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use super::TypeErrCtxt;
use rustc_errors::Applicability::{MachineApplicable, MaybeIncorrect};
use rustc_errors::{pluralize, Diag, MultiSpan};
use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_middle::traits::ObligationCauseCode;
use rustc_middle::ty::error::ExpectedFound;
use rustc_middle::ty::print::Printer;
use rustc_middle::{
traits::ObligationCause,
ty::{self, error::TypeError, print::FmtPrinter, suggest_constraining_type_param, Ty},
};
use rustc_span::{def_id::DefId, sym, BytePos, Span, Symbol};
impl<'tcx> TypeErrCtxt<'_, 'tcx> {
pub fn note_and_explain_type_err(
&self,
diag: &mut Diag<'_>,
err: TypeError<'tcx>,
cause: &ObligationCause<'tcx>,
sp: Span,
body_owner_def_id: DefId,
) {
use ty::error::TypeError::*;
debug!("note_and_explain_type_err err={:?} cause={:?}", err, cause);
let tcx = self.tcx;
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::Alias(ty::Opaque, ..), ty::Alias(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,
) = tcx.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!("{snippet}.0"),
MachineApplicable,
);
}
}
(ty::Param(expected), ty::Param(found)) => {
let generics = tcx.generics_of(body_owner_def_id);
if let Some(param) = generics.opt_type_param(expected, tcx) {
let e_span = tcx.def_span(param.def_id);
if !sp.contains(e_span) {
diag.span_label(e_span, "expected type parameter");
}
}
if let Some(param) = generics.opt_type_param(found, tcx) {
let f_span = tcx.def_span(param.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::Alias(ty::Projection | ty::Inherent, _),
ty::Alias(ty::Projection | ty::Inherent, _),
) => {
diag.note("an associated type was expected, but a different one was found");
}
// FIXME(inherent_associated_types): Extend this to support `ty::Inherent`, too.
(ty::Param(p), ty::Alias(ty::Projection, proj))
| (ty::Alias(ty::Projection, proj), ty::Param(p))
if !tcx.is_impl_trait_in_trait(proj.def_id) =>
{
let parent = tcx
.generics_of(body_owner_def_id)
.opt_type_param(p, tcx)
.and_then(|param| {
let p_def_id = param.def_id;
let p_span = tcx.def_span(p_def_id);
let expected = match (values.expected.kind(), values.found.kind()) {
(ty::Param(_), _) => "expected ",
(_, ty::Param(_)) => "found ",
_ => "",
};
if !sp.contains(p_span) {
diag.span_label(
p_span,
format!("{expected}this type parameter"),
);
}
p_def_id.as_local().and_then(|id| {
let local_id = tcx.local_def_id_to_hir_id(id);
let generics = tcx.parent_hir_node(local_id).generics()?;
Some((id, generics))
})
});
let mut note = true;
if let Some((local_id, generics)) = parent {
// Synthesize the associated type restriction `Add<Output = Expected>`.
// FIXME: extract this logic for use in other diagnostics.
let (trait_ref, assoc_args) = proj.trait_ref_and_own_args(tcx);
let item_name = tcx.item_name(proj.def_id);
let item_args = self.format_generic_args(assoc_args);
// Here, we try to see if there's an existing
// trait implementation that matches the one that
// we're suggesting to restrict. If so, find the
// "end", whether it be at the end of the trait
// or the end of the generic arguments.
let mut matching_span = None;
let mut matched_end_of_args = false;
for bound in generics.bounds_for_param(local_id) {
let potential_spans = bound.bounds.iter().find_map(|bound| {
let bound_trait_path = bound.trait_ref()?.path;
let def_id = bound_trait_path.res.opt_def_id()?;
let generic_args = bound_trait_path
.segments
.iter()
.last()
.map(|path| path.args());
(def_id == trait_ref.def_id)
.then_some((bound_trait_path.span, generic_args))
});
if let Some((end_of_trait, end_of_args)) = potential_spans {
let args_span = end_of_args.and_then(|args| args.span());
matched_end_of_args = args_span.is_some();
matching_span = args_span
.or_else(|| Some(end_of_trait))
.map(|span| span.shrink_to_hi());
break;
}
}
if matched_end_of_args {
// Append suggestion to the end of our args
let path = format!(", {item_name}{item_args} = {p}");
note = !suggest_constraining_type_param(
tcx,
generics,
diag,
&proj.self_ty().to_string(),
&path,
None,
matching_span,
);
} else {
// Suggest adding a bound to an existing trait
// or if the trait doesn't exist, add the trait
// and the suggested bounds.
