1 use crate::traits::{ObligationCause, ObligationCauseCode};
2 use crate::ty::diagnostics::suggest_constraining_type_param;
3 use crate::ty::print::{FmtPrinter, Printer};
4 use crate::ty::{self, BoundRegionKind, Region, Ty, TyCtxt};
6 use rustc_errors::Applicability::{MachineApplicable, MaybeIncorrect};
7 use rustc_errors::{pluralize, Diagnostic, MultiSpan};
9 use rustc_hir::def_id::DefId;
10 use rustc_span::symbol::{sym, Symbol};
11 use rustc_span::{BytePos, Span};
12 use rustc_target::spec::abi;
17 #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable, TypeVisitable, Lift)]
18 pub struct ExpectedFound<T> {
23 impl<T> ExpectedFound<T> {
24 pub fn new(a_is_expected: bool, a: T, b: T) -> Self {
26 ExpectedFound { expected: a, found: b }
28 ExpectedFound { expected: b, found: a }
33 // Data structures used in type unification
34 #[derive(Copy, Clone, Debug, TypeFoldable, TypeVisitable, Lift)]
35 #[rustc_pass_by_value]
36 pub enum TypeError<'tcx> {
38 ConstnessMismatch(ExpectedFound<ty::BoundConstness>),
39 PolarityMismatch(ExpectedFound<ty::ImplPolarity>),
40 UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
41 AbiMismatch(ExpectedFound<abi::Abi>),
43 ArgumentMutability(usize),
44 TupleSize(ExpectedFound<usize>),
45 FixedArraySize(ExpectedFound<u64>),
47 FieldMisMatch(Symbol, Symbol),
49 RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>),
50 RegionsInsufficientlyPolymorphic(BoundRegionKind, Region<'tcx>),
51 RegionsOverlyPolymorphic(BoundRegionKind, Region<'tcx>),
52 RegionsPlaceholderMismatch,
54 Sorts(ExpectedFound<Ty<'tcx>>),
55 ArgumentSorts(ExpectedFound<Ty<'tcx>>, usize),
56 IntMismatch(ExpectedFound<ty::IntVarValue>),
57 FloatMismatch(ExpectedFound<ty::FloatTy>),
58 Traits(ExpectedFound<DefId>),
59 VariadicMismatch(ExpectedFound<bool>),
61 /// Instantiating a type variable with the given type would have
62 /// created a cycle (because it appears somewhere within that
65 CyclicConst(ty::Const<'tcx>),
66 ProjectionMismatched(ExpectedFound<DefId>),
68 ExpectedFound<&'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>>,
70 ObjectUnsafeCoercion(DefId),
71 ConstMismatch(ExpectedFound<ty::Const<'tcx>>),
74 /// Safe `#[target_feature]` functions are not assignable to safe function pointers.
75 TargetFeatureCast(DefId),
79 pub fn involves_regions(self) -> bool {
81 TypeError::RegionsDoesNotOutlive(_, _)
82 | TypeError::RegionsInsufficientlyPolymorphic(_, _)
83 | TypeError::RegionsOverlyPolymorphic(_, _)
84 | TypeError::RegionsPlaceholderMismatch => true,
90 /// Explains the source of a type err in a short, human readable way. This is meant to be placed
91 /// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()`
92 /// afterwards to present additional details, particularly when it comes to lifetime-related
94 impl<'tcx> fmt::Display for TypeError<'tcx> {
95 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
96 use self::TypeError::*;
97 fn report_maybe_different(
98 f: &mut fmt::Formatter<'_>,
102 // A naive approach to making sure that we're not reporting silly errors such as:
103 // (expected closure, found closure).
