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};
5 use rustc_errors::Applicability::{MachineApplicable, MaybeIncorrect};
6 use rustc_errors::{pluralize, DiagnosticBuilder};
8 use rustc_hir::def_id::DefId;
9 use rustc_span::symbol::{sym, Symbol};
10 use rustc_span::{BytePos, MultiSpan, Span};
11 use rustc_target::spec::abi;
16 #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable)]
17 pub struct ExpectedFound<T> {
22 impl<T> ExpectedFound<T> {
23 pub fn new(a_is_expected: bool, a: T, b: T) -> Self {
25 ExpectedFound { expected: a, found: b }
27 ExpectedFound { expected: b, found: a }
32 // Data structures used in type unification
33 #[derive(Clone, Debug, TypeFoldable)]
34 pub enum TypeError<'tcx> {
36 ConstnessMismatch(ExpectedFound<ty::BoundConstness>),
37 PolarityMismatch(ExpectedFound<ty::ImplPolarity>),
38 UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
39 AbiMismatch(ExpectedFound<abi::Abi>),
41 ArgumentMutability(usize),
42 TupleSize(ExpectedFound<usize>),
43 FixedArraySize(ExpectedFound<u64>),
45 FieldMisMatch(Symbol, Symbol),
47 RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>),
48 RegionsInsufficientlyPolymorphic(BoundRegionKind, Region<'tcx>),
49 RegionsOverlyPolymorphic(BoundRegionKind, Region<'tcx>),
50 RegionsPlaceholderMismatch,
52 Sorts(ExpectedFound<Ty<'tcx>>),
53 ArgumentSorts(ExpectedFound<Ty<'tcx>>, usize),
54 IntMismatch(ExpectedFound<ty::IntVarValue>),
55 FloatMismatch(ExpectedFound<ty::FloatTy>),
56 Traits(ExpectedFound<DefId>),
57 VariadicMismatch(ExpectedFound<bool>),
59 /// Instantiating a type variable with the given type would have
60 /// created a cycle (because it appears somewhere within that
63 CyclicConst(&'tcx ty::Const<'tcx>),
64 ProjectionMismatched(ExpectedFound<DefId>),
66 ExpectedFound<&'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>>,
68 ObjectUnsafeCoercion(DefId),
69 ConstMismatch(ExpectedFound<&'tcx ty::Const<'tcx>>),
72 /// Safe `#[target_feature]` functions are not assignable to safe function pointers.
73 TargetFeatureCast(DefId),
76 /// Explains the source of a type err in a short, human readable way. This is meant to be placed
77 /// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()`
78 /// afterwards to present additional details, particularly when it comes to lifetime-related
80 impl<'tcx> fmt::Display for TypeError<'tcx> {
81 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
82 use self::TypeError::*;
83 fn report_maybe_different(
84 f: &mut fmt::Formatter<'_>,
88 // A naive approach to making sure that we're not reporting silly errors such as:
89 // (expected closure, found closure).
90 if expected == found {
91 write!(f, "expected {}, found a different {}", expected, found)
93 write!(f, "expected {}, found {}", expected, found)
97 let br_string = |br: ty::BoundRegionKind| match br {
98 ty::BrNamed(_, name) => format!(" {}", name),
103 CyclicTy(_) => write!(f, "cyclic type of infinite size"),
104 CyclicConst(_) => write!(f, "encountered a self-referencing constant"),
105 Mismatch => write!(f, "types differ"),
106 ConstnessMismatch(values) => {
107 write!(f, "expected {} bound, found {} bound", values.expected, values.found)
109 PolarityMismatch(values) => {
110 write!(f, "expected {} polarity, found {} polarity", values.expected, values.found)
112 UnsafetyMismatch(values) => {
113 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
