Fix curried conditional given instances

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -3468,10 +3468,12 @@ object Parsers {
             stats.foreach(checkExtensionMethod(tparams, _))
             ModuleDef(name, Template(makeConstructor(tparams, vparamss), Nil, Nil, self, stats))
           else
+            def makeGiven(params: List[ValDef]): List[ValDef] =
+              params.map(param => param.withMods(param.mods | Given))
             def conditionalParents(): List[Tree] =
               accept(ARROW)
               if in.token == LPAREN && followingIsParam() then
-                vparamss = vparamss :+ paramClause(vparamss.flatten.length)
+                vparamss = vparamss :+ makeGiven(paramClause(vparamss.flatten.length))
                 conditionalParents()
               else
                 val constrs = constrApps(commaOK = true, templateCanFollow = true)
@@ -3493,7 +3495,7 @@ object Parsers {
                 in.nextToken()
                 TypeBoundsTree(EmptyTree, annotType()) :: Nil
               else if isConditional then
-                vparamss = vparamss.head.map(param => param.withMods(param.mods | Given)) :: Nil
+                vparamss = vparamss.map(makeGiven)
                 conditionalParents()
               else
                 if !hasLabel && !(name.isEmpty && tparams.isEmpty && vparamss.isEmpty) then

tests/run/i7788.scala

@@ -0,0 +1,14 @@
+trait Show[-A] with
+  def show(a:A): String
+
+given Show[String] = x => x
+given Show[Int] = _.toString
+
+given showEither[A,B]: (sA: Show[A]) => Show[B] => Show[Either[A,B]] =
+  _.fold(a => s"Left(${summon[Show[A]].show(a)})", _ => "Right(Ignored value of B)")
+given [A,B]: (sA: Show[A]) => (sB: Show[B]) => Show[(A,B)] = (a,b) => s"(${sA.show(a)}), ${sB.show(b)})"
+
+@main def ShowDemo =
+  println(summon[Show[(Int, String)]].show(0 -> "hello"))
+  println(summon[Show[Either[Int, String]]].show(Left(-1)))
+  println(summon[Show[Either[Int, String]]].show(Right("success message")))