2 EvaluationResult, Obligation, ObligationCause, ObligationCauseCode, PredicateObligation,
6 use crate::autoderef::Autoderef;
7 use crate::infer::InferCtxt;
8 use crate::traits::normalize_projection_type;
10 use rustc_errors::{error_code, struct_span_err, Applicability, DiagnosticBuilder, Style};
12 use rustc_hir::def::DefKind;
13 use rustc_hir::def_id::DefId;
14 use rustc_hir::intravisit::Visitor;
15 use rustc_hir::lang_items;
16 use rustc_hir::{AsyncGeneratorKind, GeneratorKind, Node};
17 use rustc_middle::ty::{
18 self, suggest_constraining_type_param, AdtKind, DefIdTree, Infer, InferTy, ToPredicate, Ty,
19 TyCtxt, TypeFoldable, WithConstness,
21 use rustc_middle::ty::{TypeAndMut, TypeckTables};
22 use rustc_span::symbol::{kw, sym, Ident, Symbol};
23 use rustc_span::{MultiSpan, Span, DUMMY_SP};
26 use super::InferCtxtPrivExt;
27 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
30 pub enum GeneratorInteriorOrUpvar {
31 // span of interior type
37 // This trait is public to expose the diagnostics methods to clippy.
38 pub trait InferCtxtExt<'tcx> {
39 fn suggest_restricting_param_bound(
41 err: &mut DiagnosticBuilder<'_>,
42 trait_ref: ty::PolyTraitRef<'tcx>,
46 fn suggest_dereferences(
48 obligation: &PredicateObligation<'tcx>,
49 err: &mut DiagnosticBuilder<'tcx>,
50 trait_ref: &ty::PolyTraitRef<'tcx>,
57 err: &mut DiagnosticBuilder<'_>,
63 obligation: &PredicateObligation<'tcx>,
64 err: &mut DiagnosticBuilder<'_>,
65 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
69 fn suggest_add_reference_to_arg(
71 obligation: &PredicateObligation<'tcx>,
72 err: &mut DiagnosticBuilder<'_>,
73 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
75 has_custom_message: bool,
78 fn suggest_remove_reference(
80 obligation: &PredicateObligation<'tcx>,
81 err: &mut DiagnosticBuilder<'_>,
82 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
85 fn suggest_change_mut(
87 obligation: &PredicateObligation<'tcx>,
88 err: &mut DiagnosticBuilder<'_>,
89 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
93 fn suggest_semicolon_removal(
95 obligation: &PredicateObligation<'tcx>,
96 err: &mut DiagnosticBuilder<'_>,
98 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
101 fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span>;
103 fn suggest_impl_trait(
105 err: &mut DiagnosticBuilder<'_>,
107 obligation: &PredicateObligation<'tcx>,
108 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
111 fn point_at_returns_when_relevant(
113 err: &mut DiagnosticBuilder<'_>,
114 obligation: &PredicateObligation<'tcx>,
117 fn report_closure_arg_mismatch(
120 found_span: Option<Span>,
121 expected_ref: ty::PolyTraitRef<'tcx>,
122 found: ty::PolyTraitRef<'tcx>,
123 ) -> DiagnosticBuilder<'tcx>;
125 fn suggest_fully_qualified_path(
127 err: &mut DiagnosticBuilder<'_>,
133 fn maybe_note_obligation_cause_for_async_await(
135 err: &mut DiagnosticBuilder<'_>,
136 obligation: &PredicateObligation<'tcx>,
139 fn note_obligation_cause_for_async_await(
141 err: &mut DiagnosticBuilder<'_>,
142 interior_or_upvar_span: GeneratorInteriorOrUpvar,
143 interior_extra_info: Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>,
144 inner_generator_body: Option<&hir::Body<'tcx>>,
145 outer_generator: Option<DefId>,
146 trait_ref: ty::TraitRef<'tcx>,
148 tables: &ty::TypeckTables<'tcx>,
149 obligation: &PredicateObligation<'tcx>,
150 next_code: Option<&ObligationCauseCode<'tcx>>,
153 fn note_obligation_cause_code<T>(
155 err: &mut DiagnosticBuilder<'_>,
157 cause_code: &ObligationCauseCode<'tcx>,
158 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
162 fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder<'_>);
164 /// Suggest to await before try: future? => future.await?
165 fn suggest_await_before_try(
167 err: &mut DiagnosticBuilder<'_>,
168 obligation: &PredicateObligation<'tcx>,
169 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
174 fn predicate_constraint(generics: &hir::Generics<'_>, pred: String) -> (Span, String) {
176 generics.where_clause.tail_span_for_suggestion(),
179 if !generics.where_clause.predicates.is_empty() { "," } else { " where" },
185 /// Type parameter needs more bounds. The trivial case is `T` `where T: Bound`, but
186 /// it can also be an `impl Trait` param that needs to be decomposed to a type
187 /// param for cleaner code.
188 fn suggest_restriction(
190 generics: &hir::Generics<'tcx>,
192 err: &mut DiagnosticBuilder<'_>,
193 fn_sig: Option<&hir::FnSig<'_>>,
194 projection: Option<&ty::ProjectionTy<'_>>,
195 trait_ref: ty::PolyTraitRef<'tcx>,
196 super_traits: Option<(&Ident, &hir::GenericBounds<'_>)>,
198 // When we are dealing with a trait, `super_traits` will be `Some`:
199 // Given `trait T: A + B + C {}`
200 // - ^^^^^^^^^ GenericBounds
203 let span = generics.where_clause.span_for_predicates_or_empty_place();
204 if span.from_expansion() || span.desugaring_kind().is_some() {
207 // Given `fn foo(t: impl Trait)` where `Trait` requires assoc type `A`...
208 if let Some((bound_str, fn_sig)) =
209 fn_sig.zip(projection).and_then(|(sig, p)| match p.self_ty().kind {
210 // Shenanigans to get the `Trait` from the `impl Trait`.
211 ty::Param(param) => {
212 // `fn foo(t: impl Trait)`
213 // ^^^^^ get this string
214 param.name.as_str().strip_prefix("impl").map(|s| (s.trim_start().to_string(), sig))
219 // We know we have an `impl Trait` that doesn't satisfy a required projection.
221 // Find all of the ocurrences of `impl Trait` for `Trait` in the function arguments'
222 // types. There should be at least one, but there might be *more* than one. In that
223 // case we could just ignore it and try to identify which one needs the restriction,
224 // but instead we choose to suggest replacing all instances of `impl Trait` with `T`
226 let mut ty_spans = vec![];
227 let impl_trait_str = format!("impl {}", bound_str);
228 for input in fn_sig.decl.inputs {
229 if let hir::TyKind::Path(hir::QPath::Resolved(
231 hir::Path { segments: [segment], .. },
234 if segment.ident.as_str() == impl_trait_str.as_str() {
235 // `fn foo(t: impl Trait)`
236 // ^^^^^^^^^^ get this to suggest `T` instead
238 // There might be more than one `impl Trait`.
239 ty_spans.push(input.span);
244 let type_param_name = generics.params.next_type_param_name(Some(&bound_str));
245 // The type param `T: Trait` we will suggest to introduce.
246 let type_param = format!("{}: {}", type_param_name, bound_str);
248 // FIXME: modify the `trait_ref` instead of string shenanigans.
249 // Turn `<impl Trait as Foo>::Bar: Qux` into `<T as Foo>::Bar: Qux`.
250 let pred = trait_ref.without_const().to_predicate(tcx).to_string();
251 let pred = pred.replace(&impl_trait_str, &type_param_name);
256 .filter(|p| match p.kind {
257 hir::GenericParamKind::Type {
258 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
265 // `fn foo(t: impl Trait)`
266 // ^ suggest `<T: Trait>` here
267 None => (generics.span, format!("<{}>", type_param)),
268 // `fn foo<A>(t: impl Trait)`
269 // ^^^ suggest `<A, T: Trait>` here
271 param.bounds_span().unwrap_or(param.span).shrink_to_hi(),
272 format!(", {}", type_param),
275 // `fn foo(t: impl Trait)`
276 // ^ suggest `where <T as Trait>::A: Bound`
277 predicate_constraint(generics, pred),
279 sugg.extend(ty_spans.into_iter().map(|s| (s, type_param_name.to_string())));
281 // Suggest `fn foo<T: Trait>(t: T) where <T as Trait>::A: Bound`.
