use crate::traits::{ObligationCause, ObligationCauseCode};
use crate::ty::diagnostics::suggest_constraining_type_param;
use crate::ty::print::{FmtPrinter, Printer};
use crate::ty::{self, BoundRegionKind, Region, Ty, TyCtxt};
use rustc_errors::Applicability::{MachineApplicable, MaybeIncorrect};
use rustc_errors::{pluralize, Diagnostic, MultiSpan};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_span::symbol::{sym, Symbol};
use rustc_span::{BytePos, Span};
use rustc_target::spec::abi;
use std::borrow::Cow;
use std::fmt;
#[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable)]
pub struct ExpectedFound<T> {
pub expected: T,
pub found: T,
}
impl<T> ExpectedFound<T> {
pub fn new(a_is_expected: bool, a: T, b: T) -> Self {
if a_is_expected {
ExpectedFound { expected: a, found: b }
} else {
ExpectedFound { expected: b, found: a }
}
}
}
// Data structures used in type unification
#[derive(Clone, Debug, TypeFoldable)]
pub enum TypeError<'tcx> {
Mismatch,
ConstnessMismatch(ExpectedFound<ty::BoundConstness>),
PolarityMismatch(ExpectedFound<ty::ImplPolarity>),
UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
AbiMismatch(ExpectedFound<abi::Abi>),
Mutability,
ArgumentMutability(usize),
TupleSize(ExpectedFound<usize>),
FixedArraySize(ExpectedFound<u64>),
ArgCount,
FieldMisMatch(Symbol, Symbol),
RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>),
RegionsInsufficientlyPolymorphic(BoundRegionKind, Region<'tcx>),
RegionsOverlyPolymorphic(BoundRegionKind, Region<'tcx>),
RegionsPlaceholderMismatch,
Sorts(ExpectedFound<Ty<'tcx>>),
ArgumentSorts(ExpectedFound<Ty<'tcx>>, usize),
IntMismatch(ExpectedFound<ty::IntVarValue>),
FloatMismatch(ExpectedFound<ty::FloatTy>),
Traits(ExpectedFound<DefId>),
VariadicMismatch(ExpectedFound<bool>),
/// Instantiating a type variable with the given type would have
/// created a cycle (because it appears somewhere within that
/// type).
CyclicTy(Ty<'tcx>),
CyclicConst(ty::Const<'tcx>),
ProjectionMismatched(ExpectedFound<DefId>),
ExistentialMismatch(
ExpectedFound<&'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>>,
),
ObjectUnsafeCoercion(DefId),
ConstMismatch(ExpectedFound<ty::Const<'tcx>>),
IntrinsicCast,
/// Safe `#[target_feature]` functions are not assignable to safe function pointers.
TargetFeatureCast(DefId),
}
/// Explains the source of a type err in a short, human readable way. This is meant to be placed
/// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()`
/// afterwards to present additional details, particularly when it comes to lifetime-related
/// errors.
impl<'tcx> fmt::Display for TypeError<'tcx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
use self::TypeError::*;
fn report_maybe_different(
f: &mut fmt::Formatter<'_>,
expected: &str,
found: &str,
) -> fmt::Result {
// A naive approach to making sure that we're not reporting silly errors such as:
// (expected closure, found closure).
