SI-8786 fix generic signature for @varargs forwarder methods

When generating a varargs forwarder for

    def foo[T](a: T*)

the parameter type of the forwarder needs to be Array[Object]. If we
gnerate Array[T] in UnCurry, that would be erased to plain Object, and
the method would not be a valid varargs.

Unfortunately, setting the parameter type to Array[Object] lead to
an invalid generic signature - the generic signature should reflect the
real signature.

This change adds an attachment to the parameter symbol in the varargs
forwarder method and special-cases signature generation.

Also cleanes up the code to produce the varargs forwarder. For example,
type parameter and parameter symbols in the forwarder's method type were
not clones, but the same symbols from the original method were re-used.

1 files changed, 116 insertions, 0 deletions

diff --git a/test/files/jvm/t8786-sig.scala b/test/files/jvm/t8786-sig.scala
new file mode 100644
index 0000000000..0745b650e6
--- /dev/null
+++ b/test/files/jvm/t8786-sig.scala
@@ -0,0 +1,116 @@
+class A[U] {
+  @annotation.varargs def m1[T]          (a: T*): T = a.head
+  @annotation.varargs def m2[T <: AnyRef](a: T*): T = a.head
+  @annotation.varargs def m3[T <: AnyVal](a: T*): T = a.head
+  @annotation.varargs def m4[T <: Int]   (a: T*): T = a.head
+  @annotation.varargs def m5[T <: String](a: T*): T = a.head
+  @annotation.varargs def m6             (a: String*): String = a.head
+  @annotation.varargs def m7             (a: Int*): Int = a.head
+  @annotation.varargs def m8             (a: U*): U = a.head
+
+  def n1[T]          (a: Array[T]): T = a(0)
+  def n2[T <: AnyRef](a: Array[T]): T = a(0)
+  def n3[T <: AnyVal](a: Array[T]): T = a(0)
+  def n4[T <: Int]   (a: Array[T]): T = a(0)
+  def n5[T <: String](a: Array[T]): T = a(0)
+  def n6             (a: Array[String]): String = a(0)
+  def n7             (a: Array[Int]): Int = a(0)
+  def n8             (a: Array[U]): U = a(0)
+}
+
+object Test extends App {
+  val a = classOf[A[_]]
+
+  def sig   (method: String, tp: Class[_]) = a.getDeclaredMethod(method, tp).toString
+  def genSig(method: String, tp: Class[_]) = a.getDeclaredMethod(method, tp).toGenericString
+  def bound (method: String, tp: Class[_]) = {
+    val m = a.getDeclaredMethod(method, tp)
+    m.getGenericParameterTypes.apply(0) match {
+      case _: Class[_] => ""
+      case gat: java.lang.reflect.GenericArrayType =>
+        val compTp = gat.getGenericComponentType.asInstanceOf[java.lang.reflect.TypeVariable[_]]
+        compTp.getBounds.apply(0).toString
+    }
+  }
+
+  def check(a: String, b: String) = {
+    assert(a == b, s"found: $a\nexpected: $b")
+  }
+
+  val sq = classOf[Seq[_]]
+  val ob = classOf[Object]
+  val ao = classOf[Array[Object]]
+  val as = classOf[Array[String]]
+  val ai = classOf[Array[Int]]
+
+  check(sig("m1", sq)   , "public java.lang.Object A.m1(scala.collection.Seq)")
+  check(sig("m2", sq)   , "public java.lang.Object A.m2(scala.collection.Seq)")
+  check(sig("m3", sq)   , "public java.lang.Object A.m3(scala.collection.Seq)")
+  check(sig("m4", sq)   , "public int A.m4(scala.collection.Seq)")
+  check(sig("m5", sq)   , "public java.lang.String A.m5(scala.collection.Seq)")
+  check(sig("m6", sq)   , "public java.lang.String A.m6(scala.collection.Seq)")
+  check(sig("m7", sq)   , "public int A.m7(scala.collection.Seq)")
+  check(sig("m8", sq)   , "public java.lang.Object A.m8(scala.collection.Seq)")
+
