Handle named context bounds in poly function context bound desugaring

[Cherry-picked 8dc68c3]

Author: KacperFKorban

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

@@ -1230,15 +1230,19 @@ object desugar {
       case td @ TypeDef(name, cb @ ContextBounds(bounds, ctxBounds)) =>
         TypeDef(name, ContextBounds(bounds, List.empty))
     }
-    var idx = -1
+    var idx = 0
     val collecedContextBounds = tparams.collect {
       case td @ TypeDef(name, cb @ ContextBounds(bounds, ctxBounds)) if ctxBounds.nonEmpty =>
         // TOOD(kπ) Should we handle non empty normal bounds here?
         name -> ctxBounds
     }.flatMap { case (name, ctxBounds) =>
       ctxBounds.map { ctxBound =>
         idx = idx + 1
-        makeSyntheticParameter(idx, ctxBound).withAddedFlags(Given)
+        ctxBound match
+          case ContextBoundTypeTree(_, _, ownName) =>
+            ValDef(ownName, ctxBound, EmptyTree).withFlags(TermParam | Given)
+          case _ =>
+            makeSyntheticParameter(idx, ctxBound).withAddedFlags(Given)
       }
     }
     val contextFunctionResult =

tests/pos/contextbounds-for-poly-functions.scala

@@ -7,9 +7,11 @@ trait Ord[X]:
 
 val less1 = [X: Ord] => (x: X, y: X) => summon[Ord[X]].compare(x, y) < 0
 
+val less2 = [X: Ord as ord] => (x: X, y: X) => ord.compare(x, y) < 0
+
 // type Comparer = [X: Ord] => (x: X, y: X) => Boolean
-// val less2: Comparer = [X: Ord as ord] => (x: X, y: X) => ord.compare(x, y) < 0
+// val less3: Comparer = [X: Ord as ord] => (x: X, y: X) => ord.compare(x, y) < 0
 
 // type Cmp[X] = (x: X, y: X) => Boolean
 // type Comparer2 = [X: Ord] => Cmp[X]
-// val less3: Comparer2 = [X: Ord] => (x: X, y: X) => summon[Ord[X]].compare(x, y) < 0
+// val less4: Comparer2 = [X: Ord] => (x: X, y: X) => summon[Ord[X]].compare(x, y) < 0