Pick right type parameters in TreeUnpickler

Fixes #13190

Author: odersky

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -864,9 +864,12 @@ class TreeUnpickler(reader: TastyReader,
               override def completerTypeParams(sym: Symbol)(using Context) =
                 rhs.tpe.typeParams
             }
+            val tparamSyms = rhs match
+              case LambdaTypeTree(tparams, body) => tparams.map(_.symbol.asType)
+              case _ => Nil
             sym.info = sym.opaqueToBounds(
               checkNonCyclic(sym, rhs.tpe.toBounds, reportErrors = false),
-              rhs, rhs.tpe.typeParams)
+              rhs, tparamSyms)
             if sym.isOpaqueAlias then sym.typeRef.recomputeDenot() // make sure we see the new bounds from now on
             sym.resetFlag(Provisional)
             TypeDef(rhs)

tests/pos/i13190/A_1.scala

@@ -0,0 +1,3 @@
+object Opaque {
+  opaque type FieldType[K, +V] <: V = V
+}

tests/pos/i13190/B_2.scala

@@ -0,0 +1,15 @@
+import Opaque.*
+
+object Test {
+  type FindField[R <: scala.Tuple, K] = R match {
+    case FieldType[K, f] *: t => f
+    case _ *: t => FindField[t, K]
+  }
+
+  val f: FieldType["A", Int] = ???
+  val f1: Int = f
+  //val f2: Int = f
+
+  type R = FieldType["A", Int] *: FieldType["B", Double] *: FieldType["C", String] *: FieldType["D", Boolean] *: EmptyTuple
+  summon[FindField[R, "B"] =:= Double]
+}