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Document assoc-lang-items.rs

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许杰友 Jieyou Xu (Joe) 2024-12-08 14:24:23 +08:00
parent 5e07f6e197
commit 1e3328dd72
2 changed files with 18 additions and 4 deletions
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14
tests/ui/assoc-lang-items.rs
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@ -1,3 +1,17 @@
//! Check that associated items can be marked as lang items, so that they don't have to be looked up
//! by name or by definition order indirectly.
//!
//! This test is not *quite* high-fidelity: it checks that you can use lang items on associated
//! items by looking at the error message *as a proxy*. That is, the error message is about
//! undefined lang items and not invalid attribute target, indicating that it has reached lang item
//! machinery (which is relying on knowing the implementation detail). However, it's annoying to
//! write a full-fidelity test for this, so I think this is acceptable even though it's not *great*.
//!
//! This was implemented in <https://github.com/rust-lang/rust/pull/72559> to help with
//! <https://github.com/rust-lang/rust/issues/70718>, which is itself relevant for e.g. `Fn::Output`
//! or `Future::Output` or specific use cases like [Use `T`'s discriminant type in
//! `mem::Discriminant<T>` instead of `u64`](https://github.com/rust-lang/rust/pull/70705).
#![feature(lang_items)]
trait Foo {

8
tests/ui/assoc-lang-items.stderr
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@ -1,23 +1,23 @@
error[E0522]: definition of an unknown lang item: `dummy_lang_item_1`
--> $DIR/assoc-lang-items.rs:4:5
--> $DIR/assoc-lang-items.rs:18:5
|
LL | #[lang = "dummy_lang_item_1"]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ definition of unknown lang item `dummy_lang_item_1`
error[E0522]: definition of an unknown lang item: `dummy_lang_item_2`
--> $DIR/assoc-lang-items.rs:7:5
--> $DIR/assoc-lang-items.rs:21:5
|
LL | #[lang = "dummy_lang_item_2"]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ definition of unknown lang item `dummy_lang_item_2`
error[E0522]: definition of an unknown lang item: `dummy_lang_item_3`
--> $DIR/assoc-lang-items.rs:10:5
--> $DIR/assoc-lang-items.rs:24:5
|
LL | #[lang = "dummy_lang_item_3"]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ definition of unknown lang item `dummy_lang_item_3`
error[E0522]: definition of an unknown lang item: `dummy_lang_item_4`
--> $DIR/assoc-lang-items.rs:17:5
--> $DIR/assoc-lang-items.rs:31:5
|
LL | #[lang = "dummy_lang_item_4"]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ definition of unknown lang item `dummy_lang_item_4`