait
2573 format!("has type `{}` which {}", target_ty, trait_explanation),
2574 format!("captured value {}", trait_explanation),
2578 let mut span = MultiSpan::from_span(upvar_span);
2579 span.push_span_label(upvar_span, span_label);
2580 err.span_note(span, &span_note);
2584 // Add a note for the item obligation that remains - normally a note pointing to the
2585 // bound that introduced the obligation (e.g. `T: Send`).
2587 self.note_obligation_cause_code(
2589 obligation.predicate,
2590 obligation.param_env,
2593 &mut Default::default(),
2597 fn note_obligation_cause_code<T>(
2599 err: &mut Diagnostic,
2601 param_env: ty::ParamEnv<'tcx>,
2602 cause_code: &ObligationCauseCode<'tcx>,
2603 obligated_types: &mut Vec<Ty<'tcx>>,
2604 seen_requirements: &mut FxHashSet<DefId>,
2606 T: ToPredicate<'tcx>,
2609 let predicate = predicate.to_predicate(tcx);
2611 ObligationCauseCode::ExprAssignable
2612 | ObligationCauseCode::MatchExpressionArm { .. }
2613 | ObligationCauseCode::Pattern { .. }
2614 | ObligationCauseCode::IfExpression { .. }
2615 | ObligationCauseCode::IfExpressionWithNoElse
2616 | ObligationCauseCode::MainFunctionType
2617 | ObligationCauseCode::StartFunctionType
2618 | ObligationCauseCode::IntrinsicType
2619 | ObligationCauseCode::MethodReceiver
2620 | ObligationCauseCode::ReturnNoExpression
2621 | ObligationCauseCode::UnifyReceiver(..)
2622 | ObligationCauseCode::OpaqueType
2623 | ObligationCauseCode::MiscObligation
2624 | ObligationCauseCode::WellFormed(..)
2625 | ObligationCauseCode::MatchImpl(..)
2626 | ObligationCauseCode::ReturnType
2627 | ObligationCauseCode::ReturnValue(_)
2628 | ObligationCauseCode::BlockTailExpression(_)
2629 | ObligationCauseCode::AwaitableExpr(_)
2630 | ObligationCauseCode::ForLoopIterator
2631 | ObligationCauseCode::QuestionMark
2632 | ObligationCauseCode::CheckAssociatedTypeBounds { .. }
2633 | ObligationCauseCode::LetElse
2634 | ObligationCauseCode::BinOp { .. }
2635 | ObligationCauseCode::AscribeUserTypeProvePredicate(..)
2636 | ObligationCauseCode::RustCall => {}
2637 ObligationCauseCode::SliceOrArrayElem => {
2638 err.note("slice and array elements must have `Sized` type");
2640 ObligationCauseCode::TupleElem => {
2641 err.note("only the last element of a tuple may have a dynamically sized type");
2643 ObligationCauseCode::ProjectionWf(data) => {
2644 err.note(&format!("required so that the projection `{data}` is well-formed"));
2646 ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
2648 "required so that reference `{ref_ty}` does not outlive its referent"
2651 ObligationCauseCode::ObjectTypeBound(object_ty, region) => {
2653 "required so that the lifetime bound of `{}` for `{}` is satisfied",
2657 ObligationCauseCode::ItemObligation(_)
2658 | ObligationCauseCode::ExprItemObligation(..) => {
2659 // We hold the `DefId` of the item introducing the obligation, but displaying it
2660 // doesn't add user usable information. It always point at an associated item.
2662 ObligationCauseCode::BindingObligation(item_def_id, span)
2663 | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..) => {
2664 let item_name = tcx.def_path_str(item_def_id);
2665 let short_item_name = with_forced_trimmed_paths!(tcx.def_path_str(item_def_id));
2666 let mut multispan = MultiSpan::from(span);
2667 let sm = tcx.sess.source_map();
2668 if let Some(ident) = tcx.opt_item_ident(item_def_id) {
2670 match (sm.lookup_line(ident.span.hi()), sm.lookup_line(span.lo())) {
2671 (Ok(l), Ok(r)) => l.line == r.line,
2674 if ident.span.is_visible(sm) && !ident.span.overlaps(span) && !same_line {
2675 multispan.push_span_label(ident.span, "required by a bound in this");
2678 let descr = format!("required by a bound in `{item_name}`");
2679 if span.is_visible(sm) {
2680 let msg = format!("required by this bound in `{short_item_name}`");
2681 multispan.push_span_label(span, msg);
2682 err.span_note(multispan, &descr);
2684 err.span_note(tcx.def_span(item_def_id), &descr);
2687 ObligationCauseCode::ObjectCastObligation(concrete_ty, object_ty) => {
2688 let (concrete_ty, concrete_file) =
2689 self.tcx.short_ty_string(self.resolve_vars_if_possible(concrete_ty));
2690 let (object_ty, object_file) =
2691 self.tcx.short_ty_string(self.resolve_vars_if_possible(object_ty));
2692 err.note(&with_forced_trimmed_paths!(format!(
2693 "required for the cast from `{concrete_ty}` to the object type `{object_ty}`",
2695 if let Some(file) = concrete_file {
2697 "the full name for the casted type has been written to '{}'",
2701 if let Some(file) = object_file {
2703 "the full name for the object type has been written to '{}'",
2708 ObligationCauseCode::Coercion { source: _, target } => {
2709 err.note(&format!("required by cast to type `{}`", self.ty_to_string(target)));
2711 ObligationCauseCode::RepeatElementCopy { is_const_fn } => {
2713 "the `Copy` trait is required because this value will be copied for each element of the array",
2718 "consider creating a new `const` item and initializing it with the result \
2719 of the function call to be used in the repeat position, like \
2720 `const VAL: Type = const_fn();` and `let x = [VAL; 42];`",
2724 if self.tcx.sess.is_nightly_build() && is_const_fn {
2726 "create an inline `const` block, see RFC #2920 \
2727 <https://github.com/rust-lang/rfcs/pull/2920> for more information",
2731 ObligationCauseCode::VariableType(hir_id) => {
2732 let parent_node = self.tcx.hir().parent_id(hir_id);
2733 match self.tcx.hir().find(parent_node) {
2734 Some(Node::Local(hir::Local { ty: Some(ty), .. })) => {
2735 err.span_suggestion_verbose(
2736 ty.span.shrink_to_lo(),
2737 "consider borrowing here",
2739 Applicability::MachineApplicable,
2741 err.note("all local variables must have a statically known size");
2743 Some(Node::Local(hir::Local {
2744 init: Some(hir::Expr { kind: hir::ExprKind::Index(_, _), span, .. }),
2747 // When encountering an assignment of an unsized trait, like
2748 // `let x = ""[..];`, provide a suggestion to borrow the initializer in
2749 // order to use have a slice instead.
