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Provide help when T: ?Sized can't be suggested
1 parent d2b8e60 commit aa84b0f

10 files changed

+154
-10
lines changed

‎src/librustc_trait_selection/traits/error_reporting/mod.rs

+45-9
Original file line numberDiff line numberDiff line change
@@ -26,7 +26,7 @@ use rustc_middle::ty::{
2626
TypeFoldable, WithConstness,
2727
};
2828
use rustc_session::DiagnosticMessageId;
29-
use rustc_span::{ExpnKind, Span, DUMMY_SP};
29+
use rustc_span::{ExpnKind, MultiSpan, Span, DUMMY_SP};
3030
use std::fmt;
3131

3232
use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
@@ -1740,10 +1740,36 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
17401740
// Suggesting `T: ?Sized` is only valid in an ADT if `T` is only used in a
17411741
// borrow. `struct S<'a, T: ?Sized>(&'a T);` is valid, `struct S<T: ?Sized>(T);`
17421742
// is not.
1743-
let mut visitor = FindTypeParam { param: param.name.ident().name, valid: true };
1743+
let mut visitor = FindTypeParam {
1744+
param: param.name.ident().name,
1745+
invalid_spans: vec![],
1746+
nested: false,
1747+
};
17441748
visitor.visit_item(item);
1745-
if !visitor.valid {
1746-
continue;
1749+
if !visitor.invalid_spans.is_empty() {
1750+
let mut multispan: MultiSpan = param.span.into();
1751+
multispan.push_span_label(
1752+
param.span,
1753+
format!("this could be changed to `{}: ?Sized`...", param.name.ident()),
1754+
);
1755+
for sp in visitor.invalid_spans {
1756+
multispan.push_span_label(
1757+
sp,
1758+
format!(
1759+
"...if indirection was used here: `Box<{}>`",
1760+
param.name.ident(),
1761+
),
1762+
);
1763+
}
1764+
err.span_help(
1765+
multispan,
1766+
&format!(
1767+
"you could relax the implicit `Sized` bound on `{T}` if it were \
1768+
used through indirection like `&{T}` or `Box<{T}>`",
1769+
T = param.name.ident(),
1770+
),
1771+
);
1772+
return;
17471773
}
17481774
}
17491775
_ => {}
@@ -1782,7 +1808,8 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
17821808
/// `param: ?Sized` would be a valid constraint.
17831809
struct FindTypeParam {
17841810
param: rustc_span::Symbol,
1785-
valid: bool,
1811+
invalid_spans: Vec<Span>,
1812+
nested: bool,
17861813
}
17871814

17881815
impl<'v> Visitor<'v> for FindTypeParam {
@@ -1794,15 +1821,24 @@ impl<'v> Visitor<'v> for FindTypeParam {
17941821

17951822
fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
17961823
match ty.kind {
1797-
hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => return,
1824+
hir::TyKind::Ptr(_) | hir::TyKind::Rptr(..) | hir::TyKind::TraitObject(..) => {}
17981825
hir::TyKind::Path(hir::QPath::Resolved(None, path))
17991826
if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
18001827
{
1801-
self.valid = false;
1828+
if !self.nested {
1829+
self.invalid_spans.push(ty.span);
1830+
}
1831+
}
1832+
hir::TyKind::Path(_) => {
1833+
let prev = self.nested;
1834+
self.nested = true;
1835+
hir::intravisit::walk_ty(self, ty);
1836+
self.nested = prev;
1837+
}
1838+
_ => {
1839+
hir::intravisit::walk_ty(self, ty);
18021840
}
1803-
_ => {}
18041841
}
1805-
hir::intravisit::walk_ty(self, ty);
18061842
}
18071843
}
18081844

‎src/test/ui/issues/issue-18919.stderr

+7
Original file line numberDiff line numberDiff line change
@@ -9,6 +9,13 @@ LL | enum Option<T> {
99
|
1010
= help: the trait `std::marker::Sized` is not implemented for `dyn for<'r> std::ops::Fn(&'r isize) -> isize`
1111
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
12+
help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
13+
--> $DIR/issue-18919.rs:7:13
14+
|
15+
LL | enum Option<T> {
16+
| ^ this could be changed to `T: ?Sized`...
17+
LL | Some(T),
18+
| - ...if indirection was used here: `Box<T>`
1219