115 AbiMismatch(values) => {
116 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
118 ArgumentMutability(_) | Mutability => write!(f, "types differ in mutability"),
119 TupleSize(values) => write!(
121 "expected a tuple with {} element{}, \
122 found one with {} element{}",
124 pluralize!(values.expected),
126 pluralize!(values.found)
128 FixedArraySize(values) => write!(
130 "expected an array with a fixed size of {} element{}, \
131 found one with {} element{}",
133 pluralize!(values.expected),
135 pluralize!(values.found)
137 ArgCount => write!(f, "incorrect number of function parameters"),
138 FieldMisMatch(adt, field) => write!(f, "field type mismatch: {}.{}", adt, field),
139 RegionsDoesNotOutlive(..) => write!(f, "lifetime mismatch"),
140 RegionsInsufficientlyPolymorphic(br, _) => write!(
142 "expected bound lifetime parameter{}, found concrete lifetime",
145 RegionsOverlyPolymorphic(br, _) => write!(
147 "expected concrete lifetime, found bound lifetime parameter{}",
150 RegionsPlaceholderMismatch => write!(f, "one type is more general than the other"),
151 ArgumentSorts(values, _) | Sorts(values) => ty::tls::with(|tcx| {
152 report_maybe_different(
154 &values.expected.sort_string(tcx),
155 &values.found.sort_string(tcx),
158 Traits(values) => ty::tls::with(|tcx| {
159 report_maybe_different(
161 &format!("trait `{}`", tcx.def_path_str(values.expected)),
162 &format!("trait `{}`", tcx.def_path_str(values.found)),
165 IntMismatch(ref values) => {
166 let expected = match values.expected {
167 ty::IntVarValue::IntType(ty) => ty.name_str(),
168 ty::IntVarValue::UintType(ty) => ty.name_str(),
170 let found = match values.found {
171 ty::IntVarValue::IntType(ty) => ty.name_str(),
172 ty::IntVarValue::UintType(ty) => ty.name_str(),
174 write!(f, "expected `{}`, found `{}`", expected, found)
176 FloatMismatch(ref values) => {
179 "expected `{}`, found `{}`",
180 values.expected.name_str(),
181 values.found.name_str()
184 VariadicMismatch(ref values) => write!(
186 "expected {} fn, found {} function",
187 if values.expected { "variadic" } else { "non-variadic" },
188 if values.found { "variadic" } else { "non-variadic" }
190 ProjectionMismatched(ref values) => ty::tls::with(|tcx| {
193 "expected {}, found {}",
194 tcx.def_path_str(values.expected),
195 tcx.def_path_str(values.found)
198 ExistentialMismatch(ref values) => report_maybe_different(
200 &format!("trait `{}`", values.expected),
201 &format!("trait `{}`", values.found),
203 ConstMismatch(ref values) => {
204 write!(f, "expected `{}`, found `{}`", values.expected, values.found)
206 IntrinsicCast => write!(f, "cannot coerce intrinsics to function pointers"),
207 TargetFeatureCast(_) => write!(
209 "cannot coerce functions with `#[target_feature]` to safe function pointers"
211 ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"),
216 impl<'tcx> TypeError<'tcx> {
217 pub fn must_include_note(&self) -> bool {
218 use self::TypeError::*;
220 CyclicTy(_) | CyclicConst(_) | UnsafetyMismatch(_) | ConstnessMismatch(_)
221 | PolarityMismatch(_) | Mismatch | AbiMismatch(_) | FixedArraySize(_)
222 | ArgumentSorts(..) | Sorts(_) | IntMismatch(_) | FloatMismatch(_)
223 | VariadicMismatch(_) | TargetFeatureCast(_) => false,
226 | ArgumentMutability(_)
230 | RegionsDoesNotOutlive(..)
231 | RegionsInsufficientlyPolymorphic(..)
232 | RegionsOverlyPolymorphic(..)
