val and single given pattern combination

[bishabosha]

Compiler version

3.0.0

Minimized code

case class A(i: Int)
case class B(b: Boolean)

def test =
  val (given A) = A(23)
  val given B = B(false)

Output

compiles ok

Expectation

val given B is treated as a pattern val def, but this is too close to given B = B(false) so I would expect a syntax error in favour of the alias given,

alternatively, with #11897 fixed, it could be a way to define a (non-lazy) given?

[bishabosha]

it seems that this pattern was known about and explicitly allowed in the following test cases: https://github.com/lampepfl/dotty/blob/d09981141ea16a98c654b98ca582b9626bf0ff0b/tests/neg/given-pattern.scala#L7
https://github.com/lampepfl/dotty/blob/d09981141ea16a98c654b98ca582b9626bf0ff0b/tests/neg/given-pattern.scala#L11

[odersky]

How do you propose to change the syntax to support the distinction?

[bishabosha]

in the dotty meeting we decided to make this an error