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, 1 insertions, 1 deletions

diff --git a/README.md b/README.md
index 6ebb453176..ed42eadaaa 100644
--- a/README.md
+++ b/README.md
@@ -134,7 +134,7 @@ codebase and re-compiles too many files, resulting in long build times (check
 [sbt#1104](https://github.com/sbt/sbt/issues/1104) for progress on that front). In the
 meantime you can:
   - Enable "ant mode" in which sbt only re-compiles source files that were modified.
-    Create a file `local.sbt` containing the line `(incOptions in ThisBuild) := (incOptions in ThisBuild).value.withNameHashing(false).withAntStyle(true)`.
+    Create a file `local.sbt` containing the line `antStyle := true`.
     Add an entry `local.sbt` to your `~/.gitignore`.
   - Use IntelliJ IDEA for incremental compiles (see [IDE Setup](#ide-setup) below) - its
     incremental compiler is a bit less conservative, but usually correct.