Remove retainsArg

Author: noti0na1

compiler/src/dotty/tools/dotc/ast/untpd.scala

@@ -536,6 +536,7 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
     else
       val trefs =
         if refs.isEmpty then ref(defn.NothingType)
+        // TODO: choose a reduce direction
         else refs.map(SingletonTypeTree).reduce[Tree]((a, b) => makeOrType(a, b))
       annot = New(AppliedTypeTree(annot, trefs :: Nil), Nil)
       annot.putAttachment(RetainsAnnot, ())

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

@@ -1097,7 +1097,6 @@ class Definitions {
   @tu lazy val RetainsAnnot: ClassSymbol = requiredClass("scala.annotation.retains")
   @tu lazy val RetainsCapAnnot: ClassSymbol = requiredClass("scala.annotation.retainsCap")
   @tu lazy val RetainsByNameAnnot: ClassSymbol = requiredClass("scala.annotation.retainsByName")
-  @tu lazy val RetainsArgAnnot: ClassSymbol = requiredClass("scala.annotation.retainsArg")
   @tu lazy val PublicInBinaryAnnot: ClassSymbol = requiredClass("scala.annotation.publicInBinary")
   @tu lazy val WitnessNamesAnnot: ClassSymbol = requiredClass("scala.annotation.internal.WitnessNames")
 

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

@@ -4524,15 +4524,10 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
             true
           }
 
-      def isRetainsArg(pt: Type) = pt match
-        case AnnotatedType(arg, annot) => annot.symbol == defn.RetainsArgAnnot
-        case _ => false
-
       if (implicitFun || caseCompanion)
           && !isApplyProto(pt)
           && pt != SingletonTypeProto
           && pt != LhsProto
-          && !isRetainsArg(pt)
           && !ctx.mode.is(Mode.Pattern)
           && !tree.isInstanceOf[SplicePattern]
           && !ctx.isAfterTyper

library/src/scala/annotation/retains.scala

@@ -20,12 +20,3 @@ class retains[Elems] extends annotation.StaticAnnotation
 class retainsCap extends annotation.StaticAnnotation
   // This special case is needed to be able to load standard library modules without
   // cyclic reference errors. Specifically, load sequences involving IterableOnce.
-
-/** Internal use, only for parameters of `retains` and `retainsByName`.
- */
-@experimental
-class retainsArg extends annotation.StaticAnnotation
-  // This annotation prevents argument references to retains and retainsByName from being
-  // augmented with explicit arguments. That's unsound in general, but necessary
-  // since a captureRef could have an impure context function type, A ?=> B, but
-  // we still need to have the unapplied captureRef in the annotation.

tests/run-tasty-inspector/stdlibExperimentalDefinitions.scala

@@ -30,7 +30,6 @@ val experimentalDefinitionInLibrary = Set(
   "scala.annotation.retains",
   "scala.annotation.retainsByName",
   "scala.annotation.retainsCap",
-  "scala.annotation.retainsArg",
   "scala.Pure",
   "scala.caps.CapSet",
   "scala.caps.Capability",