Provide additional context to errors involving const traits #144194
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rustbot
added
A-run-make
|
Some changes occurred to constck cc @fee1-dead Some changes occurred to the CTFE machinery This PR modifies cc @jieyouxu |
When encountering an unmet `Ty: [const] Trait` bound, if `Trait` is `#[const_trait]` and there's an `impl Trait for Ty` point at it. If local, suggest `impl const Trait for Ty`, otherwise just point at it.
```
error[E0277]: the trait bound `NonConstAdd: [const] Add` is not satisfied
--> $DIR/assoc-type.rs:37:16
|
LL | type Bar = NonConstAdd;
| ^^^^^^^^^^^
|
note: required by a bound in `Foo::Bar`
--> $DIR/assoc-type.rs:33:15
|
LL | type Bar: [const] Add;
| ^^^^^^^^^^^ required by this bound in `Foo::Bar`
help: make the `impl` of trait `Add` `const`
|
LL | impl const Add for NonConstAdd {
| +++++
```
```
error[E0277]: the trait bound `T: [const] PartialEq` is not satisfied
--> tests/ui/traits/const-traits/call-generic-method-fail.rs:5:5
|
5 | *t == *t
| ^^^^^^^^
|
note: trait `PartialEq` is implemented but not `const`
--> /home/gh-estebank/rust/library/core/src/ptr/const_ptr.rs:1590:1
|
1590 | impl<T: PointeeSized> PartialEq for *const T {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: trait `PartialEq` is implemented but not `const`
--> /home/gh-estebank/rust/library/core/src/ptr/mut_ptr.rs:2011:1
|
2011 | impl<T: PointeeSized> PartialEq for *mut T {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
Point at trait and associated item when that associated item is used in a const context. Suggest making the trait `#[const_trait]`.
```
error[E0015]: cannot call non-const method `<() as Trait>::foo` in constant functions
--> $DIR/inline-incorrect-early-bound-in-ctfe.rs:26:8
|
LL | ().foo();
| ^^^^^
|
note: method `foo` is not const because trait `Trait` is not const
--> $DIR/inline-incorrect-early-bound-in-ctfe.rs:13:1
|
LL | trait Trait {
| ^^^^^^^^^^^ this trait is not const
LL | fn foo(self);
| ------------- this method is not const
= note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
help: consider making trait `Trait` const
|
LL + #[const_trait]
LL | trait Trait {
|
```
```
error[E0015]: cannot call non-const associated function `Foo::{constant#0}::Foo::<17>::value` in constants
--> $DIR/nested-type.rs:15:5
|
LL | struct Foo<const N: [u8; {
| __________________________-
LL | | struct Foo<const N: usize>;
LL | |
LL | | impl<const N: usize> Foo<N> {
... |
LL | | Foo::<17>::value()
| | ^^^^^^^^^^^^^^^^^^
LL | |
LL | | }]>;
| |_- calls in constants are limited to constant functions, tuple structs and tuple variants
```
oli-obk
reviewed
Jul 20, 2025
| note: trait `PartialEq` is implemented but not `const` | ||
| --> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL | ||
| note: trait `PartialEq` is implemented but not `const` | ||
| --> $SRC_DIR/core/src/ptr/mut_ptr.rs:LL:COL |
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Why is it pointing at the raw ptr impls?
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When encountering an unmet
Ty: [const] Traitbound, ifTraitis#[const_trait]and there's animpl Trait for Typoint at it. If local, suggestimpl const Trait for Ty, otherwise just point at it.Point at trait and associated item when that associated item is used in a const context. Suggest making the trait
#[const_trait]. Point at theconstcontext where theconstexpression was found.