Indentation forbidden before polymorphic functions

[Blaisorblade]

minimized code

object bug2 {
  //works:
  val id: [U] => U => U =
  [U] => (none: U) => none
  //fails to parse:
  val id2: [U] => U => U =
    [U] => (none: U) => none
}

expectation

id2 parses correctly.

actual

With version 0.20.0-RC1:

[info] Compiling 1 Scala source to /Users/pgiarrusso/git/Coq/silr-dot/code/target/scala-0.20/classes ...
[error] -- [E103] Syntax Error: /Users/pgiarrusso/git/Coq/silr-dot/code/Bug2.scala:7:4 -
[error] 7 |    [U] => (none: U) => none
[error]   |    ^
[error]   |    Illegal start of statement
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 0 s, completed Dec 1, 2019 4:00:04 PM

Ditto with sbt repl on master (eeb092524530c14dc3a110b38179e24f3c208776):

scala> val id: [U] => U => U =
     |   [U] => (none: U) => none
2 |  [U] => (none: U) => none
  |  ^
  |  Illegal start of statement

[odersky]

It also fails if the function is put in braces:

3 |  val id: [U] => U => U = { [U] => (none: U) => none }
  |                            ^
  |                            Illegal start of statement