Add an helpful message for -W option

Author: PaulCoral

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

@@ -60,7 +60,7 @@ trait CliCommand:
       def defaultValue = s.default match
         case _: Int | _: String => s.default.toString
         case _ => ""
-      val info = List(shortHelp(s), if defaultValue.nonEmpty then s"Default $defaultValue" else "", if s.legalChoices.nonEmpty then s"Choices ${s.legalChoices}" else "")
+      val info = List(shortHelp(s), if defaultValue.nonEmpty then s"Default $defaultValue" else "", if s.legalChoices.nonEmpty then s"Choices : ${s.legalChoices}" else "")
       (s.name, info.filter(_.nonEmpty).mkString("\n"))
     end help
 

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

@@ -156,14 +156,27 @@ private sealed trait VerboseSettings:
  */
 private sealed trait WarningSettings:
   self: SettingGroup =>
+  import Setting.ChoiceWithHelp
+
   val Whelp: Setting[Boolean] = BooleanSetting("-W", "Print a synopsis of warning options.")
   val XfatalWarnings: Setting[Boolean] = BooleanSetting("-Werror", "Fail the compilation if there are any warnings.", aliases = List("-Xfatal-warnings"))
 
-  val Wunused: Setting[List[String]] = MultiChoiceSetting(
+  val Wunused: Setting[List[ChoiceWithHelp[String]]] = MultiChoiceHelpSetting(
     name = "-Wunused",
     helpArg = "warning",
     descr = "Enable or disable specific `unused` warnings",
-    choices = List("nowarn", "all", "imports", "locals", "privates", "patvars", "explicits", "implicits", "params", "linted"),
+    choices = List(
+      ChoiceWithHelp("nowarn", ""),
+      ChoiceWithHelp("all",""),
+      ChoiceWithHelp("imports","Warn if an import selector is not referenced."),
+      ChoiceWithHelp("patvars","Warn if a variable bound in a pattern is unused."),
+      ChoiceWithHelp("privates","Warn if a private member is unused."),
+      ChoiceWithHelp("locals","Warn if a local definition is unused."),
+      ChoiceWithHelp("explicits","Warn if an explicit parameter is unused."),
+      ChoiceWithHelp("implicits","Warn if an implicit parameter is unused."),
+      ChoiceWithHelp("params","Enable -Wunused:explicits,implicits."),
+      ChoiceWithHelp("linted","Enable -Wunused:imports,privates,locals,implicits.")
+    ),
     default = Nil
   )
   object WunusedHas:

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

@@ -11,6 +11,7 @@ import annotation.tailrec
 import collection.mutable.ArrayBuffer
 import reflect.ClassTag
 import scala.util.{Success, Failure}
+import dotty.tools.dotc.config.Settings.Setting.ChoiceWithHelp
 
 object Settings:
 
@@ -184,6 +185,19 @@ object Settings:
       def update(x: T)(using Context): SettingsState = setting.updateIn(ctx.settingsState, x)
       def isDefault(using Context): Boolean = setting.isDefaultIn(ctx.settingsState)
 
+    /**
+     * A choice with help description.
+     *
+     * NOTE : `equals` and `toString` have special behaviors
+     */
+    case class ChoiceWithHelp[T](choice: T, description: String):
+      override def equals(x: Any): Boolean = x match
+        case s:String => s == choice.toString()
+        case _ => false
+      override def toString(): String =
+        s"\n\t- $choice${if description.isBlank() then "" else s"\t: $description"}"
+  end Setting
+
   class SettingGroup {
 
     private val _allSettings = new ArrayBuffer[Setting[?]]
@@ -265,6 +279,9 @@ object Settings:
     def MultiChoiceSetting(name: String, helpArg: String, descr: String, choices: List[String], default: List[String], aliases: List[String] = Nil): Setting[List[String]] =
       publish(Setting(name, descr, default, helpArg, Some(choices), aliases = aliases))
 
+    def MultiChoiceHelpSetting(name: String, helpArg: String, descr: String, choices: List[ChoiceWithHelp[String]], default: List[ChoiceWithHelp[String]], aliases: List[String] = Nil): Setting[List[ChoiceWithHelp[String]]] =
+      publish(Setting(name, descr, default, helpArg, Some(choices), aliases = aliases))
+
     def IntSetting(name: String, descr: String, default: Int, aliases: List[String] = Nil): Setting[Int] =
       publish(Setting(name, descr, default, aliases = aliases))