104 if expected == found {
105 write!(f, "expected {}, found a different {}", expected, found)
107 write!(f, "expected {}, found {}", expected, found)
111 let br_string = |br: ty::BoundRegionKind| match br {
112 ty::BrNamed(_, name) => format!(" {}", name),
117 CyclicTy(_) => write!(f, "cyclic type of infinite size"),
118 CyclicConst(_) => write!(f, "encountered a self-referencing constant"),
119 Mismatch => write!(f, "types differ"),
120 ConstnessMismatch(values) => {
121 write!(f, "expected {} bound, found {} bound", values.expected, values.found)
123 PolarityMismatch(values) => {
124 write!(f, "expected {} polarity, found {} polarity", values.expected, values.found)
126 UnsafetyMismatch(values) => {
127 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
129 AbiMismatch(values) => {
130 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
132 ArgumentMutability(_) | Mutability => write!(f, "types differ in mutability"),
133 TupleSize(values) => write!(
135 "expected a tuple with {} element{}, found one with {} element{}",
137 pluralize!(values.expected),
139 pluralize!(values.found)
141 FixedArraySize(values) => write!(
143 "expected an array with a fixed size of {} element{}, found one with {} element{}",
145 pluralize!(values.expected),
147 pluralize!(values.found)
149 ArgCount => write!(f, "incorrect number of function parameters"),
150 FieldMisMatch(adt, field) => write!(f, "field type mismatch: {}.{}", adt, field),
151 RegionsDoesNotOutlive(..) => write!(f, "lifetime mismatch"),
152 // Actually naming the region here is a bit confusing because context is lacking
153 RegionsInsufficientlyPolymorphic(..) => {
154 write!(f, "one type is more general than the other")
156 RegionsOverlyPolymorphic(br, _) => write!(
158 "expected concrete lifetime, found bound lifetime parameter{}",
161 RegionsPlaceholderMismatch => write!(f, "one type is more general than the other"),
162 ArgumentSorts(values, _) | Sorts(values) => ty::tls::with(|tcx| {
163 report_maybe_different(
165 &values.expected.sort_string(tcx),
166 &values.found.sort_string(tcx),
169 Traits(values) => ty::tls::with(|tcx| {
170 report_maybe_different(
172 &format!("trait `{}`", tcx.def_path_str(values.expected)),
173 &format!("trait `{}`", tcx.def_path_str(values.found)),
176 IntMismatch(ref values) => {
177 let expected = match values.expected {
178 ty::IntVarValue::IntType(ty) => ty.name_str(),
179 ty::IntVarValue::UintType(ty) => ty.name_str(),
181 let found = match values.found {
182 ty::IntVarValue::IntType(ty) => ty.name_str(),
183 ty::IntVarValue::UintType(ty) => ty.name_str(),
185 write!(f, "expected `{}`, found `{}`", expected, found)
187 FloatMismatch(ref values) => {
190 "expected `{}`, found `{}`",
191 values.expected.name_str(),
192 values.found.name_str()
195 VariadicMismatch(ref values) => write!(
197 "expected {} fn, found {} function",
198 if values.expected { "variadic" } else { "non-variadic" },
199 if values.found { "variadic" } else { "non-variadic" }
201 ProjectionMismatched(ref values) => ty::tls::with(|tcx| {
204 "expected {}, found {}",
205 tcx.def_path_str(values.expected),
206 tcx.def_path_str(values.found)
209 ExistentialMismatch(ref values) => report_maybe_different(
211 &format!("trait `{}`", values.expected),
212 &format!("trait `{}`", values.found),
214 ConstMismatch(ref values) => {
215 write!(f, "expected `{}`, found `{}`", values.expected, values.found)
217 IntrinsicCast => write!(f, "cannot coerce intrinsics to function pointers"),
218 TargetFeatureCast(_) => write!(
220 "cannot coerce functions with `#[target_feature]` to safe function pointers"
222 ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"),
227 impl<'tcx> TypeError<'tcx> {
228 pub fn must_include_note(self) -> bool {
229 use self::TypeError::*;
231 CyclicTy(_) | CyclicConst(_) | UnsafetyMismatch(_) | ConstnessMismatch(_)
232 | PolarityMismatch(_) | Mismatch | AbiMismatch(_) | FixedArraySize(_)
233 | ArgumentSorts(..) | Sorts(_) | IntMismatch(_) | FloatMismatch(_)
234 | VariadicMismatch(_) | TargetFeatureCast(_) => false,
237 | ArgumentMutability(_)
241 | RegionsDoesNotOutlive(..)
242 | RegionsInsufficientlyPolymorphic(..)
243 | RegionsOverlyPolymorphic(..)