if expected == found {
write!(f, "expected {}, found a different {}", expected, found)
} else {
write!(f, "expected {}, found {}", expected, found)
}
}
let br_string = |br: ty::BoundRegionKind| match br {
ty::BrNamed(_, name) => format!(" {}", name),
_ => String::new(),
};
match *self {
CyclicTy(_) => write!(f, "cyclic type of infinite size"),
CyclicConst(_) => write!(f, "encountered a self-referencing constant"),
Mismatch => write!(f, "types differ"),
ConstnessMismatch(values) => {
write!(f, "expected {} bound, found {} bound", values.expected, values.found)
}
PolarityMismatch(values) => {
write!(f, "expected {} polarity, found {} polarity", values.expected, values.found)
}
UnsafetyMismatch(values) => {
write!(f, "expected {} fn, found {} fn", values.expected, values.found)
}
AbiMismatch(values) => {
write!(f, "expected {} fn, found {} fn", values.expected, values.found)
}
ArgumentMutability(_) | Mutability => write!(f, "types differ in mutability"),
TupleSize(values) => write!(
f,
"expected a tuple with {} element{}, found one with {} element{}",
values.expected,
pluralize!(values.expected),
values.found,
pluralize!(values.found)
),
FixedArraySize(values) => write!(
f,
"expected an array with a fixed size of {} element{}, found one with {} element{}",
values.expected,
pluralize!(values.expected),
values.found,
pluralize!(values.found)
),
ArgCount => write!(f, "incorrect number of function parameters"),
FieldMisMatch(adt, field) => write!(f, "field type mismatch: {}.{}", adt, field),
RegionsDoesNotOutlive(..) => write!(f, "lifetime mismatch"),
// Actually naming the region here is a bit confusing because context is lacking
RegionsInsufficientlyPolymorphic(..) => {
write!(f, "one type is more general than the other")
}
RegionsOverlyPolymorphic(br, _) => write!(
f,
"expected concrete lifetime, found bound lifetime parameter{}",
br_string(br)
),
RegionsPlaceholderMismatch => write!(f, "one type is more general than the other"),
ArgumentSorts(values, _) | Sorts(values) => ty::tls::with(|tcx| {
report_maybe_different(
f,
&values.expected.sort_string(tcx),
&values.found.sort_string(tcx),
)
}),
Traits(values) => ty::tls::with(|tcx| {
report_maybe_different(
f,
&format!("trait `{}`", tcx.def_path_str(values.expected)),
&format!("trait `{}`", tcx.def_path_str(values.found)),
)
}),
IntMismatch(ref values) => {
let expected = match values.expected {
ty::IntVarValue::IntType(ty) => ty.name_str(),
ty::IntVarValue::UintType(ty) => ty.name_str(),
};
let found = match values.found {
ty::IntVarValue::IntType(ty) => ty.name_str(),
ty::IntVarValue::UintType(ty) => ty.name_str(),
};
write!(f, "expected `{}`, found `{}`", expected, found)
}
FloatMismatch(ref values) => {
write!(
f,
"expected `{}`, found `{}`",
values.expected.name_str(),
values.found.name_str()
)
}
VariadicMismatch(ref values) => write!(
f,
"expected {} fn, found {} function",
if values.expected { "variadic" } else { "non-variadic" },
if values.found { "variadic" } else { "non-variadic" }
),
ProjectionMismatched(ref values) => ty::tls::with(|tcx| {
write!(
f,
"expected {}, found {}",
tcx.def_path_str(values.expected),
tcx.def_path_str(values.found)
)
}),
ExistentialMismatch(ref values) => report_maybe_different(
f,
&format!("trait `{}`", values.expected),
&format!("trait `{}`", values.found),
),
ConstMismatch(ref values) => {
write!(f, "expected `{}`, found `{}`", values.expected, values.found)
}
IntrinsicCast => write!(f, "cannot coerce intrinsics to function pointers"),
TargetFeatureCast(_) => write!(
f,
"cannot coerce functions with `#[target_feature]` to safe function pointers"
),
ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"),
}
}
}
impl<'tcx> TypeError<'tcx> {
pub fn must_include_note(&self) -> bool {
use self::TypeError::*;
match self {
CyclicTy(_) | CyclicConst(_) | UnsafetyMismatch(_) | ConstnessMismatch(_)
| PolarityMismatch(_) | Mismatch | AbiMismatch(_) | FixedArraySize(_)
| ArgumentSorts(..) | Sorts(_) | IntMismatch(_) | FloatMismatch(_)
| VariadicMismatch(_) | TargetFeatureCast(_) => false,
Mutability
| ArgumentMutability(_)
| TupleSize(_)
| ArgCount
| FieldMisMatch(..)
