Adjust help text

Author: Som Snytt

src/compiler/scala/tools/nsc/Reporting.scala

@@ -522,6 +522,7 @@ object Reporting {
     def includes(o: WarningCategory): Boolean = this eq o
     def summaryCategory: WarningCategory = this
     lazy val name: String = WarningCategory.nameOf(this)
+    override def toString = name
   }
 
   object WarningCategory {
@@ -722,7 +723,7 @@ object Reporting {
   }
 
   object MessageFilter {
-    object Any extends MessageFilter {
+    case object Any extends MessageFilter {
       def matches(message: Message): Boolean = true
     }
 
@@ -768,7 +769,9 @@ object Reporting {
     }
   }
 
-  sealed trait Action
+  sealed trait Action {
+    override def toString = s"Action[${getClass.getSimpleName.stripSuffix("$")}]"
+  }
 
   object Action {
     object Error extends Action

src/compiler/scala/tools/nsc/settings/Warnings.scala

@@ -82,8 +82,13 @@ trait Warnings {
          |The default configuration is:
          |  -Wconf:${WconfDefault.mkString(",")}
          |
-         |User-defined configurations are added to the left. The leftmost rule matching
-         |a warning message defines the action.
+         |Under -Xsource:3-cross, the category of scala3-migration warnings are errors by default:
+         |  -Wconf:cat=scala3-migration:e
+         |Under -Xsource:3-migration, they are warnings:
+         |  -Wconf:cat=scala3-migration:w
+         |
+         |User-defined configurations override previous settings, such that the last matching
+         |configuration defines the action for a given diagnostic message.
          |
          |Examples:
          |  - change every warning into an error: -Wconf:any:error