244 | RegionsPlaceholderMismatch
246 | ProjectionMismatched(_)
247 | ExistentialMismatch(_)
250 | ObjectUnsafeCoercion(_) => true,
255 impl<'tcx> Ty<'tcx> {
256 pub fn sort_string(self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
258 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
259 format!("`{}`", self).into()
261 ty::Tuple(ref tys) if tys.is_empty() => format!("`{}`", self).into(),
263 ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did())).into(),
264 ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
266 if t.is_simple_ty() {
267 return format!("array `{}`", self).into();
270 let n = tcx.lift(n).unwrap();
271 if let ty::ConstKind::Value(v) = n.kind() {
272 if let Some(n) = v.try_to_machine_usize(tcx) {
273 return format!("array of {} element{}", n, pluralize!(n)).into();
278 ty::Slice(ty) if ty.is_simple_ty() => format!("slice `{}`", self).into(),
279 ty::Slice(_) => "slice".into(),
280 ty::RawPtr(tymut) => {
281 let tymut_string = match tymut.mutbl {
282 hir::Mutability::Mut => tymut.to_string(),
283 hir::Mutability::Not => format!("const {}", tymut.ty),
286 if tymut_string != "_" && (tymut.ty.is_simple_text() || tymut_string.len() < "const raw pointer".len()) {
287 format!("`*{}`", tymut_string).into()
289 // Unknown type name, it's long or has type arguments
293 ty::Ref(_, ty, mutbl) => {
294 let tymut = ty::TypeAndMut { ty, mutbl };
295 let tymut_string = tymut.to_string();
297 if tymut_string != "_"
298 && (ty.is_simple_text() || tymut_string.len() < "mutable reference".len())
300 format!("`&{}`", tymut_string).into()
302 // Unknown type name, it's long or has type arguments
304 hir::Mutability::Mut => "mutable reference",
310 ty::FnDef(..) => "fn item".into(),
311 ty::FnPtr(_) => "fn pointer".into(),
312 ty::Dynamic(ref inner, ..) if let Some(principal) = inner.principal() => {
313 format!("trait object `dyn {}`", tcx.def_path_str(principal.def_id())).into()
315 ty::Dynamic(..) => "trait object".into(),
316 ty::Closure(..) => "closure".into(),
317 ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(),
318 ty::GeneratorWitness(..) => "generator witness".into(),
319 ty::Tuple(..) => "tuple".into(),
320 ty::Infer(ty::TyVar(_)) => "inferred type".into(),
321 ty::Infer(ty::IntVar(_)) => "integer".into(),
322 ty::Infer(ty::FloatVar(_)) => "floating-point number".into(),
323 ty::Placeholder(..) => "placeholder type".into(),
324 ty::Bound(..) => "bound type".into(),
325 ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
326 ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
327 ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
328 ty::Projection(_) => "associated type".into(),
329 ty::Param(p) => format!("type parameter `{}`", p).into(),
330 ty::Opaque(..) => "opaque type".into(),
331 ty::Error(_) => "type error".into(),
335 pub fn prefix_string(self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
345 | ty::Never => "type".into(),
346 ty::Tuple(ref tys) if tys.is_empty() => "unit type".into(),
347 ty::Adt(def, _) => def.descr().into(),
348 ty::Foreign(_) => "extern type".into(),
349 ty::Array(..) => "array".into(),
350 ty::Slice(_) => "slice".into(),
351 ty::RawPtr(_) => "raw pointer".into(),
352 ty::Ref(.., mutbl) => match mutbl {
353 hir::Mutability::Mut => "mutable reference",
357 ty::FnDef(..) => "fn item".into(),
358 ty::FnPtr(_) => "fn pointer".into(),
359 ty::Dynamic(..) => "trait object".into(),
360 ty::Closure(..) => "closure".into(),
361 ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(),
362 ty::GeneratorWitness(..) => "generator witness".into(),
363 ty::Tuple(..) => "tuple".into(),
364 ty::Placeholder(..) => "higher-ranked type".into(),
365 ty::Bound(..) => "bound type variable".into(),
366 ty::Projection(_) => "associated type".into(),
367 ty::Param(_) => "type parameter".into(),
368 ty::Opaque(..) => "opaque type".into(),
373 impl<'tcx> TyCtxt<'tcx> {
374 pub fn note_and_explain_type_err(
376 diag: &mut Diagnostic,
377 err: TypeError<'tcx>,
378 cause: &ObligationCause<'tcx>,
380 body_owner_def_id: DefId,
