comment in let statement prevents formatting

When running the rustfmt on a line that contains a block comment, the lines doesn't get formatted at all. My expectation is that the line gets formatted correctly as if the comment block wasn't there.
rustfmt version: rustfmt 1.5.1-stable
Test case:

fn main() {
    let tup = (1, 2);
    let (first,         second)/* your pattern here */ = tup;
}

Expectation:

fn main() {
    let tup = (1, 2);
    let (first, second)/* your pattern here */ = tup;
}

Actual:

fn main() {
    let tup = (1, 2);
    let (first,         second)/* your pattern here */ = tup;
}

Start by reproducing the issue with rustfmt 1.5.1-stable using the let statement and block comment shown in the issue. Trace how rustfmt handles comments in let-pattern formatting, then add coverage for this example and confirm the spacing is normalized while preserving the comment.