Fix grammar for LiteralPattern regarding -
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traviscross
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traviscross
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May 15, 2025
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| _Literal patterns_ match exactly the same value as what is created by the literal. | ||
| Since negative numbers are not [literals], literal patterns also accept an optional minus sign before the literal, which acts like the negation operator. | ||
| _Literal patterns_ match exactly the same value as what is created by the literal. Since negative numbers are not [literals], literals in patterns may be prefixed by an optional minus sign, which acts like the negation operator. |
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I reworded this a bit, as it seemed to be saying two conflicting things. On the one hand, "literal patterns" match exactly what's parsed as a literal. But on the other, it said that "literal patterns" accept a minus sign, which isn't part of the literal. It seems better to just say that literals in patterns may be prefixed by an optional minus sign.
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We had documented that only numeric literals in patterns can be
prefixed by `-` (minus), but the Rust parser happily accepts a minus
ahead of all literals in patterns. E.g.:
```rust
match () {
-true | -false => (),
-'x' => (),
-b'x' => (),
-"x" => (),
-r"x" => (),
-br"x" => (),
-c"x" => (),
-cr"x" => (),
-1 => (),
-1.1 => (),
}
```
In the compiler, this happens in `Parser::parse_literal_maybe_minus`
and `Token::can_begin_literal_maybe_minus`.
Let's fix this by defining `LiteralPattern` as a `LiteralExpression`
optionally prefixed by the minus sign. This better matches how the
`rustc` AST models this.
ehuss
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We had documented that only numeric literals in patterns can be prefixed by
-(minus), but the Rust parser happily accepts a minus ahead of all literals in patterns. E.g.:In the compiler, this happens in
Parser::parse_literal_maybe_minusandToken::can_begin_literal_maybe_minus.Let's fix this by defining
LiteralPatternas aLiteralExpressionoptionally prefixed by the minus sign. This better matches how therustcAST models this.cc @ehuss