Unhelpful messages on badly formed unapplySeq #9538
Description
scala> object X { def unapplySeq(x: Any): Option[String] = { Some(x.toString.toUpperCase) }}
defined object X
scala> val X(z) = "hi"
<console>:11: error: too many patterns for object X offering Boolean: expected 0, found 1
val X(z) = "hi"
^
scala> val X() = "hi"
<console>:11: error: error during expansion of this match (this is a scalac bug).
The underlying error was: type mismatch;
found : Option[String]
required: Boolean
val X() = "hi"
^