2750 err.span_suggestion_verbose(
2751 span.shrink_to_lo(),
2752 "consider borrowing here",
2754 Applicability::MachineApplicable,
2756 err.note("all local variables must have a statically known size");
2758 Some(Node::Param(param)) => {
2759 err.span_suggestion_verbose(
2760 param.ty_span.shrink_to_lo(),
2761 "function arguments must have a statically known size, borrowed types \
2762 always have a known size",
2764 Applicability::MachineApplicable,
2768 err.note("all local variables must have a statically known size");
2771 if !self.tcx.features().unsized_locals {
2772 err.help("unsized locals are gated as an unstable feature");
2775 ObligationCauseCode::SizedArgumentType(sp) => {
2776 if let Some(span) = sp {
2777 if let ty::PredicateKind::Clause(clause) = predicate.kind().skip_binder()
2778 && let ty::Clause::Trait(trait_pred) = clause
2779 && let ty::Dynamic(..) = trait_pred.self_ty().kind()
2781 let span = if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
2782 && snippet.starts_with("dyn ")
2784 let pos = snippet.len() - snippet[3..].trim_start().len();
2785 span.with_hi(span.lo() + BytePos(pos as u32))
2789 err.span_suggestion_verbose(
2791 "you can use `impl Trait` as the argument type",
2792 "impl ".to_string(),
2793 Applicability::MaybeIncorrect,
2796 err.span_suggestion_verbose(
2797 span.shrink_to_lo(),
2798 "function arguments must have a statically known size, borrowed types \
2799 always have a known size",
2801 Applicability::MachineApplicable,
2804 err.note("all function arguments must have a statically known size");
2806 if tcx.sess.opts.unstable_features.is_nightly_build()
2807 && !self.tcx.features().unsized_fn_params
2809 err.help("unsized fn params are gated as an unstable feature");
2812 ObligationCauseCode::SizedReturnType => {
2813 err.note("the return type of a function must have a statically known size");
2815 ObligationCauseCode::SizedYieldType => {
2816 err.note("the yield type of a generator must have a statically known size");
2818 ObligationCauseCode::SizedBoxType => {
2819 err.note("the type of a box expression must have a statically known size");
2821 ObligationCauseCode::AssignmentLhsSized => {
2822 err.note("the left-hand-side of an assignment must have a statically known size");
2824 ObligationCauseCode::TupleInitializerSized => {
2825 err.note("tuples must have a statically known size to be initialized");
2827 ObligationCauseCode::StructInitializerSized => {
2828 err.note("structs must have a statically known size to be initialized");
2830 ObligationCauseCode::FieldSized { adt_kind: ref item, last, span } => {
2832 AdtKind::Struct => {
2835 "the last field of a packed struct may only have a \
2836 dynamically sized type if it does not need drop to be run",
2840 "only the last field of a struct may have a dynamically sized type",
2845 err.note("no field of a union may have a dynamically sized type");
2848 err.note("no field of an enum variant may have a dynamically sized type");
2851 err.help("change the field's type to have a statically known size");
2852 err.span_suggestion(
2853 span.shrink_to_lo(),
2854 "borrowed types always have a statically known size",
2856 Applicability::MachineApplicable,
2858 err.multipart_suggestion(
2859 "the `Box` type always has a statically known size and allocates its contents \
2862 (span.shrink_to_lo(), "Box<".to_string()),
2863 (span.shrink_to_hi(), ">".to_string()),
2865 Applicability::MachineApplicable,
2868 ObligationCauseCode::ConstSized => {
2869 err.note("constant expressions must have a statically known size");
2871 ObligationCauseCode::InlineAsmSized => {
2872 err.note("all inline asm arguments must have a statically known size");
2874 ObligationCauseCode::ConstPatternStructural => {
2875 err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`");
2877 ObligationCauseCode::SharedStatic => {
2878 err.note("shared static variables must have a type that implements `Sync`");
2880 ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
2881 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
2882 let ty = parent_trait_ref.skip_binder().self_ty();
2883 if parent_trait_ref.references_error() {
2884 // NOTE(eddyb) this was `.cancel()`, but `err`
2885 // is borrowed, so we can't fully defuse it.
2886 err.downgrade_to_delayed_bug();
2890 // If the obligation for a tuple is set directly by a Generator or Closure,
2891 // then the tuple must be the one containing capture types.
