Fix pretty printing unsafe match arms

[aochagavia]

Closes #19077

I would appreciate any guidance on how to write a test for this. I saw some examples in test/pretty, but there are different ways to test... With or without .pp files, with a pp-exact comment, etc.

[rust-highfive]

Warning

• These commits modify unsafe code. Please review it carefully!

[aochagavia]

The warning of rust-highfive is not correct... I guess he performs a case-insensitive search for the word unsafe.

[ghost]

@aochagavia I think pp-exact is probably the best way to go. With your change something like this:

fn main() {

    match true {
        true if true => (),
        false => unsafe { },
        true => { }
        false => (),
    }

}

should pretty-print as-is.

(it may be worth tweaking the pretty printer not to put the extra whitespace in between { } if you feel up for it)

[aochagavia]

A problem here is that pretty printing seems to be broken for match.

For example, the following code:

fn main() {
    match true {
        true => { }
        false => { }
    }
}

Is formatted as:

fn main() { match true { true => { } false => { } } }

[ghost]

@aochagavia It's not really broken so much as it's trying to be space efficient - this is probably an artifact of an old Rust coding style. If the match expression is sufficiently big, the pretty printer will use line-breaks. I tested the example I pasted and I think it should work well for your test.

[aochagavia]

Why is it better to have {} instead of { }? Is there a convention about that?

[aochagavia]

btw. I have added the test

[ghost]

@aochagavia I think there's a de-facto convention towards {}. But let's leave this for another day. Thanks!