Print bounds of TypeVars only when option is enabled.

Author: odersky

src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -173,6 +173,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val Ypatmatdebug = BooleanSetting("-Ypatmat-debug", "Trace pattern matching translation.")
   val Yexplainlowlevel = BooleanSetting("-Yexplain-lowlevel", "When explaining type errors, show types at a lower level.")
   val YnoDoubleBindings = BooleanSetting("-Yno-double-bindings", "Assert no namedtype is bound twice (should be enabled only if program is error-free).")
+  val YshowVarBounds = BooleanSetting("-YshowVarBounds", "Print type variables with their bounds")
 
   val optimise = BooleanSetting("-optimise", "Generates faster bytecode by applying optimisations to the program") withAbbreviation "-optimize"
 

src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -170,7 +170,8 @@ class PlainPrinter(_ctx: Context) extends Printer {
           val bounds =
             if (constr.contains(tp)) constr.fullBounds(tp.origin)(ctx.addMode(Mode.Printing))
             else TypeBounds.empty
-          "(" ~ toText(tp.origin) ~ "?" ~ toText(bounds) ~ ")"
+          if (ctx.settings.YshowVarBounds.value) "(" ~ toText(tp.origin) ~ "?" ~ toText(bounds) ~ ")"
+          else toText(tp.origin)
         }
       case tp: LazyRef =>
         "LazyRef(" ~ toTextGlobal(tp.ref) ~ ")"