233 | RegionsPlaceholderMismatch
235 | ProjectionMismatched(_)
236 | ExistentialMismatch(_)
239 | ObjectUnsafeCoercion(_) => true,
244 impl<'tcx> ty::TyS<'tcx> {
245 pub fn sort_string(&self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
247 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
248 format!("`{}`", self).into()
250 ty::Tuple(ref tys) if tys.is_empty() => format!("`{}`", self).into(),
252 ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did)).into(),
253 ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
255 if t.is_simple_ty() {
256 return format!("array `{}`", self).into();
259 let n = tcx.lift(n).unwrap();
260 if let ty::ConstKind::Value(v) = n.val {
261 if let Some(n) = v.try_to_machine_usize(tcx) {
262 return format!("array of {} element{}", n, pluralize!(n)).into();
267 ty::Slice(ty) if ty.is_simple_ty() => format!("slice `{}`", self).into(),
268 ty::Slice(_) => "slice".into(),
269 ty::RawPtr(_) => "*-ptr".into(),
270 ty::Ref(_, ty, mutbl) => {
271 let tymut = ty::TypeAndMut { ty, mutbl };
272 let tymut_string = tymut.to_string();
273 if tymut_string != "_"
274 && (ty.is_simple_text() || tymut_string.len() < "mutable reference".len())
276 format!("`&{}`", tymut_string).into()
278 // Unknown type name, it's long or has type arguments
280 hir::Mutability::Mut => "mutable reference",
286 ty::FnDef(..) => "fn item".into(),
287 ty::FnPtr(_) => "fn pointer".into(),
288 ty::Dynamic(ref inner, ..) if let Some(principal) = inner.principal() => {
289 format!("trait object `dyn {}`", tcx.def_path_str(principal.def_id())).into()
291 ty::Dynamic(..) => "trait object".into(),
292 ty::Closure(..) => "closure".into(),
293 ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(),
294 ty::GeneratorWitness(..) => "generator witness".into(),
295 ty::Tuple(..) => "tuple".into(),
296 ty::Infer(ty::TyVar(_)) => "inferred type".into(),
297 ty::Infer(ty::IntVar(_)) => "integer".into(),
298 ty::Infer(ty::FloatVar(_)) => "floating-point number".into(),
299 ty::Placeholder(..) => "placeholder type".into(),
300 ty::Bound(..) => "bound type".into(),
301 ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
302 ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
303 ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
304 ty::Projection(_) => "associated type".into(),
305 ty::Param(p) => format!("type parameter `{}`", p).into(),
306 ty::Opaque(..) => "opaque type".into(),
307 ty::Error(_) => "type error".into(),
311 pub fn prefix_string(&self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
321 | ty::Never => "type".into(),
322 ty::Tuple(ref tys) if tys.is_empty() => "unit type".into(),
323 ty::Adt(def, _) => def.descr().into(),
324 ty::Foreign(_) => "extern type".into(),
325 ty::Array(..) => "array".into(),
326 ty::Slice(_) => "slice".into(),
327 ty::RawPtr(_) => "raw pointer".into(),
328 ty::Ref(.., mutbl) => match mutbl {
329 hir::Mutability::Mut => "mutable reference",
333 ty::FnDef(..) => "fn item".into(),
334 ty::FnPtr(_) => "fn pointer".into(),
335 ty::Dynamic(..) => "trait object".into(),
336 ty::Closure(..) => "closure".into(),
337 ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(),
338 ty::GeneratorWitness(..) => "generator witness".into(),
339 ty::Tuple(..) => "tuple".into(),
340 ty::Placeholder(..) => "higher-ranked type".into(),
341 ty::Bound(..) => "bound type variable".into(),
342 ty::Projection(_) => "associated type".into(),
343 ty::Param(_) => "type parameter".into(),
344 ty::Opaque(..) => "opaque type".into(),
349 impl<'tcx> TyCtxt<'tcx> {
350 pub fn note_and_explain_type_err(
352 db: &mut DiagnosticBuilder<'_>,
353 err: &TypeError<'tcx>,
354 cause: &ObligationCause<'tcx>,
356 body_owner_def_id: DefId,
358 use self::TypeError::*;
359 debug!("note_and_explain_type_err err={:?} cause={:?}", err, cause);
361 ArgumentSorts(values, _) | Sorts(values) => {
362 match (values.expected.kind(), values.found.kind()) {
363 (ty::Closure(..), ty::Closure(..)) => {
364 db.note("no two closures, even if identical, have the same type");
365 db.help("consider boxing your closure and/or using it as a trait object");
367 (ty::Opaque(..), ty::Opaque(..)) => {
369 db.note("distinct uses of `impl Trait` result in different opaque types");
371 (ty::Float(_), ty::Infer(ty::IntVar(_)))
375 ) = self.sess.source_map().span_to_snippet(sp) =>
377 if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
380 "use a float literal",
381 format!("{}.0", snippet),
386 (ty::Param(expected), ty::Param(found)) => {
387 let generics = self.generics_of(body_owner_def_id);
388 let e_span = self.def_span(generics.type_param(expected, self).def_id);
389 if !sp.contains(e_span) {
390 db.span_label(e_span, "expected type parameter");
392 let f_span = self.def_span(generics.type_param(found, self).def_id);
393 if !sp.contains(f_span) {
394 db.span_label(f_span, "found type parameter");
397 "a type parameter was expected, but a different one was found; \
398 you might be missing a type parameter or trait bound",
401 "for more information, visit \
402 https://doc.rust-lang.org/book/ch10-02-traits.html\
403 #traits-as-parameters",
406 (ty::Projection(_), ty::Projection(_)) => {
407 db.note("an associated type was expected, but a different one was found");
409 (ty::Param(p), ty::Projection(proj)) | (ty::Projection(proj), ty::Param(p)) => {
410 let generics = self.generics_of(body_owner_def_id);
411 let p_span = self.def_span(generics.type_param(p, self).def_id);
412 if !sp.contains(p_span) {
413 db.span_label(p_span, "this type parameter");
415 let hir = self.hir();
417 if let Some(generics) = generics
421 .map(|id| hir.local_def_id_to_hir_id(id))
422 .and_then(|id| self.hir().find(self.hir().get_parent_node(id)))
424 .and_then(|node| node.generics())
426 // Synthesize the associated type restriction `Add<Output = Expected>`.
