New by-name implicits doesn't work anonymously

[japgolly]

Compiler version

3.0.1-RC1-bin-20210402-775d881-NIGHTLY

Minimized code

def a(using i: => Int ) = () // ok
def b(using    => Int ) = () // error
def c(using   (=> Int)) = () // error

Output

[error] -- [E040] Syntax Error: ~/scala3bug/sbt/src/main/scala/BUG.scala:2:15 
[error] 2 |def b(using    => Int ) = () // error
[error]   |               ^^
[error]   |               an identifier expected, but '=>' found
[error] -- [E022] Syntax Error: ~/scala3bug/sbt/src/main/scala/BUG.scala:3:15 
[error] 3 |def c(using   (=> Int)) = () // error
[error]   |               ^^^^^^
[error]   |               By-name parameter type => Int not allowed here.
[error] two errors found

Expectation

It should compile.