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rust-bors merged 1 commit into from
Jul 15, 2026
Merged

Improve E0277 for imperfect derives #158764

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6 changes: 4 additions & 2 deletions compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
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Expand Up @@ -4258,9 +4258,11 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
err.span_note(spans, msg);
if derived && trait_name != "Copy" {
err.help(format!(
"consider manually implementing `{trait_name}` to avoid undesired \
bounds",
"consider manually implementing `{trait_name}` to avoid undesired bounds caused by \"imperfect derives\"",
));
err.note(
"to learn more, visit <https://github.com/rust-lang/rust/issues/26925>",
);
}
point_at_assoc_type_restriction(
tcx,
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6 changes: 4 additions & 2 deletions tests/ui/associated-types/issue-38821.stderr
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Expand Up @@ -108,7 +108,8 @@ LL | pub enum ColumnInsertValue<Col, Expr> where
...
LL | Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>,
| ------------------------------------------------ unsatisfied trait bound
= help: consider manually implementing `Debug` to avoid undesired bounds
= help: consider manually implementing `Debug` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
help: consider further restricting the associated type
|
LL | Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>, <Col as Expression>::SqlType: NotNull,
Expand Down Expand Up @@ -238,7 +239,8 @@ LL | pub enum ColumnInsertValue<Col, Expr> where
...
LL | Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>,
| ------------------------------------------------ unsatisfied trait bound
= help: consider manually implementing `Clone` to avoid undesired bounds
= help: consider manually implementing `Clone` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
help: consider further restricting the associated type
|
LL | Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>, <Col as Expression>::SqlType: NotNull,
Expand Down
6 changes: 4 additions & 2 deletions tests/ui/const-generics/adt_const_params/unsizing-wfcheck-issue-126272.stderr
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Expand Up @@ -67,7 +67,8 @@ LL | #[derive(Debug, PartialEq, Eq, ConstParamTy)]
| ----- in this derive macro expansion
LL | struct Bar<T>(T);
| ^^^ - unsatisfied trait bound
= help: consider manually implementing `Debug` to avoid undesired bounds
= help: consider manually implementing `Debug` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
= note: 2 redundant requirements hidden
= note: required for `&&'static Bar<(dyn Debug + 'static)>` to implement `Debug`
= note: required for the cast from `&&&'static Bar<(dyn Debug + 'static)>` to `&dyn Debug`
Expand Down Expand Up @@ -102,7 +103,8 @@ LL | #[derive(Debug, PartialEq, Eq, ConstParamTy)]
| -- in this derive macro expansion
LL | struct Bar<T>(T);
| ^^^ - type parameter would need to implement `Eq`
= help: consider manually implementing `Eq` to avoid undesired bounds
= help: consider manually implementing `Eq` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
= note: 1 redundant requirement hidden
= note: required for `&'static Bar<dyn Debug>` to implement `Eq`
note: required by a bound in `std::cmp::AssertParamIsEq`
Expand Down
3 changes: 2 additions & 1 deletion tests/ui/derives/clone-copy/deriving-copyclone.stderr
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Expand Up @@ -38,7 +38,8 @@ LL | #[derive(Copy, Clone)]
| ----- in this derive macro expansion
LL | struct B<T> {
| ^ - type parameter would need to implement `Clone`
= help: consider manually implementing `Clone` to avoid undesired bounds
= help: consider manually implementing `Clone` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
note: required by a bound in `is_clone`
--> $DIR/deriving-copyclone.rs:19:16
|
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3 changes: 2 additions & 1 deletion tests/ui/derives/redundant-derive-note-on-unimplemented.stderr
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Expand Up @@ -21,7 +21,8 @@ LL | #[derive(Debug)]
| ----- in this derive macro expansion
LL | struct S<T>(T);
| ^ - type parameter would need to implement `Debug`
= help: consider manually implementing `Debug` to avoid undesired bounds
= help: consider manually implementing `Debug` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
help: consider annotating `X` with `#[derive(Debug)]`
|
LL + #[derive(Debug)]
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3 changes: 2 additions & 1 deletion tests/ui/proc-macro/issue-104884-trait-impl-sugg-err.stderr
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Expand Up @@ -44,7 +44,8 @@ LL | #[derive(PartialOrd, AddImpl)]
...
LL | struct PriorityQueue<T>(BinaryHeap<PriorityQueueEntry<T>>);
| ^^^^^^^^^^^^^ - type parameter would need to implement `PartialOrd`
= help: consider manually implementing `PartialOrd` to avoid undesired bounds
= help: consider manually implementing `PartialOrd` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
note: required by a bound in `Ord`
--> $SRC_DIR/core/src/cmp.rs:LL:COL

