Box bounded arguments of HKT result types in Java generic signatures

compiler/src/dotty/tools/backend/jvm/GenericSignatures.scala

@@ -222,7 +222,7 @@ object GenericSignatures {
                     builder.append("*")
                 else
                   // For bounded arguments, we can't translate it cleanly so emit an erased type
-                  jsig(erasure(a.tycon))
+                  boxedSig(erasure(a.tycon))
               case res =>
                 // value classes cannot appear as generic arguments
                 jsig(res, vcBoxing = ValueClassBoxing.Box)

tests/generic-java-signatures/26786.check

@@ -0,0 +1 @@
+public Check<java.lang.Boolean> X.foo()

tests/generic-java-signatures/26786.scala

@@ -0,0 +1,14 @@
+import compiletime.ops.int.>
+
+trait Check[Cond[T <: Int] <: Boolean]:
+  def apply(arg: Int): Unit
+
+type CondT = [t <: Int] =>> t > 0
+
+class X:
+  val foo: Check[CondT] = new Check[CondT]:
+    def apply(arg: Int): Unit = ()
+
+object Test:
+  def main(args: Array[String]): Unit =
+    classOf[X].getMethods.filter(_.getName.contains("foo")).sortBy(_.getName).foreach(m => println(m.toGenericString))