let path = format!("<{item_name}{item_args} = {p}>");
note = !suggest_constraining_type_param(
tcx,
generics,
diag,
&proj.self_ty().to_string(),
&path,
None,
matching_span,
);
}
}
if note {
diag.note("you might be missing a type parameter or trait bound");
}
}
(ty::Param(p), ty::Dynamic(..) | ty::Alias(ty::Opaque, ..))
| (ty::Dynamic(..) | ty::Alias(ty::Opaque, ..), ty::Param(p)) => {
let generics = tcx.generics_of(body_owner_def_id);
if let Some(param) = generics.opt_type_param(p, tcx) {
let p_span = tcx.def_span(param.def_id);
let expected = match (values.expected.kind(), values.found.kind()) {
(ty::Param(_), _) => "expected ",
(_, ty::Param(_)) => "found ",
_ => "",
};
if !sp.contains(p_span) {
diag.span_label(p_span, format!("{expected}this type parameter"));
}
}
diag.help("type parameters must be constrained to match other types");
if tcx.sess.teach(diag.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::CoroutineClosure(..) | ty::Coroutine(..),
) => {
let generics = tcx.generics_of(body_owner_def_id);
if let Some(param) = generics.opt_type_param(p, tcx) {
let p_span = tcx.def_span(param.def_id);
if !sp.contains(p_span) {
diag.span_label(p_span, "expected 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 = tcx.generics_of(body_owner_def_id);
if let Some(param) = generics.opt_type_param(p, tcx) {
let p_span = tcx.def_span(param.def_id);
let expected = match (values.expected.kind(), values.found.kind()) {
(ty::Param(_), _) => "expected ",
(_, ty::Param(_)) => "found ",
_ => "",
};
if !sp.contains(p_span) {
diag.span_label(p_span, format!("{expected}this type parameter"));
}
}
}
(ty::Alias(ty::Projection | ty::Inherent, proj_ty), _)
if !tcx.is_impl_trait_in_trait(proj_ty.def_id) =>
{
self.expected_projection(
diag,
proj_ty,
values,
body_owner_def_id,
cause.code(),
);
}
(_, ty::Alias(ty::Projection | ty::Inherent, proj_ty))
if !tcx.is_impl_trait_in_trait(proj_ty.def_id) =>
{
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",
);
}
}
(ty::Dynamic(t, _, ty::DynKind::Dyn), ty::Alias(ty::Opaque, alias))
if let Some(def_id) = t.principal_def_id()
&& tcx
.explicit_item_super_predicates(alias.def_id)
.skip_binder()
.iter()
.any(|(pred, _span)| match pred.kind().skip_binder() {
ty::ClauseKind::Trait(trait_predicate)
if trait_predicate.polarity
== ty::PredicatePolarity::Positive =>
{
trait_predicate.def_id() == def_id
}
_ => false,
}) =>
{
diag.help(format!(
"you can box the `{}` to coerce it to `Box<{}>`, but you'll have to \
change the expected type as well",
values.found, values.expected,
));
}
(ty::Dynamic(t, _, ty::DynKind::Dyn), _)
if let Some(def_id) = t.principal_def_id() =>
{
let mut impl_def_ids = vec![];
tcx.for_each_relevant_impl(def_id, values.found, |did| {
impl_def_ids.push(did)
});
if let [_] = &impl_def_ids[..] {
let trait_name = tcx.item_name(def_id);
diag.help(format!(
"`{}` implements `{trait_name}` so you could box the found value \
and coerce it to the trait object `Box<dyn {trait_name}>`, you \
will have to change the expected type as well",
values.found,
));
}
}
(_, ty::Dynamic(t, _, ty::DynKind::Dyn))
if let Some(def_id) = t.principal_def_id() =>
{
let mut impl_def_ids = vec![];
tcx.for_each_relevant_impl(def_id, values.expected, |did| {
impl_def_ids.push(did)
});
if let [_] = &impl_def_ids[..] {
let trait_name = tcx.item_name(def_id);
diag.help(format!(
"`{}` implements `{trait_name}` so you could change the expected \
type to `Box<dyn {trait_name}>`",
