rustfmt removes crucial code from macro calls (regression)

[nazar-pc]

Probably related to #6418, but not 100% sure.

rustfmt recently started formatting code like this incorrectly:

frame_support::construct_runtime!(
    pub struct Test {
        System: frame_system = 0,
        SelfDomainId: pallet_domain_id = 1,
    }
);

Specifically, it removes = NUMBER for some reason, resulting in this:

frame_support::construct_runtime!(
    pub struct Test {
        System: frame_system,
        SelfDomainId: pallet_domain_id,
    }
);

This is incorrect and not an equivalent change.

Affected version:

rustfmt 1.8.0-nightly (426d173423 2024-12-21)

Version that I used previously and that worked correctly:

rustfmt 1.8.0-nightly (4392847410 2024-10-21)

[ytmimi]

Thanks for the report. I tracked this change in behavior back to rust-lang/rust#129514

[nazar-pc]

Note that it also removes values which are not contiguous (let's say if = 0 is replaced with = 60), it just removes them all regardless.

[ytmimi]

@nazar-pc sorry, but I'm having a hard time understanding what you're getting at. Could you provide a code snippet?

[nazar-pc]

Sure:

frame_support::construct_runtime!(
    pub struct Test {
        System: frame_system = 60,
        SelfDomainId: pallet_domain_id = 1,
    }
);

In this case both will be removed too. I just assumed that in some cases it might remove things due to considering them being "the default", but no.

[ytmimi]

Thanks for the update. No, I don't think that's the case. An explanation for what's going on here can be found at rust-lang/rust#134668