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Const generic parameters aren't bounds, even if we end up erroring be…
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…cause of the bound that binds the parameter's type
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@oli-obk
oli-obk committed Jun 19, 2024
1 parent 1cb75dc commit e4c9a8c
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Showing 19 changed files with 146 additions and 128 deletions.
188 changes: 103 additions & 85 deletions compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2776,97 +2776,115 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
let mut this = "this bound";
let mut note = None;
let mut help = None;
if let ty::PredicateKind::Clause(clause) = predicate.kind().skip_binder()
&& let ty::ClauseKind::Trait(trait_pred) = clause
{
let def_id = trait_pred.def_id();
let visible_item = if let Some(local) = def_id.as_local() {
// Check for local traits being reachable.
let vis = &tcx.resolutions(()).effective_visibilities;
// Account for non-`pub` traits in the root of the local crate.
let is_locally_reachable = tcx.parent(def_id).is_crate_root();
vis.is_reachable(local) || is_locally_reachable
} else {
// Check for foreign traits being reachable.
tcx.visible_parent_map(()).get(&def_id).is_some()
};
if tcx.is_lang_item(def_id, LangItem::Sized) {
// Check if this is an implicit bound, even in foreign crates.
if tcx
.generics_of(item_def_id)
.own_params
.iter()
.any(|param| tcx.def_span(param.def_id) == span)
{
a = "an implicit `Sized`";
this = "the implicit `Sized` requirement on this type parameter";
}
if let Some(hir::Node::TraitItem(hir::TraitItem {
generics,
kind: hir::TraitItemKind::Type(bounds, None),
..
})) = tcx.hir().get_if_local(item_def_id)
// Do not suggest relaxing if there is an explicit `Sized` obligation.
&& !bounds.iter()
.filter_map(|bound| bound.trait_ref())
.any(|tr| tr.trait_def_id() == tcx.lang_items().sized_trait())
{
let (span, separator) = if let [.., last] = bounds {
(last.span().shrink_to_hi(), " +")
if let ty::PredicateKind::Clause(clause) = predicate.kind().skip_binder() {
match clause {
ty::ClauseKind::Trait(trait_pred) => {
let def_id = trait_pred.def_id();
let visible_item = if let Some(local) = def_id.as_local() {
// Check for local traits being reachable.
let vis = &tcx.resolutions(()).effective_visibilities;
// Account for non-`pub` traits in the root of the local crate.
let is_locally_reachable = tcx.parent(def_id).is_crate_root();
vis.is_reachable(local) || is_locally_reachable
} else {
(generics.span.shrink_to_hi(), ":")
// Check for foreign traits being reachable.
tcx.visible_parent_map(()).get(&def_id).is_some()
};
err.span_suggestion_verbose(
span,
"consider relaxing the implicit `Sized` restriction",
format!("{separator} ?Sized"),
Applicability::MachineApplicable,
);
if tcx.is_lang_item(def_id, LangItem::Sized) {
// Check if this is an implicit bound, even in foreign crates.
if tcx
.generics_of(item_def_id)
.own_params
.iter()
.any(|param| tcx.def_span(param.def_id) == span)
{
a = "an implicit `Sized`";
this =
"the implicit `Sized` requirement on this type parameter";
}
if let Some(hir::Node::TraitItem(hir::TraitItem {
generics,
kind: hir::TraitItemKind::Type(bounds, None),
..
})) = tcx.hir().get_if_local(item_def_id)
// Do not suggest relaxing if there is an explicit `Sized` obligation.
