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add UI test + docs for E0789

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Ezra Shaw 2023-01-21 21:32:05 +13:00
parent 94a300b9b8
commit 00ff718da8
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5 changed files with 59 additions and 2 deletions
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2
compiler/rustc_error_codes/src/error_codes.rs
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@ -506,6 +506,7 @@ E0785: include_str!("./error_codes/E0785.md"),
E0786: include_str!("./error_codes/E0786.md"),
E0787: include_str!("./error_codes/E0787.md"),
E0788: include_str!("./error_codes/E0788.md"),
E0789: include_str!("./error_codes/E0789.md"),
E0790: include_str!("./error_codes/E0790.md"),
E0791: include_str!("./error_codes/E0791.md"),
E0792: include_str!("./error_codes/E0792.md"),
@ -645,5 +646,4 @@ E0792: include_str!("./error_codes/E0792.md"),
// E0721, // `await` keyword
// E0723, // unstable feature in `const` context
// E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
E0789, // rustc_allowed_through_unstable_modules without stability attribute
}

30
compiler/rustc_error_codes/src/error_codes/E0789.md Normal file
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@ -0,0 +1,30 @@
#### This error code is internal to the compiler and will not be emitted with normal Rust code.
The internal `rustc_allowed_through_unstable_modules` attribute must be used
on an item with a `stable` attribute.
Erroneous code example:
```compile_fail,E0789
// NOTE: both of these attributes are perma-unstable and should *never* be
// used outside of the compiler and standard library.
#![feature(rustc_attrs)]
#![feature(staged_api)]
#![unstable(feature = "foo_module", reason = "...", issue = "123")]
#[rustc_allowed_through_unstable_modules]
// #[stable(feature = "foo", since = "1.0")]
struct Foo;
// ^^^ error: `rustc_allowed_through_unstable_modules` attribute must be
// paired with a `stable` attribute
```
Typically when an item is marked with a `stable` attribute, the modules that
enclose the item must also be marked with `stable` attributes, otherwise the
item becomes *de facto* unstable. `#[rustc_allowed_through_unstable_modules]`
is a workaround which allows an item to "escape" its unstable parent modules.
This error occurs when an item is marked with
`#[rustc_allowed_through_unstable_modules]` but no supplementary `stable`
attribute exists. See [#99288](https://github.com/rust-lang/rust/pull/99288)
for an example of `#[rustc_allowed_through_unstable_modules]` in use.