Change default value for blank_lines_upper_bound from 1 to 5

[LukasKalbertodt]

I explained my reasoning in this comment, copied here for convenience:

May I ask why the default is 1? That's basically the only thing where I disagree with the standard style. I'd love to avoid having a rustfmt.toml.

My reasoning: more space between items is a useful visual separator. Rust files tend to get fairly long and often contain many different kinds of items. Compare that to some other languages, where there is usually just one class per file, for example. So in Rust files I often have "blocks" of items that somehow belong together. Maybe it's something like:

struct A;

impl A {
}

impl Display for A {
}


struct B;

impl B {
}

impl Display for B {
}

I think it should be pretty clear that some items belong closer together than others (specifically: all the A things should be somehow separated from all B things). And this is just a small example. Often I have multiple "layers" of items. So I naturally want to have larger separation between items of different "blocks". I usually use up to three blank lines between items.

So I'd like to propose increasing the default value to 3 or even 5. I think rustfmt shouldn't really be getting in the way of the programmer in this case.

But maybe people have strong opinions against large separators. I tried searching for previous discussions about this, but I found nothing. So please let me know either way!

As people agreed with my comment and no one had any counter argument, I just changed it now.

I hope this is a step in stabilizing blank_lines_upper_bound and blank_lines_lower_bound.

CC @ForLoveOfCats

[LukasKalbertodt]

My editor removed some trailing whitespace in this file. If I should remove those stray changes, just tell me.

[LukasKalbertodt]

Will fix the tests soon, probably later today.

[calebcartwright]

I believe the default values are based on the style guide, specifically https://github.com/rust-dev-tools/fmt-rfcs/blob/master/guide/guide.md#blank-lines.

IMHO the default values for the options in rustfmt need to align with the guide.

[ForLoveOfCats]

As I was CC-ed I figured I might as well throw my two cents in. In my opinion the defaults need not change, I just would really like to be able to configure this without using the nightly toolchain

[calebcartwright]

@ForLoveOfCats - It may not be long lived, but note that you can use unstable rustfmt options on stable via cli config overrides

cargo fmt -- --config blank_lines_upper_bound=3

[LukasKalbertodt]

I found the original thread where this topic has been discussed: rust-lang/style-team#57. I commented there, explaining my position. So yeah, I guess we first need to fix the style guide, then rustfmt. So I'll close this PR for now.