| RegionsDoesNotOutlive(..)
| RegionsInsufficientlyPolymorphic(..)
| RegionsOverlyPolymorphic(..)
| RegionsPlaceholderMismatch
| Traits(_)
| ProjectionMismatched(_)
| ExistentialMismatch(_)
| ConstMismatch(_)
| IntrinsicCast
| ObjectUnsafeCoercion(_) => true,
}
}
}
impl<'tcx> Ty<'tcx> {
pub fn sort_string(self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
match *self.kind() {
ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
format!("`{}`", self).into()
}
ty::Tuple(ref tys) if tys.is_empty() => format!("`{}`", self).into(),
ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did())).into(),
ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
ty::Array(t, n) => {
if t.is_simple_ty() {
return format!("array `{}`", self).into();
}
let n = tcx.lift(n).unwrap();
if let ty::ConstKind::Value(v) = n.val() {
if let Some(n) = v.try_to_machine_usize(tcx) {
return format!("array of {} element{}", n, pluralize!(n)).into();
}
}
"array".into()
}
ty::Slice(ty) if ty.is_simple_ty() => format!("slice `{}`", self).into(),
ty::Slice(_) => "slice".into(),
ty::RawPtr(_) => "*-ptr".into(),
ty::Ref(_, ty, mutbl) => {
let tymut = ty::TypeAndMut { ty, mutbl };
let tymut_string = tymut.to_string();
if tymut_string != "_"
&& (ty.is_simple_text() || tymut_string.len() < "mutable reference".len())
{
format!("`&{}`", tymut_string).into()
} else {
// Unknown type name, it's long or has type arguments
match mutbl {
hir::Mutability::Mut => "mutable reference",
_ => "reference",
}
.into()
}
}
ty::FnDef(..) => "fn item".into(),
ty::FnPtr(_) => "fn pointer".into(),
ty::Dynamic(ref inner, ..) if let Some(principal) = inner.principal() => {
format!("trait object `dyn {}`", tcx.def_path_str(principal.def_id())).into()
}
ty::Dynamic(..) => "trait object".into(),
ty::Closure(..) => "closure".into(),
ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(),
ty::GeneratorWitness(..) => "generator witness".into(),
ty::Tuple(..) => "tuple".into(),
ty::Infer(ty::TyVar(_)) => "inferred type".into(),
ty::Infer(ty::IntVar(_)) => "integer".into(),
ty::Infer(ty::FloatVar(_)) => "floating-point number".into(),
ty::Placeholder(..) => "placeholder type".into(),
ty::Bound(..) => "bound type".into(),
ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
ty::Projection(_) => "associated type".into(),
ty::Param(p) => format!("type parameter `{}`", p).into(),
ty::Opaque(..) => "opaque type".into(),
ty::Error(_) => "type error".into(),
}
}
pub fn prefix_string(self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
match *self.kind() {
ty::Infer(_)
| ty::Error(_)
| ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Str
| ty::Never => "type".into(),
ty::Tuple(ref tys) if tys.is_empty() => "unit type".into(),
ty::Adt(def, _) => def.descr().into(),
ty::Foreign(_) => "extern type".into(),
ty::Array(..) => "array".into(),
ty::Slice(_) => "slice".into(),
ty::RawPtr(_) => "raw pointer".into(),
ty::Ref(.., mutbl) => match mutbl {
hir::Mutability::Mut => "mutable reference",
_ => "reference",
}
.into(),
ty::FnDef(..) => "fn item".into(),
ty::FnPtr(_) => "fn pointer".into(),
ty::Dynamic(..) => "trait object".into(),
ty::Closure(..) => "closure".into(),
ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(),
ty::GeneratorWitness(..) => "generator witness".into(),
ty::Tuple(..) => "tuple".into(),