2892 let is_upvar_tys_infer_tuple = if !matches!(ty.kind(), ty::Tuple(..)) {
2895 if let ObligationCauseCode::BuiltinDerivedObligation(data) = &*data.parent_code
2897 let parent_trait_ref =
2898 self.resolve_vars_if_possible(data.parent_trait_pred);
2899 let nested_ty = parent_trait_ref.skip_binder().self_ty();
2900 matches!(nested_ty.kind(), ty::Generator(..))
2901 || matches!(nested_ty.kind(), ty::Closure(..))
2907 let identity_future = tcx.require_lang_item(LangItem::IdentityFuture, None);
2909 // Don't print the tuple of capture types
2911 if !is_upvar_tys_infer_tuple {
2912 let msg = with_forced_trimmed_paths!(format!(
2913 "required because it appears within the type `{ty}`",
2916 ty::Adt(def, _) => match self.tcx.opt_item_ident(def.did()) {
2917 Some(ident) => err.span_note(ident.span, &msg),
2918 None => err.note(&msg),
2920 ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) => {
2921 // Avoid printing the future from `core::future::identity_future`, it's not helpful
2922 if tcx.parent(*def_id) == identity_future {
2926 // If the previous type is `identity_future`, this is the future generated by the body of an async function.
2927 // Avoid printing it twice (it was already printed in the `ty::Generator` arm below).
2928 let is_future = tcx.ty_is_opaque_future(ty);
2932 "note_obligation_cause_code: check for async fn"
2935 && obligated_types.last().map_or(false, |ty| match ty.kind() {
2936 ty::Generator(last_def_id, ..) => {
2937 tcx.generator_is_async(*last_def_id)
2944 err.span_note(self.tcx.def_span(def_id), &msg)
2946 ty::GeneratorWitness(bound_tys) => {
2947 use std::fmt::Write;
2949 // FIXME: this is kind of an unusual format for rustc, can we make it more clear?
2950 // Maybe we should just remove this note altogether?
2951 // FIXME: only print types which don't meet the trait requirement
2953 "required because it captures the following types: ".to_owned();
2954 for ty in bound_tys.skip_binder() {
2955 with_forced_trimmed_paths!(write!(msg, "`{}`, ", ty).unwrap());
2957 err.note(msg.trim_end_matches(", "))
2959 ty::Generator(def_id, _, _) => {
2960 let sp = self.tcx.def_span(def_id);
2962 // Special-case this to say "async block" instead of `[static generator]`.
2963 let kind = tcx.generator_kind(def_id).unwrap().descr();
2966 with_forced_trimmed_paths!(&format!(
2967 "required because it's used within this {kind}",
2971 ty::Closure(def_id, _) => err.span_note(
2972 self.tcx.def_span(def_id),
2973 "required because it's used within this closure",
2975 _ => err.note(&msg),
2980 obligated_types.push(ty);
2982 let parent_predicate = parent_trait_ref;
2983 if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
2984 // #74711: avoid a stack overflow
2985 ensure_sufficient_stack(|| {
2986 self.note_obligation_cause_code(
2996 ensure_sufficient_stack(|| {
2997 self.note_obligation_cause_code(
3001 cause_code.peel_derives(),
3008 ObligationCauseCode::ImplDerivedObligation(ref data) => {
3009 let mut parent_trait_pred =
3010 self.resolve_vars_if_possible(data.derived.parent_trait_pred);
3011 parent_trait_pred.remap_constness_diag(param_env);
3012 let parent_def_id = parent_trait_pred.def_id();
3013 let (self_ty, file) =
3014 self.tcx.short_ty_string(parent_trait_pred.skip_binder().self_ty());
3016 "required for `{self_ty}` to implement `{}`",
3017 parent_trait_pred.print_modifiers_and_trait_path()
3019 let mut is_auto_trait = false;
3020 match self.tcx.hir().get_if_local(data.impl_def_id) {
3021 Some(Node::Item(hir::Item {
3022 kind: hir::ItemKind::Trait(is_auto, ..),
3026 // FIXME: we should do something else so that it works even on crate foreign
3028 is_auto_trait = matches!(is_auto, hir::IsAuto::Yes);
3029 err.span_note(ident.span, &msg);
3031 Some(Node::Item(hir::Item {
3032 kind: hir::ItemKind::Impl(hir::Impl { of_trait, self_ty, .. }),
3035 let mut spans = Vec::with_capacity(2);
3036 if let Some(trait_ref) = of_trait {
3037 spans.push(trait_ref.path.span);
3039 spans.push(self_ty.span);
3040 let mut spans: MultiSpan = spans.into();
3042 self_ty.span.ctxt().outer_expn_data().kind,
3043 ExpnKind::Macro(MacroKind::Derive, _)
3045 of_trait.as_ref().map(|t| t.path.span.ctxt().outer_expn_data().kind),
3046 Some(ExpnKind::Macro(MacroKind::Derive, _))
3048 spans.push_span_label(
3050 "unsatisfied trait bound introduced in this `derive` macro",
3052 } else if !data.span.is_dummy() && !data.span.overlaps(self_ty.span) {
3053 spans.push_span_label(
3055 "unsatisfied trait bound introduced here",
3058 err.span_note(spans, &msg);
3065 if let Some(file) = file {
3067 "the full type name has been written to '{}'",
3071 let mut parent_predicate = parent_trait_pred;
3072 let mut data = &data.derived;
3074 seen_requirements.insert(parent_def_id);
3076 // We don't want to point at the ADT saying "required because it appears within
3077 // the type `X`", like we would otherwise do in test `supertrait-auto-trait.rs`.
3078 while let ObligationCauseCode::BuiltinDerivedObligation(derived) =
3081 let child_trait_ref =
3082 self.resolve_vars_if_possible(derived.parent_trait_pred);
3083 let child_def_id = child_trait_ref.def_id();
3084 if seen_requirements.insert(child_def_id) {
3088 parent_predicate = child_trait_ref.to_predicate(tcx);
3089 parent_trait_pred = child_trait_ref;
3092 while let ObligationCauseCode::ImplDerivedObligation(child) = &*data.parent_code {
3093 // Skip redundant recursive obligation notes. See `ui/issue-20413.rs`.
