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Rollup merge of #124389 - CensoredUsername:master, r=petrochenkov

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Add a warning to proc_macro::Delimiter::None that rustc currently does not respect it.

It does not provide the behaviour it is indicated to provide when used in a proc_macro context.

This seems to be a bug, (https://github.com/rust-lang/rust/issues/67062), but it is a long standing one, and hard to discover.

This pull request adds a warning to inform users of this issue, with a link to the relevant issue, and a version number of the last known affected rustc version.
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León Orell Valerian Liehr 2024-05-23 20:09:08 +02:00 committed by GitHub
commit f862f6d292
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library/proc_macro/src/lib.rs
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@ -815,6 +815,18 @@ pub enum Delimiter {
/// "macro variable" `$var`. It is important to preserve operator priorities in cases like
/// `$var * 3` where `$var` is `1 + 2`.
/// Invisible delimiters might not survive roundtrip of a token stream through a string.
///
/// <div class="warning">
///
/// Note: rustc currently can ignore the grouping of tokens delimited by `None` in the output
/// of a proc_macro. Only `None`-delimited groups created by a macro_rules macro in the input
/// of a proc_macro macro are preserved, and only in very specific circumstances.
/// Any `None`-delimited groups (re)created by a proc_macro will therefore not preserve
/// operator priorities as indicated above. The other `Delimiter` variants should be used
/// instead in this context. This is a rustc bug. For details, see
/// [rust-lang/rust#67062](https://github.com/rust-lang/rust/issues/67062).
///
/// </div>
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
None,
}