&& !bounds.iter()
.filter_map(|bound| bound.trait_ref())
.any(|tr| tr.trait_def_id() == tcx.lang_items().sized_trait())
{
let (span, separator) = if let [.., last] = bounds {
(last.span().shrink_to_hi(), " +")
} else {
(generics.span.shrink_to_hi(), ":")
};
err.span_suggestion_verbose(
span,
"consider relaxing the implicit `Sized` restriction",
format!("{separator} ?Sized"),
Applicability::MachineApplicable,
);
}
}
if let DefKind::Trait = tcx.def_kind(item_def_id)
&& !visible_item
{
note = Some(format!(
"`{short_item_name}` is a \"sealed trait\", because to implement it \
you also need to implement `{}`, which is not accessible; this is \
usually done to force you to use one of the provided types that \
already implement it",
with_no_trimmed_paths!(tcx.def_path_str(def_id)),
));
let impls_of = tcx.trait_impls_of(def_id);
let impls = impls_of
.non_blanket_impls()
.values()
.flatten()
.chain(impls_of.blanket_impls().iter())
.collect::<Vec<_>>();
if !impls.is_empty() {
let len = impls.len();
let mut types = impls
.iter()
.map(|t| {
with_no_trimmed_paths!(format!(
" {}",
tcx.type_of(*t).instantiate_identity(),
))
})
.collect::<Vec<_>>();
let post = if types.len() > 9 {
types.truncate(8);
format!("\nand {} others", len - 8)
} else {
String::new()
};
help = Some(format!(
"the following type{} implement{} the trait:\n{}{post}",
pluralize!(len),
if len == 1 { "s" } else { "" },
types.join("\n"),
));
}
}
}
}
if let DefKind::Trait = tcx.def_kind(item_def_id)
&& !visible_item
{
note = Some(format!(
"`{short_item_name}` is a \"sealed trait\", because to implement it \
you also need to implement `{}`, which is not accessible; this is \
usually done to force you to use one of the provided types that \
already implement it",
with_no_trimmed_paths!(tcx.def_path_str(def_id)),
));
let impls_of = tcx.trait_impls_of(def_id);
let impls = impls_of
.non_blanket_impls()
.values()
.flatten()
.chain(impls_of.blanket_impls().iter())
.collect::<Vec<_>>();
if !impls.is_empty() {
let len = impls.len();
let mut types = impls
.iter()
.map(|t| {
with_no_trimmed_paths!(format!(
" {}",
tcx.type_of(*t).instantiate_identity(),
))
})
.collect::<Vec<_>>();
let post = if types.len() > 9 {
types.truncate(8);
format!("\nand {} others", len - 8)
ty::ClauseKind::ConstArgHasType(..) => {
let descr =
format!("required by a const generic parameter in `{item_name}`");
if span.is_visible(sm) {
let msg = format!(
"required by this const generic parameter in `{short_item_name}`"
);
multispan.push_span_label(span, msg);
err.span_note(multispan, descr);
} else {
String::new()
};
help = Some(format!(
"the following type{} implement{} the trait:\n{}{post}",
pluralize!(len),
if len == 1 { "s" } else { "" },
types.join("\n"),
));
err.span_note(tcx.def_span(item_def_id), descr);
}
return;
}
_ => (),
}
};
}
let descr = format!("required by {a} bound in `{item_name}`");
if span.is_visible(sm) {
let msg = format!("required by {this} in `{short_item_name}`");
Expand Down
8 changes: 4 additions & 4 deletions tests/ui/const-generics/defaults/doesnt_infer.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -4,11 +4,11 @@ error[E0284]: type annotations needed for `Foo<_>`
LL | let foo = Foo::foo();
| ^^^ ---------- type must be known at this point
|
note: required by a bound in `Foo::<N>::foo`
note: required by a const generic parameter in `Foo::<N>::foo`
--> $DIR/doesnt_infer.rs:5:6
|
LL | impl<const N: u32> Foo<N> {
| ^^^^^^^^^^^^ required by this bound in `Foo::<N>::foo`
| ^^^^^^^^^^^^ required by this const generic parameter in `Foo::<N>::foo`
LL | fn foo() -> Self {
| --- required by a bound in this associated function
help: consider giving `foo` an explicit type, where the value of const parameter `N` is specified
Expand All @@ -22,11 +22,11 @@ error[E0284]: type annotations needed for `Foo<_>`
LL | let foo = Foo::foo();
