REPL can't handle (A*) => A

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There is a compilation error (only in the REPL) in the following example, where none should be:

scala> val f: (Int*) => Int = _.size
<console>:5: error: type mismatch;
 found   : Int* => Int
 required: Seq[Int] => Int
  lazy val $result = f
                                          ^

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-8971?orig=1
Reporter: @sschaef
Affected Versions: 2.11.4

[scabug]

@retronym said:
According to the spec,* is only allowed on method parameters. The compiler also allows them in function types, but the behaviour is unspecified. Personally, I'd like to disallow this.

[scabug]

Li Haoyi (lihaoyi) said:
This is fixed in the Ammonite REPL

@ val f: (Int*) => Int = _.size
f: Seq[Int] => Int = <function1>
@ f(1)
res2: Int = 1
@ f(1, 3, 4)
res3: Int = 3
@

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@som-snytt said (edited on Jan 16, 2017 2:29:36 AM UTC):
Surprise,

$ scala
Welcome to Scala 2.12.1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_111).
Type in expressions for evaluation. Or try :help.

scala> val f: (Int*) => Int = _.size
f: Int* => Int = $$Lambda$1042/1092382020@1687eb01

scala> f(1,2,3)
res0: Int = 3

// the relevant definitions:
// <stable> <accessor> def f: Int* => Int = $iw.this.f
// <stable> <accessor> lazy val $result: Seq[Int] => Int = $line1.$read.$iw.$iw.f;