3094 let child_trait_pred =
3095 self.resolve_vars_if_possible(child.derived.parent_trait_pred);
3096 let child_def_id = child_trait_pred.def_id();
3097 if seen_requirements.insert(child_def_id) {
3101 data = &child.derived;
3102 parent_predicate = child_trait_pred.to_predicate(tcx);
3103 parent_trait_pred = child_trait_pred;
3107 "{} redundant requirement{} hidden",
3111 let (self_ty, file) =
3112 self.tcx.short_ty_string(parent_trait_pred.skip_binder().self_ty());
3114 "required for `{self_ty}` to implement `{}`",
3115 parent_trait_pred.print_modifiers_and_trait_path()
3117 if let Some(file) = file {
3119 "the full type name has been written to '{}'",
3124 // #74711: avoid a stack overflow
3125 ensure_sufficient_stack(|| {
3126 self.note_obligation_cause_code(
3136 ObligationCauseCode::DerivedObligation(ref data) => {
3137 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
3138 let parent_predicate = parent_trait_ref;
3139 // #74711: avoid a stack overflow
3140 ensure_sufficient_stack(|| {
3141 self.note_obligation_cause_code(
3151 ObligationCauseCode::FunctionArgumentObligation {
3157 self.note_function_argument_obligation(
3165 ensure_sufficient_stack(|| {
3166 self.note_obligation_cause_code(
3176 ObligationCauseCode::CompareImplItemObligation { trait_item_def_id, kind, .. } => {
3177 let item_name = self.tcx.item_name(trait_item_def_id);
3179 "the requirement `{predicate}` appears on the `impl`'s {kind} \
3180 `{item_name}` but not on the corresponding trait's {kind}",
3184 .opt_item_ident(trait_item_def_id)
3186 .unwrap_or_else(|| self.tcx.def_span(trait_item_def_id));
3187 let mut assoc_span: MultiSpan = sp.into();
3188 assoc_span.push_span_label(
3190 format!("this trait's {kind} doesn't have the requirement `{predicate}`"),
3192 if let Some(ident) = self
3194 .opt_associated_item(trait_item_def_id)
3195 .and_then(|i| self.tcx.opt_item_ident(i.container_id(self.tcx)))
3197 assoc_span.push_span_label(ident.span, "in this trait");
3199 err.span_note(assoc_span, &msg);
3201 ObligationCauseCode::TrivialBound => {
3202 err.help("see issue #48214");
3203 if tcx.sess.opts.unstable_features.is_nightly_build() {
3204 err.help("add `#![feature(trivial_bounds)]` to the crate attributes to enable");
3207 ObligationCauseCode::OpaqueReturnType(expr_info) => {
3208 if let Some((expr_ty, expr_span)) = expr_info {
3209 let expr_ty = with_forced_trimmed_paths!(self.ty_to_string(expr_ty));
3212 with_forced_trimmed_paths!(format!(
3213 "return type was inferred to be `{expr_ty}` here",
3222 level = "debug", skip(self, err), fields(trait_pred.self_ty = ?trait_pred.self_ty())
3224 fn suggest_await_before_try(
3226 err: &mut Diagnostic,
3227 obligation: &PredicateObligation<'tcx>,
3228 trait_pred: ty::PolyTraitPredicate<'tcx>,
3231 let body_hir_id = obligation.cause.body_id;
3232 let item_id = self.tcx.hir().parent_id(body_hir_id);
3234 if let Some(body_id) =
3235 self.tcx.hir().maybe_body_owned_by(self.tcx.hir().local_def_id(item_id))
3237 let body = self.tcx.hir().body(body_id);
3238 if let Some(hir::GeneratorKind::Async(_)) = body.generator_kind {
3239 let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
3241 let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
3242 let impls_future = self.type_implements_trait(
3244 [self.tcx.erase_late_bound_regions(self_ty)],
3245 obligation.param_env,
3247 if !impls_future.must_apply_modulo_regions() {
3251 let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0];
3252 // `<T as Future>::Output`
3253 let projection_ty = trait_pred.map_bound(|trait_pred| {
3254 self.tcx.mk_projection(
3256 // Future::Output has no substs
3257 [trait_pred.self_ty()],
3260 let InferOk { value: projection_ty, .. } =
3261 self.at(&obligation.cause, obligation.param_env).normalize(projection_ty);
3264 normalized_projection_type = ?self.resolve_vars_if_possible(projection_ty)
3266 let try_obligation = self.mk_trait_obligation_with_new_self_ty(
3267 obligation.param_env,
3268 trait_pred.map_bound(|trait_pred| (trait_pred, projection_ty.skip_binder())),
3270 debug!(try_trait_obligation = ?try_obligation);
3271 if self.predicate_may_hold(&try_obligation)
3272 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
3273 && snippet.ends_with('?')
