unapply permutes case class fields

[scabug]

ticket/5082 ~/code/scala2 scala29
Welcome to Scala version 2.9.1.final (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_27).
Type in expressions to have them evaluated.
Type :help for more information.

scala> case class Y(final var x: Int, final private var y: String, final val z1: Boolean, final private val z2: Any)
defined class Y

scala> def x = Y.unapply(null)
x: Option[(Int, String, Boolean, Any)]

scala> ticket/5082 ~/code/scala2 scala-hash v2.10.0
[info] v2.10.0 => /Users/jason/usr/scala-v2.10.0-0-g18481ce
Welcome to Scala version 2.10.0-20121205-112020-18481cef9b (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_27).
Type in expressions to have them evaluated.
Type :help for more information.

scala> case class Y(final var x: Int, final private var y: String, final val z1: Boolean, final private val z2: Any)
defined class Y

scala> def x = Y.unapply(null)
x: Option[(Int, Boolean, String, Any)]

scala> val Y(a, b, c, d) = Y(0, "", true, new {})
a: Int = 0
b: String = ""
c: Boolean = true
d: Any = $anon$1@56801919

scala> Y.unapply(Y(0, "", true, new {}))
res0: Option[(Int, Boolean, String, Any)] = Some((0,true,,$anon$1@2eac0b4))

See also #5082. My proposed patch for it happens to reverse this regression.

Pattern matching, which bypasses the synthesized unapply method seems, superficially, to be immune. I seem to remember some code in there that corrected for out-of-order case accessors, but I can't find it. It does use caseAccessors when producing counter-examples, which may be subject to this bug, too.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-7035?orig=1
Reporter: @retronym
Affected Versions: 2.10.0

[scabug]

@retronym said:

      override protected def tupleSel(binder: Symbol)(i: Int): Tree = { import CODE._
        // caseFieldAccessors is messed up after typers (reversed, names mangled for non-public fields)
        // TODO: figure out why...
        val accessors = binder.caseFieldAccessors
        // luckily, the constrParamAccessors are still sorted properly, so sort the field-accessors using them
        // (need to undo name-mangling, including the sneaky trailing whitespace)
        val constrParamAccessors = binder.constrParamAccessors

[scabug]

@retronym said:

    val originalAccessors = clazz.caseFieldAccessors
    // private ones will have been renamed -- make sure they are entered
    // in the original order.
    def accessors = clazz.caseFieldAccessors sortBy { acc =>
      originalAccessors indexWhere { orig =>
        (acc.name == orig.name) || (acc.name startsWith (orig.name append "$"))
      }
    }

[scabug]

@retronym said:
scala/scala#1997