282 // FIXME: once `#![feature(associated_type_bounds)]` is stabilized, we should suggest
283 // `fn foo(t: impl Trait<A: Bound>)` instead.
284 err.multipart_suggestion(
285 "introduce a type parameter with a trait bound instead of using `impl Trait`",
287 Applicability::MaybeIncorrect,
290 // Trivial case: `T` needs an extra bound: `T: Bound`.
291 let (sp, suggestion) = match super_traits {
292 None => predicate_constraint(
294 trait_ref.without_const().to_predicate(tcx).to_string(),
296 Some((ident, bounds)) => match bounds {
298 bound.span().shrink_to_hi(),
299 format!(" + {}", trait_ref.print_only_trait_path().to_string()),
302 ident.span.shrink_to_hi(),
303 format!(": {}", trait_ref.print_only_trait_path().to_string()),
308 err.span_suggestion_verbose(
310 &format!("consider further restricting {}", msg),
312 Applicability::MachineApplicable,
317 impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
318 fn suggest_restricting_param_bound(
320 mut err: &mut DiagnosticBuilder<'_>,
321 trait_ref: ty::PolyTraitRef<'tcx>,
324 let self_ty = trait_ref.skip_binder().self_ty();
325 let (param_ty, projection) = match &self_ty.kind {
326 ty::Param(_) => (true, None),
327 ty::Projection(projection) => (false, Some(projection)),
331 // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we
332 // don't suggest `T: Sized + ?Sized`.
333 let mut hir_id = body_id;
334 while let Some(node) = self.tcx.hir().find(hir_id) {
336 hir::Node::Item(hir::Item {
338 kind: hir::ItemKind::Trait(_, _, generics, bounds, _),
340 }) if self_ty == self.tcx.types.self_param => {
342 // Restricting `Self` for a single method.
351 Some((ident, bounds)),
356 hir::Node::TraitItem(hir::TraitItem {
358 kind: hir::TraitItemKind::Fn(..),
360 }) if self_ty == self.tcx.types.self_param => {
362 // Restricting `Self` for a single method.
364 self.tcx, &generics, "`Self`", err, None, projection, trait_ref, None,
369 hir::Node::TraitItem(hir::TraitItem {
371 kind: hir::TraitItemKind::Fn(fn_sig, ..),
374 | hir::Node::ImplItem(hir::ImplItem {
376 kind: hir::ImplItemKind::Fn(fn_sig, ..),
379 | hir::Node::Item(hir::Item {
380 kind: hir::ItemKind::Fn(fn_sig, generics, _), ..
381 }) if projection.is_some() => {
382 // Missing restriction on associated type of type parameter (unmet projection).
386 "the associated type",
395 hir::Node::Item(hir::Item {
397 hir::ItemKind::Trait(_, _, generics, _, _)
398 | hir::ItemKind::Impl { generics, .. },
400 }) if projection.is_some() => {
401 // Missing restriction on associated type of type parameter (unmet projection).
405 "the associated type",
415 hir::Node::Item(hir::Item {
417 hir::ItemKind::Struct(_, generics)
418 | hir::ItemKind::Enum(_, generics)
419 | hir::ItemKind::Union(_, generics)
420 | hir::ItemKind::Trait(_, _, generics, ..)
421 | hir::ItemKind::Impl { generics, .. }
422 | hir::ItemKind::Fn(_, generics, _)
423 | hir::ItemKind::TyAlias(_, generics)
424 | hir::ItemKind::TraitAlias(generics, _)
425 | hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }),
428 | hir::Node::TraitItem(hir::TraitItem { generics, .. })
429 | hir::Node::ImplItem(hir::ImplItem { generics, .. })
432 // Missing generic type parameter bound.
433 let param_name = self_ty.to_string();
434 let constraint = trait_ref.print_only_trait_path().to_string();
435 if suggest_constraining_type_param(
441 Some(trait_ref.def_id()),
447 hir::Node::Crate(..) => return,
452 hir_id = self.tcx.hir().get_parent_item(hir_id);
456 /// When after several dereferencing, the reference satisfies the trait
457 /// binding. This function provides dereference suggestion for this
458 /// specific situation.
459 fn suggest_dereferences(
461 obligation: &PredicateObligation<'tcx>,
462 err: &mut DiagnosticBuilder<'tcx>,
463 trait_ref: &ty::PolyTraitRef<'tcx>,
466 // It only make sense when suggesting dereferences for arguments
470 let param_env = obligation.param_env;
471 let body_id = obligation.cause.body_id;
472 let span = obligation.cause.span;
473 let real_trait_ref = match &obligation.cause.code {
474 ObligationCauseCode::ImplDerivedObligation(cause)
475 | ObligationCauseCode::DerivedObligation(cause)
476 | ObligationCauseCode::BuiltinDerivedObligation(cause) => &cause.parent_trait_ref,
479 let real_ty = match real_trait_ref.self_ty().no_bound_vars() {
484 if let ty::Ref(region, base_ty, mutbl) = real_ty.kind {
485 let mut autoderef = Autoderef::new(self, param_env, body_id, span, base_ty);
486 if let Some(steps) = autoderef.find_map(|(ty, steps)| {
488 let ty = self.tcx.mk_ref(region, TypeAndMut { ty, mutbl });
490 self.mk_trait_obligation_with_new_self_ty(param_env, real_trait_ref, ty);
491 Some(steps).filter(|_| self.predicate_may_hold(&obligation))
494 if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(span) {
495 // Don't care about `&mut` because `DerefMut` is used less
496 // often and user will not expect autoderef happens.
497 if src.starts_with("&") && !src.starts_with("&mut ") {
498 let derefs = "*".repeat(steps);
501 "consider adding dereference here",
502 format!("&{}{}", derefs, &src[1..]),
503 Applicability::MachineApplicable,
512 /// Given a closure's `DefId`, return the given name of the closure.
514 /// This doesn't account for reassignments, but it's only used for suggestions.
518 err: &mut DiagnosticBuilder<'_>,
520 ) -> Option<String> {
522 |err: &mut DiagnosticBuilder<'_>, kind: &hir::PatKind<'_>| -> Option<String> {
523 // Get the local name of this closure. This can be inaccurate because
524 // of the possibility of reassignment, but this should be good enough.
526 hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, name, None) => {
527 Some(format!("{}", name))
536 let hir = self.tcx.hir();
537 let hir_id = hir.as_local_hir_id(def_id.as_local()?);
538 let parent_node = hir.get_parent_node(hir_id);
539 match hir.find(parent_node) {
540 Some(hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(local), .. })) => {
541 get_name(err, &local.pat.kind)
543 // Different to previous arm because one is `&hir::Local` and the other
544 // is `P<hir::Local>`.
545 Some(hir::Node::Local(local)) => get_name(err, &local.pat.kind),
550 /// We tried to apply the bound to an `fn` or closure. Check whether calling it would
551 /// evaluate to a type that *would* satisfy the trait binding. If it would, suggest calling
552 /// it: `bar(foo)` → `bar(foo())`. This case is *very* likely to be hit if `foo` is `async`.
555 obligation: &PredicateObligation<'tcx>,
556 err: &mut DiagnosticBuilder<'_>,
557 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
560 let self_ty = match trait_ref.self_ty().no_bound_vars() {
565 let (def_id, output_ty, callable) = match self_ty.kind {
566 ty::Closure(def_id, substs) => (def_id, substs.as_closure().sig().output(), "closure"),
567 ty::FnDef(def_id, _) => (def_id, self_ty.fn_sig(self.tcx).output(), "function"),
570 let msg = format!("use parentheses to call the {}", callable);
572 // `mk_trait_obligation_with_new_self_ty` only works for types with no escaping bound
573 // variables, so bail out if we have any.
574 let output_ty = match output_ty.no_bound_vars() {
580 self.mk_trait_obligation_with_new_self_ty(obligation.param_env, trait_ref, output_ty);
582 match self.evaluate_obligation(&new_obligation) {
584 EvaluationResult::EvaluatedToOk
585 | EvaluationResult::EvaluatedToOkModuloRegions
586 | EvaluationResult::EvaluatedToAmbig,
590 let hir = self.tcx.hir();
591 // Get the name of the callable and the arguments to be used in the suggestion.
