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Fix #4037: Fix code generation for generic arrays #4046

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Merged
merged 1 commit into from
Mar 5, 2018
Merged

Fix #4037: Fix code generation for generic arrays #4046

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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/ast/tpd.scala
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Expand Up @@ -372,7 +372,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
ref(defn.DottyArraysModule).select(defn.newArrayMethod).withPos(pos)

if (!ctx.erasedTypes) {
assert(!TypeErasure.isUnboundedGeneric(elemTpe)) //needs to be done during typer. See Applications.convertNewGenericArray
assert(!TypeErasure.isGeneric(elemTpe)) //needs to be done during typer. See Applications.convertNewGenericArray
newArr.appliedToTypeTrees(TypeTree(returnTpe) :: Nil).appliedToArgs(clsOf(elemTpe) :: clsOf(returnTpe) :: dims :: Nil).withPos(pos)
} else // after erasure
newArr.appliedToArgs(clsOf(elemTpe) :: clsOf(returnTpe) :: dims :: Nil).withPos(pos)
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10 changes: 10 additions & 0 deletions compiler/src/dotty/tools/dotc/core/TypeErasure.scala
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Expand Up @@ -216,6 +216,16 @@ object TypeErasure {
case _ => false
}

/** Is `tp` an abstract type or polymorphic type parameter, or another unbounded generic type? */
def isGeneric(tp: Type)(implicit ctx: Context): Boolean = tp.dealias match {
case tp: TypeRef => !tp.symbol.isClass
case tp: TypeParamRef => true
case tp: TypeProxy => isGeneric(tp.underlying)
case tp: AndType => isGeneric(tp.tp1) || isGeneric(tp.tp2)
case tp: OrType => isGeneric(tp.tp1) || isGeneric(tp.tp2)
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Can you explain why for both A & B and A | B, you have isGeneric(A) || isGeneric(B)?

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It's an approximation that makes sure that the erasure would not depend on any possible instantiation of the type. Erasure of AndTypes and OrTypes is quite complex, so it's hard to come up with a narrower condition.

case _ => false
}

/** The erased least upper bound is computed as follows
* - if both argument are arrays of objects, an array of the erased lub of the element types
* - if both arguments are arrays of same primitives, an array of this primitive
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4 changes: 2 additions & 2 deletions compiler/src/dotty/tools/dotc/transform/ArrayConstructors.scala
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Expand Up @@ -46,10 +46,10 @@ class ArrayConstructors extends MiniPhase {
val cs = tp.tpe.widen.classSymbol
tree.fun match {
case Apply(TypeApply(t: Ident, targ), dims)
if !TypeErasure.isUnboundedGeneric(targ.head.tpe) && !ValueClasses.isDerivedValueClass(cs) =>
if !TypeErasure.isGeneric(targ.head.tpe) && !ValueClasses.isDerivedValueClass(cs) =>
rewrite(targ.head.tpe, dims)
case Apply(TypeApply(t: Select, targ), dims)
if !TypeErasure.isUnboundedGeneric(targ.head.tpe) && !ValueClasses.isDerivedValueClass(cs) =>
if !TypeErasure.isGeneric(targ.head.tpe) && !ValueClasses.isDerivedValueClass(cs) =>
Block(t.qualifier :: Nil, rewrite(targ.head.tpe, dims))
case _ => tree
}
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/Applications.scala
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Expand Up @@ -831,7 +831,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
.select(defn.newGenericArrayMethod).withPos(tree.pos)
.appliedToTypeTrees(targs).appliedToArgs(args)

if (TypeErasure.isUnboundedGeneric(targ.tpe))
if (TypeErasure.isGeneric(targ.tpe))
newGenericArrayCall
else tree
case _ =>
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8 changes: 8 additions & 0 deletions tests/run/i4037.scala
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@@ -0,0 +1,8 @@
import scala.reflect.ClassTag

object Test {
def foo[T <: AnyRef : ClassTag] = new Array[T](42)
def main(args: Array[String]): Unit = {
val x: Array[String] = foo[String]
}
}