3275 err.span_suggestion_verbose(
3276 span.with_hi(span.hi() - BytePos(1)).shrink_to_hi(),
3277 "consider `await`ing on the `Future`",
3279 Applicability::MaybeIncorrect,
3286 fn suggest_floating_point_literal(
3288 obligation: &PredicateObligation<'tcx>,
3289 err: &mut Diagnostic,
3290 trait_ref: &ty::PolyTraitRef<'tcx>,
3292 let rhs_span = match obligation.cause.code() {
3293 ObligationCauseCode::BinOp { rhs_span: Some(span), is_lit, .. } if *is_lit => span,
3296 if let ty::Float(_) = trait_ref.skip_binder().self_ty().kind()
3297 && let ty::Infer(InferTy::IntVar(_)) = trait_ref.skip_binder().substs.type_at(1).kind()
3299 err.span_suggestion_verbose(
3300 rhs_span.shrink_to_hi(),
3301 "consider using a floating-point literal by writing it with `.0`",
3303 Applicability::MaybeIncorrect,
3310 obligation: &PredicateObligation<'tcx>,
3311 err: &mut Diagnostic,
3312 trait_pred: ty::PolyTraitPredicate<'tcx>,
3314 let Some(diagnostic_name) = self.tcx.get_diagnostic_name(trait_pred.def_id()) else {
3317 let (adt, substs) = match trait_pred.skip_binder().self_ty().kind() {
3318 ty::Adt(adt, substs) if adt.did().is_local() => (adt, substs),
3322 let is_derivable_trait = match diagnostic_name {
3323 sym::Default => !adt.is_enum(),
3324 sym::PartialEq | sym::PartialOrd => {
3325 let rhs_ty = trait_pred.skip_binder().trait_ref.substs.type_at(1);
3326 trait_pred.skip_binder().self_ty() == rhs_ty
3328 sym::Eq | sym::Ord | sym::Clone | sym::Copy | sym::Hash | sym::Debug => true,
3331 is_derivable_trait &&
3332 // Ensure all fields impl the trait.
3333 adt.all_fields().all(|field| {
3334 let field_ty = field.ty(self.tcx, substs);
3335 let trait_substs = match diagnostic_name {
3336 sym::PartialEq | sym::PartialOrd => {
3341 let trait_pred = trait_pred.map_bound_ref(|tr| ty::TraitPredicate {
3342 trait_ref: self.tcx.mk_trait_ref(
3343 trait_pred.def_id(),
3344 [field_ty].into_iter().chain(trait_substs),
3348 let field_obl = Obligation::new(
3350 obligation.cause.clone(),
3351 obligation.param_env,
3354 self.predicate_must_hold_modulo_regions(&field_obl)
3358 err.span_suggestion_verbose(
3359 self.tcx.def_span(adt.did()).shrink_to_lo(),
3361 "consider annotating `{}` with `#[derive({})]`",
3362 trait_pred.skip_binder().self_ty(),
3365 format!("#[derive({})]\n", diagnostic_name),
3366 Applicability::MaybeIncorrect,
3371 fn suggest_dereferencing_index(
3373 obligation: &PredicateObligation<'tcx>,
3374 err: &mut Diagnostic,
3375 trait_pred: ty::PolyTraitPredicate<'tcx>,
3377 if let ObligationCauseCode::ImplDerivedObligation(_) = obligation.cause.code()
3378 && self.tcx.is_diagnostic_item(sym::SliceIndex, trait_pred.skip_binder().trait_ref.def_id)
3379 && let ty::Slice(_) = trait_pred.skip_binder().trait_ref.substs.type_at(1).kind()
3380 && let ty::Ref(_, inner_ty, _) = trait_pred.skip_binder().self_ty().kind()
3381 && let ty::Uint(ty::UintTy::Usize) = inner_ty.kind()
3383 err.span_suggestion_verbose(
3384 obligation.cause.span.shrink_to_lo(),
3385 "dereference this index",
3387 Applicability::MachineApplicable,
3391 fn note_function_argument_obligation(
3394 err: &mut Diagnostic,
3395 parent_code: &ObligationCauseCode<'tcx>,
3396 param_env: ty::ParamEnv<'tcx>,
3397 failed_pred: ty::Predicate<'tcx>,
3401 let hir = tcx.hir();
3402 if let Some(Node::Expr(expr)) = hir.find(arg_hir_id)
3403 && let Some(typeck_results) = &self.typeck_results
3405 if let hir::Expr { kind: hir::ExprKind::Block(..), .. } = expr {
3406 let expr = expr.peel_blocks();
3407 let ty = typeck_results.expr_ty_adjusted_opt(expr).unwrap_or(tcx.ty_error());
3408 let span = expr.span;
3409 if Some(span) != err.span.primary_span() {
3412 if ty.references_error() {
3415 let ty = with_forced_trimmed_paths!(self.ty_to_string(ty));
3416 format!("this tail expression is of type `{ty}`")
3422 // FIXME: visit the ty to see if there's any closure involved, and if there is,
3423 // check whether its evaluated return type is the same as the one corresponding
3424 // to an associated type (as seen from `trait_pred`) in the predicate. Like in
3425 // trait_pred `S: Sum<<Self as Iterator>::Item>` and predicate `i32: Sum<&()>`
3426 let mut type_diffs = vec![];
3428 if let ObligationCauseCode::ExprBindingObligation(def_id, _, _, idx) = parent_code.deref()
3429 && let Some(node_substs) = typeck_results.node_substs_opt(call_hir_id)
3430 && let where_clauses = self.tcx.predicates_of(def_id).instantiate(self.tcx, node_substs)
3431 && let Some(where_pred) = where_clauses.predicates.get(*idx)
3433 if let Some(where_pred) = where_pred.to_opt_poly_trait_pred()
3434 && let Some(failed_pred) = failed_pred.to_opt_poly_trait_pred()
3436 let mut c = CollectAllMismatches {
3441 if let Ok(_) = c.relate(where_pred, failed_pred) {
3442 type_diffs = c.errors;
3444 } else if let Some(where_pred) = where_pred.to_opt_poly_projection_pred()
3445 && let Some(failed_pred) = failed_pred.to_opt_poly_projection_pred()
3446 && let Some(found) = failed_pred.skip_binder().term.ty()
3449 Sorts(ty::error::ExpectedFound {
3450 expected: self.tcx.mk_ty(ty::Alias(ty::Projection, where_pred.skip_binder().projection_ty)),
3456 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
3457 && let hir::Path { res: hir::def::Res::Local(hir_id), .. } = path
3458 && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(*hir_id)
3459 && let parent_hir_id = self.tcx.hir().parent_id(binding.hir_id)
3460 && let Some(hir::Node::Local(local)) = self.tcx.hir().find(parent_hir_id)
3461 && let Some(binding_expr) = local.init
3463 // If the expression we're calling on is a binding, we want to point at the
3464 // `let` when talking about the type. Otherwise we'll point at every part
3465 // of the method chain with the type.