592 let (snippet, sugg) = match hir.get_if_local(def_id) {
593 Some(hir::Node::Expr(hir::Expr {
594 kind: hir::ExprKind::Closure(_, decl, _, span, ..),
597 err.span_label(*span, "consider calling this closure");
598 let name = match self.get_closure_name(def_id, err, &msg) {
602 let args = decl.inputs.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
603 let sugg = format!("({})", args);
604 (format!("{}{}", name, sugg), sugg)
606 Some(hir::Node::Item(hir::Item {
608 kind: hir::ItemKind::Fn(.., body_id),
611 err.span_label(ident.span, "consider calling this function");
612 let body = hir.body(*body_id);
616 .map(|arg| match &arg.pat.kind {
617 hir::PatKind::Binding(_, _, ident, None)
618 // FIXME: provide a better suggestion when encountering `SelfLower`, it
619 // should suggest a method call.
620 if ident.name != kw::SelfLower => ident.to_string(),
621 _ => "_".to_string(),
625 let sugg = format!("({})", args);
626 (format!("{}{}", ident, sugg), sugg)
631 // When the obligation error has been ensured to have been caused by
632 // an argument, the `obligation.cause.span` points at the expression
633 // of the argument, so we can provide a suggestion. This is signaled
634 // by `points_at_arg`. Otherwise, we give a more general note.
635 err.span_suggestion_verbose(
636 obligation.cause.span.shrink_to_hi(),
639 Applicability::HasPlaceholders,
642 err.help(&format!("{}: `{}`", msg, snippet));
646 fn suggest_add_reference_to_arg(
648 obligation: &PredicateObligation<'tcx>,
649 err: &mut DiagnosticBuilder<'_>,
650 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
652 has_custom_message: bool,
658 let span = obligation.cause.span;
659 let param_env = obligation.param_env;
660 let trait_ref = trait_ref.skip_binder();
662 if let ObligationCauseCode::ImplDerivedObligation(obligation) = &obligation.cause.code {
663 // Try to apply the original trait binding obligation by borrowing.
664 let self_ty = trait_ref.self_ty();
665 let found = self_ty.to_string();
666 let new_self_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, self_ty);
667 let substs = self.tcx.mk_substs_trait(new_self_ty, &[]);
668 let new_trait_ref = ty::TraitRef::new(obligation.parent_trait_ref.def_id(), substs);
669 let new_obligation = Obligation::new(
670 ObligationCause::dummy(),
672 new_trait_ref.without_const().to_predicate(self.tcx),
675 if self.predicate_must_hold_modulo_regions(&new_obligation) {
676 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
677 // We have a very specific type of error, where just borrowing this argument
678 // might solve the problem. In cases like this, the important part is the
679 // original type obligation, not the last one that failed, which is arbitrary.
680 // Because of this, we modify the error to refer to the original obligation and
681 // return early in the caller.
684 "the trait bound `{}: {}` is not satisfied",
686 obligation.parent_trait_ref.skip_binder().print_only_trait_path(),
688 if has_custom_message {
691 err.message = vec![(msg, Style::NoStyle)];
693 if snippet.starts_with('&') {
694 // This is already a literal borrow and the obligation is failing
695 // somewhere else in the obligation chain. Do not suggest non-sense.
701 "expected an implementor of trait `{}`",
702 obligation.parent_trait_ref.skip_binder().print_only_trait_path(),
706 // This if is to prevent a special edge-case
707 if !span.from_expansion() {
708 // We don't want a borrowing suggestion on the fields in structs,
711 // the_foos: Vec<Foo>
717 "consider borrowing here",
718 format!("&{}", snippet),
719 Applicability::MaybeIncorrect,
729 /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
730 /// suggest removing these references until we reach a type that implements the trait.
731 fn suggest_remove_reference(
733 obligation: &PredicateObligation<'tcx>,
734 err: &mut DiagnosticBuilder<'_>,
735 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
737 let span = obligation.cause.span;
739 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
741 snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
742 if let Some('\'') = snippet.chars().filter(|c| !c.is_whitespace()).nth(refs_number) {
743 // Do not suggest removal of borrow from type arguments.
747 let mut suggested_ty = match trait_ref.self_ty().no_bound_vars() {
752 for refs_remaining in 0..refs_number {
753 if let ty::Ref(_, inner_ty, _) = suggested_ty.kind {
754 suggested_ty = inner_ty;
756 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
757 obligation.param_env,
762 if self.predicate_may_hold(&new_obligation) {
767 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
769 let remove_refs = refs_remaining + 1;
771 let msg = if remove_refs == 1 {
772 "consider removing the leading `&`-reference".to_string()
774 format!("consider removing {} leading `&`-references", remove_refs)
777 err.span_suggestion_short(
781 Applicability::MachineApplicable,
792 /// Check if the trait bound is implemented for a different mutability and note it in the
794 fn suggest_change_mut(
796 obligation: &PredicateObligation<'tcx>,
797 err: &mut DiagnosticBuilder<'_>,
798 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
801 let span = obligation.cause.span;
802 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
804 snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
805 if let Some('\'') = snippet.chars().filter(|c| !c.is_whitespace()).nth(refs_number) {
806 // Do not suggest removal of borrow from type arguments.
809 let trait_ref = self.resolve_vars_if_possible(trait_ref);
810 if trait_ref.has_infer_types_or_consts() {
811 // Do not ICE while trying to find if a reborrow would succeed on a trait with
812 // unresolved bindings.
816 if let ty::Ref(region, t_type, mutability) = trait_ref.skip_binder().self_ty().kind {
817 if region.is_late_bound() || t_type.has_escaping_bound_vars() {
818 // Avoid debug assertion in `mk_obligation_for_def_id`.
820 // If the self type has escaping bound vars then it's not
821 // going to be the type of an expression, so the suggestion
822 // probably won't apply anyway.
826 let suggested_ty = match mutability {
827 hir::Mutability::Mut => self.tcx.mk_imm_ref(region, t_type),
828 hir::Mutability::Not => self.tcx.mk_mut_ref(region, t_type),
831 let new_obligation = self.mk_trait_obligation_with_new_self_ty(
832 obligation.param_env,
836 let suggested_ty_would_satisfy_obligation = self
837 .evaluate_obligation_no_overflow(&new_obligation)
838 .must_apply_modulo_regions();
839 if suggested_ty_would_satisfy_obligation {
844 .span_take_while(span, |c| c.is_whitespace() || *c == '&');
845 if points_at_arg && mutability == hir::Mutability::Not && refs_number > 0 {
846 err.span_suggestion_verbose(
848 "consider changing this borrow's mutability",
850 Applicability::MachineApplicable,
854 "`{}` is implemented for `{:?}`, but not for `{:?}`",
855 trait_ref.print_only_trait_path(),
857 trait_ref.skip_binder().self_ty(),
865 fn suggest_semicolon_removal(
867 obligation: &PredicateObligation<'tcx>,
868 err: &mut DiagnosticBuilder<'_>,
870 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
873 |ty: ty::Binder<Ty<'_>>| ty.skip_binder().kind == ty::Tuple(ty::List::empty());
875 let hir = self.tcx.hir();
876 let parent_node = hir.get_parent_node(obligation.cause.body_id);
877 let node = hir.find(parent_node);
878 if let Some(hir::Node::Item(hir::Item {
879 kind: hir::ItemKind::Fn(sig, _, body_id), ..
882 let body = hir.body(*body_id);
883 if let hir::ExprKind::Block(blk, _) = &body.value.kind {
884 if sig.decl.output.span().overlaps(span)
885 && blk.expr.is_none()
886 && is_empty_tuple(trait_ref.self_ty())
888 // FIXME(estebank): When encountering a method with a trait
889 // bound not satisfied in the return type with a body that has
890 // no return, suggest removal of semicolon on last statement.
891 // Once that is added, close #54771.
892 if let Some(ref stmt) = blk.stmts.last() {
893 let sp = self.tcx.sess.source_map().end_point(stmt.span);
894 err.span_label(sp, "consider removing this semicolon");
901 fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span> {
902 let hir = self.tcx.hir();
903 let parent_node = hir.get_parent_node(obligation.cause.body_id);
904 let sig = match hir.find(parent_node) {
905 Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. })) => sig,
909 if let hir::FnRetTy::Return(ret_ty) = sig.decl.output { Some(ret_ty.span) } else { None }
912 /// If all conditions are met to identify a returned `dyn Trait`, suggest using `impl Trait` if
913 /// applicable and signal that the error has been expanded appropriately and needs to be
915 fn suggest_impl_trait(
917 err: &mut DiagnosticBuilder<'_>,
919 obligation: &PredicateObligation<'tcx>,
920 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
922 match obligation.cause.code.peel_derives() {
923 // Only suggest `impl Trait` if the return type is unsized because it is `dyn Trait`.
