Split impl<...> X for Y<...> at 'for'

[nagisa]

[fabric-and-ink]

I will take a look at this.

[fabric-and-ink]

@nrc can you maybe give me a hint, how to do this? My idea is simply to check if type + trait fits on one line. If not, break befose the for, indent and append the type rewrite. How do I check this condition in a nice way? Reformat the whole line (without the where-clause) with a big max_width and then check the length?

[nrc]

I would examine self_ty.rewrite, which is the concrete type of the impl declaration. If it contains a newline, then I would try reformatting it on a newline (this only requires changing the indent and budget supplied to the function). You could then compare the two versions, but I think that actually you could always put a newline before for in this case and use the second reformatting.

I think checking for a newline in the reformatted type is all you need to do - you will never affect the earlier part of the impl, and that is the only place that a linebreak can happen. You could also try this if the result of reformatting was None - in that case we couldn't fit the text into the budget, but if you give more space (by inserting the newline before for, then there might be enough space.

You should just check that when you do split, where clauses are still handled properly.

Also, you'll need to delay actually appending for until you have the final string for the type.

Ping me on irc if you want more info.

[fabric-and-ink]

Thanks @nrc!