Merge pull request #3228 from CucumisSativus/show_as_inflix_used_in_refined_printer

Enchancement #3008

Author: smarter

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

@@ -661,6 +661,8 @@ class Definitions {
   def GetterMetaAnnot(implicit ctx: Context) = GetterMetaAnnotType.symbol.asClass
   lazy val SetterMetaAnnotType = ctx.requiredClassRef("scala.annotation.meta.setter")
   def SetterMetaAnnot(implicit ctx: Context) = SetterMetaAnnotType.symbol.asClass
+  lazy val ShowAsInfixAnotType = ctx.requiredClassRef("scala.annotation.showAsInfix")
+  def ShowAsInfixAnnot(implicit ctx: Context) = ShowAsInfixAnotType.symbol.asClass
 
   // convenient one-parameter method types
   def methOfAny(tp: Type) = MethodType(List(AnyType), tp)

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -126,8 +126,8 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
     def isInfixType(tp: Type): Boolean = tp match {
       case AppliedType(tycon, args) =>
         args.length == 2 &&
-          !Character.isUnicodeIdentifierStart(tycon.typeSymbol.name.toString.head)
-          // TODO: Once we use the 2.12 stdlib, also check the @showAsInfix annotation
+        tycon.typeSymbol.getAnnotation(defn.ShowAsInfixAnnot).map(_.argumentConstant(0).forall(_.booleanValue))
+          .getOrElse(!Character.isUnicodeIdentifierStart(tycon.typeSymbol.name.toString.head))
       case _ => false
     }
 

compiler/test-resources/type-printer/infix

@@ -16,3 +16,12 @@ scala> def foo: (Int && String) &: Boolean = ???
 def foo: (Int && String) &: Boolean
 scala> def foo: Int && (Boolean &: String) = ???
 def foo: Int && (Boolean &: String)
+scala> import scala.annotation.showAsInfix
+scala> @scala.annotation.showAsInfix class Mappy[T,U]
+// defined class Mappy
+scala> def foo: Int Mappy (Boolean && String) = ???
+def foo: Int Mappy (Boolean && String)
+scala> @scala.annotation.showAsInfix(false) class ||[T,U]
+// defined class ||
+scala> def foo: Int || Boolean = ???
+def foo: ||[Int, Boolean]