values.expected,
));
}
}
(ty::Dynamic(t, _, ty::DynKind::DynStar), _)
if let Some(def_id) = t.principal_def_id() =>
{
let mut impl_def_ids = vec![];
tcx.for_each_relevant_impl(def_id, values.found, |did| {
impl_def_ids.push(did)
});
if let [_] = &impl_def_ids[..] {
let trait_name = tcx.item_name(def_id);
diag.help(format!(
"`{}` implements `{trait_name}`, `#[feature(dyn_star)]` is likely \
not enabled; that feature it is currently incomplete",
values.found,
));
}
}
(_, ty::Alias(ty::Opaque, opaque_ty))
| (ty::Alias(ty::Opaque, opaque_ty), _) => {
if opaque_ty.def_id.is_local()
&& matches!(
tcx.def_kind(body_owner_def_id),
DefKind::Fn
| DefKind::Static { .. }
| DefKind::Const
| DefKind::AssocFn
| DefKind::AssocConst
)
&& tcx.is_type_alias_impl_trait(opaque_ty.def_id)
&& !tcx
.opaque_types_defined_by(body_owner_def_id.expect_local())
.contains(&opaque_ty.def_id.expect_local())
{
let sp = tcx
.def_ident_span(body_owner_def_id)
.unwrap_or_else(|| tcx.def_span(body_owner_def_id));
diag.span_note(
sp,
"this item must have the opaque type in its signature in order to \
be able to register hidden types",
);
}
// If two if arms can be coerced to a trait object, provide a structured
// suggestion.
let ObligationCauseCode::IfExpression(cause) = cause.code() else {
return;
};
let hir::Node::Block(blk) = self.tcx.hir_node(cause.then_id) else {
return;
};
let Some(then) = blk.expr else {
return;
};
let hir::Node::Block(blk) = self.tcx.hir_node(cause.else_id) else {
return;
};
let Some(else_) = blk.expr else {
return;
};
let expected = match values.found.kind() {
ty::Alias(..) => values.expected,
_ => values.found,
};
let preds = tcx.explicit_item_super_predicates(opaque_ty.def_id);
for (pred, _span) in preds.skip_binder() {
let ty::ClauseKind::Trait(trait_predicate) = pred.kind().skip_binder()
else {
continue;
};
if trait_predicate.polarity != ty::PredicatePolarity::Positive {
continue;
}
let def_id = trait_predicate.def_id();
let mut impl_def_ids = vec![];
tcx.for_each_relevant_impl(def_id, expected, |did| {
impl_def_ids.push(did)
});
if let [_] = &impl_def_ids[..] {
let trait_name = tcx.item_name(def_id);
diag.multipart_suggestion(
format!(
"`{expected}` implements `{trait_name}` so you can box \
both arms and coerce to the trait object \
`Box<dyn {trait_name}>`",
),
vec![
(then.span.shrink_to_lo(), "Box::new(".to_string()),
(
then.span.shrink_to_hi(),
format!(") as Box<dyn {}>", tcx.def_path_str(def_id)),
),
(else_.span.shrink_to_lo(), "Box::new(".to_string()),
(else_.span.shrink_to_hi(), ")".to_string()),
],
MachineApplicable,
);
}
}
}
(ty::FnPtr(sig), ty::FnDef(def_id, _))
| (ty::FnDef(def_id, _), ty::FnPtr(sig)) => {
if tcx.fn_sig(def_id).skip_binder().unsafety() < sig.unsafety() {
diag.note(
"unsafe functions cannot be coerced into safe function pointers",
);
}
}
(ty::Adt(_, _), ty::Adt(def, args))
if let ObligationCauseCode::IfExpression(cause) = cause.code()
&& let hir::Node::Block(blk) = self.tcx.hir_node(cause.then_id)
&& let Some(then) = blk.expr
&& def.is_box()
&& let boxed_ty = args.type_at(0)
&& let ty::Dynamic(t, _, _) = boxed_ty.kind()
&& let Some(def_id) = t.principal_def_id()
&& let mut impl_def_ids = vec![]
&& let _ =
tcx.for_each_relevant_impl(def_id, values.expected, |did| {
impl_def_ids.push(did)
})
&& let [_] = &impl_def_ids[..] =>
{
// We have divergent if/else arms where the expected value is a type that
// implements the trait of the found boxed trait object.
