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unused_parens lint should not complain about parens injected by macros #22451

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pnkfelix opened this issue Feb 17, 2015 · 4 comments
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A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@pnkfelix
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The following code fails to compile:

#![deny(unused_parens)]

macro_rules! add1_block {
    ($e:expr) => {
        { let val = 1; $e + val }
    }
}

macro_rules! add1_paren_block {
    ($e:expr) => {
        ({ let val = 1; $e + val })
    }
}

fn main() {
    let w = add1_block!(2);
    let x = { add1_block!(3) as u64 };
    let y = add1_paren_block!(4);
    let z = { add1_paren_block!(5) as u64 };

    println!("w: {} x: {} y: {} z: {}", w, x, y, z);
}

The parentheses in the macro are, in general, not unnecessary (for the explanation of why they are necessary, see #22450).

In general, it is silly for lint to be trying to fix style errors of this sort within macros. The place for such stylistic judgement, IMO, is within the original source code, not within macros.

@steveklabnik steveklabnik added the A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. label Feb 17, 2015
@steveklabnik
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Triage: no change.

@Mark-Simulacrum Mark-Simulacrum added the C-enhancement Category: An issue proposing an enhancement or a PR with one. label Jul 22, 2017
@steveklabnik
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Triage: no change

@jonas-schievink jonas-schievink added A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Apr 18, 2020
@camsteffen
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Fixed by #66983

@Dylan-DPC
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Closing this as fixed

@fmease fmease added A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. and removed A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. labels Dec 21, 2024
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Labels
A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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