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False branches_sharing_code for bodies with macro call(s) #14873

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msix29 opened this issue May 22, 2025 · 4 comments · May be fixed by #14907
Open

False branches_sharing_code for bodies with macro call(s) #14873

msix29 opened this issue May 22, 2025 · 4 comments · May be fixed by #14907
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@profetia
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C-bug Category: Clippy is not doing the correct thing I-false-positive Issue: The lint was triggered on code it shouldn't have L-nursery Lint: Currently in the nursery group

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@msix29
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msix29 commented May 22, 2025 •
edited by rustbot
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Summary

If needed, this is the file (currently editing - line numbers given by the lint may be off by a small amount).

Lint Name

branches_sharing_code

Reproducer

Given:

let equal_or_colon = if parse_args.is_type {
    maybe_next_token!(lexer, temp, TokenType::Symbol(Symbol::Colon));
    temp
} else {
    maybe_next_token!(lexer, temp, TokenType::Symbol(Symbol::Equal));
    temp
};

The maybe_next_token! macro takes a pat as the final argument (thus this can't be refactored). Clippy thinks both macro calls are the same when they clearly aren't. Full message:

all if blocks contain the same code at the start
for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#branches_sharing_code
`#[warn(clippy::branches_sharing_code)]` implied by `#[warn(clippy::nursery)]`clippy[branches_sharing_code](rust-analyzer-diagnostics-view:/diagnostic%20message%20[3]?3#file:///home/Ryo/dev/rust/luau/parser/src/impl/value/table.rs)

and

table.rs(113, 21): consider moving these statements before the if: `maybe_next_token!(lexer, temp, TokenType::Symbol(Symbol::Colon));
let equal_or_colon = if parse_args.is_type {`

Version

rustc 1.87.0 (17067e9ac 2025-05-09)
binary: rustc
commit-hash: 17067e9ac6d7ecb70e50f92c1944e545188d2359
commit-date: 2025-05-09
host: x86_64-unknown-linux-gnu
release: 1.87.0
LLVM version: 20.1.1

Additional Labels

No response
@msix29 msix29 added C-bug Category: Clippy is not doing the correct thing I-false-positive Issue: The lint was triggered on code it shouldn't have labels May 22, 2025
@samueltardieu
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samueltardieu commented May 23, 2025 •
edited
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@rustbot label +L-nursery

@rustbot rustbot added the L-nursery Lint: Currently in the nursery group label May 23, 2025
@donkomura
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@msix29 Cloud you please give us a simplified reproducer?

@msix29
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msix29 commented May 27, 2025 

#![warn(clippy::nursery)]

fn foo() -> i32 {
    todo!()
}
fn bar() -> i32 {
    todo!()
}

macro_rules! qux {
    ($a:ident, $b:ident, $condition:expr) => {
        let $a = foo();
        let $b = bar();

        if $condition {
            "." // any random value to avoid other warnings.
        } else {
            ""
        }
    };
}

fn main() {
    let _ = if false {
        qux!(a, b, a == b);
    } else {
        qux!(a, b, a != b);
    };
}

The error would be valid if it isn't a macro call, but being a macro call, you can't really do anything about it.

@profetia
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@rustbot claim

@profetia profetia linked a pull request May 28, 2025 that will close this issue
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Labels
C-bug Category: Clippy is not doing the correct thing I-false-positive Issue: The lint was triggered on code it shouldn't have L-nursery Lint: Currently in the nursery group
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Fix branches_sharing_code suggests wrongly when dealing with macros profetia/rust-clippy
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@samueltardieu @donkomura @profetia @rustbot @msix29