fix: ide-assists, gen from impl for enum indent

[A4-Tacks]

mod foo {
    enum Foo {
        $0String(String),
    }
}

Old output:

mod foo {
    enum Foo {
        String(String),
    }

impl From<String> for Foo {
    fn from(v: String) -> Self {
        Self::String(v)
    }
}
}

Fixed output:

mod foo {
    enum Foo {
        String(String),
    }

    impl From<String> for Foo {
        fn from(v: String) -> Self {
            Self::String(v)
        }
    }
}

[davidbarsky]

what are the values (3 and 4) here?

[A4-Tacks]

• 4 is the number of spaces for indent
• 3 is an approximate expected number of lines used for optimization

[davidbarsky]

can you pull out the split_once/map_or into a separate statement? it makes it a bit tricky to understand what the condition here actually is.

[A4-Tacks]

Ok

[Veykril]

This is the wrong kind of API here, we already have indentation things that work on the AST. If those don't suffice this will have to wait until we have our own formatter to pretty print nodes with. Our assist output is currently best effort due to the lack of that

[A4-Tacks]

Currently, many ide-assists directly generate strings. With this API, I can quickly fix nearly ten ide-assists implements

[A4-Tacks]

Can we keep this API and continue?