382 use self::TypeError::*;
383 debug!("note_and_explain_type_err err={:?} cause={:?}", err, cause);
385 ArgumentSorts(values, _) | Sorts(values) => {
386 match (values.expected.kind(), values.found.kind()) {
387 (ty::Closure(..), ty::Closure(..)) => {
388 diag.note("no two closures, even if identical, have the same type");
389 diag.help("consider boxing your closure and/or using it as a trait object");
391 (ty::Opaque(..), ty::Opaque(..)) => {
393 diag.note("distinct uses of `impl Trait` result in different opaque types");
395 (ty::Float(_), ty::Infer(ty::IntVar(_)))
399 ) = self.sess.source_map().span_to_snippet(sp) =>
401 if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
402 diag.span_suggestion(
404 "use a float literal",
405 format!("{}.0", snippet),
410 (ty::Param(expected), ty::Param(found)) => {
411 let generics = self.generics_of(body_owner_def_id);
412 let e_span = self.def_span(generics.type_param(expected, self).def_id);
413 if !sp.contains(e_span) {
414 diag.span_label(e_span, "expected type parameter");
416 let f_span = self.def_span(generics.type_param(found, self).def_id);
417 if !sp.contains(f_span) {
418 diag.span_label(f_span, "found type parameter");
421 "a type parameter was expected, but a different one was found; \
422 you might be missing a type parameter or trait bound",
425 "for more information, visit \
426 https://doc.rust-lang.org/book/ch10-02-traits.html\
427 #traits-as-parameters",
430 (ty::Projection(_), ty::Projection(_)) => {
431 diag.note("an associated type was expected, but a different one was found");
433 (ty::Param(p), ty::Projection(proj)) | (ty::Projection(proj), ty::Param(p)) => {
434 let generics = self.generics_of(body_owner_def_id);
435 let p_span = self.def_span(generics.type_param(p, self).def_id);
436 if !sp.contains(p_span) {
437 diag.span_label(p_span, "this type parameter");
439 let hir = self.hir();
441 if let Some(generics) = generics
445 .map(|id| hir.local_def_id_to_hir_id(id))
446 .and_then(|id| self.hir().find(self.hir().get_parent_node(id)))
448 .and_then(|node| node.generics())
450 // Synthesize the associated type restriction `Add<Output = Expected>`.
451 // FIXME: extract this logic for use in other diagnostics.
452 let (trait_ref, assoc_substs) = proj.trait_ref_and_own_substs(self);
454 self.def_path_str_with_substs(trait_ref.def_id, trait_ref.substs);
455 let item_name = self.item_name(proj.item_def_id);
456 let item_args = self.format_generic_args(assoc_substs);
458 let path = if path.ends_with('>') {
461 &path[..path.len() - 1],
467 format!("{}<{}{} = {}>", path, item_name, item_args, p)
469 note = !suggest_constraining_type_param(
473 &format!("{}", proj.self_ty()),
479 diag.note("you might be missing a type parameter or trait bound");
482 (ty::Param(p), ty::Dynamic(..) | ty::Opaque(..))
483 | (ty::Dynamic(..) | ty::Opaque(..), ty::Param(p)) => {
484 let generics = self.generics_of(body_owner_def_id);
485 let p_span = self.def_span(generics.type_param(p, self).def_id);
486 if !sp.contains(p_span) {
487 diag.span_label(p_span, "this type parameter");
489 diag.help("type parameters must be constrained to match other types");
490 if self.sess.teach(&diag.get_code().unwrap()) {
492 "given a type parameter `T` and a method `foo`:
494 trait Trait<T> { fn foo(&self) -> T; }
496 the only ways to implement method `foo` are:
497 - constrain `T` with an explicit type:
499 impl Trait<String> for X {
500 fn foo(&self) -> String { String::new() }
503 - add a trait bound to `T` and call a method on that trait that returns `Self`:
505 impl<T: std::default::Default> Trait<T> for X {
506 fn foo(&self) -> T { <T as std::default::Default>::default() }
509 - change `foo` to return an argument of type `T`:
511 impl<T> Trait<T> for X {
512 fn foo(&self, x: T) -> T { x }
518 "for more information, visit \
519 https://doc.rust-lang.org/book/ch10-02-traits.html\
520 #traits-as-parameters",
523 (ty::Param(p), ty::Closure(..) | ty::Generator(..)) => {
524 let generics = self.generics_of(body_owner_def_id);
