Add alpha and infix annotations

Author: odersky

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -877,6 +877,10 @@ class Definitions {
   def ShowAsInfixAnnot(implicit ctx: Context): ClassSymbol = ShowAsInfixAnotType.symbol.asClass
   lazy val FunctionalInterfaceAnnotType = ctx.requiredClassRef("java.lang.FunctionalInterface")
   def FunctionalInterfaceAnnot(implicit ctx: Context) = FunctionalInterfaceAnnotType.symbol.asClass
+  lazy val InfixAnnotType = ctx.requiredClassRef("scala.annotation.infix")
+  def InfixAnnot(implicit ctx: Context) = InfixAnnotType.symbol.asClass
+  lazy val AlphaAnnotType = ctx.requiredClassRef("scala.annotation.alpha")
+  def AlphaAnnot(implicit ctx: Context) = AlphaAnnotType.symbol.asClass
 
   // convenient one-parameter method types
   def methOfAny(tp: Type): MethodType = MethodType(List(AnyType), tp)

library/src/scala/annotation/alpha.scala

@@ -0,0 +1,3 @@
+package scala.annotation
+
+final class alpha(name: String) extends StaticAnnotation

library/src/scala/annotation/infix.scala

@@ -0,0 +1,3 @@
+package scala.annotation
+
+final class infix extends StaticAnnotation

tests/run/infix.scala

@@ -0,0 +1,15 @@
+import annotation.{infix, alpha}
+object Test extends App {
+
+  case class Rational(n: Int, d: Int) {
+    @infix def + (that: Rational) =
+      Rational(this.n * that.d + that.n * this.d, this.d * that.d)
+    @infix @alpha("multiply") def * (that: Rational) =
+      Rational(this.n * that.n, this.d * that.d)
+  }
+
+  val r1 = Rational(1,2)
+  val r2 = Rational(2,3)
+  println(r1 * r2)
+  println(r1 + r2)
+}