SI-8743 Fix crasher with poly-methods annotated with @varargs

The code that generated the Java varargs forwarder was basing
things on the `ValDef-s` of the parameters of the source method.
But, their types refer to a type parameter skolems of the enclosing
method, which led to a type mismatch when typechecking the forwarder.

Instead, I've reworked the code to simply use the `DefDef`-s symbol's
info, which *doesn't* refer to skolems. This actually simplifies the
surrounding code somewhat; rather than repeated symbols in a map
we can just time travel the pre-uncurry method signatures to figure
out which params are releated.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/files/pos/t8743.scala b/test/files/pos/t8743.scala
new file mode 100644
index 0000000000..03b0cd7044
--- /dev/null
+++ b/test/files/pos/t8743.scala
@@ -0,0 +1,15 @@
+import annotation.varargs
+
+object VarArgs {
+   @varargs
+   def foo[A](x: A, xs: String*): A = ???
+
+   @varargs
+   def bar[A](x: List[A], xs: String*): A = ???
+
+   @varargs
+   def baz[A](x: List[A], xs: String*): A = ???
+
+   @varargs
+   def boz[A](x: A, xs: String*): Nothing = ???
+}