525 let p_span = self.def_span(generics.type_param(p, self).def_id);
526 if !sp.contains(p_span) {
527 diag.span_label(p_span, "this type parameter");
530 "every closure has a distinct type and so could not always match the \
531 caller-chosen type of parameter `{}`",
535 (ty::Param(p), _) | (_, ty::Param(p)) => {
536 let generics = self.generics_of(body_owner_def_id);
537 let p_span = self.def_span(generics.type_param(p, self).def_id);
538 if !sp.contains(p_span) {
539 diag.span_label(p_span, "this type parameter");
542 (ty::Projection(proj_ty), _) if self.def_kind(proj_ty.item_def_id) != DefKind::ImplTraitPlaceholder => {
543 self.expected_projection(
551 (_, ty::Projection(proj_ty)) if self.def_kind(proj_ty.item_def_id) != DefKind::ImplTraitPlaceholder => {
553 "consider constraining the associated type `{}` to `{}`",
554 values.found, values.expected,
556 if !(self.suggest_constraining_opaque_associated_type(
561 ) || self.suggest_constraint(
570 "for more information, visit \
571 https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
578 "note_and_explain_type_err expected={:?} ({:?}) found={:?} ({:?})",
580 values.expected.kind(),
586 // Watch out for various cases of cyclic types and try to explain.
587 if ty.is_closure() || ty.is_generator() {
589 "closures cannot capture themselves or take themselves as argument;\n\
590 this error may be the result of a recent compiler bug-fix,\n\
591 see issue #46062 <https://github.com/rust-lang/rust/issues/46062>\n\
592 for more information",
596 TargetFeatureCast(def_id) => {
598 self.get_attrs(def_id, sym::target_feature).map(|attr| attr.span);
600 "functions with `#[target_feature]` can only be coerced to `unsafe` function pointers"
602 diag.span_labels(target_spans, "`#[target_feature]` added here");
608 fn suggest_constraint(
610 diag: &mut Diagnostic,
612 body_owner_def_id: DefId,
613 proj_ty: &ty::ProjectionTy<'tcx>,
616 let assoc = self.associated_item(proj_ty.item_def_id);
617 let (trait_ref, assoc_substs) = proj_ty.trait_ref_and_own_substs(self);
618 if let Some(item) = self.hir().get_if_local(body_owner_def_id) {
619 if let Some(hir_generics) = item.generics() {
620 // Get the `DefId` for the type parameter corresponding to `A` in `<A as T>::Foo`.
621 // This will also work for `impl Trait`.
622 let def_id = if let ty::Param(param_ty) = proj_ty.self_ty().kind() {
623 let generics = self.generics_of(body_owner_def_id);
624 generics.type_param(param_ty, self).def_id
628 let Some(def_id) = def_id.as_local() else {
632 // First look in the `where` clause, as this might be
633 // `fn foo<T>(x: T) where T: Trait`.
634 for pred in hir_generics.bounds_for_param(def_id) {
635 if self.constrain_generic_bound_associated_type_structured_suggestion(
653 /// An associated type was expected and a different type was found.
655 /// We perform a few different checks to see what we can suggest:
657 /// - In the current item, look for associated functions that return the expected type and
658 /// suggest calling them. (Not a structured suggestion.)
659 /// - If any of the item's generic bounds can be constrained, we suggest constraining the
660 /// associated type to the found type.
661 /// - If the associated type has a default type and was expected inside of a `trait`, we
662 /// mention that this is disallowed.
663 /// - If all other things fail, and the error is not because of a mismatch between the `trait`
664 /// and the `impl`, we provide a generic `help` to constrain the assoc type or call an assoc
665 /// fn that returns the type.
666 fn expected_projection(
668 diag: &mut Diagnostic,
669 proj_ty: &ty::ProjectionTy<'tcx>,
670 values: ExpectedFound<Ty<'tcx>>,
671 body_owner_def_id: DefId,
672 cause_code: &ObligationCauseCode<'_>,
675 "consider constraining the associated type `{}` to `{}`",
676 values.expected, values.found
678 let body_owner = self.hir().get_if_local(body_owner_def_id);
679 let current_method_ident = body_owner.and_then(|n| n.ident()).map(|i| i.name);
681 // We don't want to suggest calling an assoc fn in a scope where that isn't feasible.
