Problem with lexical_ordering deprecation

[brson]

The deprecation note says "Just call .cmp() on an Ordering" but is misleading.

16:52 < Dr-Emann> brson: If you have 2 Ords to compare to 2 other Ords, you can use (a1, b1).cmp(&(a2, b2)). If you only have 2 Orderings, you can write out the match that 
                  lexical_ordering contains, or use (o1, o2).cmp(&(Equal, Equal)). (but that's pretty unintuitive)
16:52 < Dr-Emann> Either way, the deprecation note should be changed. (or removed. I kinda like having that as a convenience function.)

[huonw]

Fwiw I think it was normally used like lexical_ordering(a1.cmp(&a2), b1.cmp(&b2)) where the as and bs are arbitrary Ord types. The replacement for that is (a1, b1).cmp(&(a2, b2)). (That said, the message is still unhelpful, maybe it should say "tuple" instead of "ordering".)

[aturon]

cc me.

[treeman]

Deprecation comment fixed by PR #16104.

[alexcrichton]

Thanks!