introduce gradualErrorOrMigrationWarning

Author: griggt

compiler/src/dotty/tools/dotc/report.scala

@@ -68,9 +68,13 @@ object report:
     if ctx.settings.YdebugTypeError.value then ex.printStackTrace()
 
   def errorOrMigrationWarning(msg: Message, pos: SrcPos = NoSourcePosition, from: SourceVersion)(using Context): Unit =
-    if sourceVersion.isAtLeast(from) then
-      if sourceVersion.isMigrating && sourceVersion.ordinal <= from.ordinal then migrationWarning(msg, pos)
-      else error(msg, pos)
+    gradualErrorOrMigrationWarning(msg, pos, from, from)
+
+  def gradualErrorOrMigrationWarning(msg: Message, pos: SrcPos = NoSourcePosition, warnFrom: SourceVersion, errorFrom: SourceVersion)(using Context): Unit =
+    if sourceVersion.isAtLeast(warnFrom) then
+      if sourceVersion.isMigrating && sourceVersion.ordinal <= errorFrom.ordinal then migrationWarning(msg, pos)
+      else if sourceVersion.isAtLeast(errorFrom) then error(msg, pos)
+      else warning(msg, pos)
 
   def restrictionError(msg: Message, pos: SrcPos = NoSourcePosition)(using Context): Unit =
     error(msg.mapMsg("Implementation restriction: " + _), pos)