diag.multipart_suggestion(
format!(
"`{}` implements `{}` so you can box it to coerce to the trait \
object `{}`",
values.expected,
tcx.item_name(def_id),
values.found,
),
vec![
(then.span.shrink_to_lo(), "Box::new(".to_string()),
(then.span.shrink_to_hi(), ")".to_string()),
],
MachineApplicable,
);
}
_ => {}
}
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_coroutine() || ty.is_coroutine_closure() {
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 = tcx.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 Diag<'_>,
msg: impl Fn() -> String,
body_owner_def_id: DefId,
proj_ty: ty::AliasTy<'tcx>,
ty: Ty<'tcx>,
) -> bool {
let tcx = self.tcx;
let assoc = tcx.associated_item(proj_ty.def_id);
let (trait_ref, assoc_args) = proj_ty.trait_ref_and_own_args(tcx);
let Some(item) = tcx.hir().get_if_local(body_owner_def_id) else {
return false;
};
let Some(hir_generics) = item.generics() else {
return false;
};
// Get the `DefId` for the type parameter corresponding to `A` in `<A as T>::Foo`.
// This will also work for `impl Trait`.
let ty::Param(param_ty) = *proj_ty.self_ty().kind() else {
return false;
};
let generics = tcx.generics_of(body_owner_def_id);
let Some(param) = generics.opt_type_param(param_ty, tcx) else {
return false;
};
let Some(def_id) = param.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_args,
ty,
&msg,
false,
) {
return true;
}
}
if (param_ty.index as usize) >= generics.parent_count {
// The param comes from the current item, do not look at the parent. (#117209)
return false;
}
// If associated item, look to constrain the params of the trait/impl.
let hir_id = match item {
hir::Node::ImplItem(item) => item.hir_id(),
hir::Node::TraitItem(item) => item.hir_id(),
_ => return false,
};
let parent = tcx.hir().get_parent_item(hir_id).def_id;
self.suggest_constraint(diag, msg, parent.into(), proj_ty, ty)
}
/// 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 Diag<'_>,
proj_ty: ty::AliasTy<'tcx>,
values: ExpectedFound<Ty<'tcx>>,
body_owner_def_id: DefId,
cause_code: &ObligationCauseCode<'_>,
) {
let tcx = self.tcx;
// Don't suggest constraining a projection to something containing itself
if self.tcx.erase_regions(values.found).contains(self.tcx.erase_regions(values.expected)) {
return;
}
let msg = || {
format!(
"consider constraining the associated type `{}` to `{}`",
values.expected, values.found
)
};
let body_owner = tcx.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::CompareImplItemObligation { .. });
let assoc = tcx.associated_item(proj_ty.def_id);
if 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`.
