Comment before semicolon prevents formatting expression

This code:

let     unformatted =    {     1}
// comment
;

or this:

let     unformatted =    {     1} // comment
;

will pass through rustfmt unchanged. Removing the comment causes the code to be formatted correctly, and other expressions are not affected.

You may be asking "why would anybody want to do this?" I keep a semicolon on its own line in a long chain of builder methods that I frequently have to modify, e.g.

builder
    .configure(cfg_fn1)
    .configure(cfg_fn2)
    // .configure(cfg_fn3)
    ;

Playground

Occurs in rustfmt 1.5.1-nightly (b44197a 2022-09-05) and rustfmt 1.5.1-stable (4b91a6e 2022-08-08).

Start with the minimal examples in the issue or the linked Rust Playground, using the reported rustfmt versions to reproduce the behavior. Trace how rustfmt handles a comment before a semicolon in an expression, then verify that both examples are formatted while the builder-chain case remains supported.