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Rollup merge of rust-lang#116611 - mejrs:diagnostic_namespace, r=ehuss Document `diagnostic_namespace` feature This adds it to the rust unstable book. FWIW: I couldn't find a way to serve the book locally (please send help), so I can't check that this renders correctly. cc `@weiznich`
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src/doc/unstable-book/src/language-features/diagnostic-namespace.md
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# `diagnostic_namespace` | ||
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The tracking issue for this feature is: [#111996] | ||
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[#111996]: https://github.com/rust-lang/rust/issues/111996 | ||
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------------------------ | ||
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The `diagnostic_namespace` feature permits customization of compilation errors. | ||
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## diagnostic::on_unimplemented | ||
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With [#114452] support for `diagnostic::on_unimplemented` was added. | ||
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When used on a trait declaration, the following options are available: | ||
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* `message` to customize the primary error message | ||
* `note` to add a customized note message to an error message | ||
* `label` to customize the label part of the error message | ||
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The attribute will hint to the compiler to use these in error messages: | ||
```rust | ||
// some library | ||
#![feature(diagnostic_namespace)] | ||
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#[diagnostic::on_unimplemented( | ||
message = "cannot insert element", | ||
label = "cannot be put into a table", | ||
note = "see <link> for more information about the Table api" | ||
)] | ||
pub trait Element { | ||
// ... | ||
} | ||
``` | ||
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```rust,compile_fail,E0277 | ||
# #![feature(diagnostic_namespace)] | ||
# | ||
# #[diagnostic::on_unimplemented( | ||
# message = "cannot insert element", | ||
# label = "cannot be put into a table", | ||
# note = "see <link> for more information about the Table api" | ||
# )] | ||
# pub trait Element { | ||
# // ... | ||
# } | ||
# struct Table; | ||
# impl Table { | ||
# fn insert<T: Element>(&self, element: T) { | ||
# // .. | ||
# } | ||
# } | ||
# fn main() { | ||
# let table = Table; | ||
# let element = (); | ||
// user code | ||
table.insert(element); | ||
# } | ||
``` | ||
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```text | ||
error[E0277]: cannot insert element | ||
--> src/main.rs:24:18 | ||
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24 | table.insert(element); | ||
| ------ ^^^^^^^ cannot be put into a table | ||
| | | ||
| required by a bound introduced by this call | ||
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= help: the trait `Element` is not implemented for `<type>` | ||
= note: see <link> for more information about the Table api | ||
note: required by a bound in `Table::insert` | ||
--> src/main.rs:15:18 | ||
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15 | fn insert<T: Element>(&self, element: T) { | ||
| ^^^^^^^ required by this bound in `Table::insert` | ||
For more information about this error, try `rustc --explain E0277`. | ||
``` | ||
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See [RFC 3368] for more information. | ||
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[#114452]: https://github.com/rust-lang/rust/pull/114452 | ||
[RFC 3368]: https://github.com/rust-lang/rfcs/blob/master/text/3368-diagnostic-attribute-namespace.md |