ICE formatting macro

[SamRodri]

Formatting this reduced code:

macro_rules! foo {
    ($self:ident) => {
        foo!($self.Bar::X)
    };
}

Causes an unknown panic in stable and nightly:

note: rustc 1.72.1 (d5c2e9c34 2023-09-13) running on x86_64-pc-windows-msvc

query stack during panic:
end of query stack

note: rustc 1.74.0-nightly (5ae769f06 2023-09-26) running on x86_64-pc-windows-msvc

query stack during panic:
end of query stack

The nightly ICE file can't be written in Windows (os error 123, rust-lang/rust#115180), in Linux it is is empty.

[ytmimi]

Thanks for the report. Out of curiosity, does that macro compile? I think the issue is with $self.Bar::X. If we change it to $self::Bar::X then we format without the ICE.

macro_rules! foo {
    ($self:ident) => {
        foo!($self::Bar::X)
    };
}

[SamRodri]

The original macro compiles, I reduced to this one.

Here is a reduced that compiles and causes the ICE:

macro_rules! foo {
    ($self:ident) => {
        foo!($self.Bar::X)
    };
    ($self:ident.$State:ident::$Discriminant:ident) => {

    };
}

pub struct Foo {}
impl Foo {
    pub fn set_state(&mut self) {
        foo!(self);
    }
}

I worked around the issue on my end by replacing the separators with comma $self,Bar,X so the issue is probably in that line like you said.

[ytmimi]

Thanks for putting together the minimal reproduction that compiles. That should help when diving into what's going on here.

[calebcartwright]

The ICE details getting swallowed is caused by rust-lang/rust#111529

[SamRodri]

Tested this again with rustfmt 1.8.0-stable (90b35a6239 2024-11-26), the issue is fixed. Not sure when it was fixed.