Doc of gereric items format error

[frank-king]

struct Foo<
    /// doc of T
    T,
    /// doc of N
    const N: u32,
>;

After rustfmt, it becomes

struct Foo<
    /// doc of T T,
    /// doc of N
    /// doc of N const N: u32,
>;

Occurred both on rustfmt 1.4.37-stable (2021-11-01) and 1.4.38-nightly (2021-12-02).

BTW, though fresh new to rustc and rustfmt, I'm interested in rust toolchains and would like to try fixing it on my own. Unless it blocks or I cannot fix it in two or three weeks, anyone else can pick it up.