3466 self.point_at_chain(binding_expr, &typeck_results, type_diffs, param_env, err);
3468 self.point_at_chain(expr, &typeck_results, type_diffs, param_env, err);
3471 let call_node = hir.find(call_hir_id);
3472 if let Some(Node::Expr(hir::Expr {
3473 kind: hir::ExprKind::MethodCall(path, rcvr, ..), ..
3476 if Some(rcvr.span) == err.span.primary_span() {
3477 err.replace_span_with(path.ident.span, true);
3480 if let Some(Node::Expr(hir::Expr {
3482 hir::ExprKind::Call(hir::Expr { span, .. }, _)
3483 | hir::ExprKind::MethodCall(hir::PathSegment { ident: Ident { span, .. }, .. }, ..),
3485 })) = hir.find(call_hir_id)
3487 if Some(*span) != err.span.primary_span() {
3488 err.span_label(*span, "required by a bound introduced by this call");
3495 expr: &hir::Expr<'_>,
3496 typeck_results: &TypeckResults<'tcx>,
3497 type_diffs: Vec<TypeError<'tcx>>,
3498 param_env: ty::ParamEnv<'tcx>,
3499 err: &mut Diagnostic,
3501 let mut primary_spans = vec![];
3502 let mut span_labels = vec![];
3506 let mut print_root_expr = true;
3507 let mut assocs = vec![];
3508 let mut expr = expr;
3509 let mut prev_ty = self.resolve_vars_if_possible(
3510 typeck_results.expr_ty_adjusted_opt(expr).unwrap_or(tcx.ty_error()),
3512 while let hir::ExprKind::MethodCall(_path_segment, rcvr_expr, _args, span) = expr.kind {
3513 // Point at every method call in the chain with the resulting type.
3514 // vec![1, 2, 3].iter().map(mapper).sum<i32>()
3515 // ^^^^^^ ^^^^^^^^^^^
3517 let assocs_in_this_method =
3518 self.probe_assoc_types_at_expr(&type_diffs, span, prev_ty, expr.hir_id, param_env);
3519 assocs.push(assocs_in_this_method);
3520 prev_ty = self.resolve_vars_if_possible(
3521 typeck_results.expr_ty_adjusted_opt(expr).unwrap_or(tcx.ty_error()),
3524 if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
3525 && let hir::Path { res: hir::def::Res::Local(hir_id), .. } = path
3526 && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(*hir_id)
3527 && let Some(parent) = self.tcx.hir().find_parent(binding.hir_id)
3529 // We've reached the root of the method call chain...
3530 if let hir::Node::Local(local) = parent
3531 && let Some(binding_expr) = local.init
3533 // ...and it is a binding. Get the binding creation and continue the chain.
3534 expr = binding_expr;
3536 if let hir::Node::Param(param) = parent {
3537 // ...and it is a an fn argument.
3538 let prev_ty = self.resolve_vars_if_possible(
3539 typeck_results.node_type_opt(param.hir_id).unwrap_or(tcx.ty_error()),
3541 let assocs_in_this_method = self.probe_assoc_types_at_expr(&type_diffs, param.ty_span, prev_ty, param.hir_id, param_env);
3542 if assocs_in_this_method.iter().any(|a| a.is_some()) {
3543 assocs.push(assocs_in_this_method);
3544 print_root_expr = false;
3550 // We want the type before deref coercions, otherwise we talk about `&[_]`
3551 // instead of `Vec<_>`.
3552 if let Some(ty) = typeck_results.expr_ty_opt(expr) && print_root_expr {
3553 let ty = with_forced_trimmed_paths!(self.ty_to_string(ty));
3554 // Point at the root expression
3555 // vec![1, 2, 3].iter().map(mapper).sum<i32>()
3557 span_labels.push((expr.span, format!("this expression has type `{ty}`")));
3559 // Only show this if it is not a "trivial" expression (not a method
3560 // chain) and there are associated types to talk about.
3561 let mut assocs = assocs.into_iter().peekable();
3562 while let Some(assocs_in_method) = assocs.next() {
3563 let Some(prev_assoc_in_method) = assocs.peek() else {
3564 for entry in assocs_in_method {
3565 let Some((span, (assoc, ty))) = entry else { continue; };
3566 if primary_spans.is_empty() || type_diffs.iter().any(|diff| {
3567 let Sorts(expected_found) = diff else { return false; };
3568 self.can_eq(param_env, expected_found.found, ty).is_ok()
3570 // FIXME: this doesn't quite work for `Iterator::collect`
3571 // because we have `Vec<i32>` and `()`, but we'd want `i32`
3572 // to point at the `.into_iter()` call, but as long as we
3573 // still point at the other method calls that might have
3574 // introduced the issue, this is fine for now.
