Validity of single line while/until rule

Referring to this: https://github.com/bbatsov/ruby-style-guide#while-as-a-modifier

I would argue that the single line version of the syntax is a rare example of ruby being surprising and inconsistent.

We all regularly use something like

foo = bar unless bar.nasty?

This is nice. It's clear that foo = bar is the last line run if it gets run at all. If this is at the end of a method for some silly reason you're safe knowing bar will be returned under the right circumstances.

but try this to fix your nasty situation:

bar = bar.next_sibling while bar.nasty?

foo = bar.next is not the real last line run. It only looks like it. In fact the last operation is the close of the while loop which returns nil.

For this reason I prefer to keep that explicit with

while bar.nasty?
  bar = bar.next_sibling
end

Start with the linked Ruby style guide section, “while as a modifier,” and compare its current guidance with the single-line examples in this issue. Done means the guide clearly resolves whether the single-line while/until form should be discouraged in favor of an explicit loop, with the rationale and examples aligned.