Lazy modifier on a val causes its name to collide with a method's named arg

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The following code causes a compilation error:

object Foo {                                                                                                                                                                                                                                                                           
  def foo(x: Int, y: Int = 10) = x*y                                                                                                                                                                                                                                                   
  lazy val y = foo(x = 20)                                                                                                                                                                                                                                                             
}

The error is as follows:

innocuous.scala:3: error: variable definition needs type because 'y' is used as a named argument in its body.
Error occurred in an application involving default arguments.
  lazy val y = foo(x = 20)
           ^
one error found

None of the following fail in the same way:

val y = foo(x = 20)

OR

lazy val y = foo(20)

It appears that combining the lazy modifier on y with a named arg in the application of foo causes it to blow up.

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Imported From: https://issues.scala-lang.org/browse/SI-6051?orig=1
Reporter: Max Afonov (maxaf)
Affected Versions: 2.9.1, 2.10.0-M4

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@hubertp said:
This one is most probably a correct error. There was recently a similar bug report with var instead of lazy val and the problem is that both create getters and setters and the disambiguation mechanism that drives the names defaults expansion is ambiguous in this is situation.
I will see if we can improve on the error message but this is again non trivial due to some of the internal stuff in the compiler (type completers).

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@JamesIry said:
2.10.2 is about to be cut. Kicking down the road and un-assigning to foster work stealing.

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@lrytz said:
retronym/scala#7