Trailing comments on multi byte lines of a wrapped Vec are indented strangely

[is8ac]

fn main() {
    let _ = "foo"; // Comment
    let _ = "foo bar baz"; // Comment
    let _ = "quaks"; // Comment

    vec![
        "foo",         // Comment
        "foo bar baz", // Comment
        "quaks",       // Comment
    ];

    let _ = "foo"; // Comment
    let _ = "𝕋𝕙𝕖 𝕢𝕦𝕚𝕔𝕜 𝕓𝕣𝕠𝕨𝕟 𝕗𝕠𝕩"; // Comment
    let _ = "管道"; // Comment

    vec![
        "foo",                                                                 // Comment
        "𝕋𝕙𝕖 𝕢𝕦𝕚𝕔𝕜 𝕓𝕣𝕠𝕨𝕟 𝕗𝕠𝕩", // Comment
        "管道",                                                              // Comment
    ];
}

• Single byte characters in multiple statements does not align.
• Single byte characters in a Vec does allign.
• Multi byte characters in multiple statements does not align, same as with single byte.
• Multi byte characters a Vec aligns in a strange way.

I hypothesise that rustfmt is counting bytes not characters.

rustfmt --version:

rustfmt 1.4.37-nightly (539d7bd 2021-06-14)

Same behavior under

rustfmt 1.4.36-stable (7de6968 2021-02-07)

This bug was originally found by @LunarTulip

[calebcartwright]

hi thanks for reaching out with the report! rustfmt isn't supposed to visually align anything by default but there's a known bug (#4108) where it not only attempts to do so, but often does so incorrectly. Accordingly I'm going to go ahead and close this and track in #4108 which you may want to subscribe to for updates. As part of addressing the issue we'll add test cases for the snippets you've provided here.

Thanks again!