} else {
let point_at_assoc_fn = if callable_scope
&& self.point_at_methods_that_satisfy_associated_type(
diag,
assoc.container_id(tcx),
current_method_ident,
proj_ty.def_id,
values.expected,
) {
// 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".
true
} else {
false
};
// 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 tcx.sess.teach(diag.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 Diag<'_>,
msg: impl Fn() -> String,
proj_ty: ty::AliasTy<'tcx>,
ty: Ty<'tcx>,
) -> bool {
let tcx = self.tcx;
let assoc = tcx.associated_item(proj_ty.def_id);
if let ty::Alias(ty::Opaque, ty::AliasTy { 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 {
tcx.hir().expect_item(opaque_local_def_id).expect_opaque_ty()
} else {
return false;
};
let (trait_ref, assoc_args) = proj_ty.trait_ref_and_own_args(tcx);
self.constrain_generic_bound_associated_type_structured_suggestion(
diag,
&trait_ref,
opaque_hir_ty.bounds,
assoc,
assoc_args,
ty,
msg,
true,
)
} else {
false
}
}
fn point_at_methods_that_satisfy_associated_type(
&self,
diag: &mut Diag<'_>,
assoc_container_id: DefId,
current_method_ident: Option<Symbol>,
proj_ty_item_def_id: DefId,
expected: Ty<'tcx>,
) -> bool {
let tcx = self.tcx;
let items = tcx.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
.in_definition_order()
.filter(|item| {
ty::AssocKind::Fn == item.kind
&& Some(item.name) != current_method_ident
&& !tcx.is_doc_hidden(item.def_id)
})
.filter_map(|item| {
let method = tcx.fn_sig(item.def_id).instantiate_identity();
match *method.output().skip_binder().kind() {
ty::Alias(ty::Projection, ty::AliasTy { def_id: item_def_id, .. })
if item_def_id == proj_ty_item_def_id =>
{
Some((
tcx.def_span(item.def_id),
format!("consider calling `{}`", tcx.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 Diag<'_>,
body_owner_def_id: DefId,
found: Ty<'tcx>,
) -> bool {
let tcx = self.tcx;
let Some(def_id) = body_owner_def_id.as_local() else {
return false;
};
// When `body_owner` is an `impl` or `trait` item, look in its associated types for
// `expected` and point at it.
let hir_id = tcx.local_def_id_to_hir_id(def_id);
let parent_id = tcx.hir().get_parent_item(hir_id);
let item = tcx.hir_node_by_def_id(parent_id.def_id);
debug!("expected_projection parent item {:?}", item);
let param_env = tcx.param_env(body_owner_def_id);
match item {
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 } =
tcx.defaultness(item.id.owner_id)
{
let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
if self.infcx.can_eq(param_env, assoc_ty, found) {
diag.span_label(
item.span,
"associated type defaults can't be assumed inside the \
trait defining them",
);
return true;
}
}
}
_ => {}
}
}
}
hir::Node::Item(hir::Item {
kind: hir::ItemKind::Impl(hir::Impl { items, .. }),
..
}) => {
for item in &items[..] {
if let hir::AssocItemKind::Type = item.kind {
let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
if let hir::Defaultness::Default { has_value: true } =
tcx.defaultness(item.id.owner_id)
&& self.infcx.can_eq(param_env, assoc_ty, found)
{
diag.span_label(
item.span,
"associated type is `default` and may be overridden",
);
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 Diag<'_>,
trait_ref: &ty::TraitRef<'tcx>,
bounds: hir::GenericBounds<'_>,
assoc: ty::AssocItem,
assoc_args: &[ty::GenericArg<'tcx>],
ty: Ty<'tcx>,
msg: impl Fn() -> String,
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_args, 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 Diag<'_>,
span: Span,
assoc: ty::AssocItem,
assoc_args: &[ty::GenericArg<'tcx>],
ty: Ty<'tcx>,
msg: impl Fn() -> String,
) -> bool {
let tcx = self.tcx;
if let Ok(has_params) =
tcx.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(tcx), ty))
} else {
let item_args = self.format_generic_args(assoc_args);
(span.shrink_to_hi(), format!("<{}{} = {}>", assoc.ident(tcx), item_args, ty))
};
diag.span_suggestion_verbose(span, msg(), sugg, MaybeIncorrect);
return true;
}
false
}
pub fn format_generic_args(&self, args: &[ty::GenericArg<'tcx>]) -> String {
FmtPrinter::print_string(self.tcx, hir::def::Namespace::TypeNS, |cx| {
cx.path_generic_args(|_| Ok(()), args)
})
.expect("could not write to `String`.")
}
}