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.

7 files changed, 156 insertions, 39 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)")
+}
diff --git a/test/files/jvm/t8786/A_1.scala b/test/files/jvm/t8786/A_1.scala
new file mode 100644
index 0000000000..13c0ad191d
--- /dev/null
+++ b/test/files/jvm/t8786/A_1.scala
@@ -0,0 +1,3 @@
+class A {
+  @annotation.varargs def foo[T](a: Int, b: T*): T = b.head
+}
diff --git a/test/files/jvm/t8786/B_2.java b/test/files/jvm/t8786/B_2.java
new file mode 100644
index 0000000000..dc155a290f
--- /dev/null
+++ b/test/files/jvm/t8786/B_2.java
@@ -0,0 +1,22 @@
+public class B_2 {
+  private static int res = 0;
+
+  public static void m(char a[]) { res += 10; }
+  public static void m(String a) { res += 100; }
+  public static void m(Object a) { res += 1000; }
+
+  public static <T> T foo(int a, T... b) { return b[0]; }
+
+  public static <T> T bar(T b[]) { return b[0]; }
+
+  public static void main(String[] args) {
+    m(foo(15, "a", "b", "c"));
+    if (res != 100)
+      throw new Error("bad: "+ res);
+
+    A a = new A();
+    m(a.foo(16, "a", "b", "c"));
+    if (res != 200)
+      throw new Error("bad: " + res);
+  }
+}
diff --git a/test/files/jvm/t8786/Test_2.scala b/test/files/jvm/t8786/Test_2.scala
new file mode 100644
index 0000000000..76ccb4c3ed
--- /dev/null
+++ b/test/files/jvm/t8786/Test_2.scala
@@ -0,0 +1,3 @@
+object Test extends App {
+  B_2.main(null)
+}
diff --git a/test/files/jvm/varargs/JavaClass.java b/test/files/jvm/varargs/JavaClass.java
index 6928ee5adc..0cc3587c5e 100644
--- a/test/files/jvm/varargs/JavaClass.java
+++ b/test/files/jvm/varargs/JavaClass.java
@@ -1,16 +1,12 @@
-
-
-
 public class JavaClass {
-    public static <T> void varargz(int i, T... v) {
-    }
-
-    public static void callSomeAnnotations() {
-	VaClass va = new VaClass();
-	va.vs(4, "", "", "");
-	va.vi(1, 2, 3, 4);
-        varargz(5, 1.0, 2.0, 3.0);
-	va.vt(16, "", "", "");
-	System.out.println(va.vt1(16, "a", "b", "c"));
-    }
-}
\ No newline at end of file
+  public static <T> void varargz(int i, T... v) { }
+
+  public static void callSomeAnnotations() {
+      VaClass va = new VaClass();
+      va.vs(4, "", "", "");
+      va.vi(1, 2, 3, 4);
+      varargz(5, 1.0, 2.0, 3.0);
+      va.vt(16, "", "", "");
+      System.out.println(va.vt1(16, "a", "b", "c"));
+  }
+}
diff --git a/test/files/jvm/varargs/VaClass.scala b/test/files/jvm/varargs/VaClass.scala
index d83e63ace1..ee8c288a16 100644
--- a/test/files/jvm/varargs/VaClass.scala
+++ b/test/files/jvm/varargs/VaClass.scala
@@ -1,15 +1,8 @@
-
-
 import annotation.varargs
 
-
-
 class VaClass {
-
   @varargs def vs(a: Int, b: String*) = println(a + b.length)
   @varargs def vi(a: Int, b: Int*) = println(a + b.sum)
   @varargs def vt[T](a: Int, b: T*) = println(a + b.length)
-
-  // TODO remove type bound after fixing SI-8786, see also https://github.com/scala/scala/pull/3961
-  @varargs def vt1[T <: String](a: Int, b: T*): T = b.head
+  @varargs def vt1[T](a: Int, b: T*): T = b.head
 }
diff --git a/test/files/jvm/varargs/varargs.scala b/test/files/jvm/varargs/varargs.scala
index 6d2e707bdf..b09818f46f 100644
--- a/test/files/jvm/varargs/varargs.scala
+++ b/test/files/jvm/varargs/varargs.scala
@@ -1,21 +1,5 @@
-
-
-
-
-
-
 object Test {
   def main(args: Array[String]) {
     JavaClass.callSomeAnnotations
   }
 }
-
-
-
-
-
-
-
-
-
-