ty::Placeholder(..) => "higher-ranked type".into(),
ty::Bound(..) => "bound type variable".into(),
ty::Projection(_) => "associated type".into(),
ty::Param(_) => "type parameter".into(),
ty::Opaque(..) => "opaque type".into(),
}
}
}
impl<'tcx> TyCtxt<'tcx> {
pub fn note_and_explain_type_err(
self,
diag: &mut Diagnostic,
err: &TypeError<'tcx>,
cause: &ObligationCause<'tcx>,
sp: Span,
body_owner_def_id: DefId,
) {
use self::TypeError::*;
debug!("note_and_explain_type_err err={:?} cause={:?}", err, cause);
match err {
ArgumentSorts(values, _) | Sorts(values) => {
match (values.expected.kind(), values.found.kind()) {
(ty::Closure(..), ty::Closure(..)) => {
diag.note("no two closures, even if identical, have the same type");
diag.help("consider boxing your closure and/or using it as a trait object");
}
(ty::Opaque(..), ty::Opaque(..)) => {
// Issue #63167
diag.note("distinct uses of `impl Trait` result in different opaque types");
}
(ty::Float(_), ty::Infer(ty::IntVar(_)))
if let Ok(
// Issue #53280
snippet,
) = self.sess.source_map().span_to_snippet(sp) =>
{
if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
diag.span_suggestion(
sp,
"use a float literal",
format!("{}.0", snippet),
MachineApplicable,
);
}
}
(ty::Param(expected), ty::Param(found)) => {
let generics = self.generics_of(body_owner_def_id);
let e_span = self.def_span(generics.type_param(expected, self).def_id);
if !sp.contains(e_span) {
diag.span_label(e_span, "expected type parameter");
}
let f_span = self.def_span(generics.type_param(found, self).def_id);
if !sp.contains(f_span) {
diag.span_label(f_span, "found type parameter");
}
diag.note(
"a type parameter was expected, but a different one was found; \
you might be missing a type parameter or trait bound",
);
diag.note(
"for more information, visit \
https://doc.rust-lang.org/book/ch10-02-traits.html\
#traits-as-parameters",
);
}
(ty::Projection(_), ty::Projection(_)) => {
diag.note("an associated type was expected, but a different one was found");
}
(ty::Param(p), ty::Projection(proj)) | (ty::Projection(proj), ty::Param(p)) => {
let generics = self.generics_of(body_owner_def_id);
let p_span = self.def_span(generics.type_param(p, self).def_id);
if !sp.contains(p_span) {
diag.span_label(p_span, "this type parameter");
}
let hir = self.hir();
let mut note = true;
if let Some(generics) = generics
.type_param(p, self)
.def_id
.as_local()
.map(|id| hir.local_def_id_to_hir_id(id))
.and_then(|id| self.hir().find(self.hir().get_parent_node(id)))
.as_ref()
.and_then(|node| node.generics())
{
// Synthesize the associated type restriction `Add<Output = Expected>`.
// FIXME: extract this logic for use in other diagnostics.
let (trait_ref, assoc_substs) = proj.trait_ref_and_own_substs(self);
let path =
self.def_path_str_with_substs(trait_ref.def_id, trait_ref.substs);
let item_name = self.item_name(proj.item_def_id);
let item_args = self.format_generic_args(assoc_substs);
let path = if path.ends_with('>') {
format!(
"{}, {}{} = {}>",
&path[..path.len() - 1],
item_name,
item_args,
p
)
} else {
format!("{}<{}{} = {}>", path, item_name, item_args, p)
};
note = !suggest_constraining_type_param(
self,
generics,
diag,
&format!("{}", proj.self_ty()),
&path,
None,
);
}
if note {
diag.note("you might be missing a type parameter or trait bound");
}
}
(ty::Param(p), ty::Dynamic(..) | ty::Opaque(..))