427 // FIXME: extract this logic for use in other diagnostics.
428 let (trait_ref, assoc_substs) = proj.trait_ref_and_own_substs(self);
430 self.def_path_str_with_substs(trait_ref.def_id, trait_ref.substs);
431 let item_name = self.item_name(proj.item_def_id);
432 let item_args = self.format_generic_args(assoc_substs);
434 let path = if path.ends_with('>') {
437 &path[..path.len() - 1],
443 format!("{}<{}{} = {}>", path, item_name, item_args, p)
445 note = !suggest_constraining_type_param(
449 &format!("{}", proj.self_ty()),
455 db.note("you might be missing a type parameter or trait bound");
458 (ty::Param(p), ty::Dynamic(..) | ty::Opaque(..))
459 | (ty::Dynamic(..) | ty::Opaque(..), ty::Param(p)) => {
460 let generics = self.generics_of(body_owner_def_id);
461 let p_span = self.def_span(generics.type_param(p, self).def_id);
462 if !sp.contains(p_span) {
463 db.span_label(p_span, "this type parameter");
465 db.help("type parameters must be constrained to match other types");
466 if self.sess.teach(&db.get_code().unwrap()) {
468 "given a type parameter `T` and a method `foo`:
470 trait Trait<T> { fn foo(&self) -> T; }
472 the only ways to implement method `foo` are:
473 - constrain `T` with an explicit type:
475 impl Trait<String> for X {
476 fn foo(&self) -> String { String::new() }
479 - add a trait bound to `T` and call a method on that trait that returns `Self`:
481 impl<T: std::default::Default> Trait<T> for X {
482 fn foo(&self) -> T { <T as std::default::Default>::default() }
485 - change `foo` to return an argument of type `T`:
487 impl<T> Trait<T> for X {
488 fn foo(&self, x: T) -> T { x }
494 "for more information, visit \
495 https://doc.rust-lang.org/book/ch10-02-traits.html\
496 #traits-as-parameters",
499 (ty::Param(p), ty::Closure(..) | ty::Generator(..)) => {
500 let generics = self.generics_of(body_owner_def_id);
501 let p_span = self.def_span(generics.type_param(p, self).def_id);
502 if !sp.contains(p_span) {
503 db.span_label(p_span, "this type parameter");
506 "every closure has a distinct type and so could not always match the \
507 caller-chosen type of parameter `{}`",
511 (ty::Param(p), _) | (_, ty::Param(p)) => {
512 let generics = self.generics_of(body_owner_def_id);
513 let p_span = self.def_span(generics.type_param(p, self).def_id);
514 if !sp.contains(p_span) {
515 db.span_label(p_span, "this type parameter");
518 (ty::Projection(proj_ty), _) => {
519 self.expected_projection(
527 (_, ty::Projection(proj_ty)) => {
529 "consider constraining the associated type `{}` to `{}`",
530 values.found, values.expected,
532 if !(self.suggest_constraining_opaque_associated_type(
537 ) || self.suggest_constraint(
546 "for more information, visit \
547 https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
554 "note_and_explain_type_err expected={:?} ({:?}) found={:?} ({:?})",
556 values.expected.kind(),
562 // Watch out for various cases of cyclic types and try to explain.
