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docs/test: add UI test and long-form error docs for E0377

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Ezra Shaw 2022-12-20 18:31:15 +13:00
parent c43bc13562
commit e798fdf7be
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5 changed files with 55 additions and 4 deletions
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3
compiler/rustc_error_codes/src/error_codes.rs
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@ -184,6 +184,7 @@ E0373: include_str!("./error_codes/E0373.md"),
E0374: include_str!("./error_codes/E0374.md"),
E0375: include_str!("./error_codes/E0375.md"),
E0376: include_str!("./error_codes/E0376.md"),
E0377: include_str!("./error_codes/E0377.md"),
E0378: include_str!("./error_codes/E0378.md"),
E0379: include_str!("./error_codes/E0379.md"),
E0380: include_str!("./error_codes/E0380.md"),
@ -579,8 +580,6 @@ E0791: include_str!("./error_codes/E0791.md"),
// E0315, // cannot invoke closure outside of its lifetime
// E0319, // trait impls for defaulted traits allowed just for structs/enums
// E0372, // coherence not object safe
E0377, // the trait `CoerceUnsized` may only be implemented for a coercion
// between structures with the same definition
// E0385, // {} in an aliasable location
// E0402, // cannot use an outer type parameter in this context
// E0406, // merged into 420

29
compiler/rustc_error_codes/src/error_codes/E0377.md Normal file
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@ -0,0 +1,29 @@
The trait `CoerceUnsized` may only be implemented for a coercion between
structures with the same definition.
Example of erroneous code:
```compile_fail,E0377
#![feature(coerce_unsized)]
use std::ops::CoerceUnsized;
pub struct Foo<T: ?Sized> {
field_with_unsized_type: T,
}
pub struct Bar<T: ?Sized> {
field_with_unsized_type: T,
}
// error: the trait `CoerceUnsized` may only be implemented for a coercion
// between structures with the same definition
impl<T, U> CoerceUnsized<Bar<U>> for Foo<T> where T: CoerceUnsized<U> {}
```
When attempting to implement `CoerceUnsized`, the `impl` signature must look
like: `impl CoerceUnsized<Type<U>> for Type<T> where T: CoerceUnsized<U>`;
the *implementer* and *`CoerceUnsized` type parameter* must be the same
type. In this example, `Bar` and `Foo` (even though structurally identical)
are *not* the same type and are rejected. Learn more about the `CoerceUnsized`
trait and DST coercion in
[the `CoerceUnsized` docs](../std/ops/trait.CoerceUnsized.html).