924 ObligationCauseCode::SizedReturnType => {}
928 let hir = self.tcx.hir();
929 let parent_node = hir.get_parent_node(obligation.cause.body_id);
930 let node = hir.find(parent_node);
931 let (sig, body_id) = if let Some(hir::Node::Item(hir::Item {
932 kind: hir::ItemKind::Fn(sig, _, body_id),
940 let body = hir.body(*body_id);
941 let trait_ref = self.resolve_vars_if_possible(trait_ref);
942 let ty = trait_ref.skip_binder().self_ty();
943 let is_object_safe = match ty.kind {
944 ty::Dynamic(predicates, _) => {
945 // If the `dyn Trait` is not object safe, do not suggest `Box<dyn Trait>`.
948 .map_or(true, |def_id| self.tcx.object_safety_violations(def_id).is_empty())
950 // We only want to suggest `impl Trait` to `dyn Trait`s.
951 // For example, `fn foo() -> str` needs to be filtered out.
955 let ret_ty = if let hir::FnRetTy::Return(ret_ty) = sig.decl.output {
961 // Use `TypeVisitor` instead of the output type directly to find the span of `ty` for
962 // cases like `fn foo() -> (dyn Trait, i32) {}`.
963 // Recursively look for `TraitObject` types and if there's only one, use that span to
964 // suggest `impl Trait`.
966 // Visit to make sure there's a single `return` type to suggest `impl Trait`,
967 // otherwise suggest using `Box<dyn Trait>` or an enum.
968 let mut visitor = ReturnsVisitor::default();
969 visitor.visit_body(&body);
971 let tables = self.in_progress_tables.map(|t| t.borrow()).unwrap();
973 let mut ret_types = visitor
976 .filter_map(|expr| tables.node_type_opt(expr.hir_id))
977 .map(|ty| self.resolve_vars_if_possible(&ty));
978 let (last_ty, all_returns_have_same_type, only_never_return) = ret_types.clone().fold(
980 |(last_ty, mut same, only_never_return): (std::option::Option<Ty<'_>>, bool, bool),
982 let ty = self.resolve_vars_if_possible(&ty);
984 !matches!(ty.kind, ty::Error(_))
985 && last_ty.map_or(true, |last_ty| {
986 // FIXME: ideally we would use `can_coerce` here instead, but `typeck` comes
987 // *after* in the dependency graph.
988 match (&ty.kind, &last_ty.kind) {
989 (Infer(InferTy::IntVar(_)), Infer(InferTy::IntVar(_)))
990 | (Infer(InferTy::FloatVar(_)), Infer(InferTy::FloatVar(_)))
991 | (Infer(InferTy::FreshIntTy(_)), Infer(InferTy::FreshIntTy(_)))
993 Infer(InferTy::FreshFloatTy(_)),
994 Infer(InferTy::FreshFloatTy(_)),
999 (Some(ty), same, only_never_return && matches!(ty.kind, ty::Never))
1002 let all_returns_conform_to_trait =
1003 if let Some(ty_ret_ty) = tables.node_type_opt(ret_ty.hir_id) {
1004 match ty_ret_ty.kind {
1005 ty::Dynamic(predicates, _) => {
1006 let cause = ObligationCause::misc(ret_ty.span, ret_ty.hir_id);
1007 let param_env = ty::ParamEnv::empty();
1009 || ret_types.all(|returned_ty| {
1010 predicates.iter().all(|predicate| {
1011 let pred = predicate.with_self_ty(self.tcx, returned_ty);
1012 let obl = Obligation::new(cause.clone(), param_env, pred);
1013 self.predicate_may_hold(&obl)
1023 let sm = self.tcx.sess.source_map();
1024 let snippet = if let (true, hir::TyKind::TraitObject(..), Ok(snippet), true) = (
1025 // Verify that we're dealing with a return `dyn Trait`
1026 ret_ty.span.overlaps(span),
1028 sm.span_to_snippet(ret_ty.span),
1029 // If any of the return types does not conform to the trait, then we can't
1030 // suggest `impl Trait` nor trait objects: it is a type mismatch error.
1031 all_returns_conform_to_trait,
1037 err.code(error_code!(E0746));
1038 err.set_primary_message("return type cannot have an unboxed trait object");
1039 err.children.clear();
1040 let impl_trait_msg = "for information on `impl Trait`, see \
1041 <https://doc.rust-lang.org/book/ch10-02-traits.html\
1042 #returning-types-that-implement-traits>";
1043 let trait_obj_msg = "for information on trait objects, see \
1044 <https://doc.rust-lang.org/book/ch17-02-trait-objects.html\
1045 #using-trait-objects-that-allow-for-values-of-different-types>";
1046 let has_dyn = snippet.split_whitespace().next().map_or(false, |s| s == "dyn");
1047 let trait_obj = if has_dyn { &snippet[4..] } else { &snippet[..] };
1048 if only_never_return {
1049 // No return paths, probably using `panic!()` or similar.
1050 // Suggest `-> T`, `-> impl Trait`, and if `Trait` is object safe, `-> Box<dyn Trait>`.
1051 suggest_trait_object_return_type_alternatives(
1057 } else if let (Some(last_ty), true) = (last_ty, all_returns_have_same_type) {
1058 // Suggest `-> impl Trait`.
1059 err.span_suggestion(
1062 "use `impl {1}` as the return type, as all return paths are of type `{}`, \
1063 which implements `{1}`",
1066 format!("impl {}", trait_obj),
1067 Applicability::MachineApplicable,
1069 err.note(impl_trait_msg);
1072 // Suggest `-> Box<dyn Trait>` and `Box::new(returned_value)`.
1073 // Get all the return values and collect their span and suggestion.
1074 if let Some(mut suggestions) = visitor
1078 let snip = sm.span_to_snippet(expr.span).ok()?;
1079 Some((expr.span, format!("Box::new({})", snip)))
1081 .collect::<Option<Vec<_>>>()
1083 // Add the suggestion for the return type.
1084 suggestions.push((ret_ty.span, format!("Box<dyn {}>", trait_obj)));
1085 err.multipart_suggestion(
1086 "return a boxed trait object instead",
1088 Applicability::MaybeIncorrect,
1092 // This is currently not possible to trigger because E0038 takes precedence, but
1093 // leave it in for completeness in case anything changes in an earlier stage.
1095 "if trait `{}` was object safe, you could return a trait object",
1099 err.note(trait_obj_msg);
1101 "if all the returned values were of the same type you could use `impl {}` as the \
1105 err.note(impl_trait_msg);
1106 err.note("you can create a new `enum` with a variant for each returned type");
1111 fn point_at_returns_when_relevant(
1113 err: &mut DiagnosticBuilder<'_>,
1114 obligation: &PredicateObligation<'tcx>,
1116 match obligation.cause.code.peel_derives() {
1117 ObligationCauseCode::SizedReturnType => {}
1121 let hir = self.tcx.hir();
1122 let parent_node = hir.get_parent_node(obligation.cause.body_id);
1123 let node = hir.find(parent_node);
1124 if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })) =
1127 let body = hir.body(*body_id);
1128 // Point at all the `return`s in the function as they have failed trait bounds.