| (ty::Dynamic(..) | ty::Opaque(..), ty::Param(p)) => {
let generics = self.generics_of(body_owner_def_id);
let p_span = self.def_span(generics.type_param(p, self).def_id);
if !sp.contains(p_span) {
diag.span_label(p_span, "this type parameter");
}
diag.help("type parameters must be constrained to match other types");
if self.sess.teach(&diag.get_code().unwrap()) {
diag.help(
"given a type parameter `T` and a method `foo`:
```
trait Trait<T> { fn foo(&self) -> T; }
```
the only ways to implement method `foo` are:
- constrain `T` with an explicit type:
```
impl Trait<String> for X {
fn foo(&self) -> String { String::new() }
}
```
- add a trait bound to `T` and call a method on that trait that returns `Self`:
```
impl<T: std::default::Default> Trait<T> for X {
fn foo(&self) -> T { <T as std::default::Default>::default() }
}
```
- change `foo` to return an argument of type `T`:
```
impl<T> Trait<T> for X {
fn foo(&self, x: T) -> T { x }
}
```",
);
}
diag.note(
"for more information, visit \
https://doc.rust-lang.org/book/ch10-02-traits.html\
#traits-as-parameters",
);
}
(ty::Param(p), ty::Closure(..) | ty::Generator(..)) => {
let generics = self.generics_of(body_owner_def_id);
let p_span = self.def_span(generics.type_param(p, self).def_id);
if !sp.contains(p_span) {
diag.span_label(p_span, "this type parameter");
}
diag.help(&format!(
"every closure has a distinct type and so could not always match the \
caller-chosen type of parameter `{}`",
p
));
}
(ty::Param(p), _) | (_, ty::Param(p)) => {
let generics = self.generics_of(body_owner_def_id);
let p_span = self.def_span(generics.type_param(p, self).def_id);
if !sp.contains(p_span) {
diag.span_label(p_span, "this type parameter");
}
}
(ty::Projection(proj_ty), _) => {
self.expected_projection(
diag,
proj_ty,
values,
body_owner_def_id,
cause.code(),
);
}
(_, ty::Projection(proj_ty)) => {
let msg = format!(
"consider constraining the associated type `{}` to `{}`",
values.found, values.expected,
);
if !(self.suggest_constraining_opaque_associated_type(
diag,
&msg,
proj_ty,
values.expected,
) || self.suggest_constraint(
diag,
&msg,
body_owner_def_id,
proj_ty,
values.expected,
)) {
diag.help(&msg);
diag.note(
"for more information, visit \
https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
);
}
}
_ => {}
}
debug!(
"note_and_explain_type_err expected={:?} ({:?}) found={:?} ({:?})",
values.expected,
values.expected.kind(),
values.found,
values.found.kind(),
);
}
CyclicTy(ty) => {
// Watch out for various cases of cyclic types and try to explain.
if ty.is_closure() || ty.is_generator() {
diag.note(
"closures cannot capture themselves or take themselves as argument;\n\
this error may be the result of a recent compiler bug-fix,\n\
see issue #46062 <https://github.com/rust-lang/rust/issues/46062>\n\
for more information",
);
}
}
TargetFeatureCast(def_id) => {
let target_spans =
self.get_attrs(*def_id, sym::target_feature).map(|attr| attr.span);
diag.note(
"functions with `#[target_feature]` can only be coerced to `unsafe` function pointers"
);
diag.span_labels(target_spans, "`#[target_feature]` added here");
}
_ => {}
}
}
fn suggest_constraint(
self,
diag: &mut Diagnostic,
msg: &str,
body_owner_def_id: DefId,
proj_ty: &ty::ProjectionTy<'tcx>,
ty: Ty<'tcx>,
) -> bool {
let assoc = self.associated_item(proj_ty.item_def_id);
let (trait_ref, assoc_substs) = proj_ty.trait_ref_and_own_substs(self);
if let Some(item) = self.hir().get_if_local(body_owner_def_id) {
if let Some(hir_generics) = item.generics() {
// Get the `DefId` for the type parameter corresponding to `A` in `<A as T>::Foo`.
