SI-7783 Don't issue deprecation warnings for inferred TypeTrees

Deprecation checks in RefChecks were looking into all TypeTrees
to find references to deprecated type aliases. However, when the
compiler infers a type argument or type of a member it creates
a TypeTree (with a null original) that was also leading to warnings.

I ran into this problem often when upgrading a build from SBT 0.12
to 0.13: a plugin I was using used the deprecated type alias, and I
suffered transitively when I used methods from its API.

This commit disables the checks for inferred TypeTree-s.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/files/neg/t7783.scala b/test/files/neg/t7783.scala
new file mode 100644
index 0000000000..995b644a09
--- /dev/null
+++ b/test/files/neg/t7783.scala
@@ -0,0 +1,15 @@
+object O { class C; @deprecated("", "") type D = C; def foo: Seq[D] = Nil }
+
+object NoWarn {
+  O.foo                        // nowarn
+  O.foo +: Nil                 // nowarn
+  def bar(a: Any, b: Any) = () // nowarn
+  bar(b = O.foo, a = ())       // nowarn
+}
+
+object Warn {
+  type T = O.D
+  locally(null: O.D)
+  val x: O.D = null
+  locally(null.asInstanceOf[O.D])
+}