1129 let mut visitor = ReturnsVisitor::default();
1130 visitor.visit_body(&body);
1131 let tables = self.in_progress_tables.map(|t| t.borrow()).unwrap();
1132 for expr in &visitor.returns {
1133 if let Some(returned_ty) = tables.node_type_opt(expr.hir_id) {
1134 let ty = self.resolve_vars_if_possible(&returned_ty);
1135 err.span_label(expr.span, &format!("this returned value is of type `{}`", ty));
1141 fn report_closure_arg_mismatch(
1144 found_span: Option<Span>,
1145 expected_ref: ty::PolyTraitRef<'tcx>,
1146 found: ty::PolyTraitRef<'tcx>,
1147 ) -> DiagnosticBuilder<'tcx> {
1148 crate fn build_fn_sig_string<'tcx>(
1150 trait_ref: ty::TraitRef<'tcx>,
1152 let inputs = trait_ref.substs.type_at(1);
1153 let sig = if let ty::Tuple(inputs) = inputs.kind {
1155 inputs.iter().map(|k| k.expect_ty()),
1156 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1158 hir::Unsafety::Normal,
1159 ::rustc_target::spec::abi::Abi::Rust,
1163 ::std::iter::once(inputs),
1164 tcx.mk_ty_infer(ty::TyVar(ty::TyVid { index: 0 })),
1166 hir::Unsafety::Normal,
1167 ::rustc_target::spec::abi::Abi::Rust,
1170 ty::Binder::bind(sig).to_string()
1173 let argument_is_closure = expected_ref.skip_binder().substs.type_at(0).is_closure();
1174 let mut err = struct_span_err!(
1178 "type mismatch in {} arguments",
1179 if argument_is_closure { "closure" } else { "function" }
1182 let found_str = format!(
1183 "expected signature of `{}`",
1184 build_fn_sig_string(self.tcx, found.skip_binder())
1186 err.span_label(span, found_str);
1188 let found_span = found_span.unwrap_or(span);
1189 let expected_str = format!(
1190 "found signature of `{}`",
1191 build_fn_sig_string(self.tcx, expected_ref.skip_binder())
1193 err.span_label(found_span, expected_str);
1198 fn suggest_fully_qualified_path(
1200 err: &mut DiagnosticBuilder<'_>,
1205 if let Some(assoc_item) = self.tcx.opt_associated_item(def_id) {
1206 if let ty::AssocKind::Const | ty::AssocKind::Type = assoc_item.kind {
1208 "{}s cannot be accessed directly on a `trait`, they can only be \
1209 accessed through a specific `impl`",
1210 assoc_item.kind.as_def_kind().descr(def_id)
1212 err.span_suggestion(
1214 "use the fully qualified path to an implementation",
1215 format!("<Type as {}>::{}", self.tcx.def_path_str(trait_ref), assoc_item.ident),
1216 Applicability::HasPlaceholders,
1222 /// Adds an async-await specific note to the diagnostic when the future does not implement
1223 /// an auto trait because of a captured type.
1226 /// note: future does not implement `Qux` as this value is used across an await
1227 /// --> $DIR/issue-64130-3-other.rs:17:5
1229 /// LL | let x = Foo;
1230 /// | - has type `Foo`
1231 /// LL | baz().await;
1232 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
1234 /// | - `x` is later dropped here
1237 /// When the diagnostic does not implement `Send` or `Sync` specifically, then the diagnostic
1238 /// is "replaced" with a different message and a more specific error.
1241 /// error: future cannot be sent between threads safely
1242 /// --> $DIR/issue-64130-2-send.rs:21:5
1244 /// LL | fn is_send<T: Send>(t: T) { }
1245 /// | ---- required by this bound in `is_send`
1247 /// LL | is_send(bar());
1248 /// | ^^^^^^^ future returned by `bar` is not send
1250 /// = help: within `impl std::future::Future`, the trait `std::marker::Send` is not
1251 /// implemented for `Foo`
1252 /// note: future is not send as this value is used across an await
1253 /// --> $DIR/issue-64130-2-send.rs:15:5
1255 /// LL | let x = Foo;
1256 /// | - has type `Foo`
1257 /// LL | baz().await;
1258 /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later
1260 /// | - `x` is later dropped here
1263 /// Returns `true` if an async-await specific note was added to the diagnostic.
1264 fn maybe_note_obligation_cause_for_async_await(
1266 err: &mut DiagnosticBuilder<'_>,
1267 obligation: &PredicateObligation<'tcx>,
1270 "maybe_note_obligation_cause_for_async_await: obligation.predicate={:?} \
1271 obligation.cause.span={:?}",
1272 obligation.predicate, obligation.cause.span
1274 let hir = self.tcx.hir();
1276 // Attempt to detect an async-await error by looking at the obligation causes, looking
1277 // for a generator to be present.
1279 // When a future does not implement a trait because of a captured type in one of the
1280 // generators somewhere in the call stack, then the result is a chain of obligations.
1282 // Given a `async fn` A that calls a `async fn` B which captures a non-send type and that
1283 // future is passed as an argument to a function C which requires a `Send` type, then the
1284 // chain looks something like this:
1286 // - `BuiltinDerivedObligation` with a generator witness (B)
1287 // - `BuiltinDerivedObligation` with a generator (B)
1288 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (B)
1289 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
1290 // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
1291 // - `BuiltinDerivedObligation` with a generator witness (A)
1292 // - `BuiltinDerivedObligation` with a generator (A)
1293 // - `BuiltinDerivedObligation` with `std::future::GenFuture` (A)
1294 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
1295 // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
1296 // - `BindingObligation` with `impl_send (Send requirement)
1298 // The first obligation in the chain is the most useful and has the generator that captured
1299 // the type. The last generator (`outer_generator` below) has information about where the
1300 // bound was introduced. At least one generator should be present for this diagnostic to be
1302 let (mut trait_ref, mut target_ty) = match obligation.predicate.kind() {
1303 ty::PredicateKind::Trait(p, _) => {
1304 (Some(p.skip_binder().trait_ref), Some(p.skip_binder().self_ty()))
1308 let mut generator = None;
1309 let mut outer_generator = None;
1310 let mut next_code = Some(&obligation.cause.code);
1311 while let Some(code) = next_code {
1312 debug!("maybe_note_obligation_cause_for_async_await: code={:?}", code);
1314 ObligationCauseCode::DerivedObligation(derived_obligation)
1315 | ObligationCauseCode::BuiltinDerivedObligation(derived_obligation)
1316 | ObligationCauseCode::ImplDerivedObligation(derived_obligation) => {
1317 let ty = derived_obligation.parent_trait_ref.skip_binder().self_ty();
1319 "maybe_note_obligation_cause_for_async_await: \
1320 parent_trait_ref={:?} self_ty.kind={:?}",
1321 derived_obligation.parent_trait_ref, ty.kind
1325 ty::Generator(did, ..) => {
1326 generator = generator.or(Some(did));
1327 outer_generator = Some(did);
1329 ty::GeneratorWitness(..) => {}
1330 _ if generator.is_none() => {
1331 trait_ref = Some(derived_obligation.parent_trait_ref.skip_binder());
1332 target_ty = Some(ty);
1337 next_code = Some(derived_obligation.parent_code.as_ref());
1343 // Only continue if a generator was found.
1345 "maybe_note_obligation_cause_for_async_await: generator={:?} trait_ref={:?} \
1347 generator, trait_ref, target_ty
1349 let (generator_did, trait_ref, target_ty) = match (generator, trait_ref, target_ty) {
1350 (Some(generator_did), Some(trait_ref), Some(target_ty)) => {
1351 (generator_did, trait_ref, target_ty)
1356 let span = self.tcx.def_span(generator_did);
1358 // Do not ICE on closure typeck (#66868).
1359 if !generator_did.is_local() {
1363 // Get the tables from the infcx if the generator is the function we are
1364 // currently type-checking; otherwise, get them by performing a query.
1365 // This is needed to avoid cycles.
1366 let in_progress_tables = self.in_progress_tables.map(|t| t.borrow());
1367 let generator_did_root = self.tcx.closure_base_def_id(generator_did);
1369 "maybe_note_obligation_cause_for_async_await: generator_did={:?} \
1370 generator_did_root={:?} in_progress_tables.hir_owner={:?} span={:?}",
1373 in_progress_tables.as_ref().map(|t| t.hir_owner),
1377 let tables: &TypeckTables<'tcx> = match &in_progress_tables {
1378 Some(t) if t.hir_owner.to_def_id() == generator_did_root => t,
1380 query_tables = self.tcx.typeck_tables_of(generator_did.expect_local());
1385 let generator_body = generator_did
1387 .map(|def_id| hir.as_local_hir_id(def_id))
1388 .and_then(|hir_id| hir.maybe_body_owned_by(hir_id))
1389 .map(|body_id| hir.body(body_id));
1390 let mut visitor = AwaitsVisitor::default();
1391 if let Some(body) = generator_body {
1392 visitor.visit_body(body);
1394 debug!("maybe_note_obligation_cause_for_async_await: awaits = {:?}", visitor.awaits);
1396 // Look for a type inside the generator interior that matches the target type to get
1398 let target_ty_erased = self.tcx.erase_regions(&target_ty);
1399 let ty_matches = |ty| -> bool {
1400 // Careful: the regions for types that appear in the
1401 // generator interior are not generally known, so we
1402 // want to erase them when comparing (and anyway,
1403 // `Send` and other bounds are generally unaffected by
1404 // the choice of region). When erasing regions, we
1405 // also have to erase late-bound regions. This is
1406 // because the types that appear in the generator
1407 // interior generally contain "bound regions" to
1408 // represent regions that are part of the suspended
1409 // generator frame. Bound regions are preserved by
1410 // `erase_regions` and so we must also call
1411 // `erase_late_bound_regions`.