| ^^^ --- type must be known at this point
|
note: required by a bound in `Foo`
note: required by a const generic parameter in `Foo`
--> $DIR/doesnt_infer.rs:3:12
|
LL | struct Foo<const N: u32 = 2>;
| ^^^^^^^^^^^^^^^^ required by this bound in `Foo`
| ^^^^^^^^^^^^^^^^ required by this const generic parameter in `Foo`
help: consider giving `foo` an explicit type, where the value of const parameter `N` is specified
|
LL | let foo: Foo<N> = Foo::foo();
Expand Down
4 changes: 2 additions & 2 deletions tests/ui/const-generics/defaults/rp_impl_trait_fail.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -37,11 +37,11 @@ error[E0284]: type annotations needed
LL | uwu();
| ^^^ cannot infer the value of the const parameter `N` declared on the function `uwu`
|
note: required by a bound in `uwu`
note: required by a const generic parameter in `uwu`
--> $DIR/rp_impl_trait_fail.rs:16:8
|
LL | fn uwu<const N: u8>() -> impl Traitor<N> {
| ^^^^^^^^^^^ required by this bound in `uwu`
| ^^^^^^^^^^^ required by this const generic parameter in `uwu`
help: consider specifying the generic argument
|
LL | uwu::<N>();
Expand Down
4 changes: 2 additions & 2 deletions tests/ui/const-generics/generic_arg_infer/issue-91614.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ error[E0284]: type annotations needed for `Mask<_, _>`
LL | let y = Mask::<_, _>::splat(false);
| ^ -------------------------- type must be known at this point
|
note: required by a bound in `Mask::<T, N>::splat`
note: required by a const generic parameter in `Mask::<T, N>::splat`
--> $SRC_DIR/core/src/../../portable-simd/crates/core_simd/src/masks.rs:LL:COL
help: consider giving `y` an explicit type, where the value of const parameter `N` is specified
|
Expand All @@ -17,7 +17,7 @@ error[E0284]: type annotations needed for `Mask<_, _>`
LL | let y = Mask::<_, _>::splat(false);
| ^ ------------ type must be known at this point
|
note: required by a bound in `Mask`
note: required by a const generic parameter in `Mask`
--> $SRC_DIR/core/src/../../portable-simd/crates/core_simd/src/masks.rs:LL:COL
help: consider giving `y` an explicit type, where the value of const parameter `N` is specified
|
Expand Down
8 changes: 4 additions & 4 deletions tests/ui/const-generics/generic_const_exprs/issue-62504.full.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -24,11 +24,11 @@ error[E0284]: type annotations needed for `ArrayHolder<_>`
LL | let mut array = ArrayHolder::new();
| ^^^^^^^^^ ------------------ type must be known at this point
|
note: required by a bound in `ArrayHolder::<X>::new`
note: required by a const generic parameter in `ArrayHolder::<X>::new`
--> $DIR/issue-62504.rs:16:6
|
LL | impl<const X: usize> ArrayHolder<X> {
| ^^^^^^^^^^^^^^ required by this bound in `ArrayHolder::<X>::new`
| ^^^^^^^^^^^^^^ required by this const generic parameter in `ArrayHolder::<X>::new`
LL | pub const fn new() -> Self {
| --- required by a bound in this associated function
help: consider giving `array` an explicit type, where the value of const parameter `X` is specified
Expand All @@ -42,11 +42,11 @@ error[E0284]: type annotations needed for `ArrayHolder<_>`
LL | let mut array = ArrayHolder::new();
| ^^^^^^^^^ ----------- type must be known at this point
|
note: required by a bound in `ArrayHolder`
note: required by a const generic parameter in `ArrayHolder`
--> $DIR/issue-62504.rs:14:20
|
LL | struct ArrayHolder<const X: usize>([u32; X]);
| ^^^^^^^^^^^^^^ required by this bound in `ArrayHolder`
| ^^^^^^^^^^^^^^ required by this const generic parameter in `ArrayHolder`
help: consider giving `array` an explicit type, where the value of const parameter `X` is specified
|
LL | let mut array: ArrayHolder<X> = ArrayHolder::new();
Expand Down