563 if ty.is_closure() || ty.is_generator() {
565 "closures cannot capture themselves or take themselves as argument;\n\
566 this error may be the result of a recent compiler bug-fix,\n\
567 see issue #46062 <https://github.com/rust-lang/rust/issues/46062>\n\
568 for more information",
572 TargetFeatureCast(def_id) => {
573 let attrs = self.get_attrs(*def_id);
574 let target_spans = attrs
576 .filter(|attr| attr.has_name(sym::target_feature))
577 .map(|attr| attr.span);
579 "functions with `#[target_feature]` can only be coerced to `unsafe` function pointers"
581 db.span_labels(target_spans, "`#[target_feature]` added here");
587 fn suggest_constraint(
589 db: &mut DiagnosticBuilder<'_>,
591 body_owner_def_id: DefId,
592 proj_ty: &ty::ProjectionTy<'tcx>,
595 let assoc = self.associated_item(proj_ty.item_def_id);
596 let (trait_ref, assoc_substs) = proj_ty.trait_ref_and_own_substs(self);
597 if let Some(item) = self.hir().get_if_local(body_owner_def_id) {
598 if let Some(hir_generics) = item.generics() {
599 // Get the `DefId` for the type parameter corresponding to `A` in `<A as T>::Foo`.
600 // This will also work for `impl Trait`.
601 let def_id = if let ty::Param(param_ty) = proj_ty.self_ty().kind() {
602 let generics = self.generics_of(body_owner_def_id);
603 generics.type_param(param_ty, self).def_id
608 // First look in the `where` clause, as this might be
609 // `fn foo<T>(x: T) where T: Trait`.
610 for predicate in hir_generics.where_clause.predicates {
611 if let hir::WherePredicate::BoundPredicate(pred) = predicate {
612 if let hir::TyKind::Path(hir::QPath::Resolved(None, path)) =
615 if path.res.opt_def_id() == Some(def_id) {
616 // This predicate is binding type param `A` in `<A as T>::Foo` to
617 // something, potentially `T`.
625 if self.constrain_generic_bound_associated_type_structured_suggestion(
639 for param in hir_generics.params {
640 if self.hir().opt_local_def_id(param.hir_id).map(|id| id.to_def_id())
643 // This is type param `A` in `<A as T>::Foo`.
644 return self.constrain_generic_bound_associated_type_structured_suggestion(
661 /// An associated type was expected and a different type was found.
663 /// We perform a few different checks to see what we can suggest:
665 /// - In the current item, look for associated functions that return the expected type and
666 /// suggest calling them. (Not a structured suggestion.)
667 /// - If any of the item's generic bounds can be constrained, we suggest constraining the
668 /// associated type to the found type.
669 /// - If the associated type has a default type and was expected inside of a `trait`, we
670 /// mention that this is disallowed.
671 /// - If all other things fail, and the error is not because of a mismatch between the `trait`
672 /// and the `impl`, we provide a generic `help` to constrain the assoc type or call an assoc
673 /// fn that returns the type.
674 fn expected_projection(
676 db: &mut DiagnosticBuilder<'_>,
677 proj_ty: &ty::ProjectionTy<'tcx>,
678 values: &ExpectedFound<Ty<'tcx>>,
679 body_owner_def_id: DefId,
680 cause_code: &ObligationCauseCode<'_>,
683 "consider constraining the associated type `{}` to `{}`",
684 values.expected, values.found
686 let body_owner = self.hir().get_if_local(body_owner_def_id);
687 let current_method_ident = body_owner.and_then(|n| n.ident()).map(|i| i.name);
689 // We don't want to suggest calling an assoc fn in a scope where that isn't feasible.
690 let callable_scope = matches!(
693 hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(..), .. })
694 | hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. })
695 | hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }),
698 let impl_comparison = matches!(
700 ObligationCauseCode::CompareImplMethodObligation { .. }
701 | ObligationCauseCode::CompareImplTypeObligation { .. }
702 | ObligationCauseCode::CompareImplConstObligation
704 let assoc = self.associated_item(proj_ty.item_def_id);
705 if !callable_scope || impl_comparison {
706 // We do not want to suggest calling functions when the reason of the
707 // type error is a comparison of an `impl` with its `trait` or when the
708 // scope is outside of a `Body`.
