Rustfmt removes trailing comma in argument list of macro input that looks like a function #6273

jdonszelmann · 2024-08-09T12:58:48Z

Breaking example:

macro_rules! almost_function {
    (fn $name: ident($param: ident: $ty: ty,) $b: block) => {};
}

fn main() {
    almost_function!(
        fn x(something: usize,) {}
    );
}

note that this macro requires a trailing coma

I expected to see this happen: rustfmt doesn't remove the trailing comma in the input since it's required for this code to compile.
Instead, this happened: rustfmt reformats it to:

macro_rules! almost_function {
    (fn $name: ident($param: ident: $ty: ty,) $b: block) => {};
}

fn main() {
    almost_function!(
        fn x(something: usize) {}
    );
}

Note: alternatives that don't produce this problem:

macro_rules! almost_function {
    ($name: ident($param: ident: $ty: ty,) $b: block) => {};
}

fn main() {
    almost_function!(
        x (something: usize,) {}
    );
}

macro_rules! almost_function {
    (fn $name: ident $param: ident: $ty: ty, $b: block) => {};
}

fn main() {
    almost_function!(
        fn x something: usize, {}
    );
}

macro_rules! almost_function {
    (fn $name: ident [$param: ident: $ty: ty,] $b: block) => {};
}

fn main() {
    almost_function!(
        fn x [something: usize,] {}
    );
}

From those experiments, we can see that rustfmt only does it if it looks a lot like a function

Meta

rustfmt --version --verbose:

rustfmt 1.7.0-stable (25ef9e3 2024-04-09)

The text was updated successfully, but these errors were encountered:

ytmimi · 2024-08-09T13:32:39Z

Similar to #6228. In this case it would be better to write the macro definition to make the comma optional (or not required at all).

ytmimi closed this as not planned Won't fix, can't repro, duplicate, stale Aug 9, 2024

ytmimi added the a-macros label Aug 9, 2024

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Rustfmt removes trailing comma in argument list of macro input that looks like a function #6273

Rustfmt removes trailing comma in argument list of macro input that looks like a function #6273

jdonszelmann commented Aug 9, 2024

ytmimi commented Aug 9, 2024

Rustfmt removes trailing comma in argument list of macro input that looks like a function #6273

Rustfmt removes trailing comma in argument list of macro input that looks like a function #6273

Comments

jdonszelmann commented Aug 9, 2024

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ytmimi commented Aug 9, 2024