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6b24fdf811
```
error: unconstrained generic constant
--> $DIR/const-argument-if-length.rs:18:10
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LL | pad: [u8; is_zst::<T>()],
| ^^^^^^^^^^^^^^^^^^^
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help: try adding a `where` bound
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LL | pub struct AtLeastByte<T: ?Sized> where [(); is_zst::<T>()]: {
| ++++++++++++++++++++++++++
```
Detect when the constant expression isn't `usize` and suggest casting:
```
error: unconstrained generic constant
--> f300.rs:6:10
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6 | bb::<{!N}>();
| ^^^^
-Ztrack-diagnostics: created at compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs:3539:36
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help: try adding a `where` bound
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5 | fn b<const N: bool>() where [(); {!N} as usize]: {
| ++++++++++++++++++++++++++
```
Fix #122395.
55 lines
1.9 KiB
Plaintext
55 lines
1.9 KiB
Plaintext
error: unconstrained generic constant
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--> $DIR/const-argument-if-length.rs:18:10
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LL | pad: [u8; is_zst::<T>()],
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| ^^^^^^^^^^^^^^^^^^^
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help: try adding a `where` bound
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LL | pub struct AtLeastByte<T: ?Sized> where [(); is_zst::<T>()]: {
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| ++++++++++++++++++++++++++
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error[E0277]: the size for values of type `T` cannot be known at compilation time
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--> $DIR/const-argument-if-length.rs:16:12
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LL | pub struct AtLeastByte<T: ?Sized> {
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| - this type parameter needs to be `Sized`
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LL | value: T,
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| ^ doesn't have a size known at compile-time
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= note: only the last field of a struct may have a dynamically sized type
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= help: change the field's type to have a statically known size
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help: consider removing the `?Sized` bound to make the type parameter `Sized`
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LL - pub struct AtLeastByte<T: ?Sized> {
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LL + pub struct AtLeastByte<T> {
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help: borrowed types always have a statically known size
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LL | value: &T,
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| +
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help: the `Box` type always has a statically known size and allocates its contents in the heap
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LL | value: Box<T>,
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| ++++ +
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error[E0277]: the size for values of type `T` cannot be known at compilation time
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--> $DIR/const-argument-if-length.rs:7:28
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LL | pub const fn is_zst<T: ?Sized>() -> usize {
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| - this type parameter needs to be `Sized`
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LL | if std::mem::size_of::<T>() == 0 {
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| ^ doesn't have a size known at compile-time
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note: required by an implicit `Sized` bound in `std::mem::size_of`
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--> $SRC_DIR/core/src/mem/mod.rs:LL:COL
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help: consider removing the `?Sized` bound to make the type parameter `Sized`
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LL - pub const fn is_zst<T: ?Sized>() -> usize {
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LL + pub const fn is_zst<T>() -> usize {
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error: aborting due to 3 previous errors
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For more information about this error, try `rustc --explain E0277`.
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