Fix -Xmigration legacy behavior

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

@@ -301,7 +301,7 @@ private sealed trait XSettings:
   val XnoForwarders: Setting[Boolean] = BooleanSetting(AdvancedSetting, "Xno-forwarders", "Do not generate static forwarders in mirror classes.")
   val XmaxInlines: Setting[Int] = IntSetting(AdvancedSetting, "Xmax-inlines", "Maximal number of successive inlines.", 32)
   val XmaxInlinedTrees: Setting[Int] = IntSetting(AdvancedSetting, "Xmax-inlined-trees", "Maximal number of inlined trees.", 2_000_000)
-  val Xmigration: Setting[ScalaVersion] = VersionSetting(AdvancedSetting, "Xmigration", "Warn about constructs whose behavior may have changed since version.")
+  val Xmigration: Setting[ScalaVersion] = VersionSetting(AdvancedSetting, "Xmigration", "Warn about constructs whose behavior may have changed since version.", legacyArgs = true)
   val XprintTypes: Setting[Boolean] = BooleanSetting(AdvancedSetting, "Xprint-types", "Print tree types (debugging option).")
   val XprintDiff: Setting[Boolean] = BooleanSetting(AdvancedSetting, "Xprint-diff", "Print changed parts of the tree since last print.")
   val XprintDiffDel: Setting[Boolean] = BooleanSetting(AdvancedSetting, "Xprint-diff-del", "Print changed parts of the tree since last print including deleted parts.")
@@ -376,7 +376,7 @@ private sealed trait YSettings:
   val YstopBefore: Setting[List[String]] = PhasesSetting(ForkSetting, "Ystop-before", "Stop before") // stop before erasure as long as we have not debugged it fully
   val YshowSuppressedErrors: Setting[Boolean] = BooleanSetting(ForkSetting, "Yshow-suppressed-errors", "Also show follow-on errors and warnings that are normally suppressed.")
   val YdetailedStats: Setting[Boolean] = BooleanSetting(ForkSetting, "Ydetailed-stats", "Show detailed internal compiler stats (needs Stats.enabled to be set to true).")
-  val YkindProjector: Setting[String] = LegacyChoiceSetting(ForkSetting, "Ykind-projector", "[underscores, enable, disable]", "Allow `*` as type lambda placeholder to be compatible with kind projector. When invoked as -Ykind-projector:underscores will repurpose `_` to be a type parameter placeholder, this will disable usage of underscore as a wildcard.", List("disable", "", "underscores"), "disable")
+  val YkindProjector: Setting[String] = ChoiceSetting(ForkSetting, "Ykind-projector", "[underscores, enable, disable]", "Allow `*` as type lambda placeholder to be compatible with kind projector. When invoked as -Ykind-projector:underscores will repurpose `_` to be a type parameter placeholder, this will disable usage of underscore as a wildcard.", List("disable", "", "underscores"), "disable", legacyArgs = true)
   val YprintPos: Setting[Boolean] = BooleanSetting(ForkSetting, "Yprint-pos", "Show tree positions.")
   val YprintPosSyms: Setting[Boolean] = BooleanSetting(ForkSetting, "Yprint-pos-syms", "Show symbol definitions positions.")
   val YnoDeepSubtypes: Setting[Boolean] = BooleanSetting(ForkSetting, "Yno-deep-subtypes", "Throw an exception on deep subtyping call stacks.")

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

@@ -200,7 +200,7 @@ object Settings:
           case (OptionTag, _) =>
             update(Some(propertyClass.get.getConstructor().newInstance()), args)
           case (ct, args) =>
-            val argInArgRest = !argRest.isEmpty || (legacyArgs && choices.exists(_.contains("")))
+            val argInArgRest = !argRest.isEmpty || legacyArgs
             val argAfterParam = !argInArgRest && args.nonEmpty && (ct == IntTag || !args.head.startsWith("-"))
             if argInArgRest then
               doSetArg(argRest, args)
@@ -339,12 +339,8 @@ object Settings:
     def StringSetting(category: SettingCategory, name: String, helpArg: String, descr: String, default: String, aliases: List[String] = Nil): Setting[String] =
       publish(Setting(category, prependName(name), descr, default, helpArg, aliases = aliases))
 
-    def ChoiceSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[String], default: String, aliases: List[String] = Nil): Setting[String] =
-      publish(Setting(category, prependName(name), descr, default, helpArg, Some(choices), aliases = aliases))
-
-    // Allows only args after :, but supports empty string as a choice. Used for -Ykind-projector
-    def LegacyChoiceSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[String], default: String, aliases: List[String] = Nil): Setting[String] =
-      publish(Setting(category, prependName(name), descr, default, helpArg, Some(choices), aliases = aliases, legacyArgs = true))
+    def ChoiceSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[String], default: String, aliases: List[String] = Nil, legacyArgs: Boolean = false): Setting[String] =
+      publish(Setting(category, prependName(name), descr, default, helpArg, Some(choices), aliases = aliases, legacyArgs = legacyArgs))
 
     def MultiChoiceSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[String], default: List[String], aliases: List[String] = Nil): Setting[List[String]] =
       publish(Setting(category, prependName(name), descr, default, helpArg, Some(choices), aliases = aliases))
@@ -374,8 +370,8 @@ object Settings:
       val prefix = name.takeWhile(_ != '<')
       publish(Setting(category, "-" + name, descr, Nil, prefix = Some(prefix)))
 
-    def VersionSetting(category: SettingCategory, name: String, descr: String, default: ScalaVersion = NoScalaVersion): Setting[ScalaVersion] =
-      publish(Setting(category, prependName(name), descr, default))
+    def VersionSetting(category: SettingCategory, name: String, descr: String, default: ScalaVersion = NoScalaVersion, legacyArgs: Boolean = false): Setting[ScalaVersion] =
+      publish(Setting(category, prependName(name), descr, default, legacyArgs = legacyArgs))
 
     def OptionSetting[T: ClassTag](category: SettingCategory, name: String, descr: String, aliases: List[String] = Nil): Setting[Option[T]] =
       publish(Setting(category, prependName(name), descr, None, propertyClass = Some(summon[ClassTag[T]].runtimeClass), aliases = aliases))