specifying a type in pattern matching results in a spurious warning

[thesamet]

val x: String = "something"
x.foreach {
  case 's' => println("s")
  case c: Char => println(c)
} 

Results in:

[warn] 154 |        case c: Char                   => println(c)
[warn]     |             ^
[warn]     |this will always yield true, since `class Char` is a subclass of `class Char`

While it's true that I can just omit the : Char, the intent here was to increase readability by specifying the type. Feel free to close if this is not a bug but an intended change.

[allanrenucci]

It is an intended change. Since we cannot know the intent of the author, I think we should always emit a warning for fruitless type tests

[odersky]

This leads to spurious warnings for compiler-generated pattern matches. I believe it's better to revert the decision and check only explicit isInstanceOf, never patterns.

Note the scalac does not check patterns either.