argument for compiler setting with colon should follow without whitespace

Author: niktrop

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

@@ -109,7 +109,7 @@ object Settings {
         ArgsSummary(sstate, args, errors :+ msg)
       def missingArg =
         fail(s"missing argument for option $name", args)
-      def doSet(argRest: String) = ((implicitly[ClassTag[T]], args): @unchecked) match {
+      def doSet(argRest: String = "") = ((implicitly[ClassTag[T]], args): @unchecked) match {
         case (BooleanTag, _) =>
           update(true, args)
         case (ListTag, _) =>
@@ -146,10 +146,16 @@ object Settings {
           missingArg
       }
 
-      if (prefix != "" && arg.startsWith(prefix))
-        doSet(arg drop prefix.length)
-      else if (prefix == "" && name == arg.takeWhile(_ != ':'))
-        doSet(arg.dropWhile(_ != ':').drop(1))
+      if (prefix != "")
+        if (arg.startsWith(prefix)) doSet(arg.drop(prefix.length))
+        else state
+      else if (arg.contains(':') && name == arg.takeWhile(_ != ':')) {
+        val value = arg.dropWhile(_ != ':').drop(1)
+        if (value.isEmpty) missingArg
+        else doSet(value)
+      }
+      else if (name == arg)
+        doSet()
       else
         state
     }