Fix printing of infix types

 - move isInfixType back to RefinedPrinter. Types is already large enough
   and this is exclusively about printing.
 - perform argText adaptation of InfixType arguments.

Author: odersky

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

@@ -149,14 +149,6 @@ object Types {
         false
     }
 
-    def isInfixType(implicit ctx: Context): Boolean = this 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
-      case _ => false
-    }
-
     /** Does this type refer exactly to class symbol `sym`, instead of to a subclass of `sym`?
      *  Implemented like `isRef`, but follows more types: all type proxies as well as and- and or-types
      */

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

@@ -125,15 +125,23 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         ("implicit " provided isImplicit) ~ argStr ~ " => " ~ argText(args.last)
       }
 
+    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
+      case _ => false
+    }
+
     def toTextInfixType(op: Type, args: List[Type]): Text = {
       /* SLS 3.2.8: all infix types have the same precedence.
        * In A op B op' C, op and op' need the same associativity.
        * Therefore, if op is left associative, anything on its right
        * needs to be parenthesized if it's an infix type, and vice versa. */
       val l :: r :: Nil = args
       val isRightAssoc = op.typeSymbol.name.endsWith(":")
-      val leftArg = if (isRightAssoc && l.isInfixType) "(" ~ toText(l) ~ ")" else toText(l)
-      val rightArg = if (!isRightAssoc && r.isInfixType) "(" ~ toText(r) ~ ")" else toText(r)
+      val leftArg = if (isRightAssoc && isInfixType(l)) "(" ~ argText(l) ~ ")" else argText(l)
+      val rightArg = if (!isRightAssoc && isInfixType(r)) "(" ~ argText(r) ~ ")" else argText(r)
 
       leftArg ~ " " ~ toTextLocal(op) ~ " " ~ rightArg
     }
@@ -146,7 +154,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         if (tycon.isRepeatedParam) return toTextLocal(args.head) ~ "*"
         if (defn.isFunctionClass(cls)) return toTextFunction(args, cls.name.isImplicitFunction)
         if (defn.isTupleClass(cls)) return toTextTuple(args)
-        if (tp.isInfixType) return toTextInfixType(tycon, args)
+        if (isInfixType(tp)) return toTextInfixType(tycon, args)
       case EtaExpansion(tycon) =>
         return toText(tycon)
       case tp: TypeRef =>