682 let callable_scope = matches!(
685 hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(..), .. })
686 | hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. })
687 | hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }),
690 let impl_comparison =
691 matches!(cause_code, ObligationCauseCode::CompareImplItemObligation { .. });
692 let assoc = self.associated_item(proj_ty.item_def_id);
693 if !callable_scope || impl_comparison {
694 // We do not want to suggest calling functions when the reason of the
695 // type error is a comparison of an `impl` with its `trait` or when the
696 // scope is outside of a `Body`.
698 // If we find a suitable associated function that returns the expected type, we don't
699 // want the more general suggestion later in this method about "consider constraining
700 // the associated type or calling a method that returns the associated type".
701 let point_at_assoc_fn = self.point_at_methods_that_satisfy_associated_type(
703 assoc.container_id(self),
704 current_method_ident,
708 // Possibly suggest constraining the associated type to conform to the
710 if self.suggest_constraint(diag, &msg, body_owner_def_id, proj_ty, values.found)
717 self.suggest_constraining_opaque_associated_type(diag, &msg, proj_ty, values.found);
719 if self.point_at_associated_type(diag, body_owner_def_id, values.found) {
723 if !impl_comparison {
724 // Generic suggestion when we can't be more specific.
727 "{} or calling a method that returns `{}`",
734 "for more information, visit \
735 https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
738 if self.sess.teach(&diag.get_code().unwrap()) {
740 "given an associated type `T` and a method `foo`:
744 fn foo(&self) -> Self::T;
747 the only way of implementing method `foo` is to constrain `T` with an explicit associated type:
751 fn foo(&self) -> Self::T { String::new() }
758 /// When the expected `impl Trait` is not defined in the current item, it will come from
759 /// a return type. This can occur when dealing with `TryStream` (#71035).
760 fn suggest_constraining_opaque_associated_type(
762 diag: &mut Diagnostic,
764 proj_ty: &ty::ProjectionTy<'tcx>,
767 let assoc = self.associated_item(proj_ty.item_def_id);
768 if let ty::Opaque(def_id, _) = *proj_ty.self_ty().kind() {
769 let opaque_local_def_id = def_id.as_local();
770 let opaque_hir_ty = if let Some(opaque_local_def_id) = opaque_local_def_id {
771 match &self.hir().expect_item(opaque_local_def_id).kind {
772 hir::ItemKind::OpaqueTy(opaque_hir_ty) => opaque_hir_ty,
773 _ => bug!("The HirId comes from a `ty::Opaque`"),
779 let (trait_ref, assoc_substs) = proj_ty.trait_ref_and_own_substs(self);
781 self.constrain_generic_bound_associated_type_structured_suggestion(
784 opaque_hir_ty.bounds,
796 fn point_at_methods_that_satisfy_associated_type(
798 diag: &mut Diagnostic,
799 assoc_container_id: DefId,
800 current_method_ident: Option<Symbol>,
801 proj_ty_item_def_id: DefId,
804 let items = self.associated_items(assoc_container_id);
805 // Find all the methods in the trait that could be called to construct the
806 // expected associated type.
807 // FIXME: consider suggesting the use of associated `const`s.
808 let methods: Vec<(Span, String)> = items
811 .filter(|(name, item)| {
812 ty::AssocKind::Fn == item.kind && Some(**name) != current_method_ident
814 .filter_map(|(_, item)| {
815 let method = self.fn_sig(item.def_id);
816 match *method.output().skip_binder().kind() {
817 ty::Projection(ty::ProjectionTy { item_def_id, .. })
818 if item_def_id == proj_ty_item_def_id =>
821 self.def_span(item.def_id),
822 format!("consider calling `{}`", self.def_path_str(item.def_id)),
829 if !methods.is_empty() {
830 // Use a single `help:` to show all the methods in the trait that can
831 // be used to construct the expected associated type.