+  check(genSig("m1", sq), "public <T> T A.m1(scala.collection.Seq<T>)")
+  check(genSig("m2", sq), "public <T> T A.m2(scala.collection.Seq<T>)")
+  check(genSig("m3", sq), "public <T> T A.m3(scala.collection.Seq<T>)")
+  // TODO: the signature for is wrong for T <: Int, SI-9846. The signature should be
+  // `public int A.m4(scala.collection.Seq<java.lang.Object>)`. This is testing the status quo.
+  check(genSig("m4", sq), "public <T> T A.m4(scala.collection.Seq<T>)")
+  check(genSig("m5", sq), "public <T> T A.m5(scala.collection.Seq<T>)")
+  check(genSig("m6", sq), "public java.lang.String A.m6(scala.collection.Seq<java.lang.String>)")
+  check(genSig("m7", sq), "public int A.m7(scala.collection.Seq<java.lang.Object>)")
+  check(genSig("m8", sq), "public U A.m8(scala.collection.Seq<U>)")
+
+
+  // varargs forwarder
+
+  check(sig("m1", ao)   , "public java.lang.Object A.m1(java.lang.Object[])")
+  check(sig("m2", ao)   , "public java.lang.Object A.m2(java.lang.Object[])")
+  check(sig("m3", ao)   , "public java.lang.Object A.m3(java.lang.Object[])")
+  check(sig("m4", ao)   , "public int A.m4(java.lang.Object[])")
+  check(sig("m5", as)   , "public java.lang.String A.m5(java.lang.String[])")
+  check(sig("m6", as)   , "public java.lang.String A.m6(java.lang.String[])")
+  check(sig("m7", ai)   , "public int A.m7(int[])")
+  check(sig("m8", ao)   , "public java.lang.Object A.m8(java.lang.Object[])")
+
+  check(genSig("m1", ao), "public <T> T A.m1(T...)")
+  check(genSig("m2", ao), "public <T> T A.m2(T...)")
+  check(genSig("m3", ao), "public <T> T A.m3(T...)")
+  // testing status quo: signature is wrong for T <: Int, SI-9846
+  check(genSig("m4", ao), "public <T> T A.m4(T...)")
+  check(genSig("m5", as), "public <T> T A.m5(T...)")
+  check(genSig("m6", as), "public java.lang.String A.m6(java.lang.String...)")
+  check(genSig("m7", ai), "public int A.m7(int...)")
+  check(genSig("m8", ao), "public U A.m8(U...)")
+
+  check(bound("m1", ao) , "class java.lang.Object")
+  check(bound("m2", ao) , "class java.lang.Object")
+  check(bound("m3", ao) , "class java.lang.Object")
+  check(bound("m4", ao) , "class java.lang.Object")
+  check(bound("m5", as) , "class java.lang.String")
+  check(bound("m6", as) , "")
+  check(bound("m7", ai) , "")
+  check(bound("m8", ao) , "class java.lang.Object")
+
+
+  check(sig("n1", ob)   , "public java.lang.Object A.n1(java.lang.Object)")
+  check(sig("n2", ao)   , "public java.lang.Object A.n2(java.lang.Object[])")
+  check(sig("n3", ob)   , "public java.lang.Object A.n3(java.lang.Object)")
+  check(sig("n4", ob)   , "public int A.n4(java.lang.Object)")
+  check(sig("n5", as)   , "public java.lang.String A.n5(java.lang.String[])")
+  check(sig("n6", as)   , "public java.lang.String A.n6(java.lang.String[])")
+  check(sig("n7", ai)   , "public int A.n7(int[])")
+  check(sig("n8", ob)   , "public java.lang.Object A.n8(java.lang.Object)")
+
+  check(genSig("n1", ob), "public <T> T A.n1(java.lang.Object)")
+  check(genSig("n2", ao), "public <T> T A.n2(T[])")
+  check(genSig("n3", ob), "public <T> T A.n3(java.lang.Object)")
+  // testing status quo: signature is wrong for T <: Int, SI-9846
+  check(genSig("n4", ob), "public <T> T A.n4(java.lang.Object)")
+  check(genSig("n5", as), "public <T> T A.n5(T[])")
+  check(genSig("n6", as), "public java.lang.String A.n6(java.lang.String[])")
+  check(genSig("n7", ai), "public int A.n7(int[])")
+  check(genSig("n8", ob), "public U A.n8(java.lang.Object)")
+}