// This will also work for `impl Trait`.
let def_id = if let ty::Param(param_ty) = proj_ty.self_ty().kind() {
let generics = self.generics_of(body_owner_def_id);
generics.type_param(param_ty, self).def_id
} else {
return false;
};
let Some(def_id) = def_id.as_local() else {
return false;
};
// First look in the `where` clause, as this might be
// `fn foo<T>(x: T) where T: Trait`.
for pred in hir_generics.bounds_for_param(def_id) {
if self.constrain_generic_bound_associated_type_structured_suggestion(
diag,
&trait_ref,
pred.bounds,
&assoc,
assoc_substs,
ty,
msg,
false,
) {
return true;
}
}
}
}
false
}
/// An associated type was expected and a different type was found.
///
/// We perform a few different checks to see what we can suggest:
///
/// - In the current item, look for associated functions that return the expected type and
/// suggest calling them. (Not a structured suggestion.)
/// - If any of the item's generic bounds can be constrained, we suggest constraining the
/// associated type to the found type.
/// - If the associated type has a default type and was expected inside of a `trait`, we
/// mention that this is disallowed.
/// - If all other things fail, and the error is not because of a mismatch between the `trait`
/// and the `impl`, we provide a generic `help` to constrain the assoc type or call an assoc
/// fn that returns the type.
fn expected_projection(
self,
diag: &mut Diagnostic,
proj_ty: &ty::ProjectionTy<'tcx>,
values: &ExpectedFound<Ty<'tcx>>,
body_owner_def_id: DefId,
cause_code: &ObligationCauseCode<'_>,
) {
let msg = format!(
"consider constraining the associated type `{}` to `{}`",
values.expected, values.found
);
let body_owner = self.hir().get_if_local(body_owner_def_id);
let current_method_ident = body_owner.and_then(|n| n.ident()).map(|i| i.name);
// We don't want to suggest calling an assoc fn in a scope where that isn't feasible.
let callable_scope = matches!(
body_owner,
Some(
hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(..), .. })
| hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. })
| hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }),
)
);
let impl_comparison = matches!(
cause_code,
ObligationCauseCode::CompareImplMethodObligation { .. }
| ObligationCauseCode::CompareImplTypeObligation { .. }
| ObligationCauseCode::CompareImplConstObligation
);
let assoc = self.associated_item(proj_ty.item_def_id);
if !callable_scope || impl_comparison {
// We do not want to suggest calling functions when the reason of the
// type error is a comparison of an `impl` with its `trait` or when the
// scope is outside of a `Body`.
} else {
// If we find a suitable associated function that returns the expected type, we don't
// want the more general suggestion later in this method about "consider constraining
// the associated type or calling a method that returns the associated type".
let point_at_assoc_fn = self.point_at_methods_that_satisfy_associated_type(
diag,
assoc.container.id(),
current_method_ident,
proj_ty.item_def_id,
values.expected,
);
// Possibly suggest constraining the associated type to conform to the
// found type.
if self.suggest_constraint(diag, &msg, body_owner_def_id, proj_ty, values.found)
|| point_at_assoc_fn
{
return;
}
}
self.suggest_constraining_opaque_associated_type(diag, &msg, proj_ty, values.found);
if self.point_at_associated_type(diag, body_owner_def_id, values.found) {
return;
}
if !impl_comparison {
// Generic suggestion when we can't be more specific.
