Excess `{` required when using polymorphic function lambdas

[scf37]

Compiler version

3.0.0-RC3

Minimized code

  def foo(f: => () => Unit): Unit = ???
  def boo(f: [A] => () => Unit): Unit = ???

  foo { () =>  // okay
    println(1)
    println(2)
  }

  boo { [A] => () => // error
    println(1)
    println(2)
  }

  boo { [A] => () => { // okay
    println(1)
    println(2)
  }}

Output

A pure expression does nothing in statement position; you may be omitting necessary parentheses [194:13]
Found:    Unit
Required: PolyFunction{apply: [A](): Unit} [196:12]

Expectation

Same lightweight syntax for polymorphic functions as for "standard" functions
Also by-name parameter support for polymorphic functions could be useful for even clearer syntax.