Avoid assigning null to vars of derived value type #91
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`TreeGen#mkZero` returns `q"null"` for derived value classes.
```
scala> class V(val a: String) extends AnyVal
defined class V
scala> showRaw(gen.mkZero(typeOf[V]))
res0: String = Literal(Constant(null))
```
We use this API in async to generate the initial value for
ANF-lifted temporary variables.
However, this leads to NPEs, as after posterasure, we call the
unbox method on a null reference:
```
% cat sandbox/Macro.scala; scalac-hash v2.10.4 sandbox/Macro.scala; scala-hash v2.10.4 -e 'val x = Macros.myMacro'
import scala.reflect.macros.Context
import scala.language.experimental.macros
object Macros {
def macroImpl(c: Context): c.Expr[C] = {
import c.universe._
val e1 = c.Expr[C](Literal(Constant(null)).setType(typeOf[C]))
reify(e1.splice.asInstanceOf[C @annotation.unchecked.uncheckedVariance])
}
def myMacro: C = macro macroImpl
}
class C(val a: String) extends AnyVal
java.lang.NullPointerException
at Main$$anon$1.<init>(scalacmd4059893593754060829.scala:1)
at Main$.main(scalacmd4059893593754060829.scala:1)
at Main.main(scalacmd4059893593754060829.scala)
```
This commit installs a custom version of `mkZero` that instead
returns `q"new C[$..targs](${mkZero(wrappedType)})`.
Thanks to @ewiner for pinpointing the problem.
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|
Review by @phaller |
This was referenced Sep 29, 2014
| @@ -150,7 +150,6 @@ private[async] trait AnfTransform { | |||
|
|
|||
| private def defineVal(prefix: String, lhs: Tree, pos: Position): ValDef = { | |||
| val sym = currOwner.newTermSymbol(name.fresh(prefix), pos, SYNTHETIC).setInfo(uncheckedBounds(lhs.tpe)) | |||
| changeOwner(lhs, currentOwner, sym) | |||
|
LGTM |
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Avoid assigning null to vars of derived value type
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TreeGen#mkZeroreturnsq"null"for derived value classes.We use this API in async to generate the initial value for
ANF-lifted temporary variables.
However, this leads to NPEs, as after posterasure, we call the
unbox method on a null reference:
This commit installs a custom version of
mkZerothat insteadreturns
q"new C[$..targs](${mkZero(wrappedType)})