SI-6555 Better parameter name retention

We were losing track of parameter names in two places:

  1. Uncurry was using fresh names for the apply method
     parameters during Function expansion. (The parameter names
     in the tree were actually correct, they just had synthetic
     symbols with "x$1" etc.)
  2. When adding specialized overrides, the parameter names
     of the overriden method were used, rather than the parameter
     names from the overriding method in the class to which we are
     adding methods.

The upshot of this is that when you're stopped in the debugger in
the body of, say, `(i: Int) => i * i`, you see `v1` rather than `i`.

This commit changes Uncurry and SpecializeTypes to remedy this.

1 files changed, 22 insertions, 0 deletions

diff --git a/test/files/run/t6555.check b/test/files/run/t6555.check
new file mode 100644
index 0000000000..04117b7c2f
--- /dev/null
+++ b/test/files/run/t6555.check
@@ -0,0 +1,22 @@
+[[syntax trees at end of                specialize]] // newSource1
+package <empty> {
+  class Foo extends Object {
+    def <init>(): Foo = {
+      Foo.super.<init>();
+      ()
+    };
+    private[this] val f: Int => Int = {
+      @SerialVersionUID(0) final <synthetic> class $anonfun extends scala.runtime.AbstractFunction1$mcII$sp with Serializable {
+        def <init>(): anonymous class $anonfun = {
+          $anonfun.super.<init>();
+          ()
+        };
+        final def apply(param: Int): Int = $anonfun.this.apply$mcII$sp(param);
+        <specialized> def apply$mcII$sp(param: Int): Int = param
+      };
+      (new anonymous class $anonfun(): Int => Int)
+    };
+    <stable> <accessor> def f(): Int => Int = Foo.this.f
+  }
+}
+