Second line of Comment is incorrectly indentated

[davidBar-On]

Input

fn main() {
    let v = [
        "A", /* item A comment */
        "BBBBBB", /* item BBBBBB comment line 1
                   * item BBBBBB comment line 2 */
        "CCC", /* item CCC comment */
    ];
}

Output

fn main() {
    let v = [
        "A", /* item A comment */
        "BBBBBB", /* item BBBBBB comment line 1
              * item BBBBBB comment line 2 */
        "CCC", /* item CCC comment */
    ];
}

Expected output

Same as input. The second line of the comment to "BBBBBB" is wrongly aligned to the "A" comment. (Based on test case from #4518.)

Meta

• rustfmt version: rustfmt 2.0.0-rc.2-nightly (30bda450 2020-11-18)
• From where did you install rustfmt?: self build

[calebcartwright]

Another case where this is technically true, but it's really tough to justify mutli-line block comments that are trailing the element they are supposed to be associated to within a sequence. This seems like a very uncommon comment style, and I'd argue that it's significantly more difficult to read than the more common style of having multiline comments above the associated item.

Even with such a relatively simple example, it's tough from a visual glance to quickly grok what the second BBBBB line is supposed to be associated to.

If there's an easy, noninvasive code change that account for this then that'd be fine, but if it takes anything non trivial (either in implementation or runtime overhead) then I don't think that would be justified.

A big motivating factor that played into decisions when the style guide was defined was to try to avoid rightward drift and visual alignment. A comment style like this is much more likely to run out to the right and potentially run into width limits since every line of the comment block will be extended by the length of the element plus associated overhead

[davidBar-On]

I believe there is a simple solution which is backward compatible when multiline comments are not used (which from what you wrote I understand is true for almost all cases). This is by taking the approach that each multiline comment is considered a "comments indentation group" of its own, so each multiline will be indented per the list item it belongs to.

I already have a draft change using this approach, which is basically adding two if statements, one in write_list() and one in max_width_of_item_with_post_comment(). If you believe this approach may be acceptable, I can submit a PR with the changes.

Taking the above approach, the output of the original example will be:

fn main() {
    let v = [
        "A", /* item A comment */
        "BBBBBB", /* item BBBBBB comment line 1
                   * item BBBBBB comment line 2 */
        "CCC", /* item CCC comment */
    ];
}

Following is a more comprehensive expected output example. Note that A / EEE are a group and CCC / DDDDD are a group. On the other hand both BBBBBB and F are on their own group.

fn main() {
    let v = [
        "A",   /* item A comment */
        "EEE", /* item E comment */
        "BBBBBB", /* item B comment line 1
                   * item B comment line 2 */
        "F", /* item F comment line 1
              * item F comment line 2 */
        "CCC",   /* item C comment */
        "DDDDD", /* item D comment */
    ];
}

[calebcartwright]

If you believe this approach may be acceptable, I can submit a PR with the changes.

Feel free to open a PR with suggested changes, I was just speaking in general terms that uncommon/discouraged styles of comment places like this aren't a top priority, so any code changes have to be weighed accordingly