8 changes: 4 additions & 4 deletions tests/ui/const-generics/generic_const_exprs/issue-62504.min.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -28,11 +28,11 @@ error[E0284]: type annotations needed for `ArrayHolder<_>`
LL | let mut array = ArrayHolder::new();
| ^^^^^^^^^ ------------------ type must be known at this point
|
note: required by a bound in `ArrayHolder::<X>::new`
note: required by a const generic parameter in `ArrayHolder::<X>::new`
--> $DIR/issue-62504.rs:16:6
|
LL | impl<const X: usize> ArrayHolder<X> {
| ^^^^^^^^^^^^^^ required by this bound in `ArrayHolder::<X>::new`
| ^^^^^^^^^^^^^^ required by this const generic parameter in `ArrayHolder::<X>::new`
LL | pub const fn new() -> Self {
| --- required by a bound in this associated function
help: consider giving `array` an explicit type, where the value of const parameter `X` is specified
Expand All @@ -46,11 +46,11 @@ error[E0284]: type annotations needed for `ArrayHolder<_>`
LL | let mut array = ArrayHolder::new();
| ^^^^^^^^^ ----------- type must be known at this point
|
note: required by a bound in `ArrayHolder`
note: required by a const generic parameter in `ArrayHolder`
--> $DIR/issue-62504.rs:14:20
|
LL | struct ArrayHolder<const X: usize>([u32; X]);
| ^^^^^^^^^^^^^^ required by this bound in `ArrayHolder`
| ^^^^^^^^^^^^^^ required by this const generic parameter in `ArrayHolder`
help: consider giving `array` an explicit type, where the value of const parameter `X` is specified
|
LL | let mut array: ArrayHolder<X> = ArrayHolder::new();
Expand Down
4 changes: 2 additions & 2 deletions tests/ui/const-generics/generic_const_exprs/object-safety-ok-infer-err.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -4,11 +4,11 @@ error[E0284]: type annotations needed
LL | use_dyn(&());
| ^^^^^^^ cannot infer the value of the const parameter `N` declared on the function `use_dyn`
|
note: required by a bound in `use_dyn`
note: required by a const generic parameter in `use_dyn`
--> $DIR/object-safety-ok-infer-err.rs:14:12
|
LL | fn use_dyn<const N: usize>(v: &dyn Foo<N>) where [u8; N + 1]: Sized {
| ^^^^^^^^^^^^^^ required by this bound in `use_dyn`
| ^^^^^^^^^^^^^^ required by this const generic parameter in `use_dyn`
help: consider specifying the generic argument
|
LL | use_dyn::<N>(&());
Expand Down
4 changes: 2 additions & 2 deletions tests/ui/const-generics/infer/cannot-infer-const-args.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -4,11 +4,11 @@ error[E0284]: type annotations needed
LL | foo();
| ^^^ cannot infer the value of the const parameter `X` declared on the function `foo`
|
note: required by a bound in `foo`
note: required by a const generic parameter in `foo`
--> $DIR/cannot-infer-const-args.rs:1:8
|
LL | fn foo<const X: usize>() -> usize {
| ^^^^^^^^^^^^^^ required by this bound in `foo`
| ^^^^^^^^^^^^^^ required by this const generic parameter in `foo`
help: consider specifying the generic argument
|
LL | foo::<X>();
Expand Down
4 changes: 2 additions & 2 deletions tests/ui/const-generics/infer/issue-77092.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -4,11 +4,11 @@ error[E0284]: type annotations needed
LL | println!("{:?}", take_array_from_mut(&mut arr, i));
| ^^^^^^^^^^^^^^^^^^^ cannot infer the value of the const parameter `N` declared on the function `take_array_from_mut`
|
note: required by a bound in `take_array_from_mut`
note: required by a const generic parameter in `take_array_from_mut`
--> $DIR/issue-77092.rs:3:27
|
LL | fn take_array_from_mut<T, const N: usize>(data: &mut [T], start: usize) -> &mut [T; N] {
| ^^^^^^^^^^^^^^ required by this bound in `take_array_from_mut`
| ^^^^^^^^^^^^^^ required by this const generic parameter in `take_array_from_mut`
help: consider specifying the generic arguments
|
LL | println!("{:?}", take_array_from_mut::<i32, N>(&mut arr, i));
Expand Down
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