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Avoid specifying "last import wins" for MBEs #2057

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Avoid specifying "last import wins" for MBEs #2057

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7 changes: 6 additions & 1 deletion src/macros-by-example.md
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Expand Up @@ -390,7 +390,12 @@ When `macro_use` is used on a module, the module's macro scope extends beyond th
r[macro.decl.scope.macro_use.prelude]
Specifying `macro_use` on an `extern crate` declaration in the crate root imports exported macros from that crate.

Macros imported this way are imported into the [`macro_use` prelude], not textually, which means that they can be shadowed by any other name. While macros imported by `macro_use` can be used before the import statement, in case of a conflict, the last macro imported wins.
Macros imported this way are imported into the [`macro_use` prelude], not textually, which means that they can be shadowed by any other name. Macros imported by `macro_use` can be used before the import statement.

> [!NOTE]
> `rustc` currently prefers the last macro in case of conflict. Don't rely on this. This behavior is unusual, as imports in Rust are generally order-independent. This behavior of `macro_use` may change in the future.
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If there's a good issue to cite for this, we can cite it here.

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I've opened rust-lang/rust#148025 for this.

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Thanks. Added it here.

>
> For details, see [Rust issue #148025](https://github.com/rust-lang/rust/issues/148025).

When using the [MetaWord] syntax, all exported macros are imported. When using the [MetaListIdents] syntax, only the specified macros are imported.

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