Preserve blank line between match inner attrs and first arm

[ding-young]

Fixes #6005

Solution

This PR performs manual check for blank line in span between (inner attrs and first match arm) or (inner attrs and comment before match arm) and then adds it back.

Question

• Only single blank line is preserved. Should I preserve multiple blank lines instead of reducing them into single blank line?

[ytmimi]

I haven't reviewed the code yet, but I took a quick look at the test cases. When you have a moment can you add a test case where there's more than one blank line between the inner attrs and match arms. Additionally, can you add a test case where there are no blank lines between the inner attrs and match arms.

[ding-young]

@ytmimi I added test cases for multiple_blank_lines and no_blank_line each. Would you check whether it is desired formatting? Multiple blank lines are squashed into single blank line, and blank line is not added if there were no blank lines.

[ytmimi]

Thanks for another PR. Take a look at the feedback when you get a chance. I think we need to consider a few more cases, and extract the logic for blank_line_after_inner_attrs into a separate function.

[ytmimi]

Now that I'm seeing the !arms.is_empty() condition I think we should also add test cases showing how we reformat a match with inner attributes but no match arms.

[ytmimi]

Presumably the .find('/') call is searching for comments? I think it's more appropriate to use the Span from the last inner attribute instead of the open_brace_pos. I think using the open_brace_pos could lead to subtle formatting errors for these cases:

pub fn main() {
    match a {
        // comment before inner attributes
        #![attr1]
        #![attr2]
        _ => None,
    }

    match a {
        #![attr1]
        // comment between inner attributes
        #![attr2]
        _ => None,
    }
}

[ytmimi]

It would be nicer to extract the blank_line_after_inner_attrs calculation into a standalone function so that rewrite_match isn't responsible for this logic.