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Oct 21, 2024
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2024: Add reserved syntax #326

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d882e1a
2024: Add reserved syntax
ehuss Oct 12, 2024
91e1efc
Say "reserved" rather than "reserving" in title
traviscross Oct 18, 2024
dceaaca
Make some editorial tweaks
traviscross Oct 18, 2024
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Make some editorial tweaks
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@traviscross
traviscross committed Oct 18, 2024
commit dceaaca744d1d68266a70f9ae4d4552583c7fc91
11 changes: 7 additions & 4 deletions src/rust-2024/reserved-syntax.md
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Expand Up @@ -10,11 +10,14 @@ More information may be found in the tracking issue at <https://github.com/rust-

## Details

[RFC 3593] reserved syntax in the 2024 Edition for guarded string literals that do not have a prefix to future-proof against future language changes. The 2021 Edition [reserved syntax][2021] for guarded strings with a prefix, such as `ident##"foo"##`. The 2024 Edition extends that to also reserve strings without the `ident` prefix.
[RFC 3593] reserved syntax in the 2024 Edition for guarded string literals that do not have a prefix to make room for possible future language changes. The 2021 Edition [reserved syntax][2021] for guarded strings with a prefix, such as `ident##"foo"##`. The 2024 Edition extends that to also reserve strings without the `ident` prefix.

There are two reserved syntaxes: One or more `#` immediately followed by a [string literal], and two or more `#` characters in a row.
There are two reserved syntaxes:

This reservation is done across an edition boundary because of interactions with tokenization and macros. For example, with the following macro:
- One or more `#` characters immediately followed by a [string literal].
- Two or more `#` characters in a row (not separated by whitespace).

This reservation is done across an edition boundary because of interactions with tokenization and macros. For example, consider this macro:

```rust
macro_rules! demo {
Expand Down Expand Up @@ -45,7 +48,7 @@ Starting in the 2024 Edition, the `#"foo"#` line and the `###` line now generate

## Migration

The [`rust_2024_guarded_string_incompatible_syntax`] lint will identify any tokens that match the reserved syntax, and will suggest a modification to insert spaces where necessary to ensure it continues to be parsed as separate tokens.
The [`rust_2024_guarded_string_incompatible_syntax`] lint will identify any tokens that match the reserved syntax, and will suggest a modification to insert spaces where necessary to ensure the tokens continue to be parsed separately.

The lint is part of the `rust-2024-compatibility` lint group which is included in the automatic edition migration. In order to migrate your code to be Rust 2024 Edition compatible, run:

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