"short" config option for let-else statements?

[calebcartwright]

Refs #4914

When the style team was discussing the formatting rules for let-else, an unsurprisingly key consideration was if/when/how the entire statement could be formatted on one line. As noted in the now-codified rules, there is a "if short enough" element to the required conditions for one-line formatting in the spirit of being consistent with other prescriptions in the current style guide edition.

Specifically https://github.com/rust-lang/rust/blob/master/src/doc/style-guide/src/statements.md#single-line-let-else-statements

With an intentional clause added to note the anticipated need for configurability in rustfmt:

Formatters may allow users to configure the value of the threshold used to determine whether a let-else statement is short.

Therefore the only real question IMO is: do we reuse an existing option, e.g. single_line_if_else_max_width, or do we introduce a new option, e.g. single_line_let_else_max_width), and if the latter then what should the default value be?

My inclination is to do the latter (largely based on past experiences of multi-use config options being insufficiently flexible and causing problems), likely with the same default value as single_line_if_else_max_width though I feel less strongly about this.

What are your thoughts @ytmimi?

cc @rust-lang/style for awareness

[ytmimi]

I think it would be best to have a dedicated config to control the let-else formatting, so I'm leaning towards adding a single_line_let_else_max_width config option.

[joshtriplett]

Having a separate option makes sense, but I think that option should default to the same value as the existing top-level "short" threshold, so that changing that threshold by default will change all the other thresholds. That way, if someone wants to change all the thresholds they can do that in one place, and if they want to customize the individual thresholds they can set the individual options.

[calebcartwright]

Resolved via #5790

(edit: fixed issue number typo)

[digama0]

@calebcartwright The head comment on that PR says that it does not implement a "short" config option for let-else, so it seems like there is a contradiction somewhere

[calebcartwright]

Updated prior comment, thanks @digama0