1412 let ty_erased = self.tcx.erase_late_bound_regions(&ty::Binder::bind(ty));
1413 let ty_erased = self.tcx.erase_regions(&ty_erased);
1414 let eq = ty::TyS::same_type(ty_erased, target_ty_erased);
1416 "maybe_note_obligation_cause_for_async_await: ty_erased={:?} \
1417 target_ty_erased={:?} eq={:?}",
1418 ty_erased, target_ty_erased, eq
1423 let mut interior_or_upvar_span = None;
1424 let mut interior_extra_info = None;
1426 if let Some(upvars) = self.tcx.upvars_mentioned(generator_did) {
1427 interior_or_upvar_span = upvars.iter().find_map(|(upvar_id, upvar)| {
1428 let upvar_ty = tables.node_type(*upvar_id);
1429 let upvar_ty = self.resolve_vars_if_possible(&upvar_ty);
1430 if ty_matches(&upvar_ty) {
1431 Some(GeneratorInteriorOrUpvar::Upvar(upvar.span))
1439 .generator_interior_types
1441 .find(|ty::GeneratorInteriorTypeCause { ty, .. }| ty_matches(ty))
1443 // Check to see if any awaited expressions have the target type.
1444 let from_awaited_ty = visitor
1447 .map(|id| hir.expect_expr(id))
1448 .find(|await_expr| {
1449 let ty = tables.expr_ty_adjusted(&await_expr);
1451 "maybe_note_obligation_cause_for_async_await: await_expr={:?}",
1456 .map(|expr| expr.span);
1457 let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } =
1460 interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(*span));
1461 interior_extra_info = Some((*scope_span, *yield_span, *expr, from_awaited_ty));
1465 "maybe_note_obligation_cause_for_async_await: interior_or_upvar={:?} \
1466 generator_interior_types={:?}",
1467 interior_or_upvar_span, tables.generator_interior_types
1469 if let Some(interior_or_upvar_span) = interior_or_upvar_span {
1470 self.note_obligation_cause_for_async_await(
1472 interior_or_upvar_span,
1473 interior_extra_info,
1488 /// Unconditionally adds the diagnostic note described in
1489 /// `maybe_note_obligation_cause_for_async_await`'s documentation comment.
1490 fn note_obligation_cause_for_async_await(
1492 err: &mut DiagnosticBuilder<'_>,
1493 interior_or_upvar_span: GeneratorInteriorOrUpvar,
1494 interior_extra_info: Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>,
1495 inner_generator_body: Option<&hir::Body<'tcx>>,
1496 outer_generator: Option<DefId>,
1497 trait_ref: ty::TraitRef<'tcx>,
1498 target_ty: Ty<'tcx>,
1499 tables: &ty::TypeckTables<'tcx>,
1500 obligation: &PredicateObligation<'tcx>,
1501 next_code: Option<&ObligationCauseCode<'tcx>>,
1503 let source_map = self.tcx.sess.source_map();
1505 let is_async = inner_generator_body
1506 .and_then(|body| body.generator_kind())
1507 .map(|generator_kind| matches!(generator_kind, hir::GeneratorKind::Async(..)))
1509 let (await_or_yield, an_await_or_yield) =
1510 if is_async { ("await", "an await") } else { ("yield", "a yield") };
1511 let future_or_generator = if is_async { "future" } else { "generator" };
1513 // Special case the primary error message when send or sync is the trait that was
1515 let is_send = self.tcx.is_diagnostic_item(sym::send_trait, trait_ref.def_id);
1516 let is_sync = self.tcx.is_diagnostic_item(sym::sync_trait, trait_ref.def_id);
1517 let hir = self.tcx.hir();
1518 let trait_explanation = if is_send || is_sync {
1519 let (trait_name, trait_verb) =
1520 if is_send { ("`Send`", "sent") } else { ("`Sync`", "shared") };
1523 err.set_primary_message(format!(
1524 "{} cannot be {} between threads safely",
1525 future_or_generator, trait_verb
1528 let original_span = err.span.primary_span().unwrap();
1529 let mut span = MultiSpan::from_span(original_span);
1531 let message = outer_generator
1532 .and_then(|generator_did| {
1533 Some(match self.tcx.generator_kind(generator_did).unwrap() {
1534 GeneratorKind::Gen => format!("generator is not {}", trait_name),
1535 GeneratorKind::Async(AsyncGeneratorKind::Fn) => self
1537 .parent(generator_did)
1538 .and_then(|parent_did| parent_did.as_local())
1539 .map(|parent_did| hir.as_local_hir_id(parent_did))
1540 .and_then(|parent_hir_id| hir.opt_name(parent_hir_id))
1542 format!("future returned by `{}` is not {}", name, trait_name)
1544 GeneratorKind::Async(AsyncGeneratorKind::Block) => {
1545 format!("future created by async block is not {}", trait_name)
1547 GeneratorKind::Async(AsyncGeneratorKind::Closure) => {
1548 format!("future created by async closure is not {}", trait_name)
1552 .unwrap_or_else(|| format!("{} is not {}", future_or_generator, trait_name));
1554 span.push_span_label(original_span, message);
1557 format!("is not {}", trait_name)
1559 format!("does not implement `{}`", trait_ref.print_only_trait_path())
1562 let mut explain_yield = |interior_span: Span,
1564 scope_span: Option<Span>| {
1565 let mut span = MultiSpan::from_span(yield_span);
1566 if let Ok(snippet) = source_map.span_to_snippet(interior_span) {
1567 span.push_span_label(
1569 format!("{} occurs here, with `{}` maybe used later", await_or_yield, snippet),
1571 // If available, use the scope span to annotate the drop location.
1572 if let Some(scope_span) = scope_span {
1573 span.push_span_label(
1574 source_map.end_point(scope_span),
1575 format!("`{}` is later dropped here", snippet),
1579 span.push_span_label(
1581 format!("has type `{}` which {}", target_ty, trait_explanation),
1587 "{} {} as this value is used across {}",
1588 future_or_generator, trait_explanation, an_await_or_yield
1592 match interior_or_upvar_span {
1593 GeneratorInteriorOrUpvar::Interior(interior_span) => {
1594 if let Some((scope_span, yield_span, expr, from_awaited_ty)) = interior_extra_info {
1595 if let Some(await_span) = from_awaited_ty {
1596 // The type causing this obligation is one being awaited at await_span.
1597 let mut span = MultiSpan::from_span(await_span);
1598 span.push_span_label(
1601 "await occurs here on type `{}`, which {}",
1602 target_ty, trait_explanation
1608 "future {not_trait} as it awaits another future which {not_trait}",
1609 not_trait = trait_explanation
1613 // Look at the last interior type to get a span for the `.await`.
1615 "note_obligation_cause_for_async_await generator_interior_types: {:#?}",
1616 tables.generator_interior_types
1618 explain_yield(interior_span, yield_span, scope_span);
1621 if let Some(expr_id) = expr {
1622 let expr = hir.expect_expr(expr_id);
1623 debug!("target_ty evaluated from {:?}", expr);
1625 let parent = hir.get_parent_node(expr_id);
1626 if let Some(hir::Node::Expr(e)) = hir.find(parent) {
1627 let parent_span = hir.span(parent);
1628 let parent_did = parent.owner.to_def_id();
1631 // fn foo(&self) -> i32 {}
1634 // ^^^^^^^ a temporary `&T` created inside this method call due to `&self`
1637 let is_region_borrow = tables
1638 .expr_adjustments(expr)
1640 .any(|adj| adj.is_region_borrow());
1643 // struct Foo(*const u8);
1644 // bar(Foo(std::ptr::null())).await;
1645 // ^^^^^^^^^^^^^^^^^^^^^ raw-ptr `*T` created inside this struct ctor.
