Self Type shadows constructor arguments.

[scabug]

It seems that the self-type annotation shadows constructor arguments.

$$ scala
Welcome to Scala version 2.8.1.RC1 (Java HotSpot(TM) Client VM, Java 1.6.0_16).
Type in expressions to have them evaluated.
Type :help for more information.

scala> trait Y
defined trait Y

scala> abstract class X(x: Int) { self: Y => x }
<console>:6: error: not found: value x
       abstract class X(x: Int) { self: Y => x }
                                             ^

Of course, without self-type annotation, there is no problem,

scala> abstract class X(x: Int) { self => x }
defined class X

and curiously there is no problem with 'val',

scala> abstract class X(val x: Int) { self: Y => x }
defined class X

This problem, for example, will cause the following unexpected result,

scala> object X {
     |   val x: Int = 1
     |   trait Y
     |   abstract class XX(x: Int){ self: Y =>
     |     println(x)
     |   }
     |   new XX(2) with Y
     | }
defined module X
scala> X
1
res0: X.type = X$$@1df3082

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-3861?orig=1
Reporter: Atsuhiko Yamanaka (ymnk)

[scabug]

@paulp said:
For a related issue involving constructor parameter visibility, see #3194.

And your ticket made me realize that this bug represents a workaround to that one!

scala> class A(var x: Int)                                                      
defined class A

scala> class B(x: Int) extends A(x) { def f(z: Int) = this.x = z }              
<console>:6: error: reassignment to val
       class B(x: Int) extends A(x) { def f(z: Int) = this.x = z }
                                                             ^

scala> class B(x: Int) extends A(x) { self: A => def f(z: Int) = this.x = z }
defined class B

scala> new B(10)
res0: B = B@32e6e42e

scala> res0.x
res1: Int = 10

scala> res0.f(-75)

scala> res0.x
res3: Int = -75

Applying one bug to work around another: that's how we know we're engineers.

[scabug]

@dcsobral said:
I don't see the problems on trunk. I guess it was fixed?

scala> trait Y
defined trait Y

scala> abstract class X(x: Int) { self: Y => x }
defined class X

scala> scala> object X {
     |   val x: Int = 1
     |   trait Y
     |   abstract class XX(x: Int){ self: Y =>
     |     println(x)
     |   }
     |   new XX(2) with Y
     | }
defined module X
scala> X
1
res0: X.type = X$$@1df3082

Replaying 2 commands from interpreter transcript.
defined module X
2
res3: X.type = X$$@1e1370ab

[scabug]

@paulp said:
(In r24303) Test case closes #3861, no review.