Document dropping @Repeated annotation

Author: abgruszecki

compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala

@@ -277,6 +277,9 @@ trait ConstraintHandling[AbstractContext] {
    *      of `scala.Singleton`, widen `tp`.
    *   2. If `tp` is a union type, yet upper bound is not a union type,
    *      approximate the union type from above by an intersection of all common base types.
+   *
+   * At this point we also drop the @Repeated annotation to avoid inferring type arguments with it,
+   * as those could leak the annotation to users (see run/inferred-repeated-result).
    */
   def widenInferred(tp: Type, bound: Type)(implicit actx: AbstractContext): Type = {
     def isMultiSingleton(tp: Type): Boolean = tp.stripAnnots match {

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -1320,6 +1320,8 @@ class Namer { typer: Typer =>
       // Widen rhs type and eliminate `|' but keep ConstantTypes if
       // definition is inline (i.e. final in Scala2) and keep module singleton types
       // instead of widening to the underlying module class types.
+      // We also drop the @Repeated annotation here to avoid leaking it in method result types
+      // (see run/inferred-repeated-result).
       def widenRhs(tp: Type): Type = {
         val tp1 = tp.widenTermRefExpr match {
           case ctp: ConstantType if isInlineVal => ctp