1647 debug!("parent_def_kind: {:?}", self.tcx.def_kind(parent_did));
1648 let is_raw_borrow_inside_fn_like_call =
1649 match self.tcx.def_kind(parent_did) {
1650 DefKind::Fn | DefKind::Ctor(..) => target_ty.is_unsafe_ptr(),
1654 if (tables.is_method_call(e) && is_region_borrow)
1655 || is_raw_borrow_inside_fn_like_call
1659 "consider moving this into a `let` \
1660 binding to create a shorter lived borrow",
1667 GeneratorInteriorOrUpvar::Upvar(upvar_span) => {
1668 let mut span = MultiSpan::from_span(upvar_span);
1669 span.push_span_label(
1671 format!("has type `{}` which {}", target_ty, trait_explanation),
1673 err.span_note(span, &format!("captured value {}", trait_explanation));
1677 // Add a note for the item obligation that remains - normally a note pointing to the
1678 // bound that introduced the obligation (e.g. `T: Send`).
1679 debug!("note_obligation_cause_for_async_await: next_code={:?}", next_code);
1680 self.note_obligation_cause_code(
1682 &obligation.predicate,
1688 fn note_obligation_cause_code<T>(
1690 err: &mut DiagnosticBuilder<'_>,
1692 cause_code: &ObligationCauseCode<'tcx>,
1693 obligated_types: &mut Vec<&ty::TyS<'tcx>>,
1699 ObligationCauseCode::ExprAssignable
1700 | ObligationCauseCode::MatchExpressionArm { .. }
1701 | ObligationCauseCode::Pattern { .. }
1702 | ObligationCauseCode::IfExpression { .. }
1703 | ObligationCauseCode::IfExpressionWithNoElse
1704 | ObligationCauseCode::MainFunctionType
1705 | ObligationCauseCode::StartFunctionType
1706 | ObligationCauseCode::IntrinsicType
1707 | ObligationCauseCode::MethodReceiver
1708 | ObligationCauseCode::ReturnNoExpression
1709 | ObligationCauseCode::MiscObligation => {}
1710 ObligationCauseCode::SliceOrArrayElem => {
1711 err.note("slice and array elements must have `Sized` type");
1713 ObligationCauseCode::TupleElem => {
1714 err.note("only the last element of a tuple may have a dynamically sized type");
1716 ObligationCauseCode::ProjectionWf(data) => {
1717 err.note(&format!("required so that the projection `{}` is well-formed", data,));
1719 ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
1721 "required so that reference `{}` does not outlive its referent",
1725 ObligationCauseCode::ObjectTypeBound(object_ty, region) => {
1727 "required so that the lifetime bound of `{}` for `{}` is satisfied",
1731 ObligationCauseCode::ItemObligation(item_def_id) => {
1732 let item_name = tcx.def_path_str(item_def_id);
1733 let msg = format!("required by `{}`", item_name);
1734 if let Some(sp) = tcx.hir().span_if_local(item_def_id) {
1735 let sp = tcx.sess.source_map().guess_head_span(sp);
1736 err.span_label(sp, &msg);
1741 ObligationCauseCode::BindingObligation(item_def_id, span) => {
1742 let item_name = tcx.def_path_str(item_def_id);
1743 let msg = format!("required by this bound in `{}`", item_name);
1744 if let Some(ident) = tcx.opt_item_name(item_def_id) {
1745 let sm = tcx.sess.source_map();
1747 match (sm.lookup_line(ident.span.hi()), sm.lookup_line(span.lo())) {
1748 (Ok(l), Ok(r)) => l.line == r.line,
1751 if !ident.span.overlaps(span) && !same_line {
1752 err.span_label(ident.span, "required by a bound in this");
1755 if span != DUMMY_SP {
1756 err.span_label(span, &msg);
1761 ObligationCauseCode::ObjectCastObligation(object_ty) => {
1763 "required for the cast to the object type `{}`",
1764 self.ty_to_string(object_ty)
1767 ObligationCauseCode::Coercion { source: _, target } => {
1768 err.note(&format!("required by cast to type `{}`", self.ty_to_string(target)));
1770 ObligationCauseCode::RepeatVec(suggest_const_in_array_repeat_expressions) => {
1772 "the `Copy` trait is required because the repeated element will be copied",
1774 if suggest_const_in_array_repeat_expressions {
1776 "this array initializer can be evaluated at compile-time, see issue \
1777 #49147 <https://github.com/rust-lang/rust/issues/49147> \
1778 for more information",
1780 if tcx.sess.opts.unstable_features.is_nightly_build() {
1782 "add `#![feature(const_in_array_repeat_expressions)]` to the \
1783 crate attributes to enable",
1788 ObligationCauseCode::VariableType(hir_id) => {
1789 let parent_node = self.tcx.hir().get_parent_node(hir_id);
1790 match self.tcx.hir().find(parent_node) {
1791 Some(Node::Local(hir::Local {
1792 init: Some(hir::Expr { kind: hir::ExprKind::Index(_, _), span, .. }),
1795 // When encountering an assignment of an unsized trait, like
1796 // `let x = ""[..];`, provide a suggestion to borrow the initializer in
1797 // order to use have a slice instead.
1798 err.span_suggestion_verbose(
1799 span.shrink_to_lo(),
1800 "consider borrowing here",
1802 Applicability::MachineApplicable,
1804 err.note("all local variables must have a statically known size");
1806 Some(Node::Param(param)) => {
1807 err.span_suggestion_verbose(
1808 param.ty_span.shrink_to_lo(),
1809 "function arguments must have a statically known size, borrowed types \
1810 always have a known size",
1812 Applicability::MachineApplicable,
1816 err.note("all local variables must have a statically known size");
1819 if !self.tcx.features().unsized_locals {
1820 err.help("unsized locals are gated as an unstable feature");
1823 ObligationCauseCode::SizedArgumentType(sp) => {
1824 if let Some(span) = sp {
1825 err.span_suggestion_verbose(
1826 span.shrink_to_lo(),
1827 "function arguments must have a statically known size, borrowed types \
1828 always have a known size",
1830 Applicability::MachineApplicable,
1833 err.note("all function arguments must have a statically known size");
1835 if tcx.sess.opts.unstable_features.is_nightly_build()
1836 && !self.tcx.features().unsized_locals
1838 err.help("unsized locals are gated as an unstable feature");
1841 ObligationCauseCode::SizedReturnType => {
1842 err.note("the return type of a function must have a statically known size");
1844 ObligationCauseCode::SizedYieldType => {
1845 err.note("the yield type of a generator must have a statically known size");
1847 ObligationCauseCode::AssignmentLhsSized => {
1848 err.note("the left-hand-side of an assignment must have a statically known size");
1850 ObligationCauseCode::TupleInitializerSized => {
1851 err.note("tuples must have a statically known size to be initialized");
1853 ObligationCauseCode::StructInitializerSized => {
1854 err.note("structs must have a statically known size to be initialized");
1856 ObligationCauseCode::FieldSized { adt_kind: ref item, last, span } => {
1858 AdtKind::Struct => {
1861 "the last field of a packed struct may only have a \
1862 dynamically sized type if it does not need drop to be run",
1866 "only the last field of a struct may have a dynamically sized type",
1871 err.note("no field of a union may have a dynamically sized type");
1874 err.note("no field of an enum variant may have a dynamically sized type");
1877 err.help("change the field's type to have a statically known size");
1878 err.span_suggestion(
1879 span.shrink_to_lo(),
1880 "borrowed types always have a statically known size",
1882 Applicability::MachineApplicable,
1884 err.multipart_suggestion(
1885 "the `Box` type always has a statically known size and allocates its contents \
1888 (span.shrink_to_lo(), "Box<".to_string()),
1889 (span.shrink_to_hi(), ">".to_string()),
1891 Applicability::MachineApplicable,
1894 ObligationCauseCode::ConstSized => {
1895 err.note("constant expressions must have a statically known size");
1897 ObligationCauseCode::InlineAsmSized => {
1898 err.note("all inline asm arguments must have a statically known size");
1900 ObligationCauseCode::ConstPatternStructural => {
1901 err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`");
1903 ObligationCauseCode::SharedStatic => {
1904 err.note("shared static variables must have a type that implements `Sync`");
1906 ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
1907 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
1908 let ty = parent_trait_ref.skip_binder().self_ty();
1909 err.note(&format!("required because it appears within the type `{}`", ty));