710 // If we find a suitable associated function that returns the expected type, we don't
711 // want the more general suggestion later in this method about "consider constraining
712 // the associated type or calling a method that returns the associated type".
713 let point_at_assoc_fn = self.point_at_methods_that_satisfy_associated_type(
715 assoc.container.id(),
716 current_method_ident,
720 // Possibly suggest constraining the associated type to conform to the
722 if self.suggest_constraint(db, &msg, body_owner_def_id, proj_ty, values.found)
729 self.suggest_constraining_opaque_associated_type(db, &msg, proj_ty, values.found);
731 if self.point_at_associated_type(db, body_owner_def_id, values.found) {
735 if !impl_comparison {
736 // Generic suggestion when we can't be more specific.
738 db.help(&format!("{} or calling a method that returns `{}`", msg, values.expected));
743 "for more information, visit \
744 https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
747 if self.sess.teach(&db.get_code().unwrap()) {
749 "given an associated type `T` and a method `foo`:
753 fn foo(&self) -> Self::T;
756 the only way of implementing method `foo` is to constrain `T` with an explicit associated type:
760 fn foo(&self) -> Self::T { String::new() }
767 /// When the expected `impl Trait` is not defined in the current item, it will come from
768 /// a return type. This can occur when dealing with `TryStream` (#71035).
769 fn suggest_constraining_opaque_associated_type(
771 db: &mut DiagnosticBuilder<'_>,
773 proj_ty: &ty::ProjectionTy<'tcx>,
776 let assoc = self.associated_item(proj_ty.item_def_id);
777 if let ty::Opaque(def_id, _) = *proj_ty.self_ty().kind() {
778 let opaque_local_def_id = def_id.as_local();
779 let opaque_hir_ty = if let Some(opaque_local_def_id) = opaque_local_def_id {
780 let hir = self.hir();
781 let opaque_hir_id = hir.local_def_id_to_hir_id(opaque_local_def_id);
782 match &hir.expect_item(opaque_hir_id).kind {
783 hir::ItemKind::OpaqueTy(opaque_hir_ty) => opaque_hir_ty,
784 _ => bug!("The HirId comes from a `ty::Opaque`"),
790 let (trait_ref, assoc_substs) = proj_ty.trait_ref_and_own_substs(self);
792 self.constrain_generic_bound_associated_type_structured_suggestion(
795 opaque_hir_ty.bounds,
807 fn point_at_methods_that_satisfy_associated_type(
809 db: &mut DiagnosticBuilder<'_>,
810 assoc_container_id: DefId,
811 current_method_ident: Option<Symbol>,
812 proj_ty_item_def_id: DefId,
815 let items = self.associated_items(assoc_container_id);
816 // Find all the methods in the trait that could be called to construct the
817 // expected associated type.
818 // FIXME: consider suggesting the use of associated `const`s.
819 let methods: Vec<(Span, String)> = items
822 .filter(|(name, item)| {
823 ty::AssocKind::Fn == item.kind && Some(**name) != current_method_ident
825 .filter_map(|(_, item)| {
826 let method = self.fn_sig(item.def_id);
827 match *method.output().skip_binder().kind() {
828 ty::Projection(ty::ProjectionTy { item_def_id, .. })
829 if item_def_id == proj_ty_item_def_id =>
832 self.sess.source_map().guess_head_span(self.def_span(item.def_id)),
833 format!("consider calling `{}`", self.def_path_str(item.def_id)),
840 if !methods.is_empty() {
841 // Use a single `help:` to show all the methods in the trait that can
842 // be used to construct the expected associated type.
843 let mut span: MultiSpan =
844 methods.iter().map(|(sp, _)| *sp).collect::<Vec<Span>>().into();
846 "{some} method{s} {are} available that return{r} `{ty}`",
847 some = if methods.len() == 1 { "a" } else { "some" },
848 s = pluralize!(methods.len()),
849 are = if methods.len() == 1 { "is" } else { "are" },
850 r = if methods.len() == 1 { "s" } else { "" },
853 for (sp, label) in methods.into_iter() {
854 span.push_span_label(sp, label);
856 db.span_help(span, &msg);
862 fn point_at_associated_type(
864 db: &mut DiagnosticBuilder<'_>,
865 body_owner_def_id: DefId,
869 match body_owner_def_id.as_local().map(|id| self.hir().local_def_id_to_hir_id(id)) {
870 Some(hir_id) => hir_id,
871 None => return false,
873 // When `body_owner` is an `impl` or `trait` item, look in its associated types for
874 // `expected` and point at it.
