Comment after associated type bound is incorrectly discarded

[jieyouxu]

Summary

Forked out of #6234.

I tried to format this code:

trait Foo {
    type Bar: Baz1 // what
    ;
}

Expected behavior

I expected to see this happen:

• Comment is preserved

Actual behavior

Instead, this happened:

• Comment is removed

trait Foo {
    type Bar: Baz1;
}

Configuration

rustfmt cli options used (if applicable):

$ rustfmt repro.rs --check

rustfmt configuration file (e.g. rustfmt.toml, if applicable): N/A

Reproduction Steps

Trivial.

Meta

rustfmt --version:

rustfmt 1.8.0-stable (01f6ddf758 2026-02-11)