1320
error: aborting due to previous error
1421

‎src/test/ui/issues/issue-23281.stderr

+7
Original file line numberDiff line numberDiff line change
@@ -9,6 +9,13 @@ LL | struct Vec<T> {
99
|
1010
= help: the trait `std::marker::Sized` is not implemented for `(dyn std::ops::Fn() + 'static)`
1111
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
12+
help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
13+
--> $DIR/issue-23281.rs:8:12
14+
|
15+
LL | struct Vec<T> {
16+
| ^ this could be changed to `T: ?Sized`...
17+
LL | t: T,
18+
| - ...if indirection was used here: `Box<T>`
1219

1320
error: aborting due to previous error
1421

‎src/test/ui/suggestions/adt-param-with-implicit-sized-bound.rs

+11
Original file line numberDiff line numberDiff line change
@@ -2,6 +2,7 @@ trait Trait {
22
fn func1() -> Struct1<Self>; //~ ERROR E0277
33
fn func2<'a>() -> Struct2<'a, Self>; //~ ERROR E0277
44
fn func3() -> Struct3<Self>; //~ ERROR E0277
5+
fn func4() -> Struct4<Self>; //~ ERROR E0277
56
}
67

78
struct Struct1<T>{
@@ -14,4 +15,14 @@ struct Struct3<T>{
1415
_t: T,
1516
}
1617

18+
struct X<T>(T);
19+
20+
struct Struct4<T>{
21+
_t: X<T>,
22+
}
23+
24+
struct Struct5<T: ?Sized>{
25+
_t: X<T>, //~ ERROR E0277
26+
}
27+
1728
fn main() {}

‎src/test/ui/suggestions/adt-param-with-implicit-sized-bound.stderr

+49-1
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,24 @@
1+
error[E0277]: the size for values of type `T` cannot be known at compilation time
2+
--> $DIR/adt-param-with-implicit-sized-bound.rs:25:5
3+
|
4+
LL | struct X<T>(T);
5+
| - required by this bound in `X`
6+
...
7+
LL | struct Struct5<T: ?Sized>{
8+
| - this type parameter needs to be `std::marker::Sized`
9+
LL | _t: X<T>,
10+
| ^^^^^^^^ doesn't have a size known at compile-time
11+
|
12+
= help: the trait `std::marker::Sized` is not implemented for `T`
13+
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
14+
help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
15+
--> $DIR/adt-param-with-implicit-sized-bound.rs:18:10
16+
|
17+
LL | struct X<T>(T);
18+
| ^ - ...if indirection was used here: `Box<T>`
19+
| |
20+
| this could be changed to `T: ?Sized`...
21+
122
error[E0277]: the size for values of type `Self` cannot be known at compilation time
223
--> $DIR/adt-param-with-implicit-sized-bound.rs:2:19
324
|
@@ -49,11 +70,38 @@ LL | struct Struct3<T>{
4970
|
5071
= help: the trait `std::marker::Sized` is not implemented for `Self`
5172
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
73+
help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
74+
--> $DIR/adt-param-with-implicit-sized-bound.rs:14:16
75+
|
76+
LL | struct Struct3<T>{
77+
| ^ this could be changed to `T: ?Sized`...
78+
LL | _t: T,
79+
| - ...if indirection was used here: `Box<T>`
5280
help: consider further restricting `Self`
5381
|
5482
LL | fn func3() -> Struct3<Self> where Self: std::marker::Sized;
5583
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5684

