Inconsistent instantiation behavior #1088
Description
Given:
scala> class Foo { trait Qux { val x = 42 } }
defined class Foo
scala> class Bar(arg : Int) { trait Qux { val x = arg } }
defined class Bar
scala> val x : Foo = null
x: Foo = null
scala> val y : Bar = null
y: Bar = nullthe following succeeds:
scala> val b = new x.type#Qux { };
b: java.lang.Object with x.Qux = $$anon$$1@137e216but the following fails:
scala> val b = new y.type#Qux { };
java.lang.NullPointerException
at Bar$$Qux$$class.$$init$$(<console>:4)
at $$anon$$1.<init>(<console>:6)
at .<init>(<console>:6)
at .<clinit>(<console>)
at RequestResult$$.<init>(<console>:3)
at RequestResult$$.<clinit>(<console>)
at RequestResult$$result(<console>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMeth...Scala should be consistent in its operational behavior and both should fail with a NPE. Otherwise, evolving classes can have unforeseen impacts elsewhere in your code. The problem is not limited to using null, either:
scala> object Wrapper {
| lazy val x : Foo = x
| lazy val y : Bar = y
| }
defined module Wrapper
scala> val b = new Wrapper.x.type#Qux { }
b: java.lang.Object with Wrapper.x.Qux = $$anon$$1@671416
scala> val b = new Wrapper.y.type#Qux { }
java.lang.StackOverflowError
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrapper$$.y(<console>:10)
at Wrappe...The problem is also not limited to merely to adding constructor arguments:
scala> trait Foo { trait Qux { val x = 42 } }
defined trait Foo
scala> trait Bar { val arg : Int; trait Qux { val x = arg } }
defined trait Bar
scala> val x : Foo = null
x: Foo = null
scala> val y : Bar = null
y: Bar = null
scala> val b = new x.type#Qux { };
b: java.lang.Object with x.Qux = $$anon$$1@14e54d8
scala> val b = new y.type#Qux { };
java.lang.NullPointerException
at Bar$$Qux$$class.$$init$$(<console>:4)
at $$anon$$1.<init>(<console>:6)
at .<init>(<console>:6)
at .<clinit>(<console>)
at RequestResult$$.<init>(<console>:3)
at RequestResult$$.<clinit>(<console>)
at RequestResult$$result(<console>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMeth...