Weird behaviour when attempting partial application with named argument method.

Compiler version

3.0.0-RC1

Minimized code

case class State(text: String):
// val updateText = copy(text = _) // Missing parameter type: I could not infer the type of the parameter _$1
  val updateText = copy(text = (_: String))

scastie: https://scastie.scala-lang.org/a93h61tfRaeBBCqslsQgkg

Output

[error] -- [E052] Type Error: /<redacted>/State.scala:4:29
[error] 4 |  val updateText = copy(text = (_: String))
[error]   |                        ^^^^^^^^^^^^^^^^^^
[error]   |                        Reassignment to val text
[error] one error found
[error] one error found

Expectation

I’d expect this to work, but in case it is difficult to support partial application and named default arguments I’d like to see a more specific error message. In any case the parser should not see this as a reassignment in the context of a method call.

[som-snytt]

My previous comment in the middle of the night wasn’t clear that I don’t disagree with the intuition that it should just work.

I saw (because I had to look) that the spec isn’t clear about the syntax here. (There is no special production for named arg.)

Probably it could be made to work. The confusion around assignment syntax is just “for historical reasons.”

[odersky]

The most effective rule to follow is: when surprised by an error message affecting an expression with _, try to expand as a lambda and try again.