3575 primary_spans.push(span);
3579 with_forced_trimmed_paths!(format!(
3580 "`{}` is `{ty}` here",
3581 self.tcx.def_path_str(assoc),
3587 for (entry, prev_entry) in
3588 assocs_in_method.into_iter().zip(prev_assoc_in_method.into_iter())
3590 match (entry, prev_entry) {
3591 (Some((span, (assoc, ty))), Some((_, (_, prev_ty)))) => {
3592 let ty_str = with_forced_trimmed_paths!(self.ty_to_string(ty));
3594 let assoc = with_forced_trimmed_paths!(self.tcx.def_path_str(assoc));
3595 if self.can_eq(param_env, ty, *prev_ty).is_err() {
3596 if type_diffs.iter().any(|diff| {
3597 let Sorts(expected_found) = diff else { return false; };
3598 self.can_eq(param_env, expected_found.found, ty).is_ok()
3600 primary_spans.push(span);
3603 .push((span, format!("`{assoc}` changed to `{ty_str}` here")));
3605 span_labels.push((span, format!("`{assoc}` remains `{ty_str}` here")));
3608 (Some((span, (assoc, ty))), None) => {
3611 with_forced_trimmed_paths!(format!(
3612 "`{}` is `{}` here",
3613 self.tcx.def_path_str(assoc),
3614 self.ty_to_string(ty),
3618 (None, Some(_)) | (None, None) => {}
3622 if !primary_spans.is_empty() {
3623 let mut multi_span: MultiSpan = primary_spans.into();
3624 for (span, label) in span_labels {
3625 multi_span.push_span_label(span, label);
3629 "the method call chain might not have had the expected associated types",
3634 fn probe_assoc_types_at_expr(
3636 type_diffs: &[TypeError<'tcx>],
3639 body_id: hir::HirId,
3640 param_env: ty::ParamEnv<'tcx>,
3641 ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>> {
3642 let ocx = ObligationCtxt::new_in_snapshot(self.infcx);
3643 let mut assocs_in_this_method = Vec::with_capacity(type_diffs.len());
3644 for diff in type_diffs {
3645 let Sorts(expected_found) = diff else { continue; };
3646 let ty::Alias(ty::Projection, proj) = expected_found.expected.kind() else { continue; };
3648 let origin = TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span };
3649 let trait_def_id = proj.trait_def_id(self.tcx);
3650 // Make `Self` be equivalent to the type of the call chain
3651 // expression we're looking at now, so that we can tell what
3652 // for example `Iterator::Item` is at this point in the chain.
3653 let substs = InternalSubsts::for_item(self.tcx, trait_def_id, |param, _| {
3655 ty::GenericParamDefKind::Type { .. } => {
3656 if param.index == 0 {
3657 return prev_ty.into();
3660 ty::GenericParamDefKind::Lifetime | ty::GenericParamDefKind::Const { .. } => {}
3662 self.var_for_def(span, param)
3664 // This will hold the resolved type of the associated type, if the
3665 // current expression implements the trait that associated type is
3666 // in. For example, this would be what `Iterator::Item` is here.
3667 let ty_var = self.infcx.next_ty_var(origin);
3668 // This corresponds to `<ExprTy as Iterator>::Item = _`.
3669 let projection = ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::Projection(
3670 ty::ProjectionPredicate {
3671 projection_ty: self.tcx.mk_alias_ty(proj.def_id, substs),
3672 term: ty_var.into(),
3675 // Add `<ExprTy as Iterator>::Item = _` obligation.
3676 ocx.register_obligation(Obligation::misc(
3677 self.tcx, span, body_id, param_env, projection,
3679 if ocx.select_where_possible().is_empty() {
3680 // `ty_var` now holds the type that `Item` is for `ExprTy`.
3681 let ty_var = self.resolve_vars_if_possible(ty_var);
3682 assocs_in_this_method.push(Some((span, (proj.def_id, ty_var))));
3684 // `<ExprTy as Iterator>` didn't select, so likely we've
3685 // reached the end of the iterator chain, like the originating
3687 // Keep the space consistent for later zipping.
3688 assocs_in_this_method.push(None);
3691 assocs_in_this_method
3695 /// Add a hint to add a missing borrow or remove an unnecessary one.
3696 fn hint_missing_borrow<'tcx>(
3700 found_node: Node<'_>,
3701 err: &mut Diagnostic,
3703 let found_args = match found.kind() {
3704 ty::FnPtr(f) => f.inputs().skip_binder().iter(),
3706 span_bug!(span, "found was converted to a FnPtr above but is now {:?}", kind)
3709 let expected_args = match expected.kind() {
3710 ty::FnPtr(f) => f.inputs().skip_binder().iter(),
3712 span_bug!(span, "expected was converted to a FnPtr above but is now {:?}", kind)
3716 // This could be a variant constructor, for example.
3717 let Some(fn_decl) = found_node.fn_decl() else { return; };
3719 let arg_spans = fn_decl.inputs.iter().map(|ty| ty.span);
3721 fn get_deref_type_and_refs(mut ty: Ty<'_>) -> (Ty<'_>, usize) {
3724 while let ty::Ref(_, new_ty, _) = ty.kind() {
3732 let mut to_borrow = Vec::new();
3733 let mut remove_borrow = Vec::new();
3735 for ((found_arg, expected_arg), arg_span) in found_args.zip(expected_args).zip(arg_spans) {
3736 let (found_ty, found_refs) = get_deref_type_and_refs(*found_arg);
3737 let (expected_ty, expected_refs) = get_deref_type_and_refs(*expected_arg);
3739 if found_ty == expected_ty {
3740 if found_refs < expected_refs {
3741 to_borrow.push((arg_span, expected_arg.to_string()));
3742 } else if found_refs > expected_refs {
3743 remove_borrow.push((arg_span, expected_arg.to_string()));
3748 if !to_borrow.is_empty() {
3749 err.multipart_suggestion(
3750 "consider borrowing the argument",
3752 Applicability::MaybeIncorrect,
3756 if !remove_borrow.is_empty() {
3757 err.multipart_suggestion(
3758 "do not borrow the argument",
3760 Applicability::MaybeIncorrect,
3765 /// Collect all the returned expressions within the input expression.
