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Require parens for chained comparison binops#1643

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dtolnay merged 2 commits intomasterfrom
chainedcompare
May 11, 2024
Merged

Require parens for chained comparison binops#1643
dtolnay merged 2 commits intomasterfrom
chainedcompare

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@dtolnay dtolnay commented May 11, 2024

Previously, syn incorrectly accepted $a == $b == $c as an expression:

Expr::Binary {
    left: Expr::Binary {
        left: $a,
        op: BinOp::Eq,
        right: $b,
    },
    op: BinOp::Eq,
    right: $c,
}

but this is not a legal expression in Rust. The expression either needs to be parenthesized (($a == $b) == $c or $a == ($b == $c)) or turned into a conjunction ($a == $b && $b == $c).

error: comparison operators cannot be chained
 --> src/main.rs:2:18
  |
2 |     let _ = true == true == true;
  |                  ^^      ^^
  |
help: split the comparison into two
  |
2 |     let _ = true == true && true == true;
  |                          +++++++

@dtolnay dtolnay merged commit c79cea1 into master May 11, 2024
@dtolnay dtolnay deleted the chainedcompare branch May 11, 2024 03:28
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