Fix creating forwarders for simple alias givens

Fixes #16191

Author: odersky

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

@@ -571,6 +571,7 @@ object Flags {
   val GivenOrImplicit: FlagSet               = Given | Implicit
   val GivenOrImplicitVal: FlagSet            = GivenOrImplicit.toTermFlags
   val GivenMethod: FlagSet                   = Given | Method
+  val LazyGiven: FlagSet                     = Given | Lazy
   val InlineOrProxy: FlagSet                 = Inline | InlineProxy                           // An inline method or inline argument proxy */
   val InlineMethod: FlagSet                  = Inline | Method
   val InlineParam: FlagSet                   = Inline | Param

compiler/src/dotty/tools/dotc/transform/UncacheGivenAliases.scala

@@ -53,7 +53,7 @@ class UncacheGivenAliases extends MiniPhase with IdentityDenotTransformer:
    */
   override def transformValDef(tree: ValDef)(using Context): Tree =
     val sym = tree.symbol
-    if sym.isAllOf(Given, Lazy) && !needsCache(sym, tree.rhs) then
+    if sym.isAllOf(LazyGiven) && !needsCache(sym, tree.rhs) then
       sym.copySymDenotation(
         initFlags = sym.flags &~ Lazy | Method,
         info = ExprType(sym.info))

tests/run/i16191.check

@@ -0,0 +1 @@
+List(private final Context C.ctx)

tests/run/i16191.scala

@@ -0,0 +1,15 @@
+class Context
+
+def foo =
+  val ctx: Context = new Context
+  given a: Context = ctx
+
+class C:
+  private val ctx: Context = new Context
+  given Context = ctx
+  given C = this
+
+@main def Test =
+  val c = new C()
+  println(c.getClass.getDeclaredFields.toList)
+