max_width not obeyed in match arm tuple

Summary

rustfmt reformats a multi-line tuple pattern in a match arm into a single
line that exceeds max_width = 80.

I tried to format this code:

#[derive(Clone, Copy)]
enum ExampleTypeX {
    VariantAlphaSampleXYZ,
    VariantBetaXYZ,
}

fn demo(lhs: ExampleTypeX, rhs: ExampleTypeX) {
    match (lhs, rhs) {
        (
            ExampleTypeX::VariantAlphaSampleXYZ,
            ExampleTypeX::VariantBetaXYZ,
        ) => unsafe {
        }
        _ => {}
    }
}

fn main() {}

Expected behavior

rustfmt should preserve the multi-line tuple pattern, or otherwise format the
arm so that it does not exceed max_width = 80.

Actual behavior

rustfmt rewrites it to:

fn demo(lhs: ExampleTypeX, rhs: ExampleTypeX) {
    match (lhs, rhs) {
        (ExampleTypeX::VariantAlphaSampleXYZ, ExampleTypeX::VariantBetaXYZ) => unsafe {
        },
        _ => {}
    }
}

The formatted match arm is 87 columns wide, exceeding max_width = 80.

Configuration

rustfmt.toml:

max_width = 80

Reproduction Steps

1. Create a Rust file with the example above.

2. Create a rustfmt.toml containing:

   max_width = 80
   

3. Run cargo fmt (or rustfmt on the file).

4. Observe that the tuple pattern in the match arm is collapsed to one line.

5. Observe that the resulting line exceeds max_width.

Meta

rustfmt 1.8.0-stable (ed61e7d7e2 2025-11-07)