Fix #1167: Remove the magic from Arrays.newRefArray.

Previously, the method `Arrays.newRefArray` was one of the only 3
methods that are kept generic after erasure. This commit removes
this magic, by making it take an actual `j.l.Class[T]` as
parameter.

Moreover, the methods `newXArray` all receive an actual body,
implemented on top of Java reflection, which means that a back-end
does not *have to* special-case those methods for correctness.
It might still be required for performance, though, depending on
the back-end.

The JVM back-end is made non-optimal in this commit, precisely
because it does not specialize that method anymore. Doing so
requires modifying the fork of scalac that we use, which should
be done separately.

The JS back-end is adapted simply by doing nothing at all on any
of the newXArray methods. It will normally call the user-space
implementations which use reflection. The Scala.js optimizer will
inline and intrinsify the reflective calls, producing optimal
code, at the end of the day.

1 files changed, 1 insertions, 3 deletions

diff --git a/src/dotty/tools/dotc/core/Definitions.scala b/src/dotty/tools/dotc/core/Definitions.scala
index 6625cff3f..fb71fa467 100644
--- a/src/dotty/tools/dotc/core/Definitions.scala
+++ b/src/dotty/tools/dotc/core/Definitions.scala
@@ -247,8 +247,6 @@ class Definitions {
   lazy val DottyArraysModuleRef = ctx.requiredModuleRef("dotty.runtime.Arrays")
   def DottyArraysModule(implicit ctx: Context) = DottyArraysModuleRef.symbol
 
-    def newRefArrayMethod(implicit ctx: Context) = DottyArraysModule.requiredMethod("newRefArray")
-
   lazy val NilModuleRef = ctx.requiredModuleRef("scala.collection.immutable.Nil")
   def NilModule(implicit ctx: Context) = NilModuleRef.symbol
 
@@ -622,7 +620,7 @@ class Definitions {
   lazy val PhantomClasses = Set[Symbol](AnyClass, AnyValClass, NullClass, NothingClass)
 
   def isPolymorphicAfterErasure(sym: Symbol) =
-     (sym eq Any_isInstanceOf) || (sym eq Any_asInstanceOf) || (sym eq newRefArrayMethod)
+     (sym eq Any_isInstanceOf) || (sym eq Any_asInstanceOf)
 
   def isTupleType(tp: Type)(implicit ctx: Context) = {
     val arity = tp.dealias.argInfos.length