if callable_scope {
diag.help(&format!(
"{} or calling a method that returns `{}`",
msg, values.expected
));
} else {
diag.help(&msg);
}
diag.note(
"for more information, visit \
https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
);
}
if self.sess.teach(&diag.get_code().unwrap()) {
diag.help(
"given an associated type `T` and a method `foo`:
```
trait Trait {
type T;
fn foo(&self) -> Self::T;
}
```
the only way of implementing method `foo` is to constrain `T` with an explicit associated type:
```
impl Trait for X {
type T = String;
fn foo(&self) -> Self::T { String::new() }
}
```",
);
}
}
/// When the expected `impl Trait` is not defined in the current item, it will come from
/// a return type. This can occur when dealing with `TryStream` (#71035).
fn suggest_constraining_opaque_associated_type(
self,
diag: &mut Diagnostic,
msg: &str,
proj_ty: &ty::ProjectionTy<'tcx>,
ty: Ty<'tcx>,
) -> bool {
let assoc = self.associated_item(proj_ty.item_def_id);
if let ty::Opaque(def_id, _) = *proj_ty.self_ty().kind() {
let opaque_local_def_id = def_id.as_local();
let opaque_hir_ty = if let Some(opaque_local_def_id) = opaque_local_def_id {
match &self.hir().expect_item(opaque_local_def_id).kind {
hir::ItemKind::OpaqueTy(opaque_hir_ty) => opaque_hir_ty,
_ => bug!("The HirId comes from a `ty::Opaque`"),
}
} else {
return false;
};
let (trait_ref, assoc_substs) = proj_ty.trait_ref_and_own_substs(self);
self.constrain_generic_bound_associated_type_structured_suggestion(
diag,
&trait_ref,
opaque_hir_ty.bounds,
assoc,
assoc_substs,
ty,
msg,
true,
)
} else {
false
}
}
fn point_at_methods_that_satisfy_associated_type(
self,
diag: &mut Diagnostic,
assoc_container_id: DefId,
current_method_ident: Option<Symbol>,
proj_ty_item_def_id: DefId,
expected: Ty<'tcx>,
) -> bool {
let items = self.associated_items(assoc_container_id);
// Find all the methods in the trait that could be called to construct the
// expected associated type.
// FIXME: consider suggesting the use of associated `const`s.
let methods: Vec<(Span, String)> = items
.items
.iter()
.filter(|(name, item)| {
ty::AssocKind::Fn == item.kind && Some(**name) != current_method_ident
})
.filter_map(|(_, item)| {
let method = self.fn_sig(item.def_id);
match *method.output().skip_binder().kind() {
ty::Projection(ty::ProjectionTy { item_def_id, .. })
if item_def_id == proj_ty_item_def_id =>
{
Some((
self.sess.source_map().guess_head_span(self.def_span(item.def_id)),
format!("consider calling `{}`", self.def_path_str(item.def_id)),
))
}
_ => None,
}
})
.collect();
if !methods.is_empty() {
// Use a single `help:` to show all the methods in the trait that can
// be used to construct the expected associated type.
let mut span: MultiSpan =
methods.iter().map(|(sp, _)| *sp).collect::<Vec<Span>>().into();
let msg = format!(
"{some} method{s} {are} available that return{r} `{ty}`",
some = if methods.len() == 1 { "a" } else { "some" },
s = pluralize!(methods.len()),
are = pluralize!("is", methods.len()),
r = if methods.len() == 1 { "s" } else { "" },
ty = expected
);
for (sp, label) in methods.into_iter() {
span.push_span_label(sp, label);
}
diag.span_help(span, &msg);
return true;
}
false
}
fn point_at_associated_type(
self,
diag: &mut Diagnostic,
body_owner_def_id: DefId,
found: Ty<'tcx>,
) -> bool {
let Some(hir_id) = body_owner_def_id.as_local() else {
return false;
};
let hir_id = self.hir().local_def_id_to_hir_id(hir_id);
// When `body_owner` is an `impl` or `trait` item, look in its associated types for
// `expected` and point at it.
