Multivalue with default means colon is required

Author: som-snytt

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

@@ -114,7 +114,7 @@ trait CommonScalaSettings:
   val explainTypes: Setting[Boolean] = BooleanSetting(RootSetting, "explain-types", "Explain type errors in more detail (deprecated, use -explain instead).", aliases = List("--explain-types", "-explaintypes"))
   val explainCyclic: Setting[Boolean] = BooleanSetting(RootSetting, "explain-cyclic", "Explain cyclic reference errors in more detail.", aliases = List("--explain-cyclic"))
   val unchecked: Setting[Boolean] = BooleanSetting(RootSetting, "unchecked", "Enable additional warnings where generated code depends on assumptions.", initialValue = true, aliases = List("--unchecked"))
-  val language: Setting[List[ChoiceWithHelp[String]]] = MultiChoiceHelpSetting(RootSetting, "language", "feature", "Enable one or more language features.", choices = ScalaSettingsProperties.supportedLanguageFeatures, legacyChoices = ScalaSettingsProperties.legacyLanguageFeatures, default = Nil, aliases = List("--language"))
+  val language: Setting[List[ChoiceWithHelp[String]]] = MultiChoiceHelpSetting(RootSetting, "language", "feature", "Enable one or more language features.", choices = ScalaSettingsProperties.supportedLanguageFeatures, legacyChoices = ScalaSettingsProperties.legacyLanguageFeatures, aliases = List("--language"))
   val experimental: Setting[Boolean] = BooleanSetting(RootSetting, "experimental", "Annotate all top-level definitions with @experimental. This enables the use of experimental features anywhere in the project.")
   val preview: Setting[Boolean] = BooleanSetting(RootSetting, "preview", "Enable the use of preview features anywhere in the project.")
 
@@ -191,7 +191,6 @@ private sealed trait WarningSettings:
       ),
       ChoiceWithHelp("unsafe-warn-patvars", "Deprecated alias for `patvars`"),
     ),
-    default = Nil
   )
   object WunusedHas:
     def isChoiceSet(s: String)(using Context) = Wunused.value.pipe(us => us.contains(s))
@@ -225,7 +224,6 @@ private sealed trait WarningSettings:
     WarningSetting,
     "Wconf",
     "patterns",
-    default = List(),
     descr =
     raw"""Configure compiler warnings.
          |Syntax: -Wconf:<filters>:<action>,<filters>:<action>,...
@@ -287,7 +285,6 @@ private sealed trait WarningSettings:
       ChoiceWithHelp("private-shadow", "Warn if a private field or class parameter shadows a superclass field"),
       ChoiceWithHelp("type-parameter-shadow", "Warn when a type parameter shadows a type already in the scope"),
     ),
-    default = Nil
   )
 
   object WshadowHas:

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

@@ -124,8 +124,6 @@ object Settings:
 
     def isMultivalue: Boolean = classTag[T] == ListTag
 
-    def acceptsNoArg: Boolean = classTag[T] == BooleanTag || classTag[T] == OptionTag || choices.exists(_.contains(""))
-
     def legalChoices: String =
       choices match
         case Some(xs) if xs.isEmpty => ""
@@ -248,10 +246,11 @@ object Settings:
             update(Some(propertyClass.get.getConstructor().newInstance()), "", args)
           case ct =>
             val argInArgRest = !argRest.isEmpty || legacyArgs
-            inline def argAfterParam = !argInArgRest && args.nonEmpty && (ct == IntTag || !args.head.startsWith("-"))
+            inline def argAfterParam = args.nonEmpty && (ct == IntTag || !args.head.startsWith("-"))
+            inline def isMultivalueWithDefault = isMultivalue && !isEmptyDefault
             if argInArgRest then
               doSetArg(argRest, args)
-            else if argAfterParam then
+            else if argAfterParam && !isMultivalueWithDefault then
               doSetArg(args.head, args.tail)
             else if isEmptyDefault then
               missingArg
@@ -420,7 +419,7 @@ object Settings:
     def MultiChoiceSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[String], default: List[String] = Nil, legacyChoices: List[String] = Nil, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[List[String]] =
       publish(Setting(category, prependName(name), descr, default, helpArg, Some(choices), legacyChoices = Some(legacyChoices), aliases = aliases, deprecation = deprecation))
 
-    def MultiChoiceHelpSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[ChoiceWithHelp[String]], default: List[ChoiceWithHelp[String]], legacyChoices: List[String] = Nil, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[List[ChoiceWithHelp[String]]] =
+    def MultiChoiceHelpSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[ChoiceWithHelp[String]], default: List[ChoiceWithHelp[String]] = Nil, legacyChoices: List[String] = Nil, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[List[ChoiceWithHelp[String]]] =
       publish(Setting(category, prependName(name), descr, default, helpArg, Some(choices), legacyChoices = Some(legacyChoices), aliases = aliases, deprecation = deprecation))
 
     def IntSetting(category: SettingCategory, name: String, descr: String, default: Int, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[Int] =