fixed => () to => {}

[lukebhan]

This solves issue #4065. It only is really 3 lines in matches.rs, but the other files need to be changed as they all include some sort of => ().

[topecongiro]

Thank you for the PR!

Could you make sure that the trailing comma is added when match_block_trailing_comma is set to true?

[lukebhan]

I am having some issues with this trailing comma. If I just change the body_str instead of the match statement with something like

if body_str == "()" {
    body_str = "{}";
}

then the target file with the comma:

match {
    1 => {},
}

will be told by rustfmt to remove the comma, but then the source file wont match since the source file yields

match {
    1 => {},
} 

because rustfmt must treat () differently then {}. Do you have any ideas on where to start to solve this issue? Maybe by looking at ExprKind::tup ? in match arms. I'm not really sure.