let parent_id = self.hir().get_parent_item(hir_id);
let item = self.hir().find_by_def_id(parent_id);
debug!("expected_projection parent item {:?}", item);
match item {
Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Trait(.., items), .. })) => {
// FIXME: account for `#![feature(specialization)]`
for item in &items[..] {
match item.kind {
hir::AssocItemKind::Type => {
// FIXME: account for returning some type in a trait fn impl that has
// an assoc type as a return type (#72076).
if let hir::Defaultness::Default { has_value: true } = item.defaultness
{
if self.type_of(item.id.def_id) == found {
diag.span_label(
item.span,
"associated type defaults can't be assumed inside the \
trait defining them",
);
return true;
}
}
}
_ => {}
}
}
}
Some(hir::Node::Item(hir::Item {
kind: hir::ItemKind::Impl(hir::Impl { items, .. }),
..
})) => {
for item in &items[..] {
if let hir::AssocItemKind::Type = item.kind {
if self.type_of(item.id.def_id) == found {
diag.span_label(item.span, "expected this associated type");
return true;
}
}
}
}
_ => {}
}
false
}
/// Given a slice of `hir::GenericBound`s, if any of them corresponds to the `trait_ref`
/// requirement, provide a structured suggestion to constrain it to a given type `ty`.
///
/// `is_bound_surely_present` indicates whether we know the bound we're looking for is
/// inside `bounds`. If that's the case then we can consider `bounds` containing only one
/// trait bound as the one we're looking for. This can help in cases where the associated
/// type is defined on a supertrait of the one present in the bounds.
fn constrain_generic_bound_associated_type_structured_suggestion(
self,
diag: &mut Diagnostic,
trait_ref: &ty::TraitRef<'tcx>,
bounds: hir::GenericBounds<'_>,
assoc: &ty::AssocItem,
assoc_substs: &[ty::GenericArg<'tcx>],
ty: Ty<'tcx>,
msg: &str,
is_bound_surely_present: bool,
) -> bool {
// FIXME: we would want to call `resolve_vars_if_possible` on `ty` before suggesting.
let trait_bounds = bounds.iter().filter_map(|bound| match bound {
hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::None) => Some(ptr),
_ => None,
});
let matching_trait_bounds = trait_bounds
.clone()
.filter(|ptr| ptr.trait_ref.trait_def_id() == Some(trait_ref.def_id))
.collect::<Vec<_>>();
let span = match &matching_trait_bounds[..] {
&[ptr] => ptr.span,
&[] if is_bound_surely_present => match &trait_bounds.collect::<Vec<_>>()[..] {
&[ptr] => ptr.span,
_ => return false,
},
_ => return false,
};
self.constrain_associated_type_structured_suggestion(
diag,
span,
assoc,
assoc_substs,
ty,
msg,
)
}
/// Given a span corresponding to a bound, provide a structured suggestion to set an
/// associated type to a given type `ty`.
fn constrain_associated_type_structured_suggestion(
self,
diag: &mut Diagnostic,
span: Span,
assoc: &ty::AssocItem,
assoc_substs: &[ty::GenericArg<'tcx>],
ty: Ty<'tcx>,
msg: &str,
) -> bool {
if let Ok(has_params) =
self.sess.source_map().span_to_snippet(span).map(|snippet| snippet.ends_with('>'))
{
let (span, sugg) = if has_params {
let pos = span.hi() - BytePos(1);
let span = Span::new(pos, pos, span.ctxt(), span.parent());
(span, format!(", {} = {}", assoc.ident(self), ty))
} else {
let item_args = self.format_generic_args(assoc_substs);
(span.shrink_to_hi(), format!("<{}{} = {}>", assoc.ident(self), item_args, ty))
};
diag.span_suggestion_verbose(span, msg, sugg, MaybeIncorrect);
return true;
}
false
}
fn format_generic_args(self, args: &[ty::GenericArg<'tcx>]) -> String {
FmtPrinter::new(self, hir::def::Namespace::TypeNS)
.path_generic_args(Ok, args)
.expect("could not write to `String`.")
.into_buffer()
}
}