875 let parent_id = self.hir().get_parent_item(hir_id);
876 let item = self.hir().find(parent_id);
877 debug!("expected_projection parent item {:?}", item);
879 Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Trait(.., items), .. })) => {
880 // FIXME: account for `#![feature(specialization)]`
881 for item in &items[..] {
883 hir::AssocItemKind::Type => {
884 // FIXME: account for returning some type in a trait fn impl that has
885 // an assoc type as a return type (#72076).
886 if let hir::Defaultness::Default { has_value: true } = item.defaultness
888 if self.type_of(item.id.def_id) == found {
891 "associated type defaults can't be assumed inside the \
892 trait defining them",
902 Some(hir::Node::Item(hir::Item {
903 kind: hir::ItemKind::Impl(hir::Impl { items, .. }),
906 for item in &items[..] {
907 if let hir::AssocItemKind::Type = item.kind {
908 if self.type_of(item.id.def_id) == found {
909 db.span_label(item.span, "expected this associated type");
920 /// Given a slice of `hir::GenericBound`s, if any of them corresponds to the `trait_ref`
921 /// requirement, provide a structured suggestion to constrain it to a given type `ty`.
923 /// `is_bound_surely_present` indicates whether we know the bound we're looking for is
924 /// inside `bounds`. If that's the case then we can consider `bounds` containing only one
925 /// trait bound as the one we're looking for. This can help in cases where the associated
926 /// type is defined on a supertrait of the one present in the bounds.
927 fn constrain_generic_bound_associated_type_structured_suggestion(
929 db: &mut DiagnosticBuilder<'_>,
930 trait_ref: &ty::TraitRef<'tcx>,
931 bounds: hir::GenericBounds<'_>,
932 assoc: &ty::AssocItem,
933 assoc_substs: &[ty::GenericArg<'tcx>],
936 is_bound_surely_present: bool,
938 // FIXME: we would want to call `resolve_vars_if_possible` on `ty` before suggesting.
940 let trait_bounds = bounds.iter().filter_map(|bound| match bound {
941 hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::None) => Some(ptr),
945 let matching_trait_bounds = trait_bounds
947 .filter(|ptr| ptr.trait_ref.trait_def_id() == Some(trait_ref.def_id))
948 .collect::<Vec<_>>();
950 let span = match &matching_trait_bounds[..] {
952 &[] if is_bound_surely_present => match &trait_bounds.collect::<Vec<_>>()[..] {
959 self.constrain_associated_type_structured_suggestion(db, span, assoc, assoc_substs, ty, msg)
962 /// Given a span corresponding to a bound, provide a structured suggestion to set an
963 /// associated type to a given type `ty`.
964 fn constrain_associated_type_structured_suggestion(
966 db: &mut DiagnosticBuilder<'_>,
968 assoc: &ty::AssocItem,
969 assoc_substs: &[ty::GenericArg<'tcx>],
973 if let Ok(has_params) =
974 self.sess.source_map().span_to_snippet(span).map(|snippet| snippet.ends_with('>'))
976 let (span, sugg) = if has_params {
977 let pos = span.hi() - BytePos(1);
978 let span = Span::new(pos, pos, span.ctxt(), span.parent());
979 (span, format!(", {} = {}", assoc.ident, ty))
981 let item_args = self.format_generic_args(assoc_substs);
982 (span.shrink_to_hi(), format!("<{}{} = {}>", assoc.ident, item_args, ty))
984 db.span_suggestion_verbose(span, msg, sugg, MaybeIncorrect);
990 fn format_generic_args(self, args: &[ty::GenericArg<'tcx>]) -> String {
991 let mut item_args = String::new();
992 FmtPrinter::new(self, &mut item_args, hir::def::Namespace::TypeNS)
993 .path_generic_args(Ok, args)
994 .expect("could not write to `String`.");