Star `*` infix type fails compilation

[soronpo]

object InfixType {
  trait *[N1, N2]
  type Result = Int * Int
}

Gives

[error]   |  type Result = Int * Int
[error]   |                    ^
[error]   |                    ';' expected but identifier found

[smarter]

Backquoting doesn't help, same error when writing Int `*` Int instead

[smarter]

@som-snytt on Gitter mentioned that this was also the case before 2.11, then it got fixed and the spec updated: https://issues.scala-lang.org/browse/SI-8325

[odersky]

I am not sure this is a good fix. The problem is that it clashes with postfix * in varargs parameters. This would not be a problem if postfix `*' was a real postfix type op. But it isn't. Types don't have postfix ops at all. So I am not really sure how to fix this without major contortions in the parser. I would rather backout of the spec change here.

[smarter]

The parser change in scalac doesn't seem too bad: https://github.com/scala/scala/pull/3576/files

[odersky]

It requires lookahead, which is a big deal because it widens the Scanner/Parser interface. Dotty's parser does not need lookahead.

[smarter]

IIRC, lookahead is also needed to get the inline keyword to work under -language:Scala2: #1492 (comment) which is something I wanted to implement.

[odersky]

Right. But I think it is one thing to require lookahead for a backwards compatibility hack, but another to require the official grammar to support it.

[jozanek]

This is probably resolved.

[soronpo]

This is probably resolved.

In which version? I tried it on Scastie now and still produces the same compilation error.

[allanrenucci]

I can still reproduce on mater