A var defined in a script not updated after reload in REPL with -Yrepl-class-based

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It is possible to produce this problem with the Scala REPL using -Yrepl-class-based. The key to triggering this problem seems to be having an anonymous class with at least two members. Included is a new sample file that can be used to exhibit this problem. Below is a session showing the behavior:

~/t/t/6393 scala -Yrepl-class-based
Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_74).
Type in expressions for evaluation. Or try :help.

scala> :load Fail.scala
Loading Fail.scala...
X: Serializable{def getArray(n: Int): Array[Double]; def multiplySum(x: Double,v: Seq[Double]): Double} = $anon$1@5ddf0d24

scala> val a = X.getArray(100)
warning: there was one feature warning; re-run with -feature for details
a: Array[Double] = Array(0.6445967025789217, 0.8356433165638456, 0.9050186287112574, 0.06344554850936357, 0.008363070900988756, 0.6593626537474886, 0.7424265307039932, 0.5035629973234215, 0.5510831160354674, 0.37366654438205593, 0.33299751842582703, 0.3800633883472283, 0.4153963387304084, 0.2752468331316783, 0.8699452196820426, 0.31938530945559984, 0.7990568815957724, 0.6875841747139724, 0.31949965197609675, 0.026911873556428878, 0.2616536698127736, 0.5580118021155783, 0.28345994848845435, 0.1773433165304532, 0.2549417030032525, 0.9777692443616465, 0.6296846343712603, 0.8589339648876033, 0.7020098253707141, 0.8518829567943531, 0.41154622619731374, 0.1075129613308311, 0.8499252434316056, 0.3841876768177086, 0.137415801614582, 0.27030938222499756, 0.5511585560527115, 0.26252884257087217, ...
scala> X = null
X: Serializable{def getArray(n: Int): Array[Double]; def multiplySum(x: Double,v: Seq[Double]): Double} = null

scala> :load Fail.scala
Loading Fail.scala...
X: Serializable{def getArray(n: Int): Array[Double]; def multiplySum(x: Double,v: Seq[Double]): Double} = $anon$1@52c8295b

scala> X
res0: Serializable{def getArray(n: Int): Array[Double]; def multiplySum(x: Double,v: Seq[Double]): Double} = null

This has been tested with Scala 2.11.8 and 2.11.7

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Imported From: https://issues.scala-lang.org/browse/SI-9740?orig=1
Reporter: Jim Powers (corruptmemory)
Affected Versions: 2.11.7, 2.11.8
Other Milestones: 2.12.0-M5
Attachments:

• Fail.scala (created on Apr 6, 2016 5:21:50 PM UTC, 281 bytes)

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@szeiger said:
Smaller reproduction: Fail.scala:

var X = new { 
  def x = Seq.empty[AnyRef].reduce((a,b) => a)
}

Script:

scala -nc -Yrepl-class-based
:load Fail.scala
val a = X
X = null
:load Fail.scala
X
:q

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Jim Powers (corruptmemory) said:
Right. I forgot to include the information Iulian figured out. The problem is the a.

If you update the script to:

{noformat}scala -nc -Yrepl-class-based
:load Fail.scala
val aaa = X
X = null
:load Fail.scala
X
:q
{noformat}

You'll see that X updates properly.

So, the a in the def x = Seq.empty[AnyRef].reduce((a,b) => a) and the top-level a in the REPL seems to trigger the problem.

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@som-snytt said (edited on Apr 7, 2016 11:01:03 PM UTC):
Or

scala> var f: Int => Int = i => i
f: Int => Int = <function1>

scala> val i = f(10)
i: Int = 10

scala> f = null
f: Int => Int = null

scala> var f: Int => Int = i => i
f: Int => Int = <function1>

scala> f   // reports the first f, not its redefinition
res0: Int => Int = null

Both object and class templates (incorrectly or spuriously) import too much (both first f and i), but object template correctly imports the desired f, which hides the previous f. The class template has different logic that fails to import the correct f at res0, so it resolves to the incorrect one.

Imports can require previous imports:

scala> trait T ; class C { implicit val t: T = new T {} }
defined trait T
defined class C

scala> val c = new C
c: C = C@77afea7d

scala> import c.t
import c.t

scala> implicitly[T]
res0: T = C$$anon$1@5442a311

scala> val t = 17
t: Int = 17

scala> t
res1: T = C$$anon$1@5442a311

[scabug]

@som-snytt said:
scala/scala#5090