SI-8079 Only expand local aliases during variance checks

We've been flip-flopping on this one through the years, right
now we issue an two errors for the enclosed test.

After this commit, variance validation only expands aliases that
are `{private,protected}[this]`. The rest need not be expanded,
as we have already variance validated the RHS of the alias.

It also removes a seemingly incorrect check in `isLocalOnly`.

This also means that we can use `@uncheckedVariance` to create
variant type aliases for Java interfaces.

However, if such a type alias is declared private local, it
*will* be expanded. That shouldn't be a problem, other than
for the fact that we run through an as-seen-from that strips
the `@uV` annotations in the type expansion. This has been
recorded in a pending test.

1 files changed, 4 insertions, 0 deletions

diff --git a/test/files/neg/t8079a.check b/test/files/neg/t8079a.check
new file mode 100644
index 0000000000..6bbe78afa6
--- /dev/null
+++ b/test/files/neg/t8079a.check
@@ -0,0 +1,4 @@
+t8079a.scala:3: error: contravariant type I occurs in covariant position in type C.this.X of value b
+  def f2(b: X): Unit
+         ^
+one error found