Issue

Add config to format like from this issue: #4108

Currently, this code:

fn foo(
    a: usize, // Meow
    b: f32, // Bark
) {
}

Is formatted into this:

fn foo(
    a: usize, // Meow
    b: f32,   // Bark
) {
}

This can confuse the reader into thinking that the two comments are related or follow each other, even when they are unrelated.

Changes

Add a config option of fn_post_comment_alignment that has two options:

1. SameIndent
2. SingleSpace

The SameIndent option preserves the current behavior, while the SingleSpace is the new behavior.

To make the configuration highly customizable, the write_list function takes an additional PostCommentAlignment parameter now. This will allow different behavior in different places, like in match statements or imports.