Ignored parameter (`_`) in context function is still in implicit scope

[mrdziuban]

Compiler version

3.3.6, 3.4.3, 3.5.2, 3.6.4, 3.7.0, and latest nightly 3.7.2-RC1-bin-20250510-f784625-NIGHTLY

Minimized code

def foo[A](f: Int ?=> A): A = f(using 1)
def bar(using i: Int): Int = i
val x = foo(_ ?=> bar)

Output

val x: Int = 1

Expectation

Since the argument of the context function passed to foo is ignored with _, I expected a compiler error as if I had called bar with no given Int in scope, e.g.

scala> bar
-- [E172] Type Error: ----------------------------------------------------------
1 |bar
  |   ^
  |   No given instance of type Int was found for parameter i of method bar

[som-snytt]

That's an interesting expectation, but I think "placeholder syntax" just means you get a fresh name, which is not relevant for contextual (implicit) parameters, which are summoned by type. Omitting the contextual function would just mean that it is constructed for you. There is no nullary contextual function.

[mrdziuban]

I think "placeholder syntax" just means you get a fresh name, which is not relevant for contextual (implicit) parameters, which are summoned by type

Yeah I get what you're saying. I suppose my thinking is that with an explicit _ parameter, there's no way for that param to be passed to another function, so I expected the same to be true of contextual parameters, even if it's the compiler passing the param for me.