Imported From: https://issues.scala-lang.org/browse/SI-7448?orig=1
Reporter: @som-snytt
Affected Versions: 2.11.0-M2
See #6896

Tanin Na Nakorn (tanin) said:
Did you use def main(args: Array[String]) = {...}?

You should use def main(args: Array[String]) {...} (no equal sign)

@som-snytt said:
To clarify, existing tests use the incorrect idiom.

The warning should say, Scala is catholic in its notion of main, but other launchers may be unforgiving.

It's possible that Scala is an Episcopalian, that is, a lover of ceremonious incantations, but also quite capable of doing without the trappings and accepting whatever is practical.

@som-snytt said:
Similarly, for nested objects, where there is no expectation:

-t1005.scala:6: warning: FromMono has a main method with parameter type Array[String], but Test.FromMono will not be a runnable program.
-  Reason: main method must have exact signature (Array[String])Unit
-  object FromMono{

Though if the signature is exactly that, it could warn for the reason that the object is not top-level. Or warn under -Xlint or -Xnoob.

It sure would be nice for main to return Nothing ... like sys.exit.