Apply brace_style to extern blocks

[calebcartwright]

When brace_style is set to AlwaysNextLine then that should also apply to extern blocks. Until recently this config option was only utilized for items, but was recently updated to apply to unsafe blocks and makes sense to do the same for extern

Some relevant places to check in the code:

Perhaps format_extern, which adds a trailing space after the extern keyword or ABI. We don't want to leave trailing spaces at the end of a line so would need to make sure that there wouldn't be a trailing space left behind when the configured brace_style resulted in the opening brace going on the next line
https://github.com/rust-lang/rustfmt/blob/master/src/formatting/utils.rs#L149

And also format_foreign_mod/format_item

rustfmt/src/formatting/items.rs

Lines 317 to 327 in 4a88598

	fn format_item(&mut self, item: &Item<'_>) {
	self.buffer.push_str(&item.abi);
	let snippet = self.snippet(item.span);
	let brace_pos = snippet.find_uncommented("{").unwrap();
	self.push_str("{");
	if !item.body.is_empty() || contains_comment(&snippet[brace_pos..]) {
	// FIXME: this skips comments between the extern keyword and the opening
	// brace.
	self.last_pos = item.span.lo() + BytePos(brace_pos as u32 + 1);

So when brace_style is set to AlwaysNextLine rustfmt would emit:

extern "C"
{
    fn foo(x: i32);
}

otherwise

extern "C" {
    fn foo(x: i32);
}

[IceTDrinker]

I'll take a look tomorrow, not going to be super available next week, so unsure for a reasonable ETA

[blesson3]

I just opened a PR (#4450) that allows extern blocks to conform to brace_style when set to AlwaysNextLine.

I also made sure that there are no trailing spaces for the extern "C" line after formatted.

[IceTDrinker]

I also have a proposal not based on fixing the strings after the fact, I'll push it on my repo and not open a PR to spam you guys : https://github.com/IceTDrinker/rustfmt/tree/brace_style_always_new_line_extern

I took the liberty to reuse @blesson3 test files

Main issue I see with current extern formatting is comments between extern keyword and ABI string and comment between ABI string and opening bracket. Could be a separate issue

Cheers

[calebcartwright]

Thanks @IceTDrinker! I did go ahead and merge @blesson3's PR (actually didn't see the comments here til after) as it addressed the main issue. Please still feel free to submit your PR if you think we can improve, capture comments, etc.

[blesson3]

This feature has regressed in the master branch. I cannot seem to find where my PR (#4450) changes went. Either this is intentional or somehow those commits were lost. @calebcartwright I recommend this issue be re-opened until this is clarified.

[calebcartwright]

@blesson3 - please see #4801

[blesson3]

I had not seen that, thanks!