SI-7782 Derive type skolems at the ground level

Rather than at the current value of `skolemizationLevel`,
which could be influenced by an in-flight existential
subtype computation.

This method is called in `PolyTypeCompleter`, which
could be constructed by the lazy type completer of the
enclosing class. So currently it is closing over a mutable
variable; hence the Heisenbug.

This issue was exposed by the changes in b74c33eb860,
which was introduced in Scala 2.10.1.

1 files changed, 25 insertions, 0 deletions

diff --git a/test/files/pos/t7782.scala b/test/files/pos/t7782.scala
new file mode 100644
index 0000000000..037bdad673
--- /dev/null
+++ b/test/files/pos/t7782.scala
@@ -0,0 +1,25 @@
+package pack
+
+object Test {
+  import O.empty
+  empty // this will trigger completion of `test`
+        // with skolemizationLevel = 1
+}
+
+object O {
+  // order matters (!!!)
+
+  // this order breaks under 2.10.x
+  def empty[E]: C[E] = ???
+  def empty(implicit a: Any): Any = ???
+}
+
+abstract class C[E] {
+  def foo[BB](f: BB)
+  def test[B](f: B): Any = foo(f)
+  // error: no type parameters for method foo: (<param> f: BB)scala.this.Unit exist so that it can be applied to arguments (B&1)
+  // --- because ---
+  // argument expression's type is not compatible with formal parameter type;
+  // found   : B&1
+  // required: ?BB
+}