57-
error: aborting due to 3 previous errors
85+
error[E0277]: the size for values of type `Self` cannot be known at compilation time
86+
--> $DIR/adt-param-with-implicit-sized-bound.rs:5:19
87+
|
88+
LL | fn func4() -> Struct4<Self>;
89+
| ^^^^^^^^^^^^^ doesn't have a size known at compile-time
90+
...
91+
LL | struct Struct4<T>{
92+
| - required by this bound in `Struct4`
93+
|
94+
= help: the trait `std::marker::Sized` is not implemented for `Self`
95+
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
96+
help: consider further restricting `Self`
97+
|
98+
LL | fn func4() -> Struct4<Self> where Self: std::marker::Sized;
99+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
100+
help: consider relaxing the implicit `Sized` restriction
101+
|
102+
LL | struct Struct4<T: ?Sized>{
103+
| ^^^^^^^^
104+
105+
error: aborting due to 5 previous errors
58106

59107
For more information about this error, try `rustc --explain E0277`.

‎src/test/ui/unsized/unsized-enum.stderr

+7
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,13 @@ LL | fn foo2<T: ?Sized>() { not_sized::<Foo<T>>() }
1111
|
1212
= help: the trait `std::marker::Sized` is not implemented for `T`
1313
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
14+
help: you could relax the implicit `Sized` bound on `U` if it were used through indirection like `&U` or `Box<U>`
15+
--> $DIR/unsized-enum.rs:4:10
16+
|
17+
LL | enum Foo<U> { FooSome(U), FooNone }
18+
| ^ - ...if indirection was used here: `Box<U>`
19+
| |
20+
| this could be changed to `U: ?Sized`...
1421

1522
error: aborting due to previous error
1623

‎src/test/ui/unsized/unsized-inherent-impl-self-type.stderr

+7
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,13 @@ LL | impl<X: ?Sized> S5<X> {
1111
|
1212
= help: the trait `std::marker::Sized` is not implemented for `X`
1313
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
14+
help: you could relax the implicit `Sized` bound on `Y` if it were used through indirection like `&Y` or `Box<Y>`
15+
--> $DIR/unsized-inherent-impl-self-type.rs:5:11
16+
|
17+
LL | struct S5<Y>(Y);
18+
| ^ - ...if indirection was used here: `Box<Y>`
19+
| |
20+
| this could be changed to `Y: ?Sized`...
1421

1522
error: aborting due to previous error
1623

‎src/test/ui/unsized/unsized-struct.stderr

+7
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,13 @@ LL | fn foo2<T: ?Sized>() { not_sized::<Foo<T>>() }
1111
|
1212
= help: the trait `std::marker::Sized` is not implemented for `T`
1313
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
14+
help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
15+
--> $DIR/unsized-struct.rs:4:12
16+
|
17+
LL | struct Foo<T> { data: T }
18+
| ^ - ...if indirection was used here: `Box<T>`
19+
| |
20+
| this could be changed to `T: ?Sized`...
1421

1522
error[E0277]: the size for values of type `T` cannot be known at compilation time
1623
--> $DIR/unsized-struct.rs:13:24

‎src/test/ui/unsized/unsized-trait-impl-self-type.stderr

+7
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,13 @@ LL | impl<X: ?Sized> T3<X> for S5<X> {
1111
|
1212
= help: the trait `std::marker::Sized` is not implemented for `X`
1313
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
14+
help: you could relax the implicit `Sized` bound on `Y` if it were used through indirection like `&Y` or `Box<Y>`
15+
--> $DIR/unsized-trait-impl-self-type.rs:8:11
16+
|
17+
LL | struct S5<Y>(Y);
18+
| ^ - ...if indirection was used here: `Box<Y>`
19+
| |
20+
| this could be changed to `Y: ?Sized`...
1421

1522
error: aborting due to previous error
1623

‎src/test/ui/wf/wf-fn-where-clause.stderr

+7
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,13 @@ LL | struct Vec<T> {
2323
|
2424
= help: the trait `std::marker::Sized` is not implemented for `(dyn std::marker::Copy + 'static)`
2525
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
26+
help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
27+
--> $DIR/wf-fn-where-clause.rs:16:12
28+
|
29+
LL | struct Vec<T> {
30+
| ^ this could be changed to `T: ?Sized`...
31+
LL | t: T,
32+
| - ...if indirection was used here: `Box<T>`
2633

2734
error[E0038]: the trait `std::marker::Copy` cannot be made into an object
2835
--> $DIR/wf-fn-where-clause.rs:12:16

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