3766 /// Used to point at the return spans when we want to suggest some change to them.
3768 pub struct ReturnsVisitor<'v> {
3769 pub returns: Vec<&'v hir::Expr<'v>>,
3770 in_block_tail: bool,
3773 impl<'v> Visitor<'v> for ReturnsVisitor<'v> {
3774 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
3775 // Visit every expression to detect `return` paths, either through the function's tail
3776 // expression or `return` statements. We walk all nodes to find `return` statements, but
3777 // we only care about tail expressions when `in_block_tail` is `true`, which means that
3778 // they're in the return path of the function body.
3780 hir::ExprKind::Ret(Some(ex)) => {
3781 self.returns.push(ex);
3783 hir::ExprKind::Block(block, _) if self.in_block_tail => {
3784 self.in_block_tail = false;
3785 for stmt in block.stmts {
3786 hir::intravisit::walk_stmt(self, stmt);
3788 self.in_block_tail = true;
3789 if let Some(expr) = block.expr {
3790 self.visit_expr(expr);
3793 hir::ExprKind::If(_, then, else_opt) if self.in_block_tail => {
3794 self.visit_expr(then);
3795 if let Some(el) = else_opt {
3796 self.visit_expr(el);
3799 hir::ExprKind::Match(_, arms, _) if self.in_block_tail => {
3801 self.visit_expr(arm.body);
3804 // We need to walk to find `return`s in the entire body.
3805 _ if !self.in_block_tail => hir::intravisit::walk_expr(self, ex),
3806 _ => self.returns.push(ex),
3810 fn visit_body(&mut self, body: &'v hir::Body<'v>) {
3811 assert!(!self.in_block_tail);
3812 if body.generator_kind().is_none() {
3813 if let hir::ExprKind::Block(block, None) = body.value.kind {
3814 if block.expr.is_some() {
3815 self.in_block_tail = true;
3819 hir::intravisit::walk_body(self, body);
3823 /// Collect all the awaited expressions within the input expression.
3825 struct AwaitsVisitor {
3826 awaits: Vec<hir::HirId>,
3829 impl<'v> Visitor<'v> for AwaitsVisitor {
3830 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
3831 if let hir::ExprKind::Yield(_, hir::YieldSource::Await { expr: Some(id) }) = ex.kind {
3832 self.awaits.push(id)
3834 hir::intravisit::walk_expr(self, ex)
3838 pub trait NextTypeParamName {
3839 fn next_type_param_name(&self, name: Option<&str>) -> String;
3842 impl NextTypeParamName for &[hir::GenericParam<'_>] {
3843 fn next_type_param_name(&self, name: Option<&str>) -> String {
3844 // This is the list of possible parameter names that we might suggest.
3845 let name = name.and_then(|n| n.chars().next()).map(|c| c.to_string().to_uppercase());
3846 let name = name.as_deref();
3847 let possible_names = [name.unwrap_or("T"), "T", "U", "V", "X", "Y", "Z", "A", "B", "C"];
3848 let used_names = self
3850 .filter_map(|p| match p.name {
3851 hir::ParamName::Plain(ident) => Some(ident.name),
3854 .collect::<Vec<_>>();
3858 .find(|n| !used_names.contains(&Symbol::intern(n)))
3859 .unwrap_or(&"ParamName")
3864 fn suggest_trait_object_return_type_alternatives(
3865 err: &mut Diagnostic,
3868 is_object_safe: bool,
3870 err.span_suggestion(
3873 "use `impl {}` as the return type if all return paths have the same type but you \
3874 want to expose only the trait in the signature",
3877 format!("impl {}", trait_obj),
3878 Applicability::MaybeIncorrect,
3881 err.multipart_suggestion(
3883 "use a boxed trait object if all return paths implement trait `{}`",
3887 (ret_ty.shrink_to_lo(), "Box<".to_string()),
3888 (ret_ty.shrink_to_hi(), ">".to_string()),
3890 Applicability::MaybeIncorrect,
3895 /// Collect the spans that we see the generic param `param_did`
3896 struct ReplaceImplTraitVisitor<'a> {
3897 ty_spans: &'a mut Vec<Span>,
3901 impl<'a, 'hir> hir::intravisit::Visitor<'hir> for ReplaceImplTraitVisitor<'a> {
3902 fn visit_ty(&mut self, t: &'hir hir::Ty<'hir>) {
3903 if let hir::TyKind::Path(hir::QPath::Resolved(
3905 hir::Path { res: hir::def::Res::Def(_, segment_did), .. },
3908 if self.param_did == *segment_did {
3909 // `fn foo(t: impl Trait)`
3910 // ^^^^^^^^^^ get this to suggest `T` instead
3912 // There might be more than one `impl Trait`.
3913 self.ty_spans.push(t.span);
3918 hir::intravisit::walk_ty(self, t);
3922 // Replace `param` with `replace_ty`
3923 struct ReplaceImplTraitFolder<'tcx> {
3925 param: &'tcx ty::GenericParamDef,
3926 replace_ty: Ty<'tcx>,
3929 impl<'tcx> TypeFolder<'tcx> for ReplaceImplTraitFolder<'tcx> {
3930 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
3931 if let ty::Param(ty::ParamTy { index, .. }) = t.kind() {
3932 if self.param.index == *index {
3933 return self.replace_ty;
3936 t.super_fold_with(self)
3939 fn tcx(&self) -> TyCtxt<'tcx> {