1910 obligated_types.push(ty);
1912 let parent_predicate = parent_trait_ref.without_const().to_predicate(tcx);
1913 if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
1914 self.note_obligation_cause_code(
1922 ObligationCauseCode::ImplDerivedObligation(ref data) => {
1923 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
1925 "required because of the requirements on the impl of `{}` for `{}`",
1926 parent_trait_ref.print_only_trait_path(),
1927 parent_trait_ref.skip_binder().self_ty()
1929 let parent_predicate = parent_trait_ref.without_const().to_predicate(tcx);
1930 self.note_obligation_cause_code(
1937 ObligationCauseCode::DerivedObligation(ref data) => {
1938 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
1939 let parent_predicate = parent_trait_ref.without_const().to_predicate(tcx);
1940 self.note_obligation_cause_code(
1947 ObligationCauseCode::CompareImplMethodObligation { .. } => {
1949 "the requirement `{}` appears on the impl method \
1950 but not on the corresponding trait method",
1954 ObligationCauseCode::CompareImplTypeObligation { .. } => {
1956 "the requirement `{}` appears on the associated impl type \
1957 but not on the corresponding associated trait type",
1961 ObligationCauseCode::CompareImplConstObligation => {
1963 "the requirement `{}` appears on the associated impl constant \
1964 but not on the corresponding associated trait constant",
1968 ObligationCauseCode::ReturnType
1969 | ObligationCauseCode::ReturnValue(_)
1970 | ObligationCauseCode::BlockTailExpression(_) => (),
1971 ObligationCauseCode::TrivialBound => {
1972 err.help("see issue #48214");
1973 if tcx.sess.opts.unstable_features.is_nightly_build() {
1974 err.help("add `#![feature(trivial_bounds)]` to the crate attributes to enable");
1980 fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder<'_>) {
1981 let current_limit = self.tcx.sess.recursion_limit();
1982 let suggested_limit = current_limit * 2;
1984 "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate (`{}`)",
1985 suggested_limit, self.tcx.crate_name,
1989 fn suggest_await_before_try(
1991 err: &mut DiagnosticBuilder<'_>,
1992 obligation: &PredicateObligation<'tcx>,
1993 trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
1997 "suggest_await_before_try: obligation={:?}, span={:?}, trait_ref={:?}, trait_ref_self_ty={:?}",
2003 let body_hir_id = obligation.cause.body_id;
2004 let item_id = self.tcx.hir().get_parent_node(body_hir_id);
2006 if let Some(body_id) = self.tcx.hir().maybe_body_owned_by(item_id) {
2007 let body = self.tcx.hir().body(body_id);
2008 if let Some(hir::GeneratorKind::Async(_)) = body.generator_kind {
2010 self.tcx.require_lang_item(lang_items::FutureTraitLangItem, None);
2012 let self_ty = self.resolve_vars_if_possible(&trait_ref.self_ty());
2014 // Do not check on infer_types to avoid panic in evaluate_obligation.
2015 if self_ty.has_infer_types() {
2018 let self_ty = self.tcx.erase_regions(&self_ty);
2020 let impls_future = self.tcx.type_implements_trait((
2022 self_ty.skip_binder(),
2024 obligation.param_env,
2027 let item_def_id = self
2029 .associated_items(future_trait)
2030 .in_definition_order()
2034 // `<T as Future>::Output`
2035 let projection_ty = ty::ProjectionTy {
2037 substs: self.tcx.mk_substs_trait(
2038 trait_ref.self_ty().skip_binder(),
2039 self.fresh_substs_for_item(span, item_def_id),
2045 let mut selcx = SelectionContext::new(self);
2047 let mut obligations = vec![];
2048 let normalized_ty = normalize_projection_type(
2050 obligation.param_env,
2052 obligation.cause.clone(),
2058 "suggest_await_before_try: normalized_projection_type {:?}",
2059 self.resolve_vars_if_possible(&normalized_ty)
2061 let try_obligation = self.mk_trait_obligation_with_new_self_ty(
2062 obligation.param_env,
2066 debug!("suggest_await_before_try: try_trait_obligation {:?}", try_obligation);
2067 if self.predicate_may_hold(&try_obligation) && impls_future {
2068 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
2069 if snippet.ends_with('?') {
2070 err.span_suggestion(
2072 "consider using `.await` here",
2073 format!("{}.await?", snippet.trim_end_matches('?')),
2074 Applicability::MaybeIncorrect,
2084 /// Collect all the returned expressions within the input expression.
2085 /// Used to point at the return spans when we want to suggest some change to them.
2087 pub struct ReturnsVisitor<'v> {
2088 pub returns: Vec<&'v hir::Expr<'v>>,
2089 in_block_tail: bool,
2092 impl<'v> Visitor<'v> for ReturnsVisitor<'v> {
2093 type Map = hir::intravisit::ErasedMap<'v>;
2095 fn nested_visit_map(&mut self) -> hir::intravisit::NestedVisitorMap<Self::Map> {
2096 hir::intravisit::NestedVisitorMap::None
2099 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2100 // Visit every expression to detect `return` paths, either through the function's tail
2101 // expression or `return` statements. We walk all nodes to find `return` statements, but
2102 // we only care about tail expressions when `in_block_tail` is `true`, which means that
2103 // they're in the return path of the function body.
2105 hir::ExprKind::Ret(Some(ex)) => {
2106 self.returns.push(ex);
2108 hir::ExprKind::Block(block, _) if self.in_block_tail => {
2109 self.in_block_tail = false;
2110 for stmt in block.stmts {
2111 hir::intravisit::walk_stmt(self, stmt);
2113 self.in_block_tail = true;
2114 if let Some(expr) = block.expr {
2115 self.visit_expr(expr);
2118 hir::ExprKind::Match(_, arms, _) if self.in_block_tail => {
2120 self.visit_expr(arm.body);
2123 // We need to walk to find `return`s in the entire body.
2124 _ if !self.in_block_tail => hir::intravisit::walk_expr(self, ex),
2125 _ => self.returns.push(ex),
2129 fn visit_body(&mut self, body: &'v hir::Body<'v>) {
2130 assert!(!self.in_block_tail);
2131 if body.generator_kind().is_none() {
2132 if let hir::ExprKind::Block(block, None) = body.value.kind {
2133 if block.expr.is_some() {
2134 self.in_block_tail = true;
2138 hir::intravisit::walk_body(self, body);
2142 /// Collect all the awaited expressions within the input expression.
2144 struct AwaitsVisitor {
2145 awaits: Vec<hir::HirId>,
2148 impl<'v> Visitor<'v> for AwaitsVisitor {
2149 type Map = hir::intravisit::ErasedMap<'v>;
2151 fn nested_visit_map(&mut self) -> hir::intravisit::NestedVisitorMap<Self::Map> {
2152 hir::intravisit::NestedVisitorMap::None
2155 fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
2156 if let hir::ExprKind::Yield(_, hir::YieldSource::Await { expr: Some(id) }) = ex.kind {
2157 self.awaits.push(id)
2159 hir::intravisit::walk_expr(self, ex)
2163 pub trait NextTypeParamName {
2164 fn next_type_param_name(&self, name: Option<&str>) -> String;
2167 impl NextTypeParamName for &[hir::GenericParam<'_>] {
2168 fn next_type_param_name(&self, name: Option<&str>) -> String {
2169 // This is the list of possible parameter names that we might suggest.
2170 let name = name.and_then(|n| n.chars().next()).map(|c| c.to_string().to_uppercase());
2171 let name = name.as_deref();
2172 let possible_names = [name.unwrap_or("T"), "T", "U", "V", "X", "Y", "Z", "A", "B", "C"];
2173 let used_names = self
2175 .filter_map(|p| match p.name {
2176 hir::ParamName::Plain(ident) => Some(ident.name),
2179 .collect::<Vec<_>>();
2183 .find(|n| !used_names.contains(&Symbol::intern(n)))
2184 .unwrap_or(&"ParamName")
2189 fn suggest_trait_object_return_type_alternatives(
2190 err: &mut DiagnosticBuilder<'_>,
2193 is_object_safe: bool,
2195 err.span_suggestion(
2197 "use some type `T` that is `T: Sized` as the return type if all return paths have the \
2200 Applicability::MaybeIncorrect,
2202 err.span_suggestion(
2205 "use `impl {}` as the return type if all return paths have the same type but you \
2206 want to expose only the trait in the signature",
2209 format!("impl {}", trait_obj),
2210 Applicability::MaybeIncorrect,
2213 err.span_suggestion(
2216 "use a boxed trait object if all return paths implement trait `{}`",
2219 format!("Box<dyn {}>", trait_obj),
2220 Applicability::MaybeIncorrect,