832 let mut span: MultiSpan =
833 methods.iter().map(|(sp, _)| *sp).collect::<Vec<Span>>().into();
835 "{some} method{s} {are} available that return{r} `{ty}`",
836 some = if methods.len() == 1 { "a" } else { "some" },
837 s = pluralize!(methods.len()),
838 are = pluralize!("is", methods.len()),
839 r = if methods.len() == 1 { "s" } else { "" },
842 for (sp, label) in methods.into_iter() {
843 span.push_span_label(sp, label);
845 diag.span_help(span, &msg);
851 fn point_at_associated_type(
853 diag: &mut Diagnostic,
854 body_owner_def_id: DefId,
857 let Some(hir_id) = body_owner_def_id.as_local() else {
860 let hir_id = self.hir().local_def_id_to_hir_id(hir_id);
861 // When `body_owner` is an `impl` or `trait` item, look in its associated types for
862 // `expected` and point at it.
863 let parent_id = self.hir().get_parent_item(hir_id);
864 let item = self.hir().find_by_def_id(parent_id.def_id);
865 debug!("expected_projection parent item {:?}", item);
867 Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Trait(.., items), .. })) => {
868 // FIXME: account for `#![feature(specialization)]`
869 for item in &items[..] {
871 hir::AssocItemKind::Type => {
872 // FIXME: account for returning some type in a trait fn impl that has
873 // an assoc type as a return type (#72076).
874 if let hir::Defaultness::Default { has_value: true } =
875 self.impl_defaultness(item.id.def_id)
877 if self.type_of(item.id.def_id) == found {
880 "associated type defaults can't be assumed inside the \
881 trait defining them",
891 Some(hir::Node::Item(hir::Item {
892 kind: hir::ItemKind::Impl(hir::Impl { items, .. }),
895 for item in &items[..] {
896 if let hir::AssocItemKind::Type = item.kind {
897 if self.type_of(item.id.def_id) == found {
898 diag.span_label(item.span, "expected this associated type");
909 /// Given a slice of `hir::GenericBound`s, if any of them corresponds to the `trait_ref`
910 /// requirement, provide a structured suggestion to constrain it to a given type `ty`.
912 /// `is_bound_surely_present` indicates whether we know the bound we're looking for is
913 /// inside `bounds`. If that's the case then we can consider `bounds` containing only one
914 /// trait bound as the one we're looking for. This can help in cases where the associated
915 /// type is defined on a supertrait of the one present in the bounds.
916 fn constrain_generic_bound_associated_type_structured_suggestion(
918 diag: &mut Diagnostic,
919 trait_ref: &ty::TraitRef<'tcx>,
920 bounds: hir::GenericBounds<'_>,
921 assoc: &ty::AssocItem,
922 assoc_substs: &[ty::GenericArg<'tcx>],
925 is_bound_surely_present: bool,
927 // FIXME: we would want to call `resolve_vars_if_possible` on `ty` before suggesting.
929 let trait_bounds = bounds.iter().filter_map(|bound| match bound {
930 hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::None) => Some(ptr),
934 let matching_trait_bounds = trait_bounds
936 .filter(|ptr| ptr.trait_ref.trait_def_id() == Some(trait_ref.def_id))
937 .collect::<Vec<_>>();
939 let span = match &matching_trait_bounds[..] {
941 &[] if is_bound_surely_present => match &trait_bounds.collect::<Vec<_>>()[..] {
948 self.constrain_associated_type_structured_suggestion(
958 /// Given a span corresponding to a bound, provide a structured suggestion to set an
959 /// associated type to a given type `ty`.
960 fn constrain_associated_type_structured_suggestion(
962 diag: &mut Diagnostic,
964 assoc: &ty::AssocItem,
965 assoc_substs: &[ty::GenericArg<'tcx>],
969 if let Ok(has_params) =
970 self.sess.source_map().span_to_snippet(span).map(|snippet| snippet.ends_with('>'))
972 let (span, sugg) = if has_params {
973 let pos = span.hi() - BytePos(1);
974 let span = Span::new(pos, pos, span.ctxt(), span.parent());
975 (span, format!(", {} = {}", assoc.ident(self), ty))
977 let item_args = self.format_generic_args(assoc_substs);
978 (span.shrink_to_hi(), format!("<{}{} = {}>", assoc.ident(self), item_args, ty))
980 diag.span_suggestion_verbose(span, msg, sugg, MaybeIncorrect);
986 fn format_generic_args(self, args: &[ty::GenericArg<'tcx>]) -> String {
987 FmtPrinter::new(self, hir::def::Namespace::TypeNS)
988 .path_generic_args(Ok, args)
989 .expect("could not write to `String`.")