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6 changes: 4 additions & 2 deletions tests/ui/suggestions/missing-bound-in-derive-copy-impl-2.stderr
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Expand Up @@ -30,7 +30,8 @@ LL | #[derive(Debug, Copy, Clone)]
| ----- in this derive macro expansion
LL | pub struct Vector2<T: Debug + Copy + Clone> {
| ^^^^^^^ ---- unsatisfied trait bound
= help: consider manually implementing `Debug` to avoid undesired bounds
= help: consider manually implementing `Debug` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
= note: required for the cast from `&Vector2<K>` to `&dyn Debug`
help: consider further restricting type parameter `K` with trait `Copy`
|
Expand Down Expand Up @@ -72,7 +73,8 @@ LL | #[derive(Debug, Copy, Clone)]
| ----- in this derive macro expansion
LL | pub struct Vector2<T: Debug + Copy + Clone> {
| ^^^^^^^ ---- unsatisfied trait bound
= help: consider manually implementing `Clone` to avoid undesired bounds
= help: consider manually implementing `Clone` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
help: consider further restricting type parameter `K` with trait `Copy`
|
LL | pub struct AABB<K: Debug + std::marker::Copy> {
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6 changes: 4 additions & 2 deletions tests/ui/suggestions/missing-bound-in-derive-copy-impl.stderr
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Expand Up @@ -66,7 +66,8 @@ LL | #[derive(Debug, Copy, Clone)]
| ----- in this derive macro expansion
LL | pub struct Vector2<T: Debug + Copy + Clone> {
| ^^^^^^^ ---- unsatisfied trait bound
= help: consider manually implementing `Debug` to avoid undesired bounds
= help: consider manually implementing `Debug` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
= note: required for the cast from `&Vector2<K>` to `&dyn Debug`
help: consider restricting type parameter `K` with trait `Copy`
|
Expand Down Expand Up @@ -136,7 +137,8 @@ LL | #[derive(Debug, Copy, Clone)]
| ----- in this derive macro expansion
LL | pub struct Vector2<T: Debug + Copy + Clone> {
| ^^^^^^^ ---- unsatisfied trait bound
= help: consider manually implementing `Clone` to avoid undesired bounds
= help: consider manually implementing `Clone` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
help: consider restricting type parameter `K` with trait `Copy`
|
LL | pub struct AABB<K: std::marker::Copy> {
Expand Down
3 changes: 2 additions & 1 deletion tests/ui/traits/derive-implicit-bound.stderr
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Expand Up @@ -14,7 +14,8 @@ LL | #[derive(PartialEq, Eq)]
| --------- in this derive macro expansion
LL | pub struct Id<T>(PhantomData<T>);
| ^^ - type parameter would need to implement `PartialEq`
= help: consider manually implementing `PartialEq` to avoid undesired bounds
= help: consider manually implementing `PartialEq` to avoid undesired bounds caused by "imperfect derives"
= note: to learn more, visit <https://github.com/rust-lang/rust/issues/26925>
note: required by a bound in `accept_eq`
--> $DIR/derive-implicit-bound.rs:17:23
|
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