Spurious unused patvar warning when used pattern is a type pattern in a for

[martijnhoekstra]

reproduction steps

using Scala 2,

for {
  (_, _) <- Option(1 -> 2)
  (c: Int, _) = 3 -> 4
} {
  println(c)
}

under -Wunused:patvar

pattern var c in value $anonfun is never used: use a wildcard _ or suppress this warning with c@_

problem

c is used, but reported as unused

[dwijnand]

In the desugaring there will be extra patterns which end up being unused. It's unfortunate. I'll let @som-snytt close as duplicate if this is documented somewhere already.

[SethTisue]

#10287 ?

[som-snytt]

Thanks @SethTisue I couldn't find it and then got distracted looking at old tickets.

Because sometimes on a cold autumn day, it's nice to settle down under a wool blanket and take out your collection of old tickets and sort them again, fondly recalling bygone days of frustration and puzzlement.

[dwijnand]

Duplicate of #10287