Gives up on chains if any line is too long.

[ehuss]

If there is a method call chain, and just one call exceeds max_width, it seems like rustfmt gives up and doesn't format anything.

Example:

fn f() {
    foo("This text is under the max_width limit, and shouldn't cause any problems on its own.").long("But this line is extra long, and doesn't fit within 100 max_width. 1234567890123456789").baz().collect().unwrap();
}

No format changes will be applied to this. I'm also a bit surprised that error_on_line_overflow does not complain.

I would expect it to wrap each call chain element, even if one of them is too long, such as:

fn f() {
    foo("This text is under the max_width limit, and shouldn't cause any problems on its own.")
        .long("But this line is extra long, and doesn't fit within 100 max_width. 1234567890123456789")
        .baz()
        .collect()
        .unwrap();
}

All default settings.
rustfmt 1.4.8-nightly (afb1ee1 2019-09-08)

[calebcartwright]

Yeah, AFAICT that's because rustfmt is expecting to be able to rewrite each of the individual ChainItems to be able to format the Chain. When it attempts to rewrite that long string literal in the Chain it fails due to the length which results in the entire original chain being left as-is.

rustfmt/src/chains.rs

Lines 419 to 444 in a15e97f

	fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
	debug!("rewrite chain {:?} {:?}", self, shape);
	let mut formatter = match context.config.indent_style() {
	IndentStyle::Block => {
	Box::new(ChainFormatterBlock::new(self)) as Box<dyn ChainFormatter>
	}
	IndentStyle::Visual => {
	Box::new(ChainFormatterVisual::new(self)) as Box<dyn ChainFormatter>
	}
	};
	formatter.format_root(&self.parent, context, shape)?;
	if let Some(result) = formatter.pure_root() {
	return wrap_str(result, context.config.max_width(), shape);
	}
	// Decide how to layout the rest of the chain.
	let child_shape = formatter.child_shape(context, shape)?;
	formatter.format_children(context, child_shape)?;
	formatter.format_last_child(context, shape, child_shape)?;
	let result = formatter.join_rewrites(context, child_shape)?;
	wrap_str(result, context.config.max_width(), shape)
	}

I think I see a way we could support still wrapping chain elements like your expected output, though it would mean rustfmt emitting a line that exceeds the max_width (although the original line does too, and the wrapped version is more human friendly IMO even with the one longer line).

@topecongiro @scampi - any concerns with that? if not, then I'll take a look at implementing something for consideration.

[scampi]

@calebcartwright sounds good to me!

[agate-pris]

I think this issue is duplicate of #2970 .

[NilsIrl]

Using format_strings pretty much fixed it for me as strings get broken up and rustfmt can keep the line length below max_width.